Prediction of difficult laryngoscopy using spirometry: a pilot study

Prediction of difficult laryngoscopy is still the uncovered secret of anesthetic practice. This pilot study is aimed to assess the efficacy of spirometry measurements in predicting difficult laryngoscopy compared with conventional airway assessment techniques. We enrolled 202 adults, ages 18-40 years, with an American Society of Anaesthesiologists score of I or II, scheduled for elective surgery and undergoing general anesthesia. Spirometry was used for lung capacity measurements before the operation. The Mallampati classification, neck circumference, sternomental distance, thyromental distance, maximum mouth-opening measurement, and upper lip bite test of the subjects were measured. During intubation, the Cormack-Lehane grade was recorded. Spearman's correlation analysis was used to define the linearity between spirometry outputs and airway measurements. Receiver operating curves were drawn to discriminate the predictive features of the significant values. The thyromental distance showed a higher correlation with forced inspiratory vital capacity (ρ = 0.420, P < 0.001). In a multivariate linear regression model, all spirometry measurements revealed that forced inspiratory vital capacity (β = -2.050, P = 0.022) was the significant predictor for difficult laryngoscopy. The area under the curve for forced inspiratory vital capacity with a cut-off value of 3.1950 L while using thyromental distance as difficult laryngoscopy indicator is 0.754 and forced inspiratory vital capacity showed a sensitivity of 0.718 and specificity of 0.714 with a positive likelihood ratio of 2.5104 and negative likelihood ratio of 0.3949. Forced inspiratory vital capacity showed a close association with the prediction of difficult laryngoscopy.