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A man with a murmur requiring nutritional support

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Q1: At presentation what diagnosis would you consider in this patient and how does this relate to the findings on examination of the cardiovascular system?

Severe abdominal pain with bloody diarrhoea raises the possibility of ischaemic colitis. Initially the symptoms are often disproportionately more severe than the findings on examination.1 The presence of a marked leucocytosis or metabolic acidosis often reflects the presence of necrotic bowel. In addition, a raised serum amylase may be found in the presence of small bowel infarction. In this patient, at laparotomy all bowel supplied by the superior mesenteric artery was necrotic, non-viable, and hence required resection. This patient was noted to have splinter haemorrhages, to be in atrial fibrillation, and to have a diastolic murmur. Subsequent investigations demonstrated an atrial myxoma as the cardiac source for the embolus that had occluded the superior mesenteric artery.

Q2: How are feeding and fluid requirements assessed in patients who have undergone intestinal resections and what plans should be made for nutritional support for this patient after laparotomy?

Patients with at least 80–100 cm of small bowel, particularly when the colon remains, can often manage to maintain nutrition with enteral support. However with only 20 cm of remaining small bowel this patient will require life long parenteral nutrition.2 A dedicated, single lumen, central line was inserted at the time of operation and parenteral nutrition feeding started immediately.

Q3: What has happened to the patient three months after surgery and what caused the carpopedal spasm?

Patients with short bowel experience problems with fluid loss and electrolyte imbalance due to severe diarrhoea. This patient developed acute renal failure as a result and required dialysis for one month in addition to intravenous correction of the hypovolaemia. Partial recovery of renal function occurred to a serum creatinine of 250 μmol/l. Patients with short bowel can also loose magnesium from the gastrointestinal tract. On admission, the patient was mildly acidotic and the serum magnesium concentration was 0.42 mmol/l, which was the cause of the carpopedal spasms. Serum calcium concentration was within the normal range. Correction was initially with intravenous magnesium and subsequently with life long oral supplementation. Magnesium oxide tends not to exacerbate diarrhoea in short bowel.3 In addition 1-α cholecalciferol, correcting secondary hyperaldosteronism (see discussion), and reducing lipid in diet are treatments for hypomagnesaemia. One possible cause of acidosis is d-lactic acidosis. This is caused by abnormal colonic bacterial production of the d isomer of lactic acid, which cannot be metabolised, in patients on a high carbohydrate diet. It is more common with coexistent thiamine deficiency and presents with ataxia, ophthalmoplegia, and nystagmus. Treatment is with antibiotics and a low oligosaccharide diet.

Discussion

Short bowel usually occurs after extensive resection of the small bowel. The commonest causes are Crohn's disease and vascular occlusion (arterial embolus, mesenteric vasculitis, or venous thrombosis). The need for parenteral nutrition after surgery depends on the length of remaining small bowel and whether a colon remains. If a colon remains, those patients with less than 50 cm of residual small bowel are likely to require long term parenteral nutrition. If a jejunostomy is present, those patients with less than 100 cm of small bowel can be expected to require parenteral nutrition. Nutritional status can be assessed and monitored by measures such as body mass index (weight (kg)/height (m)2; normal range 20–25 kg/m2) and mid-arm circumference. In addition, to malnutrition, patients experience fluid and electrolyte loss and may require parenteral supplementation. The diarrhoea can be reduced by the use of proton pump inhibitors which reduce gastric secretions, a low fat diet (in those patients with a colon), and motility reducing agent such as loperamide at higher than usual doses. Sodium loss from the gastrointestinal tract can be compensated for by drinking fluid with added salt (equivalent to World Health Organisation oral rehydration solution or approximately double concentrated Dioralyte), although when a colon remains the need for this is small. The hyponatraemia on admission in this patient reflected marked volume depletion due to gastrointestinal fluid loss. Hyponatraemia of this type is largely due to hypovolaemia stimulated antidiuretic hormone secretion rather than simple sodium depletion. Urinary sodium concentration is also a reflection of plasma volume, because it is determined by the activity of the renin-angiotensin-aldosterone system. A low urinary sodium concentration (<10 mmol/l) in patients with short bowel reflects ongoing hyperaldosteronism secondary to volume depletion and indicates the need for additional fluid supplementation. In addition to hypovolaemia due to fluid loss, other causes of renal failure such as obstructive nephropathy should be considered. Calcium oxalate renal stones can occur in patients with a retained colon due to increased colonic absorption of oxalate following ileal resection. Hypomagnesaemia, due to increased gastrointestinal loss is a common consequence of short bowel. The neuromuscular manifestations such as the carpopedal spasm usually occur in the presence of an acidosis as in this case. In addition, hypomagnesaemia can exacerbate other electrolyte disturbances such as hypokalaemia, hypocalcaemia, and hypophosphataemia. Serum magnesium concentration should be monitored in all patients with significant gastrointestinal disturbance. Parenteral nutrition for those patients, who require it, should be given via a dedicated single lumen central line. This has been shown to reduce the incidence of complications such as catheter related infections.4 Patients can be taught to care for central lines and manage their parenteral nutrition feeding at home. Many such patients, with appropriate support, undertake long term feeding for many years without complications or the need for line changes. The care of parenteral nutrition patients at home requires a multidisciplinary approach involving gastroenterologists, specialist nutrition nurses, biochemists, dietitians, and pharmacists. Further guidance on the management of patients with a short bowel can be obtained by reading a detailed review article.5

Final diagnosis

Cardiac embolus due to atrial myxoma producing extensive intestinal infarction leading to short bowel.

References

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