Thyromental height test for prediction of difficult laryngoscopy in patients undergoing coronary artery bypass graft surgical procedure

Abstract

Background:Patients undergoing coronary artery bypass graft (CABG) procedures have higher incidence of difficult laryngoscopy and intubation than general surgery population. Accurate prediction of difficult laryngoscopy in CABG patients is desirable to reduce the hemodynamic response and myocardial oxygen requirements. Recently, thyromental height test (TMHT) has been proposed as one of the highly sensitive and specific bedside tests to predict difficult airway. We, in our prospective observational study, evaluated the accuracy of the TMHT in predicting difficult laryngoscopy.Methodology:A total of 345 patients undergoing CABG of either sex, in the age group of 35–80 years, American Society of Anesthesiologists 111, undergoing CABG, were studied. Airway assessment was performed with modified Mallampati test with the addition of thyromental distance, sternomental distance, and TMHT. Intraoperatively, direct laryngoscopy was done in accordance with Cormack and Lehane grade of laryngoscopy. The preoperative data and laryngoscopic findings were used together to evaluate the accuracy of TMHT. The sensitivity, specificity, positive and negative predictive values of other three tests were calculated according to standard formula.Results:A total of 345 patients were in the group with mean age of study population at 56.7 (standard deviation 9.1) years (35–80 years). This study showed that almost all tests had good specificity, but sensitivity was poor. However, sensitivity of TMHT was 75% with accuracy of 95%. Receiver operating characteristic curve analysis of TMHT-derived cutoff was 52.17 which increased sensitivity to 81.25% and specificity to 92.3%.Conclusion:TMHT had a higher sensitivity compared to other tests along with good positive and negative predictive value and a very high specificity.

Validity of thyromental height test as a predictor of difficult laryngoscopy: A prospective evaluation comparing modified Mallampati score, interincisor gap, thyromental distance, neck circumference, and neck extension

“…The TMHT observations from our study are comparable to the original data from an Iranian population (314 patients), and subsequent data from an Indian population (345 patients) utilising simlar cutoffs at 50 mm. [ 1 2 ] The sensitivity (84.6%), specificity (98.9%), PPV (88%), and NPV (98.6%) of TMHT from our study is comparable to the original Iranian study that produced the coresponding values as 82.6%, 99.35, 90.45, and 98.6% respectively. [ 1 ] The high PPV (88%) along with an accuracy close to 100% (98.63%) from our data might indicate that a high proportion of difficult laryngoscopy could be predicted when the TMH is below 50 mm.…”

“…[ 3 ] The study also produced a low PPV of 20.87% and failed to show the efficacy of TMHT, as revealed by us and others. [ 1 2 ] It has to be noted, however, that their mean TMH was only 45 mm, roughly 15 mm less noted by other studies. The measurement was done in a similar head and neck position reported by other studies.…”

“…A cutoff value of approximately 50 mm has been originally described in an Iranian population, and values below this were noted to be highly correlative of difficult laryngoscopy. Using manual measurements, a study in an Indian population[ 2 ] was able to reproduce a similar sensitivity, specificity, PPV, and negative predictive value (NPV) profile, as shown by the original study[ 1 ] at a cutoff value of 50 mm. Also, the study showed that TMHT was more accurate than modified Mallampati score and TMD.…”

“…TMHT was performed using a depth caliper and measured between the anterior border of the thyroid cartilage (on the thyroid notch just between the two thyroid laminae) and the anterior border of the mentum (on the mental protuberance of the mandible), with the patient lying supine with a closed mouth. A neutral position of head and neck was maintained with a pillow beneath the head [Figures 1 and 2 (reproduced with permission from Wolters Kluwer[ 2 ])]. A digital depth gauge was used to measure the height (INSIZE ® Electronic depth gauge, Insize Co Ltd; Suzhou, New District China).…”

Thyromental height test as a new method for prediction of difficult intubation with double lumen tube

“…The test is based on the height between the anterior border of the mentum and the thyroid cartilage, while the patient lies supine with the mouth closed ( Fig 2 ) [ 10 ]. Recent studies reported the TMHT to be more accurate to predict difficult intubation, compared to widely used purely anatomical measurements [ 10 , 16 ]. Clinical studies are lacking, therefore the goal of this study was to determine clinical performance and usefulness of the TMHT as a predictor of difficult intubation.…”