Continuous measurement of porcine renal cortex microcirculation with enhanced thermal diffusion technology

Identification of risk factors for vascular thrombosis may reduce early renal graft loss: a review of recent literature

Renal graft survival has improved over the past years, mainly owing to better immunosuppression. Vascular thrombosis, though rare, therefore accounts for up to one third of early graft loss. We assess current literature on transplantation, identify thrombosis risk factors, and discuss means of avoiding thrombotic events and saving thrombosed grafts. The incidence of arterial thrombosis was reported to 0.2–7.5% and venous thrombosis 0.1–8.2%, with the highest incidence among children and infants, and the lowest in living donor reports. The most significant risk factors for developing thrombosis were donor-age below 6 or above 60 years, or recipient-age below 5-6 years, per- or postoperative hemodynamic instability, peritoneal dialysis, diabetic nephropathy, a history of thrombosis, deceased donor, or >24 hours cold ischemia. Multiple arteries were not a risk factor, and a right kidney graft was most often reported not to be. Given the thrombosed kidney graft is diagnosed in time, salvage is possible by urgent reoperation and thrombectomy. Despite meticulous attentions to reduce thrombotic risk factors, thrombosis cannot be entirely prevented and means to an early detection of this complication is desirable in order to save the kidneys through prompt reoperation. Microdialysis may be a new tool for this.

Rapid 3-D imaging of contrast flow: application in a perfused kidney phantom

Previous studies indicate imaging of ultrasound contrast in 3-D is potentially superior to 2-D imaging for vascular characterization. A dual-beam, dynamic refill technique, which relies on volumetric contrast clearance and sequential imaging, was used to image a preserved porcine kidney perfused with contrast. A model was developed for the contrast profile across the renal artery to estimate fractional blood volume. This model was used along with refill curve information to measure absolute perfusion within renal cortex for a 100-cm(3) volume. Perfusion measurements from a slice within the volume were also made using a modified interval imaging technique. The measured perfusion using the dual-beam technique was consistent with the perfusion measured using the interval imaging technique (dual-beam values were 1.06 +/- 0.04 x corresponding interval imaging values). These experiments suggest that ultrasound contrast perfusion measurements are independent of the volume of contrast eliminated before refill.

Low-dose carbon monoxide inhalation prevents development of chronic allograft nephropathy

Chronic allograft nephropathy (CAN) is the primary cause for late kidney allograft loss. Carbon monoxide (CO), a product of heme metabolism by heme oxygenases, is known to impart protection against various stresses. We hypothesized that CO could minimize the chronic fibroinflammatory process and protect kidney allografts from CAN. Lewis kidney grafts were orthotopically transplanted into binephrectomized Brown-Norway rats under short-course tacrolimus. Recipients were maintained in room air or exposed to CO at 20 parts/million for 30 days after transplant. Efficacy of inhaled CO was studied at day 30 and day 80. Isografts maintained normal kidney function throughout the experiment with creatinine clearance of approximately 1.5 ml/min. Renal allograft function in air controls progressively deteriorated, and creatinine clearance declined to 0.2 +/- 0.1 ml/min by day 80 with substantial proteinuria. CO-treated animals had significantly better creatinine clearance (1.3 +/- 0.2 ml/min) with minimal proteinuria. Histological examination revealed the development of progressive CAN in air-exposed grafts, whereas CO-treated grafts had minimal tubular atrophy and interstitial fibrosis, with negligible collagen IV deposition. In vitro analyses revealed that CO-treated recipients had significantly less T cell proliferation against donor peptides via the indirect allorecognition pathway and less anti-donor IgG antibodies compared with air controls. Intragraft mRNA levels for chemokines (regulated on activation normal T cell expressed and secreted, macrophage inflammatory protein-1alpha, chemokine receptors (CCR1, CXCR3, CXCR5), IL-2, and intercellular adhesion molecule-1 were significantly decreased in CO-treated than in air-treated allografts. Furthermore, reduction of blood flow in air-treated allografts was prevented with CO. In conclusion, inhaled CO at a low concentration efficiently abrogates chronic fibroinflammatory changes associated with CAN and improves long-term renal allograft function.

