Unnervingly high rates of peri-intubation complications can occur. We’ve all heard that statement, or at least something comparable. Some of us have been fortunate enough never to have experienced anything too detrimental transpiring during the intubation procedure, but others haven’t. This could be due to sheer good or bad luck, whether the procedure was elective or emergent, how critically ill the patient was, or how we approached the RSI procedure (those that are very skilled and well-educated… and well, those who aren't).
Over the years, It seems to me that intubation proficiency has improved, and the entire RSI procedure is more appropriately executed; I see this among my peers, and I see it in my teachings as well. EMS overall seems to be improving! Is this due to the available education produced in literature, textbooks, and FOAMed? I think so! However, I feel this education has recently and overbearingly encompassed strategies for intubating with anatomic difficulties and interventions to combat it, with little mention regarding optimization. There seems to be a back-and-forth battle in my eyes. The use of difficult anatomic airway predicting mnemonics, checklists, positioning, bougie, and implementation of videolaryngoscopy (VL) as a first choice over direct laryngoscopy (DL); all have gotten a large spotlight as of recent, and optimization has only been the opening act, or at times only has a backstage pass. Does optimization content exist? Absolutely! Some very good content has been put out in the past, and I'm sure is still in the works. But my online findings recently frequent more of the EMS community that's far more aware of LEMONS, positioning, use of the bougie, and videolaryngoscopes than awareness of the shock index or implementation of a clinical bundle to reduce out-of-hospital hypoxia. What about DASH-1A or the HOp Killers? This could also be due to the "what's popular in FOAMed right now" dynamic I frequently see.
Sidetrack #1: Even in this pretend battle I have in my head, we can't take away from the importance of first-pass success. We should use both the anatomically and physiologically difficult airway predictors to best increase our chances at first pass success. In an article titled "The Importance of First Pass Success When Performing Orotracheal Intubation In the Emergency Department," the authors concluded that when performing orotracheal intubation in the ED, first pass success is associated with a relatively small incidence of adverse events and as the number of attempts increases, the incidence of adverse events increase substantially. First attempt adverse events: 14.2%. Second attempt adverse events: 47.2% . 😱 So, yes, FPS is pretty darn important.
Sidetrack #2: I don't mean to sidetrack, again, and get "political," but in regard to videolaryngoscopes and anatomically difficult airways, I am very PRO VL! I know some of you will argue that we need to be proficient in both VL and DL... and continue in with, what if it fails? What if the screen is soiled? What if... this? What if... that? Blah, blah, BLAH! Plenty of research has been produced that puts VL > DL. And while I don't believe any of them report VL as the "standard of care," just give it time.
*** 222 studies (219 RCTs, 3 quasi-RCTs) with 26,149 participants ***
Let me say this: I DO NOT DISAGREE WITH "KEEPING UP" ON YOUR DL SKILLS OR ANY THE OTHER ARGUMENTS. However, in the pre-hospital and transport environment, I have had great success with VL and have seen others with that success as well. I'm sure many of you would agree too. Anecdotal, I know. But I bet I'm not alone, and I will advocate for it under all circumstances. Plus, VL provides a superior view of the airway with less force than DL and should be considered a first-line technique for both routine and difficult airways, per the new Manual of Emergency Airway Management. The text also goes on to say, "VL is becoming more affordable and ubiquitous, provides superior laryngeal views, and because multiple meta-analyses have demonstrated improved first-attempt success when VL is used, there is little reason to use a direct laryngoscope." 
Back from the sidetracking -- YES, Anatomic difficulties! Despite having technological devices available and abundant education regarding anatomically difficult airways resulting in higher success rates, those "unnervingly high" rates of peri-intubation complications still occur in the form of desaturation, hypotension, and cardiac arrest during emergency airway management.
According to The Wall’s Manual of Emergency Airway Management (6th edition), there are cardiac arrest rates between 1% and 4%, with other complications (mostly hypoxemia and hypotension) as high as 30% in patients with first-pass success [1, 2-4]. And, according to the article “Intubation Practices and Adverse Peri-intubation Events in Critically Ill Patients from 29 Countries,” at least one major critical event occurred after intubation in 45.2% of patients, which included cardiovascular instability, severe hypoxia, and cardiac arrest .
That’s as many as 1 in 25 experiencing cardiac arrest and nearly 50% experiencing a major adverse event! 😱 😱
Not to try and scare you any further, but here’s a statement from the evidence section of The Manual of Emergency Airway Management’s “The Physiologically Difficult Airway” chapter:
“When patients are hypoxemic or hypotensive prior to intubation, they have an adjusted odds of cardiac arrest almost 6 times that of patients that are neither hypoxemic nor hypotensive, and when critically ill patients have a difficult airway, half of them have life-threatening complications. However, the major increase in the risk to critically ill patients occurs during the second attempt.”
With this brief bit of unsettling statistics, I believe there should be an adequate level of focus geared toward the physiologically difficult airway. I'm not saying I want a paradigm shift away from education on the anatomically difficult airway to the physiologically difficult airway (or a back and forth), but a co-existence of the two stressing each of their importance. I do think there is a fair amount of education out there on this topic, but I would like to see more than just one slide in a lecture discussing simply giving pressors or fluids for physiologically difficult airways -- a bit more physiologic optimization info would be great.
