Author: Michael Vlessides
Persisting neuromuscular blockade may play a role in as much as 75% of patients needing immediate postoperative reintubation, a study has found. However, the investigators noted that since train-of-four data were not available and the patient sample was not necessarily representative, the findings should be viewed as speculative.
“In looking at the research more, we found that residual neuromuscular blockade is common after surgery, affecting anywhere from 30% to 60% of patients in the PACU environment after neostigmine,” said Benjamin Matelich, MD, an assistant professor of anesthesiology at the University of Minnesota Medical School, in Minneapolis. “Alth ough the natural incidence of postoperative reintubation ends up being 0.05 to 0.1, there is actually very little data to associate residual neuromuscular blockade with actual PACU reintubations.
“Certainly this is a patient safety issue, and you could argue that any reintubations whatsoever are very dangerous, and anything we can do to improve those numbers is good, which is why we decided to look at this,” Dr. Matelich said.
Dr. Matelich and his colleagues reviewed the records of 59 patients who were reintubated at the University of Minnesota Health between 2013 and 2015. The investigators obtained a variety of patient data, including demographics, case information, dosing of neuromuscular blockade, neuromuscular reversal, and staff notes on patient condition in the PACU and events leading up to reintubation. Anesthesia practice during this period did not include routine monitoring of neuromuscular blockade, either intraoperatively or after block reversal.
Because neither qualitative nor quantitative twitch monitoring was performed in the PACU, Dr. Matelich noted that it was impossible to directly link residual paralysis to intubation. Nevertheless, the researchers designed a surrogate assessment of potential neuromuscular weakness, with a 0-3 scoring system used by three independent evaluators, as follows:
“We also looked at it less subjectively, whereby each potential risk factor was given a point,” Dr. Matelich said. “We decided that a score of 3 or more created a more likely picture of residual neuromuscular blockade that may have played a role in these PACU reintubations.” These risk factors included an age of 70 years or older, relaxant dose (expressed as per minute of case duration, >0.7 mcg/kg per minute), reversal (yes/no), magnitude of the last neuromuscular blocker dose, time from last dose of neuromuscular blocker to reversal (<20 minutes), time from reversal to extubation (<20 minutes), or use of a combination of rocuronium and cisatracurium (yes/no).
From the 59 original patient records, eight patients were excluded and seven received no neuromuscular blockers, leaving a total of 44 patients for assessment.
Median assessor scores indicated that residual paralysis was “unlikely” (score, 1) to have played a role in 38.5% of patients, while 38.7% were deemed “possible” (score, 2) and 20.5% “probable” (score, 3). The linear algorithm yielded similar values: 25.0%, 36.4% and 38.6% for scores 1, 2 and 3, respectively.
“We identified between 60% and 75% of our patients where residual neuromuscular blockade may have played a role in reintubations,” Dr. Matelich reported at the 2018 annual meeting of the International Anesthesia Research Society (abstract PS35).
These results are consistent with previous studies, in which residual paralysis was found to affect approximately half of all operative patients, the investigators said. “But since comorbidities are very significant factors in our patients, it makes sense that our numbers may be a little higher than the national average,” Dr. Matelich said.
“We also believe these results illustrate the importance of monitoring,” Dr. Matelich added. “We find that in many institutions, clinicians aren’t monitoring for residual neuromuscular blockade in the intraoperative and postoperative periods, so a lot of them tend to attribute reintubation [to] patient characteristics like [chronic obstructive pulmonary disease] exacerbation, obesity and hypoventilation.
“Certainly residual neuromuscular blockade is a very important factor,” he noted. “And going forward, now that we have much better neuromuscular monitoring available, it will be interesting to see how these data change and where we go from here.”
According to David Glick, MD, MBA, the study was a “nice entry to a politically charged point of discussion—the appropriate postoperative reintubation rate.” For him, the optimal reintubation rate is something greater than zero.
“If your goal is a zero reintubation rate, you can get zero,” said Dr. Glick, a professor of anesthesia and critical care at the University of Chicago. “But to do so, you are choosing to not extubate people in the OR and essentially saying, ‘I will not be the hand that pulled it; that won’t be on my shoulders.’
“The other side of that coin,” he continued, “is you extubate somebody and they’re in the PACU getting increasingly hypoxic and hypercarbic, and again your hand is slowed by an unholy force. What you really need to do is reintubate them, but you know you will be dinged if you do so.
“So I think that, separate from neuromuscular blockade, the bigger issue here is to be sure that we don’t all think that the optimal reintubation rate is necessarily zero, because a target rate of zero could cause anesthesiologists to do things that would be detrimental to the care of the patient.”