Nonocclusive Mesenteric Ischaemia

Nonocclusive mesenteric ischaemia is bowel ischaemia caused by splanchnic vasoconstriction and low flow without an occluding thrombus or embolus. It is a disease of critically ill and elderly patients, and a delay in diagnosis is the main cause of death.

It accounts for 20% to 30% of acute mesenteric ischaemia, and mortality is 50% to 70%. Risk factors are low cardiac output (heart failure, cardiac surgery, shock), sepsis, haemodialysis with hypotension, vasopressors, digoxin, cocaine and ergot or similar vasoconstrictors, and abdominal compartment syndrome.

Pathophysiology.

Reduced cardiac output triggers splanchnic vasoconstriction (renin, angiotensin, vasopressin), which persists after cardiac output recovers. Mucosal ischaemia, reperfusion injury and bacterial translocation lead to transmural necrosis.

Abdominal pain (absent or poorly localised in a sedated patient), distension, ileus, bloody diarrhoea, unexplained acidosis, rising lactate and sepsis. Peritonitis is a late sign.

Red flags.

• Unexplained abdominal distension in a ventilated patient.
• Rising lactate or metabolic acidosis.
• Rectal bleeding.
• Peritonitis.

Keep a high index of suspicion in any at risk patient. CT angiography shows patent mesenteric arteries with narrowing of branches (string of sausages sign), bowel wall thickening or thinning, pneumatosis and portal venous gas. Lactate, creatinine and full blood count support the diagnosis but are not specific. Selective mesenteric angiography confirms and allows treatment.

Differential diagnosis.

• Mesenteric arterial embolism or thrombosis.
• Mesenteric venous thrombosis.
• Ischaemic colitis.
• Clostridioides difficile colitis.
• Perforated viscus.
• Acute pancreatitis.

Treat the cause: restore cardiac output and volume, treat sepsis, stop vasoconstrictors and digoxin where possible, and keep mean arterial pressure at 65 mmHg or more. Give selective intra-arterial vasodilator infusion by a catheter in the superior mesenteric artery when angiography shows vasospasm. Operate for peritonitis, with resection of non-viable bowel and second look surgery within 24 to 48 hours.

• Papaverine (intra-arterial): 30 to 60 mg bolus then 30 to 60 mg/h infusion through the superior mesenteric artery catheter for 24 hours, up to 5 days while angiography shows improvement; maximum 60 mg/h; monitor blood pressure, heart rate, catheter position and repeat angiography at 24 hours; reduce in hepatic impairment and give through a line separate from heparin, because they precipitate when mixed.
• Heparin (unfractionated): 80 units/kg IV bolus (maximum 5,000 units) then 18 units/kg/h, adjusted to an activated partial thromboplastin time of 1.5 to 2.5 times control; maximum bolus 5,000 units; monitor aPTT every 6 hours, platelets and bleeding; reduce with hepatic impairment and thrombocytopenia.
• Piperacillin-tazobactam: 4.5 g IV every 6 hours for 5 to 7 days (up to 14 days after resection with contamination); maximum 18 g daily; monitor renal function and counts; reduce for creatinine clearance under 40 mL/min.

Transfuse at haemoglobin 70 g/L (80 g/L with cardiovascular disease).

Monitoring. Lactate, haemoglobin, vital signs and abdominal examination every 4 to 6 hours; angiography at 24 hours of infusion.

Referral and escalation. Critical care, vascular and general surgery, interventional radiology.

Special groups. Patients on dialysis need review of dialysis related hypotension and ultrafiltration targets.