A 55 year old man was found unconscious in the bathroom by his family. He has a GCS of 7. His vital signs on arrival are a heart rate of 130, a blood pressure of 90/55, a respiratory rate of 28, and an oxygen saturation of 89% on room air. Although he was originally making sonorous noises, after elevating the head of the bed to 30 degrees, inserting a nasopharyngeal airway, and applying a jaw thrust, he is breathing quietly at 23 breaths a minutes, and his oxygen saturation has climbed to 92% with facemask oxygen…
Many airway discussions start from the moment that a laryngoscope is pulled out. In emergency medicine and critical care, we are rarely managing an airway in isolation. We manage the airway in the context of a critically ill patient. Therefore, it is essential to consider the physiology of the patient when deciding on the most appropriate time for advanced airway interventions like intubation.
For a number of reasons, the peri-intubation period is a time of high risk for cardiovascular collapse. Occasionally, rapidly evolving airway obstruction mandates immediate intervention. However, for the vast majority of critically ill patients, rushing to an advanced airway increases risk. When intubating critically ill patients, there are 5 major risk factors for cardiovascular collapse that must be considered: hypoxemia, hypotension, severe metabolic acidosis, right ventricular failure, and severe bronchospasm. (Mosier 2015)
Address hypoxia (and ensure adequate nitrogen wash-out)
During the pre-oxygenation phase, there are really two separate priorities. First, we want to replace the nitrogen in the lungs with oxygen to delay the time to desaturation. Second, we want to get the oxygen saturation as high as possible. (Frerk 2015; Leeuwenburg 2015) Because of the shape of the oxyhemoglobin dissociation curve, if patients do not have an oxygen saturation higher than 93-95% prior to intubation, they have a higher likelihood of desaturation and complication. (Weingart 2012; Davis 2008; Baraka 1999)
Elevating the head of the bed, rather than having the patient lying flat, improves airway patency and respiratory mechanics, as well as facilitating passive oxygenation during the apneic period. (Frerk 2015; Weingart 2012; Ramkumar 2011; Altermatt 2005; Dixon 2005; Boyce 2003)
The classic teaching of 3 minutes breathing 100% oxygen, or 8 full vital capacity breaths, is all about washing the nitrogen out of the lungs. Unfortunately, it is often not adequate for emergency department patients. The non-rebreather is inadequate for nitrogen wash-out in almost all critically ill patients, as higher minute ventilations increase the amount of room air entrained around the mask. Even in healthy patients breathing at a normal minute ventilation, the standard non-rebreather set at 15 L/min doesn’t adequately denitrogenate the lungs. (Driver 2016) In the spontaneously breathing patient, I use a non-rebreather mask set at “flush rate”, meaning that the wall oxygen flow is turned up as high as it will go. (Driver 2016) In patients requiring assistance, I will use a bag valve mask with 100% oxygen and a PEEP valve set at its lowest setting to ensure I have an appropriate 1 way valve. (Driver 2016) In both cases, I add nasal prongs set at 15 L/min under the mask. (Mosier 2015; Apfelbaum 2013)
In the elective surgery patient, de-nitrogenation and oxygenation are achieved by the same maneuvers. However, in critically ill emergency department patients, we are often faced with shunt physiology, and oxygen saturation will not climb with a non-rebreather alone. These patients required positive pressure ventilation. (Mosier 2015) I use two primary methods to deliver the required PEEP:
- Place the patient on non-invasive ventilation. This is is my preferred method. It has two advantages. Some patients, such as those with CHF or COPD, may respond to the NIPPV and forgo the intubation. Additionally, NIPPV does not require my hands. I can start NIPPV, then take a few minutes to speak to family, clarify goals of care, prepare intubation equipment, etc.
- Use the bag-valve mask with a PEEP valve. In order to create consistent PEEP, I place a nasal cannula set at 15 L/minute under the mask and hold a two hand seal.
- This is a fantastic demonstration of the value of the PEEP valve:
- Another option, depending on the patient, is to first insert a supraglottic airway, such as an LMA, and pre-oxygenate through that device prior to intubation. (Mosier 2015) If the physiology of the patient allows, placement of the LMA can be facilitated by the standard RSI drugs, a procedure Darren Braude calls “rapid sequence airway”. (Braude 2007)
Finally, some patients will not be able to tolerate these pre-oxygenation procedures due to agitation. This is the time for delayed-sequence intubation. This involves providing an anxiolytic to the patient to facilitate pre-oxygenation. Ketamine, in titrated doses of 0.5mg/kg, is my go to agent. (Mosier 2015; Weingart 2015)
(This is a pretty basic discussion of pre-oxygenation. This topic is so important, I think that anyone working in emergency medicine should read the paper on this, by Scott Weingart and Richard Levitan, available for free here.)
