Intraperitoneal and intraluminal microdialysis in the detection of experimental regional intestinal ischaemia

A Randomized Porcine Study in Low Cardiac Output of Vasoactive and Inotropic Drug Effects on the Gastrointestinal Tract

BACKGROUND

Splanchnic vasodilation by inodilators is an argument for their use in critical cardiac dysfunction. To isolate peripheral vasoactivity from inotropy, such drugs were investigated, and contrasted to vasopressors, in a fixed low cardiac output (CO) model resembling acute cardiac dysfunction effects on the gastrointestinal tract. We hypothesized that inodilators would vasodilate and preserve the aerobic metabolism in the splanchnic circulation in low CO.

METHODS

In anesthetized pigs, CO was lowered to 60% of baseline by partial inferior caval vein balloon inflation. The animals were randomized to placebo (n = 8), levosimendan (24 μg kg-1 bolus, 0.2 μg kg-1 min-1, n = 7), milrinone (50 μg kg-1 bolus, 0.5 μg kg-1 min-1, n = 7), vasopressin (0.001, 0.002 and 0.006 U kg-1 min-1, 1 h each, n = 7) or norepinephrine (0.04, 0.12, and 0.36 μg kg-1 min-1, 1 h each, n = 7). Hemodynamic variables including mesenteric blood flow were collected. Systemic, mixed-venous, mesenteric-venous, and intraperitoneal metabolites were analyzed.

RESULTS

Cardiac output was stable at 60% in all groups, which resulted in systemic hypotension, low superior mesenteric artery blood flow, lactic acidosis, and increased intraperitoneal concentrations of lactate. Levosimendan and milrinone did not change any circulatory variables, but levosimendan increased blood lactate concentrations. Vasopressin and norepinephrine increased systemic and mesenteric vascular resistances at the highest dose. Vasopressin increased mesenteric resistance more than systemic, and the intraperitoneal lactate concentration and lactate/pyruvate ratio.

CONCLUSION

Splanchnic vasodilation by levosimendan and milrinone may be negligible in low CO, thus rejecting the hypothesis. High-dose vasopressors may have side effects in the splanchnic circulation.

Predictive and Diagnostic Biomarkers of Anastomotic Leakage: A Precision Medicine Approach for Colorectal Cancer Patients

Development of an anastomotic leak (AL) following intestinal surgery for the treatment of colorectal cancers is a life-threatening complication. Failure of the anastomosis to heal correctly can lead to contamination of the abdomen with intestinal contents and the development of peritonitis. The additional care that these patients require is associated with longer hospitalisation stays and increased economic costs. Patients also have higher morbidity and mortality rates and poorer oncological prognosis. Unfortunately, current practices for AL diagnosis are non-specific, which may delay diagnosis and have a negative impact on patient outcome. To overcome these issues, research is continuing to identify AL diagnostic or predictive biomarkers. In this review, we highlight promising candidate biomarkers including ischaemic metabolites, inflammatory markers and bacteria. Although research has focused on the use of blood or peritoneal fluid samples, we describe the use of implantable medical devices that have been designed to measure biomarkers in peri-anastomotic tissue. Biomarkers that can be used in conjunction with clinical status, routine haematological and biochemical analysis and imaging have the potential to help to deliver a precision medicine package that could significantly enhance a patient's post-operative care and improve outcomes. Although no AL biomarker has yet been validated in large-scale clinical trials, there is confidence that personalised medicine, through biomarker analysis, could be realised for colorectal cancer intestinal resection and anastomosis patients in the years to come.

Influence of anastomoses on intestine ischemia and cefuroxime concentrations: Evaluated in the ileum and colon in a porcine model

BACKGROUND

Anastomotic leakage is a serious complication following gastrointestinal surgery and is associated with increased morbidity and mortality. The incidence of anastomotic leakage is determined by anatomy and is reported to be between 4%-33% for colon anastomosis and 1%-3% for small intestine anastomosis. The etiology of anastomotic leakage of the intestine has been divided into three main factors: healing disturbances, communication between intra- and extra-luminal compartments, and infection. All three factors interact, and one factor will inevitably lead to the other two factors resulting in tissue ischemia, tissue necrosis, and anastomotic leakage.

AIM

To evaluate ischemic metabolites and cefuroxime concentrations in both anastomosis and non-anastomosis ileum and colon in a porcine model.

METHODS

Eight healthy female pigs (Danish Landrace breed, weight 58-62 kg) were included in this study. Microdialysis catheters were placed for sampling of ischemic metabolites (glucose, lactate, glycerol, and pyruvate) and cefuroxime concentrations in both anastomosis and non-anastomosis ileum and colon. Cefuroxime 1.5 g was administered as an intravenous infusion over 15 min. Subsequently, dialysates and blood samples were collected over 8 h and the ischemic metabolites and cefuroxime concentrations were quantified in all samples. The concentrations of glucose, lactate, glycerol and pyruvate were determined using the CMA 600 Microdialysis Analyzer with Reagent Set A (M Dialysis AB, Sweden), and the concentrations of cefuroxime and meropenem were quantified using a validated ultra-high-performance liquid chromatography assay.

RESULTS

Only the colon anastomosis induced mean ischemic lactate/pyruvate ratios above 25 (ischemic cut-off) throughout the entire sampling interval, and simultaneously decreased glucose concentrations. The mean time for which cefuroxime concentrations were maintained above the clinical breakpoint minimal inhibitory concentration for Escherichia coli (8 µg/mL) ranged between 116-128 min across all the investigated compartments, and was similar between the anastomosis and non-anastomosis ileum and colon. For all pigs and in all the investigated compartments, a cefuroxime concentration of 8 µg/mL was reached within 10 min after administration. When comparing the pharmacokinetic parameters between the anastomosis and non-anastomosis sites for both ileum and colon, only colon T_max and half-life differed between anastomosis and non-anastomosis (P < 0.03). Incomplete tissue penetrations were found in all tissues except for the non-anastomosis colon.

CONCLUSION

Administering 1.5 g cefuroxime 10 min prior to intestine surgery seems sufficient, and effective concentrations are sustained for approximately 2 h. Only colon anastomosis was locally vulnerable to ischemia.

Surface Microdialysis for Detection of Colorectal Anastomosis Ischemia-An Experimental Study

BACKGROUND

Inadequate blood supply is one of the major risk factors for anastomotic leak after low anterior rectal resection. Early detection of ischemia might predict complicated healing and enable anastomotic salvage, which is associated with better outcomes. A microdialysis offers a real-time evaluation of adequate bowel perfusion through monitoring of tissue metabolism. In this experimental study, we assessed the role of microdialysis in detecting early ischemia after colorectal anastomosis.

MATERIALS AND METHODS

Colorectal anastomosis was performed in six miniature pigs. A microdialysis catheter was placed on the bowel serosa 5 mm proximal to the anastomosis. Metabolic changes were monitored hourly before and after initiating ischemia, which was induced by ligation of the inferior mesenteric artery and skeletonization of the mesocolon.

