Chapter 3: Environmental Injury

External factors, forces, and agents play a significant role in the causation of human disease. The environment in which we live is hardly benign and we are constantly exposed to its potential hazards. These include physical, chemical, thermal, and electrical forces as well as ionizing radiation. Noncommensal microbiological organisms are also external agents. While within the spectrum of human disease there are conditions where external factors have little or no role, such as some inherited disorders of metabolism or the muscular dystrophies, in most human afflictions external factors interact with host factors to produce disease. Certain lung cancers are linked to cigarette smoking and liver disease is a well-documented consequence of heavy alcohol consumption, yet in spite of the clear evidence that links these two agents to these diseases, it is also the case that only a minority of smokers and drinkers respectively develop them. At the other end of the spectrum lie the instances where external forces or agents are essentially the only factors as in trauma from a natural catastrophe like an earthquake or a -man-made event such as a motor vehicle crash.

The environmental hazards any one individual is exposed to are determined by a variety of factors including geography, socioeconomic status, and culture. This is true not only for infectious entities such as malaria which depends on an insect vector that itself requires certain climatic conditions for its existence but also for various forms of trauma. Cobra bites are a common problem in India but not in the United States. Motor vehicle-related injuries, gunshot wounds, cutting injuries, and disorders related to contaminated air and water vary from country to country and regionally within countries just as do the incidence of infectious and other diseases.

This chapter will deal with diseases or conditions that are primarily the result of external factors but will not discuss diseases caused by microorganisms except to mention that infections, often from normal flora, are a common complication of trauma and remind readers that many vectors that spread infection require the physical trauma of a bite to inoculate the host. Tetanus caused by a toxin produced by the bacillus, Clostridium tetani, usually occurs after the introduction of that soil-dwelling organism into tissues as a consequence of a wound and similarly gas gangrene from Clostridium perfringens and other species. In the days before vaccination for tetanus, antiseptic surgery, and antibiotics, these entities were a common often-fatal complication of agricultural, martial, and other trauma and in some areas of the World today remain so.

A measure of the burden of injury to the healthcare system in the United States is the fact that one-third of all emergency department (ED) visits in 2008, some 42.8 million, were injury related (Table 3-1). Injury is the leading cause of death for people ages 1–44 years in the United States, and because these deaths are in younger individuals, the years of potential life lost is greater than many conditions that account for a greater number of deaths (Table 3-2).

Acute injuries have immediate consequences for the victim with the potential for subsequent and long-term complications. Recurring trauma, even that which has little apparent immediate consequence, can also lead to disorders. A single episode of heavy ethanol intake may lead to acute intoxication with little or no subsequent complications, while repeated episodes can result in cardiomyopathy and/or cirrhosis of the liver, two of the many potential consequences of chronic alcohol abuse. If the acute ingestion is large enough, however, it may lead to fatal respiratory depression. Moreover, in an inebriated state an individual is at greater risk of additional injury whether by falling, attempting to drive a motor vehicle, leaving a pot on the stove and starting a fire, or becoming involved in an activity that they would not have undertaken in a sober state.

A driver injured in a motor vehicle crash sustains some degree of immediate impairment, depending on the severity of the crash. The period required for recovery will also vary accordingly. During that period they are at risk of a variety of complications including infection and deep vein thrombosis with pulmonary embolism. In many instances of trauma, recovery is incomplete and the affected individual will thereafter function at a lower level than before the incident, thereby suffering a diminished quality of life. If there is sufficient impairment, such as paralysis or severe brain damage, susceptibility to pressure sores, infection, and other long-term complications may lead to a significantly reduced life span.

Repeated injuries due to chemicals or toxins can lead to disease as is the case for smoking and ethanol. This may also occur after physical and other modes of trauma. Examples include repetitive motion disorders such as carpal tunnel syndrome, osteoarthritis in the limbs of athletes, professional or otherwise, and traumatic encephalopathy. This latter condition, dementia pugilistica, was first noted in boxers following repeated blows to the head, and is now being recognized in football players and other participants in activities where concussions are common. External factors that can lead to injury can be separated into five major categories: physical, chemical, thermal, electrical, and ionizing radiation.

1. Physical injuries are those that are related to mechanical interactions and are the most common types of acute injuries from external forces seen in medicine. Motor vehicle wrecks, gunshot wounds, stabbing and cutting injuries, falls, and various mechanical asphyxias fall into this category. We include in this category the effects of pressure and altitude.

2. Chemical injury includes exposure to noxious or asphyxiant gases, medications both legal and illegal, and other chemical, metals, and mineral agents.

3. Thermal injury results from the exposure to fire and other sources of heat as well as intensely cold surfaces. Environmental exposure to heat or cold may also lead to local injury and/or systemic dysfunction.

4. Electrical forces include the natural phenomenon of lightning as well as exposure to man-made electrical currents.

5. Ionizing radiation employed as a therapeutic and diagnostic modality in medicine can also lead to unintended injury. Such radiation is also present naturally in our environment and the specter of the consequences of the detonation of a nuclear bomb or a mishap at a nuclear power plant currently "haunt" our society. Solar radiation can potentially lead to both acute and chronic health problems.

It is customary to separate traumatic injuries into three categories based on the circumstances in which they are incurred: unintentional (accidental), self-inflicted, and assaultive, (deliberately caused by another human). The latter two are referred to as "intentional" injuries and assaultive is sometimes also referred to as "violent." When applied to fatal injuries, this leads to the classification of trauma-related deaths as accident, suicide, or homicide. These designations are referred to as "manners" of death. An unintentional (accidental) injury is one that is not the consequence of a deliberate human action intended to cause harm, but it is important to appreciate that many injuries deemed unintentional are in fact the consequence of actions intentionally undertaken by the injured or another party, actions that may clearly have put the injured party at significant risk. In fact, the line that delineates intentional from unintentional when the risk of self or other injury is high and clearly apparent to the neutral observer can be difficult to draw and presents a recurring dilemma in medicolegal death investigation and certification as well as in the courts regarding legal culpability. For instance, when a chronic drug abuser dies of an overdose is it the consequence of a miscalculation, carelessness, desire for a better "high," or a calculated intent to end it all? Some "recreational" activities are more dangerous than others, for example, mountain climbing versus vegetable gardening. At what point does the likelihood of injury inherent in a voluntary activity dictate that a resulting injury and death is suicide rather than accident? Most accident insurance policies have exclusions for activities the insurance company considers too dangerous to cover even though a death occurring during that activity would be certified as accidental by a medicolegal authority. Designating an injury or death as "accidental" does not mean either that there can be no criminal or civil culpability on the part of another human agency. Similarly, classifying a death as a homicide does not necessarily mean that someone is criminally liable. Crimes and civil liability are defined by law and manner of death classification is intended primarily for epidemiological purposes as is the similar designation of nonfatal injuries as unintentional, intentional, self-intent, and assault. Strategies to reduce the number of head injuries due to falls are quite different from those due to assaults.

