Glucose, lactate, and pyruvate response in an experimental model of microvascular flap ischemia and reperfusion: A microdialysis study

Bone marrow plasma metabonomics of idiopathic acquired aplastic anemia patients using 1H nuclear magnetic resonance spectroscopy

INTRODUCTION

Idiopathic acquired aplastic anemia (AA) is a bone marrow failure disorder where aberrant T-cell functions lead to depletion of hematopoietic stem and progenitor cells in the bone marrow (BM) microenvironment. T-cells undergo metabolic rewiring, which regulates their proliferation and differentiation. Therefore, studying metabolic variation in AA patients may aid us with a better understanding of the T-cell regulatory pathways governed by metabolites and their pathological engagement in the disease.

OBJECTIVE

To identify the differential metabolites in BM plasma of AA patients, AA follow-up (AAF) in comparison to normal controls (NC) and to identify potential disease biomarker(s).

METHODS

The study used 1D 1H NMR Carr-Purcell-Meiboom-Gill (CPMG) spectra to identify the metabolites present in the BM plasma samples of AA (n = 40), AAF (n = 16), and NC (n = 20). Metabolic differences between the groups and predictive biomarkers were identified by using multivariate analysis and receiver operating characteristic (ROC) module of Metaboanalyst V5.0 tool, respectively.

RESULTS

The AA and AAF samples were well discriminated from NC group as per Principal Component analysis (PCA). Further, we found significant alteration in the levels of 17 metabolites in AA involved in amino-acid (Leucine, serine, threonine, phenylalanine, lysine, histidine, valine, tyrosine, and proline), carbohydrate (Glucose, lactate and mannose), fatty acid (Acetate, glycerol myo-inositol and citrate), and purine metabolism (hypoxanthine) in comparison to NC. Additionally, biomarker analysis predicted Hypoxanthine and Acetate can be used as a potential biomarker.

CONCLUSION

The study highlights the significant metabolic alterations in the BM plasma of AA patients which may have implication in the disease pathobiology.

Selective Application of Blood Glucose Monitoring After Free Flap Surgery: Potential Indications in Real-World Practice

BACKGROUND

For free-flap monitoring, physical examination still serves as the criterion standard. Blood glucose measurement (BGM) has been suggested to be useful in identifying flap perfusion status. Nonetheless, its routine use may not be cost-effective in real-world settings. This study aimed to share the experiences of using BGM for flap monitoring and suggest its potential indications.

METHODS

Of cases of free flap reconstruction conducted between March 2017 and May 2021, those using BGM for flap monitoring were reviewed. Blood glucose measurement was selectively conducted for the following specific situations, which included encountering a flap showing a reddish discoloration and/or rapid capillary refilling time in the immediate postoperative period, monitoring discolored flaps after conducting a salvage operation, and conducting bloodletting therapy for salvaging congestive flaps. The clinical course and outcomes were evaluated.

RESULTS

Of a total of 203 cases, 35 used BGM for flap monitoring in addition to clinical examination. In 29 cases, BGM was performed to distinguish early hyperemia from true venous insufficiency. All flaps showed BGM greater than 60 mg/dL with a mean value of 115.42, suggesting early hyperemia, and had uneventful postoperative courses. In 3 cases with already discolored flaps after a salvage operation, BGM was conducted 4 times serially every 3 hours and showed a mean value of 81.6 mg/dL with increasing trends. The flaps recovered completely. In the other 3 cases requiring bloodletting therapy, BGM was conducted an average of 11 times at a median interval of 7 hours. The bloodletting therapy was terminated with reference to the value of BGM when it showed greater than 60 mg/dL while the therapy was on hold. All flaps were successfully salvaged except one showing partial necrosis.

CONCLUSIONS

Blood glucose measurement may be helpful in assessing flap perfusion and decision making in certain clinical situations and may be useful as an ancillary tool for flap monitoring. Selective application of BGM may contribute to achieving optimal outcomes.

Diagnostic Accuracy of Microdialysis in Postoperative Flap Monitoring

Postoperative monitoring plays an important role in achieving success in microvascular free tissue transfer. A systematic review was designed to evaluate the clinical outcomes of microdialysis in flap monitoring and a meta-analysis was conducted for diagnostic accuracies. The search terms "microdialysis" and "flap" were used in a PubMed and Scopus search, resulting in 60 and 78 results, respectively. Among 78 titles, 15 articles were excluded. Among 63 abstracts, 43 abstracts were excluded. From 20 full texts, 7 articles were excluded because they did not have sufficient content (ie, the statistical values in question). A systematic review was conducted of the final 13 articles. The overall sensitivity was 97.24% [95% confidence interval (CI)=93.67%-99.10%]. Eleven of the 13 studies showed 100% sensitivity and 2 studies had 2 and 3 false negative results, resulting in sensitivity values of 85.8% and 95.3%. Specificity ranged from 91.89% to 100%, and the overall value was 98.15% (95% CI=96.80%-99.04%). The positive predictive value ranged from 84.62% to 100%, with an overall value of 93.62% (95% CI=89.33%-96.26%). The negative predictive value ranged from 94.44% to 100%, with an overall value of 99.22% (95% CI=98.17%-99.67%). The overall flap success rate (survival rate) was 93.7% (786/839). The lowest flap survival rate was 86.7% and the highest was 100%. Microdialysis provides excellent diagnostic accuracy and enables the early detection of ischemia in postoperative flap monitoring. Although microdialysis is not the most popular choice among surgeons, it should be considered adjacent to conventional clinical monitoring. Cost-effectiveness, availability, and ease of application remain hurdles.

