A femoral arterial blood gas sample is obtained from a 41 year old man.
- Describe and interpret the results
- What interventions does he require ?
PaO2 24.6 mmHg
paCO2 13.3 mmHg
HCO3 10.8 mmol/L
These blood gases are grossly abnormal.
- moderate to severe alkalaemia
- profound hypoxaemia
- severe respiratory alkalosis
- marked metabolic acidosis
To fully interpret them, it’s helpful to know that the samples were obtained when the barometric pressure was 272mmHg and the PiO2 47mmHg, making the expected alveolar O2 only 30mmHg. So they have an increased A-a gradient.
They are the averaged results from 4 climbers who had just summited Mt Everest – the ABGs were taken without supplemental oxygen at an altitude of 8400m. All had normal psychomotor function at the time. Typically such gases would be judged as inconsistent with life and would mandate aggressive and immediate resuscitation. However these climbers just need to descend. At 7000m their O2 content (but not SaO2) is normal.
That it is possible to survive & function with such gases shows the degree to which we can acclimatise to altitude. Sudden exposure to such altitude would cause loss of consciousness in unacclimatised individuals. This research will inform ICU care for patients with severe hypoxaemia.
Reference Grocott M et al, N Engl J Med 2009:360:140-149 http://archive.is/CFY8