Massive Pneumoperitoneum From Pulmonary Barotrauma: a Rare Complication

May 25, 2007
Volume 0, Issue 0

Rose Ayoob, Medical Student IV; Michael Subit, Medical Student IV; Bryan Richmond, Associate Professor of Surgery, West Virginia University School of Medicine, Charleston Division, Charleston, WV

Rose Ayoob, BS

Medical Student IV

Michael Subit, BS

Medical Student IV

Bryan Richmond, MD

Associate Professor of Surgery

West Virginia University School of Medicine

Charleston Division

Charleston, WV

The authors report a rare case of massive pneumoperitoneum resulting from barotrauma in a patient receiv-ing mechanical ventilation. Diagnostic peri?toneal lavage was successful in ruling out visceral perforation as a possible etiology of the free air observed on the patient's abdominal and chest radiographs. The authors discuss the pathophysiology of pneumoperitoneum and the various methods available to distinguish this benign phenomenon from a life-threatening intra-abdominal pathology.

Pulmonary barotrauma is a well-recognized complication of mech?anical ventilation in patients with acute lung injuries. It results from elevated airway pressures, and tension pneumothorax and pneumomediastinum are the most common sequelae.1 Pneumo?peritoneum occurs much less frequently and presents clinicians with a diagnostic challenge because it requires prompt diagnosis to rule out perforated viscus as the cause.2-6We report a case in which diagnostic peritoneal lavage was used to rule out a perforated viscus. This modality provided the necessary clinical information in a timely manner and spared the patient from other diagnostic tests or exploratory laparotomy.

Case report

A 65-year-old white man presented to the emergency department with marked confusion and new onset of dysarthria. His medical history was significant for alcohol abuse, hypertension, type 2 diabetes mellitus, a previous cerebrovascular accident, and hyperlipidemia. A computed tomography (CT) scan of his brain revealed a right frontal lobe ischemic cerebral infarction, and he was admitted to the hospital for neurological consultation. Soon after admission, he developed chest pain and dyspnea with elevated serum troponin levels, suggesting acute myocardial infarction. The patient subsequently underwent an uneventful cardiac catheterization with stenting of his right coronary artery. Shortly after stenting, his respiratory status began to decline and he was intubated due to progressively increasing oxygen requirements. Because of difficulties maintaining adequate oxygenation, it was necessary to titrate the patient's positive end expiratory pressure (PEEP) to 15 cm, during which he developed diffuse subcutaneous emphysema. Surgical consultation was required for placement of bilateral chest tubes. After?wards the patient developed increasing abdominal distention with hyperresonance to percussion. A chest radiograph revealed massive pneumoperitoneum (Figure).

Diagnostic peritoneal lavage was performed to rule out visceral perforation as the source of the free intra-abdominal air. A rush of air was noted upon entry into the peritoneal cavity. Lavage was performed and the extracted fluid was clear, nonfoul smelling, and had no particulate matter that would indicate ruptured viscus. In the days following the procedure, the patient's cardiovascular and respiratory status gradually improved and he was extubated. The remainder of his hospital stay was uneventful, except for a small retroperitoneal hematoma resulting from anticoagulation therapy. The hematoma was managed conservatively until the patient was discharged from the hospital approximately 2 weeks later.

Discussion

Pulmonary barotrauma is a well-recognized complication of elevated airway pressures associated with mechanical ventilation in patients with acute lung injuries.1 Tension pneumothorax and pneumomediastinum are the most common sequelae, with pneumoperitoneum occurring much less frequently.2-6 When identified in patients with elevated airway pressures, pneumoperitoneum presents the clinician with a diagnostic dilemma, necessitating prompt evaluation to rule out a perforated viscus, which is the etiology of 90% of cases.7,8

In mechanically ventilated patients, air enters the alveoli which may become overly distended and rupture, thereby re?leasing air into collateral spaces. Ac?cording to reports by Macklin and Macklin, air specifically migrates from the ruptured alveoli along the perivascular sheaths towards the mediastinum, which leads to mediastinal emphysema.9,10 With continuously increasing pressure, the gas can rupture through the mediastinal pleura, eventually causing pneumo-thorax.9,10 The air can also dissect downward retroperitoneally into the peritoneal cavity.9,10

Complications of pneumoperitoneum, if massive and under tension, include a decrease in central venous pressure, cardiac output, and mean arterial blood pressure secondary to an increase in intra-abdominal pressure with compression of the inferior vena cava.11 In addition, tension pneumoperitoneum reduces tidal volume, downwardly displaces the liver, which further restricts caval venous return, and, if unrelieved, may result in cardiovascular collapse.1

