Pathogenesis of nonocclusive ischemic colitis

Influence of perioperative risk factors on the development of transmural colonic ischemia after open repair of ruptured abdominal aortic aneurysm

BACKGROUND

Development of colonic ischemia (CI) after ruptured abdominal aortic aneurysm (RAAA) treatment is a lethal complication with perioperative mortality reported to be high as 50%. Therefore, the main goal of this study was to identify pre-, intra- and postoperative risk factors associated with CI in patients undergoing open repair (OR) due to RAAA, that might help to select patients who are more prone to develop CI.

METHODS

This was a single-center prospective cohort study on patients with RAAA undergoing OR between January 1st 2018 and July 1st 2019, at the Clinic for Vascular and Endovascular Surgery, Clinical Center of Serbia. During this period 89 patients were treated due to RAAA and all were included in the study. The primary endpoint was grade III CI, or transmural necrosis, diagnosed by laparotomy.

RESULTS

Out of 89 patients operated due to RAAA, CI was diagnosed in 14 (15.73%). During the operation, patients with CI had a longer duration of hypotension (42.86±35.82 vs 24.13±23.48, p=.021) and more common significant hypotension (54.54% vs 14.66%, p=.024). In the postoperative course, patients with CI had more common signs of abdominal compartment syndrome (71.42% vs 25.33%, p=.001) and higher mortality rate (78.57% vs 29.33%, p=.001). The univariate regression model showed that one of the most significant factors that were associated with CI were age higher than 75 years, significant hypotension lasting more than one hour, organ lesion, development of abdominal compartment syndrome and higher potassium values on third and fourth quartile.

CONCLUSIONS

Grade III colon ischemia (transmural) remains the important cause of mortality after ruptured abdominal aortic aneurysm repair. We identified pre- and intraoperative and postoperative risk factors that could improve the selection of patients for primary open abdomen treatment or early exploratory laparotomy in order to prevent or timely diagnose colon ischemia.

Hemodynamic Influences on Mesenteric Blood Flow in Shock Conditions

The gastrointestinal (GI) system, is most vulnerable to hypoperfusion among the splanchnic organs. Disturbed perfusion of the mesenteric area may lead to GI dysfunction, cause further injury to the patients and even vital outcomes. However, due to the limitation of detection methods, the hemodynamic influences on mesenteric blood flow in clinical practice are not fully understood. By elucidating the underlying mechanisms, we may be able to recognize disturbed GI perfusion and eventually GI dysfunction at an early phase. Thus, in this review, we will focus on situations where mesenteric blood flow is disturbed due to hemodynamic causes in shock conditions, and the present research status will be discussed. English language articles published before 2020 were identified through a computerized PubMed search using the terms "mesenteric, gastrointestinal, intestinal, splanchnic, blood flow, perfusion" and the cofactors. Relevant publications were retrieved and scanned for additional sources. There were few clinical trials focusing on mesenteric blood flow in shock patients. Most were animal experiments. Based on the best current evidence from these sources, we described the major influences on mesenteric blood flow in the context of physiologic accommodation, disease-related effects and the consequences of medical interventions related to shock conditions. During circulatory shock, sepsis, and medical interventions related to shock treatment, mesenteric blood flow changes and shows different features. We need to carefully consider these issues when making medical decisions, and more work needs to be done on early detection of GI hypoperfusion and its accurate correlation with GI dysfunction.

[Cardiogenic shock]

Cardiogenic shock (CS) is defined as end-organ hypoperfusion as the consequence of primary myocardial dysfunction. Among the diagnostic criteria are a systolic blood pressure < 90 mmHg, acute renal failure (oligoanuria), ischemic hepatitis, cyanosis and cold, clammy skin. Accepted hemodynamic cutoffs are a cardiac index < 2,2 (l/min)/m2 and a pulmonary capillary wedge pressure > 15 mmHg. It should be acknowledged, that a normal blood pressure does not rule out CS; there is a nonhypotensive variant of CS demonstrating all the signs mentioned above (including elevated lactate levels) while the blood pressure is compensated due to vasoconstriction.The single most frequent cause of CS is pump failure in the setting of an acute myocardial infarction and its mortality rate has been lowered to 40-50%, owing to the widespread availability of primary PCI. Regarding PCI, it has been demonstrated recently that a "culprit-lesion only strategy" should be followed in the setting of CS. Other important causes of CS to take into account are mechanical complications of myocardial infarction (papillary and ventricular septal rupture as well as rupture of the myocardial free wall leading to tamponade), valvular heart disease (mostly decompensated aortic stenosis) as well as myocarditis and end stage cardiomyopathy.The diagnosis of CS is made by patient history, physical examination, ECG, echocardiography and coronary angiography. Echocardiography should always be performed before coronary angiography because, in the case of mechanical complications, it significantly alters the management of the patients. Patients with clinical signs of CS but paradoxically preserved ejection fraction must be thoroughly evaluated for the presence of a papillary muscle rupture, particularly in the setting of a lateral wall infarction.Noradrenaline and dobutamine are the first-line agents for medical stabilization. When such conventional measures fail, extracorporeal support devices such as ECMO or Impella© may be used. Currently, trials are underway to assess wheter these devices confer a survival benefit in this high-risk population.

Clinical features and outcomes of nonocclusive mesenteric ischemia after cardiac surgery: a retrospective cohort study

Nonocclusive mesenteric ischemia after cardiac surgery is a life-threatening complication requiring emergent intervention. However, because of its rarity, the clinical features and outcomes of nonocclusive mesenteric ischemia remain unknown. The present study aimed to clarify patients' backgrounds, clinical features and mortality of nonocclusive mesenteric ischemia after cardiac surgery, using a Japanese national inpatient database. We identified patients undergoing cardiac or thoracic aortic surgery between July 2010 and March 2017, using the Japanese Diagnosis Procedure Combination database. We calculated the incidence proportion of nonocclusive mesenteric ischemia and examined treatment options (bowel resection and interventional radiology) and patients' discharge status (in-hospital mortality and destination of discharge). We identified 221,900 eligible patients to find 568 (0.26%) patients with bowel ischemia in the same admission. Of these, 124 (0.06%) patients developed nonocclusive mesenteric ischemia, and in-hospital mortality after nonocclusive mesenteric ischemia was 77%. Treatment options for nonocclusive mesenteric ischemia included bowel resection alone (n = 34), interventional radiology (n = 15), or both (n = 15); 27, 10, and 8 patients died, respectively. Seven patients (5.6%) were discharged to home. Among 60 patients without bowel resection or interventional radiology, 50 patients died. In multivariable regression analysis, older age, preoperative hemodialysis, preoperative circulatory support, and hypothermic cardiopulmonary bypass were associated with NOMI. The present study showed that nonocclusive mesenteric ischemia after cardiac surgery was very rare. Mortality following nonocclusive mesenteric ischemia was very high even if patients underwent bowel resection or interventional radiology.

Necrotizing Enterocolitis Associated with Congenital Heart Disease: a Different Entity?

BACKGROUND

Necrotizing enterocolitis (NEC) predominantly occurs in preterm infants (PT-NEC). In term neonates, NEC occurs more frequently when a congenital heart disease is present (CHDNEC). Our aim was to evaluate differences and similarities in disease characteristics of PT-NEC versus CHD-NEC.

