Clinical Findings Can Predict, But Should Not Exclude, Difficult Intubation

by Amy E. Hamaker •

Comment: In today’s medical age of increasingly costly technological advancement, the authors review clinical exam findings that predict difficulty in intubation. To illustrate the importance of this topic, the authors present two clinical cases and ask the reader to guess which will be the more difficult to intubate. One is a previously healthy 27-year-old undergoing elective surgery, Mallampati score of 2, inability to bite her upper lip with her lower incisors. The other is an obese 68-year-old with retrognathia and worsening hypoxemia. Prior to reading this article, I admit that I would have been more concerned about the latter patient. While the authors found several factors impacting ease of intubation (such as history of prior difficult intubation), the upper lip bite test was found to be the best quick bedside test. When abnormal, as in the second patient, it raises the probability of difficult intubation from 10% to >60%. —Jennifer A. Villwock, MD

What are the risk factors and physical findings that predict difficult intubation?

Bottom Line: Although several simple clinical findings are useful for predicting a higher likelihood of difficult endotracheal intubation, no clinical finding reliably excludes a difficult intubation.

Background: Endotracheal intubation is often required for major surgical procedures and for respiratory support in critically ill patients. Recognizing a potentially difficult intubation can help clinicians prepare for complications, which, although extremely rare, can result in major complications associated with long-term morbidity and account for 25% of anesthesia-related deaths.

Study design: Case review of 62 studies.

Setting: MEDLINE (from 1946 to June 2018) and EMBASE (from 1947 to June 2018) databases.

Synopsis: The overall proportion of patients having a difficult intubation was 10%. A history of difficult intubation was the risk factor most predictive for a difficult intubation. The upper lip bite test strongly predicted a difficult intubation. A Wilson score (≥2 in seven studies and ≥3 in one study) was strongly predictive of a difficult intubation, but a lower score did not exclude difficulty. Retrognathia and impaired mandibular protrusion were good predictors of difficult intubation. A high ratio of height to thyromental distance, as well as shorter thyromental and hyomental distances, were predictive of a difficult intubation. Impaired neck mobility, and a positive palm print test result and prayer sign result had modest predictive accuracy. A short interincisor gap had moderate accuracy for predictive accuracy. A modified Mallampati score of 3 or 4 had moderate accuracy for predicting a difficult intubation, but a lower Mallampati score (1 or 2) did not rule it out. Limitations included significant variability in reference standards, the requirement of subjective assessments in some cases, studies conducted only in the operating room, and independent analysis of predictors.

Citation: Detsky ME, Jivraj N, Adhikari NK, et al. Will this patient be difficult to intubate? The rational clinical examination systematic review. JAMA; 2019;321:493-503.