RESULTS

Significant increase in tissue levels of lactate was detected after 60 min of ischemia (13.6 [10.4-16.1] versus 6.75 [1.8-9.6] mmol/L at baseline; P < 0.005). The lactate/pyruvate ratio increased accordingly. The concentration of glycerol increased significantly after 2 hours-from a baseline value of 29.5 (3-84) to 125 (79-201) mmol/L (P < 0.005). The decrease in glucose levels was also significant after 60 minutes-0 (0-0.2) versus 4.7 (3.3-6.8) mmol/L at baseline. However, its values started to decline before ischemia.

CONCLUSIONS

Surface microdialysis can detect ischemic changes early and may be a promising method in postoperative monitoring of colorectal anastomosis.

Detection of early anastomotic leakage by intraperitoneal microdialysis after low anterior resection for rectal cancer: a prospective cohort study

AIM

Anastomotic leakage (AL) is a common and serious complication following sphincter-preserving surgery for rectal cancer. Early detection and intervention can improve clinical outcomes. The aim of this prospective cohort study was to compare intraperitoneal microdialysis with a clinical scoring system for early detection of AL.

METHOD

A microdialysis catheter was anchored near the anastomosis at low anterior resection (LAR) for rectal cancer. Peritoneal fluid samples were analysed (lactate, pyruvate, glucose and glycerol concentration) 4-hourly and compared with a daily clinical leak score (DULK = Dutch leakage). At day 7 a pelvic CT with rectal contrast enema was performed to establish if there had been a radiological leak.

RESULTS

In this two-centre study, 129 patients [median age 65 (26-82) years; 60.5% male] underwent LAR. The leak rate was 27% (grade A, n = 11; grade B, n = 12; grade C, n = 12). Receiver operator characteristic analysis demonstrated a lactate cut-off value of 9.8 mm and had 77% sensitivity, 82% specificity, 78% accuracy, a positive predictive value (PPV) of 58, a negative predictive value (NPV) of 88 (CI 79-94) and an area under the curve (AUC) of 0.9 for AL. This compared with a clinical score ≥ 4, which had 57% sensitivity, 79% specificity, 71% accuracy, a PPV of 46, a NPV of 82 and an AUC of 0.7 for AL. The mean day for a positive test when using delta lactate ≥ 6.3 mm was 1.6 days and for leak score ≥ 4 it was 3.3 days (NS).

CONCLUSION

When AL occurs, intraperitoneal lactate concentration increases over time, and at a certain cut-off has a higher sensitivity, specificity, accuracy, PPV and NPV than a clinical scoring system.

Results of postoperative microdialysis intraperitoneal and at the anastomosis in patients developing anastomotic leakage after rectal cancer surgery

Introduction: Anastomotic leakage postoperatively in patients operated with rectum resection and primary anastomosis is a common and feared complication. We have studied seven patients with an anastomotic leakage after surgery and compared them with 13 patients without complications.Methods: Metabolic measurements with microdialysis were done during the first seven postoperative days, with measurements of glucose, pyruvate, lactate and glycerol. The lactate/pyruvate ratio was calculated. Measurements were performed subcutaneously, intraperitoneally and at the anastomosis. The inflammatory cytokines, IL 6 and IL 10, were measured intravenously and intraperitoneally 48 hours postoperatively.Results: Intravenous and intraperitoneal IL 6 were higher in the leakage group. Around the small intestine (intraperitoneally), we found that patients developing anastomotic leakage had higher lactate and lactate/pyruvate ratio immediately after surgery. They also showed lower glycerol levels. At the anastomosis, we found higher lactate and lactate/pyruvate ratio in anastomotic leak patients after the fourth postoperative day.Conclusions: The results indicate that a possible mechanism behind an anastomotic leakage is an impaired circulation and thus insufficient saturation to the small intestine peroperatively. This develops into an inflammation both intraperitoneally and intravenously, which, if not reversed, spread within the gastrointestinal tract .The colorectal anastomosis is the most vulnerable part of the gastrointestinal tract postoperatively and hypoxia and inflammation may occur there, and an anastomosis leakage will be the consequence.

Peritoneal microdialysis as a tool for detecting anastomotic leakage in patients after left-side colon and rectal resection. A systematic review

OBJECTIVE

The objective was to evaluate peritoneal microdialysis in the detection of clinical anastomotic leakage after left-sided colon and rectal resection through a systematic review.

METHODS

A systematic review (PRISMA guidelines) based on a systematic search through PubMed, Cochrane Library, and EMBASE (1 February 2017) was performed. Methodological index of non-randomised studies score was selected to assess the methodological quality. Patient demographics and raw data for intraperitoneal microdialysis concentrations of glucose, lactate, glycerol and pyruvate for 5 d postoperative were obtained from the respective study groups.

RESULTS

Ten studies with a total of 128 patients were included. Thirty (23%) patients developed clinical anastomotic leakage. The area under the curve for intraperitoneal lactate concentration was significant higher in patients with anastomotic leakage (58.2; 95% CI 39.2, 77.2) compared with the no leakage group (41.0; 95% CI 35.2, 46.1; p = .007). Receiver operating characteristic curve analysis of the maximum measured lactate concentration demonstrated 25% sensitivity, 88% specificity and 74% accuracy for AL at a cut-off value of 9.8 mmol/L. The odds ratio for a 5 mmol/L increase in lactate in relation to the risk of AL was 2.9 (CI 1.1, 8.0).

CONCLUSIONS

Increased intraperitoneal lactate concentration within the first 5 d postoperative was significantly associated with clinical anastomotic leakage, but with low predictive values. The microdialysis method is not yet ready for clinical implication before large prospective studies have defined cut off values for a biologic marker in the setting of a clear definitions of leakage.

Splanchnic Circulation and Intraabdominal Metabolism in Two Porcine Models of Low Cardiac Output

The impact of acute cardiac dysfunction on the gastrointestinal tract was investigated in anesthetized and instrumented pigs by sequential reductions of cardiac output (CO). Using a cardiac tamponade (n = 6) or partial inferior caval vein balloon inflation (n = 6), CO was controllably reduced for 1 h each to 75% (CO_75%), 50% (CO_50%), and 35% (CO_35%) of the baseline value. Cardiac output in controls (n = 6) was not manipulated and maintained. Mean arterial pressure, superior mesenteric arterial blood flow, and intestinal mucosal perfusion started to decrease at CO_50% in the intervention groups. The decrease in superior mesenteric arterial blood flow was non-linear and exaggerated at CO_35%. Systemic, venous mesenteric, and intraperitoneal lactate concentrations increased in the intervention groups from CO_50%. Global and mesenteric oxygen uptake decreased at CO_35%. In conclusion, gastrointestinal metabolism became increasingly anaerobic when CO was reduced by 50%. Anaerobic gastrointestinal metabolism in low CO can be detected using intraperitoneal microdialysis.

Ischemia/reperfusion injury in porcine intestine - Viability assessment

AIM

To investigate viability assessment of segmental small bowel ischemia/reperfusion in a porcine model.

