Expected ABG Results in Decompression Sickness
In decompression sickness (DCS), the primary ABG abnormality is hypoxemia (low PaO2), with normal or low PaCO2 in most cases; hypercapnia and respiratory acidosis are uncommon unless severe cardiopulmonary complications develop. 1, 2, 3
Primary Blood Gas Pattern
The typical ABG findings in DCS reflect tissue hypoxia from bubble-induced vascular obstruction and inflammatory injury:
- Hypoxemia (↓ PaO2) is the hallmark finding, resulting from ventilation-perfusion mismatch caused by intravascular and extravascular bubbles 1, 2
- Normal or decreased PaCO2 is expected in most cases, as patients typically hyperventilate in response to hypoxia and distress 3
- Normal pH or mild respiratory alkalosis from compensatory hyperventilation 2, 3
- Normal base excess initially, unless severe shock or prolonged tissue hypoxia develops leading to metabolic acidosis 4
Severity-Dependent Variations
Mild to Moderate DCS:
- PaO2 may be only mildly reduced or even normal in minor cases 2
- Hypoxemia becomes more pronounced with increasing bubble burden and tissue involvement 3
- PaCO2 remains normal or low due to intact respiratory drive 1
Severe DCS with Cardiopulmonary Involvement:
- Marked hypoxemia (PaO2 < 60 mmHg / < 8 kPa) can occur with pulmonary edema or massive bubble embolization 5, 3
- Metabolic acidosis with negative base excess may develop from shock and tissue hypoperfusion 4, 6
- Hypercapnia is uncommon but may occur in cases of respiratory failure or cardiovascular collapse 3
Critical Distinction from Arterial Gas Embolism
While both DCS and arterial gas embolism (AGE) fall under decompression illness, their pathophysiology differs:
- DCS: Bubbles form from dissolved inert gas during decompression, typically causing gradual onset hypoxemia 2, 3
- AGE: Bubbles enter arterial circulation directly from pulmonary barotrauma, often causing acute stroke-like symptoms with similar hypoxemic pattern 1, 2
- Both conditions produce comparable ABG abnormalities (primarily hypoxemia), making clinical distinction based on ABG alone unreliable 3, 6
Clinical Monitoring Implications
Immediate oxygen administration (100% normobaric oxygen) is the cornerstone of first-aid treatment and can dramatically improve ABG parameters even before recompression therapy. 1, 3, 6, 7
- Oxygen therapy should be initiated immediately upon suspicion of DCS, targeting SaO2 > 92% and PaO2 > 8 kPa 8, 1
- Serial ABG measurements help assess response to oxygen therapy and guide need for recompression 6, 7
- Development of metabolic acidosis or worsening hypoxemia despite oxygen indicates severe disease requiring urgent hyperbaric treatment 3, 6
Common Pitfalls
- Do not withhold oxygen based on normal initial oxygen saturation by pulse oximetry, as tissue hypoxia may be present despite adequate arterial oxygenation 5, 2
- Avoid assuming hypercapnia is typical in DCS—this is a respiratory failure pattern seen in COPD or severe pulmonary disease, not uncomplicated DCS 5
- Monitor for metabolic acidosis in severe cases as a marker of tissue hypoperfusion and shock, which indicates need for aggressive fluid resuscitation and urgent recompression 4, 6