Tourniquet-induced changes of energy metabolism in human skeletal muscle monitored by microdialysis

Effect of valproic acid upon skeletal muscle subjected to prolonged tourniquet application

Background

Valproic acid (VPA), a histone deacetylase inhibitor, has shown improved outcomes when used as a pharmaceutical intervention in animal studies of hemorrhage, septic shock, and combined injuries. This study was designed to investigate the ability of VPA to mitigate ischemia-reperfusion injury produced by prolonged tourniquet application to an extremity.

Methods

The ischemia-reperfusion model in anesthetized rats was established using hemorrhage and a 3-hour tourniquet application. VPA was administered intravenously prior to tourniquet wear and removal. Ischemia-reperfusion injury was evaluated by investigating pathway signaling, immune modulation of cytokine release, remote organ injury, and skeletal muscle function during convalescence.

Results

We found that VPA sustained Protein kinase B (Akt) phosphorylation and Insulin-like growth factor signaling and modulated the systemic release of interleukin (IL)-1β, tumor necrosis factor alpha, and IL-6 after 2 hours of limb reperfusion. Additionally, VPA attenuated a loss in glomerular filtration rate at 3 days after injury. Histological and functional evaluation of extremity skeletal muscle at 3, 7, and 21 days after injury, however, demonstrated no significant differences in myocytic degeneration, necrotic formation, and maximal isometric tetanic torque.

Conclusions

Our results demonstrate that VPA sustains early prosurvival cell signaling, reduces the inflammatory response, and improves renal function in a hemorrhage with prolonged ischemia and reperfusion model. However, these do not translate into meaningful preservation in limb function when applied as a pharmaceutical augmentation to tourniquet wear.

Level of evidence

IV.

A reproducible method for biochemical, histological and functional assessment of the effects of ischaemia-reperfusion syndrome in the lower limbs

Current methodology described to mimic lower limb ischaemia-reperfusion injury (LL-IRI) does not accurately define the procedures and pressures exerted to induce and maintain ischaemia. In this piece of work, we propose a well-defined and detailed rat model that simulates the conditions established in clinical practice guidelines for tourniquet application and allows us to test treatments that aim to prevent/reduce LL-IRI. Eighty-six male WAG/RijHsd rats were subjected to hind limb IRI (LL-IRI), using a mechanical system applying a 1 kg tension to induce and maintain ischemia for 2 or 3 h, and assessed the damage caused by reperfusion at biochemical and muscular levels at different time points. At the biochemical level, both 2 and 3 h of ischemia induced changes (except for electrolyte levels); 3 h of ischemia induced greater changes in specific markers of muscular damage: creatine kinase (CK) and lactate dehydrogenase (LDH). At the histopathological level, 3 h of ischemia and 24 h of reperfusion was associated with an increase in hind limb girth, cross-sectional area, and weight and presence of neutrophils, as well as histological damage in more than 60% of muscle fibres. Our model allows to reliably reproduce the damage associated with the use of a pneumatic tourniquet. CK and LDH, as well as measures of tissue damage, allow to define and characterize the response to LL-IRI-related damage. A period of 3 h of ischemia followed by 3 h of reperfusion caused only local damage but showed greater sensitivity to detect differences in future studies on prophylactic treatments against LL-IRI.

Microdialysis for chronic exertional compartment syndrome: a pilot study

Background

Diagnosing chronic exertional compartment syndrome (CECS) is still a challenge. An increase in intramuscular pressure during and following exercise is accepted as the diagnostic standard. However, neither the methods used nor the interpretation of the obtained results are sufficiently standardized.

Methods

In the present pilot study, the metabolic state of CECS patients was investigated using microdialysis. We hypothesized that there was no difference in intramuscular concentrations of glucose, lactate, glutamate, and glycerol before and after exercise (H1₀) or between patients suffering from CECS and healthy control subjects (H2₀). This study was designed as an explorative case-control study (level of evidence III). Twelve patients suffering from CECS of the lower leg and six matched asymptomatic control subjects underwent microdialysis in the anterior (n = 7) or deep posterior compartment (n = 11) of the leg. Following ultrasound-guided insertion of the microdialysis catheters, 10-minute fractions of the dialysates were collected first during rest and then following fatigue- or pain-induced discontinuation of exercise. Dialysates were analysed for lactate, glucose, glutamate, and glycerol concentrations 6 × 10 min before and 6 × 10 min after exercise.

Results

Exercise-induced increases in lactate, glutamate, and glycerol concentrations were detected in both CECS patients and control subjects (all p < 0.001). No differences between CECS patients and control subjects were found by comparing the intramuscular glucose, lactate, glutamate, and glycerol concentrations at rest and following exercise (all p > 0.05).

Conclusions

We found exercise-induced increases in the lactate, glutamate, and glycerol levels in skeletal muscle. However, the metabolic changes did not differentiate CECS patients from healthy subjects.

Trial registration

The registration trial number is DRKS00021589 on DRKS. ‘Retrospectively registered’. Date of registration: April 4, 2020.