METHODS

In 15 pigs, five or six 30-cm segments of jejunum were simultaneously made ischemic by clamping the mesenteric arteries and veins for 1 to 16 h. Reperfusion was initiated after different intervals of ischemia (1-8 h) and subsequently monitored for 5-15 h. The intestinal segments were regularly photographed and assessed visually and by palpation. Intraluminal lactate and glycerol concentrations were measured by microdialysis, and samples were collected for light microscopy and transmission electron microscopy. The histological changes were described and graded.

RESULTS

Using light microscopy, the jejunum was considered as viable until 6 h of ischemia, while with transmission electron microscopy the ischemic muscularis propria was considered viable until 5 h of ischemia. However, following ≥ 1 h of reperfusion, only segments that had been ischemic for ≤ 3 h appeared viable, suggesting a possible upper limit for viability in the porcine mesenteric occlusion model. Although intraluminal microdialysis allowed us to closely monitor the onset and duration of ischemia and the onset of reperfusion, we were unable to find sufficient level of association between tissue viability and metabolic markers to conclude that microdialysis is clinically relevant for viability assessment. Evaluation of color and motility appears to be poor indicators of intestinal viability.

CONCLUSION

Three hours of total ischemia of the small bowel followed by reperfusion appears to be the upper limit for viability in this porcine mesenteric ischemia model.

Intraperitoneal lactate/pyruvate ratio and the level of glucose and glycerol concentration differ between patients surgically treated for upper and lower perforations of the gastrointestinal tract: a pilot study

BACKGROUND

Secondary peritonitis is a condition associated with high morbidity and mortality. Continuous postoperative monitoring of patients to ensure timely intervention to treat complications without delay is important for survival and outcome. We aimed to (1) investigate potential differences in postoperative intraperitoneal biomarker levels between patients with upper and lower gastrointestinal tract lesion, and (2) compare postoperative biomarker levels between complicated and uncomplicated patients.

METHODS

We included a total of 15 consecutive patients operated for upper (n = 7) and lower (n = 8) gastrointestinal tract perforation. We registered postoperative complications during a 30 days follow up-period. Complications were defined as intraabdominal complications, septic shock, and mortality. 5 patients were complicated. A microdialysis catheter was placed intraperitoneally in each patient. Samples were collected every 4th hour for up to 7 postoperative days. Samples were analysed for concentrations of glucose, lactate, pyruvate and glycerol.

RESULTS

Microdialysis results showed that patients with upper gastrointestinal tract lesions had significantly higher levels of postoperative intraperitoneal glucose and glycerol concentrations, as well as lower lactate/pyruvate ratios and lactate/glucose ratios. In the group with perforation of the lower gastrointestinal tract, those patients with a complicated course showed lower levels of postoperative intraperitoneal glucose concentration and glycerol concentration and higher lactate/pyruvate ratios and lactate/glucose ratios than those patients with an uncomplicated course.

CONCLUSION

Patients with upper and lower gastrointestinal tract lesions showed differences in postoperative biomarker levels. A difference was also seen between patients with complicated and uncomplicated postoperative courses.

Peritoneal fluid biomarkers in the detection of colorectal anastomotic leaks: a systematic review

PURPOSE

Anastomotic leak (AL) in colorectal surgery leads to significant morbidity, mortality and poorer oncological outcomes. Diagnosis of AL is frequently delayed as current methods of detection are not 100% sensitive or specific. 'Biomarkers', such as cytokines and markers of ischaemia, from the milieu of the anastomosis may aid early detection. This paper aims to review the evidence for their role in AL detection, allowing identification of targets for future research.

METHODS

A systematic review was performed using PubMed, MEDLINE and Cochrane Library databases. Papers concerning detection or prediction of AL with biomarkers were identified. References within the papers were used to identify further relevant articles.

RESULTS

Research has taken place in small cohorts with varying definitions of AL. Lactate has consistently been shown to be elevated in patients with intra-abdominal complications and ALs. pH on post-operative day 3 showed excellent specificity. Despite mixed results, a meta-analysis found that the cytokines tumour necrosis factor-α and interleukin-6 were elevated early in AL. Detection of bacteria in drain fluid by RT-PCR has good specificity but a high rate of false positives.

CONCLUSIONS

Peritoneal cytokines, lactate and pH have the potential to identify AL early. The consistency of the results for lactate and pH, alongside the fact that they are easy, quick and inexpensive to test, makes them the most attractive targets. Studies in larger cohorts with standardized definitions of AL are required to clarify their usefulness. Emerging biosensor technology may facilitate the development of small, low-cost and degradable intra-abdominal devices to measure peritoneal fluid biomarkers.

Integrated approach to colorectal anastomotic leakage: Communication, infection and healing disturbances

Colorectal anastomotic leakage (CAL) remains a major complication after colorectal surgery. Despite all efforts during the last decades, the incidence of CAL has not decreased. In this review, we summarize the available strategies regarding prevention, prediction and intervention of CAL and categorize them into three categories: communication, infection and healing disturbances. These three major factors actively interact during the onset of CAL. We aim to provide an integrated approach to CAL based on its etiology. The intraoperative air leak test, intraoperative endoscopy, radiological examinations and stoma construction mainly aim to detect and to prevent communication between the intra- and extra-luminal content. Other strategies including postoperative drainage, antibiotics, and infectious-parameter evaluation are intended to detect and prevent anastomotic or peritoneal infection. Most currently available interventions for CAL focus on the control of communication and infection, while strategies targeting the healing disturbances such as lifestyle changes, oxygen therapy and evaluation of metabolic biomarkers still lack wide clinical application. This simplified categorization may contribute to an integrated understanding of CAL. We strongly believe that this integrated approach should be taken into consideration during clinical practice. An integrated approach to CAL could contribute to a better understanding of the etiology of CAL and eventually better patient outcome.

Effects of inhalation of low-dose nitrite or carbon monoxide on post-reperfusion mitochondrial function and tissue injury in hemorrhagic shock swine

Introduction

Tissue reperfusion following hemorrhagic shock may paradoxically cause tissue injury and organ dysfunction by mitochondrial free radical expression. Both nitrite and carbon monoxide (CO) may protect from this reperfusion injury by limiting mitochondrial free radial production. We explored the effects of very small doses of inhaled nitrite and CO on tissue injury in a porcine model of hemorrhagic shock.

Methods

Twenty pigs (mean wt. 30.6 kg, range 27.2 to 36.4 kg) had microdialysis catheters inserted in muscle, peritoneum, and liver to measure lactate, pyruvate, glucose, glycerol, and nitrite. Nineteen of the pigs were bled at a rate of 20 ml/min to a mean arterial pressure of 30 mmHg and kept between 30 and 40 mmHg for 90 minutes and then resuscitated. One pig was instrumented but not bled (sham). Hemorrhaged animals were randomized to inhale nothing (control, n = 7), 11 mg nitrite (nitrite, n = 7) or 250 ppm CO (CO, n = 5) over 30 minutes before fluid resuscitation. Mitochondrial respiratory control ratio was measured in muscle biopsies. Repeated measures from microdialysis catheters were analyzed in a random effects mixed model.

