Chronic digitalis administration alters mesenteric vascular reactivity

Ischemic bowel syndromes

Atherosclerotic vascular disease involving the mesenteric arteries occurs frequently in the elderly population. Although the prevalence of ischemic bowel disease is difficult to determine, acute mesenteric ischemia (AMI) has been reported to cause in 1 in 1000 hospital admissions, whereas chronic mesenteric ischemia (CMI) is estimated to affect 1 in 100,000 individuals. Mesenteric ischemia generally manifests in its chronic form as postprandial abdominal pain resulting in significant weight loss, and in its acute form as an abrupt development of abdominal pain, lower gastrointestinal bleeding, and subsequent intestinal necrosis. This article discusses the cause, clinical manifestations, diagnosis, and management of AMI and CMI.

Anesthetic management of acute mesenteric ischemia in elderly patients

Ischemic insult to the splanchnic vasculature can jeopardize bowel viability and lead to devastating consequences, including bowel necrosis and gangrene. Although acute mesenteric ischemia (AMI) may occur at any age, the elderly are most commonly affected due to their higher incidence of underlying systemic pathology, most notably atherosclerotic cardiovascular disease. Treatment options include pharmacology-based actions, endovascular, and surgical interventions. AMI remains a life-threatening condition with a mortality rate of 60% to 80%, especially if intestinal infarction has occurred and surgical intervention becomes emergent. Early recognition and an aggressive therapeutic approach are essential if the usually poor outcome is to be improved. Anesthetic management is complex and must account for comorbid disease as well as the patient's presumptive acute deterioration. Blood pressure support typically involves careful, but often massive, fluid resuscitation and may also additionally require pharmacologic support.

Ischemic colitis during treatment with alosetron

Irritable bowel syndrome (IBS) is one of the most common entities observed by both primary care physicians and gastroenterologists. Alosetron is a potent and selective serotonin antagonist that recently became the first Food and Drug Administration-approved agent for diarrhea-predominant IBS. However, since approval, significant side effects have been noted with the use of alosetron including severe constipation, fecal impaction, and ischemic colitis. We describe a case of ischemic colitis in a male patient with IBS who was briefly treated with alosetron. Clinical, endoscopic, and pathologic features of the focal colitis strongly suggested ischemia. Symptoms correlated temporally with alosetron use, and symptoms abated with discontinuation of the drug. Endoscopic and pathologic resolution of the colitis were documented.

Intestinal (mesenteric) vasculopathy. I. Acute superior mesenteric arteriopathy and venopathy

Intestinal vasculopathy is not rare, comprising about 1 per 1000 hospital admissions. Primary mesenteric vasculopathy causes cardiovascular disease, whereas secondary mesenteric ischemia causes extrinsic vascular compression or vascular trauma. Acute superior mesenteric arteriopathy is caused by a mesenteric embolus, thrombus, or vasospasm (i.e., nonocclusive vasculopathy). Acute superior mesenteric venopathy is caused by a thrombus, which is often associated with a hypercoagulopathy. The clinical presentation of both diseases is often subtle and nonspecific at an early stage and becomes overt and specific only when advanced and severe, when ischemia progresses to necrosis. The mortality of acute superior mesenteric arteriopathy is still very high, whereas superior mesenteric venopathy is less rapidly progressive and has a lower, but still significant, mortality. Early diagnosis and aggressive therapy significantly reduces the mortality of these life-threatening diseases.

Abdominal vascular catastrophes

Abdominal vascular catastrophes are due to rupture of arterial aneurysms or arterial occlusion leading to end organ ischemia. In this article, we will discuss rupture of abdominal aortic aneurysms and visceral artery aneurysms. Arterial occlusion secondary to embolism, thrombosis and dissection will be presented. Mesenteric ischemia secondary to low flow states, venous thrombosis and other conditions will also be covered. These uncommon, but frequently fatal pathological processes, are of interest to both general and vascular surgeons.

Nonocclusive mesenteric ischemia

NOMI remains a challenging clinical entity that demands a heightened index of suspicion and an aggressive diagnostic and treatment strategy in order to avoid the untoward sequela of short bowel syndrome and to achieve survival. Early arteriographic diagnosis and prompt institution of vasodilator therapy have proven successful in reducing the high (70% to 90%) mortality rate observed through the 1980s to 50% to 55% during the last decade. Continued investigations into the pathophysiologic mechanisms underlying splanchnic vasospasm and intestinal IR injury will, it is hoped, add more alternate and effective therapies to the current armamentarium.

