>If the regulator mouthpiece is not still in the diver’s mouth, trying to replace it in an unconscious diver can be difficult and time consuming. Without a good seal any attempts to ventilate will be unsuccessful. If the mouthpiece is successfully placed in the diver’s mouth there is a risk of it having pushed the relaxed tongue to the back of the throat which can inadvertently block the airway.
>Assuming that the regulator mouthpiece had remained or was placed in the diver’s mouth without blocking the airway, the next task is to depress the purge button. Purge buttons do not have any true regulatory capability. They deliver breathing gas from the cylinder at whatever the intermediate pressure is from the first stage. There is therefore a risk of delivering breaths at too high a pressure, which can cause several problems. If the diver’s airway is not maintained in an open position the breathing gas delivered by the purge button can be forced into the stomach, causing gastric distention. This places the diver at risk for regurgitation, which can further compromise the airway and lead to aspiration. Even if the breathing gas is delivered to the lungs it can over-inflate the lungs.
>Trying to depress a purge valve in a completely controlled manner is very difficult especially with gloves on and in an emergent situation. In order to ventilate a patient, while pushing the button the nostrils will simultaneously have to be pinched. Inadequate ventilation is quite likely.
>Delivering rescue breaths using a pocket mask or similar method provides tactile feedback via changes in pressure required to ventilate the lungs. Supplying rescue breaths with the purge valve eliminate this important feedback. Using a scuba purge valve also means that only breathing gases can be administered (usually air). Too much resistance will cause the breathing gas to be forced out the exhalation valve(s).
>Rescue methods that are currently taught by multiple agencies are the result of years of practical experience. Purge valves were never designed to function as rescue equipment. When ventilating a diver it is best to rely on standard recommended methods.