Tourniquet-induced ischemia and reperfusion in subcutaneous tissue, skeletal muscle, and calcaneal cancellous bone

This study aimed to evaluated ischemic metabolites in subcutaneous tissue, skeletal muscle, and calcaneal cancellous bone before, during, and after tourniquet application in a simultaneous paired comparison of tourniquet-exposed and non-tourniquet-exposed legs. Ten patients scheduled for hallux valgus or hallux rigidus surgery were included. Microdialysis catheters were placed to simultaneously and continuously sample the metabolites glucose, lactate, pyruvate, and glycerol bilaterally for 12 h in subcutaneous tissue, skeletal muscle, and calcaneal cancellous bone. A tourniquet was applied on the leg planned for surgery (inflation time: 15 min, mean tourniquet duration time (range): 65 (58;77) min). During tourniquet inflation, a 2- to 3-fold increase of the mean lactate/pyruvate ratio was found for all investigated tissues in the tourniquet-exposed leg compared with the non-tourniquet-exposed leg. The lactate/pyruvate ratio recovery time after tourniquet release was within 30 min for skeletal muscle, 60 min for subcutaneous tissue, and 130 min for calcaneal cancellous bone. Only the tourniquet-exposed skeletal muscles were found to be ischemic during tourniquet inflation, defined by a significant increase of the lactate/pyruvate ratio exceeding the ischemic cutoff level of 25; however, this level decreased below 25 immediately after tourniquet release. The glycerol ratio increased instantly after inflation in the tourniquet-exposed leg in skeletal muscle and subcutaneous tissue, and recovered within 60 (skeletal muscle) and 130 min (subcutaneous tissue) after tourniquet release. These findings suggest that applying tourniquet for approximately 1 h results in limited tissue ischemia and cell damage in subcutaneous tissue, skeletal muscle, and calcaneal cancellous bone.

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.

Timing of Antimicrobial Prophylaxis and Tourniquet Inflation: A Randomized Controlled Microdialysis Study

BACKGROUND

Tourniquets are widely used during extremity surgery. In order to prevent surgical site infection, correct timing of antimicrobial prophylaxis and tourniquet inflation is important. We aimed to evaluate the time for which the free drug concentration of cefuroxime is maintained above the minimum inhibitory concentration (t > MIC) in porcine subcutaneous adipose tissue and calcaneal cancellous bone during 3 clinically relevant tourniquet application scenarios.

METHODS

Twenty-four female Danish Landrace pigs were included. Microdialysis catheters were placed bilaterally for sampling of cefuroxime concentrations in calcaneal cancellous bone and subcutaneous adipose tissue, and a tourniquet was applied to a randomly picked leg of each pig. Subsequently, the pigs were randomized into 3 groups to receive 1.5 g of cefuroxime by intravenous injection 15 minutes prior to tourniquet inflation (Group A), 45 minutes prior to tourniquet inflation (Group B), and at the time of tourniquet release (Group C). The tourniquet duration was 90 minutes in all groups. Dialysates and venous blood samples were collected for 8 hours after cefuroxime administration. Cefuroxime and various ischemic marker concentrations were quantified.

RESULTS

Cefuroxime concentrations were maintained above the clinical breakpoint MIC for Staphylococcus aureus (4 µg/mL) in calcaneal cancellous bone and subcutaneous adipose tissue throughout the 90-minute tourniquet duration in Groups A and B. Cefuroxime administration at the time of tourniquet release (Group C) resulted in concentrations of >4 µg/mL for approximately of 3.5 hours in the tissues on the tourniquet side. Furthermore, tourniquet application induced ischemia (increased lactate:pyruvate ratio) and cell damage (increased glycerol) in subcutaneous adipose tissue and calcaneal cancellous bone. Tissue ischemia was sustained for 2.5 hours after tourniquet release in calcaneal cancellous bone.

CONCLUSIONS

Administration of cefuroxime (1.5 g) in the 15 to 45-minute window prior to tourniquet inflation resulted in sufficient concentrations in calcaneal cancellous bone and subcutaneous adipose tissue throughout the 90-minute tourniquet application. Furthermore, tourniquet-induced tissue ischemia fully resolved 2.5 hours after tourniquet release.

CLINICAL RELEVANCE

Cefuroxime administration 15 to 45 minutes prior to tourniquet inflation seems to be a safe window. If the goal is to maintain postoperative cefuroxime concentrations above relevant MIC values, our results suggest that a second dose of cefuroxime should be administered at the time of tourniquet release.

Tourniquet-induced nerve compression injuries are caused by high pressure levels and gradients - a review of the evidence to guide safe surgical, pre-hospital and blood flow restriction usage

Tourniquets in orthopaedic surgery safely provide blood free surgical fields, but their use is not without risk. Tourniquets can result in temporary or permanent injury to underlying nerves, muscles, blood vessels and soft tissues. Advances in safety, accuracy and reliability of surgical tourniquet systems have reduced nerve-related injuries by reducing pressure levels and pressure gradients, but that may have resulted in reduced awareness of potential injury mechanisms. Short-term use of pre-hospital tourniquets is effective in preventing life-threatening blood loss, but a better understanding of the differences between tourniquets designed for pre-hospital vs surgical use will provide a framework around which to develop guidelines for admitting to hospital individuals with pre-applied tourniquets. Recent evidence supports the application of tourniquets for blood flow restriction (BFR) therapy to reduce muscular atrophy, increase muscle strength, and stimulate bone growth. BFR therapy when appropriately prescribed can augment a surgeon’s treatment plan, improving patient outcomes and reducing recovery time. Key risks, hazards, and mechanisms of injury for surgical, BFR therapy, and pre-hospital tourniquet use are identified, and a description is given of how advances in personalized tourniquet systems have reduced tourniquet-related injuries in these broader settings, increasing patient safety and how these advances are improving treatment outcomes.

Demystifying Lactate in the Emergency Department

The role of lactic acid and its conjugate base, lactate, has evolved during the past decade in the care of patients in the emergency department (ED). A recent national sepsis quality measure has led to increased use of serum lactate in the ED, but many causes for hyperlactatemia exist outside of sepsis. We provide a review of the biology of lactate production and metabolism, the many causes of hyperlactatemia, and evidence on its use as a marker in prognosis and resuscitation. Additionally, we review the evolving role of lactate in sepsis care. We provide recommendations to aid lactate interpretation in the ED and highlight areas for future research.

