Neonatal hypoglycaemia — viva

Stem

The examiner hands you the bedside record of a two-hour-old 39-week infant of a gestational diabetic mother: jittery on the postnatal ward, pre-feed glucose 1.6 mmol/L after a breastfeed, plump and plethoric with disproportionate truncal adiposity. [4]

Examiner: What is your opening approach to this infant? [4]

Strong answer: I would classify this as transitional hypoglycaemia in an infant of a diabetic mother — the infant is at-risk by maternal history, the glucose is below the operational threshold for the first 24 hours, and the jitteriness makes it symptomatic. I would feed and keep the infant warm, give buccal 40% dextrose gel 200 mg/kg with a feed and recheck in 30 minutes, and escalate to intravenous 10% dextrose if the glucose stays low. Because this is an IDM, I would schedule repeated pre-feed checks — a single normal reading does not clear the infant, as the hyperinsulinaemic nadir peaks over the first hours. [2] [1]

Branch 1 — Definition and thresholds

Examiner: How do you define neonatal hypoglycaemia, and what thresholds do you use? [3]

Strong answer: Neonatal hypoglycaemia is best defined as a blood glucose below the operational threshold at which intervention is warranted, rather than a single fixed number — because no single glucose value cleanly predicts brain injury. Commonly used thresholds rise with postnatal age: below 2.0 mmol/L in the first 24 hours, below 2.6 mmol/L from 24 to 48 hours, and below 3.0 mmol/L beyond 48 hours. The symptomatic infant is treated at any low value without waiting. Local policy (AAP, PES, NICE, ADIPS) varies slightly. [3]

Examiner probe: Why is the newborn brain so vulnerable to a low glucose? [1]

Strong answer: The newborn brain has essentially no glycogen reserve, and glucose is its obligatory cerebral fuel. When glucose falls, neuronal ATP production fails, the sodium–potassium pump fails, and excitotoxicity and apoptosis follow — preferentially in the occipital and parietal cortex, which is why visual impairment, seizures and posterior-predominant imaging changes are the signatures of significant injury. [1]

Branch 2 — Mechanism and treatment ladder

Examiner: Explain why this infant of a diabetic mother is hypoglycaemic, and then give me your treatment ladder. [4]

Strong answer: In the IDM, maternal glucose crossed the placenta freely but maternal insulin did not, so chronic intrauterine hyperglycaemia drove fetal pancreatic hyperinsulinaemia. At cord clamping the maternal glucose supply stops abruptly, but insulin persists — driving glucose into cells and suppressing ketogenesis, so the blood glucose falls steeply and the brain loses both glucose and ketone fuel. This is why hyperinsulinaemic hypoglycaemia is the deepest and most dangerous form. The treatment ladder is: feed and recheck; buccal 40% dextrose gel 200 mg/kg with a feed; intravenous 10% dextrose 2 mL/kg bolus; an escalating infusion titrated to a glucose infusion rate of 6–8 mg/kg/min; and glucagon or hydrocortisone for refractory cases. [4] [2]

Examiner probe: What did the Sugar Babies trial show? [2]

Strong answer: The Sugar Babies trial (Harris 2013) established that buccal 40% dextrose gel is an effective first-line treatment for neonatal hypoglycaemia, reducing the need for intravenous therapy and for mother–baby separation, and the Cochrane reviews confirmed its prophylactic and treatment role. [2]

Branch 3 — Persistent disease (a trap)

Examiner: The infant is now 5 days old and still hypoglycaemic on 14 mg/kg/min of glucose. The critical sample shows insulin 30 mU/L with low ketones and a brisk glucagon response. What is going on, and what do you do? [5]

Strong answer: This is congenital hyperinsulinaemic hypoglycaemia. The critical sample shows an inappropriately non-suppressed insulin at the time of hypoglycaemia, with suppressed free fatty acids and ketones — insulin both lowers glucose and suppresses the alternative fuels — and the brisk glucagon response is typical of a glycogen-rich liver with insulin blocking release. The high glucose requirement above 10–12 mg/kg/min and persistence beyond 48–72 hours confirm pathological disease. I would stabilise with an escalating infusion and adjuncts, take the full metabolic and endocrine workup, and refer urgently to paediatric endocrinology and genetics for a diazoxide trial and possible 18-FDOPA imaging and surgery — because early diagnosis and treatment change the neurological outcome. [5] [6]

Examiner probe: How would a presentation with acidosis and hyperammonaemia change your differential? [5]

Strong answer: It would point away from hyperinsulinaemia and toward an inborn error of metabolism — a fatty-acid oxidation defect, an organic acidaemia or a urea-cycle disorder. I would send plasma amino acids, acylcarnitines and urine organic acids, stop the offending substrate where relevant (a galactose-free feed in galactosaemia), and involve the metabolic service. [5]