Non-invasive measurement of cardiac output using an iterative, respiration-based method.

BACKGROUND: Current non-invasive respiratory-based methods of measuring cardiac output [Formula: see text] make doubtful assumptions and encounter significant technical difficulties. We present a new method using an iterative approach [Formula: see text], which overcomes limitations of previous methods. METHODS: Sequential gas delivery (SGD) is used to control alveolar ventilation [Formula: see text] and CO2 elimination [Formula: see text] during a continuous series of iterative tests. Each test consists of four breaths where inspired CO2 [Formula: see text] is controlled; raising end-tidal Pco2 [Formula: see text] by about 1.33 kPa (10 mm Hg) for the first breath, and then maintaining [Formula: see text] constant for the next three breaths. The [Formula: see text] required to maintain [Formula: see text] constant is calculated using the differential Fick equation (DFE), where [Formula: see text] is the only unknown and is arbitrarily assumed for the first iteration. Each subsequent iteration generates measures used for calculating [Formula: see text] by the DFE, refining the assumption of [Formula: see text] for the next test and converging it to the true [Formula: see text] when [Formula: see text] remains constant during the four test breaths. We compared [Formula: see text] with [Formula: see text] measured by bolus pulmonary artery thermodilution [Formula: see text] in seven pigs undergoing liver transplantation. RESULTS: [Formula: see text] implementation and analysis was fully automated, and [Formula: see text] varied from 0.6 to 5.4 litre min(-1) through the experiments. The bias (between [Formula: see text] and [Formula: see text]) was 0.2 litre min(-1) with 95% limit of agreement from -1.1 to 0.7 litre min(-1) and percentage of error of 32%. During acute changes of [Formula: see text], convergence of [Formula: see text] to actual [Formula: see text] required only three subsequent iterations. CONCLUSIONS: [Formula: see text] measurement is capable of providing an automated semi-continuous non-invasive measure of [Formula: see text].

Comparative analysis of in situ versus ex situ perfusion on micro circulation in liver procurement--an experimental trial in a porcine model.

INTRODUCTION: The Achilles heel of liver transplantation remains the biliary system. The crucial step for liver preservation is effective rinsing and perfusion of the peribiliary plexus (PBP). Due to the physiology of the vascular tree, it seems almost impossible to achieve the necessary physiologic ranges of pressure and flow by the in situ perfusion technique. We investigated the role of additional ex situ perfusion via the hepatic artery in this animal model. MATERIALS AND METHODS: Fifteen German Landrace pigs underwent standardized multiorgan procurement. In situ perfusion and additional ex situ perfusion were performed consecutively. Meanwhile the external pressure applied to the perfusion system was increased stepwise. To visualize the effects on the liver parenchyma and PBP, we administered colored microparticles (MPs; 10 µm). Frozen sections of the explanted liver were studied histologically by quantitative evaluation of the MPs. RESULTS: Ex situ perfusion was able to build up significantly higher values of pressure (P < .001) and flow (P < .001) than in situ perfusion. Those of ex situ perfusion reached physiological levels under application of an external pressure of 200 mm Hg. Considering the liver parenchyma, significantly higher amounts of MPs originating from ex situ perfusion were evident (P < .001) and PBP (P < .001). CONCLUSION: MPs provide an appropriate tool to determine organ perfusion quantitatively in experimental models. Considering flow, pressure, and microcirculation, we consider that additional ex situ perfusion of the liver is more effective than in situ perfusion.

Normothermic acellular ex vivo liver perfusion reduces liver and bile duct injury of pig livers retrieved after cardiac death.

We compared cold static with acellular normothermic ex vivo liver perfusion (NEVLP) as a novel preservation technique in a pig model of DCD liver injury. DCD livers (60 min warm ischemia) were cold stored for 4 h, or treated with 4 h cold storage plus 8 h NEVLP. First, the livers were reperfused with diluted blood as a model of transplantation. Liver injury was determined by ALT, oxygen extraction, histology, bile content analysis and hepatic artery (HA) angiography. Second, AST levels and bile production were assessed after DCD liver transplantation. Cold stored versus NEVLP grafts had higher ALT levels (350 ± 125 vs. 55 ± 35 U/L; p < 0.0001), decreased oxygen extraction (250 ± 65 mmHg vs. 410 ± 58 mmHg, p < 0.01) and increased hepatocyte necrosis (45% vs. 10%, p = 0.01). Levels of bilirubin, phospholipids and bile salts were fivefold decreased, while LDH was sixfold higher in cold stored versus NEVLP grafts. HA perfusion was decreased (twofold), and bile duct necrosis was increased (100% vs. 5%, p < 0.0001) in cold stored versus NEVLP livers. Following transplantation, mean serum AST level was higher in the cold stored versus NEVLP group (1809 ± 205 U/L vs. 524 ± 187 U/L, p < 0.05), with similar bile production (2.5 ± 1.2 cc/h vs. 2.8 ± 1.4 cc/h; p = 0.2). NEVLP improved HA perfusion and decreased markers of liver duct injury in DCD grafts.