Monitoring biomolecule concentrations in tissue using a wearable droplet microfluidic-based sensor

Knowing how biomarker levels vary within biological fluids over time can produce valuable insight into tissue physiology and pathology, and could inform personalised clinical treatment. We describe here a wearable sensor for monitoring biomolecule levels that combines continuous fluid sampling with in situ analysis using wet-chemical assays (with the specific assay interchangeable depending on the target biomolecule). The microfluidic device employs a droplet flow regime to maximise the temporal response of the device, using a screw-driven push-pull peristaltic micropump to robustly produce nanolitre-sized droplets. The fully integrated sensor is contained within a small (palm-sized) footprint, is fully autonomous, and features high measurement frequency (a measurement every few seconds) meaning deviations from steady-state levels are quickly detected. We demonstrate how the sensor can track perturbed glucose and lactate levels in dermal tissue with results in close agreement with standard off-line analysis and consistent with changes in peripheral blood levels.

Mechanisms by which hydrogen sulfide attenuates muscle function following ischemia-reperfusion injury: effects on Akt signaling, mitochondrial function, and apoptosis

Ischemia–reperfusion injury is caused by a period of ischemia followed by massive blood flow into a tissue that had experienced restricted blood flow. The severity of the injury is dependent on the time the tissue was restricted from blood flow, becoming more severe after longer ischemia times. This can lead to many complications such as tissue necrosis, cellular apoptosis, inflammation, metabolic and mitochondrial dysfunction, and even organ failure. One of the emerging therapies to combat ischemic reperfusion injury complications is hydrogen sulfide, which is a gasotransmitter that diffuses across cell membranes to exert effects on various signaling pathways regulating cell survival such as Akt, mitochondrial activity, and apoptosis. Although commonly thought of as a toxic gas, low concentrations of hydrogen sulfide have been shown to be beneficial in promoting tissue survival post-ischemia, and modulate a wide variety of cellular responses. This review will detail the mechanisms of hydrogen sulfide in affecting the Akt signaling pathway, mitochondrial function, and apoptosis, particularly in regards to ischemic reperfusion injury in muscle tissue. It will conclude with potential clinical applications of hydrogen sulfide, combinations with other therapies, and perspectives for future studies.

Regulation of the glucose supply from capillary to tissue examined by developing a capillary model

A new glucose transport model relying upon diffusion and convection across the capillary membrane was developed, and supplemented with tissue space and lymph flow. The rate of glucose utilization (J util) in the tissue space was described as a saturation function of glucose concentration in the interstitial fluid (C glu,isf), and was varied by applying a scaling factor f to J max. With f = 0, the glucose diffusion ceased within ~20 min. While, with increasing f, the diffusion was accelerated through a decrease in C glu,isf, but the convective flux remained close to resting level. When the glucose supplying capacity of the capillary was measured with a criterion of J util /J max = 0.5, the capacity increased in proportion to the number of perfused capillaries. A consistent profile of declining C glu,isf along the capillary axis was observed at the criterion of 0.5 irrespective of the capillary number. Increasing blood flow scarcely improved the supplying capacity.

Impact of Phlebotomy Tourniquet Use on Blood Lactate Levels in Acutely Ill Patients

OBJECTIVE

Lactate levels are increasingly used to guide resuscitation efforts. Some surgical literature suggests that tourniquet use during phlebotomy falsely elevates results, although studies in healthy volunteers have not demonstrated this. The purpose of this study was to determine in clinical practice whether tourniquet use during the drawing of a lactate results in significantly altered levels compared to the result of a level drawn without a tourniquet.

METHODS

A prospective cohort study was carried out on emergency department patients whose clinical presentation led a physician to order a lactate level. Written informed consent was obtained from patients or their proxies. Study lactates were obtained using a tourniquet during the draw sequence of other laboratory studies. Lactate levels for clinical use were drawn per hospital protocol with no tourniquet. The time of lactate measurements and patient demographic information were recorded. Lactate levels for each patient were compared with the Wilcoxon Rank-Sum Test.

RESULTS

40 patients were consented and enrolled. The median clinical lactate level was 1.9 (interquartile range 1.5-2.6), and the median study lactate level was 1.9 (interquartile range 1.4-2.7). There was no difference between paired lactate values (p=0.95).

CONCLUSIONS

Tourniquet use appears to have no impact on measured lactate levels. Our findings suggest that current practices at many institutions regarding lactate collection are likely too stringent and should be changed.

Tourniquet Use During Knee Replacement Surgery May Contribute to Muscle Atrophy in Older Adults

Muscle atrophy after total knee arthroplasty (TKA) occurs at a rate of 1% per day for the first 2 wk. Our hypothesis is that tourniquet-induced ischemia-reperfusion injury occurring during TKA influences metabolism and may contribute to atrophy. Identifying pathways that are upregulated during this critical "14-d window" after surgery may help us delineate therapeutic approaches to avoid muscle loss.

Tourniquet induced ischemia and changes in metabolism during TKA: a randomized study using microdialysis

Background

Tourniquet use in total knee arthroplasty (TKA) surgery is applied to minimize blood loss thereby creating better overview of the surgical field. This induces ischemia in the skeletal muscle resulting in reperfusion injury. Our aim was to investigate the in vivo metabolic changes in the skeletal muscle during TKA surgery using microdialysis (MD).

Methods

Seventy patients were randomly allocated to tourniquet group (n = 35) or non-tourniquet group (n = 35). Prior to surgery, catheters were inserted in the operated leg and non-operated leg. Interstitial dialysate was collected before and after surgery and at 20 min intervals during a 5 h reperfusion period. Main variables were ischemic metabolites: glucose, pyruvate, lactate and glycerol and L/P ratio.

