By Patty Seery
When a dive accident occurs, prompt action can greatly improve the outcome — if the rescuers respond appropriately. Oxygen administration is a critical element of first aid for dive accidents, but there are several ways to do it. Oxygen units include various delivery systems, including tight-sealing oronasal masks for use with a demand valve or for resuscitation, non-rebreather masks and, possibly, a bag- valve-mask resuscitator, so divers should know the appropriate mask to use in each situation.
Oronasal (resuscitation) Masks
The demand valve with tight-sealing oronasal mask (often referred to as a pocket-style or resuscitation mask) is the most versatile and effective delivery device in most circumstances. When used properly, it can deliver a high percentage of oxygen to breathing, responsive, injured divers. In addition, they can be used to provide oxygen-supplemented ventilations to unresponsive injured divers who are not breathing on their own. This mask can also be used with manually triggered ventilators, which are used to deliver 100% oxygen to divers who are not breathing on their own.
The resuscitation masks have air-cushioned edges that adapt to a variety of face shapes and elastic straps to facilitate a good seal. They also feature oxygen inlets for administering supplemental oxygen when using the mask to provide ventilations to a nonbreathing diver. These masks are reusable, provided they are cleaned, and their one-way valves are replaced.
When using a resuscitation mask, rescuers should ensure a good seal by using the elastic strap and proper hand positioning. When the injured diver is breathing and responsive, the diver can help with maintaining the mask seal. Rescuers using the mask for CPR or to support inadequate breathing should use two hands to create an effective seal around the entire perimeter of the mask, while, at the same time, tilting the head back and supporting the jaw.
Non-rebreather masks are a first-aid option for distressed injured divers who are unable to activate demand valves effectively. These single-use, disposable masks feature an attached reservoir bag that captures the flow of oxygen to the mask to ensure a ready supply. These masks do not conform to faces as effectively as oronasal masks, however, so some oxygen escapes, and some ambient air enters the mask via perimeter gaps. As a result, injured divers using non-rebreather masks receive a lower percentage of oxygen compared with resuscitation masks.
When using a non-rebreather mask, it is important to tighten the mask’s elastic strap and adjust the nosepiece, but there is not much more rescuers can do to improve the mask’s efficiency.
Non-rebreather masks use a continuous flow of oxygen, which exhausts the oxygen supply more quickly than with other means of oxygen delivery.
Bag Valve Masks
Bag valve masks (BVMs), which are used only on divers who are unable to breathe adequately on their own, are devices that enable rescuers to provide ventilations — with or without supplemental oxygen. They may be disposable or re-usable. Using a BVM is less fatiguing for rescuers than delivering rescue breaths through oronasal masks. These masks come with flexible tubing that connects to continuous-flow outlets of oxygen units. They also have reservoir bags that collect oxygen and are capable of providing high concentrations to injured divers.
Oxygen delivery using a BVM requires two rescuers: One rescuer maintains the mask seal and the injured diver’s open airway, while the other squeezes the bulb to deliver ventilations. The other primary disadvantage of BVMs is that, like non-rebreather masks, they deplete oxygen supplies relatively quickly.
Regardless of the mask used, a rescuer’s technique affects the concentration of oxygen delivered to the injured diver. To optimise oxygen delivery, be sure to seal the mask to avoid leaks, and continually monitor both the seal and the injured diver. Do not depend on the injured diver to keep the mask secure; their comfort, changes in their level of consciousness and fatigue can compromise mask seal.
|Delivery Device||Flow Rate: litres per minute (lpm)||Inspired Percentage*|
|Resuscitation (Oronasal) Mask||10 – 15 lpm||≤ 0.45-0.65 (45%-55%)*|
|Non-rebreather mask||10 – 15 lpm||≤ 0.8 (80%)**|
|Bag valve mask||15 lpm||≤ 0.9-0.95 (90%-95%)|
|Demand Valve||N/A||≤ 0.9-0.95 (90%-95%)|
*May vary with respiratory rate
**Less variation with changes in respiratory rate
+ Delivery percentages vary with equipment and techniques used. This table summarises various oxygen-delivery systems and potential values of inspired oxygen with their use.
Part of being a responsible diver is understanding that different oxygen masks exist, serve a different function, and offer a different level of effectiveness in terms of oxygen delivery. Should you ever require oxygen you will be able to ask that a flowrate be set to the most effective level. Knowing, having, and using the correct mask and correct flowrate is very important in the first aid management of DCI.