Abstract:
Background and objectives
Failure to secure airway can lead to morbidity and mortality. In the present
study, preoperative assessment of 131 patients posted for surgery under general
anaesthesia was carried out to evaluate the usefulness of two predictive tests Ratio of
Height to Thyro-mental distance (RHTMD) and Ratio of Height to Stern-omental
distance (RHSMD) in predicting the ease or difficulty of tracheal intubation.
Methods
The study was a prospective single blinded observational study conducted in
adult participants aged between 18 to 60 years scheduled for elective surgery under
general anaesthesia. The preoperative airway assessment was conducted using
two predictive tests Ratio of Height to Thyro-mental distance and Ratio of Height to
Sterno-mental distance. Following induction of Anaesthesia laryngoscopy was
performed and Cormack lehane laryngoscopy grade was noted. Intubation was
considered difficult if the view on laryngoscopy was Cormack and Lehane grade III
or IV, more than three attempts at tracheal intubation, duration of intubation longer
than 10 minutes, failure to intubate or if special maneuvers were required to
facilitate intubation. Sensitivity, specificity, Receiver operating Characteristic (ROC)
curve analysis was performed using RHTMD and RHSMD for predicting difficult
intubation.
Results
RHTMD has a Sn of 85.25%, Sp of 100% with 95% CI of 0.730 – 1.00 and a
P value < 0.001 which is statistically significant. On ROC curve analysis the area
under the curve for RHTMD is found to be 0.875. The optimal cut off value derived
from ROC curve for RHTMD is 21.50cms.
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RHSMD has a Sn of 84.21%, Sp of 96.42% with 95% CI of 0.777 – 1.00 and
a P value < 0.001 which is statistically significant. On ROC curve analysis the area
under the curve for RHSMD is found to be 0.890. The optimal cut off value derived
from ROC curve for RHSMD is 10.50cms.
Conclusion
• RHTMD is found to be a better predictor of difficult intubation and restricted
laryngoscopic view as it is highly sensitive and 100% specific than RHSMD.
On ROC curve analysis both RHTMD and RHSMD are found to be
statistically significant without much difference in AUC.
• The recommended cut off established by the study for RHTMD is 21.50cms
and RHSMD is 10.50cms.