Results

Significant difference in all metabolites was detected between the two groups, caused by tourniquet application. Tourniquet induced ischemia resulted in decreased levels of glucose and pyruvate to 54 and 60 % respectively, compared to baseline. Simultaneously, accumulation of lactate to 116 % and glycerol to 190 % was observed. L/P ratio was elevated indicating ischemia.

In the non-tourniquet group the metabolite changes were less profound and normalized within 60 min.

Conclusions

Microdialysis revealed that performing TKA with tourniquet is associated with increased ischemia. This affects all metabolites but the changes are normalized after 5 h

Functional expression of α7-nicotinic acetylcholine receptors by muscle afferent neurons

The exercise pressor reflex (EPR) is generated by group III and IV muscle afferents during exercise to increase cardiovascular function. Muscle contraction is triggered by ACh, which is metabolized into choline that could serve as a signal of exercise-induced activity. We demonstrate that ACh can induce current in muscle afferents neurons isolated from male Sprague-Dawley rats. The nicotinic ACh receptors (nAChRs) appear to be expressed by some group III-IV neurons since capsaicin (TRPV1) and/or ATP (P2X) induced current in 56% of ACh-responsive neurons. α7- And α4β2-nAChRs have been shown to be expressed in sensory neurons. An α7-nAChR antibody stained 83% of muscle afferent neurons. Functional expression was demonstrated by using the specific α7-nAChR blockers α-conotoxin ImI (IMI) and methyllycaconitine (MLA). MLA inhibited ACh responses in 100% of muscle afferent neurons, whereas IMI inhibited ACh responses in 54% of neurons. Dihydro-β-erythroidine, an α4β2-nAChR blocker, inhibited ACh responses in 50% of muscle afferent neurons, but recovery from block was not observed. Choline, an α7-nAChR agonist, elicited a response in 60% of ACh-responsive neurons. Finally, we demonstrated the expression of α7-nAChR by peripherin labeled (group IV) afferent fibers within gastrocnemius muscles. Some of these α7-nAChR-positive fibers were also positive for P2X3 receptors. Thus choline could serve as an activator of the EPR by opening α7-nAChR expressed by group IV (and possible group III) afferents. nAChRs could become pharmacological targets for suppressing the excessive EPR activation in patients with peripheral vascular disease.

Ischemia-reperfusion injury and volatile anesthetics

Ischemia-reperfusion injury (IRI) is induced as a result of reentry of the blood and oxygen to ischemic tissue. Antioxidant and some other drugs have protective effect on IRI. In many surgeries and clinical conditions IRI is counteract inevitable. Some anesthetic agents may have a protective role in this procedure. It is known that inhalational anesthetics possess protective effects against IRI. In this review the mechanism of preventive effects of volatile anesthetics and different ischemia-reperfusion models are discussed.

Increased post-operative ischemia in the femoral head found by microdialysis by the posterior surgical approach: a randomized clinical trial comparing surgical approaches in hip resurfacing arthroplasty

BACKGROUND

Hip resurfacing arthroplasty (HRA) is associated with osteonecrosis of the femoral head and femoral neck fracture, which may be caused by a decrease in the perfusion of the bone initiated at surgery. Several studies have demonstrated a decreased blood flow during surgery depending on the choice of surgical approach. We investigated the effect of the surgical approach on the blood flow and metabolism in the femoral head and neck in HRA by Laser Doppler flowmetry (LDF) and microdialysis.

MATERIALS AND METHODS

We conducted a randomized clinical trial on 38 patients, allocated to HRA by either the posterior (Post) or the antero-lateral (AntLat) surgical approach. LDF was performed during surgery and microdialysis after surgery to assess the concentration of the following metabolic markers: glucose, lactate, pyruvate and glycerol.

RESULTS

At 44-50 h after surgery, the mean lactate/pyruvate (L/P) and lactate/glucose (L/G) ratio was higher in the Post group compared to the AntLat group; L/P 195.3 (SEM 123) in Post and 128.5 (108.0) in AntLat; L/G 16.9 (6.5) in Post and 8.9 (3.7) in AntLat (p L/P = 0.02 and p L/G = 0.03). There was no difference in the LDF measurements (p = 0.74).

INTERPRETATION

HRA in the posterior approach results in increased post-operative ischemia in the femoral head and neck although during surgery, no difference in the blood flow was found. Still, the antero-lateral approach also causes considerable ischemia and other possible explanations, such as damage to the retinacular vessels during surgery or altered microcirculation because of heating from the cementation process, needs to be investigated.

Cooperative role of endogenous leucotrienes and platelet-activating factor in ischaemia-reperfusion-mediated tissue injury

Insufficient oxygen delivery to organs leads to tissue dysfunction and cell death. Reperfusion, although vital to organ survival, initiates an inflammatory response that may both aggravate local tissue injury and elicit remote organ damage. Polymorphonuclear neutrophil (PMN) trafficking to remote organs following ischaemia/reperfusion (I/R) is associated with the release of lipid mediators, including leucotriene (LT) B₄, cysteinyl-LTs (CysLTs) and platelet-activating factor (PAF). Yet, their potentially cooperative role in regulating I/R-mediated inflammation has not been thoroughly assessed. The present study aimed to determine the cooperative role of lipid mediators in regulating PMN migration, tissue oedema and injury using selective receptor antagonists in selected models of I/R and dermal inflammation. Our results show that rabbits, pre-treated orally with BIIL 284 and/or WEB 2086 and MK-0571, were protected from remote tissue injury following I/R or dermal inflammation in an additive or synergistic manner when the animals were pre-treated with two drugs concomitantly. The functional selectivity of the antagonists towards their respective agonists was assessed in vitro, showing that neither BIIL 284 nor WEB 2086 prevented the inflammatory response to IL-8, C5a and zymosan-activated plasma stimulation. However, these agonists elicited LTB₄ biosynthesis in isolated rabbit PMNs. Similarly, a cardioprotective effect of PAF and LTB₄ receptor antagonists was shown following myocardial I/R in mice. Taken together, these results underscore the intricate involvement of LTB₄ and PAF in each other’s responses and provide further evidence that targeting both LTs and PAF receptors provides a much stronger anti-inflammatory effect, regulating PMN migration and oedema formation.

