Surface microdialysis measures local tissue metabolism after Ivor Lewis esophagectomy; an attempt to predict anastomotic defect.

Anastomotic defect (AD) after esophagectomy can lead to severe complications with need for surgical or endoscopic intervention. Early detection enables early treatment and can limit the consequences of the AD. As of today, there are limited methods to predict AD. In this study, we have used microdialysis (MD) to measure local metabolism at the intrathoracic anastomosis. Feasibility and possible diagnostic use were investigated. Sixty patients planned for Ivor Lewis esophagectomy were enrolled. After construction of the anastomosis, surface MD (S-MD) probes were attached to the outer surface of the esophageal remnant and the gastric conduit in close vicinity of the anastomosis and left in place for 7 postoperative days (PODs). Continuous sampling of local tissue concentrations of metabolic substances (glucose, lactate, and pyruvate) was performed postoperatively. Outcome, defined as AD or not according to Esophagectomy Complications Consensus Group definitions, was recorded at discharge or at first postoperative follow up. Difference in concentrations of metabolic substances was analyzed retrospectively between the two groups by means of artificial neural network technique. S-MD probes can be attached and removed from the gastric tube reconstruction without any adverse events. Deviating metabolite concentrations on POD 1 were associated with later development of AD. In subjects who developed AD, no difference in metabolic concentrations between the esophageal and the gastric probe was recorded. The technical failure rate of the MD probes/procedure was high. S-MD can be used in a clinical setting after Ivor Lewis esophagectomy. Deviation in local tissue metabolism on POD 1 seems to be associated with development of AD. Further development of MD probes and procedure is required to reduce technical failure.

Surface Microdialysis Detects Ischemia After Esophageal Resection-An Experimental Animal Study.

BACKGROUND: After an esophageal resection, continuity is commonly restored by a gastric tube reconstruction and an intrathoracic anastomosis to the remaining proximal esophagus. Ischemia of the anastomotic region is considered to play a pivotal role in anastomotic leakage. Microdialysis (µD) is an excellent method to measure local biochemical substances and parameters in a specific organ or compartment aiming at early detection of ischemia. This animal study evaluates ischemia of the gastric tube reconstruction using a novel method-µD on organ surfaces. This promising method may have the potential to detect an anastomotic leakage before clinical symptoms develop. METHODS: Anesthetized normoventilated pigs were used. Surface microdialysis (S-µD) catheters and an intraparenchymal oxygen tension catheter were placed on the stomach. A gastric tube was made and the gastroepiploic artery was divided halfway along the greater curvature to produce severe ischemia at the top of the gastric tube. µD data from four locations (gastric tube, ileum and peritoneal cavity) were recorded every 20 min during the experiment. Tissue samples from all catheter sites underwent histopathological analysis. Intraparenchymal oxygen partial pressure, systemic blood tests, and hemodynamic parameters were recorded. RESULTS: S-µD data showed values indicating severe ischemia at the top of the gastric tube and intermediate ischemia at the level of transection of the gastroepiploic artery. Ischemia was verified by histopathological analysis of tissue samples and intraparenchymal oxygen tension data. CONCLUSIONS: S-µD can detect and grade severity of local ischemia in real time, in an animal model.

Thoracic epidural anaesthesia reduces insulin resistance and inflammatory response in experimental acute pancreatitis.

AIMS: The activity of the sympathetic nervous system (SNS) is crucial at an early stage in the development of an inflammatory reaction. A study of metabolic events globally and locally in the early phase of acute pancreatitis (AP), implying hampered SNS activity, is lacking. We hypothesized that thoracic epidural anaesthesia (TEA) modulates the inflammatory response and alleviates the severity of AP in pigs. MATERIAL AND METHODS: The taurocholate (TC) group (n = 8) had only TC AP. The TC + TEA group (n = 8) had AP and TEA. A control group (n = 8) underwent all the preparations, without having AP or TEA. Metabolic changes in the pancreas were evaluated by microdialysis and by histopathological examination. RESULTS: The relative increase in serum lipase concentrations was more pronounced in the TC group than in TC + TEA and control groups. A decrease in relative tissue oxygen tension (PtiO2) levels occurred one hour later in the TC + TEA group than in the TC group. The maintenance of normoglycaemia in the TC group required a higher glucose infusion rate than in the TC + TEA group. The relative decrease in serum insulin concentrations was most pronounced in the TC + TEA group. CONCLUSION: TEA attenuates the development of AP, as indicated by changes observed in haemodynamic parameters and by the easier maintenance of glucose homeostasis. Further, TEA was associated with attenuated insulin resistance and fewer local pathophysiological events.

