Prediction of Difficult Laryngoscopy: An Assessment of the Thyromental Distance and Mallampati Predictive Tests

Abstract

Two hundred and fifty patients were assessed preoperatively using the Mallampati classification and by measuring their thyromental distances. The ease or difficulty of direct laryngoscopy was assessed at the time of induction of anaesthesia. Retrognathia was seen in 15.6% of patients and the incidence of difficult laryngoscopy without external laryngeal pressure was 8.2%. It was found that both assessments predicted less than two in three difficult laryngoscopies and had highfalse positive rates. It was found that external laryngeal pressure often improved the view of the glottis in difficult laryngoscopies.

Comparison of direct and video-assisted views of the larynx during routine intubation

“…Difficult laryngoscopy has been defined as the inability to visualize the vocal cords or as grades 3 and 4 using the modified Cormack-Lehane scoring system [14][15][16][17][18]. The reported incidence of difficult laryngoscopy in unselected patients is 3% to 13% [14,[19][20][21].…”

Prediction of difficult tracheal intubation in Turkish patients: a multi-center methodological study

“…Each individual test when used alone has been shown to have a low sensitivity, a low positive predictive value and a low-to-moderate specificity [10,11,24,[32][33][34]. Difficult intubation is a rare but potentially lifethreatening event; through tests that predict such cases, anaesthesia becomes safer.…”

Short thyromental distance is a surrogate for inadequate head extension, rather than small submandibular space, when indicating possible difficult direct laryngoscopy

“…13,14 It can be represented by a straight line drawn between the mentum and thyroid cartilage and is measured at full head extension. This implies that the magnitude of the TMD is dependent on three factors, mandibular growth, laryngeal descent in the neck and the extent of full head extension.…”