Intermittent Surface Oxygenation Results in Similar Mitochondrial Protection and Maintenance of Aerobic Metabolism as Compared to Continuous Oxygenation during Hypothermic Machine Kidney Machine Perfusion

Short bubble and subsequent surface oxygenation is an innovative oxygenation technique and alternative for membrane oxygenation during hypothermic machine perfusion (HMP). The metabolic effect of the interruption of surface oxygenation for 4 h (mimicking organ transport) during HMP was compared to continuous surface and membrane oxygenation in a pig kidney ex situ preservation model. After 30 min of warm ischemia by vascular clamping, a kidney of a ±40 kg pig was procured and subsequently preserved according to one of the following groups: (1) 22-h HMP + intermittent surface oxygenation (n = 12); (2) 22-h HMP + continuous membrane oxygenation (n = 6); and (3) 22-h HMP + continuous surface oxygenation (n = 7). Brief perfusate O₂ uploading before kidney perfusion was either obtained by direct bubble (groups 1, 3) or by membrane (group 2) oxygenation. Bubble oxygenation during minimum 15 min was as efficient as membrane oxygenation in achieving supraphysiological perfusate pO₂ levels before kidney perfusion. Metabolic tissue analysis (i.e., lactate, succinate, ATP, NADH, and FMN) during and at the end of the preservation period demonstrated similar mitochondrial protection between all study groups. Short bubble and subsequent intermittent surface oxygenation of the perfusate of an HMP-kidney might be an effective and cheap preservation strategy to protect mitochondria, eliminating the need/costs of a membrane oxygenator and oxygen source during transport.

Current Evidence and Future Perspectives to Implement Continuous and End-Ischemic Use of Normothermic and Oxygenated Hypothermic Machine Perfusion in Clinical Practice

The use of high-risk renal grafts for transplantation requires the optimization of pretransplant assessment and preservation reconditioning strategies to decrease the organ discard rate and to improve short- and long-term clinical outcomes. Active oxygenation is increasingly recognized to play a central role in dynamic preservation strategies, independent of preservation temperature, to recondition mitochondria and to restore the cellular energy profile. The oxygen-related decrease in mitochondrial succinate accumulation ameliorates the harmful effects of ischemia-reperfusion injury. The differences between normothermic and hypothermic machine perfusion with regard to organ assessment, preservation, and reconditioning, as well as the logistic and economic implications, are factors to take into consideration for implementation at a local level. Therefore, these different techniques should be considered complementary to the perfusion strategy selected depending on functional intention and resource availability. This review provides an overview of the current clinical evidence of normothermic and oxygenated hypothermic machine perfusion, either as a continuous or end-ischemic preservation strategy, and future perspectives.

Simply Adding Oxygen during Hypothermic Machine Perfusion to Combat the Negative Effects of Ischemia-Reperfusion Injury: Fundamentals and Current Evidence for Kidneys

The use of high-risk renal grafts for transplantation requires optimization of pretransplant preservation and assessment strategies to improve clinical outcomes as well as to decrease organ discard rate. With oxygenation proposed as a resuscitative measure during hypothermic machine preservation, this review provides a critical overview of the fundamentals of active oxygenation during hypothermic machine perfusion, as well as the current preclinical and clinical evidence and suggests different strategies for clinical implementation.

Brief Bubble and Intermittent Surface Oxygenation Is a Simple and Effective Alternative for Membrane Oxygenation During Hypothermic Machine Perfusion in Kidneys

Background.

The aim of this feasibility study was to determine an alternative oxygenation technique (easy, cheap, and compatible with air transport) for membrane oxygenation during hypothermic machine perfusion (HMP) to improve early graft function in a porcine ischemia-reperfusion autotransplant model.

Methods.

The left kidney of a ±40- kg pig was exposed to 30 minutes of warm ischemia before 22 hours of preservation and autotransplantation. In the experimental group, oxygenation of the perfusate during HMP was obtained by direct bubble and 30-minute surface oxygenation at start and 1-hour end ischemic (n = 4) and outcome measures compared with historical HMP without active oxygenation (n = 6), 22-hour continuous oxygenated HMP (HMPO₂) (n = 8), and 2-hour HMPO₂ + 20-hour HMP (n = 6) using membrane oxygenation in both historical oxygenated control groups.

Results.

Brief bubble and 30-minute surface oxygenation of the perfusate effectively maintained supraphysiological Po₂ levels during the first 2 hours of HMP with improved flow dynamics. Although the metabolic profile of the perfusate (ie, flavin mononucleotide) and tissue (ie, glutamate, ATP) after brief O₂ uploading at the start of HMP seemed to be slightly better with the use of a membrane oxygenator compared with bubble and interrupted surface oxygenation, both techniques yielded similar, superior early graft function when compared with HMP without active oxygenation.

