Comparative assessment of coronary physiology using transthoracic pulsed-wave Doppler and myocardial contrast echocardiography in rats.

BACKGROUND: Coronary physiology assessment in rodents by ultrasound is an excellent noninvasive and easy to perform technique, including pulsed-wave Doppler (PWD) and myocardial contrast echocardiography (MCE). Both techniques and the corresponding calculated parameters were investigated in this study at rest as well as their response to pharmacologically induced stress. METHODS: Left ventricular myocardial function was assessed in eight anaesthetised rats using transthoracic echocardiography. Coronary physiology was assessed by both PWD of the left coronary artery and MCE using a bolus method. Measurements were performed at rest and under stimulation with adenosine and dobutamine. Effects of stimulation on the calculated parameters were evaluated and rated by effect size (η2). RESULTS: Changes could be demonstrated by selected parameters of PWD and MCE. The clearest effect in PWD was found for diastolic peak velocity (η2 = 0.58). It increased from 528 ± 110 mm/s (mean ± standard deviation) at rest to 839 ± 342 mm/s (p = 0.001) with adenosine and 1093 ± 302 mm/s with dobutamine (p = 0.001). The most distinct effect from MCE was found for the normalised wash-in rate (η2 = 0.58). It increased from 1.95 ± 0.35% at rest to 3.87 ± 0.85% with adenosine (p = 0.001) and 3.72 ± 1.03% with dobutamine (p = 0.001). CONCLUSION: Induced changes in coronary physiology by adenosine and dobutamine could successfully be monitored using MCE and PWD in anaesthetised rats. Due to the low invasiveness of the measurements, this protocol could be used for longitudinal animal studies.

Sodium Channels and Local Anesthetics-Old Friends With New Perspectives.

The long history of local anesthetics (LAs) starts out in the late 19th century when the content of coca plant leaves was discovered to alleviate pain. Soon after, cocaine was established and headed off to an infamous career as a substance causing addiction. Today, LAs and related substances-in modified form-are indispensable in our clinical everyday life for pain relief during and after minor and major surgery, and dental practices. In this review, we elucidate on the interaction of modern LAs with their main target, the voltage-gated sodium channel (Navs), in the light of the recently published channel structures. Knowledge of the 3D interaction sites of the drug with the protein will allow to mechanistically substantiate the comprehensive data available on LA gating modification. In the 1970s it was suggested that LAs can enter the channel pore from the lipid phase, which was quite prospective at that time. Today we know from cryo-electron microscopy structures and mutagenesis experiments, that indeed Navs have side fenestrations facing the membrane, which are likely the entrance for LAs to induce tonic block. In this review, we will focus on the effects of LA binding on fast inactivation and use-dependent inhibition in the light of the proposed new allosteric mechanism of fast inactivation. We will elaborate on subtype and species specificity and provide insights into modelling approaches that will help identify the exact molecular binding orientation, access pathways and pharmacokinetics. With this comprehensive overview, we will provide new perspectives in the use of the drug, both clinically and as a tool for basic ion channel research.

Effect of Aprotinin on Liver Injury after Transplantation of Extended Criteria Donor Grafts in Humans: A Retrospective Propensity Score Matched Cohort Analysis.

The number of patients awaiting liver transplantation still widely exceeds the number of donated organs available. Patients receiving extended criteria donor (ECD) organs are especially prone to an aggravated ischemia reperfusion syndrome during liver transplantation leading to massive hemodynamic stress and possible impairment in organ function. Previous studies have demonstrated aprotinin to ameliorate reperfusion injury and early graft survival. In this single center retrospective analysis of 84 propensity score matched patients out of 274 liver transplantation patients between 2010 and 2014 (OLT), we describe the association of aprotinin with postreperfusion syndrome (PRS), early allograft dysfunction (EAD: INR 1,6, AST/ALT > 2000 within 7-10 days) and recipient survival. The incidence of PRS (52.4% vs. 47.6%) and 30-day mortality did not differ (4.8 vs. 0%; p = 0.152) but patients treated with aprotinin suffered more often from EAD (64.3% vs. 40.5%, p = 0.029) compared to controls. Acceptable or poor (OR = 3.3, p = 0.035; OR = 9.5, p = 0.003) organ quality were independent predictors of EAD. Our data do not support the notion that aprotinin prevents nor attenuates PRS, EAD or mortality.

Visual quality assessment of the liver graft by the transplanting surgeon predicts postreperfusion syndrome after liver transplantation: a retrospective cohort study.