METHODS

In this retrospective case-control study we identified all CHD infants who developed NEC Bell's stage ≥2 in our center from 2004 to 2014. We randomly selected (1:2 ratio) PT-NEC infants from the same period. Biochemical and clinical variables were retrieved from patient files.

RESULTS

We found 18 CHD-NEC infants and selected 36 PT-NEC infants (gestational age 28.3 [25-35.6] weeks vs. 38.6 [31.7-40.7] weeks). Postnatal age at onset was significantly lower in CHD-NEC patients (4 [2-24] vs. 11 [4-41] days, p < 0.001). Lowest pH levels were lower (7.21 [7.01-7.47] vs. 7.27 [6.68-7.39], p = 0.02), and highest CRP levels were higher (112.5 mg/L [5.0-425.0] vs. 66.0 [5.2-189.0], p = 0.05) in PT-NEC vs. CHD-NEC. Anatomic localisation of the disease differed: the colon was significantly more often involved in CHD-NEC versus PT-NEC (86% vs. 33%, p = 0.03). Mortality caused by NEC was not different (22% vs. 11%, p = 0.47).

CONCLUSION

While outcome of NEC in both groups is similar, the predominant NEC localisation differed between CHD-NEC and PT-NEC patients. This suggests that both variants of the disease have a different underlying pathophysiological mechanism that predisposes different intestinal regions to develop NEC.

TYPE OF STUDY

Retrospective Case-Control Study.

LEVEL OF EVIDENCE

Level III.

The Pathogenesis of Nonocclusive Mesenteric Ischemia: Implications for Research and Clinical Practice

Nonocclusive mesenteric ischemia (NOMI) is a condition that can encompass ischemia, inflammation, and infarction of the intestinal wall. In contrast to most patients with acute mesenteric ischemia, NOMI is distinguished by patent arteries and veins. The clinical presentation of NOMI is often insidious and nonspecific, resulting in a delayed diagnosis. Patients most at risk are those with severe acute and critical disease, including major surgery and trauma. Nonocclusive mesenteric ischemia is part of a spectrum, from mild, asymptomatic, and an unexpected finding on CT scanning, through to those exhibiting abdominal distension and peritonitis. Severe NOMI is associated with a significant mortality rate. This review of NOMI pathophysiology was conducted to document current concepts and evidence, to examine the implications for diagnosis and treatment, and to identify gaps in knowledge that might direct future research. The key pathologic mechanisms involved in the genesis of NOMI represent an exaggerated normal physiological response to maintain perfusion of vital organs at the expense of mesenteric perfusion. A supply-demand mismatch develops in the intestine due to the development of persistent mesenteric vasoconstriction resulting in reduced blood flow and oxygen delivery to the intestine, particularly to the vulnerable superficial mucosa. This mismatch can be exacerbated by raised intra-abdominal pressure, enteral nutrition, and the use of certain vasoactive drugs, ultimately resulting in the development of intestinal ischemia. Strategies for prevention, early detection, and treatment are urgently needed.

Ischemic Colitis after Cardiac Surgery: Can We Foresee the Threat?

Introduction

Ischemic colitis (IC) remains a great threat after cardiac surgery with use of extracorporeal circulation. We aimed to identify predictive risk factors and influence of early catecholamine therapy for this disease.

Methods

We prospectively collected and analyzed data of 224 patients, who underwent laparotomy due to IC after initial cardiac surgery with use of extracorporeal circulation during 2002 and 2014. For further comparability 58 patients were identified, who underwent bypass surgery, aortic valve replacement or combination of both. Age ±5 years, sex, BMI ± 5, left ventricular function, peripheral arterial disease, diabetes and urgency status were used for match-pair analysis (1:1) to compare outcome and detect predictive risk factors. Highest catecholamine doses during 1 POD were compared for possible predictive potential.

Results

Patients’ baseline characteristics showed no significant differences. In-hospital mortality of the IC group with a mean age of 71 years (14% female) was significantly higher than the control group with a mean age of 70 (14% female) (67% vs. 16%, p<0.001). Despite significantly longer bypass time in the IC group (133 ± 68 vs. 101 ± 42, p = 0.003), cross-clamp time remained comparable (64 ± 33 vs. 56 ± 25 p = 0.150). The majority of the IC group suffered low-output syndrome (71% vs. 14%, p<0.001) leading to significant higher lactate values within first 24h after operation (55 ± 46 mg/dl vs. 31 ± 30 mg/dl, p = 0.002). Logistic regression revealed elevated lactate values to be significant predictor for colectomy during the postoperative course (HR 1.008, CI 95% 1.003–1.014, p = 0.003). However, Receiver Operating Characteristic Curve calculates a cut-off value for lactate of 22.5 mg/dl (sensitivity 73% and specificity 57%). Furthermore, multivariate analysis showed low-output syndrome (HR 4.301, CI 95% 2.108–8.776, p<0.001) and vasopressin therapy (HR 1.108, CI 95% 1.012–1.213, p = 0.027) significantly influencing necessity of laparotomy.

Conclusion

Patients who undergo laparotomy for IC after initial cardiac surgery have a substantial in-hospital mortality risk. Early postoperative catecholamine levels do not influence the development of an IC except vasopressin. Elevated lactate remains merely a vague predictive risk factor.

Hypercapnia counteracts captopril-induced depression of gastric mucosal oxygenation

Hypercapnia (HC) increases systemic oxygen delivery (DO2) and gastric mucosal oxygenation. However, it activates the renin-angiotensin-aldosterone system (RAAS), which conversely reduces mesenteric perfusion. The aims of this study were to evaluate the effect of RAAS inhibition during normocapnia and HC on oral and gastric mucosal oxygenation (μHbO2) and to assess the effect of blood pressure under these circumstances. Five dogs were repeatedly anesthetized to study the effects of ACE inhibition (ACE-I; 5 mg/kg captopril, followed by 0.25 mg/kg per h) on μHbO2 (reflectance spectrophotometry) and hemodynamic variables during normocapnia (end-tidal CO2=35 mmHg) and HC (end-expiratory carbon dioxide (etCO2)=70 mmHg). In the control group, the dogs were subjected to HC alone. To exclude the effects of reduced blood pressure, in one group, blood pressure was maintained at baseline values via titrated phenylephrine (PHE) infusion during HC and additional captopril infusion. ACE-I strongly reduced gastric μHbO2 from 72±2 to 65±2% and mean arterial pressure (MAP) from 64±2 to 48±4 mmHg, while DO2 remained unchanged. This effect was counteracted in the presence of HC, which increased gastric μHbO2 from 73±3 to 79±6% and DO2 from 15±2 to 22±4 ml/kg per min during ACE-I without differences during HC alone. However, MAP decreased similar to that observed during ACE-I alone from 66±3 to 47±5 mmHg, while left ventricular contractility (dPmax) increased from 492±63 to 758±119 mmHg/s. Titrated infusion of PHE had no additional effects on μHbO2. In summary, our data suggest that RAAS inhibition reduces gastric mucosal oxygenation in healthy dogs. HC not only abolishes this effect, but also increases μHbO2, DO2, and dPmax. The increase in μHbO2 during ACE-I under HC is in accordance with our results independent of blood pressure.

