Background Microdialysis is a clinical method used to detect ischemia after microvascular surgery. Microdialysis is easy to use and reliable, but its value in most clinical settings is hampered by a 1- to 2-h delay in the delivery of patient data. This study evaluated the effectiveness of an increase in the microdialysis perfusion rate from 0.3 to 1.0 µL/min on the diagnostic delay in the detection of ischemia. Methods In eight pigs, two symmetric pure muscle transfers were dissected based on one vascular pedicle each. In each muscle, two microdialysis catheters were placed. The two microdialysis catheters were randomized to a perfusion rate of 0.3 or 1.0 µL/min, and the two muscle transfers were randomized to arterial or venous ischemia, respectively. After baseline monitoring, arterial and venous ischemia was introduced by the application of vessel clamps. Microdialysis sampling was performed throughout the experiment. The ischemic cutoff values were based on clinical experience set as follows: CGlucose < 0.2 mmol/L, CLactate > 7 mmol/L, and the lactate/pyruvate ratio > 50. Results The delay for the detection of 50% of arterial ischemia was reduced from 60 to 25 minutes, and for the detection of all cases of arterial ischemia, the delay was reduced from 75 to 40 minutes when the perfusion rate was increased from 0.3 to 1.0 µL/min. After the same increase in perfusion, the detection of 50% of venous ischemia was reduced from 75 to 40 minutes, and for all cases of venous ischemia, a reduction from 135 to 95 minutes was found. Conclusion When using microdialysis for the detection of ischemia in pure muscle transfers, an increase in the perfusion rate from 0.3 to 1.0 µL/min can reduce the detection delay of ischemia.

Background When mobilizing free flaps, postoperative monitoring of perfusion is crucial to detect ischemia. Continuous monitoring may be feasible by applying a combination of tissue spectrophotometry and laser Doppler flowmetry (oxygen-2-see [O2C]). Material and Methods On 10 pigs, two symmetrical myocutaneous flaps were mobilized on each side of the abdomen based on the deep inferior epigastric vessels. Flaps were randomized to clamp either the artery or the vein and measurements using O2C were performed before, during, and after the intervention yielding information on blood flow, saturation (sat), and relative tissue hemoglobin (rHgb) concentration. Results Baseline values were similar in all groups. Introduction of ischemia caused a rapid decline in arterial ischemic flaps which all reached threshold levels in 3 minutes, whereas that was only the case for three of six venous ischemic flaps. Venous clamping resulted in a decline in sat, while the response to arterial clamping was an initial decline followed by an increase in sat. In all arterial ischemic flaps, rHgb concentration either decreased or remained at baseline levels but increased in all venous ischemic flaps. The median time to a 30% rise was 1 minute at an 8-mm depth. The rate of decreasing flow along with the rHgb measurements made it possible to distinguish the arterial ischemia (AI) from the venous ischemia (VI) within the first few minutes. Conclusion In this animal experimental model, O2C measurements of blood flow reliably detected ischemia. By adding information about rHgb, it was possible to distinguish between AI and VI.

Introduction: Microdialysis is one of the methods used clinically for the detection of ischemia. Although microdialysis is reliable, in most clinical settings there is a delay of 1-2 hours before the information is available. Objective:The aim of this study was to evaluate whether an increase in the Microdialysis per fusion rate from 0.3 to 1.0 or 2.0 µl/min was capable of reducing the delay in the detection of a shift in molecular composition. Methods and material:Microdialysis was performed in a container with 3 catheters per fused with 0.3, 1.0 and 2.0 µl/min. The molecular composition in the container regarding glucose and lactate was initially as follows: C Glucose =6.0 mmol/L and C Lactate =2 mmol/L. At T=90 min the composition was changed to C Glucose =1 mmol/L and C Lactate =12 mmol/L. Dialysates were harvested from the three catheters and were analysed regarding the concentration of glucose and lactate. For calculation of the relative recovery, samples were harvested directly from the liquid. The relative recovery and the delay before new steady state were calculated for each of the 3 catheters. The experiment was performed 8 times.Results: A decrease in relative recovery was found with the higher perfusion rate. For glucose, the relative recovery was 100, 88, and 69% at perfusion rates of 0.3, 1.0 and 2.0 µl/min. For lactate, the corresponding values were 103, 93, and 77%. An increase in the lactate/glucose ratio was found with the higher perfusion rate. The delays in detection of shift in molecular concentration were found to be 60, 20, and 10 minutes for catheters 0.3, 1.0 and 2.0, respectively.Conclusion: Using microdialysis it is possible to significantly reduce the delay while still detecting a shift in the concentration of glucose and lactate when the perfusionrate is increased.

The aim of this randomized porcine study was to compare surface targeted temperature management (TTM) to endovascular TTM evaluated by cerebral diffusion-weighted magnetic resonance imaging (MRI): apparent diffusion coefficient (ADC), and by intracerebral/intramuscular microdialysis. It is well known that alteration in the temperature affects ADC, but the relationship between cerebral ADC values and the cooling method per se has not been established. Eighteen anesthetized 60-kg female swine were hemodynamically and intracerebrally monitored and subsequently subjected to a baseline MRI. The animals were then randomized into three groups: (1) surface cooling (n = 6) at 33.5°C using EMCOOLSpad, (2) endovascular cooling (n = 6) at 33.5°C using an Icy cooling catheter with the CoolGard 3000, or (3) control (n = 6) at 38.5°C using a Bair Hugger™. The swine were treated with TTM for 6 hours followed by a second MRI examination, including ADC. Blood and microdialysate were sampled regularly throughout the experiment, and glucose, lactate, pyruvate, glycerol, and the lactate/pyruvate ratio did not differ among groups, neither intracerebrally nor intramuscularly. Surface cooling yielded a significantly lower median ADC than endovascular cooling: 714 (634; 804) × 10 mm/s versus 866 (828; 927) × 10 mm/s, (p < 0.05). The surface cooling ADC was lowered to a range usually attributed to cytotoxic edema and these low values could not be explained solely by the temperature effect per se. To what extent the ADC is fully reversible at rewarming is unknown and the clinical implications should be further investigated in clinical studies.