Transient tachypnoea of the newborn — short-answer questions

This stem concerns a typical transient tachypnoea of the newborn presentation in an infant delivered by elective caesarean before 39 weeks. [3]

Question 1 (10 marks)

a) Give the most likely diagnosis and outline the pathophysiology, relating it to the mode of delivery. (5 marks) [3]

The most likely diagnosis is transient tachypnoea of the newborn (wet lung syndrome). The fetal lung actively secretes fluid in utero, and at birth this fluid must be cleared by amiloride-sensitive epithelial sodium channels (ENaC) on the alveolar epithelium, which absorb sodium and water into the interstitium for lymphatic removal. [2]

Labour is the switch: the catecholamine surge upregulates ENaC and converts secretion to absorption, while vaginal delivery mechanically compresses the thorax to clear fluid. An elective caesarean without labour removes both signals, so ENaC activation is delayed, residual alveolar fluid persists, and compliance falls — producing tachypnoea and grunting that resolve as postnatal ENaC activity rises over 24–72 hours. [3]

b) State your initial investigations and the expected chest radiograph findings, and list four differential diagnoses you must exclude. (5 marks) [1]

Investigations are a chest radiograph, full blood count with CRP and blood culture to exclude sepsis, and a capillary blood gas to assess hypoxaemia. The expected chest radiograph shows perihilar streaking, hyperinflation, and fluid in the horizontal (minor) fissure; lung ultrasound showing a double lung point is highly specific. [1]

The four key differential diagnoses are respiratory distress syndrome from surfactant deficiency, neonatal sepsis or pneumonia, meconium aspiration syndrome, and congenital heart disease with a pre-post-ductal saturation gap. [1]

Question 2 (10 marks)

a) Outline your stepwise management and the criteria for safe discharge. (6 marks) [3]

Management is supportive. Begin the sepsis work-up and start empirical antibiotics pending cultures, titrate low-flow oxygen to maintain SpO₂ 91–95%, hold oral feeds while the respiratory rate exceeds 60 and use nasogastric or intravenous fluids, and add bubble CPAP at around 5–6 cmH₂O if the FiO₂ climbs above 0.30. Diuretics are not indicated. [3]

Discharge is appropriate once the baby tolerates full feeds, has a normal respiratory rate in room air, needs no supplementary oxygen, and has completed the antibiotic course with negative cultures. A rising oxygen requirement above 40% should trigger re-evaluation rather than continued reassurance. [1]

b) A colleague suggests nebulised salbutamol to speed recovery. Summarise the evidence and your recommendation. (4 marks) [4]

Salbutamol is mechanistically plausible because beta-agonism drives ENaC-mediated sodium and fluid absorption, but randomised trial evidence is inconsistent. A 2025 randomised controlled trial reported shortened duration of tachypnoea, yet the evidence is not strong enough for a consensus guideline. [4]

My recommendation is to continue supportive care as first-line and reserve salbutamol for trial or clearly refractory cases, while using a lung-ultrasound aeration score to quantify any treatment effect. [4]