To the Editor:-In a recent Letter to the Editor [1]in response to an article by Lubarsky et al. [2]I pointed out that anesthetic agents and muscle relaxants may have a significant effect that lasts beyond the PACU period, and therefore an investigation of the effect of practice guidelines on clinical outcome and cost-benefit analyses should include the period after the patients are discharged to the ward. I referred to our recent prospective, randomized, controlled study of postoperative pulmonary complications (POPC) after the use of pancuronium, atracurium, and vecuronium in nearly 700 patients. [3,4]We found that not only was the incidence and the degree of residual block in the PACU significantly increased in the pancuronium group, but also significantly more patients in this group developed POPC in the ward (16.9%) compared with the two other groups (5.4%).
In Dr. Lubarsky's response, he argued that the practice guidelines he proposed regarding the use of pancuronium are sound as long as enough medication is administered to achieve appropriate reversal, and “that reversal should be monitored by standard train-of-four monitoring, making sure a twitch is present before reversal, and one should assess the ability to sustain tetanus for 5 s in addition to having 4/4 twitches of near equal magnitude (>07, T4/T1).”
The problem is that during routine anesthesia given by anesthetists without any special interest in neuromuscular blocking agents, residual neuromuscular block after long-acting neuromuscular blocking agents is not eliminated using routine clinical tests and tactile or visual evaluation of the response to train-of-four or tetanic stimulation as described by Lubarsky. [5,6]It is not possible manually or visually to judge the degree of train-of-four or tetanic fade (50 Hz) with sufficient certainty to exclude residual block [7–10](Viby-Mogensen et al., unpublished observation). In studies claiming the opposite, the anesthetists evaluating the response to train-of-four nerve stimulation were dedicated and experienced observers. [11,12]To exclude clinically significant residual neuromuscular block after the use of the long-acting neuromuscular blocking agents during routine anesthesia, more objective methods of monitoring such as mechanomyography, electromyography, acceleromyography, or possibly double burst stimulation must be applied. [13–15]
Dr. Lubarsky claims that our patients received an inadequate dosage of neostigmine. It may or may not be so in some cases, although this is not the issue. The issue is that the anesthetists in our study were instructed to do their best to avoid residual neuromuscular block. They were instructed to aim at a level of neuromuscular block during surgery corresponding to one or two responses after train-of-four stimulation, as proposed by Lubarsky et al. A minimum of two responses was required to be present before initiation of reversal. Reversal was induced with neostigmine, 2.5 mg, but supplementary doses of neostigmine, 1.25 mg, could be given up to a total of 5 mg, if judged necessary by the anesthetists. Tracheal extubation was performed when four equal responses were felt after train-of-four stimulation and when clinically sufficient respiration was judged to be present. So once again it was documented that during routine anesthesia, clinical evaluation with manual evaluation of the train-of-four response does not exclude residual neuromuscular block after pancuronium.
On the basis of the previous, it is difficult for me to accept the conclusion of Lubarsky et al.: the routine use of the long-acting agent pancuronium did not adversely influence outcome. Lubarsky et al. have not convincingly documented by objective methods that their patients did not have residual neuromuscular block in the recovery ward, nor did they include the period after the patients were discharged to the ward in the observation period. Therefore the burden of proof that Dr. Lubarsky et al.'s patients did not experience clinically significant residual block that might have adversely influenced outcome still rests with the authors.
Jorgen Viby-Mogensen, M.D., D.M.Sc., F.R.C.A.
Professor and Chairman; Department of Anesthesia and Intensive Care; Copenhagen University Hospital; Rigshospitalet; DK-2100 Copenhagen; Denmark;viby@rh.dk
