Emergency airways commonly involve challenges of tube placement and oxygenation before and during the procedure. There are a handful of instances, however, when the issue is ventilation and, more specifically, extremes of minute ventilation. Minute ventilation is the amount of air the patient moves in one minute; it is a product of the ventilatory rate and tidal volume (minus dead-space ventilation).
Normal minute ventilation is between 5 and 8 L per minute (Lpm). Tidal volumes of 500 to 600 mL at 12–14 breaths per minute yield minute ventilations between 6.0 and 8.4 L, for example. Minute ventilation can double with light exercise, and it can exceed 40 Lpm with heavy exercise. As defined by the alveolar gas equation, increasing ventilation rate is our body’s only innate mechanism to acutely increase oxygenation. Breathing faster and deeper, we increase the alveolar oxygen tension by decreasing the partial pressure of CO2. Therapeutically, the main method of boosting oxygenation is increasing the inspired oxygen concentration (FiO2). An additional method is to increase the barometric pressure (ie, in a hyperbaric chamber or by rapidly descending from high altitude). Adding positive end-expiratory pressure (PEEP) maintains a pressure in the alveolus throughout the ventilation cycle (and stents open the alveolus, thereby providing more surface area for oxygen absorption).