Diagnostic tests used to determine the etiology of pneumoperitoneum include abdominal CT scans, exploratory laparotomy or laparoscopy, and diagnostic peritoneal lavage. Abdominal CT scanning is valuable because it is noninvasive and shows intra-abdominal pathology with great specificity. It also allows solid organ injuries to be ruled out and is useful in demonstrating associated injuries involving the retroperitoneal organs; however, it is less appropriate for those who are unstable because it requires patients to be transported to the radiology suite. CT scanning is also expensive and requires proper interpretation to be effective. Its greatest limitation is that it is not particularly sensitive for diagnosing a perforated viscus, a fact well documented in the trauma literature. For this reason, we do not think CT scanning would have been helpful in our patient's case.

Exploratory laparotomy can also be used to diagnose pneumoperitoneum, but it is extremely invasive and expensive and carries the increased risks of bleeding and infection. It also has all the morbidity and mortality associated with a general surgical procedure. A review by Hillman found that 9 of 25 ventilated pa?tients with reported pneumoperitoneum underwent unnecessary laparotomies and 6 of those patients died.8 Obviously, if intra-abdominal pathology had been identified in our patient, laparotomy would have been promptly carried out as the definitive treatment. Since this was not the case, we thought that diagnostic peritoneal lavage?an equally sensitive but less morbid procedure?was most appropriate as the primary diagnostic maneuver.

Diagnostic peritoneal lavage is designed to detect the presence of intraperitoneal bleeding or contamination. It is still considered a valuable procedure, especially for trauma patients, due to its high sensitivity in detecting intra-abdominal injuries, which are reported to be as high as 90% to 100%.12 Llorens and colleagues suggested the therapeutic se?quence for pneumoperitoneum in this setting starts with diagnostic peritoneal lavage, stating that this method relieves any tension pneumoperitoneum if present and greatly reduces the likelihood of an unnecessary laparotomy.13 Diagnostic peritoneal lavage is useful in rapidly distinguishing ruptured viscus from barotrauma as the cause of pneumoperitoneum in patients who, like ours, are severely compromised and poor candidates for surgical exploration. It is especially helpful for patients with a history of abdominal surgery in whom a "second look" would increase the risk of infection, compromise hemodynamic status, or potentially worsen their respiratory status. When performing a diagnostic peritoneal lavage, it is important to remember to insert a Foley catheter in order to avoid injuring the urinary bladder.12

Relative contraindications to diagnostic peritoneal lavage include previous abdominal surgery with a scar in the midline and an abdominal wall hematoma.12 The rate of complications ranges from 0.9% to 6.0% and encompasses hematomas, separation or infection from the abdominal incision, incisional hernia, vascular laceration, omental laceration, or bowel perforation.12 Diagnostic peritoneal lavage's advantages are that it is inexpensive, minimally invasive, can be performed at the bedside, and causes relatively little discomfort. These are all important considerations when dealing with patients in an intensive care setting, which was the case with our patient. Disadvantages include the possibility of receiving false positives in patients who have had previous abdominal surgery and failure to show any retroperitoneal etiology of pneumoperitoneum.12 Although the latter is a hypothetical shortcoming, one could certainly theorize that if an ongoing process has caused entry of air into the free peritoneal cavity, irrigation of the peritoneal cavity should find contamination of the lavage fluid. Fluid obtained during diagnostic peritoneal lavage can be evaluated for particulate matter, red blood cell count, leukocyte count, amylase level, or bile content, and to confirm the presence or absence of gastrointestinal contents.14

Conclusion

Pneumoperitoneum associated with barotrauma is a rare complication of mechanical ventilation. Diagnosis can be expedited with the use of radiographic imaging, diagnostic peritoneal lavage, surgery, or based on clinical suspicion arising from physical examination findings. Diagnostic peritoneal lavage provides a rapid means of ruling out visceral perforation as the cause of pneumoperitoneum, thereby eliminating the likelihood of dangerous or unnecessary surgical exploration. In addition, it can rapidly correct cardiovascular and respiratory decline associated with a tension pneumoperitoneum if present. Diagnostic peritoneal lavage was the diagnostic test of choice for our patient because of its sensitivity in ruling out visceral perforation, which was a major concern, and because it could be performed at the patient's bedside with little discomfort and minimal risk. Diagnostic peritoneal lavage ultimately provided us with a wealth of clinical information in a highly efficient manner.

References

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