Chapter 15. Sedation and General Anesthesia

The following vignette provides an excellent picture of typical operating room (OR) anesthesia in a resource-poor venue1:

John, an anaesthetic clinical officer, is administering a general anaesthetic [and] performs a rapid sequence induction with thiopental and suxamethonium and intubates using his own laryngoscope and a tracheal tube that has been used dozens of times before … John carries all his own equipment with him, along with a supply of drugs for the day—anything left in theatre will disappear by tomorrow. Normal saline is running in through an 18G cannula that the patient's family were asked to buy from the local pharmacy.

John administers 50 mg of pethidine—this may be the last analgesic the patient receives until the unpredictable visit of the night matron to the ward in 9 h time—and turns up the OMV [Oxford Miniature Vaporizer] to deliver 2% halothane. The inspired concentration must be estimated clinically because the halothane "expired" 8 months ago and the clinical effect is unpredictable. The EMO [Epstein-Macintosh-Oxford] vaporiser and a bottle of ether are on stand-by behind the anaesthetic machine, as we are down to our last bottle of halothane…. The modern anaesthesia monitor, looking out of place in these surroundings, was purchased, along with eight others, by the European project. The screen has a psychedelic tinge to it and I suspect it is on its last legs. The capnograph trace is flat, as the last remaining moisture trap has been "borrowed" for use in ICU, where it will be circulated around the four beds. The ECG trace is true, but periodically interrupted as the long out-of-date electrodes require a small drop of thiopental to improve their conductivity. The oximetry probe is a paediatric one and roughly taped with grubby Elastoplast around the man's little finger.

John ventilates the patient using the Oxford Inflating Bellows as part of a draw-over system, aiming to keep him deeply anaesthetised and apnoeic using a high concentration of halothane. There are no muscle relaxants apart from suxamethonium. Emergency drugs, atropine and adrenaline, are drawn up on a redundant Boyle's machine, which acts as a trolley and equipment store. A lone size H oxygen cylinder is deep in dust in the corner and has been empty for several years.

John requests a nasogastric tube, so I head to the locked anaesthetic store room where 10 or so years of unsorted donations to the department have piled up. After 15 min, I find one at the bottom of a box of out-of-date NG feed. I can tell by the look on his face that John is torn between using this valued commodity for this patient or saving it for the next.

Anesthesia in Austere Circumstances

Anesthesia's three principal functions are to keep the patient alive through surgery, to make surgery painless, and to provide the best possible surgical conditions.

The purpose of this chapter and, in fact, this entire book is illustrated by two questions that Drs. Boulton and Cole posed in their series entitled, "Anaesthesia in Difficult Situations"2:

1. What would I do if had to give an anesthetic and operate on a patient in an isolated hospital 100 miles from the nearest outpost of civilization?

2. What would I take on an expedition to the Arctic … or in the Himalayas … or on a ship … or to an area of devastation following an earthquake or nuclear holocaust?

This chapter and the next are for clinicians who may need to administer anesthesia in austere situations with limited supplies and equipment. These chapters highlight medications that can safely be used by non-anesthesiologists (e.g., ketamine), little-used anesthetics that are generally available in austere situations (e.g., IV ethanol), and anesthetics available in austere settings that are not familiar to younger anesthesiologists from industrialized nations (e.g., ether, halothane), as well as classic basic methods of delivering anesthesia (e.g., open-drop). Those trained in anesthesia obviously are more familiar with these medications and techniques than are other clinicians. The key to providing safe and effective anesthesia is to use equipment and techniques that employ the skills you already possess.

Standards and Shortages

Although international standards for anesthesia administration exist, the norm is that shortages of trained anesthesiologists, equipment, and medications limit how these standards can be implemented.

Scarcity of Trained Anesthetists/Anesthesiologists

A worldwide shortage of trained anesthetists means that in developing countries, other practitioners, including physicians, dentists, nurse practitioners, physician assistants, and paramedics, may need to provide general anesthesia with limited additional training and with minimal supervision.

The basic rule of thumb is that "a practitioner faced with the necessity of giving an emergency anesthetic, perhaps for the first time since his student days, is well advised to stick to a technique which he has at least seen used at one time or another." If an experienced anesthetist must supervise or manage multiple inexperienced practitioners giving anesthesia, which may be the case in many situations, "the technique employed would have to be as simple as possible so that it could be quickly taught."2

Commonly, the clinician must be both the surgeon and the anesthetist. In these cases, the rule is "use local and regional methods where you can. If you have to give a general anesthetic, secure the patient's airway and make sure that there is [an IV] running before you start. With a clear airway and [an IV line], most of your problems will be over. Induce and intubate the patient yourself, and don't operate until anesthesia is stable."3 During the procedure, have an assistant monitor the patient by continually checking the blood pressure (BP) and the pulse using an esophageal or precordial stethoscope.3,4 (See Chapter 5, Basic Equipment, for how to improvise these devices.)

