Thyromental Height - As a Predictor of Difficult Laryngoscopy

The fundamental responsibility of the anaesthesiologist and one of the most important steps in anaesthesia practice is the intubation and maintenance of the airway. The integral part of pre-anaesthetic evaluation to recognize a potentially difficult airway is the airway assessment. There are multitude of bedside screening tests which are helpful to predict a difficult airway but the accuracy is doubtful. Thus, pointing out a single reliable predictor of difficult intubation is important. Accordingly, this study aims to evaluate the practicality of thyromental height test alone as a sole predictor of difficult laryngoscopy in our present population. Ethical clearance was obtained and after taking an informed consent, a randomised prospective observational study was conducted on 315 adult patients who were posted for elective surgical procedures under general anaesthesia with endotracheal intubation. On the day before the surgery, airway was assessed and Thyromental height (TMHT) was measured. Laryngoscopy was performed intra-operatively and Cormack Lehane’s grading was noted. The evaluation of the accuracy of thyromental height in predicting difficult laryngoscopy was done by comparing the preoperative assessment data and laryngoscopy findings. In our study, the mean thyromental height observed was 5.4cm. Thyromental height at cut off of 50mm had a high negative predictive value of 94.1% and high sensitivity of 72.5%, but with low specificity of 64.2% (P value 0.000). When the cut off was emended to 48mm, sensitivity of the test decreased to 56.2% and specificity increased to 79.8% (P value 0.002).The conducted study demonstrates the usefulness of thyromental height. It substantiates the good sensitivity of thyromental height for predicting difficult intubation. But, the validation will require further studies in more diverse patient population.

ACROMIO-AXILLO-SUPRASTERNAL NOTCH INDEX [AASI] : A SCREENING METHOD TO PREDICT DIFFICULT LARYNGOSCOPY IN PATIENT UNDERGOING GENERAL ANAESTHESIA AND REQUIRING ENDOTRACHEAL INTUBATION

Introduction and Aims: Difficult laryngoscopy [poor visualisation of larynx] is a surrogate indicator of difficult intubation and inability to manage difficult visualisation of larynx (DVL) can be life threatening. This study is performed to assess the ability of new index –Acromio -Axillo-Suprasternal Notch Index to predict difficult laryngoscopy in patient undergoing general anaesthesia in addition to other common predictors. Material and Methods: 100 patients with ASA class I and II candidate for general anaesthesia with endotracheal intubation were enrolled to this study. The four usual tests Modified MallampatiTest[MMT], Ratio Of Height to Thyromental Distance[RHTMD], Neck Circumference/ Thyromental distance, Sternomental distance difference were assessed before induction of anaesthesia. The new test AASI is calculated as follow: 1) Using a ruler a line is drawn vertically from the top of the acromion process to the superior border of the axilla at the pectoralismajor muscle named as line A. 2) A second line is drawn perpendicular to line A from the suprasternal notch (line B) and 3)That portion of line A that lies above where line B bisects line A is line C. AASI is calculated from the length of line C divided by line A[AASI = C/A]. By a skilled anaesthesiologist with more than 5 years of experience & who was unaware of the study, A laryngoscopy was done and based on Cormack-Lehane classification, grading of laryngoscopy was recorded. Sensitivity, specificity, positive predictive value and negative predictive value with 95% Confidence Interval for each airway predictor in isolation was studied. Results: DVL observed in 12% patients. We observed that sensitivity,specificity,PPV,NPV,AUC of Roc[95% confidence interval] of AASI was 80%[44.4-97.5%], 95.56%[89-98.8%],66.67%[42.22-84.6%],97.7%[92.6-99.33%},0.985[0.898-0.988]respectively & these results are better than other conventional methods of difficult airway predictors. Conclusion: AASI more than or equal to 0.5 is a good predictor of difficult visualisation of larynx (DVL) at direct laryngoscopy.

