Pulmonary Air Leaks
Air leak is more common during the newborn period than at any other time of life. This finding probably relates to the facts that assisted ventilation is a relatively common mode of therapy in sick newborn infants, that premature infants have fragile lungs, and that high intrathoracic pressure gradients are generated during the first few breaths. It has been estimated that spontaneous air leak occurs in 1% of all live births, but many of these are asymptomatic. The sites of air leak in the newborn are the pleural cavities (pneumothorax), mediastinum (pneumomediastinum), lung interstitial tissue (interstitial emphysema), and, occasionally, pericardial sac (pneumopericardium) and peritoneal cavity (pneumoperitoneum).
Air leak is a significant problem in infants receiving assisted ventilation. The incidence of pneumothorax and interstitial emphysema in infants with respiratory distress syndrome (RDS) was significantly reduced (from about 25% to about 10%) with the use of surfactant.
TYPES OF AIR LEAK
Air leak, particularly pneumothorax, should be suspected in any infant receiving positive airway pressure who suddenly becomes cyanotic. The clinical features suggestive of a tension pneumothorax include shift of the apex beat, decreased breath sounds on the side of the pneumothorax, distention of the chest, and, occasionally, a readily palpable liver and spleen from downward displacement of the diaphragm. In addition, the infant may demonstrate poor circulation or shock.
Diagnosis and appropriate treatment of a tension pneumothorax is a matter of the greatest urgency. The differential diagnosis of an infant who deteriorates suddenly and becomes cyanotic while on a ventilator includes endotracheal tube or large airway obstruction, pneumothorax, and massive pulmonary or intracranial bleed. Once it has been established that the airway is patent, the diagnosis of tension pneumothorax frequently can be made on clinical grounds, assisted by transillumination. This involves shining a bright, focused light on the chest wall after dimming the lights in the room. The part of the chest into which air has leaked may become highly translucent. If the infant is unstable, there usually is not time to obtain a radiograph of the chest; in this situation, the suspected pneumothorax will have to be managed without the benefit of radiographic confirmation. If the infant is stable and there is no acute interference with respiration or circulation, a chest radiograph may be obtained for confirmation of the diagnosis before proceeding to treatment.
The initial step is to insert a needle, preferably a plastic needle with a metal trochar (such as is used for peripheral intravenous infusions), into the chest. The needle should be attached to a syringe by means of a three-way stopcock or, alternatively, to a short length of empty intravenous solution tubing, the end of which is placed under water below the level of the chest. If the baby is lying supine, the air usually will collect in the anterior chest; a suitable site for needle insertion is the anterior axillary line in the fifth or sixth interspace. The diagnosis of pneumothorax is made when insertion of the needle into the pleural cavity results in the release of air under tension, with accompanying improvement in the infant’s status. Once the diagnosis has been established, a chest tube should be inserted. The chest tube should be connected to a water seal that is subjected to negative pressure. Drainage should be continued as long as air is evacuated from the chest. When it is clear that air drainage has stopped, the negative pressure should be discontinued, or the chest tube may be clamped. If a chest radiograph, taken after a few hours, shows that the pneumothorax has not recurred, the tube may be removed.