Extensive colonic necrosis following cardiac arrest and successful cardiopulmonary resuscitation: report of a case and literature review

Non-occlusive colonic ischaemia is a recognized albeit rare entity related to low blood flow within the visceral circulation and in most reported cases the right colon was affected. This is the second case report in the literature of extensive colonic necrosis following cardiac arrest and cardiopulmonary resuscitation (CPR). A 83-year-old Caucasian woman was admitted to our hospital due to a low energy hip fracture. On her way to the radiology department she sustained a cardiac arrest. CPR started immediately and was successful. A few hours later, the patient developed increasing abdominal distension and severe metabolic acidocis. An abdominal multidetector computed tomography (MDCT) scan was suggestive of intestinal ischaemia. At laparotomy, the terminal ileum was ischaemic and extensive colonic necrosis was found, sparing only the proximal third of the transverse colon. The rectum was also spared. The terminal ileum and the entire colon were resected and an end ileostomy was fashioned. Although the patient exhibited a transient improvement during the immediate postoperative period, she eventually died 24h later from multiple organ failure. Histology showed transmural colonic necrosis with no evidence of a thromboembolic process or vasculitis. Therefore, this entity was attributed to a low flow state within the intestinal circulation secondary to the cardiac arrest.

Change in regional (somatic) near-infrared spectroscopy is not a useful indicator of clinically detectable low cardiac output in children after surgery for congenital heart defects

OBJECTIVE

Near-infrared spectroscopy correlation with low cardiac output has not been validated. Our objective was to determine role of splanchnic and/or renal oxygenation monitoring using near-infrared spectroscopy for detection of low cardiac output in children after surgery for congenital heart defects.

DESIGN

Prospective observational study.

SETTING

Pediatric intensive care unit of a tertiary care teaching hospital.

PATIENTS

Children admitted to the pediatric intensive care unit after surgery for congenital heart defects.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We hypothesized that splanchnic and/or renal hypoxemia detected by near-infrared spectroscopy is a marker of low cardiac output after pediatric cardiac surgery. Patients admitted after cardiac surgery to the pediatric intensive care unit over a 10-month period underwent serial splanchnic and renal near-infrared spectroscopy measurements until extubation. Baseline near-infrared spectroscopy values were recorded in the first postoperative hour. A near-infrared spectroscopy event was a priori defined as ≥20% drop in splanchnic and/or renal oxygen saturation from baseline during any hour of the study. Low cardiac output was defined as metabolic acidosis (pH <7.25, lactate >2 mmol/L, or base excess ≤-5), oliguria (urine output <1 mL/kg/hr), or escalation of inotropic support. Receiver operating characteristic analysis was performed using near-infrared spectroscopy event as a diagnostic test for low cardiac output. Twenty children were enrolled: median age was 5 months; median Risk Adjustment for Congenital Heart Surgery category was 3 (1-6); median bypass and cross-clamp times were 120 mins (45-300 mins) and 88 mins (17-157 mins), respectively. Thirty-one episodes of low cardiac output and 273 near-infrared spectroscopy events were observed in 17 patients. The sensitivity and specificity of a near-infrared spectroscopy event as an indicator of low cardiac output were 48% (30%-66%) and 67% (64%-70%), respectively. On receiver operating characteristic analysis, neither splanchnic nor renal near-infrared spectroscopy event had a significant area under the curve for prediction of low cardiac output (area under the curve: splanchnic 0.45 [95% confidence interval 0.30-0.60], renal 0.51 [95% confidence interval 0.37-0.65]).

CONCLUSIONS

Splanchnic and/or renal hypoxemia as detected by near-infrared spectroscopy may not be an accurate indicator of low cardiac output after surgery for congenital heart defects.

Colon perforation as a critical complication of exertional heat stroke

Although reduced intestinal blood flow causing barrier dysfunction and endotoxemia is well documented in the pathogenesis of heat stroke (HS), complications of the gastrointestinal tract are less appreciated in HS patients. Herein, we report the case of a young man with exertional HS complicated with colon perforation. Acute abdomen, bloody diarrhea, dilated bowel loop, and unexplained shock should be considered as warning signs of colonic ischemia and consequent perforation. Early recognition is the key factor for improving the outcome of HS patients complicated with colon perforation.

Reliability of selective surveillance colonoscopy in the early diagnosis of colonic ischemia after successful ruptured abdominal aortic aneurysm repair

PURPOSE

To evaluate the reliability of selective surveillance colonoscopy based on 6 specific perioperative risk factors in the early diagnosis of colonic ischemia (CI) after successful ruptured abdominal aortic aneurysm (rAAA) repair.

PATIENTS AND METHODS

From 1999 to 2005, 62 consecutive patients underwent rAAA repair. In 59 of them, routine aggressive surveillance colonoscopy was offered every 12 hours within the first 48 hours, and CI was graded consistently. Patients with stage I or stage II CI were treated conservatively and were followed up with repeat colonoscopy, whereas patients with stage III CI underwent immediate laparotomy and colectomy. In parallel, 6 specific perioperative risk factors (PRFs) were retrospectively analyzed.

RESULTS

Overall mortality was 33.9%. Nineteen patients (32.2%) developed CI and 12 (63.2%) of them survived. Thirteen (22%) had grade III CI and among these 6 survived. In patients with CI the mortality rate was 36.2%. Patients with less than 3 PRFs had no CI whereas all instances of CI could be diagnosed if colonoscopy was offered selectively in patients with more than 3 PRFs. The positive predictive value of CI increased with the number of PRFs. Patients with 5 or 6 PRFs were about 101 times more likely to develop CI compared with patients with 0 to 4 PRFs (P<.001).

CONCLUSION

Our study showed that CI is a frequent complication after successful rAAA repair and could reliably be early diagnosed if surveillance colonoscopy was offered selectively in patients with more than three PRFs.

Efeitos do exercício físico sobre o trato gastrintestinal

O impacto do exercício sobre o trato gastrintestinal (TGI), apesar de pouco investigado, é uma área de grande interesse. O exercício aeróbio intenso e de longa duração pode provocar sintomas gastrintestinais. Estes podem ser divididos em sintomas superiores (vômitos, náuseas e pirose retroesternal - azia) e inferiores (diarréia, cólica abdominal, perda de apetite, sangramento, aceleração dos movimentos intestinais e vontade de defecar). A etiologia desses sintomas durante o exercício é multifatorial e inclui a redução do fluxo sanguíneo intestinal, a liberação de hormônios gastrintestinais, o estresse mecânico sobre o TGI, a desidratação, os fatores psicológicos, a idade, o sexo, a dieta e o nível de treinamento do indivíduo. Por outro lado, o exercício de baixa intensidade tem efeito protetor sobre o TGI, principalmente com relação à predisposição a certas doenças como o câncer de cólon, a diverticulite, a colelitíase e a constipação. Diversos mecanismos são postulados para explicar os efeitos do exercício sobre o TGI, contribuindo para o desenvolvimento de estratégias terapêuticas no tratamento de indivíduos com sintomas e doenças gastrintestinais.

Characterization of ischemic colitis associated with myocardial infarction: an analysis of 23 patients

PURPOSE

The study characterizes the clinical presentation of ischemic colitis (IC) associated with myocardial infarction (MI) and helps determine whether the primary mechanism for this association is thrombus, embolus, or localized nonocclusive mesenteric ischemia (NOMI) associated with systemic hypotension.

METHODS

We compared 23 study patients presenting with IC occurring simultaneously with or within 3 days after MI who were admitted to 5 medical centers versus (1) 32 patients with IC without MI (IC-controls) or (2) 32 patients with MI without IC (MI-controls).

