Children have significantly different physiology and psychology and behavior to necessitate a comprehensive pediatric approach for the child and the family based on their requirements.
The percentage of total body composition that is water decreases with age; intracellular fluid increases, whereas extracellular fluid decreases.
Fat and muscle mass increase from 13% to 22% and 20% to 50%, respectively, with age.
The distribution of blood flow varies, with a decreased percentage of flow going to the vessel-rich groups with increased age.
Infants have a large tongue and relatively small jaw. Infants usually are described as having an anterior and cephalad displacement of the airway, with the narrowest segment at the level of the cricoid. The epiglottis generally is large and floppy compared with that of adults.
Younger children tend to experience airway closure and alveolar collapse with atelectasis because the end-expiratory lung volume from which tidal breathing occurs is close to closing capacity.
Although the functional residual capacity in milliliters per kilogram is smaller in infants compared with adults (30 vs 34), increased oxygen consumption is the major factor in the rapid desaturation of infants.
The perioperative risk of reversion to a transitional circulation is related to pulmonary hypertension triggered by hypoxemia, hypercarbia, hypothermia, acidosis, and increased catecholamines.
Cardiac output depends on heart rate in infants and young children. Infants have parasympathetic hypertonia, decreased sympathetic innervation, and a ventricle with less muscle and more noncontractile mass per unit volume. These all lead to a myocardium that is less able to generate adequate force than in adults.
A hematocrit nadir of approximately 35 at approximately age 3 months is the so-called physiologic anemia of infancy.
The glomerular filtration rate/1.73 m2 increases from 40 to 130 mL/min with age. Ability to concentrate urine is limited, and maximal osmolarity may be only 700 mOsm.
Slack lower esophageal sphincter tone with reflux is common in infants younger than 6 months, but the maintenance of low gastric volumes by nothing-by-mouth (NPO) regulations should be balanced by awareness of the risk of hypoglycemia.
The liver is functionally immature in children, affecting synthetic and metabolic function.
Defending the thermoneutrality of infants is a cornerstone of pediatric anesthesia.
Cold stress in neonates can increase oxygen consumption and decrease oxygen delivery, leading to increased hydrogen ion concentration and decreased glycogen and glucose. This may result in respiratory distress, disseminated intravascular coagulation, shock, and persistent fetal circulation.
The large surface-area-to-mass ratio in children and decreased subcutaneous tissue mass lead to increased heat loss via conduction, convection, radiation, and evaporation.
The large volume of distribution noted in neonates is related to decreased protein binding and a greater proportion of extracellular water.
In preoperative evaluation, the anesthesiologist should prepare himself or herself, the family, and the child for the procedure. The primary objective is to ensure that the child is in optimal condition. Developmental milestones and growth charts should be reviewed to assist in the general assessment of well-being. Optimal drug levels (eg, anticonvulsants and theophylline) should be ensured.
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