69: Pneumoperitoneum

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.

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.

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 in premature infants (spontaneous intestinal perforation [SIP]) or in the stomach (preterm and term infants); rarely occurs elsewhere in the GI tract.

      1. Spontaneous gastric perforation. Occurs most commonly between the 2nd and 7th days of life in both full-term and preterm infants. It is more common in males and African American babies. Infants present with sudden abdominal distension, respiratory distress, vomiting, lethargy, and a massive pneumoperitoneum. Perinatal stress, prematurity, and postnatal steroid use are risk factors. Many of these infants have sepsis.

      2. Spontaneous intestinal perforation (SIP). Occurs primarily in the terminal ileum (rarely in the jejunum and colon) in infants under 28 weeks' gestational age (GA), with low birthweight <1500 g (2–3%) and <1000 g (5%). Median age of presentation is 7 days, and it is more common in males. Prematurity and early steroid therapies are risk factors. Early postnatal exposure of indomethacin combined with steroids increases the risk of SIP. SIP is frequently associated with systemic candidiasis or coagulase-negative Staphylococcus. It does not have the clinical signs that NEC has (see Chapter 131).

      3. Spontaneous colonic perforations. These can occur but are very rare. They are more common in preterm infants and very difficult to diagnose. Signs include significant abdominal and scrotal distension, vomiting, cyanosis, respiratory distress, and tachypnea. Most infants have a massive pneumoperitoneum.

      4. Other perforations. Isolated perforations can occur elsewhere in the intestine, including the appendix, cecum, and Meckel diverticulum.

      5. Medications associated with spontaneous perforation include indomethacin and steroids. A meta-analysis of the effect of early treatment (<96 hours) with high doses of steroids for chronic lung disease showed an increased risk of spontaneous GI perforation. Gastro-duodenal perforation has been associated with steroid therapy. Combined therapy (early postnatal indomethacin and glucocorticoids) increases the risk of SIP.

      6. Other causes. Following exchange transfusion, perforation of small and large intestine can occur. Embolic phenomenon secondary to umbilical artery catheter can also contribute to perforation.

   2. Secondary perforations. These are caused by an underlying disease: obstruction in the gastrointestinal tract or secondary to a gastrointestinal disease process.

      1. NEC is the most common cause of secondary perforation. Mortality is high (>60%). Conflicting data exist on whether indomethacin increases the risk of NEC with intestinal perforation. The most common affected areas are the terminal ileum and ascending colon, although any part of the GI tract may be involved. Perforation occurs most commonly in the terminal ileum (ileocecal) region.

      2. Gastrointestinal obstruction. Causes increasing intraluminal pressure and the perforation occurs proximal to the obstruction. It can occur anywhere in the gastrointestinal tract. Causes include any gastrointestinal atresia (esophageal atresia with tracheoesophageal [TE] fistula, duodenal/pylorus atresia, small/large intestine or anal atresia, and others), meconium ileus/plug, duplication cyst, small left colon syndrome, obstructive bands, Hirschsprung disease, and anorectal malformations (imperforate anus, incarcerated hernia, and others). Bowel perforation occurs in ∽3–4% of infants with Hirschsprung disease.

      3. Gastritis or peptic ulcer disease. Perforation can be the initial presentation of ulcer disease. Perforations of the stomach (most common), duodenum, pylorus, or esophagus can occur.

      4. Other rare causes. Malrotation with midgut volvulus, omphalocele, ruptured appendix, gastroschisis, mesenteric thrombosis, perforated Meckel diverticulum, idiopathic gastric necrosis, and pneumatosis cystoides intestinalis.

   3. Traumatic perforations. An iatrogenic pneumoperitoneum caused by an intervention. Most gastric perforations are secondary to naso-/orogastric (NG/OG) placement or vigorous bag-and-mask/positive pressure ventilation.

      1. Normal transient finding following laparotomy or laparoscopy.

      2. Nasogastric tube trauma. Most gastric perforations are along the greater curvature due to trauma by vigorous NG/OG tube placement. Use of soft silastic feeding tubes may reduce this risk. An NG in an unusual position on x-ray (eg, right upper quadrant) indicates a possible perforation.

      3. Intubation trauma. During an intubation, the endotracheal tube (ETT) can be inadvertently placed in the esophagus and then through the posterior wall of the stomach. If the ETT on chest x-ray (CXR) is seen more distally than expected, consider intubation trauma.

      4. Bag-and-mask/positive pressure ventilation. Traumatic gastric perforation can occur from vigorous bag-and-mask ventilation or be due to positive pressure ventilation.

