Emergency medicine: Manual non-invasive ventilation with PEEP valve
When a pet arrives that is obviously having labored and difficult breathing, an immediate course of treatment is to provide supplemental oxygen at high concentrations. This is best done with a tight-fitting face mask attached to a valve system and reservoir.
The Ambu(c)bag system has an exhalation valve that directs the exhaled air into the atmosphere and an inhalation valve that allows the inhalation of oxygen from a reservoir. To the end of the exhalation port a positive end-expiratory pressure (PEEP) valve can be attached (Photo 2). Using this added valve increases the amount of air left in the lungs at the end of exhalation, increasing functional residual capacity.
This requires a flow rate of oxygen at the patient's airway during inhalation calculated to be between 12 and 100 liters per minute (avg. 66 L/min). This calculation is based on the tidal volume, minute volume and inhalation time of each breath.
As can be seen, it is impossible to provide this amount of flow rate of inhaled oxygen without the use of a reservoir that can be easily emptied and which contains 100 percent oxygen. Any other systems involving a face mask, where there are no reservoir or valves to control the direction of inhaled and exhaled air, are not recommended in emergency settings in which the work of breathing must not be increased and high concentrations of oxygen are required.
During the inhalation phase of breathing, if there is no reservoir attached to this same type of bag-valve-mask system, the highest percent of oxygen that can be achieved during inhalation is 40 percent to 50 percent; the reservoir oxygen concentrations can reach 100 percent.