• Shock

• Tissue hypoxia

• Hypoxemia (low blood oxygen)

• Pulmonary gas exchange impairment as a result of trauma, edema, asthma, infection, embolism

• Acute myocardial infarction, cerebrovascular accident

• Decompression illness, including both decompression sickness and arterial gas embolism

• Acute mountain sickness

• High-altitude pulmonary edema

• High-altitude cerebral edema

• Carbon monoxide poisoning

• Respiratory or cardiopulmonary arrest

Pulmonary Oxygen Toxicity

In situations where high concentrations of supplemental O₂ will be administered for many hours, there exists a concern for possible pulmonary O₂ toxicity, particularly if a diver with decompression illness subsequently requires hyperbaric oxygen therapy. Pulmonary O₂ toxicity becomes a risk only after many (10 to 18) hours and high O₂ concentrations (FIO₂ of 0.5 to 1). The rate of onset of symptoms may be reduced by the use of periodic “air breaks,” during which the patient breathes air for 5 to 10 minutes.

Prolonged exposure to high concentration of O₂ is also associated with the following:

Central Nervous System Oxygen Toxicity

Central nervous system O₂ toxicity is of concern when a person is exposed to O₂ at ambient pressures greater than 1 atm (sea level) and where FIO₂ exceeds 1, such as while scuba diving or in a hyperbaric O₂ chamber. It is not of concern to persons at normobaric or hypobaric ambient pressure. Signs and symptoms may appear at FIO₂ of greater than 1.6 and include (but are not limited to) the following:

During hyperbaric O₂ therapy, the likelihood of central nervous system O₂ toxicity is reduced by the use of periodic air breaks.

Cylinders

Medical O₂ cylinders or tanks are made of aluminum or steel and come in a variety of sizes (Table 11-1). In the United States, any pressure vessel that is transported on public roads is subject to U.S. Department of Transportation (DOT) regulations. The DOT requires that cylinders be visually and hydrostatically tested every 5 years and either be destroyed if they fail or be stamped and labeled appropriately if they pass. Gas suppliers will not fill cylinders that have not been appropriately tested and stamped. The working pressure of steel medical O₂ cylinders is 2015 psi (13,893 kPa). The working pressure of aluminum O₂ cylinders is either 2015 psi or 2216 psi (13,893 kPa or 15,279 kPa), depending on the type. High-pressure, lightweight cylinders used for high-altitude climbing are not discussed here.

Valves

Valves for medical O₂ cylinders sold in the United States are designed to accept only medical O₂ regulators to avoid the possibility of using a medical O₂ regulator with an incompatible gas such as acetylene. The two types of valves available in the United States are the CGA-870 and the CGA-540. The CGA-870 is also known as the pin-index valve and is used on smaller portable cylinders (e.g., D, E). The CGA-540 is used primarily on larger, nonportable cylinders, such as those mounted in ambulances (e.g., H, M). A number of other valve types are manufactured and used with medical O₂ throughout the world. For example, there are adapters available to make a U.S. pin-index regulator fit on an Australian bull-nose valve, but it must be noted that the use of adapters is discouraged by the U.S. Compressed Gas Association (CGA).

Regulators

The device that mounts directly to the cylinder is the regulator. Its function is to regulate the flow rate of the O₂ by reducing the pressure of the O₂ from either 2015 psi or 2216 psi (13,893 kPa or 15,279 kPa) to a usable flow rate. Regulators are primarily of three types: constant flow only; demand/flow-restricted oxygen-powered ventilator (FROPV) only; or multifunction, which has both constant flow and demand/FROPV capability. The regulator mounts to the cylinder with a matching-type valve. A pressure gauge allows the user to monitor the amount of O₂ in the cylinder.

Devices for Ventilation of Nonbreathing Patients

All of the following devices keep direct patient contact at a minimum to reduce the risk for disease transmission. Other body substance isolation equipment (e.g., gloves, goggles) and practices should be observed as well. In addition, when used on a nonintubated patient, all of the devices discussed depend on adequate mask seal to be able to deliver adequate ventilations and ensure adequate respiration. The single most common cause of inadequate ventilation and oxygenation is poor mask seal.