Difference between Capillary Blood Glucose of Free Flap and the Patient: A Novel Objective Marker of Free Flap Vascular Compromise during Postoperative Monitoring

Background Defining cut-off values of flap glucose levels in diagnosing free flap vascular compromise, without taking patients' glucose levels into account, does not hold good in all circumstances, especially in cases of high fluctuations in patients' capillary blood glucose and in diabetic patients. The aim of our study was to establish the role of capillary blood glucose measurements of the flap in relation to patients' fingertip, as an objective tool for postoperative free flap monitoring.

Methods A total of 76 free flaps underwent postoperative monitoring with reference test (clinical parameters) and simultaneously with our index test (difference between capillary blood glucose of free flap and the patient), in non-diabetic and diabetic patients. Patients' demography and flap characteristics were also recorded. An ROC curve was plotted to determine diagnostic accuracy and cut-offs of the index test in diagnosing free flap vascular compromise.

Results Our Index test has a cut-off value of 24.5 mg/dL with 68.75% sensitivity and 93% specificity, with an accuracy of 91.54%.

Conclusion The difference between capillary blood glucose of free flap and the patient is simple, feasible, and inexpensive, and can be done by any health care professional and does not require any specialized facilities or training. It has an excellent diagnostic accuracy to detect impending free flap vascular compromise, especially in non-diabetics. Although in diabetics, this test becomes less accurate. Being an observer-independent objective test, the difference in capillary blood glucose of patient and flap measurement can be used as a highly reliable tool for postoperative free flap monitoring.

Analysis of sex-based differences in clinical and molecular responses to ischemia reperfusion after lung transplantation

Background

Sex and hormones influence immune responses to ischemia reperfusion (IR) and could, therefore, cause sex-related differences in lung transplantation (LTx) outcomes. We compared men’s and women’s clinical and molecular responses to post-LTx IR.

Methods

In 203 LTx patients, we used the 2016 International Society for Heart and Lung Transplantation guidelines to score primary graft dysfunction (PGD). In a subgroup of 40 patients with blood samples collected before LTx (T0) and 6, 24, 48 (T48), and 72 h (T72) after lung reperfusion, molecular response to IR was examined through serial analysis of circulating cytokine expression.

Results

After adjustment, women had less grade 3 PGD than men at T48, but not at T72. PGD grade decreased from T0 to T72 more often in women than men. The evolution of PGD (the difference in mean PGD between T72 and T0) was greater in men. However, the evolution of IL-2, IL-7, IL-17a, and basic fibroblast growth factor levels was more often sustained throughout the 72 h in women. In the full cohort, we noted no sex differences in secondary clinical outcomes, but women had significantly lower peak lactate levels than men across the 72 h.

Conclusions

Men and women differ in the evolution of PGD and cytokine secretion after LTx: Women have a more sustained proinflammatory response than men despite a greater reduction in PGD over time. This interaction between cytokine and PGD responses warrants investigation. Additionally, there may be important sex-related differences that could be used to tailor treatment during or after transplantation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-021-01900-y.

The use of sentinel skin islands for monitoring buried and semi-buried micro-vascular flaps. Part I: Summary and brief description of monitoring methods

Micro-vascular flaps have been used for the repair of challenging defects for over 45 years. The risk of failure is reported to be around 5-10% which despite medical and technical advances in recent years remains essentially unchanged. Precise, continuous, sensitive and specific monitoring together with prompt notification of vascular compromise is crucial for the success of the procedure. In this review, we provide a classification and brief description of the reported methods for monitoring the micro-vascular flap and a summary of the benefits over direct visual monitoring. Over 40 different monitoring techniques have been reported but their comparative merits are not always obvious. One looks for early detection of a flap's compromise, improved flap salvage rate and a minimal false-positive or false-negative rate. The cost-effectiveness of any method should also be considered. Direct visualisation of the flap is the method most generally used and still seems to be the simplest, cheapest and most reliable method for flap monitoring. Considering the alternatives, only implantable Doppler ultrasound probes, near infrared spectroscopy and laser Doppler flowmetry have shown any evidence of improved flap salvage rates over direct visual monitoring.

Review of Flap Monitoring Technology in 2020

Advances in free flap reconstruction of complex head and neck defects have allowed for improved outcomes in the management of head and neck cancer. Technical refinements have decreased flap loss rate to less than 4%. However, the potential for flap failure exists at multiple levels, ranging from flap harvest and inset to pedicle lay and postoperative patient and positioning factors. While conventional methods of free flap monitoring (reliant on physical examination) remain the most frequently used, additional adjunctive methods have been developed. Herein we describe the various modalities of both invasive and noninvasive free flap monitoring available to date. Still, further prospective studies are needed to compare the various invasive and noninvasive technologies and to propel innovations to support the early recognition of vascular compromise with the goal of even greater rates of flap salvage.

Lamellar perfusion and energy metabolism in a preferential weight bearing model

BACKGROUND

Supporting limb laminitis (SLL) is suspected to be caused by lamellar ischaemia as a consequence of increased mechanical load.

OBJECTIVES

Examine the effects of prolonged preferential weight bearing (PWB) on lamellar perfusion and metabolism.

