Can We Prevent Recall During Anesthesia?

INTRODUCTION

Three large prospective studies of the incidence of intraoperative awareness from Australia, Europe, and North America suggest that the overall rate is in the range of 0.1% to 0.2% or 1 to 2 per 1000 patients. Intraoperative awareness can be a minor or a major complication depending on the severity and the response of the individual patient; in severe cases posttraumatic stress disorder may occur. In select patient populations the rate of intraoperative awareness may be substantially higher, such as in cardiac surgery patients where the rate has been reported to be in the range of 0.4% to 1%. ^, Prospective studies of intraoperative awareness in children found a rate of 0.8% to 1.1%. ^, Conversely, the rate of intraoperative awareness may be lower in a particular setting. A retrospective analysis of quality assurance data from a single medical center suggested that the incidence of intraoperative awareness was 0.0068% or 1 per 14,560 patients. Methodologic criticisms can be made of all of these studies of the incidence of intraoperative awareness. As a whole, however, the literature suggests that intraoperative awareness is a significant problem. Many anesthesiologists find a rate of intraoperative awareness in the vicinity of 0.1% to be unacceptably high. Most patients affected by intraoperative awareness find the experience to be unacceptable, especially if they experience pain and anxiety. Can we prevent recall during anesthesia or at least lower the rate substantially?

OPTIONS

Some episodes of intraoperative awareness are caused by specific, identifiable errors in anesthetic drug administration. Examples of these errors include the following:

• 1.

  Administration of a muscle relaxant instead of a hypnotic during induction of anesthesia resulting in an awake, paralyzed patient.

• 2.

  Unrecognized failure of a pump to deliver an intravenous (IV) hypnotic drug such as propofol. See Rowan for a particularly vivid example.

• 3.

  An unrecognized empty vaporizer.

Thus prevention of drug administration errors could be useful for reducing intraoperative awareness. Discussion of drug administration errors and strategies for prevention are beyond the scope of this chapter, and readers are referred to previous publications.

Many, if not most, cases of intraoperative awareness occur without the presence of a specific error in drug administration and are probably related to an unusually large anesthetic dose requirement, either because of lower than average sensitivity to one or more drugs or faster than average clearance of one or more drugs. Large variation between individuals in anesthetic drug effect or anesthetic drug clearance is well documented for a variety of anesthetic drugs. Identification of higher-risk individuals in advance and administration of larger doses of anesthetic to these individuals might reduce the rate of intraoperative awareness. Unfortunately, there is not currently a practical clinical method for identifying such individuals.

Patients receiving nondepolarizing muscle relaxants during the maintenance phase of anesthesia may be at greater risk for intraoperative awareness, presumably because they may not be able to move as readily and thereby give a clue to the anesthesiologist that the anesthetic depth is inadequate. ^, Some anesthesia providers take the approach of using as small a dose of muscle relaxant as possible to provide surgical exposure, with the idea that if the patient is too lightly anesthetized they will still be able to move. This practice probably makes sense, although it is clear from case reports that patients may not move during an episode of intraoperative awareness even in the absence of neuromuscular blocking drugs. Since the approval for use of sugammadex in the United States, the use of profound neuromuscular blockade throughout surgery may have increased because of the possibility for successful reversal with sugammadex at the end of surgery. ^, Whether this practice has increased the incidence of intraoperative awareness is unknown, but practitioners would be well advised to consider the potential risks.

Another option could be to give all patients very large doses of anesthetic drugs that would be adequate for even the least sensitive patient. There are numerous drawbacks to this approach, including cost, the potential for slow wakeup, and cardiovascular side effects, not to mention that there are no data that show what dose of anesthetic drug would be large enough to prevent intraoperative awareness under every circumstance in every patient.

Likewise, no particular drug has ever been shown to be uniquely reliable for preventing awareness in every circumstance in every patient; intraoperative awareness has been reported in patients receiving apparently adequate doses of just about every possible anesthetic agent. The available evidence suggests that total IV anesthesia has a risk for intraoperative awareness that is similar to inhalational anesthesia. ^,

Finally, there is the option to somehow monitor the depth of anesthesia and titrate anesthetic drugs accordingly. Hypothetically, such an approach might prevent intraoperative awareness by identifying the patients who require larger doses of anesthetic drugs. The rest of this chapter will focus on this last approach.