Neuromuscular Block in the PACU: Can You See It Now?

The August 2014 issue of Anesthesia and Analgesia includes a report on residual neuromuscular blockade in the PACU that is both highly informative and unusually forthright (Anesth Analg 2014;119:323–31). For the last 7 years we’ve been seeing reports about residual neuromuscular blockade in PACU patients. At first, they were hard to believe; after all, we were using intermediate duration nondepolarizing relaxants and reversing them when necessary. We monitored block, or recovery from block, with a peripheral nerve stimulator or “appropriate” clinical tests. We followed the rules – so patients must be reversed when they got to the PACU. And, besides, they rarely looked weak in the PACU. But despite our belief, there is scientific evidence that almost 1% of PACU patients experience a Critical Respiratory Event (CRE) after general anesthesia.1 These CREs include severe hypoxemia and upper airway obstruction and are usually not linked to residual neuromuscular block at the time they occurred. Some patients can remain up to 50% paralyzed when they arrive in the PACU and look just fine. While many of them recover without incident, we now know that they are at much greater risk for Critical Respiratory Events such as hypoxia.

Will you practice based upon evidence or belief?

Part of the problem is history. Many of us were educated at a time when a sustained tetanus or head lift was the best available test of neuromuscular function. We learned them. We used them. We followed the standard of care and didn’t detect the bad outcomes that sometimes resulted from residual block, so we thought the standard of care was working. Now, however, we have more accurate and more reliable methods to detect residual neuromuscular block. Clinical tests and peripheral nerve stimulators could detect residual block down to 50% or 33%, but newer quantitative block monitors can detect residual block down to 10% or 5%.

Remaining Neuromuscular Block Following Common Clinical Tests

Remaining Neuromuscular Block Following Common Clinical Tests

Part of the problem is culture. The authors of this report ran hard up against culture. They discovered that some anesthesia providers in their department had a “poor understanding” (their words) of muscle relaxant pharmacology, clinical signs of recovery from neuromuscular blockade, and the limitations of reversal drugs. All anesthesia providers were given scientific evidence that residual neuromuscular block was not uncommonly present in PACU patients and placed patients at risk for Critical Respiratory Events. Despite this attempt to educate, even highly experienced anesthesia providers continued to believe that no change in their practice or assessment of residual block was needed. Fourteen months into departmental efforts to eliminate residual block, anesthesia providers were still rejecting the quantitative neuromuscular block monitors and patient were still arriving in the PACU with residual block. If it were not for a bad patient outcome, clearly due to residual block despite neostigmine administration and usual tests for recovery from block, I wonder if this cultural log jam would have ever been broken.

These authors openly said they were “concerned” about the use and monitoring of neuromuscular blocking drugs in their department. They looked for residual neuromuscular block in their PACU and found it ... too much of it. We have good evidence of a problem and solutions to the problem are known to us. Are you brave enough to look at neuromuscular blockade practices, monitoring and assessment of neuromuscular block, and residual paralysis in the PACU in your department? Or, will history and culture prevent you from facing the problem? Will you practice based upon evidence or belief?

Michael A. Fiedler, PhD, CRNA

An summarized version of this article is available on