SAN FRANCISCO – Patients under general anesthesia may be getting insufficient neuromuscular blockade in 1%-45% of operations, depending on the definition, according to several studies presented in a joint session at the annual meeting of the American Society of Anesthesiologists.
Regardless of the exact definition, the findings suggest that the problem of insufficient blockade is considerably more common than expected, the anesthesiologists in attendance agreed.
A lack of clinical guidelines for neuromuscular blockade probably contributes to the problem, some speakers suggested. There is no established definition of insufficient neuromuscular blockade, which has been associated in prior studies with compromised surgical visualization, impaired ventilation leading to barotraumas, direct injury through unexpected movement, and other complications.
Investigators presented their results in posters and in a joint discussion session at the meeting. All studies were sponsored by Merck, which markets a neuromuscular blocking agent (rocuronium bromide, or Zemuron) and is seeking U.S. approval for a drug that rapidly reverses neuromuscular blockade (sugammadex, or Bridion).
One percent of 129,209 adults who underwent general anesthesia and received a nondepolarizing neuromuscular blockade agent in 2005-2013 experienced insufficient blockade in a way that interrupted surgery, either through undesired patient movement (0.3%) or an explicit request from the surgeon for additional muscle relaxation and administration of more neuromuscular blockade (0.7%), Dr. Timur Dubovoy and his associates reported.
They also found indirect evidence of insufficient neuromuscular blockade through two other criteria that were much more common, said Dr. Dubovoy of the University of Michigan, Ann Arbor. Anesthesiologists gave more neuromuscular blockade after documenting twitches on peripheral nerve stimulation (train-of-four monitoring) in 39% of patients, indicative of unintended recovery from neuromuscular blockade. Large or even "excessive" maintenance doses were given to 45% of patients, consistent with insufficient neuromuscular blockade, he said.
Those kinds of events typically don’t interrupt a procedure but can lead to residual neuromuscular blockade due to excessive dosing, potentially increasing complications and delaying recovery after anesthesia. The study looked only at the incidence of insufficient neuromuscular blockade, however, not outcomes.
"Current use of nondepolarizing neuromuscular blockade agents and subjective tactile train-of-four monitoring frequently exposes patients to inadequate neuromuscular blockade," Dr. Dubovoy said.
In a separate study, insufficient neuromuscular blockade affected 21%-28% of 48,315 adults undergoing abdominal, laparoscopic, and interventional neurovascular procedures at the Cleveland Clinic in 2005-2013, Dr. Brian D. Hesler and his associates reported.
"Our results suggest that insufficient block is relatively common, even in operations that are generally thought to require muscle relaxation," said Dr. Hesler of the Cleveland Clinic. "It is difficult to separate inadequate anesthesia from inadequate neuromuscular block, and both probably contributed in many cases."
He and his associates formed a panel of seven experienced anesthesiologists to identify anesthesiology actions that are indicative of episodes of insufficient neuromuscular block and searched for those criteria in patient records, with a three-person adjudication committee approving the search criteria through a random sample of at least 50 charts for each criterion.
Overall, 28% of operations had evidence of insufficient neuromuscular blockade, or 21% if the investigators excluded cases identified solely by electromyogram criteria.
In a separate analysis of the same cohort, Dr. Hesler and his associates searched for comments in the anesthetic records and found that insufficient blockade usually was identified more than 30 minutes before emergence, defined as the time when maintenance anesthesia was discontinued (106 cases), but 18% of the time it occurred 15-30 minutes before emergence (9 cases) or less than 15 minutes before emergence (14 cases).
The closer to the end of surgery, the more likely the anesthesiologist was to respond by deepening anesthesia instead of redosing the neuromuscular blocking agent, with other sedatives (opioids) used at a consistent rate in each time period.
A separate prospective, observational study of 448 patients undergoing elective laparoscopic or open abdominal surgical procedures at eight Canadian centers in 2011-2012 stratified residual neuromuscular blockade by train-of-four (TOF) ratios.
Lower TOF ratios at tracheal extubation and at arrival in the postanesthesia care unit (PACU) were associated with greater risk for complications and greater use of perioperative resources, Dr. Dolores McKeen and her associates reported.
Every 0.1-increment increase in the TOF ratio at tracheal extubation was associated with a 30% reduction in the odds of needing placement of an oral or nasal airway due to upper airway obstruction from the time of patient extubation to PACU discharge. Each 0.1-increment increase in the TOF ratio at tracheal extubation also was associated with 3% fewer bed visits by nurses, said Dr. McKeen of Dalhousie University, Halifax, N.S. Similar results were seen for TOF ratios upon arrival at the PACU.