69: Pneumoperitoneum

I. PROBLEM

A pneumoperitoneum (an abnormal collection of free air in the peritoneal cavity) is seen on an abdominal radiograph. The air can be secondary to perforation of the gastrointestinal (GI) tract (most common), from the respiratory tract, or secondary to iatrogenic causes. Necrotizing enterocolitis (NEC) with perforation is the most common cause of a pneumoperitoneum in the neonate. A neonate with a pneumoperitoneum requires immediate evaluation and treatment, as early recognition is important in successful management.

II. IMMEDIATE QUESTIONS

1. Is a tension pneumoperitoneum present? An emergency situation, this occurs when there is a large amount of air that impairs diaphragmatic excursion. A tension pneumoperitoneum can cause significant lung compression, severe respiratory distress, compression of the vena cava, and impaired venous return with cardiovascular compromise. If present, an emergency therapeutic paracentesis should be done (see Chapter 37).

2. Are signs of pneumoperitoneum present? These findings can include abdominal distention (most common sign), respiratory distress, deteriorating blood gas levels, and a decrease in blood pressure.

3. Were signs of necrotizing enterocolitis (NEC) present before? If so, the pneumoperitoneum is most likely to be associated with GI tract perforation. Bowel perforation typically occurs at a median interval of 1 day after clinical presentation of NEC.

4. Are any signs of air leak present? If a pneumomediastinum, pulmonary interstitial emphysema, or pneumothorax is present, the peritoneal air collection may be of respiratory tract origin.

5. Is mechanical ventilation being used? High peak inspiratory pressures (PIPs) greater than a mean of 34 cm H₂O can be associated with a pneumoperitoneum.

6. Did the infant recently undergo abdominal surgery or an invasive procedure such as paracentesis? Intra-abdominal air is normal in the immediate postoperative period and usually resolves without treatment. Paracentesis can perforate a hollow organ.

III. DIFFERENTIAL DIAGNOSIS

A pneumoperitoneum most commonly develops secondary to perforation of the GI tract (spontaneous, secondary from underlying GI disease, or traumatic), from the chest (respiratory causes: air leak with or without mechanical ventilation), or from no known cause (no respiratory or GI cause found), or a normal immediate postoperative finding. In a neonate, unless the infant is on high ventilator settings and has an air leak the cause is GI perforation until proven otherwise. Some classify pneumoperitoneum into medical (nonsurgical) versus surgical.

1. Pneumoperitoneum associated with GI perforation

   1. Spontaneous perforation. (No demonstrable cause: no obvious gastrointestinal disease, no evidence of trauma or obstruction.) This is the second most common cause of GI perforation in neonates (most common is due to NEC). Proposed etiologies include local ischemia in the perinatal period (from asphyxia or shock) or from noncommunication of right and left gastroepiploic arteries, trauma during pregnancy or delivery, sepsis, prematurity, excessive gastric acidity, lack of intestinal cajal cells (gastric perforation), maternal use of steroids or cocaine, or congenital defects in the muscular wall of the stomach. Spontaneous perforation occurs most commonly in the terminal ileum ...