Investigation of Different Methods of Intraoperative Graft Perfusion Assessment during Kidney Transplantation for the Prediction of Delayed Graft Function: A Prospective Pilot Trial

Delayed graft function (DGF) after renal transplantation is a relevant clinical problem affecting long-term organ function. The early detection of patients at risk is crucial for postoperative monitoring and treatment algorithms. In this prospective cohort study, allograft perfusion was evaluated intraoperatively in 26 kidney recipients by visual and formal perfusion assessment, duplex sonography, and quantitative microperfusion assessment using O2C spectrometry and ICG fluorescence angiography. The O2C tissue spectrometry device provides a quantitative method of microperfusion assessment that can be employed during kidney transplantation as an easy-to-use and highly sensitive alternative to ICG fluorescence angiography. Intraoperative microvascular flow and velocity in the allograft cortex after reperfusion predicted DGF with a sensitivity of 100% and a specificity of 82%. Threshold values of 57 A.U. for microvascular flow and 13 A.U. for microvascular velocity were identified by an ROC analysis. This study, therefore, confirmed that impairment of microperfusion of the allograft cortex directly after reperfusion was a key indicator for the occurrence of DGF after kidney transplantation. Our results support the combined use of intraoperative duplex sonography, for macrovascular quality control, and quantitative microperfusion assessment, such as O2C spectrometry, for individual risk stratification to guide subsequent postoperative management.

Improvement of Superficial and Deep Cutaneous Microcirculation Due to Axillary Plexus Anesthesia Impaired by Smoking

Background: Understanding microvascular physiology is key to any reconstructive procedure. Current concepts in anesthesia increasingly involve regional peripheral nerve blockade during microvascular reconstructive procedures. Whereas favorable effects on perfusion due to these techniques have been reported earlier, little evidence focusing on its effects in most peripheral vascular compartments is available. Methods: A total of 30 patients who were to receive axillary plexus blockade (APB) were included. Microcirculatory assessment of the dependent extremity was conducted utilizing combined laser-Doppler flowmetry and white light spectroscopy. Two probes (1–2 and 7–8 mm penetration depth) were used to assess changes in microcirculation. Results: APB resulted in significant changes to both superficial and deep cutaneous microcirculation. Changes in blood flow were most prominent in superficial layers with a maximum increase of +617% compared to baseline values. Significantly lower values of +292% were observed in deep measurements. Consecutively, a significant enhancement in tissue oxygen saturation was observed. Further analysis revealed a significant impairment of perfusion characteristics due to reported nicotine consumption (max Bf: +936% vs. +176%). Conclusion: Cutaneous microcirculation is strongly affected by APB, with significant differences regarding microvascular anatomy and vascular physiology. Smoking significantly diminishes the elicited improvements in perfusion. Our findings could influence reconstructive strategies as well as dependent perioperative anesthetic management.

Tissue optical perfusion pressure: a simplified, more reliable, and faster assessment of pedal microcirculation in peripheral artery disease

Oscillometry is an alternative to continuous-wave Doppler (cw-Doppler) to determine peripheral artery disease (PAD) severity using the ankle-brachial index (ABI). cw-Doppler ABI differentiates systolic pressure of ATP and ADP where either one of both values in most patients is higher (high) and the other value is lower (low). In contrast, oscillometric ABI measures the strongest signal and hence misses the lower value. Both do not take pedal perfusion into consideration. Simultaneous determination of tissue microperfusion cares for pedal PAD. ABI was determined by cw-Doppler and oscillometry. Tissue optical perfusion pressure (TOPP) was taken from the first toe using photoplethysmography. 323 patients were evaluated retrospectively in 3 independent groups. group 1 (99 patients) compared TOPP and oscillometric ABI with systolic cw-Doppler-pressure and cw-Doppler ABI. In group 2 (103 patients) TOPP was compared with toe pressure (TP). In group 3 (121 symptomatic patients) TOPP and ABI at rest and after stress were compared (ultrasound examination and magnetic resonance angiography (MRA) or computer tomography angiography (CTA) as control). Bland-Altman-plot analysis presented no significant difference between oscillometric ABI and the high cw-Doppler ABI (group 1). TOPP showed a difference of 26mmHg to the low cw-Doppler-pressure and none to the high cw-Doppler-pressure. In group 2 TOPP correlates to TP but presented a difference of 37 mmHg. group 3 showed weak or no correlation between ABI and walking distance. Oscillometric ABI correlates significantly to TOPP. To conclude, data after stress present a better correlation than at rest. We conclude that TOPP provides absolute values of pedal macro-/microcirculation at rest and after stress tests.NEW & NOTEWORTHY This new application of photoplethysmography investigated the microcirculation in peripheral artery disease at the level of the toe pad and determined the tissue optical perfusion pressure as the first pulsatile signal during automatic cuff deflation at the ankle. It is the first time that this method has been integrated for simultaneous routine examination in an automatic oscillometric ankle-brachial index (ABI) system. This quick and simple measurement technique provides clinical information on the microcirculation downstream the routine ABI measurement at rest and in particular after stress test.

