17. The Bends

Question 1

You are an anaesthetist in a seaside town and are asked to assess a
22-year-old man who has been scuba diving and brought into the
accident department unconscious.

How would you manage this patient initially?

Answer 1

The initial management would be generalised as the diagnosis is not known at
this stage.

Any history of preceding events may direct further therapy at the most likely diagnosis:

Airway
Attention should be given to the possibility of a head or neck
injury and the C-spine immobilised.

Breathing
Highest FiO2 available.

Circulation
Large bore cannulae and fluids.

Question 2

Can you list some differential diagnoses?

Answer 2

Decompression sickness

Near-drowning

Head injury

Convulsion – oxygen-induced

Hypoxia

Hypothermia

Coincidental pathology,
e.g. intracranial haemorrhage,
cerebral infarction,
epilepsy,
cardiac event,
intoxication, overdose

Question 3

What is decompression sickness?

Answer 3

Decompression ‘illness’ may be described in terms of two syndromes:

1. Decompression sickness
2. Pulmonary barotrauma and arterial gas embolism

Question 4

Decompression sickness

Answer 4

During a dive, the increased ambient pressure causes
nitrogen to dissolve into tissues.

On ascent, the decrease in pressure causes
the nitrogen that has been dissolved in the
body tissues to come out of solution.

If ascent is too rapid,
then the partial pressure of nitrogen in the tissues
will rise above tissue hydrostatic pressure
and gas bubbles form.

Symptoms range from pains in the tissues around joints
(the classical ‘Bends’) to neurological impairment such as
visual disturbances, convulsions, paraparesis and loss of consciousness.

Nitrogen bubbles may also migrate from tissues into the venous system to
cause venous gas embolism.

This is usually asymptomatic.
However, high levels of
venous gas embolism in the pulmonary circulation can cause
pulmonary hypertension,
pulmonary oedema,
retrosternal discomfort,
cough and
dyspnoea (‘the chokes’).

Question 5

Pulmonary barotrauma and arterial gas embolism

Answer 5

Pulmonary barotrauma results from a diver holding his breath during ascent.

This may cause pneumothorax, pneumomediastinum or arterial gas embolism.

Arterial bubbles occlude vessels after which platelets and fibrin may be
deposited at the bubble–blood interface.

There may also be bubble– endothelium interactions culminating
in a delayed reduction in blood flow and capillary leak.

Note that pulmonary barotrauma and arterial gas embolism may occur
after a breath-hold dive of only 1 metre, ]

whereas decompression sickness requires a significant depth-time exposure.

Question 6

How is it treated?

Answer 6

1. ABC + FLuids
2. Oxygen
3. Recompression
4. Position
5. Avoid hyperglycaemia
6. Avoid hyperthermia

Question 7

ABC:

Answer 7

Fluids Immersion diuresis and bubble-induced endothelial
damage may result in severe dehydration.

Aggressive fluid administration may also improve the rate
of nitrogen washout.

Use isotonic fluids without glucose.

Question 8

Oxygen

Answer 8

Improves delivery to underperfused tissues but also reduces

the partial pressure of nitrogen in the blood and hence in the tissues
surrounding the bubble.

The increase in tissue–bubble partial pressure gradient
facilitates diffusion of nitrogen from the

bubble back into the tissues,

thus shrinking it and reducing symptoms

Question 9

Recompression

Answer 9

The idea is to force gas back into solution initially and
then allow excretion at a more controlled rate.

A commonly used treatment table is that used by the US
Navy.

It consists of recompression at 25 ft/min to a depth of 60 ft (2.8 atm)

followed by hyperbaric oxygen therapy at two depths −
60 ft and 30 ft.

The rate of ascent is typically 1 ft/min
and the length of treatment is variable
depending on the depth and length of dive.

The inspired pressure of oxygen should not be greater than 3
atmospheres and is given typically in cycles of 20 minutes
separated by breathing air for 5−15 minutes.

If airborne transfer is required, the patient is transferred with 100% oxygen at sea-level cabin pressure.

Question 10

Position

Answer 10

Supine

Head-down position has no proven role in preventing arterial bubbles entering the cerebral circulation and may increase cerebral oedema.

There is similarly no benefit in massive venous gas embolism.

Therefore, the head-down position is
not routinely recommended except perhaps in severe hypotension.

However, placing the injured diver in the supine position has two advantages.

It may help to prevent hypotension and the
rate of nitrogen washout is greater than in the sitting position.