Treatment of decompression sickness

All patients with suspected decompression sickness must be referred to hyperbaric oxygen therapy as quickly as possible, since the reduction of bubble size and alleviation of tissue hypoxia is essential treatment for this condition ( Kizer..1995; libbles and!.sb.e.r.g 19.9.6). The beneficial action of hyperbaric oxygen therapy may rely more on its favorable effect on biochemical action at the blood-gas interface, which leads to endothelial damage, activation of leukocytes, and alteration of hemostasis, than on the reduction of the bubble size (libblesand Edelsberg 1996). The physiological effect of hyperbaric oxygen therapy is based on Boyle's law, which states that the volume of a gas in an enclosed space is inversely proportional to the pressure exerted on it. At a pressure of 3 atm bubble volume is reduced by 67 per cent and the dissolved oxygen content is 6 ml/dl, which is sufficient to meet resting cellular requirements. The administration of 100 per cent oxygen at sea level increases the amount of oxygen dissolved in the blood from 0.3 to 1.5 ml/dl ( Kizer.1995; I]bb!.§„S a.□.d Edelsberg 1996).

As emergency treatment, all patients suspected of having decompression sickness or arterial air embolism should receive 100 per cent oxygen and 1000 to 2000 ml of isotonic solution initially, followed by continuous infusion of isotonic solution at a flow rate which maintains urine output at 1 to 2 ml/kg/h to provide a favorable gradient for nitrogen washout and to support capillary perfusion ( Kize,L19.95). The administration of steroids is currently controversial. Acetylsalicylic acid (aspirin) up to 500 mg intravenously is sometimes recommended in severe decompression sickness because of its potentially beneficial effect on changes in homeostasis associated with the blood-gas interface (Kizer..1995). Benzodiazepines can be effective in improving vertigo-associated labyrinthine decompression sickness. The nearest center with a recompression chamber and experienced staff should be contacted. If a non-pressurized aircraft (helicopter) is used for patient transportation, the flight altitude should not exceed 300 m above sea level; it is better to use aircraft capable of maintaining sea-level cabin pressurization during flight ( Kizer.1995).

An example of a protocol for hyperbaric oxygen treatment is shown in Fig 1. Hyperbaric oxygen therapy sessions sometimes have to be repeated, depending on symptoms, and may be efficacious several days after the incident.

Fig. 1 Example of a hyperbaric oxygen therapy profile. The pressure in the hyperbaric chamber is rapidly (7.5 m/min) increased to 2.8 atm. The rate of descent between pressure steps is 0.3 m/min. To avoid oxygen toxicity, there are air-breathing breaks of 5 min and 15 min at 2.8 atm and 1.9 atm respectively. The total duration of the hyperbaric oxygen treatment depends on the severity of the decompression sickness.

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