CHS CHS Decompression Sickness & Diving Medicine 1 — Questions and Answers
Question 1: What is the primary pathophysiological mechanism of decompression sickness (DCS)?
- Oxygen toxicity from excessive O2 partial pressure during ascent
- Formation of nitrogen gas bubbles in tissues and blood during rapid ascent (Correct answer)
- Carbon dioxide retention from inadequate ventilation underwater
- Nitrogen narcosis progressing to tissue injury
Correct answer: Formation of nitrogen gas bubbles in tissues and blood during rapid ascent
Rapid ascent causes dissolved nitrogen in tissues to come out of solution and form bubbles, which physically obstruct vessels, compress nerves, and trigger inflammatory cascades.
Question 2: Type II (serious) DCS most commonly affects which body system, making early treatment with HBOT critical?
- Gastrointestinal system
- Spinal cord and central nervous system (Correct answer)
- Renal system
- Hepatic system
Correct answer: Spinal cord and central nervous system
Type II DCS frequently causes spinal cord and CNS injury from venous infarction and bubble emboli, presenting with paralysis, sensory deficits, or altered consciousness.
Question 3: The US Navy Treatment Table 6 (TT6) is the standard HBOT protocol for serious DCS. At what pressure is the majority of the treatment conducted?
- 1.5 ATA (15 fsw)
- 2.4 ATA (60 fsw)
- 3.0 ATA (66 fsw) (Correct answer)
- 6.0 ATA (165 fsw)
Correct answer: 3.0 ATA (66 fsw)
USN TT6 is conducted primarily at 2.8 ATA (60 fsw equivalent on the oxygen schedule), but the treatment depth reached initially may be 2.8 ATA; however TT6 is conducted at 2.8 ATA with the first oxygen breathing at 60 fsw = 2.8 ATA.
Question 4: Which clinical finding is most consistent with arterial gas embolism (AGE) in a SCUBA diver?
- Joint pain appearing 12 hours after surfacing
- Sudden loss of consciousness immediately upon or within minutes of surfacing (Correct answer)
- Mild skin rash appearing 6 hours post-dive
- Fatigue developing 24 hours after a dive
Correct answer: Sudden loss of consciousness immediately upon or within minutes of surfacing
AGE causes immediate neurological catastrophe on surfacing as air bubbles enter the pulmonary veins and travel to the cerebral circulation, producing rapid loss of consciousness or stroke-like symptoms.
Question 5: When a diver with suspected AGE presents for HBOT, what is the recommended immediate positioning during transport?
- Steep Trendelenburg (head down) position
- Supine with head at the same level as the body (Correct answer)
- Sitting upright at 90 degrees
- Left lateral decubitus (Durant's maneuver) for all cases
Correct answer: Supine with head at the same level as the body
Current guidelines recommend supine positioning; head-down positioning is no longer recommended as it may increase cerebral edema without proven benefit in reducing bubble migration.
Question 6: What is the term for the 'chokes' presentation in DCS, and which body system does it affect?
- Cutaneous DCS affecting the skin with marbling
- Pulmonary DCS causing chest pain, dyspnea, and coughing from bubbles in pulmonary vasculature (Correct answer)
- Inner ear DCS causing vertigo and hearing loss
- Type I DCS causing only joint pain
Correct answer: Pulmonary DCS causing chest pain, dyspnea, and coughing from bubbles in pulmonary vasculature
The 'chokes' is a severe pulmonary form of DCS where gas bubbles obstruct the pulmonary capillaries, causing progressive respiratory failure requiring emergency HBOT.
CHS CHS Decompression Sickness & Diving Medicine 1
What is the primary pathophysiological mechanism of decompression sickness (DCS)?