Validation of age and height based formulae to predict paediatric airway distances – a prospective observational study

BACKGROUND: Preoperative airway evaluation in children is an important part of routine preanesthetic evaluation before surgery. External airway measurements, viz., thyromental, mentohyoid, and sternomental distances, while being growth dependent, could identify pediatric patients with potentially difficult airways. OBJECTIVES: This study was conducted to validate the age- and height-based formulae, derived from a previous study conducted in our institute, to predict thyromental distance, sternomental distance, and mentohyoid distance in relation with the height and age of pediatric patients. DESIGN: Prospective cross-sectional single arm observational study. SETTING: Tertiary level university teaching hospital from July 2015 to December 2016. PATIENTS: Children (202) in the age group of 3-15 years with no obvious external airway anomaly scheduled for elective surgery under general anesthesia. OUTCOMES MEASURED: The thyromental, mentohyoid, and sternomental distances were measured preoperatively. The same parameters were then calculated based on age- and height-related formulae derived in the earlier study. RESULTS: Bland-Altman analysis of the sample patients showed a mean difference (bias) between measured and calculated values ranging from 0.14 to –0.60 (3 - 13%). Overall agreement in terms of bias were found to be more with height-based equation for mentohyoid distance and thyromental distance and age-based equation for sternomental distance. CONCLUSION: Our study validates the formulae derived in the earlier study to predict thyromental, mentohyoid, and sternomental distances in children with no obvious external airway anomalies. Further studies are needed to extend the applicability of these formulae in obese children and those with craniofacial anomalies coming for general anesthesia and surgery.