This is a 3 month old (weight 5kg) critically unwell child who requires resuscitation with concomitant assessment to determine the cause of her illness.

Her clinical picture is one of severe dehydration (at least 7%)

Severe life threatening metabolic acidosis ( BE -25, HCO3 4) with maximum compensation ( CO2 very rarely decreases to less than 10)

Anion gap = 15, high side of normal – accounted for by high lactate, severe peripheral circulatory compromise and tissue hypoperfusion. Consider severe dehydration,sepsis, toxins (glucose normal and creatinine normal). The anion gap is not large enough to explain the very low pH.

Delta ratio = 0.15 , consistent with normal anion gap metabolic acidosis

Causes – intestinal catatstrophies, diarrhoea

Osmolality = 331.5, high urea, pre renal cause ie. fluid loss and dehydartion, hypoperfusion

Mild hypokalaemia – secondary to diarrhoea and likely to reflect critically low total body potassium due to acidosis and shift. Requires careful monitoring and replacement, particularly as acidosis corrects and potassium shifts to intracellular compartment.

High sodium and chloride – pure water loss from diarrhoea, consider whether these blood tests were taken after a fluid bolus of normal saline

Normal glucose – not DKA, ketones not given

Creatinine normal – normal renal function

Venous sample so cannot interpret Aa gradient or pO2

Interpretation

An unwell 3 month old with a mixed anion gap and normal anion gap metabolic acidosis (hyperchloraemic), severe dehydration. She requires immediate iv access with 10ml/kg normal saline fluid bolus and re assessment, assessment of cause and specific treatment as indicated.

Causes include-

Gastroenteritis – infective (viral, bacterial, parasitic)

Sepsis

toxins

Inborn errors of metabolism

Intestinal catastrophies

trauma

Fluid Calculation in children:

Degree of dehydration (deficit) – weight X % dehydration X 10
plus
Maintenance fluid requirements (4;2;1 rule)
plus
Ongoing losses – best measured 

Aim to replace over 48 hours, in severe cases subtract the bolus doses given from the total.