Value of oropharyngeal Mallampati classification in predicting difficult laryngoscopy among obese patients

The prediction of difficult intubation in obese patients was investigated by co-estimating the degree of visibility of oropharyngeal structures in conjunction with the respective body mass index. Data were collected prospectively in a series of 1833 consecutive adult patients. Body mass index (BMI) in kg m-2 was used as a measure of obesity (morbid: > 40, moderate: 30-40, no obesity: < 30). The oropharyngeal class findings were assessed using the original methodology as well as by a modification requiring the tongue to be pulled forward by the examiner. Difficult intubation was defined as inadequate exposure of the glottis by direct laryngoscopy. Both oropharyngeal class methodologies were of equal sensitivity, whereas the modified technique presented a significantly higher positive predictive value (50.0% vs. 37.2%, P < 0.01). Statistical analysis revealed an increased risk of difficult laryngoscopy among obese patients compared with subjects with normal body mass index (20.2% vs. 7.6%, P < 0.001). When obesity is estimated with respect to oropharyngeal class the positive predictive value is greatly improved (66.7% vs. 20.2%, P < 0.001). We conclude that obesity which is associated with a disproportionately large base of the tongue, is a predisposing factor for difficult laryngoscopy.