Surface microdialysis on small bowel serosa in monitoring of ischemia.

BACKGROUND: Ischemic injury of an organ causes metabolic change from aerobic to anaerobic metabolism. It has been shown in experimental studies on the heart and liver that such conversion may be detected by conventional microdialysis probes placed intra-parenchymatously, as well as on organ surfaces, by assaying lactate, pyruvate, glucose, and glycerol in dialysate. We developed a microdialysis probe (S-µD) intended for use solely on organ surfaces. The aim of this study was to assess whether the newly developed S-µD probe could be used for detection and monitoring of small bowel ischemia. METHODS: In anesthetized normoventilated pigs, a control S-µD probe was applied on the jejunal serosa 50 cm downstream from the duodenojejunal junction (DJJ). Starting 100 cm from DJJ, a 100-cm long ischemic segment was created by division of all mesenteric vessels. S-µDs were applied at 2.5, 5, 20, and 50 cm from the starting point of ischemia by serosal sutures. A standard µD probe was placed in the abdominal cavity as a further control. Dialysate was harvested before inducing ischemia and subsequently every 20 min for 4 h. Central venous blood was drawn every hour to monitor systemic lactate, C-reactive protein, and white blood cell count. RESULTS: Microdialysis lactate levels were significantly higher than baseline from 20 min on into protocol time in the ischemic segment and in the control S-µD probe. The peritoneal cavity probe showed no significant elevation. Lactate levels from the ischemic segment reached a plateau at 60 min. Courses of pyruvate, glucose, and glycerol levels were in accordance with transition from an aerobic to anaerobic metabolism in the bowel wall. No statistically significant changes in hemoglobin, white blood cell count, or lactate values in central venous blood were recorded. CONCLUSIONS: Assaying the aforementioned compounds in dialysate, harvested by the newly developed S-µD probe, allowed detection and monitoring of small bowel ischemia from 20 min on following its onset.

Outcome of microdialysis sampling on liver surface and parenchyma.

BACKGROUND: To investigate whether surface microdialysis (µD) sampling in probes covered by a plastic film, as compared to noncovered and to intraparenchymatous probes, would increase the technique's sensitivity for pathophysiologic events occurring in a liver ischemia-reperfusion model. Placement of µD probes in the parenchyma of an organ, as is conventionally done, may cause adverse effects, e.g., bleeding, possibly influencing outcome. METHODS: A transient ischemia-reperfusion model of the liver was used in six anesthetized normoventilated pigs. µD probes were placed in the parenchyma and on the liver surface. Surface probes were either left uncovered or were covered by plastic film. RESULTS: Lactate and glucose levels were significantly higher in plastic film covered probes than in uncovered surface probes throughout the ischemic period. Glycerol levels were significantly higher in plastic film covered probes than in uncovered surface probes at 30 and 45 min into ischemia. CONCLUSIONS: Covering the µD probe increases the sensibility of the µD-technique in monitoring an ischemic insult and reperfusion in the liver. These findings confirm that the principle of surface µD works, possibly replacing need of intraparenchymatous placement of µD probes. Surface µD seemingly allows, noninvasively from an organ's surface, via the extracellular compartment, assessment of intracellular metabolic events. The finding that covered surface µD probes allows detection of local metabolic changes earlier than do intraparenchymatous probes, merit further investigation focusing on µD probe design.

Surface microdialysis sampling: a new approach described in a liver ischaemia model.

We recently have shown that samples from microdialysis (MD) probes placed on the surface of the heart reflect metabolic events in the myocardium. This new interesting observation challenges us to consider whether surface application of MD applies to other parenchymatous organs and their surfaces. In 13 anesthetized pigs, transient liver ischaemia was achieved by occlusion of arterial and venous inflow to the liver. Two probes on liver surface and two in parenchyma were perfused with a flow rate of 1 µl per min (n = 13). An identical set-up was used for probes with a flow rate of 2 µl per min (n = 9). Samples were collected for every 15-min period during 60 min of baseline, 45 min of ischaemia and 60 min of reperfusion. Lactate, glucose, pyruvate and glycerol were analysed in MD samples. We focused on relative changes in the present study. There was a strong agreement in relative lactate and glucose levels between probes placed on liver surface and those on parenchyma. No significant differences in relative changes in lactate and glucose levels were seen between samples from surface probes and probes in liver parenchyma during equilibration, baseline, ischaemia or reperfusion with a flow rate of 1 µl per min. MD sampling applied on the liver surface is a new application area for the MD technique and may be used to monitor liver metabolism during both physiological and pathophysiological conditions.

