History:
A 64 year old male was brought in by ambulance after his friend called them. He was unconscious in the park, is a known IV drug user and has had recurrent ED presentations with drug intoxication. He was intubated for a GCS 7.
Here is his ARTERIAL blood gas:
| pH 7.09 | Na 142 mmol/L |
| pCO2 99 mmHg | K 4.7 mmol/L |
| pO2 199 mmHg | Cl 104 mmol/L |
| HCO3 21 mmol/L | Creatinine 115 mmol/L |
| FiO2 100% | Glucose 7.1 mmol/L |
| Lactate 5.5 mmol/L |
[expand title=”Interpretation”]
What is the pH?
7.09
What is the primary process?
Respiratory acidosis.
Is there compensation?
Expected bicarb = 24 + [(pCO2 – 40)/10] = 24 + 5.9 = 29.9
Slightly lower than expected HCO3 = coexisting metabolic acidosis.
Are there other clues to diagnosis?
Anion gap = Na – (HCO3 + Cl): 17
Delta gap = (Anion gap – 12) ÷ (24 – HCO3): 5/3 = 1.666 = Pure HAGMA
A-a gradient = [(FiO2 x 713) – (pCO2 x 1.25) – pO2]
(FiO2 x 713) – (pCO2 x 1.25) – pO2 = (713 – 123.75 – 199) = 390
Expected A-a = age/4 + 4 = 20. Massive A-a gradient.
Electrolyte clues:
Renal impairment (Creat was 74 six months ago).
Elevated lactate.
Formulation:
Interpretation:
Coexisting respiratory and metabolic acidosis in the context of heroin overdose and an aspiration pneumonia. Hypoventilation from respiratory depression and consolidation. Hypoperfusion, tissue hypoxia and lactic acidosis. Elevated A-a gradient from RLL consolidation. Possible “dirty hit” and septic shower.
Consider other toxicological differentials for hyperthermia, tachycardia and altered mental state.
Case Resolution:
This patient was intubated and admitted to ICU with an impressive right lower lobe pneumonia, with ongoing O2 requirements of FiO2 0.6 after 48 hours. On quad strength norad.
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