What is the cause of this patient abdominal distension?
Bowel obstruction. Both large and small bowel loops are dilated.
What type of bowel obstruction is it?
Given the clinical situation (post cardiac surgery and admitted in ICU) pseudo-obstruction would be a reasonable suggestion given that both large and small bowel loops are dilated. But there is gas projecting in the left inguinal region, which is highly suspicious for an inguinal hernia containing bowel and subsequently a mechanical bowel obstruction.
Multiple dilated loops of small and large bowel consistent with obstruction. Locule of gas seen to overlie the left obturator foramen would suggest left inguinal hernia as the cause.