Dive accident positioning

Question:
Dive accident positioning - Which end is up?

Answer:
by R. Moon, MD, R. Dunford and C. Wachholz, RN

DAN has in the past advocated a left side, head down, body elevated position for field treatment of diving accidents, particularly where arterial gas embolism (AGE) is suspected. Traditional teaching has suggested that a head-down position is one of the measures to be used in the emergency treatment of arterial gas embolism. The hypothesized benefit of this treatment has included:

A) Minimization of the effects of embolization of residual left ventricular gas. Experimental animal data suggests that head-down position will minimize the possibility of subsequent cerebral gas embolism. In the event of residual gas in the left ventricle, head-down position would probably be of benefit in decreasing the risk of embolization to the cerebral circulation.

B) Elevation of arterial and venous pressure due to head-down position may compress intravascular bubbles in the cerebral circulation.

C) Vascular dilation resulting from the head-down position may allow distal progression of intracerebral bubbles and possibly also washout of bubbles into the venous circulation.

The disadvantages of the head-down position include:

1) The practical difficulty of setting up and maintaining a patient in this position, particularly in less than optimal circumstances (e.g. on a dive boat).

2) Difficulty in maintaining the airway.

3) Discomfort of this position in the event that the patient is awake.

4) Cerebral edema resulting from increased arterial and venous pressures.

5) The theoretical argument that in the event of cerebral arterial gas embolism due to transatrial passage of venous gas emboli through a patent foramen ovale, the right-to-left shunt may be increased by head-down position, resulting in further embolization.

Presently an animal investigation is being conducted at the Naval Medical Research Institute. Results are not available at this time. Firm animal data supports rationales (A) and (B). No definitive human data exists, although anecdotal experience supports the use of head-down position in some cases, with clinical improvement occurring in concert with the placement of the patient in the head-down position. Nevertheless, the disadvantages often outweigh the theoretical advantages of using this position. The theoretical argument proposed in disadvantage (5) may be intuitively correct, yet DAN is unaware of any definitive information on the effect of head-down position on flow through a patent foramen ovale. Moreover, severe impairment of consciousness occurring within minutes after surfacing from a dive in a sport diver is unlikely to be due to decompression sickness, but is more likely caused by massive cerebral arterial gas embolism from pulmonary barotrauma.

Recent discussions concerning the efficacy of using the head down position have prompted us to seek the opinions of other dive medicine colleagues:

"Arterial gas embolism is usually characterized by seizure activity, impairment of consciousness, or confusion occurring within minutes of surfacing, often after a rapid ascent from depths > 4-5 FSW. Emergency treatment of patients with AGE includes:*

a. Maintenance of airway breathing and circulation;

b. Placement of the patient in a left or right side down position in order to minimize the possibility of aspiration in the event of regurgitation.

c. Rapid evacuation to an appropriate medical facility.

d. Administration of 100% oxygen.

This last point in particular, we feel, has been lost in the rhetoric concerning positioning and needs greater emphasis in teaching dive first aid.

These measures form the basis for the emergency treatment of AGE. Head-down position is of uncertain benefit at the present time. It should only be used in a patient with impaired consciousness if the first two measures have been instituted. The patient should not be left in the head-down position for longer than twenty minutes. Placement of the patient in the head-down position should not interfere with rapid evacuation.

Head-down position has no therapeutic role in the emergency treatment of decompression sickness. If the patient is awake and alert, or if the symptoms are delayed more than ten minutes after surfacing from the dive, or if there is any difficulty in maintaining a clear airway (i.e. the patient is not breathing or breathing poorly), then the head down position should not be used.

We intend to make these changes in the next printing of the DAN manual. However, we see no reason to immediately change any existing literature as it is unlikely any harm can result from a head-down position -- so long as first aid responders make airway, breathing, and circulation paramount over all other concerns.

*Editors Note: The main points to emphasize here are: the diver should be stabilized; given 100% oxygen; and then transported to the nearest emergency room. The DAN emergency number, (919) 684-8111 in the USA, +41.1.1414 in Europe, should be called when the diver arrives at the hospital.

Final Summary of Recommendations:
Diving Accident Workshop, October, 1990

•Head-down position. There was no clear cut consensus on the value of head-down position. Anecdotal reports suggest that symptoms of arterial gas embolism can sometimes improve when the patient is placed in steep Trendelenburg position. Animal experimentation supporting the traditional recommendation of head-down position has been done by Atkinson (2) with embolized (open skull) cats, showing disappearance of the bubbles in the direction of arterial flow when the animals were placed in steep Trendelenburg position. However, more recent animal work (e.g. presented by Dr. Dutka at this workshop) suggests that prolonged head-down position may be detrimental, because of extravasation of additional fluid into the brain due to the higher intravascular pressures.

The possibility that head-down position may prevent cerebral AGE in the vent of on-going embolization from the lungs or trapped gas in the pulmonary vessels or heart is negated by some studies showing only a minor effect of buoyancy in determining where gas bubbles are distributed (3). Nevertheless Dr. Gorman anecdotally reported a small percentage of patients who abruptly worsened after arterial gas embolism when they were allowed to sit upright.

While a brief (less than 10 minutes) head-down position might conceivably facilitate the clearance of bubbles from the cerebral circulation after AGE, it seems prudent thereafter to keep the patient in the supine position rather than in prolonged head-down position or head-up. Head-down position has no role in the treatment of DCS. Unconscious patients should be kept in the lateral decubitus position to minimize the risk of aspiration of vomitus.