STUDY DESIGN

In vivo experiment.

METHODS

Microdialysis probes were inserted in the lamellar and sublamellar dermis of one forelimb in 13 Standardbred horses. In six horses, a platform shoe (contralateral forelimb) was used to induce increased load on the microdialysis-instrumented forelimb (PWB). The remaining seven horses were controls (CON). All horses were housed in stocks with limb weight distribution logged continuously for 92 hours. Microdialysate was collected and analysed every 4 hours for glucose, lactate, pyruvate, and lactate to pyruvate ratio (L:P). Microdialysis urea clearance was used to estimate lamellar perfusion. Data were analysed using a mixed-effects linear regression model.

RESULTS

Median [IQR] load on the microdialysis-instrumented limb was equivalent to 38.7% bwt. [37.3-40.3] in PWB and 27.3% bwt. [26.6-28] in CON. Limb offloading frequency increased in CON (P < .001) but not PWB (P = .2). Lamellar microdialysate glucose decreased in PWB (P < .001) and CON (P = .004), however, the rate of decrease was higher in PWB (P = .007). Lamellar L:P increased in PWB (P < .001) and peaked at 196 [79-656], whereas L:P did not change over time in CON (P = .6) and peaked at 42 [41-49]. Lamellar urea clearance decreased in PWB (P < .001) but not in CON (P = .3). Sublamellar L:P and urea clearance did not change over time in either group (P > .05).

MAIN LIMITATIONS

The PWB model may not be representative of naturally occurring SLL.

CONCLUSIONS

Evidence of lamellar ischaemia (increased L:P and decreased urea clearance) was detected exclusively in the lamellar dermis of PWB feet subjected to persistently increased load. Lamellar ischaemia is a consequence of increased mechanical load and likely contributes to the development of SLL.

Lamellar energy metabolism and perfusion in the euglycaemic hyperinsulinaemic clamp model of equine laminitis

BACKGROUND

Hyperinsulinaemia is associated with the development of endocrinopathic laminitis; however, the mechanisms remain unclear.

OBJECTIVES

Evaluate the effects of hyperinsulinaemia on lamellar energy metabolism and perfusion during laminitis development.

STUDY DESIGN

In vivo experiment.

METHODS

Eight Standardbred horses were instrumented with a microdialysis probe in the lamellae of a forelimb. A 24 hours baseline period (BASELINE) was followed by 48 hours of a continuous euglycaemic hyperinsulinaemic clamp (EHC) from 24 to 72 hours (CLAMP). Microdialysate was collected every 6 hours and analysed for glucose, lactate and pyruvate concentrations and lactate-to-pyruvate ratio (L:P). Microdialysis urea clearance was used to estimate lamellar tissue perfusion. Archived microdialysis samples from six identically instrumented Standardbred horses served as controls (CON). Variables were compared over time and between EHC and CON horses using a mixed-effects linear regression model.

RESULTS

Glucose concentration decreased during the CLAMP period in CON and EHC horses (P < .001), but there was no difference between CON and EHC (P > .9). Lactate concentration increased during the CLAMP period in CON and EHC horses (P < .001), however, the rate of increase was significantly higher in EHC horses relative to CON (P = .014). There was a relative increase in pyruvate concentration in EHC horses compared with CON during the CLAMP period (P = .03). L:P increased significantly in CON horses during the CLAMP period (P < .001) but not in EHC (P = .1). Urea clearance did not change in CON (P = .9) or EHC (P = .05) during the CLAMP, but did increase in EHC relative to CON (P = .02).

MAIN LIMITATIONS

The effects of microdialysis probe implantation on perfusion and metabolism remain unclear. The EHC model may not mimic natural endocrinopathic laminitis.

CONCLUSIONS

Laminitis developed without evidence of lamellar hypoperfusion or energy stress. Therapies to improve perfusion are unlikely to affect the initial development of endocrinopathic laminitis.

Intraosseous microdialysis for bone free flap monitoring in head and neck reconstructive surgery: A prospective pilot study

BACKGROUND

Although some researchers have positioned microdialysis catheters in the soft tissue surrounding bone, the results did not accurately reflect bone metabolism. The present study's objective was to establish the feasibility of microdialysis with a catheter positioned directly in bone.

METHODS

Thirty-four patients (19 males, 15 females; median age: 59) were included in a prospective, nonrandomized clinical trial in the Department of Maxillofacial Surgery at Amiens-Picardie University Hospital (Amiens, France). Fibula or iliac crest free flaps were used in reconstructive head and neck surgery (for cancer, osteoradionecrosis, trauma, or ameloblastoma) and monitored with microdialysis catheters positioned in a hole drilled into the bone. Glucose, lactate, pyruvate, and glycerol concentrations were analyzed for 5 days.

RESULTS

All catheters were positioned successfully, and thrombosis did not occur during the monitoring. In two patients, an increase in the lactate concentration and a glucose level close to 0 were associated with signs of flap necrosis, with removal on Days 9 and 50. In viable flaps, the mean glucose level was 2.02 mmol/L, the mean lactate level was 8.36 mmol/L, and the mean lactate/pyruvate ratio was 53. Forty percent of the glucose values were below 1 mmol/L, and 50% of the lactate/pyruvate ratio values were above 50-suggesting a specific metabolic pattern because these values would be considered as alert values in soft tissue.