Ischaemic preconditioning reduces myocardial calcium overload in coronary-occluded pig hearts shown by continuous in vivo assessment using microdialysis.

During ischaemia, ATP depletion leads to insufficient fuelling for Na(+) /K(+) ATPase, decreased electrochemical potential and increased influx of calcium ions. This study demonstrated a means to assess the effects of ischaemic preconditioning (IP) on the free intracellular Ca(2+) pool during prolonged ischaemia. In a porcine myocardial ischaemia model, microdialysis (MD) was used for sampling of metabolic and injury markers in IP and non-IP (control) groups. (45) Ca(2+) was delivered in microperfusate locally to ischaemic myocardium, with distribution and uptake assessed by (45) Ca(2+) recovery in microdialysate. Cardiomyocytes in vitro were exposed to a Ca(2+) ionophore and tested for (45) Ca(2+) uptake. An accentuated myocardial calcium ion influx (observed as an increased microdialysate (45) Ca(2+) recovery in the extracellular milieu) was noted in control pigs compared with IP pigs during ischaemia. Suspended cardiomyocytes preincubated with a Ca(2+) ionophore to increase the intracellular calcium ion pool and subsequently incubated with (45) Ca(2+) , displayed lower (45) Ca(2+) uptake in cells compared with control cells not exposed to the ionophore, corroborating the idea of a strong relationship between degree of intracellular calcium overload and microdialysate (45) Ca(2+) recovery. The ischaemic insult was differentially verified by metabolic and injury markers. We introduce an in vivo method for serial assessment of myocardial calcium overload during ischaemia, using a MD technique and (45) Ca(2+) inclusion. IP leads to relatively less calcium overload as assessed by this new method, and we interpret this to mean that reduction in calcium overload is an important part of the IP protective effect.

Exogenous carbon monoxide does not affect cell membrane energy availability assessed by sarcolemmal calcium fluxes during myocardial ischaemia-reperfusion in the pig.

Carbon monoxide is thought to be cytoprotective and may hold therapeutic promise for mitigating ischaemic injury. The purpose of this study was to test low-dose carbon monoxide for protective effects in a porcine model of acute myocardial ischaemia and reperfusion. In acute open-thorax experiments in anaesthetised pigs, pretreatment with low-dose carbon monoxide (5% increase in carboxyhaemoglobin) was conducted for 120 min before localised ischaemia (45 min) and reperfusion (60 min) was performed using a coronary snare. Metabolic and injury markers were collected by microdialysis sampling in the ventricular wall. Recovery of radio-marked calcium delivered locally by microperfusate was measured to assess carbon monoxide treatment effects during ischaemia/reperfusion on the intracellular calcium pool. Coronary occlusion and ischaemia/reperfusion were analysed for 16 animals (eight in each group). Changes in glucose, lactate and pyruvate from the ischaemic area were observed during ischaemia and reperfusion interventions, though there was no difference between carbon monoxide-treated and control groups during ischaemia or reperfusion. Similar results were observed for glycerol and microdialysate 45Ca(2+) recovery. These findings show that a relatively low and clinically relevant dose of carbon monoxide did not seem to provide acute protection as indicated by metabolic, energy-related and injury markers in a porcine myocardial ischaemia/reperfusion experimental model. We conclude that protective effects of carbon monoxide related to ischaemia/reperfusion either require higher doses of carbon monoxide or occur later after reperfusion than the immediate time frame studied here. More study is needed to characterise the mechanism and time frame of carbon monoxide-related cytoprotection.

Detection of myocardial ischaemia using surface microdialysis on the beating heart.

Microdialysis (MD) can be used to study metabolism of the beating heart. We investigated whether microdialysis results obtained from epicardial (surface) sampling reflect acute changes in the same way as myocardial sampling from within the substance of the ventricular wall. In anaesthetized open-thorax pigs a coronary snare was placed. One microdialysis probe was placed with the sampling membrane intramyocardially (myocardial), and a second probe was placed with the sampling membrane epicardially (surface), both in the area which was made ischaemic. Ten minutes collection intervals were used for microdialysis samples. Samples from 19 pigs were analysed for lactate, glucose, pyruvate and glycerol during equilibration, baseline, ischaemia and reperfusion periods. For both probes (surface and myocardial), a total of 475 paired simultaneous samples were analysed. Results from analyses showed no differences in relative changes for glucose, lactate and glycerol during baseline, ischaemia and reperfusion. Surface microdialysis sampling is a new application of the microdialysis technique that shows promise and should be further studied.