      5. Neonatal rectal perforations of the sigmoid colon or rectum can be caused by a rectal thermometer or rectal tubes. Because of the shape of the neonatal rectum, when a rectal thermometer is placed to a depth of 2 cm, it impinges on the anterior wall. Insert a rectal thermometer <2 cm. An attempt to push it any further may result in perforation. Enema-induced perforations occur in the anterior wall of the rectum or rectosigmoid.

      6. Improperly performed suprapubic bladder aspiration or paracentesis can perforate a hollow organ.

      7. Umbilical vein catheterization can cause perforation of Meckel diverticulum.

      8. Aerophagia (swallowing air) secondary to prolonged crying may cause gastric perforation. (There is a case report on an infant who had a circumcision with prolonged crying that may have caused a gastric rupture.)

2. Pneumoperitoneum associated with a respiratory disorder (eg, pulmonary interstitial emphysema [PIE], pneumomediastinum, or pneumothorax). A pulmonary air leak, with or without mechanical ventilation, can extend below the diaphragm resulting in a pneumoperitoneum. It can be secondary to barotrauma in ventilated neonates with severe respiratory disease. A thoracic leak can dissect transdiaphragmatically to the abdomen. An infant can have a pneumoperitoneum from thoracic air dissection without a pneumothorax or pneumomediastinum. Possibly an undetectable pulmonary rupture can occur with dissection into the peritoneal cavity. If there is a posterior pneumomediastinum, an air leak is probably the cause of the pneumoperitoneum.

3. Benign neonatal pneumoperitoneum with no known cause. There is no evidence of GI or respiratory pathology. Pulmonary rupture with a thoracic leak may not be apparent.

4. Pseudopneumoperitoneum. Occurs when there is a subphrenic lucency with no free intraperitoneal air. It can be from a subphrenic fat pad, linear atelectasis, abnormal subphrenic shape, subphrenic abscess, or Chilaiditi syndrome (interposition of a portion of the colon between the liver and diaphragm), which can present with respiratory distress. Gas can be seen between the liver and hemidiaphragm. This is gas-filled transverse colon. X-ray shadows can also cause a (false) radiographic pneumoperitoneum. A mimicked pneumoperitoneum includes a case report of transplacental passage of a nonionic contrast agent that resulted in opacification of the fetal bowel that mimicked a pneumoperitoneum.

1. Physical examination. Clinical evaluation may not help differentiate if the pneumoperitoneum is of respiratory or GI tract origin. The examination should focus on the pulmonary and abdominal aspects. Abdominal distention (most common sign) and elevation of the diaphragm with increasing respiratory difficulty are hallmarks of pneumoperitoneum. Other symptoms include bilious vomiting, tachypnea, rectal bleeding, and failure or delay to pass meconium. Is there respiratory compromise or unexplained tachypnea? Large amounts of air in the abdominal cavity can impair diaphragmatic excursion and lung compression. Cardiovascular compromise can occur secondary to compression of the vena cava and impaired venous return. Feeding intolerance and poor activity can also be present. Are there increased gastric residuals? Is there a bluish-black discoloration of the abdominal wall (with SIP but not NEC)? Scrotal swelling may indicate gastric perforation (pneumoscrotum). It can occur without significant abdominal distension. A pneumoscrotum can be secondary to a gastric perforation, perforation of Meckel diverticulum, perforation of ileum secondary to atresia, or after aggressive resuscitation or mechanical ventilation.

2. Laboratory studies

   1. Complete blood count (CBC) and serum electrolytes. Elevation of the white blood cell count or a left shift may signify a GI tract perforation. Hyponatremia can be seen with NEC secondary to third spacing of fluid. Thrombocytopenia also can be seen.

   2. Arterial blood gas levels. May reveal hypoxemia and increasing Pco₂ levels. Metabolic acidosis can be seen with peritonitis.

   3. Blood culture. Should be obtained if bowel perforation or sepsis is suspected. Infants with bowel perforation can have a positive blood culture. In one study, 18 out of 30 infants had a positive blood culture (Escherichia coli was the most common organism).

   4. C-reactive protein. Correlates with the inflammatory response and may be increased in NEC.

   5. Coagulation studies.

3. Imaging and other studies

   1. Transillumination of the abdomen with a cold fiber-optic light source, can be done and acts as a useful tool for diagnosis, especially if radiographs are not readily available.

