cardiac compressions, the cardiac output is cut to 25 to 30 percent of the normal capacity and artificial ventilation does not supply enough oxygen through the circulatory system to maintain life for a long period.

Various types of bag-valve-mask systems that come in both adult and pediatric sizes are in use in the Navy. Essentially, they consist of a self-filling ventilation bag, an oxygen reservoir, plastic face masks of various sizes, and tubing for connection to an oxygen supply.

Figure 4-12.—Placement of an oropharyngeal airway.

The bag-valve-mask system is difficult to use if the corpsman has not had a great deal of practice with it. It must not be used by inexperienced persons. The system can be hard to clean and reassemble properly, the bagging hand can tire easily, and an airtight seal at the face is hard to maintain, especially if a single rescuer must also keep the airway open. In addition, the amount of air delivered to the victim is limited to the volume that the hand can displace from the bag (approximately 1 liter per compression).

TECHNIQUE.— Hook the bag up to an oxygen supply and adjust the flow from 10 to 15 liters per minute depending on the desired concentration (15 liters per minute will deliver an oxygen concentration of 90 percent). After hyperextending the neck to open airway or inserting an oropharyngeal airway, place the mask over the face and hold it firmly in position with the index finger and thumb, while the remaining fingers keep the jaw tilted upward (fig. 4-14). The other hand is used to compress the bag once every 5 seconds. Observe the chest and abdomen for expansion. If none is observed, the face mask seal may not be airtight, the airway may be blocked, or some component of the bag-valve-mask system may be malfunctioning.