Intubating Ninja: Passive Oxygenation
Notice anything different in that picture above? Notice anything different about that intubation procedure from what usually happens in the back of your ambulance? We will come back to that in a moment.
I don’t know about you, but when I went to Paramedic school, we were taught to intubate and to intubate quickly. When it came time to practical testing, the instructor timed us with a stop watch. I believe we were allowed 30 seconds or so. But no worries, I was an INTUBATING NINJA! My 13 years of playing the drums, both full set and quints, had trained my hands to operate independently and with lightning speed. Warning: You do not want to challenge me to a game of slaps! So in school, the time restraints made intubating that mannequin a fun challenge.
Then I put on my big boy pants and went to work on an ambulance. Take a wild guess as to what my very first call was on my very first day of work as a brand new green-as-can-be paramedic…Yup, difficulty breathing (CHF). My FTO decided this patient needed to be intubated. He pushed the RSI drugs and it was my job to intubate the patient. This intubating ninja was pretty close to experiencing my very own Code Brown! The stress of my first field intubation was made much more severe due to the internalized need to hurry up! I tend to believe that many other medics also experience this stress to hurry up when intubating a patient.
Well what if we could eliminate the need to hurry up? Would your stress level go down? Would your first attempt success rate improve now that you can take your time to be more accurate with tube placement? What if there was a way to accomplish all of that by maintaining an apneic (neither breathing nor mechanical ventilation) patient’s oxygen saturation at 98-99% for approximately 100 minutes? Would that be enough time for you??
I first learned of this possibility while listening to a recorded lecture given by Dr Luke Duncan of Albany Medical College about airway management and a process he called Passive Oxygenation which he says has been in practice since the 1950’s.
Look back at the picture above. Notice anything different yet? How often do you see a patient wearing a nasal cannula while being intubated? I would bet that it is not often. When the fit is hitting the shan, we quickly rip that thing off and replace it with a mask of some sort (NRB, CPAP, BVM), right? And we do this while mumbling all kinds of obscenities about the nursing home staff who applied the cannula in the first place. Well there is a guy (not so much just a guy but more like an airway wizard) named Dr. Rich Levitan who teaches at both Jefferson Medical College and the University of Maryland and has been researching airway management for over twenty years. Dr Levitan would like you to reconsider how you use that nasal cannula. He writes:
“A simple modification in practice can protect your patients from hypoxia during emergency intubation. Imagine intubating all of your patients without the high anxiety and low tones of a falling pulse oximeter reading. During preoxygenation, applying nasal oxygen in addition to a non-rebreather face mask can significantly boost the effective inspired oxygen. After apnea created by RSI the same high flow nasal cannula will help maintain, or even increase, oxygen saturation during efforts securing the tube (oral intubation). The use of nasal oxygen during pre-oxygenation and continued during apnea can prevent hypoxia before and during intubation, even in extreme clinical cases.”
In a nutshell, he wants you to put a nasal cannula (and insert an NPA) on your soon-to-be intubated patient and crank up the oxygen to 15 L/min. Do this during the pre-oxygenation period and leave it on while placing and securing the ET tube. If you do so, your patient will continue to maintain a high level of oxygen saturation through a process called Passive Oxygenation.
Let’s discuss how this Passive Oxygenation works…
For your breathing patient during the pre-oxygenation phase: A loose-fitting NRB mask at 15 L/min merely creates a pool of oxygen outside the patient’s airway waiting to be inspired. Unfortunately, “the measured inspired oxygen in the hypopharynx with a NRB at 15 L/min is only 60-70%. The reason for this is the patient’s expired gases are mixing with the applied oxygen, and also because expired gases accumulate in the nasopharynx…High flow nasal oxygen has been shown to flush the nasopharynx with oxygen, and then when patients inspire they inhale a higher percentage of inspired oxygen. Small changes in FiO2 (fraction of inspired oxygen) create dramatic changes in the availability of oxygen at the alveolus, and these increases result in marked expansion of the oxygen reservoir in the lungs prior to the induction of apnea.” Bottom Line: Use high flow O2 via a nasal cannula along with mask oxygen delivery during the pre-oxygenation phase.
For your apneic patient after RSI induction: High flow oxygen via a nasal cannula “diffuses oxygen down the trachea to the alveolus. It is absorbed across the alveolar capillary membrane, despite the absence of respiratory movements, even as laryngoscopy is being performed.” To explain how this happens really requires getting into the nitty-gritty of gas solubility and pressure gradients. Here’s the nut of it…oxygen is absorbed into the alveolus at a rate of 250 ml/min. Conversely, carbon dioxide is excreted at only 10 ml/min. This results in a negative pressure gradient of -240 ml/min and creates a sub-atmospheric pressure in the alveolus. This negative pressure will draw oxygen in the upper airway (supplied by the high flow nasal cannula) down the trachea and into the alveolus where it is absorbed. Voila! Passive oxygenation without any respiratory movement!
Dr Levitan claims that oxygenation can be maintained in non-breathing patients for 100 minutes through this passive oxygenation. One small drawback…carbon dioxide is not expelled sufficiently through this process. The patient’s CO2 levels will continue to rise. No worries, this is easily remedied by adjusting ventilatory rates after successful intubation.
I hope we start seeing medics and instructors begin using this technique of passive oxygenation to buy additional time when intubating patients (and mannequins!). Relax, take your time, and get the tube accurately placed. After learning more about this, I know I will be adjusting my practice. This humble ninja continues to learn from the sensei.
For additional reading, check out these links: