Pulmonary function testing in the critically ill neonate, Part II: Methodology

Pulmonary function testing is an important diagnostic tool in neonatal intensive care. These tests provide a detailed assessment of an infant's pulmonary status that can be used in several ways: to monitor the progression of lung disease, to streamline ventilator management, and to assess the infant's response to new treatments, such as surfactant replacement therapy or bronchodilators. In some settings, these tests are performed by specially trained nurses, and the results are available immediately for planning nursing care. This relatively noninvasive and low-risk assessment can be performed on all infants, whether on mechanical ventilation or breathing spontaneously. A comprehensive pulmonary function evaluation can be performed at the bedside in less than 60 minutes and is generally well tolerated. In this article, the determination of pulmonary "vital signs" tidal volume, minute ventilation, respiratory rate, pulmonary compliance, resistance, resistive work of breathing, and functional residual capacity-are discussed. The esophageal balloon technique for measuring dynamic pulmonary mechanics and energetics, as well as the helium dilution technique for measuring functional residual capacity, are described.