Endoplasmic Reticulum Stress Activation during Total Knee Arthroplasty

Total knee arthroplasty (TKA) is the most common remediation for knee pain from osteoarthritis (OA) and is performed 650,000 annually in the U.S. A tourniquet is commonly used during TKA which causes ischemia and reperfusion (I/R) to the lower limb but the effects of I/R on muscle are not fully understood. Previous reports suggest upregulation of cell stress and catabolism and downregulation of markers of cap-dependent translation during and after TKA. I/R has also been shown to cause endoplasmic reticulum (ER) stress and induce the unfolded protein response (UPR). We hypothesized that the UPR would be activated in response to ER stress during TKA. We obtained muscle biopsies from the vastus lateralis at baseline, before TKA; at maximal ischemia, prior to tourniquet deflation; and during reperfusion in the operating room. Phosphorylation of 4E-BP1 and AKT decreased during ischemia (−28%, P < 0.05; −20%, P < 0.05, respectively) along with an increase in eIF2α phosphorylation (64%, P < 0.05) suggesting decreased translation initiation. Cleaved ATF6 protein increased in ischemia (39%, P = 0.056) but returned to baseline during reperfusion. CASP3 activation increased during reperfusion compared to baseline (23%, P < 0.05). XBP1 splicing assays revealed an increase in spliced transcript during ischemia (31%, P < 0.05) which diminished during reperfusion. These results suggest that in response to I/R during TKA all three branches of the ER stress response are activated.

Muscle microdialysis to confirm sublethal ischemia in the induction of remote ischemic preconditioning

Exposure of one tissue to ischemia-reperfusion confers a systemic protective effect, referred to as remote ischemic preconditioning (RIPC). Confirmation that the desired effect of ischemia is occurring in tissues used to induce RIPC requires an objective demonstration before this technique can be used consistently in the clinical practice. Enrolled patients underwent three to four RIPC sessions on non-consecutive days. Sessions consisted of 4 cycles of 5 min of leg cuff inflation to 30 mmHg above the systolic blood pressure followed by reperfusion. Absence of leg pulse was confirmed by Doppler evaluation. To evaluate limb transient ischemia, patients were monitored with muscle microdialysis. Glucose, lactate, lactate/pyruvate ratio, and glycerol levels were measured. Fourteen microdialysis sessions were performed in seven patients undergoing RIPC (42.8 % male; mean age, 51.8; Fisher grade 4 in all seven patients, Hunt and Hess grade 5 in five patients, four in one patient and one in one patient). An average follow-up of 29 days demonstrated no complications associated with the procedure. Muscle microdialysis during RIPC sessions showed a significant increase in lactate/pyruvate ratio (21.2 to 26.8, p = 0.001) and lactate (3.0 to 3.9 mmol/L, p = 0.002), indicating muscle ischemia. There was no significant variation in glycerol (234 to 204 μg/L, p = 0.43), indicating no permanent cell damage. The RIPC protocol used in this study is safe, well tolerated, and induces transient metabolic changes consistent with sublethal ischemia. Muscle microdialysis can be used safely as a confirmatory tool in the induction of RIPC.

Microdialysis in the femoral head of the minipig and in a blood cloth of human blood

INTRODUCTION

Microdialysis can detect ischemia in soft tissue. In a previous study, we have shown the development of ischemia in the femoral head removed from patients undergoing total hip replacement. That study also raised some methodological questions that this study tries to answer: what is happening in the dead space around the catheter in the drill canal, and is there an equilibrium period after the insertion of the catheter?

MATERIAL AND METHODS

In an ex-vivo study using 5 syringes with 5 mL human blood, a microdialysis catheter was inserted and microdialysis was performed over 3 h. In an in-vivo study, a drill hole was made in the proximal part of the femur in 6 mature Göttingen minipigs and microdialysis was performed over 3 h. The pigs were kept normoventilated during the experiment.

RESULTS

The ex-vivo microdialysis results showed that lactate kept a steady level and glucose and glycerol both fell; pyruvate fell but leveled out. The mean lactate/pyruvate ratio increased from 13 (SD 4) to 32 (SD 6) (p < 0.001). In vivo, relative recovery was 57% (SD 11). Lactate increased, pyruvate stayed constant, and glucose and glycerol levels fell. The lactate/pyruvate ratio increased from 30 (8) initially to 37 (8) after 1 h (p = 0.007) but no statistically significant change from 1 to 2 h was observed.

INTERPRETATION

The ex-vivo study showed a clear washout pattern, and was different from what we see in bone. The in-vivo study indicated that an equilibrium period is necessary or that a reference measurement in healthy bone must be used when performing short measurements in bone.