Acute mesenteric ischemia

The morbidity and mortality of acute mesenteric ischemia have remained high over the past 30 years despite heightened sensitivity to the diagnosis. Because the duration of the ischemic episode is the most significant determinant of outcome, an aggressive diagnostic and treatment protocol must be maintained. Although this stance may precipitate a number of negative angiographic studies, such an approach is the only opportunity for salvage in these critically ill patients.

Comparison of sufentanil/propofol versus isoflurane/nitrous oxide anaesthesia on mesenteric artery blood flow

Duplex sonography was used to determine the changes in mesenteric arterial blood flow occurring in patients undergoing aortic surgery, anaesthetised either by total intravenous anaesthesia with propofol and sufentanil (group A) or inhalational anaesthesia with isoflurane and nitrous oxide (group B). Sixteen patients were studied. Measurements were performed immediately before and 15 min after induction of anaesthesia, before surgery. There was a 38% decrease (p = 0.015) in the superior mesenteric artery end diastolic velocity in group A and a 23% decrease (p = 0.033) in the superior mesenteric artery peak systolic velocity in group B. There were no changes in any of the other sonography parameters in either group. We conclude that neither total intravenous anaesthesia with propofol and sufentanil nor inhalational anaesthesia with isoflurane and nitrous oxide have any clinically significant influence on mesenteric blood flow in the absence of surgical stimulation.

Effects of digoxin on the anabolic response to clenbuterol

The possible involvement of increased cation exchange in the anabolic response to the beta 2-selective adrenergic agonist clenbuterol was investigated using dietary admixtures of clenbuterol and the Na,K-adenosine triphosphatase (ATPase) inhibitor digoxin. In a rat feeding trial to assess the effects on body composition, it was found that the higher of two levels (5 and 30 mg/kg diet) of digoxin had an inhibitory effect on the repartitioning effects (ie, increased body weight and fat-free mass) of clenbuterol (2 mg/kg diet). In two further experiments using 30 and 60 mg digoxin/kg diet, it was found that the anabolic effects of clenbuterol on gastrocnemius muscle protein deposition were inhibited by digoxin, but the effects of clenbuterol on soleus muscle protein were more resistant to inhibition. Given the observed dose-dependent inhibition by digoxin of gastrocnemius muscle protein deposition in the three experiments, it was concluded that at least part of clenbuterol's anabolic actions on skeletal muscle may depend on increased Na,K-ATPase activity. However, different mechanisms or a different time course of Na,K-ATPase activation may occur in different muscle fiber types.

Acute mesenteric ischemia: pathophysiology, diagnosis, and treatment

Ischemia has traditionally been viewed as arising only from abnormalities of oxygen dynamics, namely the cellular hypoxia resulting from the imbalances between oxygen supply, consumption, and demand. Recently, it has become clear that such a view is too restrictive. Hypoperfusion may be caused by both anatomic and functional impediments to either inflow or to outflow from an organ. Furthermore, the pathophysiologic consequences are likely to involve not only cellular hypoxia, but also a restricted supply of nutrients and other important molecules and an abnormal elimination of physiologic wastes such as carbon dioxide. Hence the recommendation that ischemia be defined as a dual defect of oxygen deficit and carbon dioxide excess. AMI is, therefore, a severe anatomic or functional impediment to the splanchnic circulation, resulting in a dual defect of intestinal hypoxia and cellular hypercarbia. Although the functional and structural consequences of cellular hypoxia are well known, the pathophysiology of cellular hypercarbia has only begun to be explored. AMI syndromes include three related processes: occlusive mesenteric ischemia, nonocclusive ischemia, and sepsis-induced SI. Leakage of bacteria or bacterial toxins into the circulation during mesenteric ischemia forms the basis of the systemic components of this syndrome. Striving for an earlier diagnosis, treating the systemic (septic) consequences, and taking measures to promptly restore mucosal oxygen balance through aggressive pharmacologic and appropriate surgical intervention have significantly improved the prognosis. About 80% of patients with acute arterial embolism, 60% of those with nonocclusive ischemia, and only 20% of patients with arterial thrombosis are expected to live without significant residual nutritional deficits. The cause of death is usually sepsis and multisystem organ failure, and therefore, further reductions in mortality are likely to occur with the improved prevention and treatment of sepsis.