Results

Neither nitrite nor CO had any effects on the measured hemodynamic variables. Following inhalation of nitrite, plasma, but not tissue, nitrite increased. Following reperfusion, plasma nitrite only increased in the control and CO groups. Thereafter, nitrite decreased only in the nitrite group. Inhalation of nitrite was associated with decreases in blood lactate, whereas both nitrite and CO were associated with decreases in glycerol release into peritoneal fluid. Following resuscitation, the muscular mitochondrial respiratory control ratio was reduced in the control group but preserved in the nitrite and CO groups.

Conclusions

We conclude that small doses of nebulized sodium nitrite or inhaled CO may be associated with intestinal protection during resuscitation from severe hemorrhagic shock.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-0903-z) contains supplementary material, which is available to authorized users.

Mediastinal microdialysis in the diagnosis of early anastomotic leakage after resection for cancer of the esophagus and gastroesophageal junction

BACKGROUND

Anastomotic leakage (AL) after gastroesophageal resection for cancer is a serious complication. The aim was to evaluate mediastinal microdialysis in the detection of AL before clinical symptoms.

METHODS

Sixty patients were included. Samples were collected every 4 hours in the 1st 8 postoperative days and analyzed for several metabolites.

RESULTS

Forty-four patients had an uncomplicated postoperative recovery, 7 developed anastomotic-related complications, and 5 developed major nonanastomotic-related complications. Six patients were excluded (early catheter malfunction and reoperation). Logistic regression model on several metabolites demonstrated a 100% sensitivity, specificity, and positive and negative predictive values regarding the diagnosis of anastomotic complications within postoperative day 7. However, as independent markers, none of the measured metabolites were able to predict AL.

CONCLUSION

The diagnosis of anastomotic-related complications before clinical symptoms seemed possible by mediastinal microdialysis, but the diagnosis should be based on an interpretation of several metabolic events.

Validation of intraluminal and intraperitoneal microdialysis in ischemic small intestine

BACKGROUND

We sought to define the sensitivity and specificity of intraperitoneal (IP) and intraluminal (IL) microdialysate metabolites in depicting ex vivo small intestinal total ischemia during GI-tract surgery. We hypothesized that IL as opposed to IP microdialysis detects small intestinal ischemia with higher sensitivity and specificity.

METHODS

IL and IP microdialysate lactate, pyruvate, glucose and glycerol were analysed from small intestine of pancreaticoduodenectomy patients before and after occluding the mesenteric vasculature and routine resection of a segment of small intestine. Ex vivo time sequences of microdialysate metabolites were described and ROC analyses after 0-30, 31-60, 61-90 and 91-120 minutes after the onset ischemia were calculated.

RESULTS

IL lactate to pyruvate ratio (L/P ratio) indicated ischemia after 31-60 minutes with 0.954 ROC AUC (threshold: 109) in contrast to IP L/P (ROC AUC of 0.938 after 61-90 minutes, threshold: 18). At 31-60 minutes IL glycerol concentration indicated ischemia with 0.903 ROC AUCs (thresholds: 69 μmol/l). IP glycerol was only moderately indicative for ischemia after 91-120 minutes with 0,791 ROC AUCs (threshold 122 μmol/l). After 31-60 minutes IL and IP lactate to glucose ratios (L/G ratio) indicated ischemia with 0.956 and 0,942 ROC AUCs (thresholds: 48,9 and 0.95), respectively.

CONCLUSIONS

The results support the hypothesis that intraluminal application of microdialysis and metabolic parameters from the small intestinal lumen indicate onset of ischemia earlier than intraperioneal microdialysis with higher sensitivity and specificity.

Intra-peritoneal microdialysis and intra-abdominal pressure after endovascular repair of ruptured aortic aneurysms

OBJECTIVES

This study aims to evaluate intra-peritoneal (ip) microdialysis after endovascular aortic repair (EVAR) of ruptured abdominal aortic aneurysm (rAAA) in patients developing intra-abdominal hypertension (IAH), requiring abdominal decompression.

DESIGN

Prospective study.

MATERIAL AND METHODS

A total of 16 patients with rAAA treated with an emergency EVAR were followed up hourly for intra-abdominal pressure (IAP), urine production and ip lactate, pyruvate, glycerol and glucose by microdialysis, analysed only at the end of the study. Abdominal decompression was performed on clinical criteria, and decompressed (D) and non-decompressed (ND) patients were compared.

RESULTS

The ip lactate/pyruvate (l/p) ratio was higher in the D group than in the ND group during the first five postoperative hours (mean 20 vs. 12), p = 0.005 and at 1 h prior to decompression compared to the fifth hour in the ND group (24 vs. 13), p = 0.016. Glycerol levels were higher in the D group during the first postoperative hours (mean 274.6 vs. 121.7 μM), p = 0.022. The IAP was higher only at 1 h prior to decompression in the D group compared to the ND group at the fifth hour (mean 19 vs. 14 mmHg).

CONCLUSIONS

Ip l/p ratio and glycerol levels are elevated immediately postoperatively in patients developing IAH leading to organ failure and subsequent abdominal decompression.

Intraluminal intestinal microdialysis detects markers of hypoxia and cell damage in experimental necrotizing enterocolitis

BACKGROUND/PURPOSE

Necrotizing enterocolitis (NEC) represents one of the gravest complications in premature infants and carries significant morbidity and mortality. There is a great need for improved diagnostic methods to reduce the severity and incidence of NEC. The aim of the study was to investigate if intraluminal microdialysis can detect intestinal ischemia in newborn rats with induced experimental NEC.

METHODS

The studies were performed on 1-day-old Sprague-Dawley rat pups. Experimental NEC was induced using hypoxia/reoxygenation treatment. Microdialysis catheters were rectally inserted and placed in the rectosigmoid part of the colon. Microdialysate levels of glucose, lactate, pyruvate, and glycerol were measured. Intestinal specimens were collected at the end of the experiments for microscopic evaluation.

RESULTS

Intraluminal microdialysis revealed signs of intestinal hypoxia and cellular damage, with a marked increase of lactate and glycerol. Microscopic evaluation confirmed intestinal damage in the NEC group.

CONCLUSION

Intraluminal microdialysis can detect intestinal hypoxic stress and mucosal cell membrane decay in a rat model of NEC. Intestinal intraluminal microdialysis is easily accessible through the rectum and may be a useful noninvasive complement to other methods in the assessment of NEC.

Early detection of metabolic changes using microdialysis during and after experimental kidney transplantation in a porcine model

BACKGROUND

Microdialysis (MD) can detect organ-related metabolic changes before they become measurable in plasma through the biochemical parameters. This study aims to evaluate the early detection of metabolic changes during experimental kidney transplantation (KTx).

MATERIAL AND METHODS

During preparation of 8 donor kidneys, one MD catheter was inserted in the renal cortex and samples were collected. After a 6-hour cold ischemia time (CIT), kidneys were implanted in the 8 recipient pigs. Throughout the warm ischemia time (WIT) and after reperfusion, kidneys were monitored. The interstitial glucose, lactate, pyruvate, glutamate, and glycerol concentrations were evaluated.

