By Colby Costa, BS, NRP, FP-C, CCP-C
Patients with physiologically difficult airways are those requiring airway management who have underlying physiologic derangements putting them at higher risk for peri-intubation and post-intubation decompensation, including hypoxia, cardiovascular collapse, cardiac arrest, etc. Indicators of a physiologically difficult airway include physiologic derangements, including, but not limited to any of the following [1,2]:
- Hypoxemia
- Hypermetabolic state
- Hemorrhage
- Hypotension
- Right heart failure
- Severe metabolic acidosis
The presence of hypoxia before intubation provides evidence that the patient has a decreased oxygen reserve and an SpO2 near 90% increases risk of precipitous desaturation [3]. In hemorrhage, there is a decrease in total hemoglobin. Although high SpO2 levels can be easily reached in hemorrhagic shock, there is a decrease in peripheral oxygen delivery accompanied by a hypermetabolic state [4]. Critically ill patients are often in a hypermetabolic state in which cellular oxygen consumption is elevated. This can be the result of toxins, fever, inflammatory response, etc. In any of these physiologic derangements, the safe apnea time is shortened and there is a high risk for precipitous desaturation.
The effects of induction medication and initiation of positive pressure ventilation (PPV) can cause decreased cardiac output (CO) and vasodilation, negatively impacting hemodynamics. The transition to PPV increases intrathoracic pressure, which strains the right ventricle and decreases CO. Hypotension before intubation creates a lesser threshold of hemodynamic impact to proceed into hemodynamic collapse. Similarly, underlying right heart failure causes a greater hemodynamic impact on the initiation of positive pressure ventilation, which can lead to a drastic reduction in cardiac output and hemodynamic collapse [5].
In acidosis, oxygen has a decreased affinity and increased unloading to hemoglobin, complicating preoxygenation. Severe metabolic acidosis is normally accompanied by compensatory respiratory alkalosis. This compensatory mechanism involves rapid deep breaths resulting in a high minute volume which is difficult to replicate with mechanical ventilation. The increase in CO2 resulting from the apnea period and decreased minute volume causes worsening acidosis that can lead to hemodynamic collapse [6].
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Nearly all pre-hospital intubations are performed in critically ill patients with at least one, often multiple, of these physiologic derangements present. Although some of these factors can be identified in the field, often they cannot, and other physiologic derangements can result in difficult airway management. Knowing this, why arrent all pre-hospital intubations performed as if they are a physiologically difficult airway?
RSI
Rapid-sequence intubation (RSI) is the simultaneous or near simultaneous process of induction and administration of paralytic medications to facilitate intubation. RSI has been the standard for emergent airway management and has been considered one of the most advanced skills performed by a few advanced pre-hospital programs. Sedation-only intubation is still present in many services, but it has become well-supported that RSI has higher success with fewer complications [7,8].
Many pre-hospital services have begun adapting RSI protocols and although this shows an advancement in care, more techniques are available that could further enhance abilities.
DSI
One technique is delayed-sequence intubation (DSI). DSI is the separation of induction and paralytic administration to allow for procedures or interventions to be performed.
During DSI, ketamine is the induction agent of choice as it does not blunt spontaneous ventilation or airway reflexes. Many critically ill patients experience altered mental status or agitation secondary to hypoxia, hypercapnia, encephalopathy, etc. This can create difficulty in performing critical interventions such as vascular access, medication administration and preoxygenation, as these patients are often uncooperative and unable to tolerate non-rebreather or NIV masks.
After induction, patients are sedated, and these interventions can be performed without interference from the patient. Many patients with severe tachypnea and shallow respirations even tend to improve their ventilation status with slower, deeper and more effective respirations [9-11]. This allows for better preoxygenation and the effects of some physiologic derangements can be minimized. The only randomized trial comparing RSI and DSI showed DSI to have higher first-attempt success and SpO2 level before intubation with a decrease in hypoxic events when compared to RSI with no difference in hemodynamic effects of airway-related adverse events [12].
Preoxygenation
Previously, preoxygenation was emphasized by providing 100% FiO2 to increase oxygen content and denitrogenation to prolong the safe apnea time. Noninvasive positive pressure ventilation (NIPPV) has been a long-standing treatment in the management of hypoxic and hypercapnic respiratory failure; however, it has not been a standard method of preoxygenation.
A recent pragmatic randomized control trial compared standard preoxygenation (NRB and NC) to NIPPV preoxygenation, excluding crash airways. The study showed NIPPV to be superior in nearly all applications. Major takeaways from the study include occurrences of hypoxemia, cardiac arrest, SpO2 <80%, or SpO2 <70%, all of which individually were nearly half as frequent in the NIPPV compared to the standard group. There were even less occurrences of aspiration in the NIPPV group [13,14]. The addition of NIPPV with 100% FiO2 preoxygenation provides many benefits in comparison to standard preoxygenation.
The addition of PEEP and resultant increased mean airway pressure results in improved preoxygenation, thus increasing safe apnea time. This can be effective in directly minimalizing the increased risk in physiologic derangement effects of hypoxemia, hypermetabolic state, hemorrhage and severe metabolic acidosis. The use of NIPPV before intubation also allows for the hemodynamic effects of PPV to be addressed before intubation. When NIPPV is initiated, these effects can be identified and treated with IVF, vasopressors, etc. before proceeding with the procedure. This allows for treatment and mitigation of the increased risks associated with hypotension, hypovolemia and RV failure physiologic derangements.
Mitigating adverse events during intubation
Most patients in the emergent setting requiring airway management are critically ill with physiologic derangements that increase the risk of adverse events. Taking steps to mitigate the effects of these physiologic derangements may be effective at preventing adverse events [15,16].