As mentioned previously, patients may exhibit signs and symptoms from underlying natural disorders as well as injuries, the consequence of an untoward interaction with the environment. Traumatic injuries may lead to disorders that are not considered external, like pulmonary emboli or infection. It is important, however, to recognize a connection when it is there since to ignore it is akin to treating symptoms of disease without addressing the underlying cause. Pathogenic sequences connect causes and effects. In such sequences, each entity listed is the consequence of the one preceding it. A myocardial infarct results from myocardial ischemia due to diminished or interrupted coronary blood flow that is the consequence of coronary restriction from atherosclerosis. The underlying or proximate condition leading to the infarct is then atherosclerosis. An individual might develop sepsis due to peritonitis that was caused by a bowel injury incurred in a motor vehicle wreck. The wreck is then the underlying or proximate cause of the sepsis. This is particularly important in the process of death certification where the certifier must decide what the underlying disease condition leading to death was. Many deaths are inaccurately certified in regard to their cause when the certifier assigns it to the last process, the one immediately preceding death, and fails to include the underlying cause of that condition. In the case of the last example, attributing death to sepsis due to peritonitis without including the trauma would result in the death being classified as natural rather than unnatural. Failing to link pulmonary fibrosis to asbestos exposure or liver failure to acetaminophen toxicity conceals the contributions of those external factors to human disease.

Physical injury may occur when a moving individual strikes a solid object or surface or a stationary individual is impacted or compressed by a moving object or force. In such interactions, there are several factors that determine the likelihood that significant injury will result.

Quantity of Force Involved: Kinetic Energy

All moving objects or bodies have kinetic energy and as the amount of energy in an interaction increases so does the likelihood of injury. Kinetic energy is the product of the mass of an object times the square of the velocity divided by two. As the mass (weight) increases, there is a direct proportional increase in the amount of energy, while as the velocity increases the energy goes up by the square of the velocity increase. For example, if a baseball and a car were both traveling 30 miles per hour, one could safely catch the baseball, but certainly not the car because the baseball weighs less than half a pound while the car weighs 3000 lb. Similarly a jump from a 3 foot platform to the ground would seldom lead to injury, but the same person jumping from a 32 foot platform would be likely to suffer serious perhaps even fatal injury. The additional velocity imparted by the acceleration of gravity over the 29 foot difference imparts to the moving body sufficient kinetic energy to distort and disrupt internal structures when the individual impacts the ground.

Area over which force is applied: The likelihood of injury is also related to the area over which the particular force is applied. Concentration of the energy of impact over a small area can overcome the resistance of the tissues to deformation and penetration. This can allow entry of an object into the body leading to damage to deeper internal organs. Even in the absence of penetration, there may be sufficient local deformation to cause mechanical disruption of underlying organs and tissues. Bullets, knives, arrows, and other sharp objects have the potential to cause serious injury because they can overcome the resistance of the skin and often underlying bone to reach vital organs and structures, even though the quantities of kinetic energy involved are not large. Similarly a blow from a bat, pipe, or club concentrates the area over which the energy of the impact is dissipated, resulting in more local and/or even deeper injury than would have occurred if the impacting surface was broader. The same applies in reverse when a moving body impacts a stationary surface, for example, stepping on a nail or falling and striking the projecting edge of a piece of furniture.

Time interval during which force is applied: Another factor is the time interval over which the interaction occurs. If it can be lengthened, the likelihood of injury can be lessened. The padding of helmets and dashboards in part does this. It is the principal that allows "bungee" jumping and the different consequences that follow diving into a swimming pool full of water versus one that is empty. In both instances, the energy generated by the fall is safely absorbed and dissipated over distance and time by the elastic cords in the first instance and the yielding water in the second.

Tissue resistance to force: The body's tissues also vary in their resistance to trauma with bone being more resistant that skin. Internal connective tissues are more resistant than muscle that is more resistant than internal organs such as liver and spleen.

Body area(s) affected by force: The significance of any injury to the overall health of an organism is related to the parts affected in addition to the extent of tissue disruption. Injuries that compromise the vital functions of respiration and circulation have the greatest potential to be immediately life threatening, whereas injuries to the extremities or noncritical organs are more potentially survivable, particularly with timely appropriate medical treatment. Many of these factors are not only exploited in the design of weaponry but are also utilized in devising protective strategies. Seat belts, cushioned dashboards, air bags, protective armor, and bicycle helmets all attempt to decrease the likelihood of injury to internal organs in forceful interactions by dissipating the forces of collisions over a larger area extending the interval over which they are dissipated as well as shifting them to tissues of greater resistance.

Fitness of individual: A last factor to be considered is the fitness of the individual injured. Significant preexisting medical conditions as well as the extremes of age may render one individual less likely to survive a given degree of insult than a fitter individual. Older persons are often more fragile and have a diminished capacity for tissue repair. Survival from severe burns, for instance, is inversely proportional not only to the extent and severity of the burns but also to the age of the victim. Injuries of an extent that would easily be survived by younger individuals often prove fatal to the elderly, and a fall leading to a broken hip, rapid decompensation, and death is a common occurrence. Infants and small children have the optimal capacity for repair but are relatively more fragile—an impact that might only bruise an adult can prove fatal to an infant.

The histopathology of physical trauma is that of inflammation and wound repair and is virtually never employed in the evaluation of nonfatal injuries. In the investigation of fatalities, however, microscopy can aid in the determination of the age of bruises, lacerations, and hemorrhages. (Case 3-1) It may also be helpful in confirming the presence of powder residues in close range or contact gunshot wounds.

The list of substances, minerals, chemicals, toxins, etc. that are potentially toxic to humans is essentially endless, particularly if we remember Paracelsus' dictum, "sola dosis facit venenum," only the dose makes the poison. Virtually any substance can be toxic if taken in excess, even essential dietary elements. Iron is necessary for the formation of hemoglobin, and inadequate dietary intake leads to anemia but excess dietary intake can lead to hemosiderosis with resulting organ damage. Too much iron in the form of ferrous salts taken at one time can lead to acute poisoning. Is there a substance as innocuous as water? Yet water can be toxic if more is taken into the body than the kidneys can clear. Water intoxication can result from rapid excess ingestion as is sometimes seen in psychotic patients. It can also be an iatrogenic complication of therapy when nonelectrolyte solutions are given to patients with inappropriate antidiuretic hormone secretion or sterile water is used to flush operative sites. Water toxicity also occurs in marathon runners who over hydrate during their run. The excess water dilutes the intravascular volume and the resulting hyponatremia can be fatal.

Toxic chemical exposures, acute or chronic, can occur in the home, workplace, hospital, and the great outdoors. Some of these exposures are natural since numerous toxic substances are already present in the environment such as plant toxins or high arsenic concentrations in some groundwater. Others are man-made, both in regard to the origin of the toxic substance and the circumstances in which they are encountered, such as exposure to solvents in a chemical plant. Man-made substances also escape into the natural environment where they can become hazards as in the case of mercury released from industrial processes into the environment accumulating in the flesh of fish.

The determination that a particular substance is potentially toxic usually begins with the recognition of an apparent association between the use of or exposure to that substance and some malady. The association is confirmed by epidemiologic studies demonstrating that the malady is more common in exposed individuals than unexposed or in those with greater exposure than those with less. Animal models are utilized to support the association and to try to define toxic levels as well as set permissible levels for human exposure. This latter process involves exposing the animals to increasing quantities of the substance and determining the lowest dosage that produces an effect, the threshold dose, which is then used to define a permissible exposure level. Epidemiologic studies are complicated by many factors particularly those involving determining the actual exposure to the substance in questions in the subject groups and identifying an appropriate control group for comparison. Animal studies can be problematic since there are physiological differences between humans and other animals and it may be difficult to approximate conditions in the real world in the experimental setting. Many animal studies utilize exposures many times greater than what humans would experience. Particularly challenging are assessing the effects of long-term low concentration exposures given the long life of humans versus those of laboratory animals. It is in fact difficult to know what the long-term effects to low concentrations of many substances might be raising concerns about our ability to set permissible exposure limits to such substances.