Conclusions.

The data presented in this feasibility study support the conclusion that brief bubble and intermittent surface oxygenation could be an alternative oxygenation technique during HMP to achieve an improved kidney graft function compared with HMP without active oxygenation and similar functional outcome when compared with membrane HMPO₂.

Use of a miniaturized cardiopulmonary bypass circuit in neonates and infants is associated with fewer blood product transfusions

Miniaturized bypass circuits, including the Kids D100 oxygenator and the D130 arterial filter, were specially designed to reduce blood transfusions in small infants undergoing cardiac surgery. This study compared the number of blood product transfusions and short-term outcome between patients younger than 1 year undergoing cardiac surgery with a conventional and a miniaturized bypass circuit, after controlling for baseline characteristics and surgical complexity by 1:1 matching. Adjusted odds ratios (ORs) and 95% confidence intervals for exposure to transfusions and to any additional transfusion were estimated from binary and polytomous regression models. Of the 804 patients enrolled retrospectively, 246 were analyzed after matching. The use of the miniaturized circuit required a lower priming volume, 265.5 vs. 432.4 mL, p < 0.001, fewer packed red blood cell (PRBC) transfusions, 1.4 vs. 2.0 U, p < 0.001, and fewer platelet transfusions on the day of surgery, 57.7% vs. 76.4%, p < 0.001. After adjustment for the use of antifibrinolytics, the ultrafiltration rate, and the year of surgery, the use of the miniaturized circuit was independently related to a reduced risk of additional PRBC transfusions, OR 0.04 (0.01, 0.13), and exposure to platelet transfusions, OR 0.78 (0.63, 0.96). Short-term outcome was similar.

Extracorporeal life support systems: alternative vs. conventional circuits

Emerging technologies and practices for pediatric and neonatal extracorporeal life support (ECLS) are promising. This experiment sought to compare the Medtronic 0800 silicon rubber membrane oxygenator to the Quadrox-iD Pediatric oxygenator in the conventional roller pump circuit, as well as comparing the conventional circuit to an alternative circuit. Three circuits were set up in the experiment. Two conventional roller pump circuits were used to compare the two oxygenators and an alternative circuit consisting of the Quadrox-iD Pediatric oxygenator and Maquet Rotaflow centrifugal pump system was used to identify differences between circuits. All three circuits were primed with Lactated Ringers' solution and human blood, with an hematocrit of 40%. Testing occurred at flow rates of 250, 500, and 750 ml/ min at 37°C for mean arterial line pressures of 60, 80, and 100 mmHg. The results of the experiment showed lower pressure drops and greater retention of total hemodynamic energy (THE) across the Quadrox-iD Pediatric oxygenator compared to the Medtronic 0800 oxygenator. Furthermore, the centrifugal pump used in the alternative circuit showed no back flow at flow rates as low as 250 ml/min while, on the other hand, rpm levels were kept below 2200 for flow rates as high as 750 ml/min. Findings support the usage of the Quadrox-iD Pediatric oxygenator in a circuit utilizing the Maquet Rotaflow centrifugal pump system due to lower pressure drops and greater percentage of THE retained across the circuit. Additional advantages of the alternative circuit include rapid set-up time, easy transport, lower priming volumes, and no gravity-dependent venous drainage system so that it can be situated in close proximity to and at the level of the patient.

An in vitro comparison of the ability of three commonly used pediatric cardiopulmonary bypass circuits to filter gaseous microemboli

Background: The purpose of this study was to compare the ability of three commonly used pediatric cardiopulmonary bypass (CPB) circuits to filter gaseous microemboli (GME) in an in vitro model. Methods: Devices were tested at different levels of two specific independent variables: volume of air injected (1, 3, 5ml) and percentage of each oxygenator’s rated flow (50%, 75%, 100%, 125%). The air-handling ability of each CPB circuit was determined by the Emboli Detection and Classification Quantifier (Luna Innovations Inc., Roanoke,VA). Results: At all tested conditions, the FX-05 allowed a higher percentage of GME when compared to either one or both of the other two CPB circuits. When comparing oxygenators at similar absolute flow rates, the KIDS D100/D130 CPB circuit performed worse compared to the other two CPB circuits. C onclusions: The combination of the Baby RX-05 oxygenator and Capiox AF02 arterial line filter provides the highest level of protection from air emboli in an in vitro investigation.