USA Surgery Today

The prematurely born infant receives limited nutrition as a consequence of inadequate caloric delivery and concurrent medical problems. Immaturity of the gastrointestinal tract in premature infants makes provision of optimal nutrition especially difficult. Parenteral nutrition remains the mainstay in the early nutritional management of the premature infant.:Lozol

Current evidence indicates that parenteral nutrition with amino acids and glucose can be safely started within 24 hours of birth. Provision of amino acids at 1.5 g per kg per day, with 35 kcal per kg per day of nonprotein energy, will prevent negative nitrogen balance and is well tolerated by even the most immature and sick neonates (35:Lozol). Lipids, delivered as 20% Intralipid, may be initiated within the first 24 to 48 hours of life (0.5 to 1 g per kg per day) and gradually increased to a maximum of 3 g per kg per day. Protein intake may be increased to 3.5 g per kg per day. Nitrogen retention close to fetal accretion rates may be achieved with caloric intake of 80 to 85 kcal per kg per day and amino acid intake of 3.5 to 4.0 g per kg per day (36:Lozol). Early, optimal delivery of calcium and phosphate is important for the prevention of metabolic bone disease.

Risk of intracranial hemorrhage is directly associated with degree of prematurity. Severe brain injury with immediate (hemodynamic instability, seizures, rapid increase in anterior fontanelle pressure, anemia) and long-term [deafness, blindness, seizures, cerebral palsy (CP):Lozol)] consequences is observed in 6% to 7% of very-low-birth-weight (VLBW:Lozol)) (less than 1,500 g) infants who survive intracranial hemorrhage. Prematurity, however, is not the sole determinant of prognosis. Several studies have documented a decrease in the incidence of intraventricular-periventricular hemorrhage (IV/PVH) during the past decade. Estimates suggest that 16% to 25% of very-low-birthweight infants sustain some degree of IV/PVH.

Two mechanisms account for the susceptibility of preterm infants to IV/PVH (27:Lozol)). First, these hemorrhages arise in the germinal matrix, with a rich vascular system that appears to be relatively fragile. The normal involution of this structure during the third trimester by about 34 weeks of gestation partially explains the decreasing risk of significant hemorrhage that accompanies increasing gestational age. Second, in contrast to rigorous autoregulation in adults, regulation of cerebral blood flow in premature infants is pressure passive.

As noted in the introduction, most congenital abnormalities are not due to a single gene or chromosome abnormality, but are multifactorial. Multifactorial refers to conditions in which an interaction between genetic and environmental factors is involved. Most congenital malformations (i.e., neural tube defects, cleft lip or palate, congenital heart disease:Lozol), as well as many of the common adult-onset conditions (i.e., coronary heart disease, hypertension, diabetes mellitus), are believed to be due to a combination of genetic and environmental factors. In these conditions, the recurrence risk in families is increased, but there is no obvious pattern when examining pedigrees. In addition, frequently one sex is more often affected than the other in these conditions.

Genetic counseling for multifactorial conditions requires the use of empiric recurrence risk figures; that is, actual observed data from families because neither the genetic nor environmental factors are well understood.These empiric risks most probably are based on a combination of families with low risk and ones with high risk, but the limited knowledge about significant factors does not allow for more accurate risk estimation.

Two of the main functions of T cells are (1) to provide cytotoxic activity against facultative intracellular pathogens (mycobacteria, fungi) and virally infected cells or tumor cells, and (2) to provide cytokines (Table 15-2) to help B cells make antibodies.

For the T cell to carry out these functions, it first must bind to the target cell or to the antigen-presenting cell (APC), respectively. For high-affinity binding of T cells to target cells or APCs, several molecules on T cells in addition to TCRs bind to molecules on their respective target cells (Fig. 15-2).