Predictive parameters of difficult intubation in thyroid surgery: a meta-analysis

INTRODUCTION: Airway management is a fundamental goal for the anesthesiologist. The rate of difficult laryngoscopy in patients undergoing thyroid surgery ranges from 6.8% to 9.6%. An accurate and detailed preoperative evaluation of the airway seems to be a promising tool to predict a potentially difficult airway management. We aimed to identify possible risk factors and physical findings that predict difficult intubation in thyroid surgery.EVIDENCE ACQUISITION: MEDLINE, EMBASE and the Cochrane Central Register of Controlled Trials (CENTRAL) were analyzed, and the reference lists from the retrieved articles and previous reviews were searched for additional studies. Difficult intubation was defined as Cormack and Lehane grade >= 3 or Intubation Difficulty Scale score >5 by direct laryngoscopy. Studies that used advanced airway devices or ultrasound-based airway management were excluded. Gender, Mallampati Score, interincisor gap, thyromental distance, body mass index, tracheal deviation, histology, mediastinal goiter, mandibular protrusion, neck circumference and neck movement were evaluated. Qualitative analysis has been conducted in case of insufficient data for an appropriate meta-analysis.EVIDENCE SYNTHESIS: Eight studies that evaluated the accuracy of clinical findings for identifying difficult intubation in thyroid patients were reviewed (5853 patients). Two authors independently screened articles, extracted data and assessed risk of bias. 7.21% [95% CI: 6.57-7.91%] of patients undergoing thyroid surgery were difficult to intubate. The physical examination findings that best predicted a difficult intubation included Mallampati Score >= 3 (positive odds ratio 4.75 [95% CI: 2.22-10.12]); shorter thyromental distance thresholds ranging from <6.5-<6 cm; OR 3.64 [95% CI: 1.9-7.01]); `low' interincisor gap, defined as a critical distance between incisors (ranging from <3.5 - <4.4 cm; odds ratio 2.57 [95% CI: 1.83-3.62]); presence of tracheal deviation (positive odds ratio, 2.06 [95% CI: 1.58-2.69]); Body Mass Index >30 kg/m(2) (odds ratio 1.95 [95% CI: 1.20-3.15]) and males (odds ratio 1.54 [95% CI: 1.21-1.95]). Histological examination positive for cancer didn't increase the risk for difficult intubation. For mediastinal goiter, mandibular protrusion, neck circumference and neck mobility only a qualitative analysis was performed.CONCLUSIONS: In thyroid patients, the presence of high Mallampati Score, shorter thyromental distance, interincisor gap, tracheal deviation (the unique thyroid pathology linked parameter), obesity and male gender were risk factors for difficult intubation. However, all these significant parameters should be used in preoperative assessment to anticipate difficult intubation in thyroid surgery.