Medication Standards and Scarcity

The World Health Organization (WHO) lists what they consider to be the essential medications for anesthetic care, although cost and supply problems may limit the anesthetics and associated medications (Table 15-1) that are available for local, regional, and general anesthesia.

Goals of General Anesthesia

Administering general anesthesia provides three benefits: (a) hypnosis, putting the patient to sleep; (b) analgesia, relieving pain; and (c) relaxation, easing the muscles sufficiently to perform the procedure, primarily in abdominal and some orthopedic cases.6

Safety

An anesthetist's primary goal is to anesthetize patients and have them recover without ill effects from the anesthesia. Whether this happens depends a great deal on the anesthetist's abilities and how carefully he follows the rules for safely anesthetizing patients (Table 15-2).

Essential Elements

Four of the five essential elements for general anesthesia may need to be improvised or omitted in austere situations: premedication, monitoring, induction medications, and oxygen. Additionally, alternative maintenance drugs (anesthetics) or delivery methods may need to be used.

Premedication

Premedication provides mild sedation for the patient and counteracts some side effects, primarily excess salivation and increased vagal tone.

A wide variety of narcotics, benzodiazepines, phenothiazines, and other medications may be used for premedication. Try to use sedating anticholinergics (e.g., those with antihistamine activity) if the normal medication cannot be used. Premedications are usually administered parenterally, but many may be given orally.

Promethazine 50 mg (1 mg/kg) tablets (which also have anticholinergic activity) can be used in adults for nausea and very mild sedation. Give promethazine about 2 hours before anesthesia. This medication is particularly good if ketamine is used as a general anesthetic. Diazepam tablets, 10 to 20 mg (0.15 to 0.25 mg/kg), can be used as a tranquilizer before either regional or general anesthesia. Oral diazepam has a more rapid and reliable onset than does intramuscular (IM) diazepam.8 Diphenhydramine (Benadryl) is cheap, and almost always available. It can be given parenterally or orally, and is both sedating and anticholinergic.

Considered by many anesthesiologists to be the only essential preoperative medication, atropine 0.4 to 0.6 mg dries secretions and diminishes vagal tone on the heart. Atropine may be administered IM 30 to 40 minutes before induction or diluted and given IV immediately before anesthesia.6 Atropine can also be administered orally in tablet form (0.5 mg in an adult) at least 20 minutes before the general anesthetic is administered. There is no harm if the patient takes it with a small amount (~20 mL) of water.8

Basic Monitoring

In austere situations, anesthesia with only the most basic monitoring (even more basic than what you're thinking) is the norm. Often the only monitoring is checking the pulse: either constantly with an esophageal or precordial stethoscope (improvised models of both instruments are described in Chapter 5, Basic Equipment) or at least every 5 minutes while taking a BP. You can also monitor the pulse by laying a finger just anterior to the tragus of the ear to feel the superficial temporal artery pulsate. Also, monitor the patient's skin color, capillary refill, and the color of any blood from the surgical site, since this requires little or no apparatus. A wisp of cotton taped near the nostril is a useful indicator that the patient is still breathing.6

Esophageal stethoscopes are particularly important during thoracic procedures. Only one earpiece is needed, although a modified stethoscope can also be used. Precordial stethoscopes (that can also be placed over the back) are particularly important to use during procedures on babies. Likewise, only one earpiece is needed, but the bell should be securely taped to the patient before the procedure begins.

Induction

Both IV and inhalation agents are often used for induction. Ketamine needs no induction agent.

Benzodiazepines, although not often used for induction, can be used for this purpose. Diazepam, often the most readily available benzodiazepine, can be used as an IV induction agent, although it has a longer onset and longer duration (i.e., longer "hangover") than most other agents.9 The newer benzodiazepines generally work faster and have shorter half-lives.

The most feared complication during induction is laryngospasm. Since a neuromuscular blocking agent may or may not be available, provide constant positive pressure with an anesthesia bag or a bag-valve-mask (BVM). This normally breaks the spasm. If not, spray the cords with lidocaine, and be prepared to do a cricothyrotomy (rarely needed).

Oxygen

In austere situations, oxygen is frequently unavailable, and so is considered a luxury. If oxygen is scarce, use it only to preoxygenate patients who will undergo brief apneic procedures, to induce and intubate small children10, and to supplement anesthesia at altitudes >9000 feet (2743 meters). Also provide it for patients with laryngospasm, acute desaturation, significant anemia (Hgb <9 g/dL), or heart or lung disease, and to those in shock.9

Also consider using oxygen when (a) inducing anesthesia in a patient using ether and air; (b) giving anesthesia with more than 8% ether; (c) doing a Cesarean section (C-section), but use only until the baby is delivered; (d) patients have any respiratory disease or considerable airway secretions; and (e) the preoperative BP has fallen by >30%.

Stages of Anesthesia

Theoretically, all patients may go through four stages (plus substages, or planes) of anesthesia, no matter which agent is used (Table 15-3). Ether is the anesthetic that shows all the classic stages, so the pattern with ether is described more fully under "Ether" in Chapter 16, Anesthesia: Ketamine, Ether, and Halothane.

