Subcutaneous Microdialysis Research Articles

Microdialysis—A versatile technology to perform metabolic monitoring in diabetes and critically ill patients

Continuous subcutaneous glucose monitoring has been tested in type 1 diabetes (T1D). Since in critically ill patients vascular access is granted vascular microdialysis may be preferential. To test this hypothesis comparative accuracy data for microdialysis applied for peripheral venous and subcutaneous glucose monitoring was obtained in experiments in T1D patients.Twelve T1D patients were investigated for up to 30h. Extracorporeal vascular (MDv) and subcutaneous microdialysis (MDs) was performed. Microdialysis samples were collected in 15–60min intervals, analyzed for glucose and calibrated to reference. MDv and MDs glucose levels were compared against reference.Median absolute relative difference was 14.0 (5.0; 28.0)% (MDv) and 9.2 (4.4; 18.4)% (MDs). Clarke Error Grid analysis showed that 100% (MDv) and 98.8% (MDv) were within zones A and B.Extracorporeal vascular and standard subcutaneous microdialysis indicated similar performance in T1D. We suggest microdialysis as a versatile technology for metabolite monitoring in subcutaneous tissue and whole blood.

Iontophoresis of A 13 Kda Protein Monitored by Subcutaneous Microdialysis In Vivo

The purpose of this study was to optimize parameters pertaining to microdialysis technique so as to make this method feasible for evaluating transdermal transport of macromolecules. Microdialysis experiments were performed in vivo using hairless rats with daniplestim as the model protein. Two perfusion fluids - phosphate-buffered saline (PBS) and 3% dextran in PBS - were evaluated with respect to their effect on sample volume retrieval and recovery of the target protein from the microdialysis probe. Incorporation of dextran-60 in the perfusion fluid reduced fluid loss to 10% as opposed to 34% in the absence of dextran-60. Improvement in daniplestim recovery was also seen with dextran-PBS (56.5 ± 10.3%) as the perfusion fluid than with PBS alone (26.7±4.5%). Subcutaneous levels of daniplestim were measured following iontophoresis after improving recovery and minimizing fluid loss from the microdialysis probe.

Circadian and Acamprosate Modulation of Elevated Ethanol Drinking in mPer2 Clock Gene Mutant Mice

The PER2 clock gene modulates ethanol consumption, such that mutant mice not expressing functional mPer2 have altered circadian behavior that promotes higher ethanol intake and preference. Experiments were undertaken to characterize circadian-related behavioral effects of mPer2 deletion on ethanol intake and to explore how acamprosate (used to reduce alcohol dependence) alters diurnal patterns of ethanol intake. Male mPer2 mutant and WT (wild-type) mice were entrained to a 12:12 h light-dark (12L:12D) photocycle, and their locomotor and drinking activities were recorded. Circadian locomotor measurements confirmed that mPer2 mutants had an advanced onset of nocturnal activity of about 2 h relative to WTs, and an increased duration of nocturnal activity (p < .01). Also, mPer2 mutants preferred and consumed more ethanol and had more daily ethanol drinking episodes vs. WTs. Measurements of systemic ethanol using subcutaneous microdialysis confirmed the advanced rise in ethanol intake in the mPer2 mutants, with 24-h averages being ∼60 vs. ∼25 mM for WTs (p < .01). A 6-day regimen of single intraperitoneal (i.p.) acamprosate injections (300 mg/kg) at zeitgeber time (ZT) 10 did not alter the earlier onset of nocturnal ethanol drinking in the mPer2 mutants, but reduced the overall amplitude of drinking and preference (both p < .01). Acamprosate also reduced these parameters in WTs. These results suggest that elevated ethanol intake in mPer2 mutants may be a partial consequence of an earlier nighttime activity onset and increase in nocturnal drinking activity. The suppressive action of acamprosate on ethanol intake is not due to an altered diurnal pattern of drinking, but rather a decrease in the number of daily drinking bouts and amount of drinking per bout. (Author correspondence: jglass@kent.edu)

New role of oxysterols as regulators of adipogenic differentation in adipose-derived mesenchymal stem cells

