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Before the introduction of anesthesia in 1846, surgical operations were uncommon. Robertson[44] unearthed two
Vickers[45] described two degrees of inadequate depth of anesthesia. The first degree involves recall or retention of memory of an event that occurred while under anesthesia. Conscious or explicit memory refers to intentional or conscious recollection of previous experiences as assessed by tests of recall or recognition. The second degree of inadequate anesthesia involves responsiveness to auditory input, also called "wakefulness." Wakefulness has been described as the responding of a patient to a verbal command during or after surgery without recall of the stimulus. Unconscious or implicit memory refers to changes in performance or behavior that are produced by previous experience on tests that do not require any intentional or conscious recollection of those experiences. [46]
In some clinical situations, the risk of intraoperative recall is high. Bogetz and Katz[47] examined the incidence of recall in 51 patients who underwent surgical procedures after major trauma. Thirty-seven patients with stable hemodynamic status were able to receive drugs for induction and maintenance of anesthesia. In this group, four had intraoperative recall. Two of the four patients considered this awareness their worst hospital experience. Fourteen of the 51 subjects were so severely injured and hemodynamically unstable that no anesthetic was administered for at least 20 minutes of surgery. Six of 14 of these patients (43%) recalled events from their surgery. Two of the latter subjects considered this intraoperative awareness the worst aspect of their hospital experience. A more recent study by Lubke and coworkers could not find evidence of explicit memory in a series of minor and major trauma patients.[48] The difference between these two studies, one in 1984 and the second in 1999, may reflect better resuscitation of trauma patients, which would increase the tolerance of anesthetic drugs. Lubke and colleagues' patients had a mean BIS index value of 54, thus suggesting adequate hypnosis.
The most comprehensive prospective study to date on intraoperative recall has been reported by Sandin and coauthors, who found that 18 patients out of 11,785 (0.15%) had awareness under general anesthesia.[49] The incidence of awareness was 0.18% in procedures that used neuromuscular blocking drugs and 0.10% in the absence of these drugs. They interviewed patients on three different occasions: in the recovery room, when recall was detected in only 39%; again at 1 to 3 days, when recall was detected in 33%; and finally at 7 to 14 days, when the final cases were detected. They demonstrated the need for multiple attempts to detect awareness by using a structured interview technique because of the risk of underreporting from single interviews. Finally, Sandin and associates, in an analysis of individual cases, suggested that a reduced incidence of recall of intraoperative events would not be achieved by monitoring of end-tidal anesthetic gas concentrations or by more frequent use of benzodiazepines.
Ghoneim recently reviewed cases of recall in different anesthetic situations.[50] The incidence of awareness in a nonobstetric and noncardiac surgical population approximates 0.2%. A higher incidence is reported for obstetric general anesthesia, 0.4%. The incidence in cardiac surgery ranges from 1.1% to 1.5%. Finally, as indicated earlier, major trauma cases can have a range of awareness from 11% to 43%.
Intraoperative awareness or recall has occurred with high-dose opioid anesthesia. In one case report, the patient had intraoperative awareness and hypertensive crises when fentanyl (96 µg/kg) and diazepam (0.28 mg/kg) were administered after preanesthetic medication with morphine and scopolamine.[51] Previous case reports using high-dose opioid anesthesia had not documented a significant hemodynamic response associated with intraoperative awareness.[52] [53] Two clinical signs possibly predicting the occurrence of recall are movement and autonomic response. The use of muscle relaxants can eliminate the movement response, which leaves only autonomic activity as a measure of intraoperative awareness. To circumvent the problem of complete muscle paralysis, Tunstall[54] [55] proposed using the isolated forearm technique to allow the possibility of movement during and after the administration of muscle relaxants. This procedure involves the application of a tourniquet to an extremity before the administration of muscle relaxants. Because the muscles do not receive the relaxant, the extremity is not paralyzed and can be monitored for movement.
This technique has been used to study the relationship of purposeful muscle movement to intraoperative recall. Schultetus and colleagues[56] used the isolated arm technique to compare the incidence of movement and recall in patients given ketamine, thiopental, or a combination of the two induction drugs for cesarean section. For 11 of 24 subjects given thiopental (2 mg/kg) or the combination of ketamine (0.5 mg/kg) and thiopental (2 mg/kg), movement occurred in the isolated arm. Four of the 24 patients had dreams, whereas 3 of the 24 had intraoperative recall. In 12 subjects given only ketamine (1 mg/kg), 1 had a movement response, and none had recall.
Russell[57] [58] showed that the incidence of movement with the isolated arm technique can vary markedly with the choice of anesthetic. The incidence of intraoperative movement was 44% after nitrous oxide and fentanyl anesthesia, but it was only 7% after a continuous infusion of etomidate with fentanyl. The high incidence of wakefulness (as judged by movement) in the nitrous oxide-fentanyl group caused the investigators to terminate the study. Although the incidence of purposeful movement in the isolated arm was high, the incidence of actual intraoperative recall was low (only one subject).
Other investigators have not been able to correlate other clinical signs of light anesthesia or postoperative recall to the isolated arm movement response. [59] [60] [61] Moreover, the effects of ischemia from prolonged inflation of the tourniquet at pressures higher than arterial blood pressure on this methodology are unknown. Abouleish and Taylor[62] could not correlate movement, size of pupils, or changes
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