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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Blood Gas # 26

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