Growing evidence indicates that adipose tissue (AT) represents a potential source of pluripotent mesenchymal stem cells. However, the mechanisms underlying the lineage-specific commitment of human adipose-derived stem cells (ASC) remain still not fully elucidated. Oxysterols are cholesterol oxide products resulting from non-enzymatic (ie, 7-Ketocolesterol) or enzymatic (ie, 5,6-Secosterol) oxidation of cholesterol, which are now emerging as reliable markers of adipose “oxidative stress” in vivo. Recent data suggest that, by regulating the adipogenic differentiation of ASC, lipid peroxidation products may play an important role in linking the adipose dysfunction with impairment of glucose homeostasis. In this study we combined a lipidomic approach with the subcutaneous (sc) microdialysis technique to characterize the adipose-derived profile of fatty acids (FA) and oxysterols in vivo. ASC were isolated from abdominal sc, mesemteric (MES) and omental (OM) fat specimens obtained from obese nondiabetic (OB) and type 2 diabetic (OBT2D) patients. Flow cytometry (FC) was used for the evaluation of cell viability, mitochondrial status and cell immunophenotyping. In AT interstitial fluid, abundant concentrations of oxysterols (7κC and 5,6-S) and fatty acids (lipokines) were found. Experimental challenging with 7κC and 5,6-S showed a different time-dose-response effect. Indeed, the MTT assay, we found that in ASC isolated from the sc depot 5,6-S (50 and 10μM) reduced cell viability after 24, 48 and 72 h, respectively. In contrast, in the same cell-type population, the effect of 7κC at 10μM was observed only after 72 h. FC analysis indicated a similar effect of both oxysterols even after short-time exposure either in ASC from the MES or the OM fat depot. Notably, cell challenge with 7κC and 5,6-S at 10, 5 and 1 μM, respectively, was accompanied by an impairment of mitochondrial status only in OM, but not in MES. Furthermore, both the oxysterols (10μM) downregulated the expression of stemness surface markers suggesting a different “susceptibility” of the ASC to lipid peroxidation cell damage. Accordingly, 7κC at 10 and 1μM impaired the adipogenic differentiation of sc and OM ASC isolated from either OB or T2DOB, and demodulated the mitochondrial activity of the differentiated adipocytes. Altogether, our results suggest human AT as a critical compartment for storage and secretion of lipokines and oxysterols, which, when in excess, appear to detrimentally modulate the mitochondrial activity and the adipogenic differentiation of adipose precursor cells. This work was partly funded from Fondazione Cassa di Risparmio di Perugia, project 2010.020.0098, “Ricerca Scientifica e Tecnologica”

Long-term subcutaneous microdialysis sampling and qRT-PCR of MCP-1, IL-6 and IL-10 in freely-moving rats.

Cytokines are important mediators of the wound healing response. However, sampling of cytokines from the interstitial fluid at a healing wound site in experimental animals is a challenge. Microdialysis sampling is an in vivo collection option for this purpose as it permits continuous sampling, while remaining contiguous with the wound microenvironment. The polymeric membrane of the microdialysis probe is a foreign material thus allowing a unique approach to sample cytokines generated during a foreign body response (FBR). The focus of these studies was to use microdialysis sampling to collect cytokines from a microdialysis probe implant site in a rat model of a FBR up to 6 days post implantation. Fluorescent bead-based immunoassays (Luminex™) were used to quantify monocyte chemoattractant protein-1 (MCP-1/CCL2), interleukin-6 (IL-6) and interleukin-10 (IL-10) in the dialysates. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was used to cross validate the protein measurements obtained via micorodialysis sampling. A histological examination of tissue was also performed to assess the progression in leukocyte extravasation and collagen deposition surrounding implanted probes. Our findings demonstrate that in vivo microdialysis sampling can be used to collect temporal concentrations of cytokines which are consistent with wound healing and the development of a FBR.

