Beneficial effects of low-dose prostacyclin on cat intestinal perfusion during endotoxemia as evaluated with microdialysis and oxygen transport variables

The effects of continuous prostacyclin infusion on regional blood flow and cerebral vasospasm following subarachnoid haemorrhage: study protocol for a randomised controlled trial

BACKGROUND

One of the main causes of mortality and morbidity following subarachnoid haemorrhage (SAH) is the development of cerebral vasospasm, a frequent complication arising in the weeks after the initial bleeding. Despite extensive research, to date no effective treatment of vasospasm exists. Prostacyclin is a potent vasodilator and inhibitor of platelet aggregation. In vitro models have shown a relaxing effect of prostacyclin after induced contraction in cerebral arteries, and a recent pilot trial showed a positive effect on cerebral vasospasm in a clinical setting. No randomised, clinical trials have been conducted, investigating the possible pharmacodynamic effects of prostacyclin on the human brain following SAH.

METHODS

This trial is a single-centre, randomised, placebo-controlled, parallel group, blinded, clinical, pilot trial. A total of 90 patients with SAH will be randomised to one of three intervention arms: epoprostenol 1 ng/kg/min, epoprostenol 2 ng/kg/min or placebo in addition to standard treatment. Trial medication will start day 5 after SAH and continue to day 10. The primary outcome measure is changes in regional cerebral blood flow from baseline in the arterial territories of the anterior cerebral artery, medial cerebral artery and the posterior cerebral artery, measured by CT perfusion scan. The secondary outcomes will be vasospasm measured by CT angiography, ischaemic parameters measured by brain microdialysis, flow velocities in the medial cerebral artery, clinical parameters and outcome (Glasgow Outcome Scale) at 3 months.

TRIAL REGISTRATION

Clinicaltrials.gov NCT01447095.

Epoprostenol improves mucosal tissue oxygen tension in an acute endotoxemic pig model

The objective of the present study was to determine the effects of increasing dosages of continuously infused epoprostenol (PGI), a prostacyclin analog, on intestinal oxygen supply and jejunal mucosal tissue oxygen tension in an acute endotoxic pig model. Jejunal mucosal tissue PO2, oxygen saturation of jejunal microvascular hemoglobin, and gut microvascular blood flow were investigated. Systemic hemodynamic variables, mesenteric-venous and systemic acid base and blood gas variables, and lactate measurements were recorded. Measurements were performed at baseline, after Escherichia coli LPS administration, and at 20-min intervals during incremental PGI infusion (n = 8; 25, 50, 100, and 200microg x kg x h, respectively); or infusion of an equal amount of isotonic sodium chloride solution (n = 7). LPS infusion led to a significant decrease in mucosal tissue oxygen tension and microvascular hemoglobin oxygen saturation. Epoprostenol infusion led to a significant, dose-dependent increase in cardiac index and systemic oxygen delivery. Mucosal tissue oxygen tension and microvascular hemoglobin oxygen saturation increased after PGI administration and even returned to more-than-baseline values. Continuously infused PGI increased intestinal hemoglobin oxygen saturation and mucosal tissue oxygen tension in a dose-dependent manner mainly due to an increase in villus blood flow in this acute endotoxic pig model.

Decreases in myocardial glucose and increases in pyruvate but not ischaemia are observed during porcine endotoxaemia

BACKGROUND

Myocardial dysfunction occurs commonly in septic shock. It is not known whether this is due to local ischaemia and metabolic disturbances. Our hypothesis was that endotoxaemic myocardial dysfunction may be associated with interstitial ischaemic and metabolic changes, measured using interstitial microdialysis (MD).

METHODS

Eighteen pigs were randomized to control (n=6) or endotoxin infusion (n=12). MD catheters were inserted into the myocardium for measurement of interstitial glucose, pyruvate and lactate concentrations. Plasma glucose and lactate concentrations and systemic haemodynamic parameters were measured simultaneously.