Substances taken into the body are distributed within its various compartments, depending on the chemical properties of the substance. Water-soluble molecules like ethanol are distributed throughout the total body water while others that are more lipophilic move more easily into lipid-rich organs and tissues and are concentrated there. Inhaled particulate materials such as asbestos fibers lodge in the lungs where they do their damage. Most chemicals are metabolized to some degree and both metabolites and residual parent drug are cleared from the body through urine, bile, and/or feces. In some instances, the metabolite of the drug or chemical may be more toxic than the parent substance itself.

Drugs and Medications

The misuse and/or abuse of drugs and medicines is a significant medical and legal problem in much of the world. Even appropriately used medications can have side effects or produce complications more serious than the conditions for which they were prescribed. It is well recognized that iatrogenic injury from medications is a major cause of morbidity and even mortality in both inpatient and outpatient settings.

Medications can cause injury in several ways. If an excess of medication is taken, an overdose can result. Drugs vary in their therapeutic index, essentially the difference between the dosage necessary to produce a therapeutic effect and what will be toxic. Drugs with low therapeutic indexes, like digoxin, have to be carefully monitored to prevent patient injury. Drugs with abuse potential are also likely to result in overdose since users may increase dosage to "improve" the pharmacologic effect they are seeking. Drug interactions can lead to overdoses. If one medication affects the metabolism or clearance of another, it can cause a buildup of the other with a resulting increase in its pharmacologic effects. The anticoagulant, warfarin, is an example of a medication whose effects can be augmented or diminished by numerous other medications as well as dietary substances. The simultaneous intake of multiple medications that have similar potentially toxic side effects sometimes leads to injury even when none of the medications is itself present in a toxic concentration. Sometimes the respiratory depressant effect of ethanol is the additional factor that changes an instance of abuse into a fatality.

Virtually all medications have side effects and some of these can be injurious. There are a variety of hypersensitivity reactions that can occur to medications ranging from minor to disabling or even fatal such as erythema multiforme (see Chapter 20). Erythema multiforme has been associated with a number of medications including barbiturates, penicillins, sulfonamides, and phenytoin. Acute allergic reactions from hives to frank anaphylaxis can occur. These usually involve an initial exposure with sensitization and then a reaction on rechallenge but anaphylaxis may occur without a history of an initial sensitizing exposure. Drugs with greater risk of such allergic reactions include penicillin. Iodinated radiocontrast materials may also cause anaphylaxis, though it is believed to be through a different mechanism as is that seen in individuals allergic to aspirin and other NSAIDs.

When medications are abused, they are often taken by individuals for whom they are not prescribed or, if prescribed, in quantities in excess of that which was prescribed. This may result in an overdose where the pharmacological effects of the drug are paramount. In a situation of abuse, moreover, not only may the quantities of the medication be supratherapeutic but also the route of administration inappropriate. For example, medication in pill form intended for oral ingestion may be ground up and injected intravenously (IV). With street or illicit substances, there are no standards of purity, and in addition to the drug/medication of interest, a variety of other substances may be, and usually are, present. While some may be inert, others are pharmacologically active and potentially toxic. It is also common for abusers to ingest multiple substances/medications at the same time further compounding the problem.

Abusers administering drugs to themselves and/or others put themselves at risk of a variety of diseases and complications beyond those related to the pharmacological effects of the drugs involved. The sharing of syringes and needles by IV drug users has been linked to the spread of infectious agents including hepatitis B and C, HIV, and malaria. Unclean needles and poor injection hygiene can lead to abscesses or cellulitis at injection sites. Right-sided endocarditis is seen in IV drugs abusers. The insoluble components of ground oral medications or materials used to "cut" street drugs become lodged in the microvasculature of the lungs where they induce a striking foreign body granulomatous reaction that can lead to right-sided heart failure, cor pulmonale. Inhalation of powdered cocaine can lead to nasal septal perforation.

Addiction to illicit drugs, legal medications, or alcohol is itself a serious problem with a significant cost to society in addition to the damage it does to the individuals involved and their families. The addict may be unable to function normally in society or support themselves and their families. Some resort to criminal acts and enterprises in order to maintain their habits. Those addicts living marginal existences are at risk of all the medical and nutritional problems associated with such a lifestyle. The production and distribution of illegal drugs is itself a criminal enterprise often associated with violence and users, particularly those that also deal drugs, may become victims. The classes of drugs most abused with the exception of ethanol are the narcotic analgesics, the stimulants, and the anxiolytics.

Narcotic analgesics: These include the medications extracted from the opium poppy, Papaver somniferum, mainly morphine and codeine. Heroin, diacetylmorphine, is not utilized clinically but is the main form of street opiate. A variety of synthetic opioids are also available and abused including hydrocodone, oxycodone, hydromorphone, oxymorphone, and others like fentanyl, propoxyphene, and methadone. These substances are respiratory depressants and taken in overdose may cause death via central respiratory depression. There is evidence that methadone and propoxyphene, a related compound, have cardiac effects as well. Generally apart from the serious consequences of addiction noted above and those of acute intoxication, these substances (in and of themselves) have little or no long-term/chronic toxicity.

Stimulants: Cocaine and amphetamines are the major drugs in this group. They are abused for their excitatory effects and their toxicity is felt to be primarily cardiac, with deaths resulting from lethal arrhythmias. They may also precipitate what is termed "excited delirium." This is not an overdose phenomenon but a drug-induced state characterized by bizarre, hyperactive, behavior often culminating in cardiovascular collapse and death. It often becomes particularly problematic when the bizarre behavior leads to law enforcement or bystander intervention and restraint of the victim. Following the collapse concerns are understandably raised that the fatal outcome was the consequence of traumatic asphyxia or physical injuries sustained in the course of the restraint.

Cocaine: It may be taken in the form of the hydrochloride salt, powder, or in a crystalline form, the free base. The latter is often referred to as "crack" because of the cracking noise it makes as it is heated prior to inhaling its vapors. It may be inhaled, snorted—intact, inhaled while it is heated—smoked, or injected. It is not ordinarily ingested except regrettably occasionally in an attempt to hide evidence with often lethal results. Cocaine and amphetamines raise heart rate, cardiac output, and blood pressure. Acute cerebrovascular hemorrhages have also been linked to their use. Cocaine may cause coronary artery spasm, and there is ample evidence linking chronic cocaine use to accelerated coronary atherosclerosis and cardiomyopathy.

Methamphetamine: It is often produced in-house "laboratories" from the over-the-counter precursor drug pseudoephedrine and has become a serious problem in many parts of the United States. This is not only because of its potent addictive potential and its pharmacologic effects but also because its clandestine production involves the use of explosive and corrosive chemicals. These "labs" are often located in homes and trailers where families including children may be living. Chronic methamphetamine users may exhibit evidence of premature aging and striking deterioration of their dentition. The latter has also been noted in cocaine abusers. Methamphetamine may be ingested orally, smoked or injected.

Anxiolytics: There are a large number of medications in this group many of which in addition to their antianxiety properties are utilized as sleep aids and muscle relaxants. The most widely prescribed are the benzodiazepines including alprazolam, diazepam, and chlordiazepoxide among others. They vary considerably in their fatal overdose potential but when, as is often the case, they are taken with in combination with other drugs or ethanol in a situation of abuse they may augment the respiratory depressant effects of the other agents.

Hallucinogens: Hallucinogens such as LSD are dangerous largely due to their mind-altering effects that may lead intoxicated individuals to seek out or unwittingly place themselves in situations where they may be physically harmed.

