SUDDEN DETERIORATION IN A TERM BABY
History
The midwife finds a 3-day-old male baby on the postnatal ward to be very lethargic and breathing fast. The baby is taken to the neonatal unit for further evaluation. He was born at term by emergency Caesarean section for undiagnosed breech presentation. There was no prolonged rupture of membranes. The pregnancy had been unremarkable to that point and all antenatal scans had been normal. Mother is blood group O-positive, had negative HIV, hepatitis B and syphilis serology and was rubella immune. The delivery was attended by a paediatrician but the baby cried immediately and needed no resuscitation. His birth weight was 3.5 kg (50th centile) and the first-day check was unremarkable. He has been breast-fed and although there were problems latching on initially, he fed well on day 2. He seems rather sleepy and has had frequent non-bilious vomits today. His mother is a 23-year-old woman from Pakistan who speaks good English and this is her first baby.
Examination
The baby’s temperature is 36.3C, his heart rate is 160 beats/min and his respiratory rate is 70 breaths/min. Oxygen saturation is 99 per cent in air, capillary refill is 2–3 s, and blood pressure is 60/40 mmHg. There is subcostal and mild sternal recession. He responds to vigorous stimulation and pain, but otherwise is very lethargic. The chest is clear, heart sounds and femoral pulses are normal, and the abdomen is normal. The fontanelle is normotensive. He has a strong odour which is slightly unpleasant.
INVESTIGATIONS
Normal
Venous blood gas analysis
pH 6.98 7.35–7.42 PaCO2 2.62 4.7–6.0 kPa
Base excess 25.5 2.5 to 2.5 mmol/L
Lactate 2.1 1.0–1.8 mmol/L
Glucose 5.2 2.2–4.4 mmol/L
Urinalysis
Glucose Negative Negative
Protein Negative Negative
Ketones Negative
Questions
• What are the possible causes of this type of presentation?
• How do you interpret the blood gas analysis?
• What is the most likely cause in this case?
• What is the emergency management?
Medicine
The history describes a term neonate who became very ill over a short period of time. The important diagnoses to consider are discussed in Case 10 (p. 31–32).
Approach to blood gas interpretation
In this case
Look at the pH pH 7.35, acidosis
Look at the PCO2 PCO2 4.7 kPa, respiratory compensation
Look at the base excess Lower than 2.5, metabolic acidosis
The blood gas analysis shows a severe metabolic acidosis, with unsuccessful respiratory compensation. This fits with the clinical picture of a tachypnoeic baby. Important points to note are the absence of risk factors for sepsis, the absence of signs of circulatory compromise, a lethargic baby with a strong odour, ketonuria and a severe metabolic acidosis without significant hyperlactataemia or hypoglycaemia. These findings point to an inborn error of metabolism, where excess acid is accumulating in the blood due to a metabolic defect. Possible causes include propionic, methylmalonic and isovaleric acidaemias. Remembering the names is less important than recognizing this type of presentation. Emergency management consists of stopping feeds and starting an infusion of 10 per cent dextrose. Whilst sepsis is unlikely to be the sole cause of the illness, it could be a contributing factor and antibiotics should be administered. The baby needs to be assessed promptly by an experienced paediatrician as he is likely to require intubation and ventilation if he starts to tire or cannot protect his airway. It is likely that sodium bicarbonate would be beneficial to partially correct the acidosis, and the case should be discussed urgently with the regional paediatric metabolic centre, as specific therapies may be recommended even before a certain diagnosis is available. To assist in making a diagnosis, blood should be sent for ammonia, plasma amino acid profile, and urine for amino and organic acid profiles. This baby had consanguineous parents (first cousins), increasing the risk of an autosomal recessive inborn error of metabolism. He required intubation and ventilation until the acidosis was corrected and he was then transferred to the regional metabolic unit. The diagnosis turned out to be isovaleric acidaemia.
KEY POINTS
• Metabolic disease can present as a sudden deterioration in the neonatal period.
• Metabolic disease is rare and management must be discussed with an expert.
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