RESULTS

Compared with the control group, the endotoxaemic animals had significantly decreased left ventricular stroke work and venous oxygen saturation (SvO2), and increased mean pulmonary artery pressure and plasma lactate. In the endotoxaemic group, decreases in interstitial glucose were observed, occurring simultaneously with increases in interstitial pruvate. Interstitial lactate: pyruvate ratios decreased with time in all animals.

CONCLUSIONS

Despite severe systemic and pulmonary haemodynamic changes, interstitial MD measurements revealed no evidence of anaerobic metabolism in the myocardium of endotoxaemic pigs. There were, however, changes in glucose and pyruvate concentrations, suggesting local energy metabolic disturbances.

Influence of obesity on sepsis

Sepsis is the leading cause of death in non-coronary intensive care units worldwide, with a very high cost of care. There is a growing body of evidence suggesting that the increase in morbidity associated with severe obesity in critically ill patients results in increased resource utilization adding further to the cost of care. There is a relative paucity of information regarding the pathophysiology and treatment of obese critically ill patients, especially with sepsis. Obesity as an exclusion criterion in landmark trials is partly responsible for this paucity. While the preventive strategies for obesity will be the most definitive long-term solution, it will take a long time to affect outcomes in our intensive care units. In the meantime, our hospitals, including the intensive care units must continue to treat obese/morbidly obese critically ill patients with sepsis, making it essential to study and understand the pathophysiology and develop treatment strategies for obese with sepsis. Available laboratory data suggests an increased inflammatory response in obese septic individuals. However, the association between obesity and sepsis in the clinical setting is unclear due to controversial results. This article reviews the available clinical and laboratory data that addresses the effects of obesity on sepsis.

The effects of activated protein C and prostacyclin on arterial oxygenation and protein leakage in the lung and the gut under endotoxaemia in the rat

BACKGROUND

Based on the anti-adhesive/anti-aggregatory and permeability-reducing properties of activated protein C (APC) and prostacyclin (PGI(2)), we analysed and compared these substances regarding their efficacy in counteracting transcapillary leakage of albumin in the lung and the gut, and in improving arterial oxygenation under a condition of inflammation.

METHODS

The randomized and blinded study was performed on 31 adult male Sprague-Dawley rats. Inflammation was induced by continuous infusion of Escherichia coli endotoxin (lipopolysaccharide, LPS). Six hours after the start of the LPS infusion (240,000 U/kg/h), a simultaneous infusion of saline (control group) or 8 microg/kg/min of human recombinant APC or 2 ng/kg/min of PGI(2) was started and continued for 24 h (n=8 per group). The study also included a sham group. Transcapillary leakage of albumin was measured from the ratio between tissue radioactivity [counts per minute (cpm)/g tissue] and actual amount of radioactivity given (cpm/g body weight of (125)I-albumin). Oxygenation was assessed from arterial and central venous blood samples.

RESULTS

LPS induced albumin leakage in the gut and the lung, and impaired blood oxygenation. In the lung, the leakage was lower in the PGI(2) group than in the APC and the control groups (P<0.05). In the gut, it was lower in the APC and the PGI(2) groups than in the control group (P<0.05). Oxygenation was better in the APC and PGI(2) groups than in the control group.

CONCLUSION

Our data suggest that both APC and low-dose PGI(2) are beneficial in LPS-induced inflammation in the rat, by reducing albumin leakage and improving blood oxygenation.