Gastric submucosal microdialysis in the detection of rat stomach ischemia--a comparison of the 3H2O efflux technique with metabolic monitoring

Microdialysis has been utilized for nutritive blood flow measurements, but both the advantages and disadvantages of various approaches have not been evaluated in parallel in the stomach yet. Our aim was to compare the (3)H(2)O efflux technique with biochemical monitoring during temporary celiac artery occlusion in anesthetized rats. Microdialysis probes were implanted in the gastric submucosa and perfused with (3)H(2)O; samples were analyzed for β-activity, glucose, lactate, pyruvate and glycerol. Gastric mucosa and plasma were subjected to morphometry and analysis of myeloperoxidase, total thiols and lactatdehydrogenase. The most dramatic responses to ischemia were observed in lactate/pyruvate and lactate/glucose (%) ratios (6.1-9.3×, p < 0.0001); the changes in (3)H(2)O efflux and glycerol were less pronounced (1.1-1.7×, p < 0.0001 and < 0.01, respectively). (3)H(2)O efflux correlated best with the lactate/glucose ratio and glucose alone (r = 0.693 and -0.681, respectively, p < 0.0001). A correlation was also found between plasma lactatdehydrogenase and relative glycerol release (r = 0.600, p < 0.05). Myeloperoxidase, lactatdehydrogenase and histology score were increased by ischemia/reperfusion (0.06-0.12 nkat g(-1), p < 0.05, 0.26-0.44 nkat g(-1), p < 0.05 and 1.79-2.33, p < 0.05, respectively), macroscopy and plasma thiols remained unchanged. Microdialysis is useful in monitoring gastric ischemia, metabolic monitoring being superior to the (3)H(2)O efflux technique. The results question the efficacy of the utilized model to produce standardized major gastric damage.

Microdialysis of paraspinal muscle in healthy volunteers and patients underwent posterior lumbar fusion surgery

Paraspinal muscle damage is inevitable during conventional posterior lumbar fusion surgery. Minimal invasive surgery is postulated to result in less muscle damage and better outcome. The aim of this study was to monitor metabolic changes of the paraspinal muscle and to evaluate paraspinal muscle damage during surgery using microdialysis (MD). The basic interstitial metabolisms of the paraspinal muscle and the deltoid muscle were monitored using the MD technique in eight patients, who underwent posterior lumbar fusion surgery (six male and two female, median age 57.7 years, range 37-74) and eight healthy individuals for different positions (five male and three female, age 24.1 +/- 0.8 years). Concentrations of glucose, glycerol, and lactate pyruvate ratio (L/P) in both tissues were compared. In the healthy group, the glucose and glycerol concentrations and L/P were unchanged in the paraspinal muscle when the body position changed from prone to supine. The glucose concentration and L/P were stable in the paraspinal muscle during the surgery. Glycerol concentrations increased significantly to 243.0 +/- 144.1 microM in the paraspinal muscle and 118.9 +/- 79.8 microM in the deltoid muscle in the surgery group. Mean glycerol concentration difference (GCD) between the paraspinal muscle and the deltoid tissue was 124.1 microM (P = 0.003, with 95% confidence interval 83.4-164.9 microM). The key metabolism of paraspinal muscle can be monitored by MD during the conventional posterior lumbar fusion surgery. The glycerol concentration in the paraspinal muscle is markedly increased compared with the deltoid muscle during the surgery. It is proposed that GCD can be used to evaluate surgery related paraspinal muscle damage. Changing body position did not affect the paraspinal muscle metabolism in the healthy subjects.

Dexmedetomidine reduces the ischemia-reperfusion injury markers during upper extremity surgery with tourniquet

PURPOSE

We examined the effect of dexmedetomidine on ischemia-reperfusion injury due to tourniquet application during upper-extremity surgery by determining blood malondialdehyde and hypoxanthine levels. Alterations in aspartate aminotransferase, alanine aminotransferase, creatine phosphokinase, lactate dehydrogenase, uric acid, and creatinine levels were also assessed.

METHODS

Forty patients of American Society of Anesthesiologists physical status I to II having hand and forearm surgery with tourniquet were randomly allocated into 2 groups. Brachial plexus anesthesia via axillary approach was performed for upper-limb block in all patients. In the dexmedetomidine group, a continuous infusion of dexmedetomidine (1 microg/kg for 10 minutes, followed by 0.5 microg kg(-1) h(-1)) was used until the end of surgery, whereas the control group received an equivalent volume of saline. Venous blood samples were obtained before brachial plexus anesthesia, at 1 minute before tourniquet release, and 15 minutes after tourniquet release for biochemical analysis.

RESULTS

Dexmedetomidine significantly attenuated plasma hypoxanthine production in the ischemia and plasma malondialdehyde production in the reperfusion periods. Blood creatine phosphokinase and uric acid levels were significantly lower in the dexmedetomidine group compared with those in the control group after reperfusion.

CONCLUSIONS

Our results suggest that dexmedetomidine may offer advantages by inhibiting lipid peroxidation in the case of anticipated ischemia-reperfusion injury, such as would occur in upper-extremity surgery requiring tourniquet application.

TYPE OF STUDY/LEVEL OF EVIDENCE

Prognostic II.

Sevoflurane but not propofol increases interstitial glycolysis metabolites availability during tourniquet-induced ischaemia-reperfusion

BACKGROUND

Ischaemia/reperfusion (I/R) is one of the main pathophysiological phenomena involved in the anaesthetic practice. The authors hypothesized that anaesthetic regimens can influence skeletal muscle tolerance to tourniquet-induced I/R that should be reflected by the interstitial metabolite levels of anaerobic glycolysis.

METHODS

Microdialysis probes were implanted in three groups of 10 patients each receiving either sevoflurane (SEVO), propofol (PRO), or spinal (SA) anaesthesia (for induction and maintenance). SA group was considered as a control group. Interstitial fluid was obtained during tourniquet-induced I/R and was analysed for interstitial glucose, lactate, pyruvate, and glycerol.