RESULTS

Of 17,500 patients admitted to the study sites with MI, 23 (0.13%) had IC. Study patients had a high in-hospital mortality of 39%. An Acute Physiology and Chronic Health Evaluation (APACHE) II score greater than 15 was a significant predictor of mortality in these patients (P<.04). Compared with the IC-controls, study patients had a significantly lower mean arterial pressure (MAP) (76.0 +/- 17.1 mm Hg vs 98.3 +/- 18.6 mm Hg, P<.0001) and a significantly higher rate of hypotension (57% vs 9%, odds ratio [OR] = 12.6, confidence interval [CI]: 3.10-49.7, P<.001). The 2 groups, however, had a similar mean number of risk factors for thromboembolism per patient. Study patients had more severe illness than IC-controls, as demonstrated by mean APACHE II scores (19.0 +/- 5.5 vs 10.4 +/- 4.8, P<.0001). Study patients had a significantly higher incidence of complications, including respiratory failure (57% vs 13%, P=.001), altered mental status (48% vs 13%, P<.01), and renal insufficiency or failure (61% vs 28%, P<.04). Study patients had a significantly lower minimum hematocrit. Study patients had a significantly higher rate of prolonged hospitalization (>30 days) or in-hospital death (74% vs 19%, OR = 12.3, CI: 3.47-43.5, P<.0001). Compared with MI-control patients, study patients had a significantly lower MAP, significantly higher rate of hypotension, much higher mean APACHE II score, much higher incidence of complications, and significantly worse hospital outcome.

CONCLUSIONS

Patients with both IC and MI present as a clinically distinct group from patients with either IC alone or MI alone. They have significantly more complications and worse in-hospital prognoses. They present with a dramatically lower MAP and a higher frequency of hypotension. This last finding suggests that the most common and most important mechanism for IC with MI may be hypotension from cardiogenic shock. Hypotension is the cardinal risk factor for generalized NOMI with acute mesenteric ischemia and may be an important risk factor for localized NOMI with IC. An APACHE II score greater than 15 may be a predictor of mortality from IC after MI.

Fundamentals of neurogastroenterology: basic science

The focus of neurogastroenterology in Rome II was the enteric nervous system (ENS). To avoid duplication with Rome II, only advances in ENS neurobiology after Rome II are reviewed together with stronger emphasis on interactions of the brain, spinal cord, and the gut in terms of relevance for abdominal pain and disordered gastrointestinal function. A committee with expertise in selective aspects of neurogastroenterology was invited to evaluate the literature and provide a consensus overview of the Fundamentals of Neurogastroenterology textbook as they relate to functional gastrointestinal disorders (FGIDs). This review is an abbreviated version of a fuller account that appears in the forthcoming book, Rome III. This report reviews current basic science understanding of visceral sensation and its modulation by inflammation and stress and advances in the neurophysiology of the ENS. Many of the concepts are derived from animal studies in which the physiologic mechanisms underlying visceral sensitivity and neural control of motility, secretion, and blood flow are examined. Impact of inflammation and stress in experimental models relative to FGIDs is reviewed as is human brain imaging, which provides a means for translating basic science to understanding FGID symptoms. Investigative evidence and emerging concepts implicate dysfunction in the nervous system as a significant factor underlying patient symptoms in FGIDs. Continued focus on neurogastroenterologic factors that underlie the development of symptoms will lead to mechanistic understanding that is expected to directly benefit the large contingent of patients and care-givers who deal with FGIDs.

[Nonocclusive ischemia of the right colon]

BACKGROUND

Nonocclusive disease (NOD) is known to be a common cause of ischemic colitis, which is frequently underestimated.

MATERIAL AND METHODS

A computer-assisted search of radiological reports at our institute over a period of 18 months, describing ischemic colitis of the ascending colon with an unimpaired perfusion of the superior mesenteric artery, was performed.

RESULTS

A retrospective analysis of the clinical and radiological data of 14 patients was performed. In ten cases colonic ischemia was confirmed clinically or intraoperatively. Most of our patients needed intravenous catecholamines due to severe hypotension. However, no significant radiographic predictors could be identified.

CONCLUSION

Awareness of NOD seems to be crucial. Especially in cases of acute abdominal pain associated with severe hypotension, renal insufficiency, or pancreatitis, one should include NOD as a differential diagnosis at an early stage.

Angiotensin receptors and actions in guinea pig enteric nervous system

Actions of ANG II on electrical and synaptic behavior of enteric neurons in the guinea pig small intestine were studied. Exposure to ANG II depolarized the membrane potential and elevated neuronal excitability. The number of responding neurons was small, with responses to ANG II in 32% of submucosal neurons and 25% of myenteric neurons. Hyperpolarizing responses were evoked by ANG II in 45% of the neurons. The hyperpolarizing responses were suppressed by alpha2-noradrenergic receptor antagonists, which suggested that the hyperpolarizing responses reflected stimulation of norepinephrine release from sympathetic neurons. Exposure to ANG II enhanced the amplitude and prolonged the duration of noradrenergic inhibitory postsynaptic potentials and suppressed the amplitude of both fast and slow excitatory postsynaptic potentials. The selective ANG II(1) receptor (AT1R) antagonists, ZD-7115 and losartan, but not a selective AT2R antagonist (PD-123319), suppressed the actions of ANG II. Western blot analysis and RT-PCR confirmed expression of AT1R protein and the mRNA transcript for the AT1R in the enteric nervous system. No expression of AT2R protein or mRNA was found. Immunoreactivity for AT1R was expressed by the majority of neurons in the gastric antrum and small and large intestine. AT1R immunoreactivity was coexpressed with calbindin, choline acetyltransferase, calretinin, neuropeptide Y, and nitric oxide synthase in subpopulations of neurons. The results suggest that formation of ANG II might have paracrine-like actions in the enteric nervous system, which include alterations in neuronal excitability and facilitated release of norepinephrine from sympathetic postganglionic axons. The enhanced presence of norepinephrine is expected to suppress fast and slow excitatory neurotransmission in the enteric microcircuits and to suppress neurogenic mucosal secretion.

Role of neutrophils on shock/resuscitation-mediated intestinal arteriolar derangements

Adequate resuscitation from hemorrhagic shock that preserves hemodynamics is associated with a generalized and progressive intestinal arteriolar vasoconstriction and hypoperfusion coupled with impairment of the endothelium-dependent dilation response. This study was performed to investigate the role of neutrophils on the postresuscitation intestinal arteriolar derangements. Experiments were performed in anesthetized rats 24 h after neutrophil depletion. Neutropenia was induced with antineutrophil serum by tail vein injection. Rats injected with rabbit serum lacking anti-rat neutrophil antibody served as controls. Hemorrhagic shock was 50% of mean arterial pressure for 60 min. Resuscitation was with the shed blood returned plus 2 volumes of saline. A nonhemorrhage group served as control. Intravital videomicroscopy of the terminal ileum was used to measure microvascular diameter and centerline red cell velocity. Endothelial function was assessed from the response to the endothelium-dependent dilator acetylcholine (10(-9) to 10(-4) M). Regardless of neutrophil count, hemorrhagic shock caused selective vasoconstriction of inflow A1 arterioles (-21.49 +/- 0.67%) from baseline, which was not seen in the premucosal A3 vessels (pA3, dA3). At 2 h postresuscitation, there was a generalized vasoconstriction from baseline diameter in A1 (-21.26 +/- 2.29%), pA3 (-22.66 +/- 5.02%), and dA3 (-17.62 +/- 4.84%). Neutrophil depletion caused a significant reset of baseline A1 blood flow from 701 +/- 90 nL/s to 978 +/- 90 nL/s and attenuated the postresuscitation hypoperfusion. This occurred independently of the A1 diameter change. Hemorrhagic shock/resuscitation caused impairment of the endothelium-dependent dilation response irrespective of neutrophil count. This study demonstrates that neutrophils do not contribute to the hemorrhagic/resuscitation-mediated intestinal arteriolar derangements, but appear to possess a role in the intestinal arteriolar blood flow regulation under normal and low flow states possibly via a rheologic effect.