That brings me to an article where a mnemonic originates - I believe - and was created to educate and assist providers with identifying the most seen pre-intubation abnormalities that should be considered. Within the article (HERE), posted in 2020, they put emphasis on physiologically difficult airways and insist that those airways deserve their own mnemonic. CRASH is that mnemonic, and it can be used to remember the physiologically difficult airway abnormalities most commonly encountered and how to intervene. What seems to separate this mnemonic from others with similar purposes is the inclusion of increased oxygen consumption, RV failure/dysfunction, severe acidosis, and hypotension, with the others not including ALL of these derangements. The mnemonic has also surfaced as a large portion of one of the chapters in the new Manual of Emergency Airway Management textbook, which I have been heavily referencing.
Before we really get into what C-R-A-S-H is, I would first like to start with a little Q&A.
What is the anatomically difficult airway?
An airway in which obtaining a glottic view or passing an endotracheal tube is challenging . An airway in which identifiable anatomic attributes predict technical difficulty with securing the airway .
What is the physiologically difficult airway?
An airway in which physiologic derangements place the patient at higher risk of cardiovascular collapse with intubation and conversion to positive pressure ventilation . An airway that requires the operator to optimize overall patient physiology in the context of critically low oxygen saturation, hemodynamic instability, or severe metabolic acidosis .
I ask and answer these first two questions because when the question “what is a difficult airway” is asked, it is usually met with answers regarding anatomic abnormalities, how hard the glottic opening was to see, and how hard it was to “get the tube.” While those issues do indeed make the airway difficult, verbiage matters with respect to the complications associated with each of the “difficulties.”
How do I predict a physiologically difficult airway?
For a host of reasons, the patient can decompensate from physiologic abnormalities during the intubation procedure. These abnormalities can be seen as a single finding or in conjunction with many, and with the administration of induction agents, the apneic period, and the transition to PPV, the patient’s hemodynamic status may be exacerbated. With the use of the mnemonic CRASH, we can identify the most seen pre-intubation abnormalities that should be considered .
Now that we have covered predicting the physiologically difficult airway with mention of the CRASH mnemonic, let's dive into what it consists of:
C – Consumption
Abnormality: Increased Oxygen Consumption.
Pediatric patients, sepsis, acute respiratory distress syndrome (ARDS), or other high-demand states such as excited delirium, thyrotoxicosis, and pregnancy all increase the consumption of oxygen. Patients at or near their anaerobic threshold with critical illness that increases oxygen consumption and decreases oxygen delivery are at risk of rapid desaturation despite normal or near-normal oxygen saturation during preoxygenation . These patients may exhibit a normal saturation during preoxygenation; however, the increased peripheral consumption may still result in rapid desaturation .
Optimize preoxygenation, utilize apneic oxygenation, and anticipate shorter (safe) apnea time [1, 6].
R – Right Ventricular Failure
Abnormality: Dysfunction or Failure of the Right Ventricle
Patients with right ventricular (RV) dysfunction or failure are at very high risk of decompensation during intubation. The right ventricle has very little reserve to overcome increased afterload. Early on, the right ventricle can increase contractility through interventricular dependence with the left ventricle, but as dilation and regurgitant flow across the tricuspid valve worsens, contractility worsens, and further dilation eventually impairs left ventricular diastolic filling. Cardiac output is only maintained by tachycardia at this point, and any further increase in RV afterload, or further volume loading of the right ventricle, can push the right ventricle too far and result in cardiac arrest. Hypercapnia, atelectasis, hypoxemia all independently increase pulmonary vascular resistance, and positive pressure can increase RV afterload as well – often to the point of cardiovascular collapse .
Optimize preoxygenation, inhaled pulmonary vasodilators, choice of induction agents, early use of vasopressors . Cardiac ultrasound can help identify a failing RV and guide judicious fluid resuscitation, appropriate vasoactives, and inhaled pulmonary dilator medication use .
A – Acidosis
Abnormality: Metabolic Acidosis
Severe metabolic acidemia increases risk by further decreasing the pH with any interruption of compensatory ventilation during intubation or unmatched alveolar ventilation requirement after intubation. Although many patients can handle an increase in their PaCO2 during intubation, those trying to compensate for a severe metabolic acidosis can be tipped over the edge during this brief period. Profound acidosis can have negative inotropic effects on the heart, worsen shock states, and instigate malignant ventricular dysrhythmias . Of note, a recent study by West, et al. (2017), “The Effect of the Apneic Period on the Respiratory Physiology of Patients Undergoing Intubation in the Emergency Department,” showed that an apneic phase of greater than 60 seconds caused statistically significant changes in pH and PaCO2 by 0.15 and 12.5 respectively .
Correct the underlying issues; avoid mechanical ventilation, if possible; minimize apnea time; consider awake intubation (not us medics and nurses 😩); maintain increased minute ventilation.
