The most consistent finding in surveys conducted to determine the reproductive success of female operating room personnel has been a questionably higher-than-expected incidence of miscarriages. However, there are several problems in interpreting these studies. The association of obstetric problems with surgery and anesthesia in pregnant patients is also an important consideration. In the United States, at least 50,000 pregnant women each year undergo anesthesia and surgery for indications unrelated to pregnancy. The risk of abortion is clearly higher following this experience. It is not obvious, however, whether the underlying disease, surgery, anesthesia, or a combination of these factors is the cause of the increased risk.
2. Carcinogenicity—Epidemiologic studies suggested an increase in the cancer rate in operating room personnel who were exposed to trace concentrations of anesthetic agents. However, no study has demonstrated the existence of a causal relationship between anesthetics and cancer. Many other factors might account for the questionably positive results seen after a careful review of epidemiologic data. Anesthesia machines are now equipped with gas scavenging systems to remove concentrations of anesthetics administered to patients, and operating rooms rely on high air exchange rates to remove any trace concentrations of anesthetics released from anesthesia machines.
Intravenous nonopioid anesthetics play an essential role in the practice of modern anesthesia. They are used to facilitate rapid induction of anesthesia and have replaced inhalation as the preferred method of anesthesia induction in most settings except for pediatric anesthesia. Intravenous agents are also commonly used to provide sedation during monitored anesthesia care and for patients in ICU settings. With the introduction of propofol, intravenous anesthesia also became a good option for the maintenance of anesthesia. However, similar to the inhaled agents, the currently available intravenous anesthetics are not ideal anesthetic drugs in the sense of producing all and only the five desired effects (unconsciousness, amnesia, analgesia, inhibition of autonomic reflexes, and skeletal muscle relaxation). Therefore, balanced anesthesia employing multiple drugs (inhaled anesthetics, sedative-hypnotics, opioids, neuromuscular blocking drugs) is generally used to minimize unwanted effects.
The intravenous anesthetics used for induction of general anesthesia are lipophilic and preferentially partition into highly perfused lipophilic tissues (brain, spinal cord), which accounts for their rapid onset of action. Regardless of the extent and speed of their metabolism, termination of the effect of a single bolus is determined by redistribution of the drug into less perfused and inactive tissues such as skeletal muscle and fat. Thus, all drugs used for induction of anesthesia have a similar duration of action when administered as a single bolus dose despite significant differences in their metabolism. Figure 25–6 shows the chemical
FIGURE 25–6 Chemical structures of some intravenous anesthetics.
structures of common clinically used intravenous anesthetics. Table 25–2 lists pharmacokinetic properties of these and other intravenous agents.
In most countries, propofol is the most frequently administered drug for induction of anesthesia, and it has largely replaced barbiturates in this setting. Because its pharmacokinetic profile allows for continuous infusions, propofol is a good alternative to inhaled anesthetics for maintenance of anesthesia and is a common choice for sedation in the setting of monitored anesthesia care. When used during maintenance of anesthesia, propofol infusion can be supplemented with intravenous opioids and neuromuscular blockers as needed to completely avoid the use of inhaled anesthetics (total intravenous anesthesia, TIVA). Alternatively, a propofol infusion might be used to reduce the required concentration of inhaled anesthetics so that undesired effects can be minimized. Increasingly, propofol is also used for sedation in the ICU as well as conscious sedation and