Aerobic training increases skin perfusion by a nitric oxide mechanism in type 2 diabetes

Aerobic training increases skin perfusion by a nitric oxide mechanism in type 2 diabetes Sheri R Colberg1, Laura C Hill2, Henri K Parson3, Kathleen S Thomas1, Aaron I Vinik31Old Dominion University, Norfolk; 2State University of New York at Cortland, New York; 3Eastern Virginia Medical School, Norfolk, VirginiaAbstract: It is well known that a number of locally released vasodilatory and &shy;vasoconstrictive &shy;compounds can affect skin perfusion. This study investigated the effects of aerobic training on the contribution of nitric oxide (NO), prostaglandins (PG), and endothelial-derived &shy;hyperpolarizing factor (EDHF) in stimulated dorsal foot skin perfusion in individuals with type 2 diabetes (T2DM). Ten previously sedentary, older individuals with T2DM (57.0 &plusmn; 3.1 years) and nine sedentary controls (53.5 &plusmn; 3.2 years) were tested before and after undertaking six months of moderate a&shy;erobic training three times weekly in a supervised setting. All subjects underwent measurement of &shy;baseline (32&deg;C) and heat-stimulated (40&deg;C and 44&deg;C) dorsal foot skin perfusion starting one hour after &shy;ingestion of a single, oral 325 mg dose of aspirin, a known inhibitor of PG synthesis. Before aspirin &shy;ingestion, a subcutaneous microdialysis probe was inserted into each foot dorsum to administer either saline (PG pathway only blocked by aspirin in the left foot) or L-NAME (N(G)-nitro-l-arginine methyl ester; thereby inhibiting both PG and NO pathways in the right foot). Normative data collected previously on subjects undergoing saline administration via &shy;microdialysis without aspirin ingestion served as a control group. Significantly lower responsiveness of maximal perfusion was found with the EDHF pathway alone unblocked compared with NO and EDHF unblocked after training. Maximal suppression attributable directly to NO, PG, and EDHF was not significantly different when examined by subject group and training status. However, &shy;contributions of NO, PG, and EDHF to maximal perfusion were significantly increased, decreased, and unchanged by aerobic training, respectively, with diabetic and control subjects combined due to nonsignificant differences between groups. Improvements in maximally stimulated dorsal foot skin perfusion resulting from six months of aerobic training appear to have primarily an NO basis, with lesser contributions from PG following training, regardless of diabetes status.Keywords: skin perfusion, aerobic training, type 2 diabetes, nitric oxide, prostaglandins, endothelial-derived hyperpolarizing factor, microdialysis

Aerobic training increases skin perfusion by a nitric oxide mechanism in type 2 diabetes

It is well known that a number of locally released vasodilatory and vasoconstrictive compounds can affect skin perfusion. This study investigated the effects of aerobic training on the contribution of nitric oxide (NO), prostaglandins (PG), and endothelial-derived hyperpolarizing factor (EDHF) in stimulated dorsal foot skin perfusion in individuals with type 2 diabetes (T2DM). Ten previously sedentary, older individuals with T2DM (57.0 ± 3.1 years) and nine sedentary controls (53.5 ± 3.2 years) were tested before and after undertaking six months of moderate aerobic training three times weekly in a supervised setting. All subjects underwent measurement of baseline (32°C) and heat-stimulated (40°C and 44°C) dorsal foot skin perfusion starting one hour after ingestion of a single, oral 325 mg dose of aspirin, a known inhibitor of PG synthesis. Before aspirin ingestion, a subcutaneous microdialysis probe was inserted into each foot dorsum to administer either saline (PG pathway only blocked by aspirin in the left foot) or L-NAME (N(G)-nitro-l-arginine methyl ester; thereby inhibiting both PG and NO pathways in the right foot). Normative data collected previously on subjects undergoing saline administration via microdialysis without aspirin ingestion served as a control group. Significantly lower responsiveness of maximal perfusion was found with the EDHF pathway alone unblocked compared with NO and EDHF unblocked after training. Maximal suppression attributable directly to NO, PG, and EDHF was not significantly different when examined by subject group and training status. However, contributions of NO, PG, and EDHF to maximal perfusion were significantly increased, decreased, and unchanged by aerobic training, respectively, with diabetic and control subjects combined due to nonsignificant differences between groups. Improvements in maximally stimulated dorsal foot skin perfusion resulting from six months of aerobic training appear to have primarily an NO basis, with lesser contributions from PG following training, regardless of diabetes status.