RESULTS

The microdialysis flow rate was 0.5 microl min(-1). Compared with the control group, the SEVO group had a higher level of both lactate and pyruvate and an increase in glucose during ischaemia. In contrast, the PRO group had a lower level of pyruvate, resulting in a significant higher increase (eight times from baseline) of the lactate pyruvate ratio. Glucose level remained low in this group. During reperfusion, lactate, pyruvate, and glucose remained at a significantly higher level in the SEVO group. In the PRO group, there was no difference in lactate, pyruvate, and glucose levels compared with the control group. The interstitial level of glycerol exhibits only few and comparable changes during I/R between the groups.

CONCLUSIONS

Our results indicate that there is a better availability of interstitial glycolysis metabolites (glucose, lactate, and pyruvate) in the skeletal muscle during ischaemia and reperfusion after sevoflurane exposure than after propofol, suggesting a potential preconditioning effect of sevoflurane on tourniquet-induced skeletal muscle I/R.

Bayesian flux balance analysis applied to a skeletal muscle metabolic model

In this article, the steady state condition for the multi-compartment models for cellular metabolism is considered. The problem is to estimate the reaction and transport fluxes, as well as the concentrations in venous blood when the stoichiometry and bound constraints for the fluxes and the concentrations are given. The problem has been addressed previously by a number of authors, and optimization-based approaches as well as extreme pathway analysis have been proposed. These approaches are briefly discussed here. The main emphasis of this work is a Bayesian statistical approach to the flux balance analysis (FBA). We show how the bound constraints and optimality conditions such as maximizing the oxidative phosphorylation flux can be incorporated into the model in the Bayesian framework by proper construction of the prior densities. We propose an effective Markov chain Monte Carlo (MCMC) scheme to explore the posterior densities, and compare the results with those obtained via the previously studied linear programming (LP) approach. The proposed methodology, which is applied here to a two-compartment model for skeletal muscle metabolism, can be extended to more complex models.

Blood flow and microdialysis in the human femoral head

BACKGROUND

If it would be possible to detect lack of flow and/or the development of ischemia in bone, we might have a way of predicting whether a broken bone will heal. We established microdialysis (MD) and laser Doppler (LD) flow measurement in the human femoral head in order to be able to detect ischemia and measure changes in blood flow.

MATERIAL AND METHODS

In 9 patients undergoing total hip arthroplasty for primary osteoarthrosis, two MD catheters were inserted into the femoral head through two drill holes after the blood flow had been visualized by LD. Then primary samples were collected with the femoral head in situ; thereafter, the head was removed and samples were collected over the following 4 hours ex vivo. The variables obtained by MD were concentrations of glucose, lactate, pyruvate, and glycerol in extracellular fluid.

RESULTS

The results showed development of ischemia with a statistically significant decrease in glucose concentration and elevation of the lactate/pyruvate ratio over time. The LD showed flow with the femoral head in situ and lack of flow when the femoral head was removed.

INTERPRETATION

The use of MD was established in the human femoral head. Ischemic levels were detected within 2 h of cessation of blood flow in most patients.

Pharmacologic modulation of skeletal muscle metabolism: a microdialysis study

Microdialysis is a valuable tool to measure tissue responses. We hypothesized that skeletal muscle metabolism can be modulated by microdialysis applied drugs which alter cytosolic calcium concentration. With approval of the local animal care committee, the hind limbs of sacrificed male Sprague Dawley rats were perfused either with Ringer's solution or with dantrolene 1 microM at 30 ml hr(-1) and 21 degrees. Microdialysis probes in both hind limbs were perfused at 1 microl min(-1) either with sorbitol 80 mM, calcium 20 mM, 40 mM, 80 mM, caffeine 40 mM, 80 mM, and halothane 10 vol% respectively, and at the contralateral adductor muscle with Ringer as control. Lactate was measured spectrophotometrically in the dialysate at 15 min. intervals. Lactate levels as measured by intramuscular microdialysis were not influenced by intramuscular application of sorbitol 80 mM compared to control measurements with Ringer's solution. Local application of calcium 20 mM, 40 mM, 80 mM, caffeine 40 mM, 80 mM, and halothane 10 vol% via microdialysis increased lactate concentrations, while organ perfusion by dantrolene 1 microM reduced the caffeine-induced lactate increase. Modulation of intramuscular lactate metabolism by exogenous compounds via microdialysis probes generates new insights in skeletal muscle metabolism.

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.

Ketamine Sedation During Spinal Anesthesia for Arthroscopic Knee Surgery Reduced the Ischemia-Reperfusion Injury Markers

We studied the effect of ketamine sedation on oxidative stress during arthroscopic knee surgery with tourniquet application by determining blood and tissue malonyldialdehyde (MDA) and hypoxanthine (HPX) levels. Thirty ASA I-II patients undergoing arthroscopic knee surgery with tourniquet were randomly divided into two groups. Spinal anesthesia induced with 12.5 mg bupivacaine was administered to all patients. In the ketamine group, after IV administration of 0.01 mg/kg midazolam, a continuous infusion of ketamine (0.5 mg . kg(-1) . h(-1)) was used until the end of surgery whereas the placebo group received a volume-equivalent placebo infusion. Ramsey Sedation Scale (RSS) was used for assessing the sedation level. Venous blood and synovial membrane tissue samples were obtained before ketamine infusion, at 30 min of tourniquet ischemia, and at 5 min after tourniquet deflation for MDA and HPX measurements. Tissue MDA and HPX levels were significantly less in the ketamine group than the control group after reperfusion. RSS scores were higher in the ketamine group without any adverse effect. We conclude that ketamine sedation attenuates lipid peroxidation markers in arthroscopic knee surgery with tourniquet application.

