Administering emergency oxygen is the proper first response for many pulmonary injuries; it is also essential treatment for divers with decompression illness (DCI). Its prompt administration can alleviate a diver’s symptoms and reduce the damage caused by DCI. Additionally, areas of the body with compromised blood flow may receive enough oxygen to minimize or prevent the tissue damage that results from oxygen deprivation.
By Reilly Fogarty
Understanding Partial Pressure
Students in Emergency Oxygen Provider courses frequently ask questions about partial pressure of oxygen. Those who have undergone nitrox courses may have particular questions based on that training. Understanding the concept of partial pressure is essential for the safe use of oxygen while diving and for proper oxygen administration in an emergency.
To calculate the partial pressure of a gas in a gas mix, take the percentage of that gas in the mix and multiply it by the ambient pressure. At sea level the ambient pressure is 1 atmosphere absolute, or 1 ATA. Air contains 21 percent oxygen. Multiplying 1 ATA by 21 percent gives you 0.21: the partial pressure of oxygen (PO2) in air at sea level. Using this same calculation you can determine that the PO2 of 100 percent oxygen is 1.0.
At a depth of 66 feet of salt water (3 ATA), the PO2 of air is 0.63 (21 percent oxygen x 3 ATA), but the PO2 of 100 percent oxygen is 3.0. A PO2 that is too high or too low can be dangerous for humans to breathe; a PO2 below 0.16 puts divers at risk for loss of consciousness due to hypoxia and a PO2 greater than 1.6 puts divers at risk of oxygen toxicity, which can result in convulsions and drowning. A partial pressure of oxygen of 1.0, like that found in 100 percent oxygen at sea level, is safe to breathe and can aid an injured diver by enhancing oxygenation of tissues and promoting offgassing of inert gas in tissue.
Administration of emergency oxygen can involve a range of equipment, including demand valves, nonrebreather masks (NRBs), bag-valve masks, manually triggered ventilators and nasal cannulas. The two most commonly used oxygen delivery devices in diving are the demand valve and the nonrebreather mask.
A demand valve used for oxygen administration is the same type of valve found in a second-stage scuba regulator; this device delivers gas only when the user inhales. With a well-sealed mask, a demand valve can deliver about 95 percent oxygen, but it is designed only for conscious and alert people whose respirations are strong enough to engage the valve and prompt the flow of oxygen.
Nonrebreather masks are designed for injured or distressed divers who do not have the stamina to draw oxygen from a demand valve. These masks provide a constant flow of oxygen and have a reservoir bag attached to capture any oxygen that is not immediately inhaled. The flow rate is manually adjustable and typically set between 10 and 15 liters per minute. A high flow rate does not necessarily equate to more effective treatment, and to avoid wasting oxygen you should set the flow rate just high enough to prevent the reservoir bag from fully collapsing when the patient inhales. Take care to ensure that the mask maintains a good seal for as long as you are using it.
Use What You Have
The primary goal of oxygen administration to an injured diver is to promote the elimination of inert gas. To accomplish this a partial pressure gradient must be established; this is achieved by delivering the highest concentration of oxygen available, ideally pure oxygen, until the supply runs out or more advanced medical care becomes available. Many Emergency Oxygen Provider course students ask if they should reduce flow rate to extend a limited supply of oxygen; this is reasonable but reduces the (PO2) gradient and thus the efficacy of the care. Whether you have access to pure oxygen or just a cylinder of nitrox provide the injured diver with the greatest concentration of oxygen available until your supply runs out.
For more information on emergency oxygen or first aid training, visit DAN.org.