A Breath of Fresh Air: Emerging Data on Managing “Physiologically Difficult Airways”

Jordan Francke, MD, MPH

Every anesthesiologist has been trained in evaluating the airway to identify anatomy that might present a difficult intubation. On Saturday, May 18, at the session, cosponsored by SOCCA, “The Nuts and Bolts of Managing a ‘Physiologically Difficult Airway,’” Carlee Clark, MD, anesthesiologist-intensivist at Medical University of South Carolina, moderated a session contrasting patients with anatomically difficult airways with those possessing physiologically difficult airways, and the expert speakers discussed the data surrounding the management of the latter.

Kunal Karamchandani, MD, associate professor of anesthesiology and critical care medicine at UT Southwestern Medical Center, opened the session by defining a physiologically difficult airway. He described a patient in the surgical ICU in acute hypoxemic respiratory failure who, despite a robust blood pressure at time of induction and a straightforward anatomic airway, experiences cardiovascular collapse within minutes of being intubated. He proceeded to ask the audience how many had encountered patients with this presentation, and nearly every member raised their hand. “That is a physiologically difficult airway,” he responded. He presented the INTUBE study (https://jamanetwork.com/journals/jama/fullarticle/2777715), which pooled data from 2,964 patients across 197 sites in 29 countries. Nearly half of these patients had at least one adverse peri-intubation event: 42.6% experienced cardiovascular instability and 9.3% developed severe hypoxemia, while only 4.5% had anatomically difficult airways. The INTUPROS study (https://pubmed.ncbi.nlm.nih.gov/38259143/), with roughly 3,000 patients in Spanish ICUs, mirrored INTUBE’s data with 40% of patients experiencing at least one adverse peri-intubation event. Dr. Karamchandani posited that many critically ill patients have severe metabolic derangements that place them at serious risk of complications, even if the endotracheal tube is placed uneventfully. Furthermore, their hypoxemia triggers significant catecholamine surges, and even a gentle anesthetic induction can precipitously decrease catecholamine levels to induce profound cardiovascular collapse.

Mary Jarzebowski, MD, an associate professor at the Michigan State University College of Human Medicine of Michigan, combed the literature trying to answer the question of whether any interventions can be employed to prevent this collapse in patients with physiologically difficult airways. Dr. Jarzebowski presented data from France (https://pubmed.ncbi.nlm.nih.gov/29261566/) suggesting that five risk factors predict cardiac arrest following an intubation in the ICU: age older than 75, BMI > 25, absence of preoxygenation, oxygenation saturation < 90% and systolic arterial pressure < 90 mmHg. While the first two risk factors are nonmodifiable, the latter three represent key opportunities for intensivists to optimize patients prior to attempting intubation. Some have posited that providing patients with a 500 milliliter isotonic fluid bolus prior to intubation would increase their preload, and thus reduce the likelihood of cardiovascular collapse. The PREPAREII trial (https://pubmed.ncbi.nlm.nih.gov/35707974/) did not find that this improved outcomes. Dr. Jarzebowski remarked that vasopressor use during the peri-intubation period has minimal evidence currently, but is actively being investigated in a current clinical trial (https://classic.clinicaltrials.gov/ct2/show/NCT05014581). The induction medication of choice also represents an opportunity for future research: data from the INTUBE trial suggest that use of propofol at doses higher than 0.7 mg/kg was significantly associated with cardiovascular instability and collapse (https://pubmed.ncbi.nlm.nih.gov/35536310/), while etomidate may have less postinduction hypotension compared with ketamine (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8783236/).

Craig S. Jabaley, MD, FCCM, associate professor of anesthesiology at Emory University, was curious whether preoxygenation might be able to be optimized in critically ill patients to reduce peri-intubation collapse. He explained that hypoxemia in these patients is often a result of ventilation-perfusion mismatch or intrapulmonary shunting. While the former may be improved with more aggressive preoxygenation, the latter is unlikely to be altered. He presented data from the FLORALI-2 trial (https://pubmed.ncbi.nlm.nih.gov/30898520/), which did not find significant differences between hypoxemic patients preoxygenated with noninvasive ventilation compared to high-flow nasal cannula. However, data from the OPTINIV trial (https://pubmed.ncbi.nlm.nih.gov/27730283/) suggest that a combination of these two modalities may be superior to isolated noninvasive ventilation for preoxygenation.

Ravindra Alok Gupta, MD, FASA, FCCP, assistant professor of anesthesiology and critical care medicine at Northwestern Medicine Feinberg School of Medicine, closed out the session by explaining that studying these patients and training providers to adequately care for them takes time due to their extreme rarity: 6.2% of all patients are considered difficult intubations, 1.4% are difficult masks, and 0.4% are both (https://pubmed.ncbi.nlm.nih.gov/25999010/). He advocated that design of medical equipment and spaces should include input from those who most frequently encounter difficult airways (e.g., intensivists and anesthesiologists), that checklists and time-out procedures should be employed when performing endotracheal intubations, and interprofessional simulation trainings can improve performance in management of these uncommon events.