BACKGROUND: The discrepancy between demand and supply for liver transplants (LT) has led to an increased transplantation of organs from extended criteria donors (ECD). METHODS: In this single center retrospective analysis of 122 cadaveric LT recipients, we investigated predictors of postreperfusion syndrome (PRS) including transplant liver quality categorized by both histological assessment of steatosis and subjective visual assessment by the transplanting surgeon using multivariable regression analysis. Furthermore, we describe the relevance of PRS during the intraoperative and postoperative course of LT recipients. RESULTS: 53.3% (n = 65) of the patients suffered from PRS. Risk factors for PRS were visually assessed organ quality of the liver grafts (acceptable: OR 12.2 [95% CI 2.43-61.59], P = 0.002; poor: OR 13.4 [95% CI 1.48-121.1], P = 0.02) as well as intraoperative norepinephrine dosage before reperfusion (OR 2.2 [95% CI 1.26-3.86] per 0.1 µg kg- 1 min- 1, P = 0.01). In contrast, histological assessment of the graft was not associated with PRS. LT recipients suffering from PRS were hemodynamically more instable after reperfusion compared to recipients not suffering from PRS. They had lower mean arterial pressures until the end of surgery (P < 0.001), received more epinephrine and norepinephrine before reperfusion (P = 0.02 and P < 0.001, respectively) as well as higher rates of continuous infusion of norepinephrine (P < 0.001) and vasopressin (P = 0.02) after reperfusion. Postoperative peak AST was significantly higher (P = 0.001) in LT recipients with PRS. LT recipients with intraoperative PRS had more postoperative adverse cardiac events (P = 0.05) and suffered more often from postoperative delirium (P = 0.04). CONCLUSIONS: Patients receiving ECD liver grafts are especially prone to PRS. Anesthesiologists should keep these newly described risk factors in mind when preparing for reperfusion in patients receiving high-risk organs.

Adaptation to acute pulmonary hypertension in pigs.

The extent of right ventricular compensation compared to the left ventricle is restricted and varies among individuals, which makes it difficult to define. While establishing a model of acute pulmonary hypertension in pigs we observed two different kinds of compensation in our animals. Looking deeper into the hemodynamic data we tried to delineate why some animals could compensate and others could not. Pulmonary hypertension (mean pressure 45 mmHg) was induced gradually by infusion of a stable thromboxane A2 analogue U46619 in a porcine model (n = 22). Hemodynamic data (pressure-volume loops, strain-analysis of echocardiographic data and coronary flow measurements) were evaluated retrospectively for the short-term right ventricular compensatory mechanisms and limits (Roehl et al. [2012] Acta Anaesthesiol. Scand., 56:449-58) 10 animals showed stable arterial blood pressures, whereas 12 pigs exhibited a significant drop of 16.4 ± 9.9 mmHg. Cardiac output and heart rate were comparable in both groups. In contrast, right ventricular contractility and coronary flow only rose in the stable group. The unchanging values in the decrease group correlated with an increasing ST-segment depression and a loss of ventricular synchronism and resulted in a larger septum bulging to the right ventricle. Simultaneously, a reduced left-ventricular end-diastolic volume and a missing improvement in contractility in the posterior septal and inferior free wall of the left ventricle have been observed. Our findings suggest that right ventricular compensation during acute pulmonary hypertension is strongly dependent on the individual capability to increase coronary flow. The cause for inter-individual variability could be the dimension and reactivity of the coronary system.

Xenon protects left ventricular diastolic function during acute ischemia, less than ischemic preconditioning.

Anesthetics modify regional left ventricular (LV) dysfunction following ischemia/reperfusion but their effects on global function in this setting are less clear. Aim of this study was to test the hypothesis that xenon would limit global LV dysfunction as caused by acute anterior wall ischemia, comparable to ischemic preconditioning. In an open-chest model under thiopental anesthesia, 30 pigs underwent 60-minute left anterior descending coronary artery occlusion, followed by 120 minutes of reperfusion. A xenon group (constant inhalation from previous to ischemia through end of reperfusion) was compared to control and ischemic preconditioning. Load-independent measures of diastolic function (end-diastolic pressure-volume relation, time constant of relaxation) and systolic function (end-systolic pressure-volume relation, preload-recruitable stroke work) were determined. Heart rate, arterial pressure, cardiac output, and arterial elastance were recorded. Data were compared in 26 pigs. Ischemia impaired global diastolic but not systolic function in control, which recovered during reperfusion. Xenon limited and preconditioning abolished diastolic dysfunction during ischemia. Arterial pressure decreased during reperfusion while arterial elastance increased. Tachycardia and antero-septal wall edema during reperfusion were observed in all groups. In spite of ischemia of 40% of LV mass, global systolic function was preserved. Deterioration in global diastolic function was limited by xenon and prevented by preconditioning.

Risk factors for coagulopathy after liver resection.

