Basic considerations for pediatric anesthesia

Anesthetic care of infants and children requires an understanding of the differences that exist between the adult and pediatric population with respect to anatomy, physiology, and pharmacology. It also requires attention to the unique psychology of the child and family, which has an effect on the conduct of anesthesia.Respiratory By approximately 24 weeks gestation, the lung has developed primitive gas exchange. Over 26 to 35 weeks of gestation, respiratory epithelial cells begin to form terminal sacs (which will later become mature alveoli), and the cells begin to differentiate and to produce surfactant. Mature alveoli develop beginning at 35 weeks gestation. At birth, children have approximately one sixth of their adult number of alveoli; this helps to explain the sensitivity of premature and newborn lungs to mechanical ventilation and other insults. The majority of alveoli are formed by the age of 2 years, and the adult number is reached by ∼8 years. Relative to body size, infant tidal volumes approximate adult values (7–10 ml/kg). Respiratory rate is higher to match the infant's greater oxygen consumption (6 ml/kg/min vs. 3 ml/kg/min in adults) and metabolic rate. (See Table 127.1 for normal pediatric vital signs by age.) The infant chest wall lacks rigidity, and the lung has poorly developed elastic fibers, which leads to less negative intrapleural pressure and predisposes to early airway closure and decreased functional residual capacity (FRC). Compensatory mechanisms are abolished by anesthesia, causing FRC to fall markedly. High compliance of the infant chest wall means that less positive airway pressure is required during mechanical ventilation. The infant's increased alveolar ventilation to FRC ratio and greater oxygen consumption results in faster oxygen desaturation during ventilatory depression. Lung mechanics approach the adult state by 1 year of age.