Changes in regional blood flow and pCO2 gradients during isolated abdominal aortic blood flow reduction

OBJECTIVE

pCO(2) gradients are used for the assessment of splanchnic regional and local mucosal blood flow changes in experimental and clinical research. pCO(2) gradients may not parallel blood flow changes because of concomitant changes in metabolism, hemoglobin, temperature, and the Haldane effect.

DESIGN AND SETTING

A randomized, controlled animal experiment in a university experimental research laboratory.

INTERVENTIONS

An extracorporeal shunt with reservoir and roller pump was inserted between the proximal and the distal abdominal aorta in 16 pigs. In animals randomized to the low-flow group ( n=8) splanchnic perfusion was reduced by running the roller pump. At baseline and after 45 min of stable shunt flow superior mesenteric artery, celiac trunk, spleen artery, and portal vein blood flows and regional venous-arterial and jejunal and gastric mucosal-arterial pCO(2) gradients were measured, and the respective regional O(2) consumption rates (VO(2)) calculated.

MEASUREMENTS AND RESULTS

In the low-flow group all regional blood flows and the associated VO(2) decreased to roughly 50% of baseline values, and hemoglobin decreased from 7.3 (4.4-9.6) g/dl to 5.7 (4.1-8.9) g/dl. Decreasing regional blood flows were consistently associated with increasing regional and mucosal pCO(2) gradients.

CONCLUSIONS

During isolated reduction in abdominal aortic blood flow there is no preferential distribution to any splanchnic vascular bed and changes in regional pCO(2) gradients reflect consistently the associated blood blow changes.

Splanchnic blood flow in low-flow states

IMPLICATIONS

Insufficient splanchnic blood flow in critically ill patients is the result of a multitude of different diseases, treatment modalities and their interplay, and is associated with increased morbidity and mortality. A combination of diminished and heterogeneous mesenteric blood flow, impaired or exhausted regulatory mechanisms and adverse drug effects may coexist with normal systemic hemodynamics.

Mesenteric hemodynamic response to circulatory shock

PURPOSE OF REVIEW

The mesenteric hemodynamic response to circulatory shock is substantial and asymmetrical; the vasoconstrictive response disproportionately affects the mesenteric organs. The cardiac output is sustained partially, at no cost in nutrient flow to the mesenteric organs, by vasoconstriction of the mesenteric veins, resulting in the "autotransfusion" of up to 30% of the circulating blood volume into the systemic circulation.

RECENT FINDINGS

Hemorrhagic or cardiogenic shock also results in decreased perfusion pressure, prompting selective vasoconstriction of the mesenteric arterioles to maintain perfusion pressure of the vital organs, here at the selective expense of the mesenteric organs. Septic shock may be associated with increased or decreased mesenteric blood flow but is characterized by increased oxygen consumption, exceeding the capability of mesenteric oxygen delivery.

SUMMARY

The response to any of these conditions can, variably and unpredictably, cause hemorrhagic gastric stress erosions, nonocclusive mesenteric ischemia of the small bowel, ischemic colitis, ischemic hepatitis, acalculous cholecystitis, and/or ischemic pancreatitis. Injury to the mesenteric organs can also initiate the systemic inflammatory response syndrome and, consequently, multiple organ failure.

Neonatal necrotizing enterocolitis: clinical considerations and pathogenetic concepts

Necrotizing enterocolitis (NEC), a disease affecting predominantly premature infants, is a leading cause of morbidity and mortality in neonatal intensive care units. Although several predisposing factors have been identified, such as prematurity, enteral feeding, and infection, its pathogenesis remains elusive. In the past 20 years, we have established several animal models of NEC in rats and found several endogenous mediators, especially platelet-activating factor (PAF), which may play a pivotal role in NEC. Injection of PAF induces intestinal necrosis, and PAF antagonists prevent the bowel injury induced by bacterial endotoxin, hypoxia, or challenge with tumor necrosis factor-a (TNF) plus endotoxin in adult rats. The same is true for lesions induced by hypoxia and enteral feeding in neonatal animals. Human patients with NEC show high levels of PAF and decreased plasma PAF-acetylhydrolase, the enzyme degrading PAF. The initial event in our experimental models of NEC is probably polymorphonuclear leukocyte (PMN) activation and adhesion to venules in the intestine, which initiates a local inflammatory reaction involving proinflammatory mediators including TNF, complement, prostaglandins, and leukotriene C4. Subsequent norepinephrine release and mesenteric vasoconstriction result in splanchnic ischemia and reperfusion. Bacterial products (e.g., endotoxin) enter the intestinal tissue during local mucosal barrier breakdown, and endotoxin synergizes with PAF to amplify the inflammation. Reactive oxygen species produced by the activated leukocytes and by intestinal epithelial xanthine oxidase may be the final pathway for tissue injury. Protective mechanisms include nitric oxide produced by the constitutive (mainly neuronal) nitric oxide synthase, and indigenous probiotics such as Bifidobacteria infantis. The former maintains intestinal perfusion and the integrity of the mucosal barrier, and the latter keep virulent bacteria in check. The development of tissue injury depends on the balance between injurious and protective mechanisms.

Ischemic colitis in young adults: a single-institution experience

Ischemic colitis is not well characterized in the young adult population, despite its commonness in older patients. The aim of this study was to investigate the demographics, etiology, clinical features, and prognosis of ischemic colitis in young adults. We conducted a retrospective study of 39 young adults (<50 years of age) diagnosed with ischemic colitis over a period of 9 years (1990 to 1998). The mean age at diagnosis was 38 +/- 2 years (range 18 to 49 years); the female:male ratio was 1.8. Fifty-two percent (13 of 25) of women were using oral contraceptives at the time of diagnosis. Other potential associations identified were vascular thromboembolism (4 of 39), vasoactive drugs (4 of 39), hypovolemia (4 of 39), and vasculitis (2 of 39); 19 patients (49%) had no identifiable predisposing factors. Dominant presenting symptoms were abdominal pain (77%), bloody diarrhea (54%), and hematochezia (51%). Most patients were diagnosed at colonoscopy, and most disease was left sided. Twenty-nine patients were successfully managed with intravenous fluids, broad-spectrum antibiotics, and bowel rest; 10 patients required surgery. There was one disease-related death in the operative group. We found a strong female predominance and an association with oral contraceptive use, but almost half of the patients did not have an identifiable etiology. Mortality from ischemic colitis in this patient population is low.

Effect of prolonged selective intramesenteric arterial vasodilator therapy on intestinal viability after acute segmental mesenteric vascular occlusion

OBJECTIVE

To evaluate the effect of selective intramesenteric artery vasodilator infusion on intestinal viability in a rat model of acute segmental mesenteric vascular occlusion.

