Head and neck surgery requires a cooperative relationship between surgeon and anesthesiologist. This is especially true in surgical procedures involving the airway. In fact, in most situations a common bond exists between otolaryngologist and anesthesiologist. In critical situations, where airway compromise is anticipated, it is the anesthesiologist and the otolaryngologist who have the best appreciation for the severity of the situation. In this chapter we will discuss briefly the pharmacology of some of more commonly used drugs in anesthesia. While a majority of these drugs are used by anesthetists in monitored conditions, these drugs may also be used in procedures requiring conscious sedation. It is hence of great importance for the physician or nurse involved on conscious sedation to be knowledgeable about the use and limitations of drugs used in conscious sedation.
This is followed by an overview of anesthesia equipment as pertains to the needs of the otolaryngologist. Quite often, surgery of the head and neck will involve the use of special equipment for endotracheal intubation. The otolaryngologist must have some knowledge of the available equipment for optimum operating conditions. This section is followed by a review of the difficult airway and suggested methods for control of the difficult airway. In the final section, an outline of the presurgical evaluation for patients with coexisting cardiovascular and pulmonary disease is presented, and anesthetic considerations for some common head and neck surgical procedures are presented. These procedures are discussed in greater detail in other parts of the text.
Analgesics, Sedatives & Hypnotics
Opioids mediate analgesia through a complex interaction of opioid receptors in the supraspinal central nervous system (CNS). They produce reliable analgesia as well as provide some sedation and euphoria. There is no significant impairment of myocardial contractility, but sympathetically mediated vascular tone is reduced. Ventilation is depressed due to elevation of the carbon dioxide threshold for respiration. Opioids given at recommended doses do not reliably produce unconsciousness. They may, however, cause decreased bowel motility, biliary spasm, nausea, and pruritus. A brief review of some of the pharmacology of some of the more common opioids is presented below.
Morphine is relatively hydrophilic and thus has a slower onset with a longer clinical effect. Only a small amount of administered morphine gains access to the CNS, but it accumulates rapidly in the kidneys, liver, and skeletal muscles. Profound vein vasodilatation may be induced due to the effects of histamine release and reduction of sympathetic nervous system tone.
A synthetic opioid, fentanyl has similar effects, but is more lipid soluble and has more rapid onset and shorter duration of action. This reflects faster entrance into the CNS and prompt redistribution. Elevated doses may lead to progressive saturation in adipose tissues. When this occurs, plasma concentrations do not decline promptly. Thus, pharmacodynamic effects, including ventilatory depression, may be prolonged.