Inhalants: Another broad group of abused substances is the inhalants. Many of these are low molecular weight hydrocarbons that serve as the propellants in aerosol dispensers. Some inhalants are volatile solvents while others gases with various uses. The propellants include propane, butane, and isobutane as well as fluorinated hydrocarbons. Chlorofluorocarbons (CFCs) were once utilized as propellants but are now banned in most countries because of concerns about their effects on earth's ozone layer. Some CFCs, however, are still used as refrigerants and may be diverted for abuse in that form. When inhaled, "sniffed" or "huffed," for a high, these chemicals have the potential to destabilize the myocardium and consequently precipitate lethal cardiac arrhythmias. Volatile solvents like toluene in glue can have similar effects. Helium, nitrous oxide, and propane may also be sniffed. Asphyxiation may result if a volatile is utilized in a setting where it displaces the air that the abuser is breathing creating an oxygen-deficient atmosphere. This most commonly involves putting a plastic bag over the head to confine the fumes or utilizing a mask.

Acetaminophen: This commonly utilized analgesic and antipyretic deserves inclusion because of its potential for hepatotoxicity in overdose; as such it is the most common cause of acute liver failure in the United States and Great Britain. The drug came into wide usage as a replacement for aspirin in large part because of its much lower incidence of undesirable gastric side effects. Probably because of its availability, ingestion of large quantities in suicide attempts and "gestures" occurs frequently. In overdose, the liver becomes unable to conjugate the drug into the forms in which it is ordinarily excreted from the body in the urine. This leads to the formation of a toxic metabolite and cellular damage. Liver necrosis appears some days after the ingestion that histopathologically is characterized by bland central necrosis. This catastrophe can be averted by the administration of N-acetylcysteine within the first 8–10 hours of ingestion. This helps restore liver glutathione stores needed for the conjugation of the parent drug. Chronic alcohol abuse, fasting, and use of some anticonvulsant drugs can increase the potential for acetaminophen to reach toxic levels with heavy but otherwise nontoxic ingestions. Another important factor is the presence of acetaminophen in many different products. Individuals may be unaware of how many of the over-the-counter medications they are taking contain the drug and inadvertently attain toxic concentrations.

Alcohols: There are four alcohols commonly involved in human toxicity: methanol, ethanol, isopropanol, and ethylene glycol.

Methanol, methyl alcohol or wood alcohol, is most commonly used as a solvent. It is at times ingested, usually by alcoholics, as a substitute for ethanol. It is highly toxic and metabolized to formaldehyde and formic acid. It initially produces intoxication, and one of the potential complications of its use is blindness. It is metabolized by alcohol dehydrogenase and thus one of the treatments for methanol poisoning is to administer ethanol which competes with and slows methanol's metabolism.

Isopropanol, isopropyl or rubbing alcohol, is used as a disinfectant and a fuel. It is approximately three times as toxic as ethanol and like methanol is metabolized via the alcohol dehydrogenase pathway. Its major metabolite is acetone, and acetone levels in individuals who ingest isopropanol will approach the same levels that were initially achieved by the parent compound as metabolism proceeds. As with methanol treatment of isopropanol ingestion consists of the administration of ethanol. Like methanol, isopropanol may be utilized as a substitute of ethanol by alcoholics.

Ethanol, ethyl or beverage alcohol, is a widely consumed and equally widely abused drug. Produced via the fermentation of sugars by yeast it is the "active" ingredient in a vast range of alcoholic beverages including beers, wines, and the stronger distilled spirits. Ethanol in beverages is usually described in terms of the percentage of ethanol present per unit of volume. Beers range from 3.2 to 3.5% upward, wines 9% to 13% and distilled spirits 20% to 50%, although there are exceptions. Distilled spirits are sometimes classed by their "proof" which is a number that is equal to twice the ethanol percentage. The highest percentage of ethanol that can be distilled from an aqueous solution is 95 yielding a 190 proof "beverage." Ninety-five percent ethanol has a variety of laboratory and commercial uses including a solvent and disinfectant. Sometimes substances will be added to 95% ethanol to discourage its consumption—this process is called "denaturing" and the resulting product "denatured alcohol."

Ethanol is an anesthetic and in low doses has a disinhibiting effect. At higher concentrations, it affects coordination and in toxic dosages can lead to loss of consciousness, coma, respiratory depression, and death. Extensive studies have demonstrated that slowing of reflexes and loss of coordination begins in the vast majority of individuals at blood ethanol concentrations of 50 mg/dL. Consequently driving while intoxicated/driving under the influence (DWI/DUI) levels in the United States are set at 80 mg/dL, although this is usually phrased as .08%, a concentration of ethanol in the body of .08% by volume. In a "standard" 70 kg male, a quickly ingested standard drink (a drink consisting of a 12 oz beer, 4 oz glass of wine, or mixed drink containing an ounce of ethanol) on an empty stomach will produce a blood ethanol concentration of 15–20 mg/dL. Thus, such an individual would have to consume approximately four "standard drinks" in the space of an hour to be judged as DWI/DUI using the .08% level. Ethanol distributes throughout total body water and concentrations achieved after a particular dose will thus vary, depending on the weight of the individual. There is also data that indicate that women will experience a more rapid increase in blood alcohol after an equivalent ingestion versus a male of the same weight. Food in the stomach blunts the rise after ingestion and may lower the peak ethanol concentration versus intake with an empty one. Ethanol is metabolized in the stomach and liver primarily by the enzyme alcohol dehydrogenase to acetaldehyde that is then metabolized to acetic acid. Ethanol is metabolized or cleared at a rate of approximately 19 mg/dL per hour.

There is some variability among individuals in the intoxicating effects of alcohol, and chronic heavy users develop some degree of tolerance. Naïve drinkers are at risk of respiratory depression and death at concentrations of 350–400 mg/dL. Lower concentrations can prove fatal as well if they lead to loss of consciousness in a position where respiration is mechanically compromised or the inebriate vomits and cannot clear their airway. Acute intoxication can also lead to a variety of injuries through falls, loss of control of moving vehicles, or an innumerable variety of circumstances where the alcohol "altered" senses lead the inebriate into a dangerous situation or prompt him/her into an action they would not have undertaken in a sober state.

While mild regular ethanol consumption, 3–4 standard drinks per day, is not necessarily harmful and may even have beneficial cardiovascular effects, heavy chronic consumption, 10 or more drinks per day, is dangerous. Consequences may include alcoholic liver disease, gastritis, pancreatitis, and dilated cardiomyopathy. See Chapters 9, 10, and 11 for additional details. Alcoholics can suffer from skeletal muscle weakness and alcohol negatively affects the immune system leading to an increased susceptibility to infection. Heavy consumption is also linked to cancers of the oral cavity, larynx, and esophagus. Consumption of alcohol by pregnant women may lead to fetal alcohol syndrome in their infants characterized by microcephaly, facial dysmorphology and malformations of the brain, and cardiovascular and genitourinary systems.

Carbon monoxide: This colorless, odorless gas is the product of the incomplete combustion of carbon containing compounds and oxygen. It has an affinity for hemoglobin that is approximately 240 times greater than that of oxygen, and the resulting carboxyhemoglobin is unable to transport oxygen to the tissues. It also binds to mitochondrial enzymes and interferes with cellular respiration at the molecular level. CO in the body is commonly measured and expressed in terms of the percentage of hemoglobin saturation. CO bonding to hemoglobin is not an irreversible process but the equilibrium greatly favors it over formation of oxyhemoglobin. In individuals unexposed to elevated ambient CO there is only a fraction of a % carboxyhemoglobin in the blood. With CO exposure through cigarette smoking saturations of 5–6% can be seen. Symptoms of headache and nausea can develop at saturations of 20% and saturations over 40 can be fatal in individuals with preexisting medical conditions, while 50–60% is fatal in healthy individuals.

