Thursday, August 28, 2008
I was involved in a quintessentially typical case of acute embolic mesenteric ischemia recently. This devastating disease is the bane of vascular and general surgeons. Despite all the advances of modern medicine, the mortality for acute mesenteric ischemia has remained 70-90% for over 25 years. Unfortunately, my patient was a victim of the statistics, expiring despite 48 hours of dogged perserverance by everyone involved in her care.
She was a 89 year old lady who presented to the ER with several hours of severe abdominal pain. Her history included atrial fibrillation (a-fib) but she had been taken off coumadin (blood thinner) because of persistent bleeding issues. In a-fib the heart flutters irregularly which predisposes one to the formation of blood clots in the atrium. These blood clots can fragment, shooting little pieces of clot into the general circulation, like surface to air missiles . The danger is that these clots (emboli) will lodge into a terminal artery branch causing ischemic damage to the tissues being supplied. Most commonly, the embolus will lodge in a branch of the cerebral circulation causing an embolic stroke. Alternatively, the embolus will occlude the superior mesenteric artery, just distal to the take-off of the middle colic artery. Other than the duodenum and the first foot or so of jejeunum, the SMA is the main blood supply of the entire length of the small intestine. SMA occlusions are more dangerous than heart attacks. 26 feet of dying bowel don't give you a lot of time to intervene.
My patient was classic. She had "pain out of proportion to physical exam". No peritoneal signs, but she couldn't get comfortable, needed dilaudud every 20 minutes. Her lactate was also elevated and her WBC count was over 20k. I sent her for a STAT CT angiogram which showed a classic cut-off of the SMA just distal to the middle colic branch. I called the OR. I called our vascular surgeon. But she was 89 years old. What were her chances, realistically? There's no answer to those kinds of questions, I have found. People always want numbers. What percent chance do I have? I try to be as honest as I can. There's no reason to bury the truth under a deluge of numbers and odds. Most people die from this problem I told the patient and her family. It's a tough spot we're in. At her age, the odds aren't good. The patient winced again. I motioned the nurse for more dilaudid. Try and fix it, she whispered. Try and fix it.
I looked at the CT again. There was no evidence of portal venous gas or pneumotosis (indicators of irreversible bowel necrosis). She hadn't yet developed peritoneal signs. Maybe if we....basically I talked myself into it. Try and fix it, she had said. So we went to the OR.
She had had multiple previous operations. I spent the first 30 minutes delicately, but as expeditiously as possible, sharply excising adhesions with the knife. Finally I was able to free up the transverse colon mesentery and I started the dissection of the SMA. The bowels were dusky and blue-hued, but lacked that distinctive scent of frankly necrotic bowel. But the clock was ticking. Every minute that passed led to progressive injury of the oxygen starved bowel. The SMA was isolated and controlled. The vascular surgeon then did the embolectomy with a Fogarty catheter, scooping out large chunks of blackened gelatinous clot. Pulsatile flow was re-established. The SMA was sewn up and the clamps were removed. We watched the bowel. Within seconds, the bruised, pallid appearance changed to a fleshy, vibrant pink. It was a sight to behold. But were we too late?
When you re-establish blood flow to an ischemic organ, you also return to the general circulation all the toxic metabolites that were generated during the state of oxygen deprivation. This is the "reperfusion injury" phase of the disease which is probably what greatly contributes to the high mortality rates we see even today. The anaerobic waste products incite a severe inflammatory response that can overwhelm even a healthy patient, let alone one who is 89 years old. In these situations, the safest course of action is to re-assess the bowels within 24 hours of reperfusion; the "second look laparotomy". The next morning, she was still on vasopressors and wasn't making as much progress as I would have liked. At the re-exploration, I was able to see why. Ten feet of bowel had progressed to frank gangrene; blood flow had indeed been re-established too late for this segment. I resected it. I checked the SMA again; good strong, pulsatile flow. To assess the seemingly viable remaining small bowel, I utilized the flourescein dye/wood lamp technique. You turn off all the lights except for the UV Wood's lamp and you can see the flourescein dye glowing trippily throughout all parts of the bowel that are well perfused. The lamp showed several other areas of bowel that were ominously dark. I took out some more bowel and closed her up. Later that night I took her back again for a final assessment. But the end game had set in. Now her stomach and left colon were starting to look dusky. The downward spiral was firmly entrenched. There wasn't anything more to do. I closed her back up and we made her DNR-CC. She expired several hours later....