Long-term calibration considerations during subcutaneous microdialysis sampling in mobile rats

The level at which implanted sensors and sampling devices maintain their calibration is an important research area. In this work, microdialysis probes with identical geometry and different membranes, polycarbonate/polyether (PC) or polyethersulfone (PES), were used with internal standards (Vitamin B 12 (MW 1355), antipyrine (MW 188) and 2-deoxyglucose (2-DG, MW 164)) and endogenous glucose to investigate changes in their long-term calibration after implantation into the subcutaneous space of Sprague-Dawley rats. Histological analysis confirmed an inflammatory response to the microdialysis probes and the presence of a collagen capsule. The membrane extraction efficiency (percentage delivered to the tissue space) for antipyrine and 2-DG was not altered throughout the implant lifetime for either PC- or PES membranes. Yet, Vitamin B 12 extraction efficiency and collected glucose concentrations decreased during the implant lifetime. Antipyrine was administered i.v. and its concentrations obtained in both PC- and PES-membrane probes were significantly reduced between the implant day and seven (PC) or 10 (PES) days post-implantation suggesting that solute supply is critical for in vivo extraction efficiency. For the low molecular weight solutes such as antipyrine and glucose, localized delivery is not affected by the foreign body reaction, but recovery is significantly reduced. For Vitamin B 12, a larger solute, the fibrotic capsule formed around the probe significantly restricts diffusion from the implanted microdialysis probes.

Fetal cerebral energy metabolism and electrocardiogram during experimental umbilical cord occlusion and resuscitation

Objective. The purpose of this experimental study was to elucidate alterations in fetal energy metabolism in relation to ECG changes during extreme fetal asphyxia, postnatal resuscitation and the immediate post-resuscitatory phase.Study design. Five near-term fetal sheep were subjected to umbilical cord occlusion until cardiac arrest followed by delivery, resuscitation and postnatal pressure-controlled ventilation. Four sheep served as sham controls and were delivered immediately after ligation of the umbilical cord. Fetal ECG was analysed online for changes of the ST segment. Fetal metabolism was monitored by intracerebral and subcutaneous microdialysis catheters.Results. Fetal ECG reacted on cord occlusion with an increase in the T-wave height followed by changes in intracerebral levels of oxidative parameters. Cerebral lactate/pyruvate ratio and glutamate increased to median (range) of 240 (200–744) and 34.0 (22.6–60.5) mmol/l, respectively; both parameters returned to baseline after resuscitation. Cerebral glucose decreased to 0.1 (0.08–0.12) mmol/l after occlusion and increased above baseline upon resuscitation. In subcutaneous tissue as well as blood the increase in lactate occurred with a delay compared to cerebral levels.Conclusion. The fetal ECG changes related to asphyxia preceded the increase in excitotoxicity as determined by increase in cerebral glutamate during asphyxia. Cerebral lactate increase was superior to subcutaneous lactate increase.

Continuous Glucose Monitoring: An Overview of Its Development

Continuous Glucose Monitoring: An Overview of Its Development

Mediastinal microdialysis: early diagnosis of anastomotic leakage after resection for esophageal cancer

The aim of the present study was to evaluate the safety of mediastinal microdialysis and its efficacy regarding the early diagnosis of anastomotic leakage after gastroesophageal resection for esophageal cancer. Eight consecutive patients were included; one patient was excluded for reasons of catheter malfunction. The tip of the mediastinal microdialysis catheter was placed close to the anastomosis and held by a 4-0 absorbable suture. A subcutaneous microdialysis catheter placed in the pectoral region served as a reference. Samples collected every 4 h in the first 8 postoperative days were analyzed for lactate, glucose, pyruvate, and glycerol and the lactate/pyruvate ratio (L/P ratio) was calculated. There were no procedure-related complications. Six patients had an uncomplicated postoperative course. In one patient, the L/P ratio was within normal range during the first 20 h postoperatively, but a steady and significant increase in L/P ratio then occurred, reaching a maximum of 105 after 124 h. The patient developed leakage symptoms on day 3, but endoscopy was unable to demonstrate any leakage. On the sixth postoperative day, blue dye administered through the nasogastric tube was recovered in the pleural drain. The leakage was treated with a covered selfexpanding metal stent; an immediate and significant drop in the L/P ratio occurred. Mediastinal microdialysis seems to be a safe and promising tool in the early diagnosis of anastomotic leakage in patients undergoing gastroesophageal resection for cancer.

