Higher Force Metrics Associated With Known Risk Factors for Difficult Intubation

Introduction: Factors such as, thyromental distance (TM), mallampati score, and BMI are reported by anesthesiologists as predictors of difficult intubation. The objective of this study is to investigate potential predictive factors of difficult laryngeal exposure during suspension microlaryngoscopy (SML) and direct laryngoscopy utilizing force metrics recorded by the laryngeal force sensor (LFS) and patient characteristics identified by anesthesiologists as predictors of difficult intubation.

Methods: The LFS recorded force metrics (maximum force, average force, and tissue compression) during SML in 394 laryngeal surgeries. We recorded force metrics, along with demographic factors. Post-anesthesia care unit data (including pain and dysphagia), and various patient factors. Individual factors include age, weight, BMI, height, inter-incisor distance, Mallampati scores, and perioperative factors such as mouth opening, cervical spine stiffness, TM distance, and laryngeal grade view during intubation.

Results: Weight correlated with average force (r2 = 0.3), with patients experiencing greater force in each increasing BMI class. Similarly, an increasing Mallampati score corresponded to a higher average force. Patients with an inter-incisor distance of ≤4.0 cm experienced nearly double the average force when compared to edentulous patients (p = 0.0006). A shorter TM distance was associated with higher average force when compared to normal TM distance (p = 0.04). Patients with a laryngeal grade of 1 experienced less force than those with a grade of 2 (p = 0.004).

Conclusions: Anesthesiologist-reported predictive factors for potentially difficult intubation align with factors linked to elevated force metrics during SML. Patients with challenging laryngeal exposure during SML exhibit increased force metrics, indicating the need for higher pressure to achieve adequate glottic exposure. These force metric readings are indicative of the predictive factors for difficult intubation, suggesting their potential use in identifying patients at a higher risk of increased force during both intubation and SML procedures.