When anesthesia is given with basic equipment and few medications, tracking anesthetic stages can be a useful safeguard against over-medication.

Anesthetics vary widely in their effects, so staging must be used with the particular drug's effects in mind. The general pattern follows the oversimplified, but useful, concept that anesthetics suppress the central nervous system from above downward, as blood concentration increases. This progression (stages) is based upon the patient's body movements, respiratory rhythm, oculomotor reflexes, and muscle tone. The classic anesthetic stages are detailed in the following paragraphs.

Stage 1: Analgesia

There is suppression of the highest cerebral centers, with the patient gradually losing the sensation of pain. Patients remain conscious and rational, and have decreased pain perception. Muscle tone, breathing, and pulse are normal. Stage 1 anesthesia is indicated for obstetric analgesia, and as a supplement to local anesthesia for minor procedures.

Stage 2: Excitement (Delirium)

This stage begins when patients lose consciousness and become excited, struggle, and (possibly) become difficult to control. Patients retain their gag reflex and can protect their airway, although they breathe irregularly and may hold their breath. Their pupils generally become dilated. Their abdominal muscles contract during expiration. They lose their eyelash reflex and have roving eye movements and dilated but reactive pupils. They retain reflex responses to any painful or irritating stimuli, including noxious anesthetic vapors.

Stage 3: Surgical Anesthesia

In this stage, patients no longer respond to painful stimuli. Muscular relaxation progressively increases, spontaneous respiration diminishes, and patients lose their protective gag reflex. Non-anesthesiologists need only recognize two planes: acceptable ("Light") and too deep.11

Plane: Light Surgical Anesthesia

This is the optimal anesthetic level for most patients during surgery. Patients' breathing becomes regular again, although they will inspire deeply every 2 to 3 minutes. The eyes no longer move and, as the anesthesia level deepens, the pupils gradually dilate. The patient no longer moves and muscular tone decreases. The abdomen and chest move synchronously. An artificial airway or endotracheal (ET) tube may be inserted in this plane—but not earlier.

Plane: Deep Surgical Anesthesia (Too Deep)

In this plane of anesthesia, patients' intercostal muscles become progressively paralyzed, eventually having paradoxical movement (moving in with inspiration). Sudden inspirations pull on the mediastinum and trachea, drawing it downward (the "tracheal tug"). Patients' pupils become progressively less reactive to light. Abdominal surgery is actually very difficult at this anesthesia level if the patient is not pharmacologically paralyzed.

Stage 4: Medullary Depression (Way Too Deep)

During stage 4, the brainstem's respiratory center becomes depressed, which causes patients to stop breathing and lose all muscle tone. Their pupils are fixed and dilated. The heart may (as with chloroform) or may not (as with ether) be dangerously depressed.6 If a patient stays in this stage too long, his heart stops and he dies.11

Trauma Patients

Assume that all trauma patients have full stomachs; the elective anesthesia standard of "nothing-by-mouth (NPO) for six hours" is a pure fantasy. Airway control, preventing aspiration, and being prepared to provide anesthesia immediately to hypovolemic, unstable patients optimize trauma anesthesia.

Altitude and General Anesthesia

High altitude (arbitrarily considered to be above 3000 meters or 10,000 feet) and extreme cold may affect anesthesia delivery. Three types of individuals may present for anesthesia at high altitude: the unacclimatized newcomer, the acclimatized newcomer, and the resident native.

Patients

The unacclimatized newcomer, who has been at altitudes above 3000 meters for less than 4 months, is in an extremely unstable physiological state, and initially may suffer from acute mountain sickness (e.g., high-altitude pulmonary edema, high-altitude cerebral edema).12 This makes sedation and general anesthesia precarious, at best.

Acclimatized newcomers may also be in danger of pulmonary edema. They have probably acquired similar physiological characteristics to the natives, including polycythemia, hypervolemia, increased pulmonary blood volume, pulmonary hypertension, right ventricular hypertrophy, and increased diffusion capacity. Nevertheless, give oxygen to these patients during any emergency surgery and, if at all possible, return them to sea level for surgical treatment.12

Resident natives, who were born and live at altitude, are capable of exhaustive physical exercise despite their often plethoric, cyanotic, and barrel-chested appearance. After visiting lower altitudes for a few days, however, they too may get acute pulmonary edema on returning to altitude.12

Anesthetic Agents

The conduct and choice of anesthesia and analgesia at high altitudes depends on three factors: (a) the patient's pathophysiological state, (b) the decreased oxygen tension due to low barometric pressure, and (c) the peculiarities of inhalational agents. With some modifications, particularly the addition of oxygen, general inhalation anesthesia may be administered.13

When preparing to deliver general anesthesia above 3000 meters (approx. 10,000 feet), try not to use any drug that depresses the respiratory center. If you must use such a drug, reduce the dose of premedication. The increase in respiratory tract secretions at high altitudes, especially when using ether, suggests using higher doses of atropine even though that risks increasing preexisting tachycardia. Provide careful fluid replacement because of the increased risk of pulmonary edema.