CONCLUSION

Monitoring bone free flaps with intraosseous microdialysis is feasible. This technique specifically assesses bone viability, and further studies are now necessary to define the alert values in bone.

Microdialysis in postoperative monitoring of microvascular free flaps: Experiences with a decision algorithm

BACKGROUND

Reconstruction with free flaps has become a usual practice in maxillofacial surgery. Clinical monitoring is still the standard approach for postoperative follow-up, but can be difficult or impossible with intraorally situated or buried flaps. Microdialysis is a sampling technique that offers the possibility to monitor the metabolism of flaps continuously. It is a reliable method for early diagnosis of ischemia.

MATERIALS AND METHODS

48 microvascular free flaps applied following oral cancer resection were monitored with a microdialysis (MD) catheter, placed in the flap. Glucose, lactate, and lactate/pyruvate ratio were monitored using a bedside analyser for 5 days. 48 free flaps served as controls and were assessed (refill, flap temperature, and color) by clinical monitoring (CM).

RESULTS

12 flaps monitored by MD showed abnormal metabolism and underwent revision. Eight flaps were saved and four were lost within the first 5 days postoperatively. In addition, two flaps were lost at days 15 and 30 postoperatively, without previous complications. Four flaps assessed by CM developed complications, underwent revision, and were saved. In addition, five flaps were lost between the 8th and 23rd days postoperatively, without revision, due to missing previous clinical signs.

CONCLUSION

Postoperative monitoring of free flaps using a microdialysis decision algorithm allows early diagnosis of anastomotic complications. It is a clinically feasible and sensitive monitoring method for microvascular flaps, allowing surgical revision to be undertaken before clinical alteration takes place.

A method using the cephalic vein for superdrainage in breast reconstruction

BACKGROUND

In breast reconstruction, a superdrainage procedure using the superficial inferior epigastric vein has been described. The purpose of this study was to investigate whether the utility of cephalic vein (CV) was equivalent to that of serratus anterior muscle branch of the thoracodorsal vein (SA) and lateral thoracic vein (LTV) for recipient vein.

METHODS

Eighty-eight patients were enrolled in this study. The superdrainage was not performed if the internal mammary vein diameter was greater than, or equal to, that of the deep inferior epigastric vein diameter. In superdrainage cases, the SA or LTV was used as the recipient vein firstly, and the CV was used when both of them were unsuitable.

RESULTS

The superdrainage was performed in 45 (51.1%) patients. No significant differences were observed between with and without superdrainage. In superdrainage group, the CV was used in 7 (15.5%) patients. In two groups (CV vs. LTV and SA), because we added to perform superdrainage to the CV at the time of re-exploration and tried to use the SA or the LTV firstly, the re-exploration rate (28.6 vs. 0%) and operating time (652.1 vs. 591.1 min) of CV group were significantly high (p = .023 and .028). No complications were observed, due to CV harvesting. Other characteristics showed no significant differences.

CONCLUSIONS

At the point of superdrainage, the CV was equivalent to the SA and LTV. Using of the CV would only be essential in rare cases; nonetheless, the possibility of its use should be considered.

Relevance of lactate level detection in migrane and fibromyalgia

The aim of this study was to determine the blood lactate levels in healthy and pathological subjects, particularly with migraine and fibromyalgia. Moreover we investigated the possible correlation between lactate concentration, postural stability and balance disorders; the composition of the groups were: migraine (n = 25; age 49.7 ± 12.5), fibromyalgia (n = 10; age 43.7 ± 21.2), control group (n = 16 age 28.52 ± 2.4). The results showed that patients with fibromyalgia (FG) had higher lactate levels compared to migraine (MG) and control group (CG) (mean ± sd: FG = 1.78 ± 0.9 mmol/L; MG = 1.45±1 mmol/L; CG = 0,85 ± 0,07 mmol/L). The same situation was highlighted about the sway path length with eyes closed (FG = 518 ± 195 mm; MG = 465 ± 165 mm; CG = 405 ± 94,72 mm) and with eyes open (FG = 430 ± 220 mm; MG = 411 ± 143 mm; CG = 389 ± 107 mm). This can be explained by the fact that energy-intensive postural strategies must be used to optimize both static and dynamic coordination, in particular with repeated contractions of tonic oxidative muscle cells responsible for postural control.

A Simple Way to Measure Glucose and Lactate Values During Free Flap Head and Neck Reconstruction Surgery

PURPOSE

Evaluation of flap blood flow is necessary to detect flap blood flow abnormalities and perform salvage surgery. This study determined whether intra-flap blood glucose and lactate values measured with a simple instrument could detect impaired blood flow during head and neck reconstruction.

MATERIALS AND METHODS

We prospectively analyzed 82 cases of head and neck cancer reconstruction (62 men and 20 women; mean age, 64.0 years [range, 20 to 88 years]), of which 74 had impeded blood flow. Glucose and lactate levels were regularly measured over a period of 48 hours, from the time of flap elevation, as predictor variables. Blood flow obstruction was the outcome variable. Other study variables included primary site, flap type, gender, age at operation, height, weight, body mass index, presence or absence of diabetes, ischemia time, and operative time. Logistic analysis, using glucose and lactate values at the time of blood flow failure, was performed. Cutoff values were calculated using a receiver operating characteristic analysis.

