The premature neonate’s ratio of skin surface area to lean body mass is higher than that in an older infant or child. In the neonate, increased metabolic demands and the absence of a normal thermogenic shivering mechanism produce peripheral vasodilatation, resulting in rapid surface cooling and systemic hypothermia. This concern is particularly valid both in the stressed preterm infant, whose nutritional reserves are minimal, and when body cooling also leads to increased metabolism, which raises oxygen requirements. As heat loss continues, peripheral vasoconstriction occurs, with shunting of arterialized blood, increased lactic acid load, and eventually a profound metabolic acidosis.

Hypothermia is minimized by examining the infant under a radiant heat warmer and by exposing the infant only for short periods when it is essential. Particularly concerning is the infant with gastroschisis or omphalocele, because evaporative fluid loss compounds the hypothermia. The use of a warming mattress and supplementary radiant heating lamps are additional helpful measures to prevent hypothermia. Once the initial evaluation of the infant is complete, a humidified and warmed isolation incubator (Isolette) provides the best substitute for the uterus.

Careful attention must be given to the airway and lungs because hypoxemia, hypercapnia, and oxygen desaturation often occur in the face the of extrinsic compression of the airway or because of the pulmonary aspiration of salivary or gastrointestinal secretions. This complication may develop rapidly in babies with cervical cystic hygroma involving the floor of the mouth and paratracheal tissues, those with such thoracic problems as congenital diaphragmatic hernia, or those with esophageal atresia with tracheoesophageal fistula. Abdominal distention and upward displacement of the diaphragm also may restrict ventilation in babies with neonatal intestinal obstruction. This problem is particularly common with more distal obstruction, such as meconium ileus, and in babies with a large ovarian or duplication cyst or hydronephrotic kidney. Careful monitoring of respiratory status is essential to detect apneic spells. These risks are magnified in a preterm infant because of the intrinsic tendency to irregular respiratory patterns. Any tendency toward desaturation mandates continuous monitoring, use of supplementary oxygen, and (often) institution of nasal continuous positive pressure or placement of an endotracheal tube with intermittent mandatory ventilation. A primary example of the importance of careful respiratory monitoring is seen in a newborn with congenital diaphragmatic hernia with adequate ventilation at birth. Because of the tendency toward an accumulation of air in the herniated intrathoracic stomach or bowel, the contralateral lung rapidly becomes compromised. In these patients, a combination of peripheral oxygen saturation and arterial blood gas determinations is important to detect hypoxia or a rising carbon dioxide level. A mixed respiratory and metabolic acidosis is a common occurrence.

Many infants with cyanotic congenital heart disease, such as aortic stenosis or hypoplastic left heart syndrome, appear to be
perfectly stable at birth and begin to show evidence of deoxygenation after the ductus arteriosus closes 24 to 48 hours after birth. Increased resistance in the pulmonary vascular bed, such as occurs in infants with pulmonary hypoplasia and congenital diaphragmatic hernia, tends to keep the ductus patent and cause right-to-left shunting of deoxygenated blood into the systemic circulation. The infant with a noncardiac anomaly also may have increased pulmonary vascular resistance secondary to hypoxia, acidosis, hypothermia, and hypovolemia. Unnecessary delays in treating newborns with intestinal obstruction predispose such infants to pulmonary aspiration that will aggravate any underlying tendency to increased pulmonary vascular resistance.

At least one set of radiographic studies is obtained in any baby needing an abdominal or thoracic operation. Additional studies, including ultrasonography, CT, and MRI also may be useful.

The plain chest roentgenogram is diagnostic of the great majority of surgically correctable thoracic problems, including diaphragmatic hernia (Fig. 30.1), tension disturbances secondary to pneumothorax or hydrothorax, and even those lesions intrinsic to the lungs, such as lobar emphysema or congenital adenomatoid malformation. Caution must be exercised in distinguishing suspected congenital pulmonary cysts from a diaphragmatic hernia by obtaining an ultrasonography of the diaphragm or even by gastrointestinal contrast studies. Ventilation perfusion scans will give valuable information about the possibility of pulmonary hypoplasia in patients with diaphragmatic eventration, a condition that may be either congenital or secondary to brachial plexus birth injury.

Plain abdominal roentgenograms obtained in multiple views (i.e., supine, prone, and oblique) remain the gold standard in evaluating babies for intestinal obstruction, perforation, or a mass lesion. The oblique view is our choice for detecting free air with necrotizing enterocolitis. When such roentgenograms are repeated at 6-hour intervals, perforation with free air over the liver may be recognized before peritonitis is established and the baby becomes septic. Visualizing the number, distribution, and size of the dilated intestinal loops is very helpful in determining the site of obstruction. A diagnosis of duodenal stenosis can be facilitated by having the radiologist inject 30 or 40 cc of air through the nasogastric tube and then obtaining a prone view of the abdomen to best visualize a “double bubble.” When the etiology of duodenal obstruction remains uncertain, barium is introduced through the nasogastric tube to assess the location of the duodenum and thereby rule out malrotation, which can be associated with midgut volvulus. With more distal obstruction, the differential diagnosis among meconium ileus, ileal stenosis, meconium plug syndrome, and Hirschsprung disease can be confusing. Because plain films are nondiagnostic, a barium (or water-soluble contrast) enema should be carried out on an emergency basis. In many instances, the enema is therapeutic, but a submucosal biopsy must be obtained if Hirschsprung disease remains a diagnostic possibility.