Prostacyclin in sepsis: A systematic review

According to current literature, infective processes greatly modify both vascular hemodynamics and anti-oxidant properties of affected tissues, causing a change in homeostasis that regulates the correct functioning of all cells responsible for the physiological and metabolic balance of various organs. As a consequence, the response to the infection that has caused the change is also likely to be weaker and, in the case of septic shock, ineffective. In this review, we will take into consideration these mechanisms and then focus on a group of vasodilator drugs (prostacyclin and its analogs) which, though have been used for over 20 years mainly to treat obstructive vascular diseases, have such hemodynamic and anti-inflammatory properties which prevent homeostatic changes. It is obvious that prostacyclin does not definitively have anti-infective characteristics; however, in association with anti-infective drugs (antibiotics, etc.), the effectiveness of the latter appears improved, at least in some circumstances. Similarly, the fact that prostacyclin and its analogs have a cytoprotective effect on the liver and reduce the ischemia-reperfusion damage following liver transplant is not a novelty and evidence that they improve hepatic hemodynamics suggests their use in those pathologies characterized by possible reduced perfusion or ascertained ischemia of the liver.

Intestinal microdialysis--applicability, reproducibility and local tissue response in a pig model

BACKGROUND AND AIMS

Microdialysis has been applied to the intestinal wall for the purpose of monitoring local ischemia. The aim of this study was to investigate the applicability, reproducibility and local response to microdialysis in the intestinal wall.

MATERIALS AND METHODS

In 12 pigs two microdialysis probes were inserted into the ileal wall, one in the peritoneal cavity and one in the psoas muscle. Relative recovery was measured for all probes by the no net flux method. Metabolic measurements of glucose, lactate and glycerol were performed over six hours. The ileal wall segments containing the probes were processed for histological examination.

RESULTS

Large intra- and inter-group differences in the relative recovery were found between all locations. Absolute values of metabolites showed no significant changes during the study period. The lactate in blood was 25-30% of the intra-tissue values. A severe inflammatory reaction was seen in the ileal wall around all probes.

CONCLUSION

Measurement of the relative recovery is essential for valid measurements of metabolites when using microdialysis. The inflammatory reaction around the probe in the intestinal wall is likely to affect metabolism and measurements hereof. Therefore intestinal wall microdialysis seems confined to experimental research, and future studies should consider the intra-peritoneal approach.

Small-dose epoprostenol decreases systemic oxygen consumption and splanchnic oxygen extraction during normothermic cardiopulmonary bypass

Normothermic, nonpulsatile cardiopulmonary bypass (CPB) impairs systemic and splanchnic oxygen transport and increases gastrointestinal permeability. It is an important therapeutic goal to avoid splanchnic dysoxia during CPB. Small-dose prostacyclin therapy improves splanchnic oxygen transport and microcirculation in septic patients. In this study, we sought to determine if during cardiac surgery, the prostacyclin analog epoprostenol improves the balance of systemic and splanchnic oxygen transport. Eighteen patients undergoing cardiac valve replacement were randomized to receive either epoprostenol (3 ng x kg(-1) x min(-1)) or placebo during, and for 1 hour after, surgery. Systemic and splanchnic oxygen delivery, consumption, and extraction and arterial, mixed venous, and hepato-venous lactate concentrations were measured before, during, and after CPB. Gastrointestinal permeability was measured 1 day before and 1 day after surgery using the triple sugar permeability test. During CPB, the epoprostenol group had decreased systemic oxygen consumption and splanchnic oxygen extraction (P = 0.024). These effects were not present 1 hour after the end of epoprostenol infusion. The study was not adequately powered to determine whether epoprostenol altered the trend towards increased lactate metabolism and increased postoperative gastrointestinal permeability, nor could we demonstrate any differences between groups in clinically relevant end-points. In conclusion, these findings suggest that during normothermic CPB, small-dose epoprostenol therapy may reduce systemic oxygen consumption and splanchnic oxygen extraction.

