Decompression Sickness

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A scuba diver breathes air that is 79% nitrogen and 21% O2. The greater partial pressure of nitrogen means increased nitrogen absorption in a diver at depth for an extended period of time (104). Nitrogen, an inert gas, is more soluble in fat than in blood (188). Both can become saturated with nitrogen. The duration of time, not depth, determines the degree of saturation of blood with nitrogen (104,189,195). The depth of

Fig. 21. Diving accident. Quick ascent to surface. Gastric mucosal lacerations. (Courtesy of Dr. K. Newell, Grey Bruce Health Services, Owen Sound, Ontario, Canada.)

the dive determines the total quantity of nitrogen absorbed. Repeated dives increase the risk (188). If there is rapid ascent, then gradual elimination of nitrogen by exhalation cannot keep pace (104,189). Nitrogen bubbles out of solution in the blood and fat, analogous to the bubbles that form when a soda is opened (104,188,189). Entry of nitrogen bubbles into capillaries in adipose tissue lead to venous gas embolism (104,195,196). In dives less than 10 m (33 ft), gradual decompression during ascent is not needed (104). When the depth exceeds 40 m (130 ft), decompression stops are needed. Decompression sickness can still occur with proper pauses on ascent (188,189). Flying after diving can precipitate decompression sickness (189).

Mechanical distension by nitrogen bubbles is a possible cause for pain, which typically affects dense tissue such as ligaments or tendons around joints (the "bends") (104,188,189,195). Joint symptoms usually appear within 24 h, but more severe symptoms occur within half an hour (188,195). Paresis caused by spinal cord involvement occurs when bubbles form in the epidural vein plexus around the spinal cord (104,188,189,195,202,203). A large volume (80-100 mL) of venous gas in the right heart leads to serious effects (see Chapter 7, Subheading 12.1.1. and ref. 192). Numerous bubbles in the pulmonary circulation lead to the "chokes" (104,188,189,195,208). Paradoxical gas embolism to systemic organs (brain, heart) across a patent foramen ovale can occur (188,195,208). Seizures are possible. A DIC picture may arise from decompression sickness (191,195,208). Decompression sickness can occur in combination with air embolism (188,195,208).

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