During surgery, use oxygen supplementation, if available, on all anesthetized patients. To achieve an oxygen tension equivalent to that at sea level (150 mm Hg), 32% supplementation is required at 3000 meters (approx. 10,000 feet) and 42% at 5000 meters (16,500 feet). However, unsupplemented ether–air anesthesia has been successfully used at altitudes of 2500 to 3000 meters.12 On the other hand, nerve blocks and anesthetic infiltration may be limited by the vasoconstriction accompanying hypothermia.13

Consider using IV ketamine, since at doses of 2.0 mg/kg, it produces a dissociative anesthesia while not depressing the hypoxic drive or interfering with the pharyngeal or laryngeal reflexes. Use supplemental oxygen when available, especially during recovery, for less-acclimatized individuals.14,15 Avoid using N2O.

Equipment

Both anesthetics and the associated equipment work progressively less well as the altitude increases. The practical limits for general inhalation anesthesia are not precisely known, but, whenever possible, surgery should not be performed at altitudes higher than 4000 meters (~13,000 feet).16

Extreme Cold and General Anesthesia

Use caution when giving general anesthesia—or doing surgery—in extremely cold environments. Aside from the obvious problem of IV fluids freezing if not properly insulated, vasoconstriction reduces the size of veins, which makes IV placement difficult and reduces the absorption of drugs injected subcutaneously. Increased static electricity and open-flame heating units may augment the explosive hazard of the inhalational agents. To humidify the extra-dry air, use an IV infusion set to deliver normal (0.9%) saline (NS) at 2 to 4 drops/minute through a very fine hypodermic needle inserted into the connector between a BVM and the patient's ET tube.13

What Is Sedation?

While sedation implies that patients have a depressed consciousness rather than being asleep, there is often little difference between procedural sedation and short-term general anesthesia, except that the former usually does not include the use of neuromuscular blockade or invasive airways (e.g., ET tube or laryngeal mask airway [LMA]). The similarity between the two is highlighted in the ASA's description of sedation levels (Table 15-4).

Uses

In the acute, outpatient setting, the most common reasons to sedate patients are for fracture reductions/treatments, joint relocations, laceration repairs, and lumbar punctures. The fewest complications occur with ketamine (0.7% of cases), propofol (0.8%), or morphine (2.9%). The most complications occur when the sedative is hydromorphone (9.7%), fentanyl (9.5%), midazolam (6.4%), or etomidate (6.2%).18

Sedation is often used for pediatric procedures. However, if a practitioner does not have the skills or the appropriate medications and equipment to sedate the child safely, "tie and cry" (see Fig. 14-4) with liberal use of local or regional anesthesia is a more prudent way to proceed.19

Medications

Various medications can be used for sedation, depending upon their availability and the clinician's comfort level and experience using them. These include ketamine, narcotics, ethanol, benzodiazepines, and propofol (Table 15-5).

Ketamine

Ketamine is often used for sedation, especially in children, and is discussed in Chapter 16, Anesthesia: Ketamine, Ether, and Halothane.

Narcotics

Using IV narcotics to a point short of anesthesia is a valuable technique to know when "extreme emergency" conditions are physically dangerous to both the patient and clinician.2,6 An initial dose of l0 mg of diluted morphine or 50 mg of meperidine will give you an idea of the patient's reaction, but at least 30 mg of morphine or 200 to 300 mg of meperidine may be required before adequate sedation is achieved if local anesthesia is not used simultaneously.6 Maintaining an adequate airway may become a problem when using this method.

Ethanol

Since ancient times, ethanol (ETOH) has been a known soporific.22–24 Intravenous alcohol has been used successfully as an anesthetic induction agent for nearly a century.25 In the 1960s, Dundee used an 8% (weight/volume) solution prepared by adding 110 mL of 95% ethanol to a 1-L bag of Hartmann's solution (similar to lactated Ringer's solution). Its pH was about 6.4. Each otherwise healthy adult patient received just over 500 mL of the solution. Of those receiving a strong opiate (meperidine) and often pentobarbital as a premedication, 70% could be induced with ethanol–nitrous oxide and 60% had the surgery completed with only these medications. He found that the onset of sleep with ethanol induction was accompanied by a progressive fall in oxygenation (PaO2) and that any post-ethanol delirium could be rapidly controlled by small IV doses of benzodiazepines.26

Benzodiazepines

Benzodiazepines can induce relaxation and cooperation, and often provide an amnestic response. Titrate doses (Table 15-5) to patient tolerance depending upon the patient's age, the patient's other illnesses, the use of additional medications, and the procedure's complexity. Significant respiratory depression can occur, but is more common if these medications are combined with opiates. The two most commonly used medications in this class are midazolam (best) and diazepam (most readily available worldwide).

