6-9
partial pressure of oxygen delays the onset of the physiological, hypercapnia-induced drive to breathe. By
the time that drive induces him to surface, the diver may have stayed too long at depth. He may then have
insufficient oxygen to sustain him during ascent as the partial pressure of oxygen decreases quickly. The
diver can become hypoxic and unconscious under the surface. This phenomenon is called a “shallow water
blackout” and is seen more frequently in breath hold diving. Divers with an underwater breathing apparatus
are trained to surface with residual oxygen in their tanks to avoid this danger.
Subjective: Symptoms
Light-headedness, confusion, tingling, or numbness
Objective: Signs
Using Basic Tools: Brief period of confusion and ataxia preceding unconsciousness, which is often the
first sign.
Using Advanced Tools: Hypoxia can be assessed with a pulse oximeter. CXR can help determine whether
or not there is a Pulmonary Over Inflation Syndrome (see adjacent section in this chapter).
Assessment:
Differential Diagnosis - arterial gas embolism (AGE), carbon monoxide poisoning, decompression sick-
ness, trauma, shock and other causes.
Plan:
Treatment: Treat all unconscious divers (who were breathing compressed gas) for an AGE until proven
otherwise.
Primary: Perform ABCs of resuscitation. Place patient on 100% oxygen, maintain oxygen until full recovery,
and then slowly wean. Keep patient prone until full recovery. Monitor for 24 hours for residual symptoms. If
patient was breathing compressed gas, treat for an AGE until proven otherwise (i.e., diver is witnessed passing
out secondary to holding breath too long and responds quickly and completely to oxygen treatment). Secure
diver’s breathing source and tanks for testing.
Primitive: Perform artificial respiration if patient in respiratory arrest.
Patient Education
General: Educate divers on hypoxia and shallow water blackout
Diet: Normal
Prevention and Hygiene: Education and training in diving practices. Do not hyperventilate before a breath
hold dive - hyperventilating drives carbon dioxide level even lower
No Improvement/Deterioration: Consult Diving Medical Officer (DMO); treat as AGE
Follow-up Actions
Return Evaluation: Monitor for 24 hours for full improvement.
Consultation Criteria: Any residual symptoms need to be evaluated by a DMO.
Dive Medicine: Oxygen Toxicity
CPT Jeffrey Morgan, MC, USAIntroduction: Depth provides circumstances in which oxygen may become toxic to the body. As a diver
descends in water, the partial pressure of oxygen (ppO 2 ) increases. The US Navy Dive Manual limits the ppO 2
during diving operations based the depth and duration of dives. Exceeding these limits risks an oxygen toxicity
injury for the diver. Oxygen toxicity affects various tissues in the body, most notably the pulmonary system
and the central nervous system (CNS).