Neonates and infants have fewer and smaller alveoli, reducing lung compliance; in contrast, their cartilaginous rib cage makes their chest wall very compliant. The combination of these two characteristics promotes chest wall collapse during inspiration and relatively low residual lung volumes at expiration. The resulting decrease in functional residual capacity (FRC) limits oxygen reserves during periods of apnea (eg, intubation attempts) and readily predisposes them to atelectasis and hypoxemia.
Compared with older children and adults, neonates and infants have a proportionately larger head and tongue, narrower nasal passages, an anterior and cephalad larynx, a longer epiglottis, and a shorter trachea and neck. These anatomic features make neonates and young infants obligate nasal breathers until about 5 months of age. The cricoid cartilage is the narrowest point of the airway in children younger than 5 years of age.
Cardiac stroke volume is relatively fixed by the immature, noncompliant left ventricle in neonates and infants. The cardiac output is therefore very sensitive to changes in heart rate.
Thin skin, low fat content, and a greater surface area relative to weight promote greater heat loss to the environment in neonates. Heat loss can be made worse by prolonged exposure to an inadequately warmed operating room environment, administration of room-temperature intravenous fluid, and dehumidified anesthetic gases, and the effects of anesthetic agents on temperature regulation. Hypothermia has been associated with delayed awakening from anesthesia, cardiac arrhythmias, respiratory depression, increased pulmonary vascular resistance, and increased susceptibility to anesthetics and other agents.
Neonates, infants, and young children have relatively greater alveolar ventilation and reduced FRC compared with older children and adults. This greater minute ventilation-to-FRC ratio contributes to a rapid increase in alveolar anesthetic concentration that, combined with relatively greater blood flow to the brain, speeds inhalation induction.
The minimum alveolar concentration (MAC) for halogenated agents is greater in infants than in neonates and adults. In contrast to other agents, no increase in the MAC of sevoflurane can be demonstrated between neonates and infants. Sevoflurane appears to have a greater therapeutic index than halothane and is the preferred agent for inhaled induction in pediatric anesthesia.
Children are more susceptible than adults to cardiac arrhythmias, hyperkalemia, rhabdomyolysis, myoglobinemia, masseter spasm, and malignant hyperthermia associated with succinylcholine. When a child experiences cardiac arrest following administration of succinylcholine, immediate treatment for hyperkalemia should be instituted.
Unlike adults, children may have profound bradycardia and sinus node arrest following the first dose of succinylcholine without atropine pretreatment.
A viral infection within 2 to 4 weeks before general anesthesia and endotracheal intubation appears to place the child at an increased risk for perioperative pulmonary complications, such as wheezing, laryngospasm, hypoxemia, and atelectasis.
Temperature must be closely monitored in pediatric patients because of their greater risk for malignant hyperthermia and greater susceptibility for intraoperative hypothermia or hyperthermia.
Meticulous attention to fluid intake and loss is required in younger pediatric patients because these patients have limited margins of error. A programmable infusion ...