ABG: Pulm embolism

Clinical - Respiratory/Pulmonary, Critical Care

The more massive the obstruction, the more severe the hypoxemia is likely to be, with an SpO2 < 95% on room air being predictive for increased morbidity and mortality. However, many other conditions also cause hypoxemia, and embolism often does not cause hypoxemia or even a widening of the alveolar-arterial Po2 difference . Hypocapnia usually is present with embolism; hypercapnia, on the other hand, is rare. A massive PE may cause a combined respiratory (hypercapnea) and metabolic acidosis due to hemodynamic collapse. 18% of patients will have a PaO2 85-105 mmHg and 6% will have a normal A-a gradient.

  • Classic finding: hypoxemia and hypocapnea (respiratory alkalosis)
  • Normal ABG: 18% will have PaO2 > 85 mm Hg and 6% will have normal A-a gradient
  • Mixed Acidosis: in setting of hemodynamic collapse
  • Utility of ABG: minimal , even when combined with other modalities (see Roger MA et al., below)
  • Outcome: SpO2 < 95% on room air may be predictive of poor outcome, however


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