While people who are morbidly obese are more likely to undergo moderately difficult intubation, they do not have an increased rate of severely difficult intubation, according to a study presented here at the 2018 Annual Meeting of the American Society of Anesthesiologists (ASA).
“Morbidly obese patients have changes in their anatomy and pulmonary physiology that predispose them to rapid desaturation on induction of anaesthesia, as well as difficult mask ventilation,” said lead author Tiffany S. Moon, MD, University of Texas Southwestern Dallas, Texas. “These factors can give anaesthesia providers the perception that they are more difficult to intubate, but when we really look at it, that does not seem to be the case.”
“Factors such as age, male gender, and high Mallampati score are actually much more predictive of a difficult intubation than BMI alone,” she noted.
Airway management complications that cause temporary patient harm are common, although serious injury is rare. Because serious injury is rare, most of the data around airway management complications comes from large litigation and critical incident databases that help identify patterns and areas where care can be improved: but both of these sources have their limitations.
A significant percentage of airway complications occur in intensive care units and emergency departments, and these cases more frequently result in patient harm or even death and are usually associated with suboptimal care. The most common cause of airway-related deaths is hypoxia, and obesity is a known major risk factor for airway complications.
The fact that obesity rates are rising warrants investigation into if the morbidly obese are more difficult to intubate. Previous studies have attempted to determine the predictive value of body mass index (BMI), but their results are contradictory and complicated by varying definitions of intubation difficulty.
For the current study, the researchers looked at the incidence of difficult intubation in morbidly obese patients and also studied which preoperative measures could predict difficult intubation. The study included 2,013 patients categorised into 3 groups based on BMI (BMI <30, n = 736; (BMI ≥30 but <40, n = 685), and morbidly obese (BMI >40, n = 592).
Prior to laryngoscopy, the morbidly obese patients were placed in the “ramped” position, while all other patients were in the “sniffing” position. The difficulty of intubation was determined by the intubation difficulty scale (IDS).
Of the entire study population, 39.7% of intubations were moderately difficult and 4.1% were severely difficult. The respective incidence of moderately and severely difficult intubation in the morbidly obese cohort was 44.4% and 3.2%. Compared with the lean cohort, the morbidly obese group had an increased incidence of moderately difficult intubation but similar incidence of severely difficult intubation.
They found that increasing age was a significant risk factor for difficult intubation, with yearly increase in age increasing the risk of moderately difficult and severely difficult intubation by 2% and 3%, respectively. Male gender and a higher Mallampati scores were also independent predictive factors for both moderately difficult and severely difficult intubation, with Mallampati score being the strongest predictor.
“We aren’t saying that morbidly obese patients are not difficult to intubate because certainly some of them are, but the incidence does not seem to differ from that of the lean population,” said Dr. Moon. “Of course, if difficulty with intubation is encountered in a morbidly obese patient, they will be at increased risk of adverse events due to their pathophysiology. Also, we want to distinguish that we are not talking about mask ventilation here, which is indeed more difficult in morbidly obese patients and may also contribute to the perception that these patients are more difficult to intubate. Mask ventilation and intubation are 2 very different things.”