Adequacy of Ventilation

Adequacy of ventilation is usually determined by physical examination and analysis of arterial blood gases. Both sides of the chest should rise equally and simultaneously with inspiration. However, the amount of rise should not exceed that of normal breathing in neonates. If one side of the chest rises before the other, the tip of the endotracheal tube may be in a mainstem bronchus, or there may be a pneumothorax or congenital anomaly of the lung. Listening to the breath sounds may be misleading. Because the chest is small, breath sounds are well transmitted within the thorax. Consequently, the breath sounds may be normal, even though the neonate has a pneumothorax or a congenital anomaly of the lung. A difference in breath sounds between the two sides of the chest should raise suspicion that an endobronchial intubation, a pneumothorax, atelectasis, or a congenital anomaly of the lung is present. Breath sounds are usually heard over the stomach, but these sounds are not as loud as the breath sounds heard over the chest. If they are as loud, determine whether an esophageal intubation has occurred or the neonate has a tracheoesophageal fistula. If ventilation is adequate, the neonate will become pink, initiate rhythmic breathing, and have a normal heart rate. Normal blood gas levels eventually are restored.

Most asphyxiated neonates do not have lung disease. They usually can be effectively ventilated with less than 25 cm H₂ O peak pressure, even for the first few breaths. Excessive airway pressures cause pulmonary gas leaks and may cause lung injury.^[63] Neonates whose lungs are stiff (e.g., erythroblastosis fetalis, congenital anomalies of the lung, pulmonary edema, severe meconium aspiration, diaphragmatic hernia) often require much higher inspiratory pressures to ventilate their lungs. If so, they are likely to develop pulmonary gas leaks. To reduce this likelihood, the lungs should first be ventilated with inspiratory pressures of 15 to 20 cm H₂ O and rates of 150 to 200 breaths/min. If this low-pressure (low-volume), high-rate ventilation does not improve the blood gases, higher pressures and volumes may be required. Failure to adequately ventilate the lungs at birth may make hypoxemia worse and lead to CNS damage or even death. However, excessive pressures can be equally problematic. If a pulmonary gas leak occurs and interferes with oxygenation, CO₂ removal, or the circulation, the pleural gas should be drained with a thoracostomy tube. Pneumopericardium or pneumomediastinum seldom requires drainage.

The effects of ventilation should be monitored closely. If the PaO₂ is greater than 70 to 80 mm Hg or the SaO₂ exceeds 94%, the inspired oxygen concentration should be reduced in 5% to 10% steps until the PaO₂ is between 50 and 80 mm Hg or the SaO₂ is between 87% and 94%. In a controlled trial, resuscitation with room air was just as effective as with 100% oxygen.^[49] This must be confirmed before it can be recommended. It is especially important to maintain oxygenation within this range when resuscitating neonates of 34 weeks' gestation or less, because they can develop retinopathy of prematurity (i.e., retrolental fibroplasia). ^{[66] [67]} Although it is not clear what level of PaO₂ (or SaO₂ ) causes retinopathy of prematurity, we know that it can occur in premature neonates with a PaO₂ of about 150 mm Hg for 2 to 4 hours. Repeated increases in PaO₂ to these levels may be as dangerous because the retinal vessels do not immediately relax after reduction of the PaO₂ to normal levels. It may take more than 30 minutes for this to occur. The neonate's heart rate should be continuously monitored during endotracheal intubation because arrhythmias are common during this procedure, especially if the neonate is hypoxic at the time of tracheal intubation.