TOP: CXR of a morbidly obese woman with CHF, pulmonary fibrosis, and pneumonia, in whom PEEP was needed before intubation, during onset of drugs, and after intubation to prevent desaturation. This case triggered me to change practice and put PEEP valves on all the BVMs in our department.
BVM + PEEP Valve + Nasal Cannula = Continuous Flow & PEEP
Not too long ago, severe hypoxia in the ED was treated with a 15 lpm non-re-breather, bag mask ventilation, and preparing for intubation. CPAP systems have changed the rules and we often now use CPAP to avert intubation or to maximize pre-oxygenation prior to airway management. CPAP prior to intubation (with the use of pharmacologic assistance for sedation) was termed Delayed Sequence Intubation (DSI) several years ago by Dr. Scott Weingart. The whole point of this approach is to maximize pre-oxygenation and prolong safe apnea prior to intubation attempts. DSI requires either a CPAP system (in the patient who can initiate their own breaths) or a ventilator (in the patient who needs assistance).
CPAP machines are pretty straightforward and EPs can and should do better knowing the nuts and bolts of operating these devices and ventilators. I have learned first hand the value of this knowledge working in critical care access hospitals where respiratory therapy was not in house.
Over the last several years, however, I have arrived at a completely different view of oxygenation. I now realize we have techniques immediately available which further change the rules, buy us tremendous amounts of time, and protect our patients. To best explain this, it is important to review two fundamental requirements of oxygen absorption in the lungs. O2 absorption requires open alveoli into which oxygen is present, along with an oxygen gradient for diffusion across the alveolar membrane. Oxygen is not very soluble in blood; one oxygen molecule binds to hemoglobin, changing the protein structure, and allowing binding at all four sites on the hemoglobin molecule. The see-saw nature of oxygenation and desaturation is in part due to the all-or-none phenomenon of how oxygen binds, along with the shape of the oxyhemoglobin desaturation curve; it plateaus above 94-95% but it is very steep south of 94%. When our patients desaturate they do not do so incrementally – its precipitous after the low nineties (i.e. 94%, 93%, 92%, 84%, 70%). Many times in my career I have heard the uncomfortable tones of beep beeop, boop, booouuup, and “Doctor the pulse ox is falling!”
To maximize our patient’s oxygen absorption we need to think about open alveoli and oxygen gradients. Alveolar patency is about positioning. As humans we are meant to breathe upright; when patients lie flat the lower dependent portions of the lungs collapse. Half the alveolar space is then unavailable and the patient has a physiologic right-to-left shunt. Secondly, when there is fluid in the alveoli (whether its pulmonary edema, blood, or aspirated stomach contents) we need to make sure the alveoli are as open as possible. Here’s where CPAP is critically important. Without CPAP the alveoli do not open and positive pressure is only present during a fraction of the ventilatory cycle. There is simply no available space on the alveolar membrane where oxygen can diffuse across and into the capillary.
ABOVE: Non-rebreather mask with and without underlying nasal cannula. I run the non-rebreather at maximum. In other words I turn up oxygen until ball is bouncing at top end of the flow meter (>15 lpm). In the wide awake patient I would start with 4-6 liters via nasal cannula. When the patient has been induced I increase to 15 lpm via nasal cannula during intubation (NO DESAT).
The miracle of the nose is that it is a passively patent route to get oxygen to the pharynx. By sitting the patient upright and applying a jaw thrust (so the tongue does not obstruct the hypopharynx), we can easily flow oxygen via the nose into the hypopharynx. High flow rates (15 lpm) also blow open the soft palate, separating it from the posterior pharyngeal wall. I call this technique OOPS – Oxygen On, Pull the mandible forward, and Sit the patient up. Combining nasal and face mask oxygen tremendously boosts the FiO2. This happens because the nasal oxygen addition doubles flow rates (15 lpm via nose and 15 lpm via non-rebreather), it forces open the soft palate, and the nose is a significant oxygen reservoir. When the patient takes their next breath, they inspire a higher FiO2 than with a face mask alone. While we are taught a non-rebreather at 15 lpm is almost 100% FiO2, it is actually closer to only 60% due to the accumulation and rebreathing of CO2 in the mask, hypopharynx, and nasopharynx. With nasal cannula and non-rebreather mask combined we can effectively reach almost 100% FiO2.
As an example of this technique, I recently had an obese, severe heart failure patient who my nurse immediately placed on a non-rebreather. Despite 15 lpm (tachypneic and hyperpneic) the patient could not get above 80%. Ashen grey, sweating bullets, he kept removing the NRB due to subjective dyspnea. By adding nasal cannula at high flow (15 lpm) the patient immediately felt and looked better, and the pulse ox came up to 92%. The nasal cannula bought time, allowing me time to get the CPAP set-up, and start delivering nitroglycerin and Lasix. I kept the nasal cannula (6 lpm) while I initiated CPAP. He was diuresed and comfortable within a few hours on nasal cannula only. We averted intubation in a patient who previously might have had a rough course, wrestling with CPAP vs. intubation, etc...
I have also seen numerous instances when excessive sedation led to precipitous desaturation – quickly rectified by my combination of nasal cannula and a non-rebreather together – until the patient resumed ventilation a few minutes later. Another beautiful thing about this approach is that you avert positive pressure ventilation. Furthermore, having the patient upright as much as possible helps prevent passive regurgitation.
ABOVE: PEEP and continuous oxygen flow without the complexity of running a ventilator. Combine a nasal cannula, a BVM, and a PEEP valve (that attaches to the BVM).
BELOW: BVM with and without underlying nasal cannula and PEEP valve on BVM. Add an assistant to distract the mandible forward and help create patency. The person squeezing the bag should be able to do so with one hand (only about half a bag – 6 to 7 cc/kg is only 490 cc on a 70 kg person). The face mask should be held firmly against the nasal bridge, but the person distracting the mandible forward can help seal the mask on the lower face (without pushing mandible backward).
Attach a PEEP valve to your BVM
Combining nasal cannula with a bag valve mask can create an effective CPAP or assisted ventilation PEEP system without a machine. All we need is an inexpensive PEEP valve attached to our BVM, which costs less than $10. Through a standard BVM the patient gets no oxygen unless the bag is being squeezed. By using a nasal cannula under the face mask, oxygen flows continuously to the patient. We still need a way to provide continuous opening of the alveoli, however. The PEEP valve does this by maintaining a slightly positive end expiratory pressure through the ventilation cycle. This combination of nasal cannula and a PEEP valve on our BVM does what otherwise would require an RT and a ventilator – but it is immediately available in any bed throughout your ED.
I recommend you place a PEEP valve (set the dial at 5 of PEEP) on every bag mask unit in your ED. It is then immediately available when you need it. For situations where auto-PEEP is common (i.e. severe asthma, COPD) a PEEP of 5 itself is not a problem, but make sure to keep your vent rate slow and your tidal volumes low, and follow peak pressures to avoid hemodynamic compromise. In these situations, I start at only 6 breaths per minute and no more than 500 cc tidal volume.
Nasal cannula (before and during intubation, NO DESAT), the OOPS technique, and PEEP valves on your bag mask units will save lives, prevent hypoxic brain injury, and extend your career (by reducing YOUR stress).
Richard Levitan, MD, works at several hospitals in rural New Hampshire, has academic affiliations at the University of Maryland and Dartmouth Medical School, and runs the world’s largest fresh-tissue cadaver airway course every month in Baltimore. More at CEME.org
Assistance with photographs:
Samantha Perkins, RN
Jennifer Oakley, RN
Bill Collier, RN.