Lab Case 172 Interpretation

6 month old female presents with 2 day history of watery diarrhoea and severe nappy rash. She has had poor oral intake, but mother is unsure of urine output due to the frequent stools.

pH –7.2

Primary process –metabolic acidosis HCO3 13

Compensation –Expected CO2 = (1.5xHCO3)+8 = 27.5 – > not fully compensated or underlying respiratory acidosis

Metabolic Acid base disorder –

                AG = Na –(HCO3+CL) =10 – NAGMA

Other results –electrolytes, lactate, and glucose – Mildly low sodium and potassium, normal lactate and glucose.

The following VBG shows a NAGMA. The acidosis is not fully compensated, or there is an underlying respiratory acidosis.  There is mildly low sodium and potassium with a high normal chloride and normal lactate and glucose.

NAGMA is caused by chloride gain – normal saline or HCO3 loss – either renal (RTA, acetazolamide, Adrenal insufficiancy) or GIT (diarrhoea,  bowel or pancreatic fistulas) or decreased H excreation – RTA


In this clinical context the NAGMA could be due to the diarrhoea or an underlying RTA –either type I d/t reduced secretion of H+ in the distal tubules or type II d/t impaired reabsorption of bicarbonate in the proximal tubule.  There could be an underlying respiratory acidosis secondary to altered mental state due to severe dehydration, or an underlying infective process – pneumonia

Despite the normal lactacte this is a sick child, that shows signs of moderate to severe dehydration with 10% LOW, as well as signs of NAI. The management of this child would include

resuscitation -20ml/kg normal saline bolus, assess response and repeat as necessary. Cardiac monitoring,  Monitor input and output

definitive management – IVI fluids (maintenance + deficit + ongoing losses). Potassium replacement and check Mg and replace if necessary.  Antibiotics for likely secondarily infected nappy rash (flucloxacilin  or vancomycin).  Search and treat underlying cause of diarrhoea eg UTI.  Search and treat other NAI.

supportive care – analgesia, barrier cream to buttocks

  • disposition – this child needs to be admitted to hospital. If the child does not respond to initial resuscitation and treatment, one needs to consider HDU/ICU care.  Ideally she should be admitted to a hospital with a CPU, with input from allied health services and child protection services.