RESULTS

A significant decline in glucose level was observed at the end of CIT. The lactate level was reduced to the minimum point of 0.35 ± 0.08 mmol/L in CIT. After reperfusion, lactate values raised significantly. During the WIT, the pyruvate level increased, continued until the end of the WIT. For glutamate, a steady increase was noted during explantation, CIT, WIT, and early reperfusion phases. The increase of glycerol value continued in the early postreperfusion, which was then followed by a sharp decline.

CONCLUSION

MD is a fast and simple minimally invasive method for measurement of metabolic substrates in renal parenchyma during KTx. MD offers the option of detecting minor changes of interstitial glucose, lactate, pyruvate, glutamate, and glycerol in every stage of KTx. Through the use of MD, metabolic changes can be continuously monitored during the entire procedure of KTx.

Intraperitoneal microdialysis in the postoperative surveillance after surgery for necrotizing enterocolitis: a preliminary report

BACKGROUND/PURPOSE

The aim of the present pilot study was to evaluate the safety and clinical application of intraperitoneal microdialysis (MD) in preterm infants operated on for necrotizing enterocolitis (NEC).

METHODS

Fourteen infants underwent MD. Two were excluded from analysis: 1 because of catheter malfunction and 1 because of fatal outcome immediately after surgery. The median MD time was 122 hours. Samples were collected every 4 hours, and the concentration of glucose, lactate, pyruvate, and glycerol was measured.

RESULTS

Three infants were reoperated on: 2 because of recurrent NEC and 1 because of ileal stenosis. In the 2 cases with recurrent NEC, changes in MD variables were found. Another had a prolonged postoperative period owing to diffuse fecal peritonitis. The values of MD normalized along with the return of bowel function. In 8 infants, the postoperative course was uncomplicated. The results of peritoneal MD in patients with complications were significantly different from those with an uncomplicated course (lactate/pyruvate ratio and glucose concentration).

CONCLUSION

Peritoneal MD is a safe procedure and an applicable method in surveillance of the metabolic and inflammatory changes in the peritoneal cavity after surgery for NEC. Larger series are needed to evaluate the clinical significance and use of this method.

Peritoneal microdialysis. Early diagnosis of anastomotic leakage after low anterior resection for rectosigmoid cancer

BACKGROUND

The aim of the present study was to evaluate the efficacy and safety of intraperitoneal microdialysis in early detection of anastomotic leakage after low anterior resection for rectosigmoid cancer.

METHODS

In a series of 116 consecutive patients scheduled for low anterior resection for rectosigmoid cancer, a total of 50 patients consented to participate. Peritoneal microdialysis was performed by a 1 mm thin catheter anchored in close proximity to the anastomosis. Five patients were excluded due to catheter malfunction. Average microdialysis time in the remaining 45 patients was 177.6 (80-252) hours. Samples were collected every 4-hours, and the concentration of glucose, lactate, pyruvate and glycerol was measured.

RESULTS

Four patients developed symptomatic anastomotic leakage. Two patients developed non-abdominal sepsis. In 38 patients the postoperative course was uncomplicated, considering major complications, and they served as controls. In three patients with late (>or=10 days) anastomotic leakage a significant increase in concentration of lactate and lactate/pyruvate ratio (L/P-ratio) was seen several days prior to development of clinical symptoms. In one patient with early anastomotic leakage it coincided with the development of clinical symptoms. In the two patients with non-abdominal sepsis the values were within normal range.

CONCLUSION

Peritoneal microdialysis is a safe and promising tool in early diagnosis of anastomotic leakage after low anterior resection for rectosigmoid cancer.

Use of rapid sampling microdialysis for intraoperative monitoring of bowel ischemia

PURPOSE

Intestinal ischemia is a major cause of anastomotic leak and death and remains a clinical challenge as the physician relies on several nonspecific signs, biologic markers, and radiologic studies to make the diagnosis. This study used rapid sampling online microdialysis to evaluate the biochemical changes occurring in a segment of human bowel during and after resection, and assessed for the feasibility and reproducibility of this technique in monitoring intestinal ischemia.

METHODS

A custom made, rapid sampling online microdialysis analyzer was used to monitor the changes in the bowel wall of specimens being resected intraoperatively. Two patients were recruited for the pilot study to optimize the analyzer and seven patients undergoing colonic resections were recruited for the data collection and analysis.

RESULTS

The concentration of glucose in the extracellular bowel wall fluid decreased transiently after division of individual feeding arteries followed by a rebound increase in the concentration back to baseline concentrations. After completion of resection, glucose concentrations continued to decrease while lactate concentrations increased constantly.

CONCLUSION

Rapid sampling microdialysis was feasible in the clinical environment. These results suggest that tissue responds to ischemic insult by mobilizing glucose stores which later decrease again, whereas lactate concentrations constantly increased.

The effects of vasopressors on perfusion of gastric graft after esophagectomy. An experimental study

AIMS

To evaluate the impact of the perioperative administration of norepinephrine on the perfusion of the esophageal graft.

METHODS

This is an experimental study. Six swine underwent transhiatal esophagectomy; the stomach was used to replace the resected esophagus. We provoked hemorrhagic shock to the animals and then we administered noradrenaline to restore the blood pressure. We monitored the graft perfusion perioperatively using the technique of microdialysis.

RESULTS

In all animals, the graft experienced severe hypoperfusion after the administration of noradrenaline that was statistically significant.

CONCLUSIONS

Our data support the hypothesis that norepinephrine should be used with extreme caution in the perioperative setting after esophagectomy. Further studies, however, will be required to evaluate the clinical significance of this finding.

Diagnostic accuracy of plasma biomarkers for intestinal ischaemia

OBJECTIVE

Intestinal ischaemia is a life-threatening condition with high mortality, and the lack of accurate and readily available diagnostic methods often results in delay in diagnosis and treatment. The aim of this study was to investigate the accuracy of different plasma biomarkers in diagnosing intestinal ischaemia.

MATERIAL AND METHODS

Prospective inclusion of patients older than 50 years with acute abdomen admitted to hospital in Karlskrona, Sweden, between 2001 and 2003. Venous blood was sampled prior to any surgery and within 24 h from onset of pain. D-lactate, alpha glutathione S-transferase, intestinal fatty acid binding protein, creatine kinase B, isoenzymes of lactate dehydrogenase (LD) and alkaline liver phosphatase (ALP) were analysed. D-dimer was analysed using four different commercially available test kits.

RESULTS

In-hospital mortalities among patients with (n = 10) and without (n = 61) intestinal ischaemia were 40 % and 3 %, respectively (p = 0.003). D-dimer was associated with intestinal ischaemia (p = 0.001) independently of which assay was used. No patient presenting with a normal D-dimer had intestinal ischaemia. D-dimer >0.9 mg/L had a specificity, sensitivity and accuracy of 82 %, 60 % and 79 %, respectively. Total LD, isoenzymes of LD 1-4 and liver isoenzyme of ALP (ALP liver) were significantly higher in patients with intestinal ischaemia, and accuracies for LD 2 (cut-off 2.3 microkat/L) and ALP liver (cut-off 0.7 microkat/L) were 69 % and 66 %, respectively.