Bench-to-bedside review: microdialysis in intensive care medicine

Microdialysis is a technique used to measure the concentrations of various compounds in the extracellular fluid of an organ or in a body fluid. It is a form of metabolic monitoring that provides real-time, continuous information on pathophysiological processes in target organs. It was introduced in the early 1970s, mainly to measure concentrations of neurotransmitters in animal experiments and clinical settings. Using commercial equipment it is now possible to conduct analyses at the bedside by collecting interstitial fluid for measurement of carbohydrate and lipid metabolites. Important research has been reported in the field of neurosurgery in recent decades, but use of metabolic monitoring in critical care medicine is not yet routine. The present review provides an overview of findings from clinical studies using microdialysis in critical care medicine, focusing on possible indications for clinical biochemical monitoring. An important message from the review is that sequential and tissue-specific metabolic monitoring, in vivo, is now available.

Tourniquet-induced ischemia and reperfusion in human skeletal muscle

Microdialysis conceivably enables longitudinal and simultaneous investigation of several metabolites by repeated measurements in skeletal muscle. We used and evaluated microdialysis as an in vivo method to characterize the time-course and relative kinetics of pyruvate, glucose, lactate, glycerol, hypoxanthine, uric acid, and urea, in skeletal muscles, exposed to ischemia and reperfusion, in eight patients having arthroscopic-assisted anterior cruciate ligament reconstruction. A dialysis probe was implanted before surgery in the rectus femoris muscle. Dialysate samples were collected at 10-minute intervals at a flow rate of 1 microL/minute until 2 hours after tourniquet deflation. Ninety minutes of ischemia resulted in accumulation of lactate (234% +/- 38%), hypoxanthine (582% +/- 166%), and glycerol (146% +/- 46%), consumption of glucose (54% +/- 9%) and pyruvate (16% +/- 44%), and a slight decrease of urea (78% +/- 11%) compared with baseline (100%). Uric acid was unchanged (95% +/- 12%). Within 90 minutes after tourniquet deflation the concentrations were virtually normalized for all measured metabolites, suggesting that the duration of ischemia was well tolerated by the patients. The results indicate that the use of microdialysis for monitoring energy metabolic events during orthopaedic surgery that requires ischemia and reperfusion is feasible and safe.

Intestinal ischaemia during cardiac arrest and resuscitation: comparative analysis of extracellular metabolites by microdialysis

Intestinal ischaemia is a major complication of shock syndromes causing translocation of bacteria and endotoxins and multiple organ failure in intensive care patients. The present study was designed to use microdialysis as a tool to monitor intestinal ischaemia after cardiac arrest and resuscitation in pigs. For this purpose, microdialysis probes were implanted in pig jejunal wall, peritoneum, skeletal muscle and brain, and interstitial fluid was obtained during circulatory arrest (induced by ventricular fibrillation) and after return of spontaneous circulation (ROSC). Cardiac arrest for 4 min caused a prolonged (60 min) reduction of blood flow in jejunal wall, muscle and brain as determined by the ethanol technique. This was accompanied by cellular damage in heart muscle and brain as indicated by increased levels of troponin-I and protein S-100, respectively. Plasma levels of glucose, lactate and choline were increased at 15-60 min following cardiac arrest. In contrast, cardiac arrest induced a rapid but variable decrease of interstitial glucose levels in all monitored organs; this decrease was followed by an increase over baseline during reperfusion. In the intestine, lactate, glutamate and choline levels were increased during ischaemia and reperfusion for 60-120 min; intestinal and peritoneal samples yielded parallel changes of lactate levels. Brain and muscle samples showed similar changes as in intestinum and peritoneum except for glutamate, which was increased in brain but not in muscle. We conclude that intestinal ischaemia occurs as a consequence of cardiac arrest and resuscitation and can be monitored by in vivo microdialysis. Comparative analysis by multi-site microdialysis reveals that the intestine is equally or even more sensitive to ischaemia than brain or muscle.

Metabolic changes detected by microdialysis during endotoxin shock and after endotoxin preconditioning

OBJECTIVE

Preconditioning with low doses of endotoxin has been shown to induce endotoxin hyporesponsiveness. The present study was designed to assess the metabolic response of various tissues during endotoxemia and after pretreatment with endotoxin.

DESIGN

Controlled experimental animal study.

SETTING

Research laboratory of a university hospital.

MEASUREMENTS AND RESULTS

Ten pigs were randomly assigned to a control ( n = 5) or a treatment group ( n = 5), the latter receiving incremental doses of endotoxin 5-2 days prior the experiments. Apart from hemodynamics and oxygen transport variables, lactate, glucose, and glycerol were measured in muscle, subcutaneous fat, and hepatic tissue using microdialysis. Endotoxin was infused (1 micro g.kg.h) until the animals died. A significant increase in tissue lactate (eightfold) and glycerol (fivefold) was observed in the control animals. This effect was almost completely abolished in the endotoxin pretreated group. Endotoxin pretreatment had no significant effects on mean arterial pressure [56 (range 34-89) mmHg vs 70 (47-88) mmHg, n.s.] or cardiac output [4.8 (3.0-5.9) l/min vs 3.2 (2.1-4.2) l/min, n.s.], but significantly improved arterial pO(2) and pH ( P<0.05). Increase of oxygen extraction was higher in control animals [from 34% (range 24-47%) to 72% (range 61-79%)] compared to the pretreatment group [from 30% (range 22-42%) to 44% (range 34-50%), P<0.05]. Endotoxin pretreatment increased survival time from 5.3 h (5.0-5.8) to 8.0 h (7.0-8.5) ( P<0.05), respectively.

CONCLUSIONS

Microdialysis monitoring revealed that endotoxin preconditioning ameliorates the increase in tissue metabolism during endotoxemia, accompanied by decreased systemic oxygen demand despite unchanged global hemodynamics.