Effects of magnesium sulfate on supraceliac aortic unclamping in experimental dogs

Intravascular administration of magnesium (Mg) causes vasodilation and increases renal blood flow. The aim of this study was to investigate the renal effect of Mg following unclamping of the supraceliac aorta. Mongrels were divided into two groups, control (group C, n=7) and Mg group (group Mg, n=7). In group Mg, 30 mg/kg MgSO4 was injected as a bolus immediately prior to unclamping the supraceliac aorta and thereafter as an infusion (10 mg/kg/hr). The group C received an equivalent volume of saline solution. Systemic hemodynamics, renal artery blood flow, renal cortical blood flow (RCBF), renal vascular resistance, and renal function were compared. Following the aortic unclamping, cardiac output and RCBF were less attenuated, and the systemic and renal vascular resistance was elevated to a lesser degree in the group Mg compared to the group C. There was no significant difference in the plasma renin activity, serum creatinine and Cystatin-C between the two groups. The present study shows that Mg infusion improves systemic hemodynamics and RCBF after aortic unclamping. However, we did not observe any improvement in renal function when Mg was administered after supraceliac aortic unclamping.

The Effects of Pulsatile Flow Upon Renal Tissue Perfusion During Cardiopulmonary Bypass: A Comparative Study of Pulsatile and Nonpulsatile Flow

This study was conducted to directly compare the effects of pulsatile and nonpulsatile blood flow in the extracorporeal circulation upon renal tissue perfusion by using a tissue perfusion measurement system. A total cardiopulmonary bypass circuit was constructed to accommodate twelve Yorkshire swine, weighing 20 approximately 30 kg. Animals were randomly assigned to group 1 (n = 6, nonpulsatile centrifugal pump) or group 2 (n = 6, pulsatile T-PLS pump). A tissue perfusion measurement probe (Q-Flow 500) was inserted into the renal parenchymal tissue, and the extracorporeal circulation was maintained for an hour at a pump flow rate of 2 L/min after aortic cross-clamping. Tissue perfusion flow in the kidney was measured before bypass and every 10 minutes after bypass. Renal tissue perfusion flow was substantially higher in the pulsatile group throughout bypass (ranging 48.5-64.1 ml/min/100 g in group 1 vs. 51.0-88.1 ml/min/100 g in group 2). The intergroup difference was significant at 30 minutes (47.5 +/- 18.3 ml/min/100 g in group 1 vs. 83.4 +/- 28.5 ml/min/100 g in group 2; p = 0.026). Pulsatile flow achieves higher levels of tissue perfusion of the kidney during short-term extracorporeal circulation. A further study is required to observe the effects of pulsatile flow upon other vital organs and its long-term significance.

Different impact of normo- and hypotensive brain death on renal macro- and microperfusion--an experimental evaluation in a porcine model

BACKGROUND

Despite the growing use of kidneys from living donors, organs harvested from brain dead donors are the dominant graft types used in renal transplantation. It is accepted that brain death (BD) has a damaging effect on the renal allograft, with a lower graft survival. Amongst various causes, changes in renal microperfusion could be responsible. Renocortical microperfusion was assessed during BD using thermal diffusion in a porcine model.

METHODS

Two types of BD were induced in two groups of pigs [hypotension (Hypo-BD): n = 11; normotension (Normo-BD): n = 10] and compared to controls (n = 5) over a period of 210 min. We analysed systemic parameters [heart rate (HR), mean arterial blood pressure (MAP)], aortic blood flow (ABF) and renal perfusion [renal artery blood flow (RABF) and renocortical blood flow (RCBF)].

RESULTS

Following the two distinct forms of BD induction, a stable normo- or hypotension was observed. Haemodynamic parameters were only slightly changed (control group: MAP, 62+/-2 mmHg; HR, 95+/-3/min; Normo-BD: MAP, 56+/-4 mmHg; HR, 104+/-8/min; Hypo-BD: MAP, 43+/-3 mmHg; HR, 112+/-7/min). Solely dependent on systemic haemodynamics, RABF and RCBF decreased in the Hypo-BD (RABF: 142+/-19 to 94+/-9 ml/100 g/min; RCBF: 80+/-4 to 52+/-2 ml/100 g/min), while in Normo-BD group RABF mildly changed (158+/-13 ml/100 g/min) and RCBF decreased slightly from 76+/-3 to 70+/-6 ml/100 g/min. As opposed to the Normo-BD group, animals with Hypo-BD showed a significant decrease in RABF (reduction of 34%) and RCBF (reduction of 35%) with a sharp drop of MAP (reduction of 25%), however ABF remained relatively constant.

