Managing the Physiologically Difficult Airway

Educational Objectives

The goal of this program is to improve the management of the physiologically difficult airway. After hearing and assimilating this program, the clinician will be better able to:

1. Evaluate the outcomes of intubation in critically ill adults in the intensive care unit.
2. Develop strategies for preventing adverse events before, during, and after airway management.
3. Review relevant literature to synthesize an integrated approach to airway management in critically ill patients.

Summary

Physiologically difficult airway: there is a growing focus on managing airways in critically ill adults, especially in the intensive care unit (ICU); the INTUBE study (Rusotto et al [2021]) showed that cardiovascular (CV) instability and hypoxemia during intubation and outside the operating room (OR) are more common than tube placement difficulties (requiring >2 attempts); “physiologically difficult airway” refers to patients with baseline conditions (eg, hypoxemia, shock) that increase risks during tracheal intubation and the shift to positive pressure ventilation

Transient ICU intubation instability: recent findings from the INTUBE and INTUPROS (Garnacho-Montero et al [2024]) studies suggest that even brief physiologic disturbances during ICU or emergency department intubations (eg, drops in blood pressure or oxygen saturation) may have long-term effects on patient outcomes; strategies are needed to mitigate these issues; De Jong et al (2013) developed and validated the MACOCHA score to identify patients at risk for difficult intubation in the ICU; the score is based on key predictors related to the patient (eg, anatomic factors), pathology (eg, coma, severe hypoxemia), and the operator (eg, anesthesia training); points are assigned to each factor, with a higher total score indicating a greater likelihood of difficult intubation; a score of 3 or 4 marks the threshold at which the incidence of difficult intubation significantly increases

Oxygenation

Overview: the 2 primary causes of hypoxemia in the ICU are ventilation-perfusion (V/Q ratio) mismatch and physiologic shunt, both of which are often unresponsive to supplemental oxygen; shunt physiology — as the shunt fraction increases, the effectiveness of increasing the fraction of inspired oxygen (Fi_O2) diminishes; in patients without a shunt, the relationship between Fi_O2 and Pa_O2 is nearly linear; however, ICU patients often have a high shunt fraction due to certain conditions, eg, hypoxemic respiratory failure, acute respiratory distress syndrome (ARDS), pulmonary edema, or pneumonia; in such cases, in addition to preoxygenation, positive airway pressure (PAP) is sometimes necessary

Noninvasive ventilation (NIV): sometimes called bilevel PAP (BiPAP), NIV involves using a mask connected to a machine that allows precise control of Fi_O2 and PAP; while NIV is effective for delivering these settings, it poses a challenge during endotracheal intubation since the BiPAP mask must be removed to insert the endotracheal tube, making continuous airway management difficult

Heated high-flow nasal oxygen (HFNO): provides the advantage of continuous oxygen delivery during airway management and tracheal intubation; while it does not generate significant PAP, HFNO can still effectively provide apneic oxygenation

BiPAP vs HFNO: BiPAP generally outperforms HFNO due to its mask interface, which ensures a better seal and allows precise control over PAP, making it more effective in maintaining a higher Pa_O2 for longer, especially in patients with severe respiratory failure; a critical threshold for considering alternative interventions is a Pa_O2/Fi_O2 ratio of ≈200; studies indicate that the effectiveness of HFNO decreases significantly once the Pa_O2/Fi_O2 ratio drops below 200, while BiPAP remains more effective in such situations

BiPAP with HFNO

OPTINIV method: the OPTINIV trial (Jaber et al [2016]) explored combination of HFNO with a mask seal, a technique that can potentially merge the advantages of both modalities; the combination demonstrated a significant reduction in oxygen desaturation during tracheal intubation

Changeover method: involves transitioning from BiPAP to HFNO right before intubation; this approach requires removing the BiPAP mask, quickly applying HFNO, then securing the airway; while this method can be effective, it may cause delays due to equipment swapping, which can prolong the procedure and potentially lead to reduced oxygenation

Bag-mask ventilation (BMV): can be crucial for maintaining oxygen saturation during intubation or rescue ventilation, especially in the ICU; while older training emphasized the risks for aspiration and severe complications with BMV, recent studies, including the PreVent (Casey et al [2019]) and FELLOW (Vaughan et al [2022]) trials, demonstrate that using, eg, an Ambu Bag, to ventilate patients before intubation or during extended apneic periods can effectively sustain oxygen saturation without increasing adverse events or complications

Adaptive preoxygenation approach: for patients with a Pa_O2/Fi_O2 ratio >200, HFNO can be used effectively for apneic oxygenation; conventional oxygen therapy (COT) combined with BMV can also be employed for preoxygenation or rescue ventilation, providing flexibility in approach; for patients with a Pa_O2/Fi_O2 ratio <200, it is crucial to use NIV at relatively low positive end-expiratory pressure (PEEP) settings, with or without HFNO, for apneic oxygenation; for patients with severe respiratory failure or severe ARDS and an unsecure airway, consider starting NIV with higher PEEP settings; in such cases, the risk for desaturation during intubation is 100%; ideally, HFNO should also be used to keep up the saturation during intubation

