Blood Gas #24

Describe and interpret this venous blood gas:

History: A 56-year-old female found drowsy in bed in the evening after going to bed the night before.  Had last been seen the night before going to bed after an argument.  Took 30 x panadeine forte, 30 x combination antihypertensive (amlodipine 10mg / olmesartan 40mg / hydrochlorothiazide 30mg).  Brought in to rural hospital GCS 14.

pH 7.08 Na 132 mmol/L
pCO2 85 mmHg K 5.1 mmol/L
pO2 28 mmHg Cl 92 mmol/L
HCO3 25.2 mmol/L Glucose 6.3 mmol/L
Creatinine 350 μmol/L

(84 two years ago)

Lactate 5.1 mmol/L
INR 1.4 Platelets 28 x 10*9/L
Paracetamol 110 mg/L

(22h post-ingestion)


[expand title=”Interpretation”]

What is the pH?


What is the primary process? 

Respiratory acidosis.

Is there compensation?

Expected HCO3 = 24 + [(pCO -40) / 10]: 

24 + [(pCO2 – 40) / 10] = 24 + 4.5 = 28.5.  Lower than expected HCO3 so there is a coexisting mild metabolic acidosis as well.

Are there other clues to diagnosis?

Anion gap = Na – (HCO3 + Cl):

132 – (92 + 25.2) = 14.8 = NAGMA.

Electrolyte clues:

Elevated lactate.  Renal failure.



Coexisting respiratory acidosis and metabolic acidosis in the context of delayed paracetamol and antihypertensive overdose.

Hypotension, antihypertensive related shock and hypoperfusion throughout the day resulting in prerenal failure and lactic acidosis.

Lactic acidosis and hepatotoxicity from massive paracetamol overdose.  Plt 28 very unusual for only 22hr post ingestion – likely to have been taking multiple smaller paracetamol overdoses prior to the larger single overdose on Wednesday night.  Thrombocytopenia not usually a feature until approx. >72hr post ingestion.  Very unlikely to have only taken 30 x panadeine forte given overall clinical and biochemical picture.

Respiratory acidosis from altered mental state and hypoventilation.

ALT was 1070 and peaked at >9000 despite NAC treatment.


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