Patient presents with symptoms suggestive of pneumoperitoneum, including abdominal pain, distension, and in some cases, shoulder pain referred from diaphragmatic irritation.  Physical examination may reveal abdominal tenderness, guarding, rigidity, and decreased or absent bowel sounds.  Depending on the underlying cause, signs of shock such as hypotension, tachycardia, and tachypnea may be present.  Imaging studies, specifically an upright chest X-ray or abdominal CT scan, are crucial for confirming the diagnosis of free air under the diaphragm, indicating pneumoperitoneum.  Differential diagnoses considered include perforated viscus, such as a perforated peptic ulcer or diverticulitis, bowel obstruction, abdominal trauma, and iatrogenic causes such as recent laparoscopic surgery.  Laboratory tests, including a complete blood count (CBC), comprehensive metabolic panel (CMP), and blood cultures, may be ordered to evaluate for infection, inflammation, and other systemic abnormalities.  The severity of pneumoperitoneum and the underlying etiology dictate the management plan.  Treatment options may include surgical intervention, such as laparotomy or laparoscopy, to identify and repair the source of the free air.  Conservative management with bowel rest, nasogastric suction, intravenous fluids, and antibiotics may be appropriate in select cases.  Patient monitoring for clinical deterioration, including serial abdominal examinations and repeat imaging, is essential.  ICD-10 code K66.0 is typically used for pneumoperitoneum, and CPT codes for associated procedures, such as laparotomy or laparoscopy, will vary depending on the specific surgical approach.  Accurate and detailed clinical documentation is crucial for appropriate medical billing, coding, and reimbursement.