Limiting oxygen delivery attenuates intestinal reperfusion injury

Since free radical-mediated injury is dependent on the reintroduction of oxygen into ischemic tissues, restriction of oxygen content in the initial reperfusate has therapeutic potential. The degree to which oxygen must be restricted is crucial since hypoxic injury would continue if reperfusion O2 delivery remained below the ischemic threshold of the tissue. We examined this treatment strategy in 20 pump-perfused intestinal preparations subjected to 30 min of flow interruption. The oxygen content of the reperfusate was varied by utilizing arterial (A) or venous (V) blood; as a further modification, we also performed experiments in which hemodiluted arterial blood (HD) was the reperfusate at normal (NHD) and high (HHD) flow rates. The flow rates and O2 contents of the reperfusates were adjusted to produce either high (approximately 12 ml O2/min/100 g) or low (approximately 8 ml O2/min/100 g) levels of O2 delivery. Histologic sections, obtained after ischemia and after 1 hr of reperfusion, were blindly evaluated for mucosal injury (1 = normal to 5 = severe injury). Immediately after 30 min of ischemia, all groups had comparable histologic grades (A 2.0 +/- 0.3, V 1.8 +/- 0.3, NHD 1.6 +/- 0.3, HHD 2.3 +/- 0.3). One hour after reperfusion, intestines reperfused with blood with high O2 content and hence high O2 delivery showed significantly more damage (P < 0.001) than those with exposed to low O2 delivery during reperfusion: A 3.9 +/- 0.5 and HHD 4.4 +/- 0.4 versus V 2.7 +/- 0.5 and NHD 2.9 +/- 0.3.(ABSTRACT TRUNCATED AT 250 WORDS)

Intermittent ischemia potentiates intestinal reperfusion injury

We hypothesized that even brief periods of reperfusion interjected between ischemic episodes would increase tissue injury. Studies were performed in a rat small intestine preparation in which metabolic, hemodynamic, and histologic responses to ischemia have been well characterized. Animals were subjected to a total of 30 or 45 minutes of complete intestinal ischemia. Flow interruption was continuous (C, single episode) or intermittent (I, two or three episodes of 15-minute ischemia separated by 5 minutes of reperfusion). In some experiments 5-minute reperfusions were performed with arterial blood depleted of leukocytes (IL). This additional perturbation was included to determine the role of neutrophils that have been strongly implicated in reperfusion injury. In all three protocols histologic sections were obtained after each ischemic insult and after 1 hour of reperfusion with arterial blood. Villous histology was graded in a blinded fashion with 1 = normal and 5 = severe injury. No significant differences were found between groups in immediate postischemic histologies before reperfusion. After 1 hour of reperfusion, intermittent episodes of ischemia were associated with significantly worse histologic injury than that seen with comparable durations of continuous ischemia (30 min: I, 4.4 +/- 0.5 vs C, 2.7 +/- 0.4; 45 min: I, 4.9 +/- 0.2 vs C, 2.8 +/- 0.3). However, if 5-minute reperfusions were with leukopenic blood, this effect was markedly reduced (30 min IL, 3.4 +/- 0.3; 45 min IL, 3.6 +/- 0.2). Even short periods of reperfusion during an ischemic insult greatly increased mucosal injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucagon potentiates intestinal reperfusion injury

Vasoactive agents, including glucagon, have been used in treatment of mesenteric ischemia. Such drugs change both intestinal blood flow and metabolism. Since reperfusion injury reflects the metabolic state of an organ as well as the duration and severity of ischemia, we investigated the effect of glucagon in a standard model of intestinal ischemia. Data were generated from denervated isoperfused rat small intestinal preparations (n = 39). Arterial and venous pressures, intestinal blood flow, and oxygen consumption were monitored. Animals were subjected to 15, 30, or 45 minutes of ischemia followed by 1 hour reperfusion. Experiments were performed without drug infusion or during intravenous glucagon administration (0.1, 0.2, or 0.4 micrograms/kg/min). After the rats were killed, histologic sections of intestine were graded 1 through 5 in a blinded fashion with 1 = normal villi and 5 = severe injury. Results (mean +/- SD) were analyzed by analysis of variance (*p less than 0.05). Glucagon at all concentrations increased intestinal blood flow and oxygen consumption before ischemia. For example, with 0.2 micrograms/kg/min glucagon, intestinal blood flow increased from 80.78 +/- 13.5 to 114.79 +/- 21.02 ml/min.100 gm* and oxygen consumption increased from 3.65 +/- 0.73 to 5.73 +/- 1.37 ml/min.100 gm.* Mucosal injury after ischemia reflected duration of ischemia and glucagon infusion rate. At all ischemic intervals, increased glucagon concentrations were associated with greater mucosal injury. In fact the histologic injury with 15 minutes of ischemia + 0.2 microgram/kg/min glucagon (3.04 +/- 0.49) exceeded that of 30 minutes of ischemia (2.87 +/- 0.06).(ABSTRACT TRUNCATED AT 250 WORDS)