We are grateful for the comments by this Canadian group, experts in the field of rapid extubation after cardiac surgery. They question the use of neuromuscular blocking drugs without appropriate monitoring . We must acknowledge that even today, neuromuscular transmission monitoring is not practised routinely in many anaesthesia centres . Moreover, the patients in our control group were only extubated after careful clinical testing. While we agree that neuromuscular monitoring is highly desirable, it is not mandatory (e.g. ASA Standards for Basic Anesthetic Monitoring, House of Delegates, last affirmed 15 October 2003). There is no general agreement as to which outcome variable should be addressed to substantiate the need for neuromuscular transmission monitoring. The editorial from Eriksson referred to by Olivier and Hemmerling also states that: 'One crucial question is: do residual effects of muscle relaxants actually affect patient outcome?' . We think it would be incorrect to insist that neuromuscular monitoring is obligatory before this question has been satisfactorily addressed.
We do realize that different patterns of practice exist that recommend different uses of, and indications for, neuromuscular blocking drugs. Depending on the technique used, a neuromuscular blocker may not be needed at all, something that certainly deserves to be re-evaluated with the increased use of, e.g. sevoflurane, as the authors point out. It is therefore interesting that, even though they claim to use sufficiently deep anaesthesia to prevent awareness, they themselves still rely on neuromuscular blocking drugs to ensure immobility - thereby removing the best way of preventing awareness, the non-paralysed patient. There is no such thing as a little bit of paralysis that enables the patient to move when they are aware but not when the surgeon does not want them to. If neuromuscular blocking drugs are to be used, the only way of having some idea of the amnesia/hypnotic component of anaesthesia is to measure the depth of anaesthesia unless inhaled agents are used at measured concentrations well above the minimum alveolar concentration.
The third issue concerns the analgesic regimen which we used. There is no doubt that adequate analgesia is imperative for successful extubation after cardiac surgery and it was inadequate in many of our patients. It was not the initial intent to register pain scores, nor did we routinely extubate patients after cardiac surgery before undertaking this study. We only draw conclusions on this matter because we observed it and we agree that a more stringent regimen of analgesia than ours should be used if one opts to extubate the patient in the operating room. Thoracic epidural anaesthesia may be superior to other modes of analgesia, although there is an extensive literature dealing with its complications. The question still remains whether the advantages of the technique outweigh the risks in cardiac surgery . Concerns about epidural or spinal haematomas after neuraxial blockade in cardiac surgery have stimulated some to try and estimate the risk of this adverse event . Available data provide us with statistical incidences in study populations. However, incidences from observations in populations can never predict the chance for the single individual. There is no mathematical relation between the incidence of all-or-none events in a large population and the chance of the event occurring in an individual patient. Moreover, in countries such as ours, guidelines from our specialty's national society restrict the use of neuraxial blocks with catheters where patients are heparinized.
To conclude, we share the same concerns as Olivier and Hemmerling. Routine immediate extubation after off-pump coronary artery bypass grafting is not possible without normothermia or sufficient analgesia. Our study underscores the importance of neuromuscular monitoring when using a neuromuscular blocking drug if immediate extubation is the objective although the use of these drugs during cardiac surgery is still open to debate. So, we suggest, the remarks made by Olivier and Hemmerling in their letter are not substantially at odds with the conclusions in our article.
Department of Anaesthesia and CCM; O.L.V. Clinic; Aalst, Belgium
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