1 Exeter, UK 2 New York, USA 3 Dublin, Eire
EditorWe were interested to read the short communication regarding residual neuromuscular block after atracurium administration by McCaul and colleagues.1 We have recently conducted a similar survey in our hospital, based on the work by Hayes and colleagues.2 We measured the train-of-four ratio (TOFR) in adult patients in our recovery ward using a Datex Ohmeda Accelerometer. The project was performed without the knowledge of the patients anaesthetist, in an attempt to avoid a change in their usual clinical practice. We recorded type and dose of neuromuscular blocking agent, the timing and doses of increments, whether antagonism was given, and whether a peripheral nerve stimulator (PNS) was used (Table 1).
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In our study, only 11 (46%) patients were recorded as having received neostigmine. Of these, 64% had TOFR >0.8. This compares with 46% with a TOFR >0.8 in the group that did not receive any antagonizing agent. It was striking that 80% of patients who had received increments of neuromuscular blocking agent had TOFR <0.8, despite receiving an antagonist. In none of these cases was a PNS charted as being used.
Complications associated with postoperative residual curarization (PORC) are well described.5 6 Although our sample was small, we also demonstrated that medium duration neuromuscular blocking agents may have a more prolonged action than appreciated, despite pharmacological antagonism. As a result of our study, we would advocate the use of a PNS, but note that this did not appear to reduce the incidence of PORC in McCauls study.1 We agree that time pressures often contribute to the problem, and that the administration of an antagonist does not necessarily provide acceptable extubating conditions.
R. Appelboam
R. Mulder
J. Saddler
Exeter, UK
EditorThe anaesthetist who today might propose that routine pulse oximetry or capnography is for sissies, would certainly be considered eccentric, or more probably an embarrassment to his/her department and a danger to public health. Nevertheless, the recent paper of McCaul and colleagues1 gives us yet another confirmation that an equally antiquated level of thought remains commonplace and is tolerated even in academic centres.
As part of a departmental quality assurance project, the authors studied the frequency of residual neuromuscular weakness at extubation in 40 patients receiving atracurium. They report 26 of 40 individuals had TOFR of 0.70 or less at this point in time. Despite rather substantial doses of neuromuscular blocking agents (0.65 mg kg1 on average in the first hour), peripheral nerve stimulators were employed only 50% of the time. The authors correctly point out that there is a strong correlation between suboptimal antagonism of residual neuromuscular block when extubation occurs shortly after initiation of antagonism. I would draw a more pointed conclusion. The time has come to state unequivocally that failure to monitor the indirectly evoked neuromuscular response intraoperatively following the administration of non-depolarizing blocking agents represents substandard care.
It is true that subjective estimation of the TOFR can miss minor degrees of residual block. That was not the case in this report. In the majority of patients, antagonism was attempted when the TOFR count was less than four, and extubation was initiated at a TOFR of 0.24, where fade is easily detected by the palpating thumb. It thus appears that decades of data and advice on the safe use of muscle relaxants in the operating room has gone unread.
Approximately 50 yr ago, Sir Robert Macintosh in a lecture to the New York State Society of Anesthesiologists remarked that the pressing need in an academic department of anaesthesia today is not for the acquisition of new knowledge, but the application of principles already well known. This sentiment remains equally true a half century later.
A. F. Kopman
New York, USA
EditorThank you for the opportunity to respond to the letters received in response to our short communication in the BJA. Drs Appelboam, Mulder and Saddlers data provide further evidence that residual curarization remains a real problem, persisting into the recovery room, despite the use of neuromuscular blocking drugs with intermediate durations of action viz. atracurium and rocuronium.
However, their study differs from ours in a number of ways, the biggest difference being that only 46% of their patients received pharmacological antagonism with neostigmine, while all our patients received an antagonist. While acknowledging that the letter format may preclude complete clarity, it would be helpful to know the drug dosages, size and frequency of top-ups, and the intervals between drug administration and extubation. Also it would be useful to know the interval from last drug administration/extubation to arrival in the recovery room and study commencement. In addition, the temperature difference (1°C) between the two groups of patients could be significant.
While we support the comments of Kopman advocating the use of peripheral nerve stimulators (PNS) whenever neuromuscular blocking drugs are used, our study like others,7 does not lend scientific weight to this position. Peripheral nerve stimulators were used in 14 of 26 patients who had a TOFR 0.7 at extubation, compared to their use in six of 14 patients who had a TOFR >0.7 at extubation.
The limitations of PNS have been well documented.811 Our study again points to their inadequacies and the need to make good this deficit. A change in emphasis in tuition might help, with greater consideration as to how neuromuscular blocking agents should be used. If trainees were taught to question whether a top-up of blocking agent is actually required, to note the time interval since the last dose of blocking agent and administration of an antagonist, and to allow adequate time and TOFR testing before extubation, the situation might improve. The doses of blocking agent used in our study, 0.36 mg kg1 h1 for those with TOFR at extubation >0.7, and 0.66 mg kg1 h1 for those with TOFR at extubation 0.7 (P<0.005), lend support to this conjecture.
Recognition of the persistent reality of residual curarization12 demands that we continue to seek improvements in training and patient care. Towards this end, we have retrospectively examined the data in our study group and using a simple neural network, have shown that human performance can be dramatically improved upon.13 We would therefore strongly disagree with Dr Kopmans assertion that we do not need new knowledge.
A. J. McShane
Dublin, Eire
References
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