By applying DSI and NIV, preoxygenation and denitrogenation can be more effective by improving compliance with oxygen delivery, ventilation status and mean airway pressure. With this technique, the hemodynamic effect of each step (induction administration, PPV and intubation) can be individually treated and appropriately managed; contrary to RSI where the hemodynamic effects of all steps are compounded to one event with a greater risk for precipitous hemodynamic collapse.
This technique, like all others, does have limitations. Some patients, such as those with severe airway contamination (blood, vomit, foreign body, etc.), complete airway obstruction, crash intubation, etc. would not be appropriate candidates for this technique. However, these patients are rare even in the emergency medicine setting.
In most intubations performed in the emergency setting, utilizing a combination of DSI with NIPPV preoxygenation could minimize the effects of physiologic derangements, improve success rates, and decrease adverse events during emergent airway management.
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REFERENCES
1. Mosier JM, Joshi R, Hypes C, Pacheco G, Valenzuela T, Sakles JC. The Physiologically Difficult Airway. West J Emerg Med. 2015;16(7):1109-1117. doi:10.5811/westjem.2015.8.27467
2. Myatra SN, Divatia JV, Brewster DJ. The physiologically difficult airway: an emerging concept. Curr Opin Anaesthesiol. 2022;35(2):115-121. doi:10.1097/ACO.0000000000001102
3. Weingart SD, Levitan RM. Preoxygenation and Prevention of Desaturation During Emergency Airway Management. Ann Emerg Med. 2012;59(3):165-175.e1. doi:10.1016/j.annemergmed.2011.10.002
4. Pehböck D, Wenzel V, Voelckel W, et al. Effects of preoxygenation on desaturation time during hemorrhagic shock in pigs. Anesthesiology. 2010;113(3):593-599. doi:10.1097/ALN.0b013e3181e73f07
5. Corp A, Thomas C, Adlam M. The cardiovascular effects of positive pressure ventilation. BJA Educ. 2021;21(6):202-209. doi:10.1016/j.bjae.2021.01.002
6. Lentz S, Grossman A, Koyfman A, Long B. High-Risk Airway Management in the Emergency Department. Part I: Diseases and Approaches. J Emerg Med. 2020;59(1):84-95. doi:10.1016/j.jemermed.2020.05.008
7. Bouska R, Stolz U, Sakles J, Mosier J. Rapid Sequence Intubation Compared to Non-RSI for Out-of-OR Intubations with Video Laryngoscopy. Crit Care Med. 2013;41(12):A218. doi:10.1097/01.ccm.0000440111.34502.7f
8. Okubo M, Gibo K, Hagiwara Y, Nakayama Y, Hasegawa K. The effectiveness of rapid sequence intubation (RSI) versus non-RSI in emergency department: an analysis of multicenter prospective observational study. Int J Emerg Med. 2017;10:1. doi:10.1186/s12245-017-0129-8
9. Haag, CCEMT-P, CIC, CACCADS JDH CCEMT P, CIC, CAC. Delayed Sequence Intubation. EMS Airw. Published online December 3, 2021. Accessed September 19, 2024. https://emsairway.com/2021/12/03/delayed-sequence-intubation/
10. Suleiman A, Santer P, Munoz-Acuna R, et al. Effects of Ketamine Infusion on Breathing and Encephalography in Spontaneously Breathing ICU Patients. J Intensive Care Med. 2023;38(3):299-306. doi:10.1177/08850666221119716
11. Weingart SD. Preoxygenation, reoxygenation, and delayed sequence intubation in the emergency department. J Emerg Med. 2011;40(6):661-667. doi:10.1016/j.jemermed.2010.02.014
12. Bandyopadhyay A, Kumar P, Jafra A, Thakur H, Yaddanapudi LN, Jain K. Peri-Intubation Hypoxia After Delayed Versus Rapid Sequence Intubation in Critically Injured Patients on Arrival to Trauma Triage: A Randomized Controlled Trial. Anesth Analg. 2023;136(5):913-919. doi:10.1213/ANE.0000000000006171
13. Gibbs KW, Semler MW, Driver BE, et al. Noninvasive Ventilation for Preoxygenation during Emergency Intubation. N Engl J Med. 2024;390(23):2165-2177. doi:10.1056/NEJMoa2313680
14. Gibbs KW, Ginde AA, Prekker ME, et al. Protocol and statistical analysis plan for the PREOXI trial of preoxygenation with noninvasive ventilation vs oxygen mask. medRxiv. Published online March 24, 2023:2023.03.23.23287539. doi:10.1101/2023.03.23.23287539
15. Peth, BSEMS, NRP Aaron. Management of the Physiologically Difficult Airway for Out-Of-Hospital Care Providers. EMS Airw. Published online February 12, 2024. Accessed September 19, 2024. https://emsairway.com/2024/02/12/management-of-the-physiologically-difficult-airway-for-out-hospital-care-providcers/
16. Winniford, BA, EMT-P, CCP-C, FP-C Cody. Operational Realities of Evidence-Based Medicine in Prehospital Airway Management. EMS Airw. Published online July 15, 2024. Accessed September 19, 2024. https://emsairway.com/2024/07/15/operational-realities-of-evidence-based-medicine-in-prehospital-airway-management/
ABOUT THE AUTHOR
Colby Costa, BS, NRP, FP-C, CCP-C, began his career in emergency services as a firefighter/EMT and over the past 6 years, has gained experience working 911, critical care transport and in hospital. He serves as the education coordinator for the CHI Saint Joseph Health Emergency Medicine Center of Excellence. In this role, he acts as the program coordinator and primary instructor for their Critical Care Paramedic Program and leads advanced multidisciplinary trainings across the Commonwealth of Kentucky.