Midazolam is short-acting, with a short recovery period. A dose of 0.02 mg/kg to 0.1 mg/kg IV typically produces sedation in 2 to 3 minutes, with the clinical effects lasting from 10 to 30 minutes. In elderly or debilitated patients, use lower doses, since these patients may be more sedated and have longer recovery periods at lower doses. Repeat doses until the desired effect is achieved. Side effects include dose-related respiratory depression, especially in elderly patients, patients with chronic obstructive pulmonary disease (COPD), or patients who have taken alcohol, barbiturates, opioids, or other central nervous system depressants. Hypotension can be significant in hypovolemic and elderly patients. Midazolam has no analgesic activity. It crosses the placenta and enters breast milk.27

Diazepam is also used for conscious sedation. However, because of its long half-life, it may be difficult to titrate and may provide a duration of action that is longer than desired. Compared to midazolam, diazepam poses greater risk for phlebitis, has less associated amnesia, and has erratic absorption if given IM. If no other sedative agent is available, it may be useful, especially if given orally about 30 minutes prior to a procedure.

Propofol

Propofol, due to its high cost, will often be unavailable in austere settings. If it is available, use it in increments of 0.5 mg/kg every 60 seconds IV until the desired effect is achieved and to maintain that level of sedation. Because of its pharmacokinetics, oral administration will not sedate the patient. (Angela M. Plewa, PharmD, personal communication, April 8, 2008.) Similarly scarce will be the popular ketamine-propofol combination (ketofol), which is a 1:1 mixture of ketamine 10 mg/mL and propofol 10 mg/mL titrated in 1- to 3-mL aliquots to attain deep or dissociative sedation.

Introduction

One method of administering IV agents is to use a syringe attached to an in-line three-way stopcock. This allows frequent administration of anesthetic boluses; a reservoir of additional anesthetic is in the IV bag/bottle. If supplies are limited and there has been no backward gross contamination from the patient (which is probably more common than realized), only the IV needle and the extension tubing flowing from the three-way stopcock to the patient need be changed between patients.6

Narcotics, ketamine, and short-acting barbiturates can be used in this fashion.

How much to give? In resource-scarce situations in which patients do not receive neuromuscular blockade, slight movements of the fingers or toes indicate a need for supplementary anesthetic injections. 28

Neuromuscular Blockade

Do not even consider using a neuromuscular blocking agent unless you are highly proficient at obtaining (and have the equipment to control) an airway using several means (e.g., BVM, intubation, LMA, and cricothyrotomy).

If a neuromuscular blockade (NMB) is to be used, it may be important, especially for those not experienced in giving general anesthesia, to know whether the patient is awake. During surgery, paralyzing a patient who is awake is not, to say the least, good medical practice. The "isolated arm test" can help to determine whether a patient is awake. Just before administering the NMB, inflate a BP cuff on one arm to about 30 mm Hg above the systolic pressure, effectively isolating that arm from blood flow. Ten minutes after giving the NMB, ask the patient to signal to you by squeezing your hand or moving his thumb. If he does it, he is not asleep. Then, of course, deflate the BP cuff and either put the patient to sleep or stop the procedure—or both.29,30

Overview

This section is designed only for clinicians who are highly experienced in airway and critical care monitoring and management. Optimally, general anesthesia will be administered only by clinicians experienced in delivering anesthetics, although that may not be possible in resource-poor situations. The most common inhalation anesthetics used in resource-poor settings are discussed in Chapter 16, Anesthesia: Ketamine, Ether, and Halothane.

Basic Pharmacology

Inhaled anesthetics pass through the lungs, enter the circulation, and produce anesthesia in the brain. Anesthetics that are more soluble in blood, such as ether, take longer to act (induction) and to wear off (emergence; recovery). Those, such as N2O, that are relatively insoluble in blood have much faster induction and emergence.

Shortages

Ether (most portable) and halothane (inexpensive) are the inhalation agents commonly used in Africa and other places where resources are limited. Other inhaled anesthetics commonly used by anesthesiologists in developed countries, including N2O, are generally not available. As Boulton noted, "In all isolated situations, the most likely commodities to be in short supply are composed medical gases. Not only are cylinders heavy and bulky and difficult to transport in regions where communications are limited, but they provide relatively few ‘anesthesia-hours' in proportion to their bulk in comparison with volatile agents vaporized in ambient air."2

Cost

Both logistics and cost affect the availability of anesthetic agents. The following are approximate costs for common anesthetics, which vary greatly by region; some are also available from chemical supply companies.31,32

• Chloroform—$27.00 (100 mL)
• Halothane—$50.00 (200 mL)
• Ether—$5.00 (500 mL)
• Procaine—(for injection) $1.66 (20 mg/2 mL)
• Ketamine—$7.69 (500 mg/10 mL)

Anesthesia Machines

In austere circumstances, improvising even the most basic methods of delivering anesthetic gases is vital, since more modern anesthesia machines may not be available. So-called "portable" anesthesia machines may not really be so portable in rough terrain. As Boulton and Cole pointed out, "If the only available transport is the flat-footed anesthetist himself, even such apparatus as the EMO [Epstein-Macintosh-Oxford] air-ether outfit, which weighs 25 lb (11 Kg), or the ‘Haloxair' halothane-air-oxygen apparatus [at] 13 lb (6 Kg) may prove to be intolerably heavy. In such a circumstance, the anesthetist might well prefer [a very] simple apparatus or even a resuscitator bag and intravenous drugs alone."2 A can of ether and a mask, of course, weigh much less than any of these, and they don't even take much backpack space.