SUMMARY BACKGROUND DATA

Although intramesenteric arterial vasodilator infusion may be an effective treatment for nonocclusive mesenteric ischemia, it has also been advocated to increase collateral blood flow after mesenteric vascular occlusion. However, the authors have previously found that intraarterial vasodilators actually reduce collateral blood flow acutely, by preferentially dilating the vasculature of adjacent, nonischemic mesenteric vascular beds, a phenomenon well established in other organs.

METHODS

A segment of rat ileum was acutely devascularized, with blood flow provided only by collateral arterial vessels from adjacent, nonischemic bowel. Papaverine (30 or 40 microg/kg/min), isoproterenol (0.06 microg/kg/min), norepinephrine (0.1 or 0.2 microg/kg/min), or vehicle saline was continuously infused into the cranial (superior) mesenteric artery for 48 hours. Viability was then assessed using previously established, objective gross and microscopic criteria.

RESULTS

Although papaverine increased total mesenteric blood flow in normally vascularized rats, it not only failed to improve but actually significantly reduced the length of the devascularized segment maintained viable by collateral blood flow after 48 hours. Isoproterenol had a similar effect. Norepinephrine infusion decreased both normal mesenteric blood flow and viable segment length.

CONCLUSIONS

These findings suggest that intraarterial vasodilator therapy fails to improve intestinal viability after segmental mesenteric vascular occlusion.

Ischaemia/reperfusion contributes to colonic injury following experimental aortic surgery

OBJECTIVES

ischaemia of the colon is an important complication of abdominal aortic aneurysm (AAA) repair. The aim of this animal study was to investigate the effect of sequential ischaemia and reperfusion on sigmoid mucosal pO2 and its association with local ET-1 release.

MATERIAL AND METHODS

twelve pigs underwent colonic ischaemia followed by complete reperfusion. Six other animals were sham controls. A Clark-type microcatheter was used for continuous mucosal pO2 measurements. Serial systemic and inferior mesenteric vein blood samples were obtained for determination of ET-1 concentration. Neutrophil extravasation was assessed by tissue myeloperoxidase (MPO) activity.

RESULTS

arterial occlusion was associated with a gradual decrease of mucosal pO2 and local release of ET-1. After restoration of blood flow, mucosal pO2 returned to near baseline values, whereas ET-1 reached its maximum concentration during the reperfusion period. MPO activity was significantly increased.

CONCLUSIONS

colonic ischaemia and reperfusion causes neutrophil extravasation and local ET-1.

Visceral Ischemia after Cardiopulmonary Bypass

The diagnosis and management of gastrointestinal complications associated with cardiopulmonary bypass is often hindered by a complicated clinical picture and equivocal examination. To better define the incidence, risk factors, and mortality, we reviewed the records of all patients undergoing cardiopulmonary bypass from 1988 through 1996. The database for this study comprised 14,521 patients who underwent cardiac surgery. The patients (543) with gastrointestinal complications were identified, and those with major complications (166) were individually reviewed. Major complications included pancreatitis, gastritis, laparotomy, gastric ulcer, cholecystitis, colonic perforation, gastrointestinal bleeding, diverticulitis, bowel obstruction, perforation, and visceral ischemia. Our results were the following. 1) Gastrointestinal complications were noted in 3.7 per cent (543) of patients with major complications occurring in 1.2 per cent. In 166 patients, 187 major complications were noted. 2) Visceral ischemia, an infrequent but usually fatal (71%) complication, occurred in 24 (0.17%). 3) Of the ischemic events, 83 per cent (20 of 24) affected the bowel; with the colon involved 80 per cent of the time (16 of 20). 4) Patients with visceral ischemia were more likely to be female (relative risk 2.1), have longer pump times (92.2 versus 74.2), have cardiac procedures other than coronary artery bypass graft (relative risk 2.6), and have end-stage renal disease (relative risk 16.7). We conclude that, given the incidence and mortality related to visceral ischemia, especially to the colon, patients with risk factors (end-stage renal disease, female sex, non-coronary artery bypass graft, and longer pump times) should undergo routine endoscopic examination of the colon early after bypass and when clinically indicated thereafter.

Understanding gastrointestinal perfusion in critical care: so near, and yet so far

An association between abnormal gastrointestinal perfusion and critical illness has been suggested for a number of years. Much of the data to support this idea comes from studies using gastric tonometry. Although an attractive technology, the interpretation of tonometry data is complex. Furthermore, current understanding of the physiology of gastrointestinal perfusion in health and disease is incomplete. This review considers critically the striking clinical data and basic physiological investigations that support a key role for gastrointestinal hypoperfusion in initiating and/or perpetuating critical disease.

Perioperative predictors of colonic ischemia after ruptured abdominal aortic aneurysm

PURPOSE

Colonic ischemia and colonic resection occur frequently after ruptured abdominal aortic aneurysm (rAAA). The purpose of this study was to identify the perioperative risk factors that might help to determine earlier in the postoperative period which patients are at risk for colonic ischemia and colonic resection.

METHODS

The medical records of the 43 patients who underwent repair of rAAA from January 1989 to November 1997 were reviewed. The data were reviewed for the following factors: acidosis, pressor agents, lactate levels, guaiac status, cardiac index, coagulopathy, early postoperative bowel movement, the lowest intraoperative pH level, the temperature at the conclusion of the case, the location and duration of aortic cross clamping, the amount of fluid boluses administered after surgery, the amount of packed red blood cells administered during the case, and the average systolic blood pressure at admission and during surgery. Univariate analysis was performed with Fisher exact test, chi2 test, and Student t test. Multivariate analyses also were performed with the variables that were found to be significant on the univariate analysis.

RESULTS

Thirteen of the 43 patients (30. 2%) had colonic ischemia, and seven of the 13 underwent colonic resection (53.8%). The overall mortality rate was 51.2% (22/43) five of the deaths were intraoperative and excluded from the study. In a comparison of the patients who had colonic ischemia with those who did not, statistically significant differences were found in the following variables: average systolic blood pressure at admission 90 mm Hg or less, hypotension of more than 30 minutes' duration, temperature less than 35 degreesC, pH less than 7.3, fluid boluses administered after surgery 5 L or more, and packed red blood cells 6 units or more. Multivariate analysis indicated that the number of these variables present correlated significantly with the positive predicted probability of colonic ischemia occurring. No patient with two factors or fewer had an ischemic bowel, and the positive predictive probability of colonic ischemia for those patients with six factors was 80%.

CONCLUSION

The results of this study show that: (1) colonic ischemia after rAAA may be predicted with the presence of two or more specific perioperative factors, (2) the lack of a guaiac-positive bowel movement may be misleading for the early diagnosis of colonic ischemia, and (3) more than 50% of the patients with colonic ischemia will require a colonic resection. We recommend that any patient with rAAA with more than two perioperative factors undergo sigmoidoscopy every 12 hours after surgery for 48 hours to rule out colonic ischemia without waiting for early or guaiac-positive bowel movement.

Aetiology of running-related gastrointestinal dysfunction. How far is the finishing line?

30 to 65% of long distance runners experience gastrointestinal (GI) symptoms related to exercise. Several hypotheses have been postulated; however, the aetiology and pathophysiology are far from clear. The mechanical effect of running on the viscera must be involved in the development of GI symptoms in this sport. Reduction of splanchnic blood flow due to visceral vasoconstriction is another widely supported theory; nevertheless, it does not explain many of the clinical findings. Examination of the GI tract during exercise is a difficult task, and measurements of both orocaecal and whole-gut transit time have shown equivocal results. GI hormones, and especially prostaglandins, may be of crucial importance for the production of symptoms. Intestinal absorption, secretion and permeability may also be altered during exercise, provoking intestinal dysfunction. Factors such as stress, diet, dehydration, infections and other factors need to be analysed in order to present a global view of the hypotheses regarding the aetiology of this common and often overlooked problem.