   2. Radiographs. Small amounts of air can be missed on a routine film; some infants have air but it cannot be seen on x-ray. Repeat radiographs frequently if air is suspected. Simple observation of free air is often sufficient, particularly if the air leak is large (see Figure 11–22). Supine films (some infants are too sick for an upright) are usually done. A massive pneumoperitoneum suggests gastric or colonic perforation.

      1. Supine anterior-posterior radiograph of the chest and abdomen. The chest may show signs of air leak syndrome (pneumomediastinum or pneumothorax) if it is suspected that the intraperitoneal air is from the respiratory tract. The abdomen may show signs of NEC (pneumatosis intestinalis or portal venous gas; see Figures 11–23 and 11–24) or ileus. Air-fluid levels in the peritoneal cavity usually indicate ileus. SIP will have a pneumoperitoneum without pneumatosis intestinalis or portal venous gas. X-ray findings pathognomonic of a pneumoperitoneum:

         1. Right upper quadrant sign. The most common finding is the presence of right upper quadrant subdiaphragmatic free air (collection of gas in the right upper quadrant adjacent to the liver, gas in the anterior subhepatic space).

         2. Doge's cap sign. Air between the right kidney and liver. It is often the first sign and appears as an oval or triangular gas shadow.

         3. Cupola sign. An inverted cup-shaped lucency (dome) of air accumulation that appears over the lower thoracic spine near the posterior part of the heart.

         4. Rigler sign (double wall sign). Gas is seen on both sides of the bowel wall (the outer and inner walls of the bowel are seen). Normally only the inner wall of the bowel is seen. If the mean wall thickness of the bowel is >1 mm, it is a positive sign. If the thickness is ≤1 mm, it may be a false positive.

         5. Falciform ligament sign. Gas outlining the falciform ligament.

         6. Football sign. A large oval radiolucency (gas outlining the peritoneal cavity) in the shape of an American football. It can also include when the falciform ligament is seen in the center as a vertical strip surrounded by gas (the radiographic appearance of pneumoperitoneum outlining the falciform ligament was renamed falciform ligament sign; see previous text). It appears as a white streak, which is surrounded by the oval lucency of a pneumoperitoneum. The football sign is most frequently seen in infants with spontaneous or iatrogenic gastric perforation.

         7. Inverted V sign. Gas outlines the medial umbilical folds (umbilical arteries) on the supine radiograph.

         8. Saddle bag sign. Spleen and liver are displaced downward toward the midline.

         9. Arcade sign. Air is seen between bowel loops and creates triangular-shaped areas of gas.

         10. A gasless abdomen. May represent a perforation if there is no bowel gas to go into the peritoneal cavity (it is walled off).

      2. Left lateral decubitus radiographic study of the abdomen. With the right side up, it is the best examination for the detection of free abdominal air; air (seen as a homogeneous lucency or streak-like lucencies) is seen over the liver if a perforation has occurred. This is also done to show smaller leaks not appreciated on the anteroposterior (AP) abdominal film. A lateral decubitus radiograph should be serially taken when NEC is suspected. Lateral decubitus studies have been shown to be more sensitive in detecting a pneumoperitoneum than upright view studies.

      3. Upright view of the chest abdomen. This will show air below the diaphragm but is rarely done because of the difficulty in positioning a sick infant.

   3. Ultrasound or color Doppler ultrasonography of the abdomen can be used to diagnose NEC by visualizing pneumatosis intestinalis and portal venous air, and can be obtained to assess ascites. The presence of particulate matter probably indicates perforation. Complex ascites (ascites with debris) verifies bowel perforation. Extraluminal calcifications usually indicate intrauterine intestinal perforation with intraperitoneal extravasation of meconium. It can also be used to diagnose NEC. (Central echogenic focus with hypoechoic rim can indicate necrotic bowel or presence of intermittent gas bubbles in the portal venous system and liver). Color Doppler studies can detect bowel necrosis.

   4. Paracentesis, diagnostic. See Chapter 37.

      1. Air. Air obtained by paracentesis may be tested for its oxygen level. If the baby is receiving oxygen supplementation and the oxygen level is high (greater than room air, 0.21 Fio₂), the air is probably from a respiratory tract leak. If the oxygen if similar to room air or lower, the air is probably from the GI tract.

      2. Fluid (peritoneal lavage). Fluid may be obtained by paracentesis if the diagnosis is still undetermined. If green or brownish fluid is obtained, especially if bacteria are present on the Gram stain, the air is probably of GI tract origin. A microscopic smear of the fluid for white blood cells, if present, suggests peritonitis.

1. Emergency measures. For tension pneumoperitoneum, an emergency therapeutic paracentesis must be done to reduce the pressure and allow the diaphragm to mobilize (see Chapter 37).