Using Volatile Agents

Anesthetic gases can be used for both the induction and the maintenance phases of anesthesia. Alternatively, an IV induction agent or a faster-acting volatile agent (e.g., chloroform to induce ether) can be used, followed by an anesthetic gas for maintenance.33 Intravenous inductions are done with the agents discussed previously in "General Anesthesia Guidelines: Essential Elements." Take great care not to cause respiratory depression from the synergistic action of the induction agent and the inhaled anesthetic.

Inhalational induction requires a seal between the face and the mask for the gas to be drawn through the vaporizer. If there is no seal, the patient will breathe room air around the mask and remain conscious. In adult anesthesia it is relatively easy to coax a mask on the face and still keep the patient calm and cooperative."34 Premedicating patients, especially anxious ones, assists the process.

Use in Closed Spaces

Using anesthetic gases is problematic in closed spaces, such as on a ship or in "closed down" conditions such as might occur after a nuclear, chemical, or biological attack or contamination. This situation becomes more dangerous when using open methods, such as open-drop ether. Try to eliminate as much of the ambient anesthetic as possible.35

Nitrous Oxide

Nitrous oxide (laughing gas; N2O), in combination with oxygen, is a commonly used anesthetic gas in developed countries. It has a sweet, pleasant aroma (although to a patient, it appears odorless in the presence of the smell from the anesthesia mask) and, when inhaled, it is absorbed by the body and has a calming effect. Normal breathing eliminates N2O from the body. Nitrous oxide has a rapid onset and recovery. It is a good analgesic supplement for halothane and reduces the incidence of awareness. It produces minimal cardiovascular and respiratory effects.

A World War I physician described the benefits of nitrous oxide: "Nitrous oxide is particularly useful for multiple short procedures in mass casualty situations. Induction and emergence take a matter of seconds rather than minutes and most of the patients can walk out of the OR alone or with minimal assistance."36

The main problem with N2O is that it will usually be unavailable in situations of scarcity, since it is expensive to produce and transport. Anesthesiologists familiar with disaster and austere environments believe that N2O should not be used due to the logistical nightmare of supplying it, the possibility of errors when using it, the high cost, and its tendency to diffuse into air-containing spaces, such as pneumothoraces, the gut, middle ear, and ET tube cuff.33,35

At least 50% N2O must be delivered to be effective. It is delivered to the patient through a rotameter (a clear tapered tube with a float inside that is pushed up by flow and pulled down by gravity) and is mixed with oxygen to produce an inspired mixture of not less than 30% O2. A hypoxic gas mixture may result from using it with an oxygen concentrator. Nitrous oxide should not be used in draw-over circuits and should never be given to a patient with an untreated pneumothorax or who has been scuba diving within the previous 24 hours due to the potential for decompression sickness.33 Some places may have cylinders of a 50% mixture of nitrous oxide in oxygen, primarily used for self-administered outpatient analgesia.

Rectal anesthesia, sedation, or analgesia (see also Chapter 13, Analgesics) is relatively uncommon, although it has been shown to be effective in children for "preinduction" sedation. This method requires less technical skill and equipment than IV or IM drug administration.

A major limitation of this method is the poor predictability of the clinical effects. These are determined by the anatomical properties of the patient's rectum and, owing to individual variance, the result is inconsistent anesthetic absorption and elimination.37 Using hydrophilic solutions and larger volumes with lower concentrations results in improved absorption by enlarging the mucosal surface in contact with the drug.

In clinical practice, rectally administering anesthetic medications is more common for procedural sedation or as an anesthetic premedication, where a lighter stage is needed and the exact timing of medication onset is not as vital. The medication can be delivered to children via a lubricated tip of a small (14-Fr) suction catheter or nasogastric tube. A similar-sized urethral catheter also works, as does simply using a syringe and holding it there for 2 or 3 minutes. Medications for sedation and anesthesia that can be used rectally include the benzodiazepines, barbiturates, and ketamine. Ether, although not commonly administered by this method, is also an option.