Effects of an angiotensin II antagonist on organ perfusion during the post-resuscitation phase in pigs

BACKGROUND: The aim of this study was to compare pre-arrest and post-resuscitation organ perfusion values and to investigate whether, during the post-resuscitation phase, administration of the angiotensin II antagonist telmisartan (TELM) 10 min after restoration of spontaneous circulation (ROSC) could improve organ flow in comparison to placebo. RESULTS: Five minutes after ROSC in the TELM group, blood flow in the cortex and myocardium increased to 583% (P < 0.05) and 137% (not significant), respectively, whereas blood flow of the colon, stomach and pancreas decreased to 50% (P < 0.05), 28% (P < 0.05) and 19% (P < 0.05) of pre-arrest values, respectively. At 90 min after ROSC, pre-arrest perfusion values both in non-splanchnic and splanchnic organs were achieved. At no point in time were there significant differences between the two groups with respect to organ blood flow or speed of recovery of organ perfusion. CONCLUSIONS: During the post-resuscitation phase, organ blood flow is characterized by the coincidence of increased cerebral and myocardial blood flow and decreased intestinal blood flow. Administration of TELM 10 min after ROSC did not improve the recovery of organ perfusion.

A simple method for frequent monitoring of gastric carbon dioxide

Intragastric PCO2 has been recognized to rise in states of gastric hypoperfusion. A device including a gas-permeable balloon on a conventional sump nasogastric tube (TRIP catheter, Tonometrics) has permitted simple measurement of the intragastric PCO2 following equilibration of intragastric PCO2 with saline in the balloon. This method is slow to equilibrate and time-consuming. We describe an automated method using air instead of saline in the balloon with measurement using capnography. Equilibration is much faster using air and the automated system permits measurements to be taken at regular intervals (10 minutes) without additional workload.

Bacterial translocation, intestinal morphology, and enzyme activities after ileal ischemia in newborn piglets

Intestinal ischemia was created after a limited laparotomy by ligation of the terminal mesenteric vessels in the last 10 cm of distal ileum in 2-day-old piglets. Five groups (each n = 15) were studied: 1 (unoperated control group, killed on day 4), 2 (sham control with laparotomy, killed on day 4), 3 (ischemia, killed on day 4), 4 (ischemia, killed on day 9), and 5 (unoperated control on day 9, not killed). All animals in groups 1, 2 and 5 survived. Two animals in group 3 and 1 in group 4 died (peritonitis and distal ileal perforation). In animals killed on day 9, less weight gain was observed in group 4 compared to the unoperated controls. Macroscopically, no alteration was found at laparotomy in the animals in group 1, whereas in group 2, 1 animal showed beginning peritonitis and another some degree of peritoneal adhesions in group 3, 1 piglet had an intestinal perforation and 4 had intestinal distention above the ischemic loop. In group 4, 7 animals had dilatation of the upper loops, 4 a complete stricture, and 3 peritonitis with complete necrosis of the distal ileum. Microscopic examination revealed severe lesions of the ischemic area in groups 3 and 4 and mild lesions of the upper loop. The kidney was contaminated by translocation of gram-positive cocci in 36% of cases in group 2. Germ carriage for staphylococci was estimated at 80% in the terminal ileum of animals in group 3 versus 8.3% in group 2. In groups 3 and 4, the translocation rate was 30% in the kidney and 40% in the liver. Low disaccharidase activities were found in ischemic areas in groups 3 and 4, with no difference in activity in the upper loops.

The gastric tonometer. A valuable monitor of splanchnic perfusion?

Minimally invasive assessment of the adequacy of perfusion of the gastrointestinal tract has become clinically feasible with the availability of the gastric tonometer. This modified nasogastric tube permits calculation of the pH of the gut mucosal cells; a low tissue pH may indicate tissue hypoxia due to regional hypoperfusion. Such regional hypoperfusion is often undetected by other monitors and, if it occurs intra-operatively, may result in a poor outcome following major surgery. In critical illness, the splanchnic area seems to be particularly vulnerable to hypoperfusion and such a regional oxygen deficit is implicated in the causation of organ dysfunction/failure. Recent studies have begun to define the circumstances in which splanchnic tissue acidosis develops and several therapies have been proposed to reverse the regional oxygen deficit. This review seeks to clarify whether or not the tonometer is a valuable addition to our current monitoring aids.

Shock-associated right colon ischemia and necrosis

Ischemic complications associated with hemorrhagic shock after blunt or penetrating trauma can result in acute renal, pulmonary, or hepatic failure. Less well described is the association between hemorrhagic shock and ischemic necrosis of the right colon, with only 14 cases reported in the literature. Herein, we report three previously healthy young trauma victims with shock-associated right colon necrosis. Each patient suffered a period of hypotension after injury. Diagnosis and operation took place within 2 days of initial injury in all three cases. In each patient, a right colectomy and primary anastomosis was performed without complication. Pathologic examination of the resected specimens showed ischemic necrosis, but no evidence of vascular thrombosis or embolic occlusion of the mesenteric vessels. The etiology of this type of ischemic colitis is not clear, but seems to represent a form of nonocclusive mesenteric ischemia. Knowledge of this disease process will lead to early recognition, prompt treatment, and a satisfactory outcome.

Nonocclusive ischemic colitis following glycerin enema in a patient with coronary artery disease. A case report

Acute colonic ischemia is the most common form of intestinal ischemia. Nonocclusive ischemic colitis contributes to some of these disorders. Heart disease, such as congestive heart failure, myocardial infarction, arrhythmias, aortic valve disease, and atherosclerotic cardiovascular disease, account for many of its risk factors. The majority of cases are associated with severe congestive heart failure with low cardiac output, or disease states resulting in dehydration, or the splanchnic vasoconstrictive effect of some medications. Reactive splanchnic vasoconstriction is responsible for nonocclusive ischemic colitis. Ischemic colitis induced by a cleansing enema has been reported once before. The authors present a case of coronary artery disease complicated by colonic ischemia following glycerin enema in preparation for coronary bypass surgery. Reactive inferior mesenteric artery spasm in response to the enema was noted in this case, rather than diffuse mesenteric artery spasm in response to low cardiac output state and vasoconstrictive drugs.

Local colonic blood pressure degree through aortic reconstruction procedures: a porcine model

Sigmoideal ischemia after aortic grafting is a severe complication with high morbidity and mortality. To investigate the basics of this circulatory problem an animal model was created with sigmoideal ischemia that could be quantified. For this purpose a new pig model was developed with stable general circulatory and ventilatory parameters for several hours, while at the same time controlled sigmoideal ischemia was induced. In five pigs a left retroperitoneal approach to the aorta was performed to isolate the caudal mesenteric artery (CMA). Sigmoideal ischemia was achieved by ligating the collateral circulation and constricting the distal aorta. A flow probe was applied to the CMA. An intravascular saturation probe was introduced in the caudal mesenteric vein (CMV) and a pulse oximeter was applied to the serosal surface of the sigmoid. Every hour, blood gas analyses from the carotic artery, CMA, and CMV were completed. Registrations of all circulatory and ventilatory parameters were performed with the help of a computer. The mean flow in the CMA was 29 mL/min (13-45) and decreased to 5 mL/min (3-7) after aortic constriction. Parameters reflecting the stability of the model, such as the cardiac index (mean 89 mL/min kg-1), the mixed venous oxygen saturation (mean 67%), and the total body oxygen consumption (mean 3.3 mL/min kg-1), did not change with statistical significance during 4 h of partial aortic constriction. The conclusion is that a new model has been developed of quantitative sigmoideal ischemia in the pig that was stable for several hours.