CONCLUSIONS

D-dimer may be used as an exclusion test for intestinal ischaemia, but lacks specificity. The other plasma biomarkers studied had insufficient accuracy for this group of patients. Further studies are needed.

Tyrosine: a possible marker of severe intestinal injury during ischemia

BACKGROUND

Long periods of ischemia can cause organ injury and dysfunction. The protein degradation occurring in the muscular layer and in the mucosa of the intestinal wall during ischemia may release amino acids into the intestinal lumen or into the circulation. The small intestine, like skeletal muscle, cannot synthesize or degrade tyrosine. Thus, the tyrosine concentration released from the gut mucosa reflects the balance between protein synthesis and degradation. We aimed to determine whether tyrosine can be used as a marker of intestinal injury during ischemia.

METHODS

In 19 anesthetized rabbits, an ultrasonic flow probe was placed around the superior mesenteric artery to estimate blood flow. A segment from the ileum was isolated using two multilumen catheters with inflated balloons to create a closed segment for perfusion. Animals were allocated into three groups: a sham group without intervention (group I); a group submitted to superior mesenteric artery ligation only (group II); and a group submitted to 1 h of SMA clamping followed by 1 h of reperfusion (group III). Concentrations of lactate and tyrosine (fluorometry) were determined in the serum and the gut luminal perfusate.

RESULTS

Gut luminal perfusate tyrosine concentrations increased significantly in group II (from 10 +/- 8 to 93 +/- 63 mm/mL at 2 h) and were significantly higher than in group I (26 +/- 24 mm/mL) and group III (11 +/- 13 mm/mL) (P < 0.05 for all).

CONCLUSION

Tyrosine is released from cells into the lumen during severe intestinal ischemia. Regional measurements of tyrosine levels may be a useful indicator of severe intestinal villus compromise.

Diagnostic value of plasminogen activity level in acute mesenteric ischemia

AIM: To investigate the changes in plasminogen activity level during mesenteric ischemia.

METHODS: We performed laparotomy in 90 female Wistar-Albino rats (average weight 230 g). In sham groups (SL) (GroupsIand II) the superior mesenteric artery (SMA) and vein (SMV) were explored, but not tied. In SMA groups (Groups III and IV) the SMA was ligated, and in SMV groups (Groups V and VI) the SMV was ligated. On re-laparotomy 2 mL of blood was drawn at 1 h in groupsI, III and V, and at 3 h in groups II, IV and VI. Plasminogen levels were assessed and comparisons were made between groups and within each group.

RESULTS: The mean plasminogen activity in the SL group was significantly higher than SMA (25.1 ± 10.8 vs 11.8 ± 4.6, P < 0.001) or SMV (25.1 ± 10.8 vs 13.7 ± 4.4, P < 0.001) groups both at 1 h and at 3 h (29.8 ± 8.9 vs 15.1 ± 5.7, P < 0.0001; 29.8 ± 8.9 vs 14.2 ± 2.9, P < 0.0001). There were no significant differences between the values of SMA and SMV groups at 1 h (P = 0.28) and at 3 h (P = 0.71). In each group, plasminogen activity levels did not change significantly between the two measurements performed at 1 h and 3 h.

CONCLUSION: We conclude that blood plasminogen activities decrease during early phases of both arterial and venous mesenteric ischemia which may be a useful marker for early diagnosis.

Metabolic changes in the pig liver during warm ischemia and reperfusion measured by microdialysis

AIM

Portal triad clamping can cause ischemia-reperfusion injury. The aim of the study was to monitor metabolic changes by microdialysis before, during, and after warm ischemia in the pigliver.

MATERIAL AND METHODS

Eight pigs underwent laparotomy followed by ischemia by Pringle's maneuver. One microdialysis catheter was placed in each of four liver lobes. A reference catheter was placed in a muscle. Microdialysis samples were collected at intervals of 30 min starting 2 h before 1 h of total ischemia followed by 3 h of reperfusion. Glucose, lactate, pyruvate, and glycerol concentrations were measured. Blood samples were drawn for determination of alanine aminotransferase, alkaline phosphatase, and bilirubin together with total leukocytes and prothrombin time.

RESULTS

All parameters were stable during the baseline period. During the ischemic period, lactate levels increased significantly (P < 0.05) followed by a rapid decrease after reperfusion. A transient increase was observed for glucose and glycerol. Pyruvate showed a slight increase from the time of ischemia. The lactate-pyruvate ratio increased rapidly after initiating ischemia and decreased immediately after reperfusion. A slight increase in transaminase levels was observed.

CONCLUSIONS

During and after warm ischemia, there were profound metabolic changes in the pigliver observed with an increase in lactate, glucose, glycerol, and the lactate-pyruvate ratio. There were no differences between the four liver lobes, indicating the piglivers homogeneity.

Anastomotic leakage, the search for a reliable biomarker. A review of the literature

BACKGROUND

Colorectal anastomotic leakage (AL) is a severe complication leading to severe infection, sepsis and sometimes death. At present the diagnosis is made clinically, usually at 6-8 days after surgery. An objective biomarker reflecting the intra-abdominal milieu surrounding the anastomosis would be a useful additional diagnostic tool to make the diagnosis of AL before its clinical presentation. This review aims to assess the current status of the search for such a biomarker in peritoneal fluid.

METHOD

A literature search was carried out, using MEDLINE, PubMed and the Cochrane library, for all publications concerning human peritoneal fluid in relation to postoperative complications in general, and, more specific, anastomotic leakage after colorectal surgery.

RESULTS

Analysis of several immune parameters, tissue repair parameters, parameters for ischaemia and microbiological composition of peritoneal fluid show that these can be determined reliably in the fluid, albeit with a large variance. Furthermore the data show that changes in concentration of these parameters precede AL and other postoperative complications by several days.

CONCLUSION

The results of the review demonstrate that it is possible to distinguish between patients with and without AL by measuring biomarkers in fluid from the peritoneal drain. Prospective studies with larger numbers of patients should, however, be performed and additional biomarkers should be studied to explore the full diagnostic potential of this approach.

L-Lactate After Embolization of the Superior Mesenteric Artery

BACKGROUND

Plasma markers for intestinal ischemia have not proven to be accurate. The value of L-lactate is unclear. Experimental models based on open surgery confound the effects of surgical trauma with that of ischemia. The aim was to create an endovascular model for acute superior mesenteric artery thromboembolism, and then to study L-lactate and lactate dehydrogenase (LD) activity in plasma and peritoneal fluid in pigs with extensive, high-grade intestinal ischemia.

MATERIALS AND METHODS

Nine pigs underwent full superior mesenteric artery embolization with 4 h of intended intestinal ischemia, whereas six were control animals. Sampling of central venous and arterial blood was performed throughout the experiment, ending with laparotomy to collect peritoneal fluid and segmental intestinal biopsies. A pathologist, blinded to the performed interventions, graded the ischemic lesions.