Measurement of tissue cortisol levels in patients with severe burns: a preliminary investigation

IntroductionThe assessment of adrenal function in critically ill patients is problematic, and there is evidence to suggest that measurement of tissue glucocorticoid activity may be more useful than estimation of plasma cortisol concentrations. Interstitial cortisol concentrations of cortisol represent the available pool of glucocorticoids able to enter the cell and bind to the glucocorticoid receptor. However the concentrations of plasma cortisol may not accurately reflect interstitial concentrations. We elected to perform a preliminary study into the feasibility of measuring interstitial cortisol by microdialysis, and to investigate the relationship between total plasma cortisol, free plasma cortisol and interstitial cortisol in patients with severe burns.MethodsA prospective observational study carried out in a tertiary intensive care unit. Ten adult patients with a mean total burn surface area of 48% were studied. Interstitial cortisol was measured by microdialysis from patient-matched burnt and non-burnt tissue and compared with that of 3 healthy volunteers. Plasma sampling for estimations of total and free cortisol concentrations was performed concurrently.ResultsIn the burn patients, mean total plasma and free plasma cortisol concentrations were 8.8 +/- 3.9, and 1.7 +/- 1.1 mcg/dL, (p < 0.001), respectively. Mean subcutaneous microdialysis cortisol concentrations in the burn and non-burn tissue were 0.80 +/- 0.31 vs 0.74 +/- 0.41 mcg/dL (p = 0.8), respectively, and were significantly elevated over the mean subcutaneous microdialysis cortisol concentrations in the healthy volunteers. There was no significant correlation between total plasma or free plasma and microdialysis cortisol concentrations. Plasma free cortisol was better correlated with total burn surface area than total cortisol.ConclusionsIn this preliminary study, interstitial cortisol concentrations measured by microdialysis in burnt and non-burnt skin from patients with severe thermal injury are significantly elevated over those from healthy volunteers. Plasma estimations of cortisol do not correlate with the microdialysis levels, raising the possibility that plasma cortisol may be an unreliable guide to tissue cortisol activity.

Exercise status affects skin perfusion via prostaglandin, nitric oxide, and EDHF pathways in diabetes

Participation in regular exercise training improves dorsal skin perfusion, while type 2 diabetes mellitus (T2 DM) often limits it via reductions in the action or release of vasodilatory compounds. This study was undertaken to investigate the relative contributions of prostaglandins (PG), nitric oxide (NO), and endothelial-derived hyperpolarizing factor (EDHF) in dorsal foot skin perfusion in individuals with and without T2 DM and a sedentary lifestyle. Participants included 24 individuals with T2 DM and 28 nondiabetic controls whose exercise status was determined via questionnaire. Their dorsal foot skin perfusion was measured at rest using laser Doppler assessment during localized heating to 44 °C with oral aspirin (ASA, 325 mg) treatment. In addition, they received an infusion via a subcutaneous microdialysis probe of either saline (left foot) or L-NAME, a NOS-inhibitor (right foot). Compared to normative data without ASA, heat-stimulated perfusion in regular exercisers ( n = 22) was significantly more suppressed by ASA and by ASA/L-NAME than in sedentary individuals ( n = 30). Chronic exercisers exhibit a greater reliance on PG and lesser involvement of EDHF with unchanged NO compared to sedentary individuals, who rely more on EDHF and less on PG release. One possible exception may be diabetic, sedentary individuals, who may rely somewhat more on NO than EDHF. These results suggest that regular exercise may exhibit the greatest effect on the normal functioning of these vasodilatory pathways, although diabetes and a sedentary state together may somewhat alter their relative importance.

Tissue Accumulation of Cephalothin in Burns: a Comparative Study by Microdialysis of Subcutaneous Interstitial Fluid Cephalothin Concentrations in Burn Patients and Healthy Volunteers

Burn tissue sites are a potential source of bacteremia during debridement surgery. Burn injury is likely to affect the distribution of antibiotics to tissues, but direct evidence of this is lacking. The aim of this study was to directly evaluate the influence of burn trauma on the distribution of cephalothin to peripheral tissues. We used subcutaneous microdialysis techniques to monitor interstitial fluid concentrations of cephalothin in the burnt and nonburnt tissues of adult patients with severe burns following parenteral administration of 1 g cephalothin for surgical prophylaxis. Analogous simultaneous studies conducted with healthy adult volunteers provided reference tissue concentration data. Equivalent tissue exposures were seen for burn and nonburn sites, giving overall median interstitial cephalothin concentrations (from 0 to 240 min) of 2.84 mg/liter and 3.06 mg/liter, respectively. A lower overall median interstitial cephalothin concentration of 0.54 mg/liter was observed for healthy individuals, and the patient nonburnt tissue and volunteer control tissue cephalothin concentrations exhibited significantly different data distributions (P < 0.001; Kolmogorov-Smirnov nonparametric test). The duration of tissue residence for cephalothin was longer for burn patients than for healthy volunteers. The results demonstrate the potential fallibility of using healthy population models to extrapolate tissue pharmacodynamic predictions from plasma data for burn patients.

