A 45 year old man had a non-emergency abdominoperineal resection for rectal cancer.

A 45 year old man had a non-emergency abdominoperineal resection for rectal cancer.

The rectal cancer was diagnosed by colonoscopy and the biopsy at the time revealed a poorly differentiated adenocarcinoma. He denies any symptoms of constipation, diarrhea, abdominal pain, or weight loss. He has had rectal bleeding but this is longstanding and unchanged over the previous 3 years, and previously was ascribed to haemarrhoids. He has no history of heavy alcohol intake, tobacco use, or illicit or therapeutic drug use. He does not have a family history of malignancy. He underwent APR without complication. Postoperatively his state was stable, but on day 3 he suddenly became short of breath without chest pain or palpitations. He is not sweating or nauseated.

PEx reveals a BP of 135/64 mm Hg, aregular pulse at 112 bpm. His respiratory rate is 32 bpm, with a temperature of 37.1°C and SaO2 of 89% (room air) and 97% (rebreather mask). Although mildly distressed, he is still speaks complete sentences without accessory muscles use. There are decreased breath sounds at the right lung base. Heart sounds show S1, S2, no murmurs and no gallops. Abdominal exam is unremarkable for a post op abdomen (soft, non-tender, slight distension, bowel sounds, clean non-tender midline scar. Allperipheral arterial pulses are palpable without oedema or tenderness in the lower extremities.

FBC, UEC and LFTs were normal. ABG showed pH 7.44, pCO2 31 mmHg and pO2 60 mmHg (SaO2 93%). There was bibasal atelectasis on CXR. Also an ECG and CT scan were performed.

The next day his hypoxia worsened and did not improve on increased oxygen delivery. He was intubated and transferred to ICU.

What is your diagnosis?
Why did it occur?
What is his prognosis?

Discussion
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