Carbon monoxide concentration in donated blood: relation to cigarette smoking and other sources.

BACKGROUND: Carbon monoxide (CO) is normally present in the human body due to endogenous production of CO. CO can also be inhaled by exposure to external sources such as cigarette smoke, car exhaust, and fire. The purpose of this study was to investigate CO concentrations in blood from 410 blood donors at the blood center in Umeå, Sweden. To further evaluate the effects of cigarette smoking on CO concentrations, the elimination time for CO was examined in six volunteer smokers after a smoked cigarette. STUDY DESIGN AND METHODS: Blood samples from whole blood donors were obtained during the blood center's routine operation. In connection with blood donations, demographic and behavioral data were collected from the donors. The CO concentration was determined using gas chromatography. RESULTS: The majority of blood donors had approximately the same CO concentration (mean, 84.5 micromol/L). In 6 percent of the samples, the concentrations were higher than 130 micromol per L. The highest CO concentration was 561 micromol per L. The main source for these high CO concentrations appeared to be cigarette smoking. In the volunteer smokers, the elimination time after a smoked cigarette varied significantly, with elimination half-lives from 4.7 to 8.4 hours. CONCLUSION: These results show that blood bank red blood cell bags may have CO concentrations above the physiologic level. The time interval between cigarette smoking and blood donation seems to be a particularly important factor for elevated CO concentrations.

Optimised sample handling in association with use of the CMA 600 analyser.

A large degree of variability for batched analysis of serially collected microdialysis samples measured with the CMA 600 analyser has been described. This study was designed to identify sources of variability related to sample handling. Standard concentrations of four solutes were placed in microdialysis vials and then stored and analysed at intervals. Results were analysed for variability related to vial and cap type, duration and temperature of storage, centrifugation and re-analysis. The main results were that centrifugation of samples reduced variability. When a batch of 24 samples was analysed, the use of crimp caps reduced evaporation. Samples in glass vials with crimp caps could be stored in a refrigerator for up to 14 days without large variability in concentration compared to plastic vials which demonstrated variability already when stored for more than 1 day. We conclude that variability in microdialysis results can occur in relation to storage and analysis routines if routines are not optimised concerning evaporation. Centrifugation before analyses, glass vials with crimp caps even during frozen storage, and attention to minimal times for samples to be uncapped during analysis all contribute to minimise variability in the handling and analysis of microdialysis samples.

Does carbon monoxide treatment alter cytokine levels after endotoxin infusion in pigs? A randomized controlled study.

BACKGROUND: Carbon monoxide (CO) has recently been suggested to have anti-inflammatory properties, but data seem to be contradictory and species-specific. Thus, in studies on macrophages and mice, pretreatment with CO attenuated the inflammatory response after endotoxin exposure. On the other hand, human studies showed no effect of CO on the inflammatory response. Anti-inflammatory efficacy of CO has been shown at concentrations above 10% carboxyhaemoglobin. This study was undertaken to elucidate the possible anti-inflammatory effects of CO at lower CO concentrations. METHODS: Effects of CO administration on cytokine (TNF-alpha, IL-6, IL-1beta and IL-10) release were investigated in a porcine model in which a systemic inflammatory response syndrome was induced by endotoxin infusion. Endotoxin was infused in 20 anaesthetized and normoventilated pigs. Ten animals were targeted with inhaled CO to maintain 5% COHb, and 10 animals were controls. RESULTS: In the control group, mean pulmonary artery pressure increased from a baseline value of 17 mmHg (mean, n = 10) to 42 mmHg (mean, n = 10) following 1 hour of endotoxin infusion. Similar mean pulmonary artery pressure values were found in animals exposed to carbon monoxide. Plasma levels of all of the measured cytokines increased in response to the endotoxin infusion. The largest increase was observed in TNF-alpha, which peaked after 1.5 hours at 9398 pg/ml in the control group and at 13395 pg/ml in the carbon monoxide-exposed group. A similar peak was found for IL-10 while the IL-6 concentration was maximal after 2.5 hours. IL-1beta concentrations increased continuously during the experiment. There were no significant differences between carbon monoxide-exposed animals and controls in any of the measured cytokines. CONCLUSION: Our conclusion is that 5% COHb does not modify the cytokine response following endotoxin infusion in pigs.

