A SUDDEN COLLAPSE IN A VENTILATED PRETERM NEONATE
History
A 3-day-old neonate born at 26 weeks gestation, weighing 830 g, is being ventilated on the neonatal intensive care unit. A chest X-ray at 4 hours of age demonstrated severe respiratory distress syndrome. He is being ventilated by conventional mechanical ventilation with pressure settings of 24/3 cmH2O, a ventilator rate of 60 breaths/min and an Fi O2 of 0.55. He has received surfactant and is sedated with an intravenous morphine infusion. His latest arterial gas showed a pH of 7.31, a PO2 of 7.2 kPa and a PCO2 of 6.2 kPa. Having been very stable over the previous 24 hours, he suddenly deteriorates and becomes deeply cyanosed with an oxygen saturation of 48 per cent. He also becomes bradycardic with a heart rate of 64 beats/min. The nurse immediately puts up the FiO2 to 0.95 and the oxygen saturation rises to 84 per cent and the heart rate to above 100 beats/min.
Examination
The infant is being hand bagged by the neonatal unit sister with an FiO2 of 0.95, pressures of 30/4 cmH2O at a rate of approximately 40 breaths/min. The oxygen saturation is 92 per cent. Heart rate is now 170 beats/min. The left hemithorax is moving poorly and auscultation confirms that there is normal air entry on the right but poor air entry on the left. A pneumothorax is suspected. The room lights are lowered and the chest is transilluminated with a fibreoptic cold-light source. The result is inconclusive. Heart sounds are normal and the anterior fontanelle is level. An urgent chest X-ray is ordered (Fig. 80.1) and an arterial blood gas is performed.
INVESTIGATIONS
Arterial gas Normal
pH 7.22 7.36–7.44
PO2 6.1 kPa 80–12.0 kPa
PCO2 7.9 kPa 4.0–6.5 kPa
Base excess –6.8 ( 2.5)–(2.5) mmol/L
Questions
• What are the causes of a sudden desaturation in a ventilated neonate?
• What is the diagnosis?
• What is the treatment?
Medicine
This question is best answered by considering whether the chest is not moving, whether chest movement is decreased or asymmetrical, or whether chest movement is normal:
• no chest movement – ventilator not working or tubing disconnected or kinked – endotracheal tube blocked or dislocated
• chest movement decreased or asymmetrical – pneumothorax – worsening respiratory disease
• chest movement normal – right-to-left shunt, e.g. across a patent ductus arteriosus – large periventricular haemorrhage – severe sepsis. The diagnosis in this case is a left-sided tension pneumothorax with mediastinal shift to the right (away from the side of the pneumothorax). A chest drain should be inserted immediately. If a pneumothorax is suspected clinically and cold-light transillumination demonstrates that the chest ‘lights up’ on that side (the two sides should be compared), this is indicative of a pneumothorax and a chest drain should be inserted and a chest X-ray is unnecessary. If the child deteriorates, a 23g butterfly needle can be inserted into the second intercostal space in the mid-clavicular line. Air can then be aspirated from the pleural space and this can ‘buy time’ pending the insertion of a chest drain. The largest possible chest drain should be used (usually 8, 10 or 12 FG depending on the size of the infant). The drain should be inserted above the rib as the intercostal vessels lie immediately below the rib. It should be inserted into the third, fourth or fifth intercostal space in the mid-axillary line. Following insertion and the appropriate connections to an underwater seal, air bubbles should be seen, swinging should be observed on breathing and the infant should rapidly improve. A chest X-ray should be done to ensure that the lung has re-inflated and to check the position of the drain.
KEY POINTS
• A pneumothorax is a common cause of a sudden deterioration in a ventilated preterm neonate.
• Diagnosis is by cold light transillumination and/or a chest X-ray.
• Urgent treatment is necessary. A needle aspiration can be done in the first instance if the child is very unwell or deteriorating, but definitive treatment is with a chest drain.
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