RESULTS

The breakdown of the flaps was as follows: 20 free jejunum, 19 anterolateral thigh, 12 fibular, 11 radial forearm, 8 rectus abdominis myocutaneous, and 4 other flaps. Congestion was observed in 8 of the 82 flaps, including 3 anterolateral thigh flaps, 3 radial forearm flaps, 1 free jejunum flap, and 1 rectus abdominis myocutaneous flap. The intra-flap blood glucose values in the normally progressing cases gradually decreased until 16 hours postoperatively and thereafter recovered to normal levels. Intra-flap blood lactate values increased until 8 hours postoperatively and subsequently decreased. The odds ratio during congestion was only significantly different for lactate (odds ratio, 2.55, P = .014), and the cutoff values for sensitivity and specificity were 4.2 mmol/L and 6.7 mmol/L, respectively.

CONCLUSIONS

Intra-flap blood glucose and lactate values may reflect the transition of the postoperative circulation of free flaps. During congestion, lactate values change more sensitively than blood glucose values.

Glucose level evaluation in monopedicled rectus abdominis myocutaneous flap after venous occlusion: experimental study in rats

OBJECTIVE

to validate an experimental model for the measurement of glycemic levels in surgical flaps with the use of common glucometers, and to analyze the diagnostic criteria for hypoperfusion of such flaps.

METHODS

we performed vertical myocutaneous rectus abdominis flaps with upper pedicles bilaterally in 20 male Wistar rats, divided into two groups: with and without venous occlusion of the pedicle. We measured glucose levels in the flaps and in the systemic circulation with standard glucometers. We tested the accuracy of alternative diagnostic criteria for the detection of hypoperfusion.

RESULTS

from 15 minutes of venous occlusion on, there was a significant reduction in glucose levels measured in the congested flap (p<0.001). Using a minimum difference of 20mg/dl in the glycemic levels between the flap and systemic blood, 30 minutes after occlusion, as a diagnostic criterion, the sensitivity was 100% (95% CI 83.99-100%) and specificity of 90% (95% CI 69.90-97.21%) for the diagnosis of flap congestion.

CONCLUSION

It is possible to measure glucose levels in vertical myocutaneous rectus abdominis flaps of Wistar rats, perfused or congested, using a common glucometer. The diagnostic criteria that compare the glucose levels in the flaps with the systemic ones were more accurate in the evaluation of tissue perfusion.

The emerging role of microdialysis in diabetic patients undergoing amputation for limb ischemia

Lower limb ischemia in diabetic patients is a result of macro- and microcirculation dysfunction. Diabetic patients undergoing limb amputation carry high mortality and morbidity rates, and decision making concerning the level of amputation is critical. Aim of this study is to evaluate a novel microdialysis technique to monitor tissue microcirculation preoperatively and predict the success of limb amputation in such patients. Overall, 165 patients with type 2 diabetes mellitus undergoing lower limb amputation were enrolled. A microdialysis catheter was placed preoperatively at the level of the intended flap for the stump reconstruction, and the levels of glucose, glycerol, lactate and pyruvate were measured for 24 consecutive hours. Patients were then amputated and monitored for 30 days regarding the outcome of amputation. Failure of amputation was defined as delayed healing or stump ischemia. Patients were divided into two groups based on the success of amputation. There was no difference between the two groups regarding gender, ASA score, body mass index, comorbidities, diagnostic modality used, level of amputation, as well as glucose, glycerol, and pyruvate levels. However, local concentrations of lactate were significantly different between the two groups and lactate/pyruvate (L/P) ratio was independently associated with failed amputation (threshold defined at 25.35). Elevated preoperative tissue L/P ratio is independently associated with worse outcomes in diabetic patients undergoing limb amputation. Therefore, preoperative tissue L/P ratio could be used as a predicting tool for limb amputation's outcome, although more clinical data are needed to provide safer conclusions.

Resistance to systemic inflammation and multi organ damage after global ischemia/reperfusion in the arctic ground squirrel

INTRODUCTION

Cardiac arrest (CA) and hemorrhagic shock (HS) are two clinically relevant situations where the body undergoes global ischemia as blood pressure drops below the threshold necessary for adequate organ perfusion. Resistance to ischemia/reperfusion (I/R) injury is a characteristic of hibernating mammals. The present study sought to determine if arctic ground squirrels (AGS) are protected from systemic inflammation and multi organ damage after CA- or HS-induced global I/R and if, for HS, this protection is dependent upon their hibernation season.

METHODS

For CA, rats and summer euthermic AGS (AGS-EU) were asphyxiated for 8 min, inducing CA. For HS, rats, AGS-EU, and winter interbout arousal AGS (AGS-IBA) were subject to HS by withdrawing blood to a mean arterial pressure of 35 mmHg and maintaining that pressure for 20 min before reperfusion with Ringers. For both I/R models, body temperature (Tb) was kept at 36.5-37.5°C. After reperfusion, animals were monitored for seven days (CA) or 3 hrs (HS) then tissues and blood were collected for histopathology, clinical chemistries, and cytokine level analysis (HS only). For the HS studies, additional groups of rats and AGS were monitored for three days after HS to access survival and physiological impairment.

RESULTS

Rats had increased serum markers of liver damage one hour after CA while AGS did not. For HS, AGS survived 72 hours after I/R whereas rats did not survive overnight. Additionally, only rats displayed an inflammatory response after HS. AGS maintained a positive base excess, whereas the base excess in rats was negative during and after hemorrhage.

