0071643192.pdf

ENVIRONMENTAL EMERGENCIES

A 50-year-old male complains of a headache, and then abruptly loses

consciousness 3 minutes after surfacing from a dive. What is the most

likely diagnosis?

This patient has likely experienced an arterial air embolism. Any diver who

develops CNS symptoms within 10 minutes of surfacing should be assumed to

have an arterial air embolism. Treatment includes administering 100% O 2 by

mask, placing victim supine, administering intravenous fluids, and rapid trans-

port for hyperbaric therapy.

DYSBARISM

Dysbarism refers to diving injuries from underwater pressure changes. It is

easiest to think of dysbarism in regard to timing of symptom onset (see

Table 13.12):

■ Descent dysbarism(“the squeeze”)

■ Dysbarism at depth:

■ Nitrogen narcosis

■ O 2 toxicity

■ Alternobaric vertigo

■ Ascent dysbarism:

■ Ascent barotrauma

■ Decompression sickness (DCS)

■ Arterial air embolism

PHYSIOLOGY OFGASES

■ Boyle’s lawstates that as the pressure (P) on a given air space increases,

the volume of gas (V) decreases (PV = constant).

■ Henry’s lawstates that the amount of a gas dissolved in a liquid is directly

proportional to the partial pressure of that gas.

■ Atmospheric pressure at sea level = 760 mmHg or 1 atm. As one descends

to 33 ft (in seawater), the atmospheric pressure ↑to 2 atm and the volume

of air-filled spaces decreases by 50%. For each gas within the space, both

the partial pressure and the amount dissolved in solution (eg, blood) will

↑accordingly.

TABLE 13.12. Types of Dysbarism

Descent Dysbarism (“the squeeze”)

Dysbarism at depth

Nitrogen narcosis

O 2 toxicity

Alternobaric vertigo

Ascent dysbarism

Ascent barotrauma

Decompression sickness

Arterial air embolism

Boyle’s law (for any given air

space):

PV = k

where P = pressure, V =

volume, k = constant;

if P increases, V must ↓).