To the Editor
In the August 2014 issue of Anesthesia & Analgesia, we published our experiences with the introduction of quantitative, electromyography-based neuromuscular blockade monitoring in an academic anesthesia department.1 In that work, we demonstrated a significant reduction in the incidence of postanesthesia care unit (PACU) patients with train-of-four (TOF) ratio ≤0.9, from 31% to 15%. Additional information, now from a total of 843 monitored PACU patients, shows maintenance of this decreased incidence of incomplete reversal (Fig. 1).
We also reported in our previous publication that, in the 2 years since the start of our quantitative monitoring efforts, we had seen no PACU reintubations because of residual paralysis compared with 2 to 4 such events per year in the years preceding our project. At the time of the acceptance of this article, this statement was correct. However, in the interval since acceptance and publication of our report, we have encountered 2 relaxant-related reintubations in the PACU. A closer look at these 2 cases is enlightening.
The patient was an elderly man with body mass index 37 kg/m2, with type II diabetes mellitus, and a history of colorectal cancer treated with surgery and chemoradiation, both completed approximately 6 months before. He presented to the hospital with a 2-week history of progressively severe shortness of breath, dyspnea on exertion, and orthopnea. Evaluation revealed a large right-sided pleural effusion, which was treated initially by pleurocentesis. Subsequent to the removal of the pleural fluid, a computed tomography angiogram revealed bilateral pulmonary emboli as well as evidence of pulmonary fibrosis. The patient was scheduled for a surgical pleurodesis. The operation was performed under general anesthesia by using a double-lumen endotracheal tube. The procedure lasted 130 minutes, during which time he received 90 mg IV rocuronium. Near the end of the procedure, approximately 25 minutes after the last rocuronium dose (20 mg—with 20 mg given 10 minutes before this), the patient was given 3.75 mg neostigmine, extubated, and taken to the PACU. On arrival, he was noted to be in obvious respiratory distress. Mask ventilation was started. An arterial blood gas showed a PaCO2 of 123 mm Hg. Qualitative TOF assessment showed a clear fade. The patient was reintubated, given additional neostigmine, and subsequently extubated uneventfully.
A review of the intraoperative records, and interviews with the anesthesia providers, revealed no indication of any monitoring of neuromuscular blockade for either rocuronium dosing or the assessment of reversal by using either the quantitative system or any other (nonquantitative) methods.
The patient was a middle-aged woman with body mass index 34 kg/m2 and with a history of anuric, hemodialysis-dependent end-stage renal disease. A previous kidney transplant had failed, and she was scheduled for a second kidney transplant under general anesthesia. Her most recent preoperative creatinine level was 9 mg/dL. During the 4-hour procedure, she received 100 mg rocuronium. The anesthesia providers noted that the quantitative electromyographic (EMG) system was not working, but there was only a single notation of a qualitative TOF assessment (0 twitches) midway through the case. Five milligrams neostigmine was given in divided doses starting 23 minutes after the last rocuronium dose (10 mg), and the patient was extubated in the operating room. On arrival in the PACU, the patient was in obvious respiratory distress with a pulse oximetry value of 60% decreasing to values in 40% range. Mask ventilation with 100% oxygen was started, and the patient was reintubated. Immediately thereafter, quantitative TOF monitoring revealed a TOF ratio of 0.2.
A subsequent note by the anesthesia provider indicated that, before extubation, a TOF measured at the obicularis oculi showed 4 twitches, that the patient had resting tidal volumes (via the endotracheal tube) of 230 to 280 mL, and that she was able to squeeze and release her hand on command.
Although the occurrence of these events is disappointing, given our efforts during the past 3 years, they serve to reinforce the value of neuromuscular blockade monitoring and specifically quantitative monitoring. These cases demonstrate the unarguable hazards of both (1) failing to monitor and (2) relying on qualitative monitoring only.
Based on these 2 cases, we need to modify our previous statement. Since the introduction of department-wide quantitative neuromuscular blockade monitoring, we have seen no PACU reintubations in appropriately monitored patients. The continued failure by some of our providers to use the available technology also reinforces our comments regarding the difficulties in changing long-held, but dangerously erroneous, beliefs that such monitoring is unnecessary (case 1) and/or that qualitative assessment of reversal is sufficient (case 2). In addition, as we reviewed and discussed in our previous publication, EMG neuromuscular monitoring has some important technical challenges that require users to often engage in real-time troubleshooting. This decreases the day-to-day practicality of this technology because some users are unable or unwilling to diagnose and correct EMG signal acquisition problems and/or to distinguish artifacts from true EMG waveforms. Users may give up and simply not use the device at all or not trust the TOF values even when they are accurate.
The authors would like to thank David DeMik for providing data on the postanesthesia care unit reversal status of the most recent group of patients described herein.
Michael M. Todd, MD
Bradley J. Hindman, MD
Department of Anesthesia
University of Iowa Carver College of Medicine
Iowa City, Iowa