Ambulatory Anesthesia: Brief Report
Postoperative residual paralysis may increase postoperative morbidity and mortality (1,2). After an internal audit, we tested the hypothesis that the incidence of residual paralysis is the same in outpatients and inpatients, despite the use of short-acting neuromuscular blocking drugs (NMBD) in outpatients, and that the clinical tests used to identify residual muscle paralysis inadequately predict this important condition. We assessed the use of NMBD and the management of residual paralysis in both patient populations.
The study population comprised 640 surgical patients (the first 320 inpatients and the first 320 outpatients scheduled for anesthesia during the study period who met the study criteria). All were scheduled to receive NMBD and tracheal intubation. Patients with evidence of renal, hepatic, metabolic, or neuromuscular disorders were excluded, as were pediatric patients and those undergoing cardiothoracic and emergency surgery. The study had ethical committee approval and participants gave written informed consent.
The anesthesiologists involved were aware that a study was being performed on residual paralysis. Intraoperative variables under examination included the monitoring of neuromuscular transmission (NMT), the pharmacological reversal of neuromuscular blockade, and the use of clinical criteria before tracheal extubation. The clinical criteria were those used in daily practice, at the discretion of the individual anesthesiologist.
Immediately after the patients' arrival in the postanesthetic care unit (PACU), a study nurse recorded their tympanic temperatures and the acceleromyographic responses of their adductor pollicis muscle as percent of the train-of-four (TOF%) on stimulation of the ulnar nerve (TOF-Watch®; NV Organon, Oss, The Netherlands). A TOF of 90% was used as cut-off value to exclude residual paralysis (3). Within the first 5 min after arrival in the PACU, the following clinical tests and signs were assessed by a second study nurse who was blinded as to the TOF data: the patient's inability to smile, swallow and speak; general muscular weakness; inability to lift the head for 5 s, to lift the leg for 5 s, inability to sustain a hand grip for 5 s; and inability to perform the sustained tongue depressor test (resisting the removal of a spatula from between the clenched teeth).
The ability of a clinical test to predict residual paralysis (TOF <90%) was described by sensitivity, specificity, and positive and negative predictive values. By giving one point for a positive test result and zero for a negative result, a maximum sum of eight could be obtained for each patient. The ability of each possible sum to predict residual paralysis (TOF <90%) was then described by sensitivity and specificity. Mean variables were compared by the Wilcoxon two-sample test. Contingency tables were analyzed with a χ2 test. Values of P < 0.05 were considered statistically significant. Data are expressed as mean ± sd or % (n).
Anesthetic and surgical variables were similar in outpatients and inpatients, except for age (37 ± 16 versus 55 ± 17 yr), ASA physical status I–II–III (69%–26%–5% versus 36%–45%–19%), and duration of anesthesia (52 ± 25 min versus 92 ± 52 min).
The different NMBD used intraoperatively and the management of residual paralysis are shown in Table 1. The most frequently selected NMBD were mivacurium (50%) for outpatients and rocuronium (44%) and atracurium (36%) for inpatients. The methods used to determine and treat residual paralysis did not differ between the outpatient and inpatient groups. In almost half of the patients clinical criteria were used before tracheal extubation, followed by pharmacological reversal, NMT monitoring, or a combination of these.
The incidence of residual paralysis was 38% in the outpatient group and 47% in the inpatient group (P = 0.001). In the outpatient group, 43 patients (14%) had a TOF <70%; 78 (24%) had a TOF between 70% and 90%. In the inpatient group, 57 (18%) had a TOF <70%, whereas 92 (29%) had a TOF between 70% and 90%. Mean tympanic temperature was 36°C ± 0.7°C in outpatients and 35.5°C ± 0.9°C in inpatients (P < 0.00001) (Table 1). Three hypothermic inpatients arrived tracheally intubated in the PACU.
One inpatient required reintubation in the PACU. In all patients in whom NMT monitoring had been used but residual paralysis was observed, NMT monitoring had been qualitative (visual or tactile).
The results of the clinical tests made after arrival in the PACU for patients with a TOF ≥90% are shown in Table 2. A positive test result indicates an inability to smile, swallow and speak; general muscular weakness, etc. Table 3 shows the sensitivity and specificity, as well as the positive and negative predictive values, for a TOF <90%, of each clinical test used in the PACU to detect residual paralysis. “General weakness” was the most sensitive but had the highest negative predictive value. “Inability to sustain hand grip” was the most specific test, and the “inability to perform the sustained tongue depressor test” had the highest positive predictive value. For every clinical test, the specificity and the negative predictive values were more than 62%, and the sensitivity and the positive predictive values were <53%.
The sum of clinical test results predicting a TOF <90% is shown in Table 4. By combining the tests, the maximum sensitivity for the detection of residual paralysis was 46%, whereas specificity decreased progressively from 94% to 67%.
The incidence of residual paralysis was less frequent in the outpatient group (38%) than in the inpatient group (47%). This might have been a result of the more frequent use of mivacurium in our outpatients. However, the incidence was similar to the one observed after NMBD administration in previous studies (4–8). The use of longer-acting NMBD and a lower postoperative body temperature might have influenced the incidence of residual paralysis in our inpatients.
None of the methods used to determine and treat residual paralysis could prohibit residual paralysis (Table 1). For all patients in whom residual paralysis was observed despite NMT monitoring, the records showed that NMT monitoring had been qualitative. This finding is consistent with previous studies (9,10). Quantitative NMT monitoring can detect residual paralysis in the PACU; therefore, its use during surgery may be recommended.
The sensitivity and the positive predictive values of the clinical tests studied in the PACU were low, and such tests therefore have a low ability to predict residual paralysis as measured by a quantitative TOF%. A combination of clinical tests did not increase the sensitivity for the detection of residual paralysis. However, the clinical tests studied here indicate that neuromuscular weakness can persist even with a TOF ≥90% (Table 2). Although the outcome of these tests is influenced by the degree of consciousness and postoperative pain (4), it seems logical to attribute at least part of the problem to NMBD.
In conclusion, residual paralysis is frequent in outpatients, although its incidence is less frequent than in inpatients, probably because of the use of shorter-acting NMBD. Qualitative NMT monitoring, pharmacological reversal and clinical tests did not adequately predict residual paralysis. Only quantitative NMT monitoring might prevent residual paralysis. Previous studies in inpatients, especially with longer-acting NMBD, have demonstrated morbidity because of residual paralysis. Such outcomes have not yet been determined in outpatients receiving intermediate- or short-acting blockers and need to be more fully evaluated.
We would like to thank Els De Paepe, MSc, for her assistance.
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© 2006 International Anesthesia Research Society
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