RECALL during general anesthesia is a relatively rare but disturbing event that has generated increasing interest in both medical and popular literature. Part of this interest is attributable to the introduction of monitors that may assist in determining the level of consciousness during anesthesia. 1–3Although not marketed as an “awareness monitor,” there has been speculation that using the Bispectral Index® monitor (BIS®, Aspect Medical Systems, Natick, MA) might reduce the possibility of recall. 2,3This reliance on bispectral index (BIS) data can be supported by reports indicating that if the BIS® is used correctly and scores are kept below 60, recall should be rare. 4We report the case of a patient whose anesthetic plan was in part based on BIS data, who had intraoperative BIS scores only occasionally above 60, and who had recall of intraoperative events.

The patient was a 70-yr-old man who had been diagnosed with renal cell cancer and was scheduled for a nephrectomy. His past medical history was significant for non-insulin–dependent diabetes mellitus, peripheral vascular disease, atherosclerotic coronary artery disease, myocardial infarction and congestive heart failure (ejection fraction estimated at 20%), hypertension, obstructive lung disease, chronic renal insufficiency, atrial fibrillation, colon cancer, and hyperlipidemia. Past surgical history included coronary artery bypass grafting, multiple infra-inguinal vascular bypass grafting procedures, and sigmoid colectomy. Review of systems, physical examination, and diagnostic workup were consistent with the disease states noted above. Medical and cardiology consultants thought that the patient had been optimally prepared for surgery. Anesthetic options were discussed with the patient and his family, who agreed to the patient's receiving general anesthesia with arterial and pulmonary artery catheter placement and BIS monitoring.

The patient was brought to the operating room, where, in addition to standard monitoring, a radial artery arterial catheter was placed. A pulmonary artery catheter was also placed. Vital signs and anesthetic gas concentrations were recorded using the “Arkive” anesthesia recording system (BIS scores were entered manually). The patient had intravenous induction of anesthesia with midazolam (1.5 mg), fentanyl (50 μg), propofol (90 mg), and succinylcholine (80 mg). Anesthesia was maintained with isoflurane (inspiratory concentration between 0.1–0.4%), remifentanil infusion (0.01 to 0.15 μg · kg−1· min−1), and vecuronium (a bolus of 4 mg after intubation followed by an infusion totaling 3.5 mg over 3 h). After induction, a BIS® monitor (model A 2000) was placed and showed good signal quality throughout. BIS scores were between 40 to 60 throughout the operation, except for three instances. On the first occasion, the BIS score was 70 and the systolic blood pressure was in the 70- to 80-mmHg range. The patient was treated with a single phenylephrine bolus, with return of blood pressure and BIS score to desired levels within 5 min. On the second occasion, the BIS score increased to 70 and the patient was given morphine (10 mg) with return to levels below 60 within 10 min. There was a third period of 15 min when the BIS score was noted to be 65 (systolic blood pressure in the 100–85 range) and the patient moved. He was treated with midazolam (0.5 mg) and an increase in isoflurane concentration, with return of the BIS score to 40 and no further movement. At the end of surgery, when the BIS score was in the 80–90+ range, the endotracheal tube was removed and he was transferred to the intensive care unit.

Several hours after surgery, the patient informed his nurse that he had recall of intraoperative events. We interviewed the patient the day of and the day after surgery, and he stated that he had “felt everything but was not able to move…heard conversation.” He had no clear memory of specific events but stated that he remembered the entire procedure. He noted that it was a “bad experience.” Careful and repeated questioning revealed no similar problems after general or regional anesthetics in the past. We told the patient that we believed him and apologized for these events. The patient was offered a mental health consult to deal with the stress associated with recall, which he refused. The remainder of the patient's postoperative course was uneventful. He has not been bothered by signs and symptoms of an acute stress reaction or posttraumatic stress disorder.

In an update of cases reported to Aspect Medical, the incidence of recall when using a BIS® monitor was less than 1 per 40,000. 4When awareness occurred with BIS monitoring in place, it was usually associated with BIS values above 60, more frequently during cardiac surgery, and in younger (< 60 yr old), predominantly female (60%) patients. 4Although this may be the overall pattern, there are reports of recall (BIS 47), 5failure to lose consciousness (BIS 43), 6and awareness reactions during induction (BIS 50–60), 7with BIS values clinically appropriate for general anesthesia.

When evaluating this patient before surgery, we had estimated that he was at low risk for recall because of the scheduled surgery and his previous anesthetic history. These previous anesthetics had been largely inhalation agents (and/or regional anesthetics), as opposed to the more balanced technique used in this instance. The change in the planned anesthetic in this case was attributable to what we believed to be a worsening of the patient's cardiac status. Also, BIS was not available for any of these patient's previous operations, and we were more comfortable altering the previously successful anesthetic plan with the knowledge that we would have additional information concerning the patient's level of consciousness to assist in drug dosing. Our goal was to limit this patient's medication exposure during surgery while achieving BIS values in the acceptable range of 40–60. Specifically, we were aiming for the higher end of this range, hoping to maintain hemodynamic stability and account for this patient's individual anesthetic needs while limiting the possibility of recall of intraoperative events.

This patient may have been placed at increased risk of recall due to a lack of amnesic premedication and the intraoperative use of opioids and muscle relaxants. 8However, he did receive midazolam during induction of anesthesia and had a consistent but low inspiratory concentration of isoflurane throughout the surgery. These smaller amounts of medications were based on hemodynamic data and BIS: when the highest blood pressure reading of 130/60 was noted, the BIS score was 40–50. Also, dopamine and phenylephrine infusions were needed intermittently, despite what might be thought to be light anesthesia. Muscle relaxant use may have masked an awake patient, but at least toward the end of surgery (despite a vecuronium infusion) the patient was able to move. This movement was treated not with more muscle relaxants but rather with a dose of midazolam and (increased) isoflurane, and movement ceased. If we had placed the BIS® before induction of anesthesia, we might have seen a lower BIS baseline because of senile dementia. 9However, we observed a return to (near) normal BIS (90+) before extubation, making an altered baseline an unlikely starting point. Finally, it can be argued that our patient did not have recall because of his lack of detailed memories of intraoperative conversations and details. The patient claimed, on several occasions to multiple interviewers, that he was never asleep and remembered the entire operation, specifically denying occasional or intermittent memories of the surgery. We chose to accept his version and not to challenge his claims, as we believe these actions are an important part of postoperative therapy for patients with recall. 10We believe this represents recall of intraoperative events, as the patient's memory fits well within the parameters established in published reports. 11Also, we have not found errors in labeling or vigilance on our part that could account for recall in this case. 8Finally, we did not use a convection air-warming blanket, which might have falsely elevated the BIS. 12 

After a case of intraoperative recall similar to ours, 5the question was posed, “How might one alter one's practice to avoid similar occurrences?”13From this experience and our review of the literature, we suggest that when a BIS® monitor is used that there be strict adherence to the recommended range of values and rapid treatment to return scores to the appropriate range. This may be especially true when constitutional factors (such as cardiac disease with limited reserve) dictates the administration of light anesthesia, reducing the margin of error when dealing with variable surgical stimulation. In addition, the judicious use of muscle relaxants to allow patient movement in response to stimulation is also indicated, using amnesic agents and supplementation with adequate concentrations (0.6–1.3 minimal alveolar concentration) of volatile agents. 10The operative team must maintain decorum at all times so that if the patient's memory (implicit or explicit) is a problem, negative personal information will not be included. 10Planning must allow enough flexibility for reaction to the variability in surgical stimulation so that anesthetic delivery and requirement can be balanced. 14 

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