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
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.

Blood Gas # 26

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