CO from internal combustion engines is a particular hazard to humans, although the addition of catalytic converters to automobile exhaust systems and requirements that those systems be intact have decreased the number of fatalities due to unintentional auto exhaust poisonings. Auto exhaust also contains other asphyxiant gases including CO₂ and nitrous oxides so suicidal "poisonings" via exhaust run into the passenger compartment and closed garages still occur even though blood carbon monoxide saturation levels are not always elevated. Serious intoxications and deaths are seen when other types of internal combustion devices are utilized in enclosed spaces, for example, generators and gasoline powered tools. Motorcycles, lawn mowers, and other garden and home devices if run in a garage, shed, or basement can generate enough CO to produce poisoning and death. CO is also produced in varying quantities by portable heating devices that burn hydrocarbons. CO poisoning should be suspected in individuals presenting with symptoms of weakness, nausea, and headache during the heating season particularly if the symptoms are present in multiple household members. In these cases, the source of the CO is usually a heating system/device that has been improperly installed or when an exhaust vent becomes obstructed. In times of power failures, generators and inadequately vented gas-powered space heaters are often the culprits. Burning charcoal generates a large volume of CO, and when it is used for heat or cooking inside a dwelling can have tragic consequences. It may even be utilized as a means of suicide. CO poisoning is treated with oxygen. Inhalation of 100% oxygen decreases the half life of carboxyhemoglobin in the body from 4–5 hours to a little over 1 hour and under hyperbaric circumstances to less than half an hour.

Tobacco: Tobacco use, mainly in the form of cigarette smoking, constitutes a significant public health hazard in the United States and other countries. Cigarette smoking is felt to cause approximately 400,000 premature deaths yearly in the United States and as such the single greatest potentially preventable cause. Smoking has been linked to cancer, cardiovascular disease, pulmonary disease, and low birth weights in infants born to smokers. Smokers have a decreased life expectancy that is proportional to the number of years smoked. Many of the risks of smoking decrease significantly if the smoker quits.

It is estimated that 85% of cases of lung cancer are smoking related and smokers also are at greater risk of cancers of the oral cavity, larynx, esophagus, kidney, colon, and cervix. Consumers of smokeless tobacco products, chewing tobacco, and snuff are also at risk of oral cancer as well as gum and dental disease.

Coronary atherosclerosis is the primary cardiovascular consequence of smoking, and smokers have a greater incidence of sudden cardiac death. Atherosclerotic disease is not confined to the coronaries but may be noted in the aorta and other vessels. Respiratory complications in addition to neoplasms include bronchitis and chronic obstructive pulmonary disease, mainly in the form of emphysema.

These conditions are not confined solely to the smokers themselves. Nonsmokers who are exposed to cigarette smoke in the workplace or home may also be affected demonstrating an increased risk of lung cancer and coronary atherosclerosis versus the nonexposed. Children growing up in homes where cigarettes are smoked have a higher incidence of respiratory illnesses. Because smoking involves combustion it is an underlying cause in many fire and/or explosion related injuries and deaths.

Cyanide: Sodium and potassium cyanide salts are not commonly present in the home but are readily available in laboratories and utilized in industrial processes. Cyanide is a potent and fast-acting poison that binds to cytochrome c oxidase involved in cellular oxidative processes. It has been famously utilized for suicides and homicides—in the case of the latter particularly in fiction. When the salts are combined with acid, hydrocyanic gas is produced—this was the method utilized in judicial executions involving so-called gas chambers, and hydrogen cyanide gas was infamously employed by the Nazis in their extermination camps. Cyanide containing baits have been utilized to control "undesirable" animals in the wild such as feral pigs, foxes, and coyotes. There were a number of drug tampering incidents in the 1980s where capsules containing acetaminophen were removed from store shelves, refilled with cyanide, and then replaced. In one episode, never solved, seven people were killed. These tragedies led to extensive changes in the packaging of over-the-counter medications including moving away from capsules to solid tablets and tamper resistant packaging. Some plants contain compounds that can produce cyanide on ingestion. A notorious episode involved a quack cancer "cure" called laetrile made from apricot pits that resulted in cases of cyanide poisoning and notably uncured cancers.

Insecticides: Many of these compounds are neurotoxins and highly toxic to humans. Exposure can occur in agricultural situations or tragically in the home or shop when such chemicals are mishandled or improperly stored. The reuse of milk, drink, or other food containers to mix or store such chemicals has led to many unintentional poisonings. This is also the case for other substances in the home from detergents to plant fertilizers. Should containers normally containing food or similar consumables be reused for the storage of other substances, they should be clearly relabeled and never be stored near consumables. Conversely consumables should never be kept near potentially toxic materials.

Heavy metals: Those of primary concern are lead, mercury, and arsenic. These elements have and continue to have numerous industrial and other uses and are common in the environment.

Lead was once a common constituent of paint pigments and while now banned for that purpose in most parts of the world is still found in dangerous concentrations in some older paints. When lead containing paints deteriorate, the dust and flakes may be ingested by young children. Lead is neurotoxic, particularly in the young, and can lead to stunted intellectual development at levels of intake below those required to produce signs of overt intoxication.

Mercury is similarly highly neurotoxic to the developing human. This concern has led to recommendations that pregnant women abstain from or limit their consumption of fish that may contain higher concentrations of mercury because of contamination of the waters in which they grew. Top predatory fish like tuna are also considered potentially dangerous since they accumulate in their flesh the mercury contained in the smaller fish that they feed on.

Arsenic is an element that is naturally present in some areas of the world in sufficient quantity to contaminate water supplies without the assistance of man (Bangladesh being notable). These lower concentrations are associated with higher prevalence of certain cancers in the affected populations. Arsenic was once a common ingredient in insecticides and rodenticides where it caused both unintentional and intentional poisonings. It was a favorite poison in the middle ages and later to the extent that laws were passed to prohibit its inclusion in embalming fluids in order to prevent poisoners from claiming that the arsenic found in their victims was an artifact of the embalming process.

Occupational Chemical and Substance Exposure

Chronic exposure to a variety of chemicals and other substances in occupational or industrial settings has been linked to a variety of specific diseases: benzene to aplastic anemia and leukemia and vinyl chloride to angiosarcoma of the liver. Acute injury from contact with toxic chemicals or substances is a hazard in any occupation where such substances are present. Poisoning from pesticides, for instance, is a particular risk of agricultural workers.

Exposure to dusts among miners, welders, sand blasters, and others causes a group of pulmonary diseases termed the pneumoconioses. These dusts include coal, silica, asbestos, and beryllium as well as some metal salts. While there are differences in their pathogenesis and their histopathology, these conditions all primarily result in pulmonary scarring and can cause significant disability or death. Additionally asbestos has been linked to mesothelioma and cancers of the upper and lower respiratory tract as well as the gastrointestinal (GI) tract. Various industrial or agricultural organic dust exposures have been linked to hypersensitivity pneumonitis and reactive airway disease, asthma.