CONCLUSIONS

Regardless of season, AGS are resistant to organ damage, systemic inflammation, and multi organ damage after systemic I/R and this resistance is not dependent on their ability to become decrease Tb during insult but may stem from an altered acid/base and metabolic response during I/R.

The effect of hemodynamic remodeling on the survival of arterialized venous flaps

Objective

To evaluate the effect of hemodynamic remodeling on the survival status of the arterialized venous flaps (AVFs) and investigate the mechanism of this procedure.

Materials and Methods

Two 7 x 9 cm skin flaps in each rabbit (n=36) were designed symmetrically in the abdomen. The thoracoepigastric pedicle and one femoral artery were used as vascular sources. Four groups were included: Composite skin grafts group and arterial perfusion group were designed in one rabbit; AVF group and hemodynamic remodeling group by ligation of the thoracoepigastric vein in the middle were outlined in another rabbit. Flap viability, status of vascular perfusion and microvasculature, levels of epidermal metabolite and water content in each group were assessed.

Results

Highly congested veins and simple trunk veins were found using angiography in the AVF group; while a fairly uniform staining and plenty of small vessels were observed in the hemodynamic remodeling group. The metabolite levels of the remodeling group are comparable with those in the arterial perfusion group. There was no statistically significant difference in the percentage of flap survival between the arterial perfusion group and hemodynamic remodeling group; however, significant difference was seen between the AVF group and the hemodynamic remodeling group.

Conclusions

Under the integrated perfusion mode, the AVFs are in an over-perfusion and non-physiological hemodynamic state, resulting in unreliability and unpredictability in flap survival; under the separated perfusion mode produced by remodeling, a physiological-like circulation will be created and therefore, better flap survival can be expected.

Implications for burn shock resuscitation of a new in vivo human vascular microdosing technique (microdialysis) for dermal administration of noradrenaline

INTRODUCTION

Skin has a large dynamic capacity for alterations in blood flow, and is therefore often used for recruitment of blood during states of hypoperfusion such as during burn shock resuscitation. However, little is known about the blood flow and metabolic consequences seen in the dermis secondary to the use vasoactive drugs (i.e. noradrenaline) for circulatory support. The aims of this study were therefore: to develop an in vivo, human microdosing model based on dermal microdialysis; and in this model to investigate effects on blood flow and metabolism by local application of noradrenaline and nitroglycerin by the microdialysis system simulating drug induced circulatory support.

METHOD

Nine healthy volunteers had microdialysis catheters placed intradermally in the volar surface of the lower arm. The catheters were perfused with noradrenaline 3 or 30 mmol/L and after an equilibrium period all catheters were perfused with nitroglycerine (2.2 mmol/L). Dermal blood flow was measured by the urea clearance technique and by laser Doppler imaging. Simultaneously changes in dermal glucose, lactate, and pyruvate concentrations were recorded.

RESULTS

Noradrenaline and nitroglycerine delivered to the dermis by the microdialysis probes induced large time- and dose-dependent changes in all variables. We particularly noted that tissue glucose concentrations responded rapidly to hypoperfusion but remained higher than zero. Furthermore, vasoconstriction remained after the noradrenaline administration implicating vasospasm and an attenuated dermal autoregulatory capacity. The changes in glucose and lactate by vasoconstriction (noradrenaline) remained until vasodilatation was actively induced by nitroglycerine.

CONCLUSION

These findings, i.e., compromised dermal blood flow and metabolism are particularly interesting from the burn shock resuscitation perspective where noradrenaline is commonly used for circulatory support. The importance and clinical value of the results obtained in this in vivo dermal model in healthy volunteers needs to be further explored in burn-injured patients.

Microdialysis: characterisation of haematomas in myocutaneous flaps by use of biochemical agents

Metabolic markers are measured by microdialysis to detect postoperative ischaemia after reconstructive surgery with myocutaneous flaps. If a haematoma develops around the microdialysis catheter, it can result in misinterpretation of the measurements. The aim of the present study was to investigate whether a haematoma in a flap can be identified and dissociated from ischaemia, or a well-perfused flap, by a characteristic chemical profile. In 7 pigs, the pedicled rectus abdominal muscle flap was mobilised on both sides. A haematoma was made in each flap and two microdialysis catheters were placed, one in the haematoma, and the other in normal tissue. One flap was made ischaemic by ligation of the pedicle. For 6 hours, the metabolism was monitored by measurement every half-an-hour of the concentrations of glucose, lactate, pyruvate, and glycerol from all 4 catheters. After 3 hours of monitoring, intravenous glucose was given as a challenge test to identify ischaemia. The non-ischaemic flap could be differentiated from the ischaemic flap by low glucose, and high lactate, concentrations. It was possible to identify a catheter surrounded by a haematoma in ischaemic as well as non-ischaemic muscle from a low or decreasing concentration of glucose together with a low concentration of lactate. All four sites could be completely dissociated when the concentrations of glucose and lactate were evaluated and combined with the lactate:glucose ratio and a flow chart. The challenge test was useful for differentiating between haematomas in ischaemic and non-ischaemic tissue.