Evaluation of Ultrasound Guided Measurement of Anterior Neck Soft Tissue Thickness in Predicting Difficult Laryngoscopy in Obese Patients

Background: The incidence of unanticipated difficult airway is 14.3-17.5% in obese. Preoperative difficult airway prediction is important to avoid postoperative morbidity and mortality. USG guided measurement of anterior neck soft tissue thickness can be used to predict difficult laryngoscopy in obese patients and we thus undertook this study to determine the role of USG guided measurement of anterior neck thickness at the level of vocal cords in difficult laryngoscopy prediction. Methods: Sixty obese patients (BMI≥30kg/m2), 18-70 years of age of either sex, were included. Anterior neck soft tissue thickness was measured by ultrasound as the distance from the skin to the anterior commissure of vocal cord. Neck circumference was measured at mid neck just below the laryngeal prominence with the subjects standing upright and facing forward with shoulders relaxed. Thyromental distance, sternomental distance, Mallampatti score and neck circumference were also recorded. Results: The cut off values of BMI (46.94 kg/m2), neck circumference (41.5 cm) and anterior neck soft tissue thickness (22.1mm). Four patients in the morbidly obese and 80% of the superobese patients had a difficult laryngoscopy. Sixteen (26.67%) patients had an anterior neck soft tissue thickness of >22.1mm. Of these, 11 (91.67%) patients had difficult laryngoscopy while one (8.33%) patient with anterior neck soft tissue thickness ≤ 22.1mm had difficult laryngoscopy (P<0.05). There was also significant association between neck circumference and BMI. Conclusion: The USG guided measurement of anterior neck soft tissue thickness, BMI and neck circumference can reliably predict difficult laryngoscopy in obese patients.

Predicting Difficult Laryngoscopy in Morbidly Obese Patients by Ultrasound of Distance from Skin to Epiglottis: A Prospective Observational Study

BackgroundIn morbidly obese patients, airway management is challenging since the incidence of difficult intubation is 3 times that in normal patient. Standard preoperative airway evaluation may help to indicate for probability of difficult laryngoscopy. Recent studies have used ultrasonography-measured distance from skin to epiglottis and pretracheal soft tissue at the level of vocal cords, and cut-points of 27.5 mm and 28 mm respectively, to predict difficult laryngoscopy. The purpose of this study is to use ultrasonography-measured distance from skin to epiglottis for predicting difficult laryngoscopy in morbidly obese Thai patients.MethodsThis prospective observational study was approved by the Ethics Committee of the Faculty of Medicine, Prince of Songkla University. Data were collected from January 2018 to August 2020. Eighty-eight morbidly obese patients (BMI ≥ 35 kg/m2) requiring general anesthesia with endotracheal intubation for elective surgery in Songklanagarind Hospital were enrolled. Preoperatively, anesthesiologists or nurse anesthetists who were not involved with intubating the patients evaluated and recorded measurements (body mass index, neck circumference, inter incisor gap, sternomental distance, thyromental distance, modified Mallampati scoring, upper lip bite test, and distance from skin to epiglottis by ultrasound. The laryngoscopic view was graded on the Cormack and Lehane scale. ResultsMean BMI of the eighty-eight patients was 45.3 ± 7.6 kg/m2. The incidence of difficult laryngoscopy was 14.8%. Univariate analysis for difficult laryngoscopy indicated differences in thyromental distance, sternomental distance and the distance from skin to epiglottis by ultrasonography. The median (IQR) of thyromental distance in difficult laryngoscopy was 6.5 (6.3, 8.0) cm compared with 7.5(7.0, 8.0) cm in easy laryngoscopy (p-value 0.03). The median (IQR) of sternomental distance in difficult laryngoscopy was 16.8 (15.2, 18.0) cm compared with 16.0 (14.5, 16.0) cm in easy laryngoscopy (p-value 0.05). The mean distance from skin to epiglottis was 12.2 ± 3.3 mm Mean of distance from skin to epiglottis in difficult laryngoscopy was 12.5 ± 3.3 mm compared with 10.6 ± 2.9 mm in easy laryngoscopy (p-value 0.05). Multivariate logistic regression indicated the following factors associated with difficult laryngoscopy: age more than 43 years (A), thyromental distance more than 68 mm(B) and the distance from skin to epiglottis more than 13 mm(C). The scores to predict difficult laryngoscopy was calculated as 8A+7B+6C. One point is given for A if age was more than 43 years old, 1 point is given for B if thyromental distance was less than 6.8 cm and 1 point is given for C if the distance from skin to epiglottis by ultrasonography was more than 13.0 cm. The maximum predicting score is 21, which indicates a probability of difficult laryngoscopy among our patients of 36.36%, odds 0.57, likelihood ratio 3.29 and area under the ROC curve of 0.78.ConclusionsAge, thyromental distance and ultrasonography for the distance from skin and epiglottis can predict difficult laryngoscopy among obese Thai patients. The predictive score indicates the probability of difficult laryngoscopy.

