Blood Gas 025

A 35 year old male is brought in by ambulance post arrest

For a basic approach to blood gas interpretation see here

1. What is the Acid-Base disturbance?

pH 6.76 ∴ life-threatening acidosis

Work out the cause of the acidosis:

• CO2 = 59 ∴ respiratory acidosis
  • Expected HCO3 (acute resp disease) = 24 + 0.1(59 - 40) = 25.9
  • Actual HCO3 = 8 ∴ concomitant metabolic acidosis
• HCO3 = 8
  
  • Expected pCO2 = 1.5 x 8 + 8 = 20
    
  • Actual CO2 = 60 ∴ respiratory acidosis
• ​Mixed metabolic and respiratory acidosis

Work out the cause of the metabolic acidosis:

• Anion Gap = 16 ∴ HAGMA
  • Delta Ratio = (16-12)/(24-8) = 0.25
  • 0.25 < 0.4 = hyperchloraemia
• HAGMA (likely caused by the lactic acidosis)

Overall acid-base disturbance: Mixed Respiratory Acidosis & HAGMA with hyperchloraemia

2. Are there any electrolyte issues?

Potassium (correct for pH)

• Expected K = 5(7.4 - pH) + 5 = 8.2
• Actual K = 3.4 ∴ severe hypokalaemia

Sodium (correct for glc)

• Actual Na = mNa + (Glc - 5)/3 = 142 + (21.3 - 5)/3 = 147 
  
• ∴ slight hypernatraemia

​
​Calcium (for albumin)

• Neither Ca or Albumin reported

3. Are there any oxygenation issues?

It's an arterial gas - so we can address this question

Aa = PAEO2 - PaO2
      = [713 x 0.50 ] - 1.25 x 59 - 122
      = 356.5 - 73.75 - 122
      = 160.75

Expected Aa = age/4 + 4 = 35/4 + 4 = 12.75

∴ High A-a gradient

4. What is your overall impression?

Life-threatening blood gas, which is compatible with the story - a patient who died and was brought back to life. Still a long way to go to get back to normal. 

For context, this patient in fact had a Massive PE with aspiration pneumonitis.