Use of tissue microdialysis to investigate hyperlactataemia following paediatric cardiac surgery

We investigated tissue lactate, pyruvate and lactate:pyruvate (LP) ratio post cardiac surgery and the relationship of cardiac index and oxygen delivery to late onset hyperlactataemia in ICU. It involved a prospective study of 10 children, mean age 4.9 (0.4) years, post-Fontan operation admitted with normo-lactataemia. Tissue lactate, pyruvate and LP ratio were monitored postoperatively every 30 min for 12 h via subcutaneous microdialysis in the abdominal wall. Cardiac index was measured by PiCCO at 0, 4, 8 and 12 h. Blood and subcutaneous tissue lactate were strongly correlated (r=0.87; P=0.001). Mean (S.D.) blood lactate rose from 2.23 (0.49) to 3.73 (1.16) mmol l(-1) in the first 5 h after ICU admission (P=0.008), only one child remaining normal. Microdialysis revealed lactate rising from 3.8 (0.83) to 5.3 (1.6) (P=0.011), with a parallel pyruvate rise. LP ratio remained below 20, indicating no tissue oxygen debt. Cardiac index increased from 2.83 (0.63) to 3.77 (1.34) l min(-1) m(-2) over the same period (P=0.05), with a corresponding increase in oxygen delivery from 4556 (1094) to 6076 (2322) ml min(-1) (P=0.04). Tissue microdialysis provides near-continuous measurement of tissue lactate and pyruvate, post cardiac surgery. Blood lactate rise post-Fontan is mirrored by tissue lactate and pyruvate concentrations, and not associated with a low or falling cardiac index or with tissue oxygen debt.

In Vivo Time‐Course Changes in Ethanol Levels Sampled With Subcutaneous Microdialysis

The objective of this study was to determine time-course changes in in vivo ethanol (EtOH) concentrations using a novel subcutaneous (s.c.) microdialysis sampling technique. The hypothesis to be tested was that EtOH concentrations in the s.c. fluid would reflect blood EtOH concentrations. If this is the case, then s.c. microdialysis could allow a more detailed analysis of changes in in vivo levels of EtOH under different drinking paradigms. Adult male and female Wistar rats and male alcohol-preferring (P) rats were used in this study. A loop-style microdialysis probe was designed for s.c. applications. After initial in vitro characterization, probes were implanted under the skin between the shoulder blades. Animals were allowed to recover 4 to 24 hours prior to microdialysis collection (2.0 microl/min flow rate with isotonic saline). In vivo microdialysis experiments were then conducted to determine (i) the extraction fraction (or clearance) using EtOH no-net-flux (NNF) coupled with the alcohol clamp method, (ii) the dose-response and time-course effects after systemic EtOH administration and to compare with blood EtOH levels, and (iii) the time-course changes in EtOH levels during and after an EtOH drinking episode. In vivo probe recovery (extraction fraction) obtained using the alcohol clamp method was 69 +/- 3%, and was comparable to the in vitro recovery of 73 +/- 2%. For the EtOH dose-response experiment, rats injected i.p. with 0.5, 1.0, or 2.0 g/kg EtOH showed a clear dose-response effect in the s.c. dialysate samples. Peak concentrations (70, 123, and 203 mg%, respectively) were reached by 15 minutes after injection. In an experiment comparing levels of EtOH in s.c. dialysis and arterial blood samples in rats administered 1.0 g/kg EtOH, similar time-course changes in in vivo EtOH concentrations were observed with both i.g. and i.p. EtOH administration. In P rats drinking 15% EtOH during a 1-hour scheduled access period, EtOH levels in s.c. microdialysates rose rapidly over the session and peaked at approximately 50 mg% at 60 to 80 minutes. Overall, these experiments indicate that s.c. EtOH and blood EtOH concentrations follow a similar time course. Moreover, s.c. microdialysis can be useful as an experimental approach for determining detailed time-course changes in in vivo EtOH concentrations associated with alcohol drinking episodes.