2. General measures. Place a double-lumen tube (replogle) on low suction. This allows one lumen for drainage of fluid and the other as an air vent.

3. Sepsis evaluation and antibiotics if indicated.

4. Differentiate surgical from nonsurgical pneumoperitoneum to guide treatment. If the cause of the pneumoperitoneum is in doubt, attempts to distinguish pneumoperitoneum from GI perforation and that of pulmonary air leak can be done by the following:

   1. Contrast studies. A low-osmolality, water-soluble contrast medium (eg, metrizamide) can be given through a nasogastric tube. If there is a pneumoperitoneum secondary to a GI perforation, contrast material will pass into the peritoneal cavity and confirm the diagnosis. Barium should never be used because of the morbidity of barium peritonitis.

   2. Measurement of Po₂ in peritoneal air. See Section IV.C.4a.

   3. Presence of air leak in the chest. Increases the chance it is from an air leak.

5. Specific measures

   1. Pneumoperitoneum of GI tract origin. Stop all feedings, insert NG/OG tube to decompress the abdomen, provide supportive care (respiratory and circulatory support: correct hypoxia and acidosis, correct dehydration, correct any electrolyte disturbance), correct any coagulopathy, administer IV antibiotics, and call for an immediate surgical consult. Optimal surgical management is controversial. The debate is whether the infant needs to go to the operating room for a primary laparotomy or have primary peritoneal drainage. It is best to discuss options with the surgeon and make the decision based on each individual patient.

      1. Surgical management with exploratory laparotomy has been the traditional therapy. Unless the pneumoperitoneum is of a known iatrogenic origin (eg, postoperative), immediate surgical evaluation is often necessary. Exploratory laparotomy is often the treatment of choice. Preoperative management includes

         1. Preoperative laboratory values should be available.

         2. The infant should be stabilized as much as possible before being taken to the operating room.

         3. IV antibiotics should be started. Choice depends on the institution but should include broad spectrum antibiotics with anaerobic coverage.

         4. The surgical team may request a study with a water-soluble contrast medium given through the nasogastric tube to try to localize the perforation.

         5. Laparotomy with primary repair or laparoscopy. “Mini laparotomy” is a newer bedside option.

      2. Primary peritoneal drainage with conservative management is used selectively. Some suggest this for infants with the following: perforation without peritonitis, a normal abdominal examination or mild abdominal distension, normal blood gases and platelets, minimal free air, and no air-fluid levels on x-ray. Others suggest this for isolated perforations or for infants who may be too sick for anesthesia and surgery. Recent studies have shown that primary peritoneal drainage was more effective than primary laparotomy in infants with NEC. Conservative management includes

         1. NPO, fluids, and antibiotics. Make infant NPO, start IV fluids, total parenteral nutrition (TPN), blood transfusion if indicated, and IV antibiotics.

         2. Primary peritoneal drainage (PPD) (closed abdominal drainage) is done at the bedside; peritoneal drain is removed when the drainage resolves.

         3. Close observation and frequent physical examinations, serial radiographs, and follow-up laboratory evaluations are required.

         4. Delayed laparotomy may be required in many of these infants if they fail to improve clinically (increasing need for respiratory support, increasing inotrope requirement, increasing abdominal distension), or have persistent intestinal obstruction. Continued acidosis or free air that persists may also signify the need for laparotomy. Reviews have found that 38–74% infants required a delayed laparotomy.

   2. Pneumoperitoneum of respiratory tract origin. The pulmonary air leak should be treated first if this is the cause of the pneumoperitoneum.

      1. Asymptomatic patients. Observation is often the treatment of choice, with follow-up radiographic studies usually performed every 8–12 hours but more frequently if the patient's clinical course changes.

      2. Symptomatic patients. Emergency paracentesis can be performed with treatment of coexisting pneumothorax if present. Review the ventilator settings to avoid high pressures that will contribute to the problems.

   3. Traumatic pneumoperitoneum

      1. Pneumoperitoneum. A pneumoperitoneum caused by rectal thermometers, NG/OG placement, suprapubic bladder aspiration, umbilical venous lines, enemas, attempted intubation, or paracentesis may require surgical exploration.

      2. Postlaparotomy or laparoscopy. A pneumoperitoneum associated with an uncomplicated surgical procedure will resolve spontaneously over several days.

   4. Benign neonatal pneumoperitoneum with no known cause. Depending on the infant and his or her clinical examination, observation with conservative management, primary peritoneal drainage, or surgical exploration may be indicated.