Chapter 74: Pneumoperitoneum

I. PROBLEM

A pneumoperitoneum is seen on an abdominal radiograph. A pneumoperitoneum is an abnormal collection of free air in the peritoneal cavity. The air can be secondary to perforation of the gastrointestinal (GI) tract (most common, approximately 90% of cases) or from the respiratory tract, or it can be idiopathic with no known cause. Necrotizing enterocolitis (NEC) with perforation is the most common cause of a pneumoperitoneum in the neonate, and it carries a high mortality rate. Approximately 78.5% of pneumoperitoneums were secondary to NEC; therefore, a neonate with a pneumoperitoneum requires immediate evaluation and treatment because early recognition is important in successful management. It is important to note that a diagnosis of a pneumoperitoneum does not always imply a GI perforation. Careful assessment of each case can limit unnecessary laparotomies and their surgical complications.

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 40).

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

3. Were signs of necrotizing enterocolitis 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. Risk factors for NEC are gestational age <32 weeks, birth weight <1500 g, and enteral feeding.

4. Does the infant have any dysmorphic features or congenital anomalies? An infant with any dysmorphic features or congenital anomalies increases the likelihood that the perforation is GI in origin.

5. 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.

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

7. Were antenatal nonsteroidal anti-inflammatory medications used? Is the infant presently on steroids or indomethacin? These have all been associated with GI perforation.

8. Was an antenatal ultrasound done? Were any gastrointestinal anomalies detected? If an antenatal ultrasound showed any GI anomalies, then the pneumoperitoneum is more likely to be from a GI perforation.

9. Did the infant recently undergo abdominal surgery or an invasive procedure such as paracentesis? Intra-abdominal air is normal in the immediate postoperative period following abdominal surgery 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). It can also be secondary ...