A 68-year-old white man presented to our Emergency Department with sudden onset of upper abdominal pain and vomiting 8 days after undergoing an elective hepatic resection via a bilateral subcostal incision. He had been discharged home the day before following an uneventful hepatic bisegmentectomy (4 and 5), cholecystectomy, and extensive perihepatic adhesiolysis for a metachronous colon cancer metastasis. His past history was significant for a transverse colectomy with end colostomy and mucous fistula 2 years earlier for an obstructive, moderately differentiated, Stage IIIC (pT3pN2b) adenocarcinoma. His recovery from the colorectal surgery was complicated with surgical site infection and fascia dehiscence requiring three reoperations. Adjuvant leucovorin, fluorouracil, and oxaliplatin (FOLFOX) chemotherapy was completed without significant side effects and the colostomy was reversed. An initial examination revealed that he was alert, body mass index (BMI) 25.6 kg/m2, mildly pale, afebrile, and dyspneic, with hemodynamic instability (blood pressure 90/60 mmHg, heart rate 112). His recent bilateral subcostal incision had been closed with skin staples and was healing without complications. Surgical scars from former bilateral stomas and midline laparotomy were normal. His abdomen was tender upon palpation of the right upper quadrant. Laboratory findings included: hemoglobin 8.9 g/dL; lactate 3.3 mmol/L; and creatinine 1.83 mg/dL. Arterial blood gas values showed: pH 7.30, partial pressure of carbon dioxide (pCO2) 27 mmHg, partial pressure of oxygen (pO2) 95 mmHg, and bicarbonate (HCO3) 13 mmol/L (on 3 liters of supplemental oxygen per minute). Hypotension and tachycardia promptly responded to intravenous volume expansion with 2 liters of normal saline and 2 units of packed red blood cells, but no urine output was present. A triphasic computed tomography of his abdomen was obtained, and a small to moderate volume hemoperitoneum (predominantly in the lesser sac and perihepatic regions) was identified. Celiac arteriography also defined a small bleeding branch of his right hepatic artery, which was arrested with selective transcatheter arterial embolization. He remained hemodynamically stable after the procedure, and he was admitted to our Surgery Unit. Four hours following presentation, he complained of mild upper abdominal pain and presented minimal urine output, but he was otherwise comfortable on 3 liters of supplemental oxygen per minute, intravenous crystalloids, and analgesics. Laboratory results showed: hemoglobin 11.2 g/dl, creatinine 1.8 mg/dl, pH 7.30, pCO2 32 mmHg, pO2 81 mmHg, and HCO3 16 mmol/L. Over the subsequent 24 hours, his hemodynamic and hematologic parameters remained stable, but his urine output was still minimal, and he developed worsening upper abdominal pain and respiratory failure. A physical examination revealed a tense abdomen with signs of associated ventilatory restriction. Laboratory results showed: pH 7.43, pCO2 34 mmHg, pO2 80 mmHg, HCO3 23 mmol/L (on 15 liters per minute of supplemental oxygen on high flow mask), lactate 2.4 mmol/L, and creatinine 4.86 mg/dL. In this setting of abdominal distension with evolving restrictive respiratory failure, and acute kidney injury, an IAP measurement of 21 mmHg was obtained via a three-way urinary catheter, by the end of expiration, and in the absence of abdominal contractions. Sustained IAH was confirmed by repeated IAP measurements and a diagnosis of ACS was made, approximately 28 hours from readmission. He was promptly transferred to our Intensive Care Unit to receive sedation and ventilatory support; follow-up IAP measures at 21 mmHg were again obtained. The mechanics of IAH were felt to be poorly explained by such a limited volume of intra-abdominal fluid (estimated on computed tomography to be far less than 2 liters), but considering the imaging findings of a dominant central collection of blood clots in his lesser sac and accelerated clinical deterioration, surgical decompression was indicated. Within 2 hours following the diagnosis of ACS, surgical decompression was performed. A surgical approach through his recent bilateral subcostal incision allowed direct access to his hemoperitoneum, which was confined to the recently dissected perihepatic region. The remaining peritoneal space was completely obliterated with firm adhesions and defined to be surgically inaccessible. A total of 1.2 liters of blood clots and ascites under significant pressure were evacuated. Dramatic improvement in his ventilatory pressure was immediate (peak airway pressures decreased from 37 cmH2O to 20 cmH2O; tidal volumes increased from 120 ml to 450 ml). The surgical site was irrigated with saline, the fascia was left open, and a negative pressure device was placed for temporary abdominal closure. After the operation he was returned to our Intensive Care Unit, and extubation was possible within 24 hours, in the presence of normal hemodynamics and improving renal function (urine output >1 ml/kg/minute; creatinine 2.86 mg/dl). The fascia was formally closed within 48 hours without complication. Renal replacement therapy was not necessary, and he was discharged home the following week.