Capsule Summary

For decades, preoxygenation for emergency medicine and critical care intubations was provided by a nonrebreather mask [1]. Despite the limitations of this device and copious literature demonstrating its inadequacies, its ease of use and ubiquity lent the device a staying power beyond its utility [2]. With the publication of the PREOXI (Pragmatic Trial Examining Oxygenation Prior to Intubation) trial [3], the evidence has reached a tipping point in which a simple nonrebreather mask is no longer acceptable for preoxygenation for intubations in critically ill patients.

PREOXI was a multicenter, pragmatic, randomized controlled trial of 1,301 patients being intubated in the emergency department (ED) or intensive care unit [3]. Patients were randomized to either noninvasive positive pressure ventilation (NIPPV) preoxygenation, using a ventilator or a NIPPV machine or standard care. The standard care group was instructed to use flush rate (>50 L/min) flow settings if they used a nonrebreather mask to try to eliminate inadequate fraction of inspired oxygen as a confounder. Hypoxemia (pulse oximetry saturation <85%) was halved in the treatment group (9.1% vs. 18.5%). Secondary outcomes such as peri-intubation arrest and severe desaturation were also significantly lower in the treatment group. It was posited that NIPPV preoxygenation could lead to aspiration, however, there was no statistically significant difference in aspiration between the two groups. Essentially, the PREOXI trial tested a bundle of therapies: high fraction of inspired oxygen (FiO₂) preoxygenation, positive end expiratory pressure (PEEP) preoxygenation, apneic ventilations, and apneic PEEP.

It is difficult to separate out if any individual intervention drove the benefits seen in the trial, so any clinical application of the trial results must include all of these interventions. In the study, a ventilator or NIPPV machine needed to be brought to the bedside prior to the intubation. In addition, a clinician or technician familiar with the machine must be available to set up the machine for the PREOXI-appropriate settings. Further, a properly sized NIPPV mask must be available. While these necessities are almost universally present in intensive care units, many EDs may struggle to have machines and skilled personnel at the bedside with the alacrity necessary to allow preoxygenation before a critically ill patient intubation.

A method that accomplished all aspects of the PREOXI bundle without requiring machinery or respiratory therapy is easily available in the ED or in the prehospital environment. First the patient should be placed on a standard nasal cannula (NC) at 10 to 15 L/min oxygen. Then a bag valve mask (BVM) should be hooked up to oxygen at the highest flow rate the regulator can provide. In the United States and Canada, this flush rate will be >50 L/min. In other countries, this may be limited to 20 L/min. A PEEP valve should then be added to the BVM’s exhalation port and set to 5 cmH2O as a starting point. The BVM can then be used during the preoxygenation period without squeezing the bag. A tight seal must be maintained throughout preoxygenation and the apneic period or the apparatus cannot maintain PEEP. All necessary equipment is shown in Fig. 1.

In this setup, the NC serves two purposes. First, it augments the flow rate of the BVM when the maximum flush rate is 20 L/min; many patients who are hyperpneic may exceed this minute ventilation and start entraining room air without the NC augmentation. Second, the NC serves as a continuous source of pressure during apneic PEEP provision. Without this continuous pressure, any small leak at the patient-mask interface will cause a loss of PEEP. This converts this setup from a low-flow PEEP system to a high-flow PEEP system. The PEEP valve also serves dual roles. The first one is obviously that it forces exhalation to be against a diaphragm backed with the clinician set pressure allowing continuous positive airway pressure (CPAP) or PEEP. It also converts a BVM without a one-way valve on its exhalation port from a device that allows spontaneously breathing patients to breathe room air to one in which gas can only flow out of, not into the exhalation port. Unfortunately, many currently available BVMs lack this one-way valve and therefore without a PEEP valve, they are only suitable for positive pressure breaths, not spontaneous ventilations.

Numerous options exist for the patient-mask interface with this setup. Ideally, the ED or ambulance will stock NIPPV masks in the appropriate size for the patient. If this device is used, the BVM will hook directly to the NIPPV mask. It is essential that the masks stocked do not have an integrated exhalation port. The same masks that would be appropriate to use with a mechanical ventilator are the ones needed to use this BVM method. Lacking NIPPV masks, the next best option is the use of reusable or disposable anesthesia mask straps and prongs. These items allow a standard BVM mask to be secured to the patient without having to have a clinician continue to maintain a mask seal. Lastly, lacking any additional items, a two-hand mask seal can be maintained by a clinician during preoxygenation and the apneic period.

During the preoxygenation period, the NC/BVM/PEEP valve apparatus is placed on the patient for at least 3 minutes to allow denitrogenation. The PEEP setting can be adjusted to optimize pre-intubation oxygen saturations and allow for alveolar recruitment. After intubation medications are administered, slow, gentle respirations should be provided during the apneic period at a rate of 6 to 10 breaths per minute. When ready to insert the laryngoscope, the mask is removed, but the NC is left in place. This allows apneic oxygenation to be provided during laryngoscopy. Apneic oxygenation has been shown to be effective to prevent hypoxemia during prolonged apneic periods in the operating room, but results have been mixed during critical care intubations. We posit that discrepancy is explained by shunting from derecruited alveoli leading to an attenuation of apneic oxygenation’s benefits. However, with CPAP and PEEP augmentation during the preoxygenation and apneic period, we believe that apneic oxygenation may be markedly more effective.

Standard ED preoxygenation with a nonrebreather mask is no longer acceptable in critically ill patients given the current state of the literature. Using a mechanical ventilator or NIPPV machine has demonstrated proven benefits. However, this may be logistically difficult in many ED and emergency medical services environments. We provide an easy and readily available alternative that allows the same benefits without the need for additional bedside equipment or specially trained personnel.

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