Air Pollutants

The burning of wood and fossil fuels releases large quantities of combustion product gases and particulate matter into the atmosphere that can cause or contribute to human disease. These gases include nitrogen and sulfur dioxides as well as carbon monoxide and dioxide. Within the atmosphere, the nitrogen and sulfur oxides may be further oxidized to sulfuric and nitric acids. In summer, nitrogen oxides and other hydrocarbons interact with solar radiation to produce ozone, one of the major components of smog. These elements are primarily irritants to the lower respiratory system and are particularly hazardous to children and individuals with preexisting pulmonary disease, especially reactive airway disease, asthma.

Toxins of Natural Origin

Many toxins of natural origin are present in the environment including the previously mentioned arsenic. These include toxic chemicals within food plants such as oxalic acid in the leaves of rhubarb and cyanogenic glycosides in cassava or manioc, an important staple in many parts of the world. Inadequate processing of the latter prior to consumption can lead to poisoning. Various mushroom species contain potent hepatotoxins. Most of these plant toxins do not pose a great risk to those buying their food in stores but are a potential risk to those who go out and harvest naturally growing edible plants. Misidentification of plants is the cause of numerous ED visits and some fatalities in the United States. Epidemic poisoning from ergot alkaloids produced by molds growing on rye and other grains was a common affliction during the middle ages and was called Saint Anthony's Fire. Aflatoxin B produced by a fungus that grows on peanuts and corn is one of the most potent carcinogens known and is felt to contribute to the high incidence of liver cancer in some parts of the world. In the United States, aflatoxin levels in milk are monitored because of potential feed-corn contamination. Animal tissues are not immune from risks. Both wild and domesticated animals harbor parasites and bacteria that can lead to human disease if the flesh is inadequately prepared like enterohemorrhagic Escherichia coli that causes hemolytic-uremic syndrome. Some fish and shellfish may accumulate toxins from the dinoflagellates that they feed on and their consumption can cause ciguatera poisoning.

Hormones: Hormonally active medications include oral contraceptives (OC), estrogens, somatropin, and others.

OC users have a higher risk of deep venous thromboses and resulting pulmonary emboli, although that risk is decreased with modern formulations. Some studies indicate a slightly increased risk of breast cancer in OC users who started using them at a young age. OC users had a decreased risk of ovarian and endometrial cancer. Benign tumors of the liver, hepatic adenomas are associated with OC use. Estrogen therapy for menopausal symptoms and osteoporosis prevention increases the users risk of endometrial cancer. The addition of progestin, a synthetic progesterone, decreases that risk but may increase the risks of breast cancer and various cardiovascular complications, venous thrombosis and dementia. Diethylstilbestrol (DES) is a synthetic estrogen that was prescribed to pregnant women beginning in the 1940s to prevent premature labor and miscarriages. Women who took DES during their pregnancy were later found to have an increased risk of breast cancer and their daughters a greatly increased risk of a rare vaginal and cervical cancer, clear cell adenocarcinoma, as well as an increased risk of breast cancer.

Somatropin, human growth hormone, used to be obtained from processing donated human pituitary obtained at autopsy. In 1985, several cases of Creutzfeldt–Jakob disease were diagnosed in individuals who had received the hormone and subsequently some 28 cases were identified. Somatropin is now synthesized rather than obtained from human tissues, so this is no longer a risk. This example demonstrates the risks inherent in using materials collected from human sources for therapeutic purposes. When biological source materials are pooled (as was the case for the pituitaries and also for HIV contaminated factor VIII and IX concentrates used to treat hemophilia), there is the possibility that a sample obtained from one infected individual can lead to the infection of many others. The development of screening tests and improved methods of processing such materials have minimized these risks.

Testing for Toxic Agents

Implicating drugs, medications, and toxins as causative agents in human disease can be a complicated matter. In the case of an acute fatal exposure, such as a drug overdose, the appropriate history and symptoms coupled with the finding of the offending agent in the blood and/or tissues of the victim in toxic concentrations usually suffice. This involves both the qualitative and quantitative characterization of the agent since the mere presence of a substance does not necessarily mean that it was the cause of the overdose. For forensic, legal, purposes drug identifications must ordinarily be confirmed by more than one independent methodology. In the clinical setting of a possible drug intoxication, qualitative "screens" are often run on urine. The results are useful in clinical decision making but positive results may be invalid for legal purposes unless confirmed by another methodology because of the possibility of false positives due to cross reacting substances. For some substances, quantitation is important in the clinical setting as it is essential for treatment decisions; for example, acetaminophen concentrations are measured to determine whether N-acetylcysteine will be administered.

Postmortem toxicology is further complicated by sample issues. Clean uncontaminated blood or urine can be obtained from living individuals for analysis but in the deceased the samples are often hemolyzed or even decomposed and cannot be analyzed by the same methods employed in the clinical lab. Drugs and medications in the living are distributed, often unevenly, within the various body compartments and this distribution is maintained by the circulation, the integrity of cellular membranes, and other active processes. After death, these substances often redistribute in the body leading to the finding of concentrations in some samples that are different from what they would have been at the moment of death. To avoid misinterpretations, the testing of samples drawn from different sites including tissues is required.

When attempting to implicate environmental factors, testing is required to demonstrate the presence of the substance in question in the air, food, water, etc. that is thought to be the source. Often, however, the substance is not present continuously in the environment or the concern arises years after the period of exposure may have occurred. The offending substance may not be stored in the body of its victims or by the time that the concern is raised may have been cleared. As the sensitivity and capability of testing methodologies improve, it has become possible to detect quantities of substance at levels orders of magnitude lower than previously with the not unexpected finding of chemicals that had not been detected before in environmental samples. The significance of many of these findings in terms of human disease causation is unknown.

Burns

Contact with hot surfaces, fluids, gases, flame, and exposure to radiant heat can lead to burns. Cutaneous burns may be separated into three categories, first-, second-, and third-degree based on the depth of injury.

First-degree burns are characterized by redness, erythema, and pain. Sunburn from exposure to excess solar radiation or the lamps of a tanning device are typical examples. These heal without short-term sequelae, except in the more severe instances where subsequent superficial desquamation of the keratin-containing layer of the skin (peeling) occurs. The melanocytes in the skin are also stimulated to produce melanin leading to a tan. Long-term consequences of exposure to such radiant energy include a variety of degenerative actinic changes as well as an increased incidence of basal and squamous cell carcinomas. Malignant melanoma has been linked to episodes of heavy sun exposure with burns at a young age—particularly in lightly pigmented individuals.

Second-degree burns are characterized by the separation of the epidermis from the underlying dermis with blister formation. Because islands of epidermis remain around the dermal adnexal structures, hair shafts, sweat, and other glands, the epidermis can regenerate to cover the denuded areas and such burns generally heal without scarring.

Third-degree burns damage the adnexal structures of the dermis and lack any surviving epidermis. Hence, these burns can only heal by growth inward from the viable margins of the wound. Third-degree burns of any significant size cannot completely close in this fashion and remain as open sores. Such injuries must be treated with grafts of epidermis taken from areas of intact, uninjured skin. Deeper, charring, injuries are sometimes called fourth-degree burns. Some prefer to dispense with this classification and more simply characterize burns as either partial or full thickness. First- and second-degree burns would thus be partial thickness while third- and fourth-degree burns would be full thickness (Figure 3-15).

Direct acute thermal injury leads to denaturation of proteins. Most such injuries will involve the skin but internal "burns" can occur as the result of the ingestion of caustic substances such as strong acids and bases. Although no heat is involved, tissue injuries caused by such substances, whether external or internal, are also referred to as burns. Lasers and electrocautery devices work through the thermal coagulation of tissue. Focal internal thermal damage beyond what was therapeutically intended can be a complication of operative and other therapeutic procedures.