Blood glucose measurement for flap monitoring to salvage flaps from venous thrombosis

Early detection and rapid re-exploration are important for flap salvage, and for this, a reliable monitoring method is required. The purpose of the current study was to evaluate blood glucose measurement (BGM) for flap monitoring and to establish a simple method that can be used widely to decrease the flap loss rate after tissue transplantation. We noted the BGM in 33 free or pedicled tissue transfers (57 BGM points) over time postoperatively. Skin punctures and blood glucose measurements were made using a Medisafe-finetouch needle and Medisafe-Mini (Terumo, Japan), which are commonly used by diabetic patients. Partial necrosis of the vascular territory was found at 5 points (9%), and blood flow disorder due to a venous thrombus was found at 5 points (9%). The mean blood glucose level in the congestive flaps was significantly lower than that in healthy flaps. ROC curve analysis was used to determine a cutoff value for BGM of 62 mg/dL, at which the sensitivity and specificity were 88% and 82%, respectively (p < 0.0001). In conclusion, BGM is an easy and accessible adjunct to flap monitoring, and the combination of BGM and previously established methods is likely to reduce postoperative complications caused by the development of a venous thrombus after free tissue transplantation.

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.

Metabolism during anaesthesia and recovery in colic and healthy horses: a microdialysis study

BACKGROUND

Muscle metabolism in horses has been studied mainly by analysis of substances in blood or plasma and muscle biopsy specimens. By using microdialysis, real-time monitoring of the metabolic events in local tissue with a minimum of trauma is possible. There is limited information about muscle metabolism in the early recovery period after anaesthesia in horses and especially in the colic horse. The aims were to evaluate the microdialysis technique as a complement to plasma analysis and to study the concentration changes in lactate, pyruvate, glucose, glycerol, and urea during anaesthesia and in the recovery period in colic horses undergoing abdominal surgery and in healthy horses not subjected to surgery.

METHODS

Ten healthy university-owned horses given anaesthesia alone and ten client-owned colic horses subjected to emergency abdominal surgery were anaesthetised for a mean (range) of 230 min (193-273) and 208 min (145-300) respectively. Venous blood samples were taken before anaesthesia. Venous blood sampling and microdialysis in the gluteal muscle were performed during anaesthesia and until 24 h after anaesthesia. Temporal changes and differences between groups were analysed with an ANOVA for repeated measures followed by Tukey Post Hoc test or Planned Comparisons.

RESULTS

Lactate, glucose and urea, in both dialysate and plasma, were higher in the colic horses than in the healthy horses for several hours after recovery to standing. In the colic horses, lactate, glucose, and urea in dialysate, and lactate in plasma increased during the attempts to stand. The lactate-to-pyruvate ratio was initially high in sampled colic horses but decreased over time. In the colic horses, dialysate glycerol concentrations varied considerably whereas in the healthy horses, dialysate glycerol was elevated during anaesthesia but decreased after standing. In both groups, lactate concentration was higher in dialysate than in plasma. The correspondence between dialysate and plasma concentrations of glucose, urea and glycerol varied.

CONCLUSION

Microdialysis proved to be suitable in the clinical setting for monitoring of the metabolic events during anaesthesia and recovery. It was possible with this technique to show greater muscle metabolic alterations in the colic horses compared to the healthy horses in response to regaining the standing position.

Deep sedation with dexmedetomidine in a porcine model does not compromise the viability of free microvascular flap as depicted by microdialysis and tissue oxygen tension

BACKGROUND

Deep sedation is often necessary after major reconstructive plastic surgery in the face and neck regions to prevent sudden spontaneous movements capable of inflicting mechanical injury to the transplanted musculocutaneous flap(s). An adequate positioning may help to optimize oxygenation and perfusion of the transplanted tissues. We hypothesized that dexmedetomidine, a central alpha2-agonist and otherwise potentially ideal postoperative sedative drug, may induce vasoconstriction in denervated flaps, and thus increase the risk of tissue deterioration.

METHODS

Two symmetrical myocutaneous flaps were raised on each side of the upper abdomen in 12 anesthetized pigs. The sympathetic nerve fibers were stripped from the arteries in one of the flaps (denervated flap), while nerve fibers were kept untouched in the other (innervated flap). After simulation of ischemia and reperfusion periods, the animals were randomized to deep postoperative sedation with either propofol (n = 6) or dexmedetomidine (n = 6). Flap tissue metabolism was monitored by microdialysis and tissue-oxygen partial pressure. Glucose, lactate, and pyruvate concentrations were analyzed from the dialysate every 30 min for 4 h.

RESULTS

Mean arterial blood pressure was higher in the dexmedetomidine group (P = 0.036). Flap tissue metabolism remained stable throughout the experiment as measured by lactate-pyruvate and lactate-glucose ratios (median ranges 14.3-24.5 for lactate-pyruvate and 0.3-0.6 for lactate-glucose) and by tissue-oxygen partial pressure, and no differences were found between groups.

CONCLUSIONS

Our data suggest that dexmedetomidine, even if used for deep sedation, does not have deleterious effects on local perfusion or tissue metabolism in denervated musculocutaneous flaps.

Microdialysis shows metabolic effects in skin during fluid resuscitation in burn-injured patients

INTRODUCTION

Established fluid treatment formulas for burn injuries have been challenged as studies have shown the presence of tissue hypoxia during standard resuscitation. Such findings suggest monitoring at the tissue level. This study was performed in patients with major burn injuries to evaluate the microdialysis technique for the continuous assessment of skin metabolic changes during fluid resuscitation and up to four days postburn.