The permeability-reducing effects of prostacyclin and inhibition of Rho kinase do not counteract endotoxin-induced increase in permeability in cat skeletal muscle

cAMP stimulation and Rho kinase inhibition are shown to decrease microvascular permeability during noninflammatory conditions, most likely by decreasing contractility of actomyosin filaments in the endothelial cell, but their effects on permeability during inflammatory conditions are not clarified. The objective of this in vivo study, performed on the autoperfused and denervated calf muscle of the cat, was therefore to evaluate to what extent cAMP stimulation and inhibition of Rho kinase reduce permeability at endotoxemia. Change in osmotic reflection coefficient for albumin was used as a measure of altered protein permeability and change in capillary filtration coefficient (CFC) as a measure of altered fluid permeability. After inducing a significant increase in protein and fluid permeability by infusion of lipopolysaccharide (LPS), we determined to what extent the increased permeability was decreased by the cAMP stimulator prostacyclin [1.0 ng/kg/min intravenously (iv)] or the Rho kinase inhibitor Y-27632 [1.05 microg/ml plasma/h intraarterially (ia)]. These doses are known to decrease permeability under noninflammatory conditions. The reflection coefficient for albumin and CFC were determined before and during LPS, and during LPS plus prostacyclin (n = 6) or LPS plus Y-27632 (n = 6). The reflection coefficient was reduced by about 30% (P < 0.05) and CFC was increased by about 25% (P < 0.05) by LPS, and these permeability parameters were not affected by prostacyclin or Y-27632. We conclude that cAMP stimulation and Rho kinase inhibition reduce permeability by other pathways and mechanisms than those by which permeability is increased during endotoxemia.

Opposite effects of prostacyclin on hepatic blood flow and oxygen consumption after burn and sepsis

BACKGROUND

Burn and sepsis are associated with hepatic ischemia and reperfusion injury. This study examines the hypothesis that postburn treatment with the vasodilator prostacyclin would be beneficial for hepatic perfusion and oxygenation.

METHODS

Female pigs (n = 18, 20-25 kg) underwent laparotomy, during which ultrasonic flow probes were placed on the portal vein and the common hepatic artery. Catheters were inserted in the superior mesenteric and left hepatic veins. After 5 days, all animals were anesthetized and 12 of them received 40% total body surface area third-degree burn; 100 microg/kg Escherichia coli lipopolysaccharide (LPS) was intravenously administered 18 hours postburn. Burned animals were randomized to receive a constant infusion of iloprost (20 ng/kg per minute) or an equivalent amount of carrier solution (normal saline). All animals were studied for 42 hours.

RESULTS

Burn caused a 2.5-fold increase in hepatic arterial vascular resistance (HAVR) and a 39% decrease in hepatic arterial blood flow (HABF). Postburn administration of iloprost did not improve the hepatic arterial hemodynamics (1.8-fold increase in HAVR and 38% decrease in HABF). Post-LPS, HABF was significantly reduced to 22% of baseline and HAVR was 15-fold increased (P < 0.05 vs. baseline, ANOVA). In contrast, iloprost-treated animals did not show hepatic arterial vasoconstriction, as both HABF and HAVR remained baseline values during the endotoxic phase (P < 0.05 vs. nontreated group, ANOVA). Postburn iloprost treatment yielded a significant improvement in post-LPS portal venous blood flow (PVBF, 79% of baseline vs. 45% of baseline in nontreated animals, P < 0.05, ANOVA). Portal venous pressure showed 16% and 56% increases after burn and endotoxin, respectively. Portal hypertension did not occur in iloprost-treated animals, as portal venous pressure remained within baseline range (P < 0.05 vs. nontreated group, ANOVA). Burn and endotoxemia resulted in a significant decrease of hepatic oxygen delivery (hDO2, 63% and 12% of baseline, respectively) and hepatic oxygen consumption (hVO2, 61% and 21% of baseline, respectively). Only during the postburn endotoxic phase, iloprost improved hDO2 and hVO2 (140% and 79%, respectively; P < 0.05 vs. nontreated group, ANOVA).

CONCLUSIONS

Postburn prostacyclin treatment appears to have no beneficial effects on hepatic perfusion early postburn. However, during the late postburn endotoxic phase, prostacyclin seems to significantly improve hepatic total blood flow and oxygenation. In addition, prostacyclin treatment attenuated burn- and endotoxin-induced portal hypertension.

