Elderly patient with collapse presents critically unwell.
Her ABG shows:
1.
Normal pH with severe respiratory acidosis and metabolic alkalosis
A-a gradient: 40, high indicating VQ mismatch or shunt
Calculations:
Assuming that the primary disorder is Respiratory and acute (a CO2 of 89 is very uncommonly chronic even in patients with Emphysema) –
if compensated (1:4 rule) the HCO3 should be max of 44
Assuming that the primary disorder is metabolic, you can never compensate to a CO2 of 89
calculation for expected CO2 = 0.7XHCO3 + 20 = 58, which is probably maximal CO2 compensation
2. Causes include:
Respiratory acidosis
– central (stroke, haemorrhage, drugs)
– peripheral (lung, chest wall – less likely)
Metabolic alkalosis
– severe dehydration
– severe vomiting
– drug – diuretics
VQ mismatch/ shunt
– pneumonia
– PE
– aspiration
3. Management:
– establish limits of care
– secure airway
– hyperventilate to blow off CO2, reverse ??opioid toxicity
– look for underlying cause and treat appropriately