METHODS

We conducted an experimental study in patients with a burn injury, as represented by percentage of total body surface area burned (TBSA), of more than 25% in a university eight-bed burns intensive care unit serving about 3.5 million inhabitants. Six patients with a median TBSA percentage of 59% (range 33.5% to 90%) and nine healthy controls were examined by intracutaneous MD, in which recordings of glucose, pyruvate, lactate, glycerol, and urea were performed.

RESULTS

Blood glucose concentration peaked on day two at 9.8 mmol/l (6.8 to 14.0) (median and range) and gradually declined on days three and four, whereas skin glucose in MD continued to increase throughout the study period with maximum values on day four, 8.7 mmol/l (4.9 to 11.0). Controls had significantly lower skin glucose values compared with burn patients, 3.1 mmol/l (1.5 to 4.6) (p < 0.001). Lactate from burn patients was significantly higher than controls in both injured and uninjured skin (MD), 4.6 mmol/l (1.3 to 8.9) and 3.8 mmol/l (1.6 to 7.5), respectively (p < 0.01). The skin lactate/pyruvate ratio (MD) was significantly increased in burn patients on all days (p < 0.001). Skin glycerol (MD) was significantly increased at days three and four in burn patients compared with controls (p < 0.01).

CONCLUSION

Despite a strategy that fulfilled conventional goals for resuscitation, there were increased lactate/pyruvate ratios, indicative of local acidosis. A corresponding finding was not recorded systemically. We conclude that MD is a promising tool for depicting local metabolic processes that are not fully appreciated when examined systemically. Because the local response in glucose, lactate, and pyruvate metabolism seems to differ from that recorded systemically, this technique may offer a new method of monitoring organs.

Decreasing gut wall glucose as an early marker of impaired intestinal perfusion

OBJECTIVE

The aim of this study was to assess the microcirculatory and metabolic consequences of reduced mesenteric blood flow.

DESIGN

Prospective, controlled animal study.

SETTING

The surgical research unit of a university hospital.

SUBJECTS

A total of 13 anesthetized and mechanically ventilated pigs.

INTERVENTIONS

Pigs were subjected to stepwise mesenteric blood flow reduction (15% in each step, n = 8) or served as controls (n = 5). Superior mesenteric arterial blood flow was measured with ultrasonic transit time flowmetry, and mucosal and muscularis microcirculatory perfusion in the small bowel were each measured with three laser Doppler flow probes. Small-bowel intramucosal Pco2 was measured by tonometry, and glucose, lactate (L), and pyruvate (P) were measured by microdialysis.

MEASUREMENTS AND MAIN RESULTS

In control animals, superior mesenteric arterial blood flow, mucosal microcirculatory blood flow, intramucosal Pco2, and the lactate/pyruvate ratio remained unchanged. In both groups, mucosal blood flow was better preserved than muscularis blood flow. During stepwise mesenteric blood flow reduction, heterogeneous microcirculatory blood flow remained a prominent feature (coefficient of variation, approximately 45%). A 30% flow reduction from baseline was associated with a decrease in microdialysis glucose concentration from 2.37 (2.10-2.70) mmol/L to 0.57 (0.22-1.60) mmol/L (p < .05). After 75% flow reduction, the microdialysis lactate/pyruvate ratio increased from 8.6 (8.0-14.1) to 27.6 (15.5-37.4, p < .05), and arterial-intramucosal Pco2 gradients increased from 1.3 (0.4-3.5) kPa to 10.8 (8.0-16.0) kPa (p < .05).

CONCLUSIONS

Blood flow redistribution and heterogeneous microcirculatory perfusion can explain apparently maintained regional oxidative metabolism during mesenteric hypoperfusion, despite local signs of anaerobic metabolism. Early decreasing glucose concentrations suggest that substrate supply may become crucial before oxygen consumption decreases.

Microdialysis in Clinical Practice

Clinical examination is still the gold standard of postoperative free flap monitoring, but with intraorally situated and/or buried flaps, it can be difficult or impossible. Microdialysis is a sampling technique which offers the possibility to monitor the metabolism of a flap continuously. Ischemia can be detected by monitoring the changes in glucose, lactate, and pyruvate levels in interstitial fluid of the specific tissue. Our aim was to use microdialysis to monitor the metabolism of free flaps used for reconstructions inside the oral cavity/oropharynx and to evaluate the reliability and usefulness of this new monitoring method.Twenty-five consecutive patients who underwent oral cavity/oropharynx cancer resection and immediate reconstruction with free flap were included in the study. A microdialysis catheter was placed into the subcutaneous adipose tissue of the flap in the end of the surgical procedure. Dialysate samples were taken on an hourly basis for 72 hours postoperatively. Routine clinical monitoring was carried out by experienced nursing staff. Clinical findings were recorded and later compared with microdialysis values. Two flaps out of 25 failed in spite of reoperations. In both problem cases, microdialysis indicated ischemia 1 to 2 hours before it became clinically evident. During flap ischemia, the lactate/pyruvate ratio increased, glucose concentrations reduced, whereas lactate level increased when compared with normal values. Our results indicate that microdialysis is safe for the patient and the flap. It can reliably detect flap ischemia at an early stage. This is especially useful in buried flaps when clinical monitoring is difficult. Microdialysis may also reduce the patient discomfort caused by repeated clinical examination of the flap.