Lab Case 205 Interpretation

66 year old female presents anuric

Metabolic Acidosis pH 6.94 and HCO3 1.9mmol/l

Compensation – Expected PCO2 = 1.5 x HCO3 + 8 = 10.85

AG = Na – (HCO3 +Cl) =32.1

Delta Gap = AG-12/24-HCO3 = 0.9

PAO2=713xFiO2 – (CO2/0.8)=273mmHg  PaO2= 168mmHg

A-a gradient = 105mmHg

Corrected K – 0.5 increase in potassium for every 0.1 decrease in pH – K =3.2mmol/l

The above ABG shows a severe high anion gap metabolic acidaemia with adequate respiratory compensation. The delta gap of 0.9 indicates that it is a pure HAGMA, with no other underlying disorder. There is a markedly raised A-a gradient of 105.  There is a markedly elevated lactate, and creatinine and a mildly elevated potassium, but when corrected for pH it is mildly decreased.  There is a mild anaemia and a normal glucose.

The most common causes of a HAGMA are toxins, ketones, renal failure and lactic acidosis. In this clinical context the HAGMA is due to a combination of renal failure and lactic acidosis. The patients acute on chronic renal failure is likely due to a number of factors – ? contrast related from recent angiograms, dehydration from vomiting (however this could be due to uraemia), drugs eg ACE inhibitors, diuretics. Post renal causes also need to be considered.

The severe lactic acidosis is also likely to be multifactorial  – hypovolaemia, renal failure, metformin related, underlying sepsis and shock. The corrected potassium needs to be considered, as correction of the acidosis and renal failure will lead to a correction of the hyperkalaemia and lead to a drop in potassium. This needs to be monitored.

The elevated A-a gradient in this context could be due to an underlying pneumonia, or a PE as the patient has had a recent hospital admission and surgery, as well as multiorgan failure and ARDS.

The mild anaemia could be a result of the patients CRF, as well as recent surgery. An upper GI bleed should be excluded as the patient will be on dual antiplatelets.

There are 2 types of lactic acidosis – type A and B

Type A – Decreased oxygen delivery/increased demand

eg shock, hypoxia, anaemia, CO poisoning, seizures, exercise, shivering

Type B –

B1 – underlying disease – liver and renal failure, lymphoma, leukaemia, ketoacidosis, thiamine deficiency

B2 Associated with drugs -cyanide, beta agonists, metformin, salicylates, alcohol, valproate, iron, isoniazid

B3 IEM