CONCLUSIONS

In this model, a reduction of renocortical microperfusion in brain dead pigs was only found during haemodynamic instability (hypotension) and could not be attributed to BD as such. Our findings would support intensive cardiocirculatory stabilization for potential BD donors in order to minimize kidney preservation damage.

Assessment of renal graft function by perioperative monitoring of cortical microcirculation in kidney transplantation

BACKGROUND

We evaluated the significance of perioperative cortical microperfusion for graft function and long-term prognosis after renal allotransplantation. Thermodiffusion technology was clinically applied for the first time, after previous validation for perfusion monitoring of the renal cortex in pigs.

METHODS

A thermodiffusion probe was inserted into the renal cortex in 30 transplant recipients after graft reperfusion. Real-time measurements were recorded until the end of the operation. In 14 patients perfusion was measured daily until postoperative day 7. Microcirculation was correlated to serum creatinine level, scintigraphic findings, and long-term outcome.

RESULTS

In primary graft function, intraoperative perfusion was 85+/-7 mL/100 g per min compared with significantly lower values in cases with subsequent graft dysfunction. The best discrimination was defined for a level of 70 mL/100 g per min with a positive predictive value of 88% for detection of good graft function and 86% for nonfunction. Intraoperative perfusion was significantly different in patients with normal grafts, delayed function, and graft loss. Postoperatively, lower perfusion was found in acute tubular necrosis; a significant correlation could be noted between microcirculation and perfusion index measured by nuclear scanning (r=0.78, P<0.01). Living-related grafts were characterized by higher intraoperative perfusion and superior graft quality.

CONCLUSION

Thermodiffusion could be clinically applicable for the perioperative monitoring of renal graft perfusion. Intraoperative reduction of cortical microcirculation has a high predictive value with respect to detection of delayed renal function. Postoperatively, impaired renal microperfusion is associated with acute tubular necrosis. Living-related donor grafts show less microcirculatory alteration than cadaveric kidneys.

Characterization of hepatic parenchymous perfusion heterogeneity and regional flow kinetics after porcine liver transplantation

BACKGROUND

In clinical practice, a heterogeneous hepatic tissue microperfusion (MC) is often observed after liver resection or transplantation (LTx). Nevertheless this hepatic perfusion phenomenon has never been really quantified with respect to its anatomic distribution and time course in detail. The aim of the study was to characterize liver perfusion heterogeneity and local flow kinetics both in the physiological situation and after standardized ischemia and reperfusion using an established model of porcine LTx.

METHODS

Regional distribution of hepatic MC in healthy native porcine livers (control group; n = 8) was analyzed in comparison with data derived 60 min, 24 h, and 72 h after porcine LTx (transplantation group; n = 8 each subgroup; cold ischemia time: 5.7 +/- 1.2 h). MC was measured with implanted thermal diffusion electrodes (TD). Flow in hepatic artery and portal vein was continuously detected by ultrasonic probes. For standardization of measurement localizations, porcine liver lobes were divided anatomically into three horizontal layers (cranial, medial, caudal), defining 12 distinct hepatic measurement regions.

RESULTS

In the control group, a homogenous liver MC with a mean flow of 81.6 +/- 13.9 ml/100 g/min was detected in all regions. After LTx, a marked MC heterogeneity was noted 60 min after reperfusion. MC rehomogenization was first documented within horizontal liver planes 24 h later. Comparison of MC between planes showed persisting heterogeneity with a significant intralober drop of mean MC in the cranio-caudal direction. Complete MC rehomogenization (both between horizontal and vertical liver planes) was detected 72 h after reperfusion. Still, an overall reduction of mean liver perfusion by about 15% was existent.

CONCLUSIONS

A homogenous tissue perfusion was observed in healthy porcine livers. In contrast, marked heterogeneity of hepatic MC was detected after LTx. Heterogeneity presents as a very dynamic and temporary phenomenon. Early horizontal flow rehomogenization and reconstitution of normal blood flow, particularly primarily in the cranial liver layers, appear to be characteristic features during early flow reconstitution after postischemic reperfusion. Due to heterogeneity and time-dependent flow dynamics, measurement of MC volumes at single hepatic regions may not always allow a valid characterization of liver perfusion quality during the first 24 h after postischemic reperfusion.

