Resuscitation of the depressed newborn.

The role of the nurse anesthetist as a member of the obstetrical team can be manifold. Not only are we available to assist the obstetrician in providing anesthesia to the mother for the delivery, but often we also are asked to assist in resuscitative procedures for an infant who is expectedly or unexpectedly depressed at birth. The purpose of this article is to review some causes of infant depression and to provide some basic concepts on resuscitation of the depressed newborn. "The transition from intrauterine to extrauterine life is the most dangerous time of our existence." 1 Unless this transition is smooth, serious and permanent disabilities may result. Several important changes must occur at birth. First, the lung must expand. Expansion, however, may not be a good word, since the lung is not collapsed in utero but is filled with 20-30 ml of fluid per kg of body weight. This fluid, which is made in the lungs and secreted into the oropharynx, has a high protein content and a pH of approximately 6.8. At birth, this fluid must be removed from the lung and replaced with gas. Second, the fetal circulation must be converted to that of an adult. The cardiac output must be redistributed so that the lung receives 90-100% of the right ventricular output instead of the 5-10% that it received in utero. Third, the lung, rather than the placenta, must oxygenate and remove carbon dioxide from the blood. 1 Fluids may be removed from the lungs during and after birth by several means. Changes in esophageal pressure are related to tidal volumes during the birth process. At the time that the infant's head is delivered and the shoulders are still in the vagina, the esophageal pressure is greater than 60 cm of water.1 The large pressure gradient that exists between the lung and mouth forces fluid from the lung into the larynx and out the mouth. As much as 60 ml of fluid may be ejected. The intrathoracic pressure drops to atmospheric level as the thorax is expelled from the vagina. During the first breath, a negative pressure of 60 cm of water is generated; air is slowly taken into the lungs; the breath is held for approximately two seconds; and the gas is exhaled. "Approximately 75% of the first breath is retained within the lung as part of the developing functional residual capacity."1 The next few breaths are very similar to the first, with lesser amounts of gas retained each time. This pattern of ventilation aids not only in removing fluid from the lungs, but also ventilates all areas of the lungs. After birth, the fluid that remains in the lungs is either