Lab Case 21 – Interpretation


1. Critically unwell patient with septic shock

Source – Respiratory, other

2. Breast Cancer

Is patient on Chemotherapy – consider febrile Neutropaenia

Is there metastatic disease

Patient requires simultaneous assessment and resuscitation in a resuscitation bay. Treatment is aimed at effective treatment of septic shock (as per surviving sepsis guidelines) which include fluid therapy, early antibiotics, source control, inotropic support if shock refractory to fluids and early HDU referral.

ABG shows:

metabolic acidosis -ph 7.28, base XS -8, HCO3 18

Anion gap = 12 which is normal


expected CO2 35 (actual 38) – adequate compensation

This is a normal anion gap metabolic acidosis (NAGMA). This is atypical for this type of presentation as you would expect a lactic acidosis with sepsis.

Is there another reason that contributes to this abnormality?

pO2, pCo2, Na, K, Cl,Glucose and Lactate are all acceptable and within normal limits There is some degree of hyperchloraemic acidosis.

Expect some Potassium decline as acidosis resolves.

A-a gradient = 31 which is slightly elevated, consider shunt/ VQ mismatch (pneumonia, atelectasis, pleural effusion, infected PE etc)

Causes of NAGMA in this patient:

Saline therapy

Addison’s disease ( in fact her shock was resistant to fluids, she required increasing inotropic support, at which point hydrocortisone 200mg iv was administered as per the sepsis guidelines). Atypical here is the normal Sodium and Potassium.

Other causes to consider (unlikely here):


drugs – carbonic anhydrase inhibitors

renal tubular acidosis

Pancreatic, small bowel or ureteric fistulas