A 40 year old male is brought to ED by police. He has been found acting erratically at the shops.

Below is the patients VBG

pH 7.70                                               Na 142 mmol/l

pCO2 15.8 mmHg                               K 3.0 mmol/l

HCO3 20 mmol/l                                 Cl 109 mmol/l

B/E 2.7                                                Glucose 5.7 mmol/l

Lactate 2.9 mmol/l

Describe and Interpret the VBG

Answer

Respiratory alkalaemia pH 7.7 pCO2 15.8mmHg

Compensation – Expected HCO3 – in acute respiratory alkalosis for every 10 decrease in CO2 from 40, there is a 2 decrease in HCO3 = 19mmol/l

Mildly raised lactate

Mildly decreased K but corrected potassium 4.5mmol/l

The above VBG shows a compensated acute respiratory alkalosis, with a mildly decreased potassium, but when corrected for is normal. There is also a mildly raised lactate.

In this clinical context of a patient showing abnormal behaviour one needs to consider sympathomimetic drugs causing an increase in respiratory rate.  Other pathologies to consider would be an intracranial haemorrhage, panic attack/psychogenic cause (diagnosis of exclusion).

Other causes, for example hypermetabolic states, sepsis, hyperthermia, are usually associated with a metabolic acidosis