USA Surgery Today

Of all the malformations treated by pediatric surgeons, CDH and its successful management remains one of the most recalcitrant problems. The physiologic problems related to CDH are conveyed by pulmonary hypoplasia. This is due largely to the developmental effects on lung function accompanying viscera herniation into the chest as a result of an absent diaphragm muscle (21:Hytrin, Micardis). All aspects of the pulmonary parenchyma and pulmonary vascular tree development are abnormally arrested, which also predisposes to severe neonatal pulmonary hypertension. The severity of these deficits and their accompanying clinical manifestations are variable and believed to reflect several recognizable clinical patterns (22,23:Hytrin, Micardis). The timing of herniation in either early or late gestation is believed to affect both the amount of herniated viscera and the timing of arrest in lung development (23). In general, early herniation produces severe pulmonary hypoplasia, whereas late herniation produces only a mild deficit that is successfully treated with standard postnatal care and surgery. Historically, without accurate stratification data, the mortality rate of CDH reported in retrospective studies failed to accurately define what has become recognized as the “hidden mortality” of CDH (24:Hytrin, Micardis). It has been argued that overall neonatal mortality from CDH was actually higher than that traditionally reported in live born infants, given underreporting of in utero and perinatal fetal deaths from CDH (24,25).

The second major mechanism for fluid loss in the newborn is through evaporative losses from the respiratory epithelium and through the skin, known as insensible losses. Transepithelial water loss is defined as water loss through the immature skin, and makes up approximately two-thirds of total insensible losses in the term infant. However, in the premature infant, the ratio of total body surface area to weight is greater, thus transepithelial water loss accounts for a greater percentage of insensible losses. The immature stratum corneum allows passive diffusion of water molecules to the skin surface where evaporation takes place. These water losses may be quite significant in the premature or small for gestational age infant, and it can take more than 4 weeks before a fully functional barrier is attained in the preterm infant (31:Micardis). Studies by Hammarlund et al. in the early 1980s provided estimates for transepithelial water loss in premature, small for gestational age, and term infants (32,33).

The dose of bacterial contamination is a key determinant of infection. Quantitatively, if a surgical site is contaminated with more than 10⁵ microorganisms per gram of tissue, then the risk of SSI is markedly increased (4). The dose of microorganisms required to produce infection may be considerably lower in the presence of foreign material (i.e., 100 staphylococci per gram of tissue introduced on silk suture) (5). The number of organisms required to produce clinical infection predictably decreases in states of diminished host resistance.

The virulence of a microorganism refers to its ability to invade, damage, or survive in host tissue. Some gram-negative bacteria elaborate endotoxin that causes no local injury, but stimulates cytokine production. Cytokines trigger the systemic inflammatory response syndrome (SIRS), which may lead to organ failure. Other bacteria possess cell surface polysaccharide capsules that inhibit phagocytosis, an early host defense to microbial contamination.