Invasive Assessment of the Myocardial Microcirculation during Beating Heart Coronary Artery Bypass Grafting

Coronary artery bypass grafting may be associated with several cardiac complications, including ischemia, acute myocardial infarction, arrhythmias, or hemodynamic instability. Accumulating evidence suggests that well-developed coronary collateral circulation may protect against adverse effects, including myocardial ischemia. Assessment of myocardial microvascular perfusion is, therefore, of great clinical interest in beating heart surgery. In this paper, myocardial microvascular perfusion is continuously assessed on the beating heart using laser Doppler flowmetry in consecutive patients who underwent coronary artery bypass grafting procedures. No significant (p = 0.110) differences were found between the averaged perfusion signal (n = 42) at the baseline, during artery occlusion, or after reperfusion (732.4 ± 148.0 vs. 711.4 ± 144.1 vs. 737.0 ± 141.2, respectively). In contrast, significantly different (p < 0.001) mean perfusion signals (n = 12) were found (805.4 ± 200.1 vs. 577.2 ± 212.8 vs. 649.3 ± 220.8) in a subset of patients who presented with hemodynamic instability and myocardial ischemia. Additionally, a strong positive correlation between the plasma levels of high-sensitivity troponin I and perfusion decrease level after artery occlusion was found (r = 0.854, p < 0.001). This study argues that myocardial microvascular perfusion remains constant during coronary artery bypass grafting on the beating heart in advanced coronary artery disease. This phenomenon is most likely due to an extensive coronary collateral circulation.

Autofluorescence spectroscopy for NADH and flavoproteins redox state monitoring in the isolated rat heart subjected to ischemia-reperfusion

BACKGROUND

Reduction of myocardial ischemia-reperfusion injury in the patients undergoing cardiac surgery under cardiopulmonary bypass represents an important goal. Intraoperative monitoring of myocardial metabolic state using continuous registration of nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) fluorescence might contribute to the solution of the problem. The successful application of fluorescent spectroscopy in the clinical field requires additional refinement of the technique, particularly using excitation of both NADH and FAD with different wavelengths.

METHODS

The experiments were performed on the isolated Langendorff-perfused rat hearts (n=28) subjected to either regional or global ischemia-reperfusion. Two principles of NADH and FAD autofluorescence (AF) measurement were used for ischemia monitoring: (1) analysis of photographs and videos obtained with multispectral organoscopy technique allowing the assessment of both spatial and temporal characteristics of the process (n=16); (2) continuous registration of tissue redox state in a representative area of the heart by application of local spectroscopy, assisted by fiber optic spectrometer (n=12).

RESULTS

It was found that regional myocardial ischemia resulted in a rapid, substantial increase in the intensity of NADH AF excited at 360nm in the ischemic versus non-ischemic area of the heart. The same result was obtained when the heart was made globally ischemic, while the restoration of perfusate flow completely reversed the increase in NADH AF. During the transition from ischemia to reperfusion, the spatial heterogeneity of myocardial AF was noted on video recordings, probably reflecting the microheterogeneity of myocardial blood flow. Local spectroscopy studies demonstrated opposite changes in the NADH and FAD AF during ischemia. Using both methodological approaches, we found that repetitive brief episodes of global myocardial ischemia resulted in progressive decrease in the magnitude of AF elevation, which might point to preconditioning effect.

CONCLUSIONS

The application of multispectral fluorescent organoscopy offers the advantage of monitoring myocardial redox state at the level of the entire heart. Local spectroscopy is characterized by better precision and, in addition, provides the unique opportunity to measure AF in different parts of the spectrum. AF measurements are non-invasive, rapid, and technically easy to perform. For future clinical applications, it might be recommended to combine the measurement of redox state of both NADH and FAD, using excitation wavelength and emission filter optimal for each fluorophore.