Caroline Helwick

October 19, 2011

October 19, 2011 (Chicago, Illinois) — Risk factors for "failed" intraoperative laryngeal-mask airways have been identified; these can help shape airway management plans in ways that might reduce the risk for adverse respiratory events associated with such episodes.

The use of a laryngeal mask airway (LMA) under general anesthesia has steadily gained favor, and intraoperative success has been well documented. However, as with endotracheal intubation with general anesthesia, LMAs are not without patient risks, noted Michael Mathis, MD, from the University of Michigan, Ann Arbor, who presented findings here at the American Society of Anesthesiologists 2011 Annual Meeting.

Dr. Mathis presented the findings at the Best Clinical Abstracts session. The study's first author is Satya-Krishna Ramachandran, MD, who is also from the University of Michigan.

Minor risks include gastric aspiration and postoperative sore throat or cough. More concerning are the risks for airway obstruction and laryngospasm; they can lead to life-threatening hypoxemia, he said.

The aim of the study was to examine the profiles of LMA failures that necessitate acute airway intervention. "Our hypothesis was that patient history and intraoperative characteristics exist that predispose to LMA failure," he said.

Dr. Mathis and colleagues obtained prospective observational perioperative data on 15,795 adult patients who underwent general anesthesia with a planned LMA from 2006 to 2009 at a tertiary care center. The primary outcome was an LMA "failure," defined as any acute airway event requiring LMA removal and subsequent endotracheal tube placement.

A secondary outcome was LMA failure in the setting of a difficult mask ventilation, defined as a mask ventilation that was inadequate, unstable, required 2 or more providers, or impossible. For each patient in the study, history, airway exam, and intraoperative characteristics were evaluated.

Failed LMA Rates

Of the 15,795 cases, 170 (1.1%) experienced a failed LMA.

Through logistic regression, the investigators identified 4 independent risk factors for a failed LMA: poor dentition, an elevated body mass index (BMI), and intraoperative surgical table rotation, and being male.

"Interestingly, the intraoperative characteristic of high importance was surgical table rotation of 90 or 180 degrees," he said. This was associated with a marked 5.0 adjusted odds ratio; the odds ratios for the other factors were 1.74 for being male, 1.58 for poor dentition, and 1.06 for an elevated BMI.

A 3-fold increased incidence of difficult mask ventilation was observed for patients experiencing LMA failure. Also, 13.7% of failed LMA patients from ambulatory care centers required hospital admission, and 2 of all LMA failures required admission to the intensive care unit.

"The low failure incidence (1.1%) in our study confirms previous studies of the utility of LMA in intraoperative airway management. However, given the potentially severe consequences of a failed LMA, the risk factors we identified provide valuable information to anesthesia caregivers when assessing the feasibility of an LMA for a particular surgical case," Dr. Mathis explained.

Because "patients experiencing LMA failure more frequently experienced difficult mask ventilation, our study raises the question of considering a patient's mask ventilation grade as a parameter in assessing the likelihood of LMA failure," he added.

"In patients with multiple comorbidities, LMA failure risk may not be acceptable to the anesthesiologist; the provider can consider these risk factors using an evidence-based practice rather than intuition," he concluded.

Jeanine Wiener-Kronish, MD, chief of anesthesia and critical care at Massachusetts General Hospital, Boston, and the Henry Isaiah Professor of Research and Teaching in Anesthetics and Anesthesia, noted that the findings are "intriguing," but should be validated before being clinically applied.

The 1% failure rate might be partly explained by the fact that spontaneous ventilation was allowed, she said. She finds the association with surgical table rotation interesting, and said that this movement might cause some shifting or dislodging of the equipment, but "this is association, not cause and effect," adding that a prospective study would be informative.

Dr. Mathis and Dr. Weiner-Kronish have disclosed no relevant financial relationships.

American Society of Anesthesiologists (ASA) 2011 Annual Meeting: Abstract BCO01. Presented October 18, 2011.

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