Assessment of tissue hypoperfusion by subcutaneous microdialysis during septic shock: cases with bacteremia versus nonbacteremia

Plasma lactate has been used as a better marker of tissue hypoperfusion in patients with sepsis. Plasma lactate elevation can be delayed compared with tissue hypoperfusion. Microdialysis has been used for an assessment of tissue hypoperfusion in the area of neurosurgery; however, limited studies have been published in the area of septic shock. We hypothesized that septic patients with bacteremia (BA) suffered from more severe hypoperfusion than those with nonbacteremia (Non-BA). We therefore investigated subcutaneous lactate and lactate/pyruvate ratio in cases with BA versus Non-BA for an assessment of tissue hypoperfusion in both groups.

The Rare Side Effect During Microdialysis Continuous Subcutaneous Glucose Monitoring in Type 1 Diabetic Patient

Continuous subcutaneous microdialysis glucose monitoring system (GlucoDay, A. Menarim Diagnostics, Florence, Italy) was applied to a 31-year-old man with type I diabetes mellitus. At the end of a 48-hour monitoring period, it was found that the hollow fiber dialysis chamber had become disconnected from the nylon tube. The hollow fiber was localized by a radiograph of the abdominal wall, and was later successfully removed by a plastic surgeon. This is the first report of this complication of continuous glucose monitoring.

Application of in vivo microdialysis for studying the efficacy of protective preparations against sulfur mustard penetrating the skin

Subcutaneous microdialysis was employed for monitoring thiodiglycol (2,2'-thiodiethanol, TDG) levels with the aim of characterizing the transdermal penetration of topically applied liquid sulfur mustard (2,2'-dichlorodiethyl sulfide, SM) in rats. TDG levels, evaluated in 20 min dialysates collected over a 6 h sampling period, were plotted against time after pooling. Linear correlation was identified between the SM dose and the mean areas under the 0-60 min or the whole curve (AUC(0-60) and AUC, respectively) as well as mean peak concentrations (C(max)) in the range of 1.0-3.0 microl applied volume (7.2-21.7 nmol).A commercially available barrier cream, a perfluoropolyether oil and a vaseline based ointment containing zinc oxide were subsequently tested as topical protectants. Each preparation was layered on the skin surface prior to the application of 2.0 microl SM. The evaluation of the efficacy of the preparations was based on obtained AUC(0-60), AUC and C(max) values. A statistical comparison of these parameters with those obtained when 2.0 microl SM was applied without pretreatment indicated that the barrier cream and the perfluoropolyether oil significantly (P < 0.01) reduced the amount of penetrating SM within the sampling period. In addition, the perfluoropolyether oil almost completely prevented the penetration of SM for 20 min. Pretreatment with the ointment did not prove to be an effective countermeasure as its administration resulted in no significant reduction in AUC(0-60), AUC and C(max) values.

Monitoring Blood Glucose with Microdialysis of Interstitial Fluid in Critically Ill Children

Hyperglycemia, a common feature in critically ill patients, was traditionally perceived as an adequate stress response reflecting the severity of the disease state and was treated only if glycemia exceeded 11–13.5 mmol/L. In recent studies in intensive care patients, we showed that tight glycemic control (TGC) with intensive insulin therapy (IIT) reduced the risk of organ failure and death (1). In critically ill children, peak blood glucose (BG) and duration of hyperglycemia are associated with risk of mortality (2). Implementing TGC and avoiding hypoglycemia with intensive insulin therapy requires frequent BG sampling. Microdialysis of interstitial fluid (ISF) is a promising approach to reduce diagnostic blood loss. Continuously sampling dialyzed ISF and converting the ISF glucose concentration (IFG) to a BG value is a promising new method for glucose monitoring in diabetes patients. We conducted a prospective clinical trial in critically ill children to evaluate the feasibility of prolonged subcutaneous microdialysis and the correlation between BG and IFG. The study was approved by the Institutional Ethical Review Board. Twenty children were …