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LETTERS TO THE EDITOR

Neuromuscular Blockers and Awareness

King’s College Hospital, London, UK

To the Editor:

Dr. Tempe (1) recognizes that in the absence of neuromuscular blockers (NMBs) awareness does not occur. A critique of the current use of NMBs during general anesthesia is, however, missing. The understanding of unconsciousness and its monitoring may take as many years as it will take to understand the physiology of consciousness. Instead, the practical problem of eliminating awareness during surgery is achievable today. All it takes is a rethink of the current use of NMBs (2). I abandoned the use of NMBs during cardiac surgery 11 yr ago. As Dr. Tempe correctly states, modern anesthetics have improved the delivery of anesthesia (1). Indeed, they allow good general anesthesia without NMBs. With rare exceptions, all my cardiac patients are breathing spontaneously at closure of the skin and talking to me 3 h later. Not one instance of awareness occurred in over 2,000 cases, although more propofol or remifentanil is sometimes required in response to movement of eyebrows or toes. Surprisingly, the use of NMBs during general anesthesia escaped serious appraisal during the 1980s, when their use in intensive care suffered a drastic reduction (2).

References

1. Tempe DK. In search of a reliable awareness monitor. Anesth Analg 2001; 92: 801–4.[Free Full Text]
2. Ponte J. Neuromuscular blockers during general anaesthesia: less may be better. BMJ 1995; 310: 1218–9.[Free Full Text]

Response

G. B. Pant Hospital, J.L. Nehru Marg, New Delhi, India

In Response:

I take this opportunity to thank Dr. Ponte for his comments and showing keen interest in my recent article (1). The need to minimize the doses of muscle relaxants during cardiac surgery is being increasingly appreciated, and a less liberal use of muscle relaxants is noticeable at most centers. However, total omission of muscle relaxants as suggested by Ponte (2) and Metz (3) is still not widely practiced. This may be related to the fact that total omission of muscle relaxants entails increasing the doses of adjuvant anesthetic drugs that may compromise the hemodynamic stability. In addition, inadvertent muscle movement, especially that of the diaphragm might disturb the surgeon during a crucial surgical step.

Although rare, awareness has been known to occur even in the days when muscle relaxants were not used. Moreover, implicit awareness even in the absence of any intraoperative movement has been detected by psychologic testing. This implies that eliminating awareness totally might not be as easy as it seems. With no infallible method of monitoring awareness currently available, the sensitivity of methods such as Bispectral or auditory evoked potential index appear to be greater compared with monitoring gross body movement. However, it seems that future work in this area only can help to resolve the issue.

References

1. Tempe DK. In search of a reliable awareness monitor. Anesth Analg 2001; 92: 801–4.
2. Ponte J. Neuromuscular blockers during general anaesthesia: less may be better. BMJ 1995; 310: 1218–9.
3. Metz S. Awareness during cardiac surgery [letter]. J Cardiothorac Vasc Anesth 2000; 14: 107–8.[Web of Science][Medline]

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