There are times when a patient cannot maintain an adequate oxygen or carbon dioxide level, and they need a mechanical ventilator. The procedure to place a patient on invasive mechanical ventilation is intubation, which means placing a plastic tube into the trachea of a patient through the mouth and throat. The ventilator, then, is connected to the patient's lungs through that tube.
The period before and immediately after this procedure can potentially be fraught with the danger of low oxygen levels. To help mitigate this risk, we "preoxygenate" the patient, which means placing the patient on high amounts of oxygen to fill the lungs with as much oxygen as possible to protect the patient from hypoxia. We usually do this through a loose-fitting mask with oxygen flowing through it. The potential problem with this is that, depending on how much the patient is breathing, the amount of oxygen delivered to the lungs can get "diluted" by room air being entrained through gaps in the mask.
So, some preoxygenate using noninvasive ventilation, in which oxygen is delivered through a tight-fitting mask connected to a CPAP or BiPAP machine. The potential problem with this method is that the positive pressure delivered by the noninvasive ventilator can put a lot of air in the stomach, placing the patient at risk for vomiting and aspiration into the lungs.
This begs the question: is one method better than the other? Enter this study published in the New England Journal of Medicine.
This was a randomized trial in multiple hospital ICUs and emergency departments in the United States, and 1301 patients were randomized to receive either noninvasive ventilation or simple mask oxygen for preoxygenation prior to intubation. They left the exact method of each use up to the individual clinician, and they defined hypoxia after intubation as an oxygen saturation of 85% or less from the time of induction of anesthesia through two minutes after intubation.
They found that the group that received noninvasive ventilation had less hypoxia: 9.1% for the noninvasive ventilation group vs 18.5% in the oxygen mask group. In addition, they did not find an increasing in aspiration associated with noninvasive ventilation (0.9% vs 1.4%).
Now, it is important to point out that the study excluded those patients who were already on noninvasive ventilation prior to intubation. So, we can't comment on the efficacy of noninvasive ventilation for preoxygenation in those patients.
Still, for me, this was a practice changing study. Normally, I will preoxygenate by bagging with a valve mask. As much as feasible, I will try to preoxygenate with noninvasive ventilation in the future, or if they are already on noninvasive ventilation.
