Failure to predict difficult tracheal intubation for emergency caesarean section

Abstract

Difficult tracheal intubation following induction of general anaesthesia for caesarean section is a cause of morbidity and mortality. Our aim was to evaluate five bedside predictors that might identify women with potential intubation difficulty immediately prior to emergency caesarean section. Women requiring emergency caesarean section with general anaesthesia and tracheal intubation who had been assessed by the same experienced anaesthesiologist preoperatively were included in this study. Mallampati score, sternomental distance, thyromental distance, interincisor gap and atlantooccipital extension were all measured. The same anaesthesiologist performed laryngoscopy and graded the laryngeal view according to Cormack and Lehane. Exact logistic regression was used to identify significant independent predictors for difficult intubation (Cormack and Lehane grades ≥ 3) with two-sided P value less than 0.05 considered as significant. In 3 years, 239 women were recruited. Cormack and Lehane grades of 2 or less (easy) were found in 225 and grade of at least 3 (difficult) in 14 women. Patients' characteristics (age, height, weight, BMI or weight gain) were not significantly associated with difficulty of intubation. The incidence of difficult intubation was 1/17 women [95% confidence interval (CI) from 1/31 to 1/10]. A positive result from any of the five predictors combined had a sensitivity of 0.21 (95%CI 0.05-0.51), a specificity of 0.92 (95%CI 0.88-0.96), a positive predictive value of 0.15 (95%CI 0.032-0.38) and a negative predictive value of 0.95 (95%CI 0.91-0.97) for a Cormack and Lehane grade of at least 3 at laryngoscopy. Airway assessment using these tests cannot be relied upon to predict a difficult intubation at emergency caesarean section as the low sensitivity means that 79% (95%CI 49-95) of difficult intubations will be missed.