A 4 week old baby is brought to ED with a history of vomiting over 1 week. The vomiting initially thought to be normal, has increased and baby appears to be hungry all the time. The baby’s weight gain over this week has been around 100 grams. Prior to this the baby had been feeding well and gaining weight. Birth and antenatal history unremarkable. VBG was done:
pH 7.51 Na 137mmol/l
pCO2 50mmHg K 3.9mmol/l
HCO3 36 mmol/l Cl 90mmol/l
B/E 11 BSL 4.6 mmol/l
Lactate 1.3mmol/l Cr 28 umol/l
- Describe and interpret the VBG
- What is the normal weight gain for an infant?
Answer
Matabolic alkalaemia pH 7.51 HCO3 36mmol/l
Compensation – Expected PCO2 = 0.7 x HCO3 + 20 = 45 mmHg (+/- 5)
Low chloride, normal sodium, potassium and BSL
The above VBG shows a compensated hypochloraemic metabolic alkalosis. In this clinical context it is most likely due to the vomiting and contraction alkalosis. Differential diagnosis of vomiting in neonate includes pyloric stenosis, sepsis, malrotation with volvulus, raised intracranial pressure (consider NAI)
Weight gain in an infant:
Loss of 10% of birth weight in first week
Day 10-14 regained weight
0-3 months 150-200g/week
3-6 months 100-150g/week
6-12 months 70-90g/week
6 months double birth weight
1 year tripled birth weight