Reducing intracranial pressure may increase survival among patients with bacterial meningitis

We reported findings concerning continuous intracranial pressure (ICP) and cerebral perfusion pressure (CPP) measurements and mortality in patients with severe bacterial meningitis treated on the basis of an ICP-targeted approach. Eighteen patients with severe bacterial meningitis were admitted for neurointensive care at Umeå University Hospital (Umeå, Sweden). In 15 patients, ICP was measured continuously through an ICP measuring device. During care, all patients but one developed intracranial hypertension with an ICP of >or=15 mm Hg (14 [93%] of 15 patients). Ten (67%) of 15 patients survived and were discharged, and 5 patients (33%) died. Mean ICP was significantly higher and CPP was markedly decreased in nonsurvivors, compared with survivors. Among the survivors, ICP was gradually reduced. Treatment of patients with severe bacterial meningitis should include neurointensive care and continuous ICP measurement. Increased ICP may be reduced by using the ICP-targeted therapy that closely resembles the "Lund concept."

Non-occlusive mesenteric ischaemia: a common disorder in gastroenterology and intensive care

Non-occlusive mesenteric ischaemia is characterized by gastrointestinal ischaemia with normal vessels. In gastroenterology it is recognized as rare disease occasionally causing acute bowel infarction or ischaemic colitis. From intensive care literature this disorder is recognized as an early phenomenon during circulatory stress. This early mucosal ischaemia then leads to increased permeability, bacterial translocation, and further mucosal hypoperfusion. The damage is produced mainly during reperfusion following ischaemia with fresh inflow of oxygen and outflow of waste products into the systemic circulation. The mechanisms underlying non-occlusive mesenteric ischaemia include macrovascular vasoconstriction, hypoperfusion of the tips of the villi and shunting. It is very common in critically ill and perioperative patients, but also occurs in pancreatitis, renal failure and sepsis. Treatment options include aggressive fluid resuscitation and careful choice of vasoactive drugs. Control of reperfusion damage and new endothelin-antagonists are potentially useful new treatment options.

Hypovolemia is a main factor behind disturbed perfusion and metabolism in the intestine during endotoxemia in cat

Disturbances in intestinal metabolism and perfusion during SIRS can be direct effects of toxic substances, and/or effects secondary to hypovolemia. An attempt to evaluate the significance of hypovolemia for intestinal disturbances during SIRS was made in the present study on feline by evaluating the degree to which the intestinal alterations following endotoxin infusion were restored by a clinically relevant volume infusion. The results were compared with control animals treated identically except that they were not given a volume infusion. We analyzed effects of a colloid infusion during endotoxemia on intestinal perfusion, and on the metabolites lactate, pyruvate, glucose, and glycerol in the intestinal wall, the latter by a microdialysis technique. Arterial and central venous blood pressures, and superior mesenteric artery blood flow were measured, and intestinal oxygen delivery and uptake were calculated. To evaluate to what extent a restoring effect of a colloid infusion was dependent on the type of colloid solution used, three different colloids with about the same volume expanding effects (6% albumin, 6% dextran 70 and 6% hydroxyethyl starch, n = 3 x 6) were tested randomly and blinded. Four hrs after start of endotoxin (1 mg/kg + 1 mg/kg/h), the colloid was infused at a rate of 5 mL/kg for 30 min followed by 2.5 mL/kg/h. Endotoxin caused a marked deterioration of perfusion and metabolic parameters. Most of these parameters turned towards normalization, though not fully reaching baseline values within 4 hrs after start of the colloid infusion. In the control experiments (n = 4), the endotoxin-induced deteriorations persisted or were aggravated during the corresponding time period. The results indicated that hypovolemia is an essential factor but not the only one behind alterations in metabolism and perfusion in the intestine during SIRS, and the alterations can be significantly reduced by adequate volume substitution. In this respect no differences could be seen between the three colloids tested.