Induction by endotoxin of nitric oxide synthase in the rat mesentery: lack of effect on action of vasoconstrictors

1. Male Sprague-Dawley or Wistar rats were injected with bacterial lipopolysaccharide (LPS; 5 mg kg-1, i.p.) and killed after 1, 3, 6, 15, and 24 h. The brains, mesenteries, spleens, lungs, livers, kidneys, hearts, aortae and diaphragms were removed and frozen immediately. Control rats were injected with sterile saline and killed after 6 h. 2. The organs were homogenized in a semi-frozen state and NO synthase (NOS) activity measured in tissues from both LPS-treated and saline-treated groups by the ability of homogenates to convert [3H]-L-arginine to [3H]-L-citrulline in a NADPH-dependent manner. 3. The NOS activity in all organs taken from control animals was found to be calcium-dependent, with the highest activity being in the brain. After LPS-treatment an induced calcium-independent NOS was detected in all tissues tested, with the exception of the brain. The spleen, lung, mesentery and liver had the highest amounts of LPS-induced NOS activity. No induction of calcium-dependent NOS was detected. 4. Induction of NOS was maximum 6 h after administration of LPS and had returned to control levels in 24 h. 5. The constitutive NOS in brain and mesentery and the LPS-induced activities in the spleen, lung, liver and mesentery were inhibited by NG-monomethyl-L-arginine (L-NMMA) or NG-nitro-L-arginine methyl ester (L-NAME) according to concentration. The IC50 for L-NAME was 2.5 microM against the constitutive NOS from brain, and 20-25 microM against the inducible NOS. For L-NMMA the IC50 was 20-25 microM against either NOS isoform. 7. The vascular responses to endothelin-I (ET-1), the thromboxane A2-mimetic 11 alpha,9 alpha-epoxymethanoprostaglandin F2alpha (U46619), phenylephrine (PE) or 5-hydroxytryptamine (5-HT) were measured in the simultaneously perfused arterial and venous mesenteric vascular beds from both control and LPS-treated(6 h) rats. Vasoconstrictor responses to all agonists tested were unaffected by LPS treatment. In the presence of L-NAME (100 microM) vasoconstrictor responses were potentiated in both the arterial and venous portion of the mesenteric beds from both control and LPS-treated rats. The potentiation of responses to U46619 was significantly greater in beds from LPS-treated rats.8. Injection of LPS i.p. is associated with induction of NOS in all organs tested, except for the brain. In the mesentery this is not accompanied by a hyporesponsiveness to constrictor agents suggesting an increased sensitivity, particularly to U46619. This may explain the poor perfusion and tissue damage in the splanchnic circulation associated with sepsis.

The role of angiotensin in the intestinal vascular response to hypotension in a canine model

It was previously shown that the vasoconstrictory response to hypotension was similar in the mucosa of the small bowel and the colon but was significantly higher in the muscularis of the latter than that of the former. To understand the mechanism of this differential response of the muscularis of the small bowel and the colon, the present study investigated the effect of an angiotensin II inhibitor (saralasin) on the hypotension-induced vasoconstriction of the mucosa and the muscularis of these two locations of the gastrointestinal tract. Dogs were used. Hypotension was induced by hemorrhage to reduce blood pressure by 40 mm Hg. Blood flow was measured by 15-microns radiolabeled microspheres. Saralasin was infused intravenously for 20 minutes at a rate of 0.05 mg.kg-1 bolus followed by 1 microgram.kg-1.min-1. Saralasin had no effect on the basal blood flow of the mucosa or the muscularis of the small bowel or on the hypotension-induced vasoconstriction of these two layers of the small bowel. In contrast, saralasin decreased blood flow to the mucosa (-28%; P less than 0.001) and increased blood flow to the muscularis (+140%; P less than 0.001) of the colon under basal conditions and also reduced the hypotension-induced vasoconstriction of the colonic muscularis (P less than 0.01). These and supplementary data indicate that there is a difference between the small bowel and the colon in local activity of vascular angiotensin system and that this system is most active in the colonic muscularis where it plays a significant role in the vasoconstrictory response to hypotension.

Mesenteric vasoconstriction in cardiogenic shock in pigs

The quantitative impact of mesenteric vasoconstriction on the systemic hemodynamic response to cardiogenic shock induced by pericardial tamponade was evaluated. Graded increases in pericardial pressure produced corresponding decreases in cardiac output to 44% +/- 2% and arterial pressure to 64% +/- 3% of baseline and increases in total peripheral vascular resistance to 131% +/- 4% of baseline. Total mesenteric blood flow decreased disproportionately, to 28% +/- 3% of baseline, because of a disproportionate increase in mesenteric vascular resistance to 223% +/- 6% of baseline. Nonmesenteric vascular resistance increased only to 119% +/- 4% of baseline. Thus mesenteric vasoconstriction accounted for 42% of the increase in total peripheral resistance. Prior blockade of the renin-angiotensin axis ablated this response and eliminated the mesenteric contribution to systemic vascular resistance, while confirmed blockade of the alpha-adrenergic system or vasopressin system had no effect. Without shock, central intravenous infusions of angiotensin II (but not norepinephrine or vasopressin) closely mimicked this selective vasoconstriction. Angiotensin-mediated selective mesenteric vasoconstriction accounts for more than 40% of the overall increase in systemic vascular resistance in cardiogenic shock.

Necrotizing enterocolitis in infancy

The most common gastrointestinal emergency in the newborn is necrotizing enterocolitis. Premature babies are the most likely victims, but it also occurs in full-term infants. Although great strides have been made in elucidating some of the factors responsible for necrotizing enterocolitis, such as intestinal ischemia, bacterial overgrowth, and feeding dysfunction, the exact etiology is as yet unclear. The timing and indications for surgery differ from institution to institution, but the long-term outcome is similar in most large series. The overall mortality rate remains about 20% to 40%, and of the survivors, about one half seem to have no sequelae, the remaining infants having neurologic and gastrointestinal deficits of various degrees of significance.

Whole body and regional O2 uptake/delivery and lactate flux in endotoxic dogs

We infused endotoxin into anesthetized dogs while maintaining cardiac output. Whole body O2 uptake and arterial lactate concentration were measured at the same time with regional O2 uptake and lactate fluxes in muscle and gut. Even though whole body O2 uptake increased, so did arterial lactate levels. The different behavior of organ systems was marked by the fact that muscle took up lactate while its O2 uptake didn't change whereas gut produced lactate as it decreased its O2 uptake. Comparison with critical levels of O2 delivery and O2 extraction ratio for whole body and the two regions opened considerable doubt that generalized and significant hypoxia explained the rise in arterial lactate. Addition of mild hypoxic hypoxia also neither caused O2 uptake to fall nor lactate to rise which reinforced our conclusion that there was little or no tissue hypoxia in endotoxin treated animals given adequate resuscitation with red blood cells and colloid solutions.