Experimental monitoring of hepatic glucose, lactate, and glutamate metabolism by microdialysis during surgical preparation of the liver hilus

Mechanical liver manipulation can lead to hepatic microcirculation (MC) impairment. The pathobiochemical relevance of this phenomenon is not fully understood. Microdialysis (MD) allows a quantification of metabolic products in interstitial fluid, thus enabling analysis of the hepatic metabolic state during changes of liver perfusion. The aim of the study was to quantify the functional effects of standardized surgical liver preparation both on liver metabolism and microperfusion. Two groups of animals (pigs, n = 25) were formed: In the trial group (TG; n = 13) the liver was mobilized, followed by hilar preparation. In the control group (CG; n = 12) mobilization of the liver without hilar dissection was performed. Surgical manipulation was followed by an observation in both groups. Hepatic interstitial glucose, lactate, and glutamate concentrations were detected by MD and liver MC by thermodiffusion. During liver mobilization MC decreased significantly in both groups (TG; 86.7 +/- 2.0 to 73.4 +/- 2.3 ml/100 g min; and CG; 88.3 +/- 3.1 to 71.9 +/- 2.2 ml/100 g/min). In the trial group levels decreased further during hilar preparation reaching minimal values of 65.6 +/- 2.8. After preparation MC recovered to baseline. Glucose, lactate, and glutamate concentrations increased significantly during liver mobilization in the trial (glucose; 0.52 +/- 0.13 to 0.88 +/- 0.19 mmol/L; lactate; 0.34 +/- 0.07 to 0.54 +/- 0.07 mmol/L; glutamate; 34.5 +/- 3.6 to 52.6 +/- 8.0 micromol/L) and control group (glucose; 0.58 +/- 0.06 to 0.95 +/- 0.13 mmol/L; lactate; 0.30 +/- 0.06 to 0.49 +/- 0.07 mmol/L; glutamate; 32.9 +/- 2.36 to 56.1 +/- 5.12 micromol/L). Throughout hilus preparation maximum values could be measured in TG (glucose; 1.69 +/- 0.34; lactate; 0.90 +/- 0.18; glutamate; 63.5 +/- 7.2). After termination of mobilization or preparation baseline concentrations were reached again. MD allows monitoring of metabolic changes in hepatic parenchyma. Surgical liver preparation leads to changes of intrahepatic glucose, lactate, and glutamate levels (without alterations of parameters in systemic plasma) along with hepatic MC impairment. Reconstitution of hepatic MC was accompanied by rapid normalization of metabolic parameters. By measuring specific parameters, MD could prove to be of use for functional assessment of metabolic effects due to MC disturbances.

Characterization of renal parenchymal perfusion during experimental infrarenal aortic clamping and declamping with enhanced thermodiffusion electrodes

Despite multiple previous experimental and clinical investigations, it has not been fully clarified until now whether infrarenal aortic cross-clamping (IRAC) induces a significant disturbance of renal parenchymal perfusion. Most renal cortical flow data collected thus far have been heterogenous because of inherent limitations of available measurement technology. The enhanced thermal diffusion (TD) electrode is a newly developed and previously validated prototype device that allows continuous quantification of parenchymal kidney perfusion after local probe implantation. We monitored renal perfusion during experimental IRAC with TD for the first time, thereby also evaluating the potential applicability of the method in clinical aortic surgery. IRAC (20 min) followed by sudden declamping was performed in pigs under general anesthesia (n = 14). Renal cortical blood flow (RCBF) was continuously quantified by TD, total aortic flow (TABF) and renal artery flow (RABF) were measured by ultrasonic flow probes, and parameters of systemic circulation were determined by Swan-Ganz catheter. Our results showed that kidney perfusion can be continuously quantified using TD electrodes during experimental aortic surgery in a porcine model. IRAC does not lead to a significant impairment of RCBF in young pigs as measured by TD. Renal perfusion appears to be predominantly pressure driven. Consequently, abrubt aortic declamping can bring about prolonged renal ischemia. Transfer of the TD method to RCBF monitoring during clinical aortic surgery appears to be feasible and should be investigated in selected cases.