A 35 year old male presents to ED confused and combative.  No further information is known.

VBG:

pH 7.07                                Na 141 mmol/l

pCO2 70 mmHg                   K 3.2 mmol/l

HCO3 20 mmol/l                  Cl 99 mmol/l

B/E -13                                 Cr 85 umol/l

BSL 6.9 mmol/l                     Lactate 16 mmol/l

Describe and Interpret the VBG

Answer:

pH 7.07 acidaemia

Respiratory acidosis – pCO2 70 mmHg

Compensation – expected pCO2 – for every 10 increase in CO2 there is a 1 increase in HCO3 = 27mmol/l

AG = Na – (HCO3 + Cl) = 22 – HAGMA

Delta ratio = Change in AG/ Change in HCO3 = 22-12/24-20 = 2.5

Marked elevated lactate and relatively low potassium

The above VBG shows  a moderate mixed respiratory and metabolic acidosis. The metabolic component is a high anion gap metabolic acidosis with a raised AG >2 indicating either an associated preexisting compensated respiratory acidosis  or coexisting metabolic alkalosis. There is a severely raised lactate and relatively low potassium.

In this clinical context the HAGMA is likely due to a lactic acidosis. Lactic Acidosis can be caused by Type A – increased metabolic demand, or Type B due to drugs and liver failure and thiamine deficiency.  In the context of a combined respiratory acidosis and the clinical context,  the lactic acidosis is likely due to seizure, but toxins eg alcohol toxicity, massive paracetamol overdose, cyanide poisoning.

The patient had underlying COPD, and a CO2 retainer which explained the raised delta ratio.