Evaluation of intestinal preconditioning in a porcine model using classic ischemic preconditioning or lung recruitment maneuvers.

To test the hypotheses that repeated brief intestinal ischemic insults would elicit an intestinal preconditioning response to a subsequent intestinal I/R injury and that a similar response would be elicited by repeated lung recruitment maneuvers (RMs). Randomized experimental controlled animal study. University hospital animal laboratory. Eighteen anesthetized pigs. Animals were randomized to one of three groups, with six animals in each group. Control group 75-min superior mesenteric artery (SMA) occlusion followed by 60-min reperfusion. Ischemic preconditioning group, three 5-min-long SMA occlusions preceding 75-min SMA occlusion and 60-min reperfusion. Recruitment maneuver (RM) group, three 2-min-long RMs preceding 75-min SMA occlusion and 60-min reperfusion. We measured systemic and mesenteric hemodynamic parameters, jejunal mucosal perfusion, net mesenteric lactate flux, jejunal tissue oxygen tension, and mesenteric oxygenation. Every 15 min, jejunal microdialysate samples were collected and analyzed for glucose, lactate, and glycerol. Jejunal tissue samples were collected postmortem. After occlusion of SMA, regional parameters in all groups indicated abolished perfusion and gradually increasing intraluminal microdialysate lactate and glycerol levels. At reperfusion, regional parameters indicated mesenteric hyperperfusion, whereas microdialysis markers of mucosal anaerobic metabolism and cell injury decreased, although not reaching baseline. Histological examination revealed severe mucosal injury in all groups. There were no significant differences between groups in the observed parameters. No protective preconditioning response could be observed when performing repeated brief intestinal ischemic insults or repeated lung RMs before an intestinal I/R injury.

An assessment of calibration and performance of the microdialysis system.

To improve the reliability of microdialysis measurements of tissue concentrations of metabolic substances, this study was designed to test both the performance and the internal validity of the microdialysis methods in the hands of our research group. The stability of the CMA 600 analyser was tested with a known glucose solution in 72 standard microvials and in 48 plastic vials. To evaluate if variation in sampling time makes any difference in sample concentration (recovery), sampling times of 10, 20 and 30 min were compared in vitro with a constant flow rate of 1 microl/min. For testing of sampling times at different flow rates, an in vitro study was performed in which a constant sample volume of 10 microl was obtained. With the no net flux method, the actual concentration of glucose and urea in subcutaneous tissue was measured. The CMA 600 glucose analysis function was accurate and stable with a coefficient of variability (CV) of 0.2-0.55%. There was no difference in recovery for the CMA 60 catheter for glucose when sampling times were varied. Higher flow rates resulted in decreased recovery. Subcutaneous tissue concentrations of glucose and urea were 4.4 mmol/l and 4.1 mmol/l, respectively. To conclude, this work describes an internal validation of our use of the microdialysis system by calibration of vials and catheters. Internal validation is necessary in order to be certain of adequate sampling times, flow rates and sampling volumes. With this in mind, the microdialysis technique is useful and appropriate for in vivo studies on tissue metabolism.

Circulatory effects and kinetics following acute administration of carbon monoxide in a porcine model.

Carbon monoxide is produced in the endothelial cells and has possible vasodilator activity through three different pathways. The aim of this study was to demonstrate circulatory effects after administration of saturated carbon monoxide blood and to describe the pharmacokinetics of carbon monoxide. Six pigs were anesthetized and 150 ml blood was removed. This blood was bubbled with carbon monoxide until the carboxyhemoglobin (COHb) levels were 90-99%. A specific amount of this blood was then injected back to the animal. At predetermined times; arterial and mixed venous blood was drawn and analyzed for carbon monoxide. Systemic and pulmonary vascular resistance index (SVRi and PVRi) were measured and exhaled air was sampled and measured for carbon monoxide. Blood samples were gathered over 300 minutes along with measurements of invasive pressures, heart rate, cardiac output, oxygen saturation (SpO2), Hb, temperature and blood gases. We conclude that this type of exposure to carbon monoxide appears to have little or no effect on general vasomotor tone and, after correcting for basal levels of carbon monoxide, elimination occurs through the lungs as predicted by a single compartment model. The half-life of carbon monoxide was determined to be 60.5 minutes (SEM 4.7).