Loss of the protective epidermis of the skin has several consequences including fluid loss through the now exposed dermal and subdermal tissues and providing a route for the entry for microorganisms into the body. Patients with extensive burns have serious problems with fluid balance and require vigorous volume and electrolyte support. They are in a hypermetabolic state and at great risk of infections. Their management is one of the most challenging in medicine and is optimally undertaken in specialized burn centers. Recovery and rehabilitation is a long and daunting process and great efforts must be expended during that process to minimize scarring and preserve the mobility and function of damaged limbs and other mobile structures.

Another potential complication is lower respiratory tract injury from the inhalation of toxic products of combustion as well as particulate matter. This can cause both acute and long-term pulmonary damage. ARDS is a feared complication. Hot or superheated air can cause upper airway damage but will not reach the lower airways. Steam and hot particulate matter, however, can carry thermal energy deep into the airways and lungs.

Scalding

Scalding is a mode of thermal injury that warrants further discussion. While this most commonly occurs when hot water comes into contact with skin, any sufficiently hot liquid can produce the same effect. Scalding can result from splashing, pouring, or immersion and the pattern of burns produced mirrors the mechanism (Case 3-4). As the temperature of a liquid increases above normal body temperature so does its potential to scald. Water at 160°F will burn adult human skin essentially instantaneously while 30 seconds exposure is required at 130° (Figure 3-16).

Since the process involves the transfer of heat energy from the liquid to the skin, the length of time of contact and the volume of liquid may also be factors. Liquids of greater density carry more energy so a droplet of boiling water contains less heat energy than one of cooking oil. Moreover, the oil may be heated to temperatures that greatly exceed that of boiling water.

Environmental exposure to heat and cold represents a threat to organisms whose biochemical processes require maintenance of an optimal internal temperature. When internal temperatures stray significantly above or below that temperature, 37°C in humans, those processes break down with eventually fatal consequences.

Hyperthermia: Hyperthermia occurs when ambient temperatures exceed normal body temperature, and normal cooling mechanisms such as sweating are overwhelmed. It may also occur as a consequence of excessive internal heat generation due to fever or hypermetabolic states.

Heatstroke represents the most severe of several stages of heat stress. In heatstroke, sweating fails and as body temperature rises cardiovascular collapse may ensue. The victim may develop confusion, delirium, headache, chills, and seizures. Their skin is usually hot and dry.

Heat exhaustion is a milder form with symptoms of weakness and nausea. They are usually sweating with a normal or slightly elevated body temperature and appear pale and clammy with fast shallow breathing. Other milder heat stress-related symptoms can include cramps, syncope, and rash. Heat stress is often seen in the context of vigorous exercise in a warm environment, particularly if the victim is not accustomed to the heat and/or there is inadequate fluid intake to match the losses from sweat and exercise. The body has an adaptive mechanism for hot environments in heat acclimatization. This response to exercise-induced elevation of core temperatures in a hot environment includes a reduced threshold for sweating and cutaneous vasodilatation accompanied by increased sweat output and skin blood flow. Hence, it is no surprise that heatstroke tends to appear in athletes early in the course of rigorous late summer training regimens after they have spent the earlier part of the summer in relative inactivity.

Hyperthermia deaths also increase in the United States during heat waves particularly in large northern cities among the infirm and elderly whose living quarters lack adequate ventilation let alone air conditioning. Preexisting medical conditions are an important contributing factor. Some medications, such as the phenothiazines, can interfere with internal thermoregulatory function and predispose individuals to heatstroke.

Hypothermia: In hypothermia, a low ambient temperature leads to a drop in internal temperature below 35°C. The body initially responds by reducing blood flow to the skin and involuntary shivering follows, the muscular activity generating heat. When at some point these mechanisms fail, blood flow to the skin resumes and the resulting flushing may lead to a perception of overheating and a phenomenon known as "paradoxical undressing" where the victim removes items of clothing in spite of clearly being in an environment where such was needed. As the body cools, metabolic activity slows along with oxygen consumption (allowing induced hypothermia to be utilized as an operative adjunct in cardiac and brain surgery). The danger of hypothermia increases as ambient temperature drops. Adequacy of protective clothing is a factor as well as host fitness. As is the case in hyperthermia, the risk increases with age. Body habitus plays a role with heavier individuals less susceptible than thin ones. Loss of heat is greatly accelerated by convection and moisture. Wet clothing often loses its insulating properties and cold water immersion leads to rapid cooling. Water temperatures that are acceptable as outdoor air temperatures can lead to hypothermia. For example, prolonged exposure to water at a temperature of 26°C (79°F) can lead to hypothermia. A water temperature of 10°C (50°F) often leads to death in 1 hour; water temperatures near freezing can cause death in as little as 15 minutes. Ethanol consumption is a risk factor for hypothermia in two ways. First its behavioral effects can put the individual in an environment where they are at risk, and second its vasodilator effects increase heat loss from the skin.

Hypothermia can also cause local injury, the most familiar of which is frostbite. The lowered temperature leads to a failure of local circulation and resulting ischemic injury to the tissues. Small vessels are damaged and if circulation is restored there is vascular leakage, thrombosis, and ultimately necrosis of the devitalized tissues. Chronic exposure to cold in some individuals can lead to skin ulcers, chilblains, and a severe debilitating condition called "trench foot" often appeared in soldiers forced to spend long periods sitting or standing in wet trenches in the winter.

Electricity is characterized in units of pressure, electromotive force (EMF) or volts, and volume of flow, amperes. The relationship between these is expressed by Ohm's law, I = E/R, where "I" is current flow or amperes, "E" is EMF or volts, and "R" is the resistance of the medium through which the current is passing in ohms. Thus as voltage rises, given a fixed resistance, the flow, amperage, also rises. If resistance increases with constant voltage, current flow decreases. As current passes through a medium, a conductor, it generates heat that is proportional to the volume of current and the resistance of the conductor.

Static Electricity Injury

Electricity has two forms for our concern: static and generated. Static electricity results from the frictional buildup of charges on moving objects or surfaces in the environment. We are all familiar with this phenomenon as it manifests itself in the shock we experience when we touch an object after shuffling across the carpet on a winter day. While the actual voltages involved are high, there is negligible current flow and such discharges are not ordinarily directly harmful to individuals. However, a static discharge can serve as an ignition source in the presence of inflammable fumes or dusts and they also represent a significant hazard to sensitive electronic equipment.

The truly dangerous form of static electricity is lightning. Peak current flow in a discharge can approach 3000 amperes and generate temperatures over 20,000°C. Lightning strikes kill approximately 60 people yearly in the United States and injure several hundred more. Most individuals struck are engaged in outdoor activities. In the United States, the states with the highest number of fatalities are Florida and Colorado, respectively. The mechanism of death is usually cardiac asystole, although burns can also result. Survivors may have neurological sequelae.

Generated Electricity Injury

Generated electrical currents come in two forms: direct and alternating. In direct current, the flow of charge is unidirectional by convention from "positive," high potential to "negative," low potential. In alternating current, the direction of flow reverses or "cycles" a certain number of times per second, commonly 60. Most electronic and battery-powered devices utilize direct current, while virtually all electric transmission is AC since it is a much more efficient means of sending current long distances utilizing high voltages that can be easily stepped down to lower voltages by transformers for end users. AC current is more dangerous to humans because of its potential to induce ventricular fibrillation should a current pass through the heart. High-voltage transmission lines carry current in the hundreds of thousands of volts; neighborhood distribution lines are at approximately 7000 volts that is stepped down to residential electrical service in the United States at 120 and 220 volts. Voltages of greater than 50 are potentially sufficient to overcome skin resistance in humans so even household circuits can produce fatal "shocks." Household service lines are usually insulated, but the distribution lines are not and many electrocutions occur when ladders, antennas, pruning devices, and other conductors inadvertently contact these lines.