Doses and Method

• Midazolam 1.0 mg/kg (preinduction): Administer at least 30 minutes, but no longer than 90 minutes, prior to anesthetic induction.38
• Methohexitone (Methohexital): Administer 15 mg/kg of 10% methohexitone for anesthetic induction or for short procedures.39
• Ketamine 10 mg/kg: This medication has a delayed onset. Ketamine occasionally causes respiratory distress and, at the recommended 10 mg/kg rectal dose, may result in prolonged postoperative sedation if used for brief procedures.37,40

A common, but somewhat dangerous situation is for the surgeon doing the Cesarean section (C-section) also to administer the anesthetic. If this is the only option, employ one of the methods (described in the following paragraphs) using ketamine. Other methods include local infiltration (described in the subsequent text), spinal anesthesia (discussed here and also in Chapter 14, Anesthesia—Local and Regional), or epidural anesthesia for those having experience with the technique. In these cases, having a trained assistant to monitor and care for the patient throughout the operation is vital.

Local Infiltration

The main advantages of using local anesthesia infiltration in austere situations are that it is safe, inexpensive, and uses few resources. Especially for mothers in poor condition and those who are hypotensive, local anesthesia may provide the best safety margin, especially if adjunctive sedatives are not used. Epinephrine added to the anesthetic reduces local bleeding. However, using local infiltration requires significant operator experience, and even then, it may not be completely effective. It also takes time to administer.41

Technique

Determine the maximum safe anesthetic dose and, if not premixed, add 0.1 mL epinephrine 1:1000 to each 20 mL of anesthetic to make a 1:200,000 solution. If available, give oxygen to the mother until delivery. Using a 10-cm (4-inch) needle, infiltrate two long bands of skin on either side of the proposed incision line. Keep the needle parallel to the skin; remember that the abdominal wall is very thin at term—do not stick the needle into the uterus. Infiltrate the rectus sheath after incising the skin. To anesthetize the parietal peritoneum, inject 10-mL anesthetic under the linea alba. Then inject 5 mL more into the loose visceral peritoneum of the uterus where the incision will be made.

Collins provided some additional advice: "Reassure the patient and explain that after the local anesthetic has been given, she will still feel certain sensations of touch. She may experience discomfort if the head is well engaged in the pelvis. However, the anesthetic will prevent her feeling significant pain."41 Giving additional sedatives or analgesics, while desirable from an anesthetic standpoint, may adversely affect the baby. It is optimal to give nothing until the cord is clamped, after which small doses of narcotic or sedative may be used.

Ketamine

Ketamine is contraindicated in pregnancy before term, since it is oxytocic and is a US FDA fetal-risk category C drug. It is also relatively contraindicated in patients with eclampsia or preeclampsia. When the woman goes into labor, ketamine 10 mg to 20 mg IV can be used to provide analgesia. It can be repeated every 2 to 5 minutes, but do not administer >1 mg/kg in 30 minutes; the total dose should not exceed 100 mg.14

While ketamine may be used for vaginal delivery, only an experienced anesthetist who can adjust the dose according to the circumstances should use it.42

Ketamine is often used for C-sections because it has some unique advantages: (a) There is less discomfort than with spinal or epidural anesthesia for patients in advanced labor. (b) Although ketamine crosses the placenta easily and concentrations in the fetus are the same or higher than those in the mother, its use results in less fetal and neonatal depression than with other anesthetics.14–16 (c) Babies have good APGAR scores, even after periods of neonatal asphyxia—an important consideration when limited neonatal resuscitation equipment is available. This depends in part on the skill and speed of the surgeon.43 However, be careful with the dose, since a dose above 2 mg/kg may cause both respiratory depression and chest wall rigidity in the newborn.44 (d) Uterine contractility is unimpaired, so there is less danger of postpartum hemorrhage. (e) Ketamine supports maternal blood pressure, which may be important in the face of significant hypotension.14 This blood pressure increase can be ameliorated for those with eclampsia by using hydralazine or similar medications.45

If the mother experiences an emergence reaction to the ketamine, do not administer sedatives (benzodiazepines) to block the reaction until the baby is delivered, since these also can cause respiratory depression in the newborn. In cases of fetal distress, avoid ketamine, since it causes the uterus to contract.44

Methods for Cesarean Section

The following two methods describe how ketamine can be used successfully for C-sections.

In a remote Kenyan hospital, Dr. Veeken describes the successful use of a combination of local infiltration and a ketamine drip:

No premedication is given. An intravenous line is set up; local anesthesia (lidocaine 0.5%) is injected in the midline from symphysis up to the umbilicus. The doctor then scrubs. Opening is performed under this local anesthesia only. It's impressive how well the women tolerate this. If necessary, more local anesthetic could be administered for the deeper layers, but we never do. Atropine 0.6 mg is given IV. Just before the opening of the uterus, a bolus of 75 mg ketamine is given IV. The child is quickly delivered. The uterus is closed during the effect of the ketamine; a bilateral tubal ligation can be performed. Usually the women start waking up while closing the abdomen, the local anesthesia still enables us to close the fascia and the skin. If necessary, diazepam is given IV during the closure. This method is very safe for both mother and child.… Although not very elegant, it is satisfactorily cheap, very easy to administer, and extremely safe. It is highly recommended for working under primitive circumstances.46