Post intubation hypotension, or even cardiovascular collapse, is very common in critically ill patients. (Perbet 2015; Mosier 2015)
Any patient with hypotension needs resuscitation before the induction agent is given and positive pressure ventilation is introduced. A shock index (HR/SBP) >0.8 also suggests the need for pre-intubation resuscitation. (Mosier 2015) Appropriate management of hypotension will depend on the cause of hypotension. For an approach to undifferentiated hypotension, see this post.
- Fluid bolus
- Give blood if the patient is bleeding
- Start a vasopressor. For me this is usually norepinephrine 5-20 mcg/min, but any vasopressor is probably appropriate. (Leeuwenburg 2015; Mosier 2015)
Prepare for deterioration
We should be ready for post-intubation hypotension in all patients. Remember to adjust your monitor to take blood pressure readings at frequent intervals. (Most monitors will have a “STAT” mode, which will provide a few minutes of continuous readings using only one pulse per reading instead of the usual 3). Although not every patient requires intervention before intubation, my preparation for every emergency department intubation includes ensuring adequate vascular access for fluid resuscitation and preparation of a push dose pressor. (Epinephrine is my push dose pressor of choice. My instructions for preparation can be found here.) For patients with an adequate blood pressure, but who I think are at a higher risk of deterioration, I like to have a norepinephrine drip either prepared, or running at a very low dose so that it can be rapidly titrated up.
In high risk patients, alter your approach
In patients starting with a low blood pressure, or with a high shock index, I alter my approach to intubation. The two key drivers of hemodynamic collapse during intubation are the drugs we use and the transition to positive pressure ventilation. The ideal approach is probably an awake intubation, limiting sedatives and maintaining the patient on negative pressure ventilation throughout. This approach is discussed in the EMCrit post “The hemodynamically neutral intubation”. If an awake intubation is not positive, my rule of thumb is to use half my usual sedative dose and double my usual paralytic dose. I would also have a norepinephrine drip on the pump ready to go, or already running, in these patients.
Consider metabolic acidosis
Key point: Pause and check the respiratory rate before every single intubation. If the patient is moving a lot of air, you have to ask yourself: could this be metabolic acidosis?
Patients with severe metabolic acidosis require very high minute ventilations as part of their compensatory respiratory alkalosis. These patients are at extremely high risk of decompensation, both during the apneic phase of RSI, and also when our ventilator is unable to (or not set to) match their pre-intubation minute ventilation. The best strategy: delay the intubation. If at all possible, temporize with NIPPV and work on correcting the metabolic acidosis before considering intubation. (Mosier 2015) If intubation is necessary, maintaining the minute ventilation is essential. This will require bagging the patient (or putting them on a ventilator) during the apneic period, ensuring rapid first pass success, and setting the ventilator with a high respiratory rate and tidal volume (none of which we are used to). An awake intubation, that allows the patient to continue to set their own respiratory rate, is recommended for these patients if possible.
Consider right ventricular failure
RV dysfunction is an often overlooked problem that can have disastrous consequences when transitioning to positive pressure ventilation. Increases in intrathoracic pressure result in increased pulmonary vascular pressures, worsening RV function. In patients with known RV dysfunction, focusing on medical therapy and noninvasive ventilation with a low PEEP is preferable to early intubation. (Mosier 2015) Although beyond the scope of this post, bedside echo can be used to assess RV function prior to intubation. If intubation is necessary, choose a hemodynamically stable agent, such as etomidate. You should aim to keep the mean arterial pressure higher than the pulmonary artery pressure, which means that any patient with RV dysfunction should have norepinephrine running or primed and ready prior to intubation. (Mosier 2015) Epinephrine can also be used to support RV function. Avoid hypoxia at all costs. Although we should avoid hypoxia in all intubation attempts, hypoxia results in increased pulmonary vascular resistance, potentially pushing the patient with RV dysfunction into cardiovascular collapse. Ensure ideal pre-oxygenation and apply apneic oxygenation (nasal prong at 15 L/min through the intubation attempt). (Mosier 2015) Once again, the ideal approach to these patients is probably an awake intubation.
