Investigation

For patients with postoperative nausea and vomiting, firstly check patients drug therapy:

• look for possible drug interactions. Also be aware of interactions of different therapies, e.g. if an elderly patient is on iv fluids and diuretics then they may develop hypokalaemia - if they are also on digoxin then the hypokalaemia may precipitate drug toxicity
  
  
• look for features of obstruction, vomiting, abdominal pain, absolute constipation of flatus and faeces, abdominal distension, succussion splash, absent bowel sounds. If intestinal obstruction is cause of vomiting then the onset gives clues as to whether it is paralytic or mechanical obstruction.
  
  
• if the nausea and vomiting has just started after the onset of oral fluids after abdominal surgery then this is likely to be due to persistent paralytic ileus - abdominal distension and absent bowel sounds should be searched for
  
  
• if the nausea and vomiting occur after the patient has tolerated oral fluids then obstruction is likely to be mechanical - fibrinous adhesions, intussusception, volvulus. Characteristically there is colicky abdominal pain, localised tenderness, active bowel sounds.
  
  
• abdominal X-ray will reveal the site of obstruction (supine) and fluid levels (erect). A paralytic ileus will show generalised bowel distension. Mechanical obstruction will generally be large bowel - haustra do not go all the way across the large bowel, caecum is the first part to dilate - or small bowel - plica circulares go all the way across the small bowel, the loops of bowel are central and folded.