S – Saturation
Abnormality: Risk of DeSaturation
Critically ill patients with airspace disease such as ARDS have limitations in the ability to preoxygenate to provide an adequate safe apnea duration .
Optimize preoxygenation, including noninvasive ventilation and DSI, and apneic oxygenation, including high-flow nasal delivery .
Preoxygenation should address the three components required for a safe apneic interval: denitrogenation, improving functional residual capacity (FRC), and reducing ventilation/perfusion mismatch .
H – Hypotension
Critically ill patients are at significant risk of peri-intubation hypotension from many factors. Volume depletion, vasoplegia, and cardiomyopathy are all relatively easily identified, and steps can be taken to address them prior to intubation. The response to induction agents and positive pressure are more difficult to predict and, when combined with any of the former, increase the risk of precipitating a decompensated state. An elevated shock index (SI) is helpful in predicting those patients at high risk, but a low SI should not necessarily be reassuring .
Volume resuscitation and vasopressors .
There you have it. The CRASH mnemonic in a nutshell. One that can be used when preparing and assessing your patient for the RSI procedure and attempting to remember the most seen pre-intubation physiologic abnormalities. A brain tool you can use to lessen the risk of those scary peri-intubation adverse effects.
Thank you for nerding out with me 🤓
Wanna nerd out with me a tad more? Check these must-read (per me) articles:
Implementation of a Clinical Bundle to Reduce Out-of-Hospital Peri-intubation Hypoxia
Evaluation and Management of the Physiologically Difficult Airway: Consensus Recommendations From Society for Airway Management
Shock Index as a Predictor of Post-Intubation Hypotension and Cardiac Arrest; A Review of the Current Evidence
Peri-Intubation Cardiovascular Collapse in Patients Who Are Critically Ill: Insights from the INTUBE Study
Etomidate Versus Ketamine for Emergency Endotracheal Intubation: A Randomized Clinical Trial
Jared Patterson, CCP-C, One Rad Medic
Killin' It Since 1989
* Images found within this article were created by the author utilizing the resources provided within the citations. The images are recreations of information to be used for the blog *
1. Brown, C.A. and Walls, R.M. (2023) The Walls Manual of Emergency Airway Management. 6th edn. Edited by J.C. Sackles et al. Philadelphia, PA: Wolters Kluwer.
2. De Jong A, Rolle A, Molinari N, Paugam-Burtz C, Constantin JM, Lefrant JY, Asehnoune K, Jung B, Futier E, Chanques G, Azoulay E, Jaber S. Cardiac Arrest and Mortality Related to Intubation Procedure in Critically Ill Adult Patients: A Multicenter Cohort Study. Crit Care Med. 2018 Apr;46(4):532-539. doi: 10.1097/CCM.0000000000002925. PMID: 29261566.
3. Heffner AC, Swords DS, Neale MN, Jones AE. Incidence and factors associated with cardiac arrest complicating emergency airway management. Resuscitation. 2013 Nov;84(11):1500-4. doi: 10.1016/j.resuscitation.2013.07.022. Epub 2013 Aug 1. PMID: 23911630.
4. April MD, Arana A, Reynolds JC, Carlson JN, Davis WT, Schauer SG, Oliver JJ, Summers SM, Long B, Walls RM, Brown CA 3rd; NEAR Investigators. Peri-intubation cardiac arrest in the Emergency Department: A National Emergency Airway Registry (NEAR) study. Resuscitation. 2021 May;162:403-411. doi: 10.1016/j.resuscitation.2021.02.039. Epub 2021 Mar 5. PMID: 33684505.
5. Russotto V, Myatra SN, Laffey JG, et al. Intubation Practices and Adverse Peri-intubation Events in Critically Ill Patients From 29 Countries. JAMA. 2021;325(12):1164–1172. doi:10.1001/jama.2021.1727
6. Crash, a Mnemonic for the Physiological Difficult Airway (no date) ACEP Now. Available at: https://www.acepnow.com/article/crash-a-mnemonic-for-the-physiological-difficult-airway/?singlepage=1 (Accessed: October 31, 2022).
7. Mosier JM, Joshi R, Hypes C, Pacheco G, Valenzuela T, Sakles JC. The Physiologically Difficult Airway. West J Emerg Med. 2015 Dec;16(7):1109-17. doi: 10.5811/westjem.2015.8.27467. Epub 2015 Dec 8. PMID: 26759664; PMCID: PMC4703154.
8. West JR, Scoccimarro A, Kramer C, Caputo ND. The effect of the apneic period on the respiratory physiology of patients undergoing intubation in the ED. Am J Emerg Med. 2017 Sep;35(9):1320-1323. doi: 10.1016/j.ajem.2017.03.076. Epub 2017 Apr 2. PMID: 28412161.
9. Sakles JC, Chiu S, Mosier J, Walker C, Stolz U. The importance of first pass success when performing orotracheal intubation in the emergency department. Acad Emerg Med. 2013 Jan;20(1):71-8. doi: 10.1111/acem.12055. PMID: 23574475; PMCID: PMC4530518.