Mechanism of Injury

Currents passing through the body can, in addition to affecting cardiac activity, affect other muscles inducing contraction of voluntary muscles. A current flow of 20 mA can cause tetany, 100 mA can cause ventricular fibrillation, while 2 amperes can lead to ventricular standstill. Current passing through the brain can cause seizures. While the internal tissues offer little resistance to electrical current, dry skin has a high resistance. Thus, when a person comes into contact with a sufficient source of current to effect entry, burns may be produced at the point of contact with the electrical source as well as at the point where the current "exits," that is, where the body is grounded to a point of lower electrical potential. Such burns often take a characteristic appearance with a central pale area or blister and a surrounding ring of reddening or erythema. With high current flow, there may be charring at the points of contact (Figure 3-18).

In very high-voltage electrocutions, there may be deep internal injury from the heat generated as the large volume current passes through muscle and other tissues; survivors may require extensive debridement of the damaged areas. Such injuries are a serious risk for lineman and other occupations that work with high-voltage electrical lines.

When voltages above 5–700 are involved, actual direct contact with a conductor at high potential is not necessary as the current can jump or "arc" to the point of lower potential.

Radiation is energy in the form of waves and/or particles traveling through space. It includes electromagnetic energy and particles (alpha and beta particles for example) emitted by radioactive elements and other sources. It can be subdivided into ionizing and nonionizing based on whether the radiation has sufficient energy to remove electrons from atoms or molecules. Ionizing radiation is more likely to cause injury to humans than nonionizing via generation of free radicals and other reactive compounds.

Environmental Radiation

Radiation is ubiquitous in the environment from multiple natural sources primarily cosmic rays from space and naturally occurring radionucleotides. Any individual's exposure to these is determined by geography, for instance, greater at higher altitudes and in areas with more natural radioactive elements in soils, rocks, and water. Stone and brick houses have a higher level of background radiation than wooden ones. Currently about half of the radiation exposure the average person is subject to comes from man-made sources, more than 95% of this from medical procedures. Absent medical sources, the bulk of exposure that the average person is subject to comes from natural sources (especially radon) (Table 3-3).

Radon is an element of particular public health concern because it is present in significant concentrations in rocks in many parts of the world and can accumulate in better-sealed modern structures when it seeps out into soils, air, and water. Radon decay products, radon daughters, are inhaled by the inhabitants of these buildings. It is believed that radon is the second leading cause of lung cancer behind only cigarette smoking.

Acute and Chronic Effects of Radiation

Ionizing radiation is measured in terms of the ionization potential—the amount of radiation necessary to create a charge in a volume of matter. Traditionally, this was expressed in roentgens. A more biologically significant measurement is the absorbed dosage or energy deposited. This is expressed in rads or grays (Gy). A Gy is the amount of radiation required to deposit a joule of energy in 1 kg of matter (100 rad = 1 Gy). A rem is the dose of radiation that causes a biological effect equivalent to one rad of x or gamma rays. Another term is the sievert (Sv) that is the absorbed dose in Gy multiplied by a weighting factor to reflect the fact that certain forms of radiation have greater biological effects than others.

High-energy ionizing radiation has the capacity to directly kill cells as well as to produce alterations in DNA by hydrolyzing water creating free radicals. Replicating cells are more sensitive to such damage than those that are not. Thus, many of the manifestations of radiation poisoning appear in the GI tract and hematopoietic systems where normal cellular replication occurs at high rates and whole body radiation is not tolerated as well as localized exposure.

Whole body doses of 200 rem, 2 Sv, can prove fatal from GI and hematopoietic complications over a course of several weeks. Dosages of greater than 1000 rem, 10 Sv, can prove fatal in hours secondary to CNS injury. These conditions are referred to as acute radiation syndrome or radiation sickness (Table 3-4).

The chronic effects of radiation exposure are also dose dependent and primarily involve an increase in the incidence of neoplasms. Linked cancers include those of the skin, leukemia, bone, lung, and in children thyroid.

Nonionizing electromagnetic radiation can produce injury mainly through the generation of heat leading to burns. There are concerns about the carcinogenic potential of radio and microwaves but at this time there is no convincing evidence to that effect. The hazards of ultraviolet radiation are well documented and range from the acute agony of sunburn to the changes of premature aging with repeated intense exposures. Basal and squamous cell cancers of the skin are another consequence as well as malignant melanomas. Fair skinned individuals are at much greater risk of these complications than heavily pigmented ones.

Radiation Therapy-Associated Injury

Radiation therapy involves divided, fractionated, doses of up to 80 Gy to localized areas. In addition to the intended target tissue, usually a neoplasm, surrounding normal tissues will be damaged. Vascular injury with thrombosis and resulting ischemic injury leads to fibrosis within the tumor and immediately adjacent tissues. As the beam of ionizing radiation passes through other tissues on its way to the target, those tissues will also incur injury. Radiation-induced pneumonitis, gastritis, proctitis, cystitis, and dermatitis are common complications of radiation therapy when those tissues are in the path of the directed beam or adjacent to implanted radioactive materials, brachytherapy. Delayed complications may be seen as a result of radiation-induced fibrosis. Secondary neoplasms can also appear in patients successfully treated with radiation. In the case of Hodgkin disease radiation therapy, an increased risk of neoplasms of the lung, breast, and thyroid has been noted in addition to excess late mortality from cardiac disease. Of note is that younger age at treatment is related to a greater incidence of breast and thyroid cancers in this group reflecting greater organ radiosensitivity in the young.

Iatrogenic injury includes all injuries or illnesses that are caused by medical treatment or diagnostic procedure. By this definition, it encompass some conditions that would not fit within the meaning of trauma and injury that we have used previously in this chapter such as an infection complicating surgery or developing from an indwelling catheter. Considered in a broad perspective, however, iatrogenic injuries are a hazard of a specific "environment" and often do involve external agents in the form of chemicals (therapeutic drugs or solutions), physical manipulations of the patient or radiation. Institute of Medicine reports have identified medication errors as the most common of such events and estimated that tens of thousands of preventable deaths and hundreds of thousands of injuries to patients occur yearly. Regardless of the true numbers incidents of iatrogenic injury are unfortunately not rare and are costly in terms of morbidity and mortality.

Medication errors include administering the wrong drug as well as the right drug in either excessive or inadequate quantity Case 3-5. Drug side effects or reactions that lead to patient injury are not necessarily errors but have similar consequences.

Physical injuries also occur in hospitals, clinics, physician's offices, or other treatment facilities and range from falls to surgical mishaps. All operative and interventional procedures have some degree of inherent risk that must be balanced against their potential benefit to the patient as attested by informed consent documentation. Some errors have occurred so frequently that what seem to be obvious strategies are routinely employed to prevent them. These include placing patient identification bands immediately upon admission to be sure that right person receives the correct medication or goes to the OR. Marking the site of planned procedure to ensure that the right organ or extremity gets operated on is another example. It is a continuing challenge to develop protocols, refine procedures, and implement strategies to ensure that such events do not occur and medicine is actively examining other procedurally oriented disciplines for inspiration.