Other measures: keeping the head of the bed elevated can improve diaphragm function and lung expansion; during intubation, rescue ventilation using BMV or a BiPAP machine can be beneficial; in extremely severe cases, awake intubation may be considered to secure the airway more safely, as it provides an option for patients who are likely to desaturate quickly when apneic; in the PREOXI trial, Gibbs et al (2024) compared COT vs BiPAP in critically ill adults and found that BiPAP is much more effective than COT, particularly in patients with baseline respiratory failure and those on a higher starting Fi_O2

Hemodynamic instability: anesthesia professionals often favor propofol; studies have found that the proportion of patients who received propofol is directly proportional to the percentage of anesthesiologists managing the airways; study by Russotto et al (2022) — among various factors, use of propofol was the only factor that was independently associated with CV instability after intubation; this suggests that propofol may not be suitable for many critically ill patients; the alternatives are etomidate and ketamine; the EvK trial (Matchett et al [2022]) — compared etomidate vs ketamine and found that patients who received etomidate were more likely to be dead at 7 days; 28-day survival rates for etomidate and ketamine were not statistically significantly different; etomidate is probably not the safest drug for critically ill adults

Use of fluids to prevent CV collapse: 2 trials (PrePARE and PREPARE II) investigated the impact of administering a 500-mL saline bolus to all ICU patients undergoing intubation, regardless of their volume status or hemodynamic risk; no significant difference in outcomes was found between those who received the fluid bolus and those who did not

First-pass Success (FPS)

Overview: in the OR, where apneic intervals can be prolonged, multiple attempts at securing the airway are often feasible; however, in the ICU, where patients cannot tolerate extended intubation attempts, achieving FPS is crucial; the INTUBE study showed that major adverse events (eg, severe hypoxemia [oxygen saturation ≤80%]) increase with each additional intubation attempt; these findings were corroborated by the INTUPROS study

Video laryngoscopy (VL): effective in increasing FPS rates; meta-analyses indicate that different video laryngoscope designs (conventional, hyperangulated, or channel-based) generally perform well; the DEVICE trial (Prekker et al [2023]) showed significantly improved FPS and overall intubation success rates using video laryngoscopes vs direct laryngoscopes; in the ICU, VL not only enhances procedural success but also fosters a collaborative approach by allowing the entire team to visualize the airway, potentially reducing stress and improving outcomes

Neuromuscular blockade: use of neuromuscular blocking drugs in the OR or the ICU significantly improves the ease of BMV, increases the probability of first-pass intubation success, and reduces complication rates; historical trials consistently show an almost linear relationship between use of neuromuscular blockade and the likelihood of successful first-pass intubation

Planning: findings of a study by Russotto et al (2021) indicate that, globally, NIV or HFNO are not commonly used in airway management outside the OR; although the overall FPS rate is ≈80%, VL is also underutilized outside the OR, and medications like etomidate or ketamine are not frequently used; this suggests that there is considerable room for improvement in airway management practices in non-OR settings

Use of checklists: effective for improving compliance with complex, multistep processes; however, impact on patient-centered outcomes is debatable; De Jong et al (2022) emphasize the need for well-structured checklists that address critical aspects (eg, oxygenation, preoxygenation, maintaining oxygen saturation during the apneic interval, optimizing oxygenation postintubation) and the importance of FPS, (recommend the presence of 2 airway operators at the bedside and the use of VL during pre- and peri-intubation phases); the checklist should cover hemodynamic optimization before, during, and after airway management, and include best practices for safety and quality