RESULTS

There were no differences in plasma L-lactate (P = 0.61) or LD activity levels (P = 0.69), measured at different time points from baseline to end of study, between animals with extensive, high-grade intestinal ischemia and sham. Intraperitoneal L-Lactate (P = 0.005) and LD activity (P = 0.018) levels were elevated compared with sham. There were differences in grades of ischemia in the duodenum (P = 0.003), small intestine (P < 0.001), proximal (P < 0.001), and sigmoid (P = 0.032) colon between experimental animals and sham. The grade of small bowel ischemia (n = 15) correlated to intraperitoneal fluid L-lactate (r = 0.80; P < 0.001) and LD activity levels (r = 0.72; P = 0.003).

CONCLUSIONS

This endovascular study in a porcine model showed that L-lactate and LD activity levels in peritoneal fluid, not in plasma, reflect intestinal ischemia. The study suggests that plasma L-lactate not is a useful early marker in patients with suspicion of intestinal ischemia.

Indirect determination of pyruvic acid by capillary electrophoresis with amperometric detection

A method of indirectly measuring pyruvic acid (PA) by capillary electrophoresis with amperometric detection is proposed for the first time. It is based on the oximation reaction between PA and hydroxylamine (NH(2)OH), and the quantification of PA was performed by direct and sensitive amperometric detection of excessive NH(2)OH after the oximation reaction. This method displayed a good sensitivity, and the detection limits of NH(2)OH and PA are 1.76 x 10(-7) and 3.88 x 10(-7)mol/L, respectively at S/N=3. The linear relationship between the peak current and PA concentration is exhibited over the range from 4 x 10(-6) to 1 x 10(-4)mol/L. This method has been applied to determine PA in rat plasma with satisfactory results.

Lactate and glycerol released to the intestinal lumen reflect mucosal injury and permeability changes caused by strangulation obstruction

BACKGROUND

The present study evaluates whether microdialysis of glycerol and lactate reflects mucosal injury and permeability changes after strangulation obstruction of the pig small intestine.

METHODS

Strangulation obstruction was induced by tightening a rubber band around a small bowel loop until its venous pressure increased to a level just below diastolic aortic pressure (partial strangulation), or further until cessation of flow in the main feeding artery (total strangulation). Mucosal injury and permeability of marker molecules from blood to lumen and vice versa was compared to release of glycerol and lactate to the intestinal lumen.

RESULTS

Mucosal injury, hyperpermeability, and release of glycerol were more pronounced after total than after partial strangulation. In animals with partial strangulation there was a complete restitution of the surface epithelium, and luminal glycerol and lumen-to-blood permeability of polyethylene glycol 4000 remained low. Such animals showed a sustained elevation of lactate and blood-to-lumen permeability of fluorescein isothiocyanate dextran after 2 h of partial strangulation, but a decline to baseline levels of these parameters in animals with 1 h partial strangulation.

CONCLUSION

Microdialysis of lactate and glycerol in the intestinal lumen may be used to assess structural and functional changes of the intestinal mucosa after strangulation obstruction.

Peritoneal microdialysis in freely moving rodents: An alternative to blood sampling for pharmacokinetic studies in the rat and the mouse

By performing microdialysis in the peritoneal cavity, we studied the pharmacokinetics of Tramadol in awake, freely moving small laboratory animals. The systemic exposure to Tramadol was determined using both microdialysis sampling and collection of whole blood following a single intravenous injection (10 mg/kg) or a single oral dose (100 mg/kg) of Tramadol HCl. The sampling frequency of the dialysate was 10 min (mouse study) or 20 min (rat study). In rats and in mice, intraperitoneal microdialysis sampling gets reliable pharmacokinetic results without taking blood. The concentration-time curves obtained from peritoneal microdialysis were parallel to the concentration-time curves obtained from classical blood sampling. Accordingly, dose independent pharmacokinetic parameters were similar. A scaling factor, however, has to be introduced (e.g. peritoneal versus plasma AUC ratio) in order to obtain comparable pharmacokinetic results also with dose-dependent parameters. As there was no blood loss during the experiment, peritoneal microdialysis allowed the investigation of complete concentration-time curve profiles. Thus, the number of animals could be kept to a minimum. In conclusion, in vivo peritoneal microdialysis is a unique tool to obtain a complete set of free drug concentrations to determine reliable pharmacokinetic parameters from awake, freely moving rodents. Therefore, we suppose that the technique will have relevance for pharmacokinetic studies in future.

Prediction of postoperative complications after urgent laparotomy by intraperitoneal microdialysis: A pilot study

OBJECTIVE

The aim of the present study was to investigate the role of intraperitoneal microdialysis (IPM) techniques in monitoring the evolution of postoperative critically ill patients requiring urgent laparotomy.

SUMMARY BACKGROUND DATA

Postoperative intraabdominal sepsis is associated with an important degree of morbidity and mortality in acutely ill patients. Early diagnosis is critical to improve outcomes.

METHODS

: The study included 25 consecutive patients admitted to the intensive care unit (ICU) after urgent laparotomy. Measurements of microdialysate fluid were performed through a microdialysis catheter, positioned intraperitoneally, during the first 5 postoperative days and lactate/pyruvate (L/P) ratios calculated. Patients were followed until hospital discharge.

RESULTS

Ten patients had a complicated postoperative course, including 4 deaths (3 refractory shock, 1 mesenteric ischemia), 3 reinterventions (1 necrotic collection, 1 mesenteric ischemia, 1 biliary leak), 2 secondary peritonitis, and 1 intraabdominal collection. The IPM L/P ratio in these patients was already significantly higher during the first 24 postoperative hours compared with patients who had no complications (35 +/- 21 vs. 18 +/- 6, P < 0.01). An IPM L/P ratio above 22 on postoperative day 1 had a sensitivity of 0.64 and a specificity of 0.79 for complications. There were no significant differences between the two groups in pH, lactate, white blood cell count, or subcutaneous L/P ratio. No complication was associated with the technique.

CONCLUSIONS

IPM is safe and reliable and provides valuable information after urgent laparotomy. Persistently high L/P values should raise the possibility of serious postoperative complications.

Membrane microdialysis: Evaluation of a new method to assess splanchnic tissue metabolism

OBJECTIVE

Measuring peritoneal lactate concentrations could be useful for detecting splanchnic hypoperfusion. The aims of this study were to evaluate the properties of a new membrane-based microdialyzer in vitro and to assess the ability of the dialyzer to detect a clinically relevant decrease in splanchnic blood flow in vivo.

DESIGN

A membrane-based microdialyzer was first validated in vitro. The same device was tested afterward in a randomized, controlled animal experiment.

SETTING

University experimental research laboratory.

SUBJECTS

Twenty-four Landrace pigs of both genders.