Dr. Zimmermann described the method used in Bangladesh for 8000 C-sections (with one avoidable anesthetic death): "Routine premedication is omitted.… If necessary, oxygen is administered via mask or nasal tube. For induction, 0.6 mg atropine plus 100 mg ketamine diluted to 5 cc is administered IV over about 60 seconds."45 While ketamine is normally given as an mg/kg dose, a standard dose is used to avoid errors. It results in <2 mg/kg in virtually all these patients. This injection achieves an adequate surgical stage of anesthesia, and the patient continues to breathe spontaneously. For C-sections, administer oxygen if there is fetal distress. Maintenance anesthesia is achieved using a ketamine drip of 200 mg ketamine diluted in 200-mL NS or dextrose solution, resulting in 1 mg ketamine/1 mL fluid. This is run at 20 to 30 drops/min, which is 1 to 1.5 mg/min. A benzodiazepine (diazepam 10 to 20 mg has been used successfully) can be added once the baby is delivered. It provides a sound sleep and decreases possible psychomimetic reactions. The ketamine drip is discontinued once the surgical incision is closed.45

Improvised Vaporizers

Vaporizers deliver safe concentrations of volatile anesthetic vapor into the anesthetic system going to the patient. The volatile agent enters the vaporizer in liquid form, and comes out as a vapor. Vaporizers can be improvised.

The ideal vaporizer has a clear chamber so the amount of anesthetic is visible. Keeping the anesthetic temperature relatively constant is also important, since the liquid's temperature falls as it passes into vapor. This, in turn, lowers the output of the vaporizer. In improvised vaporizers, the equipment sits in a water bath, which transfers heat to the anesthetic to minimize any fall in temperature.34

The Coffee Jar Vaporizer

Boulton devised a very workable vaporizer for a draw-over system using two sizes of jars. To make the large vaporizer suitable for ether administration, he used a 135-g (118-mL; 4-oz) Maxwell House coffee jar (7.5-cm [3-inch] diameter, 13-cm [5-inch] tall). Other containers of THIS SIZE can be used instead. The jar's size partially determines the anesthetic concentration. The smaller jar, which can be used for ether, halothane, or trichloroethane, has a 5-cm diameter and is 19-cm (7.5-inch) tall.

Put a piece of plastic tubing with a 1.25-cm (0.5-inch) diameter through one of two holes of that size that you have punched into the lid; the tube should just fit. Cut the end of this obliquely, so that fluid is less likely to be sucked through it. Cut a wide hole in the tube, in such a position that you can lift it above the lid to reduce the vapor concentration, if necessary (Fig. 15-1). Fix a piece of cotton at one edge of the other open hole in the lid. Each time the patient breathes, it will move, allowing you to monitor his ventilation. If available, add oxygen through a tube that fits loosely in the open hole.6

Fill the large jar by adding 150 mL—about 4-cm deep—of ether. Once the patient is induced, the vaporizer is ready to put in-line with whatever system you are using (a non-rebreathing valve and an Oxford bellows or a self-inflating bag, or attached directly to a tracheal tube). The initial 11% ether concentration falls to 8% in 5 minutes and remains relatively constant thereafter. Gently shaking the bottle for 1 minute doubles the concentration. The concentration can be halved by opening a T-piece closed by the finger cot (the cut finger from a surgical glove) and still further reduced by tightening the screw clamp. Using trichloroethane, a constant 1% concentration is obtained, which is halved by opening the T-piece. Halothane gives too high a concentration for use with the larger vaporizer.

The apparatus is converted to a "semi-one-way" system by snipping off the end of the finger cot, thus creating a simple valve that closes on inspiration and opens on expiration. As it vaporizes, the ether will get cold and the concentration will diminish. At that point, gently agitate the bottle for about a minute, or put it in a bath of warm water. When using trichloroethylene, no water bath is needed.

If using the smaller bottle, prepare it the same way, but with 50 mL of halothane. A constant 1% vapor concentration is obtained, which is halved by opening the T-piece or doubled by shaking the jar for 1 minute. Secure this bottle firmly to the table or another fixed structure—the vaporizer is dangerous if knocked over.6,47

Anesthesia (Plenum) Machines

Under normal circumstances, anesthesiologists in developed countries use plenum machines to deliver inhalational anesthetics. Boulton described the "frustrating experience of administering anesthesia with the ‘rag and bottle' in a well-equipped OR while a typical modern anesthesia machine stood idle because of the lack of cylinders."2

In situations with limited resources and few trained personnel, the safest place for an anesthetized patient to recover is in the operating room. The key is ensuring that the patient is awake when he leaves the OR. Boulton notes that "if vigilance is relaxed when the drama of the operating room is over, death can still strike if the patient is left unsupervised."48 To prevent this, leave the patient intubated until pharyngeal reflexes return.49

Postoperatively, place patients in the "recovery" position, lying on their side (see Fig. 8-1). As often as possible, check their airway, vital signs, blood loss, and temperature. The latter is important because, while many operating rooms in hot climates are now air-conditioned or cooled, patients run the risk of hyperpyrexia when they are transferred to a hot ward.48