Readings

Casey JD, Janz DR, Russell DW, et al; PreVent Investigators and the Pragmatic Critical Care Research Group. Bag-mask ventilation during tracheal intubation of critically ill adults. N Engl J Med. 2019 Feb 28;380(9):811-821. doi: 10.1056/NEJMoa1812405; De Jong A, Molinari N, Terzi N, et al; AzuRéa Network for the Frida-Réa Study Group. Early identification of patients at risk for difficult intubation in the intensive care unit: development and validation of the MACOCHA score in a multicenter cohort study. Am J Respir Crit Care Med. 2013 Apr 15;187(8):832-9. doi: 10.1164/rccm.201210-1851OC; De Jong A, Myatra SN, Roca O, et al. How to improve intubation in the intensive care unit. Update on knowledge and devices. Intensive Care Med. 2022 Oct;48(10):1287-1298. doi: 10.1007/s00134-022-06849-0; Gibbs KW, Semler MW, Driver BE, et al; PREOXI Investigators and the Pragmatic Critical Care Research Group. Noninvasive Ventilation for Preoxygenation during Emergency Intubation. N Engl J Med. 2024 Jun 20;390(23):2165-2177. doi: 10.1056/NEJMoa2313680. Epub 2024 Jun 13. PMID: 38869091; PMCID: PMC11282951; Garnacho-Montero J, Gordillo-Escobar E, Trenado J, et al; Intubation Prospective (INTUPROS) Study Investigators. A Nationwide, Prospective Study of Tracheal Intubation in Critically Ill Adults in Spain: Management, Associated Complications, and Outcomes. Crit Care Med. 2024 May 1;52(5):786-797. doi: 10.1097/CCM.0000000000006198. Epub 2024 Jan 23. PMID: 38259143; Jaber S, Monnin M, Girard M, et al. Apnoeic oxygenation via high-flow nasal cannula oxygen combined with non-invasive ventilation preoxygenation for intubation in hypoxaemic patients in the intensive care unit: The single-centre, blinded, randomised controlled OPTINIV trial. Intensive Care Med. 2016 Dec;42(12):1877-1887. doi: 10.1007/s00134-016-4588-9; Janz DR, Casey JD, Semler MW, et al; Pragmatic Critical Care Research Group. Effect of a fluid bolus on cardiovascular collapse among critically ill adults undergoing tracheal intubation (PrePARE): A randomised controlled trial. Lancet Respir Med. 2019 Dec;7(12):1039-1047. doi: 10.1016/S2213-2600(19)30246-2; Matchett G, Gasanova I, Riccio CA, et al; EvK clinical trial collaborators. etomidate versus ketamine for emergency endotracheal intubation: A randomized clinical trial. Intensive Care Med. 2022 Jan;48(1):78-91. doi: 10.1007/s00134-021-06577-x; Prekker ME, Driver BE, Trent SA, et al; DEVICE Investigators and the Pragmatic Critical Care Research Group. Video versus direct laryngoscopy for tracheal intubation of critically ill adults. N Engl J Med. 2023 Aug 3;389(5):418-429. doi: 10.1056/NEJMoa2301601; Russell DW, Casey JD, Gibbs KW, et al; PREPARE II Investigators and the Pragmatic Critical Care Research Group. Effect of fluid bolus administration on cardiovascular collapse among critically ill patients undergoing tracheal intubation: A randomized clinical trial. JAMA. 2022 Jul 19;328(3):270-279. doi: 10.1001/jama.2022.9792; Russotto V, Myatra SN, Laffey JG, et al; INTUBE Study Investigators. Intubation practices and adverse peri-intubation events in critically ill patients from 29 countries. JAMA. 2021 Mar 23;325(12):1164-1172. doi: 10.1001/jama.2021.1727. Erratum in: JAMA. 2021 Jun 22;325(24):2507. doi: 10.1001/jama.2021.9012; Russotto V, Tassistro E, Myatra SN, et al. Peri-intubation cardiovascular collapse in patients who are critically ill: Insights from the INTUBE Study. Am J Respir Crit Care Med. 2022 Aug 15;206(4):449-458. doi: 10.1164/rccm.202111-2575OC; Vaughan EM, Seitz KP, Janz DR, et al. Bag-mask ventilation versus apneic oxygenation during tracheal intubation in critically ill adults: A secondary analysis of 2 randomized trials. J Intensive Care Med. 2022 Jul;37(7):899-907. doi: 10.1177/08850666211058646.

Disclosures

For this program, members of the faculty and planning committee reported nothing relevant to disclose. Dr. Jabaley’s lecture includes information related to the off-label or investigational use of a therapy, product, or device.

Acknowledgements

Dr. Jabaley was recorded at the Carolina Refresher Course 2024: 35th Annual Update in Anesthesiology, Pain, and Critical Care Medicine, held June 19-22, 2024, in Kiawah Island, SC, and presented by University of North Carolina at Chapel Hill, School of Medicine. For information on upcoming CME activities from this presenter, please visit med.unc.edu/cpd. Audio Digest thanks the speakers and University of North Carolina at Chapel Hill for their cooperation in the production of this program.

CME/CE INFO

Accreditation:

The Audio- Digest Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Audio- Digest Foundation designates this enduring material for a maximum of 1.25 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Audio Digest Foundation is accredited as a provider of continuing nursing education by the American Nurses Credentialing Center's (ANCC's) Commission on Accreditation. Audio Digest Foundation designates this activity for 1.25 CE contact hours.

Lecture ID:

AN663902

Expiration:

This CME course qualifies for AMA PRA Category 1 Credits™ for 3 years from the date of publication.

Instructions:

To earn CME/CE credit for this course, you must complete all the following components in the order recommended: (1) Review introductory course content, including Educational Objectives and Faculty/Planner Disclosures; (2) Listen to the audio program and review accompanying learning materials; (3) Complete posttest (only after completing Step 2) and earn a passing score of at least 80%. Taking the course Pretest and completing the Evaluation Survey are strongly recommended (but not mandatory) components of completing this CME/CE course.

Estimated time to complete this CME/CE course:

Approximately 2x the length of the recorded lecture to account for time spent studying accompanying learning materials and completing tests.

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