Combined use of a Total Control Introducer and a hyperangulated video laryngoscope to place a left-sided double lumen endotracheal tube in a patient with a history of difficult laryngoscopy

We describe the use of a Total Control Introducer (TCI) in combination with video laryngoscopy (VL) to place a left-sided double-lumen endotracheal tube (DLT) in a patient with a history of difficult laryngoscopy undergoing video-assisted thoracoscopic surgery (VATS). VL was used to obtain visualisation of the glottis and a TCI articulating introducer was used to dynamically navigate the airway and access the trachea. A 39 French DLT was subsequently passed over the TCI shaft and into the trachea under indirect visualisation. The TCI shaft was removed and the DLT was gently guided into the left main bronchus. Successful endobronchial intubation was confirmed with capnography, auscultation and fibreoptic bronchoscopy. We propose that the combined use of VL and a TCI can facilitate placement of a DLT in a patient with a known difficult airway who may otherwise be limited to a bronchial blocker placement for lung isolation during VATS.

Useful Ultrasonographic Parameters to Predict Difficult Laryngoscopy and Difficult Tracheal Intubation—A Systematic Review and Meta-Analysis

Unexpected difficult airway management can cause significant morbidity and mortality in patients admitted for elective procedures. Ultrasonography is a promising tool for perioperative airway assessment, nevertheless it is still unclear which sonographic parameters are useful predictors of difficult laryngoscopy and tracheal intubation. To determine the ultrasonographic predictors of a difficult airway that could be applied for routine practice, a systematic review and meta-analysis was conducted. Literature search was performed on PubMED, Web of Science and Embase using the selected keywords. Human primary studies, published in English with the use of ultrasonography to prediction of difficult laryngoscopy or tracheal intubation were included. A total of 19 articles (4,570 patients) were analyzed for the systematic review and 12 articles (1,141 patients) for the meta-analysis. Standardized mean differences between easy and difficult laryngoscopy groups were calculated and the parameter effect size quantified. A PRISMA methodology was used and the critical appraisal tool from Joanna Briggs Institute was applied. Twenty-six sonographic parameters were studied. The overall effect of the distance from skin to hyoid bone (p = 0.02); skin to epiglottis (p = 0.02); skin to the anterior commissure of vocal cords (p = 0.02), pre-epiglottis space to distance between epiglottis and midpoint between vocal cords (p = 0.01), hyomental distance in neutral (p &lt; 0.0001), and extended (p = 0.0002) positions and ratio of hyomental distance in neutral to extended (p = 0.001) was significant. This study shows that hyomental distance in the neutral position is the most reliable parameter for pre-operative airway ultrasound assessment. The main limitations of the study are the small sample size, heterogeneity of studies, and absence of a standardized ultrasonographic evaluation method [Registered at International prospective register of systematic reviews (PROSPERO): number 167931].