Comparison of five methods in predicting difficult laryngoscopy: Neck circumference, neck circumference to thyromental distance ratio, the ratio of height to thyromental distance, upper lip bite test and Mallampati test.
BACKGROUND
Preoperative airway assessment tests have been presented to help in anticipating a difficult airway. We conducted this study to compare five methods in prediction of difficult laryngoscopy: Neck circumference (NC), NC to thyromental distance ratio (NC/TMD), the ratio of height to thyromental distance (RHTMD), upper lip bite test (ULBT) and Mallampati test (MMT). These five methods are the most commonly used ones and have different powers for it. It was not clear which of these methods predicts difficult laryngoscopy better.


METHODS
Six hundred consecutive patients participated in this study. NC, NC/TMD and RHTMD were measured, and ULBT and MMT were performed and recorded. The laryngoscopy view was graded according to Cormack and Lehane's scale (CLS) and difficult laryngoscopy was defined as CLS grades 3 and 4. Accuracy of tests in predicting difficult laryngoscopy was assessed using the area under a receiver-operating characteristic curve.


RESULTS
The area under the curve in ULBT and RHTMD were significantly larger than that in TMD, NC and MMT. No statistically significant differences were noted between TMD, NC and MMT (all P > 0.05) (ULBT = RHTMD > NC/TMD > TMD = NC = MMT). RHTMD (>22.7 cm) exhibited the highest sensitivity (sensitivity = 64.77, 95% confidence interval [CI]: 53.9-74.7) and the most specific test was ULBT (specificity = 99.41%, 95% CI: 98.3-99.9).


CONCLUSIONS
RHTMD and ULBT as simple preoperative bedside tests have a higher level of accuracy compared to NC/TMD, TMD, NC, MMT in predicting a difficult airway.
Anesthesiology and Critical Care Research Center, Isfahan University of Medical Sciences, Isfahan, Iran.
Azim
A
Honarmand
Anesthesiology and Critical Care Research Center, Isfahan University of Medical Sciences, Isfahan, Iran.
Mohammadreza
M
Safavi
Anesthesiology and Critical Care Research Center, Isfahan University of Medical Sciences, Isfahan, Iran.
Ahmad
A
Yaraghi
Anesthesiology and Critical Care Research Center, Isfahan University of Medical Sciences, Isfahan, Iran.
Mohammadali
M
Attari
Anesthesiology and Critical Care Research Center, Isfahan University of Medical Sciences, Isfahan, Iran.
Mehdi
M
Khazaei
Department of Emergency Medicine, Alzahra Hospital, Isfahan University of Medical Sciences, Isfahan, Iran.
Majid
M
Zamani
Airway management; intubation; laryngoscopy