Residual paralysis is supposed to be potentially harmful to the patient. Several trials have investigated the effects after a single administration of a neuromuscular blocking agent with an intermediate duration of action and found a widespread incidence of residual paralysis between 4 and 64% using acceleromyographic monitoring.1 According to recent recommendations, acceleromyographic devices should be individually calibrated at least when they are used for scientific purposes.2 However, most of these trials did not use a calibrated monitoring device. Moreover, many of the measurements were done in the postanaesthesia care unit. The present study analyses the potential incidence of residual paralysis (defined as a train-of-four ratio less than 0.9 at the end of surgery) following a single administration of a neuromuscular blocking agent with an intermediate duration of action in a comparable setting to previous studies,3 but using an individually calibrated acceleromyograph in each patient. Moreover, all measurements were completed before emergence from anaesthesia.
With institutional ethics approval, a quality assessment trial was performed in our institution (Saarland University Hospital, Homburg, Germany) that was designed as an observational and nonrandomized trial over a 6-month period. After informed consent, patients who required general anaesthesia with endotracheal intubation were scheduled for inclusion.
All patients received standardized monitoring, including temperature monitoring and bispectral index (BIS) measurement. For neuromuscular monitoring, a TOF-Watch SX nerve stimulator with additional hand adapter (Organon, Cork, Ireland) was installed at the volar side of the distal phalanx of the respective thumb and later used with continuous train-of-four stimulation (four pulses of 0.2 ms in duration with a frequency of 2 Hz every 15 s). After induction of anaesthesia and signal stabilization, the device was calibrated using the internal calibration mode (CAL2). Thereafter, atracurium was used to facilitate endotracheal intubation at a dosage of 0.5 mg kg−1. Anaesthesia was maintained at the discretion of the anaesthesiologist either with propofol or with desflurane. According to the protocol, a BIS of 40–50 was targeted. Remifentanil was used for intraoperative analgesic supplementation. The recovery times until a train-of-four ratio of 0.7 and 0.9 were recorded as benchmarks. Further, the final train-of-four ratio at the end of surgery (defined as completing the surgical wound cover) was documented. In cases of suspected residual paralysis, defined as a train-of-four ratio less than 0.9 at the end of surgery, neostigmine was used at the discretion of the anaesthesiologist before the patient emerged from anaesthesia or the patient was ventilated until neuromuscular monitoring implied a train-of-four ratio more than 0.9. Data are expressed as mean (± SD) except where indicated.
One hundred and ten patients were primarily evaluated during the study period. Six patients had to be excluded from data analysis owing to the following reasons: battery failure of the monitoring device in three patients, unexpected additional need for neuromuscular block in two patients, and accidental administration of atracurium before completing the calibration process in one patient. Therefore, data from 104 patients were analysed: 66 were men and 38 women with a mean age of 44.4 years (SD ± 1.6). Mean duration of surgery was 116 min (SD ± 50 min). The mean final train-of-four ratio at the end of surgery was 0.95 (SD ± 0.3). The overall incidence of residual paralysis defined as a train-of-four ratio less than 0.9 at the end of surgery was 14%. Twelve per cent of all patients showed a train-of-four ratio less than 0.7. Only six patients underwent a procedure that lasted less than 60 min. Eighty-three per cent of patients in this group showed a train-of-four ratio less than 0.7 or 0.9 at the end of surgery. In 30 patients, the duration of the surgical procedure was between 61 and 90 min. The incidence of a train-of-four ratio of 0.7 and 0.9 in these patients was 20 and 27%, respectively. In 29 patients, surgery took between 91 and 120 min. Here, a train-of-four ratio less than 0.7 was found in 3%, whereas 8% of this group had a train-of-four ratio less than 0.9. Finally, in none of the patients with a procedure lasting longer than 120 min (n = 39) was a train-of-four ratio of less than 0.7 or 0.9 found at the end of surgery.
Data from the presented trial imply a relatively low incidence of residual paralysis even 90 min after a single injection of atracurium and stand in contrast to findings from other authors with a comparable setting.3 Some minor modifications were made in the methodology of the present study. First, only atracurium was used uniformly in all patients. However, data from one of the comparator studies did not show a significant difference between the single neuromuscular blockers with an intermediate duration of action regarding the incidence of residual paralysis.3 Second, an individually calibrated acceleromyograph was used in all patients. This might improve the performance of acceleromyography.4 Further, the estimation of a potential residual paralysis was finished before emergence from anaesthesia was initiated. It has been shown that the use of acceleromyography in awake patients may produce a greater variability in the results than in patients under anaesthesia.5 Thus, the use of calibrated acceleromyography and the finalization of measurement before the emergence from anaesthesia may explain the different outcome to some extent.
According to the data from our study, one may suggest that the incidence of residual paralysis could have been overestimated in previous publications.3,6 However, owing to the observational design of our study, this suggestion should be confirmed in a larger controlled trial.
The use of reversal agents such as neostigmine in the absence of a neuromuscular block has been shown to be potentially harmful at least in animals as a result of an impairment of the upper airway function.7 Therefore, the use of neuromuscular monitoring should identify patients without a residual block as reliably as possible to prevent such events through the inadequate use of neostigmine. This may emphasize the need for further data about the necessity of standardized measurement techniques even in the clinical setting.
In conclusion, data from the present trial show that the overall incidence of residual paralysis may vary from other studies owing to the use of an individually calibrated acceleromyographic device in patients under anaesthesia. Further controlled studies with a larger study population are required to estimate the impact of different neuromuscular blocking agents and factors such as calibration on the diagnosis ‘residual paralysis’ more precisely. This might also be helpful in the decision of whether to use a reversal agent or not.
There are no conflicts of interest. This trial was supported solely from departmental resources.
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