INTERVENTIONS

In vitro: Membrane microdialyzers were kept in warmed sodium lactate baths with lactate concentrations between 2 and 8 mmol/L for 10-120 mins, and microdialysis lactate concentrations were measured repeatedly (210 measurements). In vivo: An extracorporeal shunt with blood reservoir and roller pump was inserted between the proximal and distal abdominal aorta, and a microdialyzer was inserted intraperitoneally. In 12 animals, total splanchnic blood flow (measured by transit time ultrasound) was reduced by a median 43% (range, 13% to 72%) by activating the shunt; 12 animals served as controls.

MEASUREMENTS AND MAIN RESULTS

In vitro: The fractional lactate recovery was 0.59 (0.32-0.83) after 60 mins and 0.82 (0.71-0.87) after 90 mins, with no further increase thereafter. At 60 and 90 mins, the fractional recovery was independent of the lactate concentration. In vivo: Abdominal blood flow reduction resulted in an increase in peritoneal microdialysis lactate concentration from 1.7 (0.3-3.8) mmol/L to 2.8 (1.3-6.2) mmol/L (p = .006). At the same time, mesenteric venous-arterial lactate gradient increased from 0.1 (-0.2-0.8) mmol/L to 0.3 (-0.3 -1.8) mmol/L (p = .032), and mesenteric venous-arterial Pco2 gradients increased from 12 (8-19) torr to 21 (11-54) torr (p = .005).

CONCLUSIONS

Peritoneal membrane microdialysis provides a method for the assessment of splanchnic ischemia, with potential for clinical application.

Microdialysis of the bowel: the possibility of monitoring intestinal ischemia

Assessment of the intestinal circulation in a clinical setting still presents a significant diagnostic challenge. In patients suspected of having intestinal ischemia pre- or postoperatively, there is no clinically relevant marker which can determine whether the bowel is suffering from lack of oxygen or not. Microdialysis is a microinvasive technique that makes it possible to continuously detect tissue-specific metabolic changes. Recently, it has been demonstrated that intestinal ischemia can be detected and monitored continuously by the use of a microdialysis catheter placed in the proximity of the ischemic bowel. This review summarizes the clinical dilemma of intestinal ischemia and the latest experimental results using the microdialysis technique to detect critical perfusion in the small intestine. The possibility of using microdialysis in a clinical setting is outlined with the perspective of using it as a pre- or postoperative monitoring tool in relevant patients.

24-h storage of pig livers in UW, HTK, hydroxyethyl starch, and saline solution: is microdialysis an appropriate method for the continuous graft monitoring during preservation?

Recent studies demonstrate the feasibility of microdialysis to monitor metabolism in ischemic livers. Whether these parameters correlate with markers of liver cell integrity in an experimental model using pig livers and different preservation solutions was an aim of this study. Pig livers were flushed with either 4 degrees C Histidine-Typtophan-Ketoglutarate solution (HTK) (Custodiol), University of Wisconsin solution (ViaSpan), and hydroxyethyl starch, or 12 degrees C saline solution. After 24-h storage, the livers were rinsed with saline to measure liver enzymes and lactate from the effluate. Utilizing microdialysis, intraparenchymal lactate, pyruvate, glucose, and glycerol was monitored. Tissue biopsies were taken for histological examinations. Cold preservation resulted in a decrease of metabolic activity measured by intrahepatic glucose, lactate, and pyruvate levels, as well as lactate in the effluate, independently of the solution used. Of particular interest, glycerol levels partially reflected the extent of hepatocellular damage and liver enzyme release. Glycerol levels partially discriminated preservation of different quality and were in accordance to histological findings and liver enzyme release. Lactate, pyruvate, and glucose levels were not appropriate as markers during cold storage. Whether or not glycerol monitoring could represent an additional and rational complementation to the current practice of macroscopic, microscopic and donor evaluation has to be clarified by further studies.

Microdialysis study of imipenem distribution in the intraperitoneal fluid of rats with or without experimental peritonitis

The purpose of this study was to extend the use of microdialysis to the investigation of antibiotic distribution into the intraperitoneal fluid of rats with or without peritonitis. Microdialysis probes were inserted into the jugular vein and peritoneal cavity of control rats or rats with intra-abdominal sepsis (n = 8 in each group) induced by cecal ligation and punctures. Imipenem (IPM) probe recoveries were determined in each rat by retrodialysis by drug. IPM was infused intravenously at a dose of 30 mg . kg(-1) over 30 min, microdialysis samples were collected for 120 min, and IPM concentrations were determined by high-performance liquid chromatography. Intraperitoneal infection had no statistically significant effect on IPM clearance (11.9 +/- 2.3 ml.min(-1).kg(-1) in control rats versus 10.9 +/- 2.1 ml.min(-1).kg(-1) in rats with peritonitis) or the volume of distribution (296 +/- 47 ml.kg(-1) in control rats versus 310 +/- 49 ml.kg(-1) in rats with peritonitis). IPM concentration profiles in intraperitoneal fluid and blood were virtually superimposed in control rats, whereas in infected animals, the mean intraperitoneal IPM concentrations were apparently slightly lower than corresponding blood levels. However, the areas under the concentration-versus-time curve estimated in intraperitoneal fluid and blood were not significantly different in both groups, with the corresponding ratios close to unity (1.01 +/- 0.19 and 0.89 +/- 0.28 in control rats and rats with peritonitis, respectively). In conclusion, IPM distribution in intraperitoneal fluid is rapid and complete both in control rats and in rats with peritonitis.

A Study of the Metabolites of Ischemia-Reperfusion Injury and Selected Amino Acids in the Liver Using Microdialysis during Transplantation

BACKGROUND

Preservation and ischemia-reperfusion injury still impact the outcome of orthotopic liver transplantation. The authors used microdialysis with a view to monitoring its effect on graft function.

METHODS

A microdialysis catheter was inserted into the graft immediately after reperfusion and perfused with an isotonic solution for 48 hr. Metabolites of the ischemia-reperfusion injury and selected amino acids were studied. There were 18 patients, with a median age of 52 years (range, 38-62 years), 8 of whom were men. Lactate, pyruvate, glycerol, and glucose levels were measured. In addition, alanine, arginine, citrulline, gamma-aminobutyric acid (GABA), glutamate, glutamine, glycine, and taurine were determined.

RESULTS

All grafts functioned well. High lactate, pyruvate, and glycerol levels were observed in the immediate postoperative period. These showed a significant rapid decrease and stabilized to baseline levels. Alanine, glutamate, GABA, and taurine levels declined significantly to baseline values. Arginine levels were low immediately postreperfusion and then increased, reaching significantly higher values beyond 19 hr.

CONCLUSIONS

These data may represent "normal" changes seen in the immediate posttransplant period because all grafts functioned well. Two important metabolic fates of arginine in the liver are in the detoxification of ammonia by means of the urea cycle, and in the synthesis of nitric oxide (NO). Low extracellular arginine may reflect influx of the amino acid into hepatocytes, resulting in formation of NO in the presence of inducible NO synthase or conversion to ornithine in the presence of arginase in the urea cycle. As the organ stabilizes, restriction of arginine uptake may give rise to the observed increase in extracellular arginine.