Predictors of difficult tracheal intubation during general anaesthesia: an analysis of an obstetric airway management registry

Abstract

Background: Complications during airway management can be life-threatening. This study aimed to identify anatomical and physiological risk factors for hypoxaemia during tracheal intubation in obstetric general anaesthesia (GA). 
Methods: A retrospective analysis was performed of data from an obstetric airway management registry (ObAMR) on tracheal intubation during GA in patients with a gestational age from 20 weeks, and until 7 days post-delivery. The primary outcome was arterial desaturation to < 90% during airway management. Logistic regression was performed to identify associations with hypoxaemia. 
Results: Data were collected for 1 095 general anaesthetics in the ObAMR. Overall, 143/1 091 of patients (13.1%, 95% CI 11.1–15.4%) experienced arterial oxygen desaturation. Univariate analysis showed that 91/142 (64.1%) of patients who desaturated were obese (body mass index [BMI] > 30 kg/m2), compared with 347/915 (37.9%) who were obese and did not experience desaturation (p < 0.001). A receiver operating characteristic curve was constructed post hoc, which showed a cut-off point for BMI of 29.76 kg/ m2, with a sensitivity of 0.66 and specificity of 0.62 for predicting hypoxaemia. Desaturation occurred in 17.0% of patients with hypertensive disorders of pregnancy, versus 11.0% without the condition (p = 0.005). Increasing Mallampati class was associated with an increased incidence of hypoxaemia. The incidence of hypoxaemia was 25.8% when intubation was performed by interns, compared with 8.0% for specialist anaesthetists (p = 0.005). In the multivariate analysis of factors associated with hypoxaemia, BMI (p < 0.001), room air saturation prior to preoxygenation (p = 0.008), and airway oedema (p = 0.027) were independently associated with hypoxaemia. 
Conclusion: In this study, hypoxaemia was used as a composite indicator of anatomical and physiological difficulty. Using this concept, a predictive tool could be developed to identify a difficult airway in obstetrics. Further research is required to show whether simple interventions such as face mask ventilation and the use of high-flow nasal oxygenation during intubation reduce the incidence of life-threatening hypoxaemia.