As is discussed in the post on asthma, as well as in part 5 of this series, severe bronchospasm can also set patients up for peri-intubation collapse. These patients are generally hypovolemic and have significant lung hyperinflation limiting venous return. Add to that hypercapnea, acidosis, and hypoxia and it is not hard to understand why the chances of a peri-intubation arrest are so high. A common teaching is: when thinking about intubating an asthma patient, wait, and then wait some more, and then continue to wait, but don’t wait too long. If you are considering intubation, non-invasive ventilation should almost certainly be attempted first. (We are intubating to help with respiratory muscle fatigue. The plastic tube in the airway does nothing to help these patients.) If you do end up intubating an asthmatic patient, appropriate ventilator settings are key. These will be discussed at length in Part 5 of this series, but the primary goal is to allow complete expiration to avoid breath stacking. This will require low respiratory rates, low tidal volumes, and a close eye on the ventilator waveforms.
The rest of the airway series:
Part 2: Is this patient ready for intubation?
A special thanks to Dr. Laura Duggan (@drlauraduggan) and Dr. Casey Parker (@broomedocs ) for providing peer review for this post. Be sure to check out the airway app designed for reporting cases of front of neck airway access, as well as the 3D printed Cric trainer by Dr. Duggan: http://www.airwaycollaboration.org/
It is possible to measure end-tidal oxygen to ensure adequate pre-oxygenation. This is routinely done in many operating rooms. The goal is an end-tidal oxygen of about 90%. Some ED monitors are capable of measure end-tidal oxygen, but I don’t know of anyone using this technology routinely at this point.
Rapid sequence airway can be followed by intubation through the LMA:
Other FOAMed Resources
Altermatt FR, Muñoz HR, Delfino AE, Cortínez LI. Pre-oxygenation in the obese patient: effects of position on tolerance to apnoea. British journal of anaesthesia. 2005; 95(5):706-9. PMID: 16143575
Apfelbaum JL, Hagberg CA, Caplan RA. Practice guidelines for management of the difficult airway: an updated report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology. 2013; 118(2):251-70. PMID: 23364566
Baraka AS, Taha SK, Aouad MT, El-Khatib MF, Kawkabani NI. Preoxygenation: comparison of maximal breathing and tidal volume breathing techniques. Anesthesiology. 1999; 91(3):612-6. PMID: 10485768
Boyce JR, Ness T, Castroman P, Gleysteen JJ. A preliminary study of the optimal anesthesia positioning for the morbidly obese patient. Obesity surgery. 2003; 13(1):4-9. PMID: 12630606
Braude D, Richards M. Rapid Sequence Airway (RSA)–a novel approach to prehospital airway management. Prehospital emergency care. 2007; 11(2):250-2. PMID: 17454819
Davis DP, Hwang JQ, Dunford JV. Rate of decline in oxygen saturation at various pulse oximetry values with prehospital rapid sequence intubation. Prehospital emergency care : official journal of the National Association of EMS Physicians and the National Association of State EMS Directors. 2008; 12(1):46-51. PMID: 18189177
Dixon BJ, Dixon JB, Carden JR. Preoxygenation is more effective in the 25 degrees head-up position than in the supine position in severely obese patients: a randomized controlled study. Anesthesiology. 2005; 102(6):1110-5; discussion 5A. PMID: 15915022
Driver BE, Prekker ME, Kornas RL, Cales EK, Reardon RF. Flush Rate Oxygen for Emergency Airway Preoxygenation. Annals of emergency medicine. 2017; 69(1):1-6. PMID: 27522310
Frerk C, Mitchell VS, McNarry AF. Difficult Airway Society 2015 guidelines for management of unanticipated difficult intubation in adults. British journal of anaesthesia. 2015; 115(6):827-48. PMID: 26556848 [free full text]
Perbet S, De Jong A, Delmas J. Incidence of and risk factors for severe cardiovascular collapse after endotracheal intubation in the ICU: a multicenter observational study. Critical care (London, England). 19:257. 2015. PMID: 26084896 [free full text]
Ramkumar V, Umesh G, Philip FA. Preoxygenation with 20º head-up tilt provides longer duration of non-hypoxic apnea than conventional preoxygenation in non-obese healthy adults. Journal of anesthesia. 2011; 25(2):189-94. PMID: 21293885
Weingart SD, Trueger NS, Wong N, Scofi J, Singh N, Rudolph SS. Delayed sequence intubation: a prospective observational study. Annals of emergency medicine. 65(4):349-55. 2015. PMID: 25447559