Research Article: Prediction of difficult tracheal intubations in thyroid surgery. Predictive value of neck circumference to thyromental distance ratio

Date Published: February 27, 2019

Publisher: Public Library of Science

Author(s): Alessandro De Cassai, Francesco Papaccio, Giorgia Betteto, Chiara Schiavolin, Maurizio Iacobone, Michele Carron, Andrea Ballotta.

http://doi.org/10.1371/journal.pone.0212976

Abstract

Difficult tracheal intubation (DTI) contributes to perioperative morbidity and mortality. There are conflicting study results about the most predictive DTI risk criteria in patients undergoing thyroid surgery.

We conducted a prospective observational study on 500 consecutive patients aged ≥18 years to identify predictors for DTI. Body weight, body mass index (BMI), inability to prognath, head movement, mouth opening, Mallampati score, neck circumference (NC), thyromental distance (TMD), neck circumference to thyromental distance ratio (NC/TMD), tracheal deviation apparent on chest x-ray, mediastinal goiter, histology and history of DTI were measured as possible predictors of DTI. Spearman’s rank correlation test and multiple logistic regression analysis were performed.

DTI was observed in 9.6% of all patients. Compared with the group of patients without DTI, the group of patients with DTI had significantly greater median values for body weight, BMI, NC, NC/TMD, Mallampati score, el-Ganzouri score, incidence of mediastinal goiter, and had reduced TMD and mouth opening. Significant correlations between BMI ≥30 kg/m2 and the Mallampati score ≥3 (R = 0.124, p = 0.00541), Cormack-Lehane ≥3 (R = 0.128, p = 0.00409), NC ≥40 cm (R = 0.376, p<0.001), and NC/TMD ≥5 (R = 0.103, p = 0.0207) were found. The logistic regression analysis revealed that an NC ≥40 cm at the goiter level, but not an NC/TMD ratio ≥5, was the strongest predictor of DTI (p<0.001). The area under the receiver operating characteristic curve for NC/TMD was better than the curve for NC. The sensitivity and specificity of NC/TMD were also greater, compared with NC. An NC of 40.00 cm and an NC/TMD of 5.85 were the estimated cut-off points. This study found that NC was a strong predictor of DTI. The results also suggested that NC/TMD could be used as a measure to stratify the risk of DTI in patients undergoing thyroid surgery.

Partial Text

Difficult tracheal intubation (DTI) contributes to perioperative morbidity and mortality [1,2]. Identification of DTI risk criteria is essential while planning the best way to proceed with anesthesia [1]. There are conflicting study results about the most predictive DTI risk criteria in patients undergoing thyroid surgery [3–7]. Neck circumference (NC) seems to be an important predictor for DTI in this population of patients [5–7]. A study of a large cohort of patients undergoing thyroidectomy found that the size of the neck (circumference and length) is one of most important independent predictors of DTI in thyroid surgery [5]. Cut-off values for neck width have not been established. The relationships between neck circumference and length as predictors of DTI have also not been evaluated [5]. One study of a population of patients with obesity found that the NC to thyromental distance (NC/TMD) ratio is a better method for predicting DTI than other established indices [8].

A total of 515 patients were enrolled in this study from 1st September 2017 to 17th September 2018. Fifteen patients were excluded before the final analysis was performed (5 patients refused to participate, 10 patients had no standard approach to the airway available). The remaining 500 patients completed the study (Fig 3). The data from these patients were included in the analysis.

This study revealed a high incidence of DTI in this population of patients undergoing thyroid surgery. The results indicated that NC was a strong predictor, but that the NC/TMD ratio was the best assessment to use to predict the risk of DTI.

Our study confirms the increased risk of DTI in patients undergoing thyroid surgery. Several predictors should be considered in clinical practice, such as reduced mouth opening, a high Mallampati score, an increased NC, a history of difficult intubation and a mediastinal goiter. This study found that increased NC ≥40 cm was the strongest predictor of DTI. The results also suggested that NC/TMD ≥5.85 could be used as a measure to stratify the risk of DTI in patients undergoing thyroid surgery. Measurement of NC and NC/TMD should be considered during preoperative evaluation in order to predict DTI in patients undergoing thyroid surgery.

 

Source:

http://doi.org/10.1371/journal.pone.0212976

 

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