STUDY OBJECTIVE: To identify risk factors for coagulopathy in patients undergoing liver resection. DESIGN: A retrospective cohort study. SETTING: Patients who underwent liver resection at a university hospital between April 2010 and May 2011 were evaluated within seven days after surgery. PATIENTS: One hundred forty-seven patients were assessed for eligibility. Thirty needed to be excluded because of incomplete data (23) or a preexisting coagulopathy (7). MEASUREMENTS: Coagulopathy was defined as 1 or more of the following events: international normalized ratio ≥1.4, platelet count <80,000/µL, and partial thromboplastin time >38 seconds. Related to the time course and coagulation profile thresholds, 3 different groups could be distinguished: no coagulopathy, temporary coagulopathy, and persistent coagulopathy. MAIN RESULTS: Seventy-seven patients (65.8%) had no coagulopathy, whereas 33 (28.2%) developed temporary coagulopathy and 7 (6%) developed persistent coagulopathy until day 7. Preoperative international normalized ratio (P = .001), postoperative peak lactate levels (P = .012), and resected liver weight (P = .005) were identified as independent predictors. Preoperative liver transaminases and transfusion volumes of red blood cells and fresh frozen plasma were significantly higher in patients with persistent coagulopathy. CONCLUSIONS: Epidural anesthesia is feasible in patients scheduled for liver resection. Caution should be observed for patients with extended resection (≥3 segments) and increased postoperative lactate. In patients with preexisting liver disease, epidural catheters should be avoided.

The role of hypoxia-inducible factor-1α and vascular endothelial growth factor in late-phase preconditioning with xenon, isoflurane and levosimendan in rat cardiomyocytes.

OBJECTIVES: The protective effects of late-phase preconditioning can be triggered by several stimuli. Unfortunately, the transfer from bench to bedside still represents a challenge, as concomitant medication or diseases influence the complex signalling pathways involved. In an established model of primary neonatal rat cardiomyocytes, we analysed the cardioprotective effects of three different stimulating pharmaceuticals of clinical relevance. The effect of additional ß-blocker treatment was studied as these were previously shown to negatively influence preconditioning. METHODS: Twenty-four hours prior to hypoxia, cells pre-treated with or without metoprolol (0.55 µg/ml) were preconditioned with isoflurane, levosimendan or xenon. The influences of these stimuli on hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF) as well as inducible and endothelial nitric synthase (iNOS/eNOS) and cyclooxygenase-2 (COX-2) were analysed by polymerase chain reaction and western blotting. The preconditioning was proved by trypan blue cell counts following 5 h of hypoxia and confirmed by fluorescence staining. RESULTS: Five hours of hypoxia reduced cell survival in unpreconditioned control cells to 44 ± 4%. Surviving cell count was significantly higher in cells preconditioned either by 2 × 15 min isoflurane (70 ± 16%; P = 0.005) or by xenon (59 ± 8%; P = 0.049). Xenon-preconditioned cells showed a significantly elevated content of VEGF (0.025 ± 0.010 IDV [integrated density values when compared with GAPDH] vs 0.003 ± 0.006 IDV in controls; P = 0.0003). The protein expression of HIF-1α was increased both by levosimendan (0.563 ± 0.175 IDV vs 0.142 ± 0.042 IDV in controls; P = 0.0289) and by xenon (0.868 ± 0.222 IDV; P < 0.0001) pretreatment. A significant elevation of mRNA expression of iNOS was measureable following preconditioning by xenon but not by the other chosen stimuli. eNOS mRNA expression was found to be suppressed by ß-blocker treatment for all stimuli. In our model, independently of the chosen stimulus, ß-blocker treatment had no significant effect on cell survival. CONCLUSIONS: We found that the stimulation of late-phase preconditioning involves several distinct pathways that are variably addressed by the different stimuli. In contrast to isoflurane treatment, xenon-induced preconditioning does not lead to an increase in COX-2 gene transcription but to a significant increase in HIF-1α and subsequently VEGF.

Levosimendan limits reperfusion injury in a rat middle cerebral artery occlusion (MCAO) model.

BACKGROUND: Neuroprotective strategies in ischemic stroke are an important challenge in clinical and experimental research as an adjunct to reperfusion therapy that may reduce neurologic injury and improve outcome. The neuroprotective properties of levosimendan in traumatic brain injury in vitro, transient global brain ischemia and focal spinal cord ischemia suggest the potential for similar effects in transient brain ischemia. METHODS: Transient brain ischemia was induced for 60 min by intraluminal occlusion of the middle cerebral artery in 40 male Wistar rats under general anesthesia with s-ketamine and xylazine and with continuous monitoring of their blood pressure and cerebral perfusion. Five minutes before inducing reperfusion, a levosimendan bolus (24 µg kg -1) was administered over a 20 minute period. Infarct size, brain swelling, neurological function and the expression of inflammatory markers were quantified 24 hours after reperfusion. RESULTS: Although levosimendan limited the infarct size and brain swelling by 40% and 53%, respectively, no effect on neurological outcome or mortality could be demonstrated. Upregulation of tumor necrosis factor α and intercellular adhesion molecule 1 was significantly impeded. Cerebral blood flow during reperfusion was significantly reduced as a consequence of sustained autoregulation. CONCLUSIONS: Levosimendan demonstrated significant neuroprotective properties in a rat model of transient brain ischemia by reducing reperfusion injury.

Xenon and isoflurane reduce left ventricular remodeling after myocardial infarction in the rat.

BACKGROUND: Xenon and isoflurane are known to have cardioprotective properties. We tested the hypothesis that these anesthetics positively influence myocardial remodeling 28 days after experimental perioperative myocardial infarction and compared their effects. METHODS: A total of 60 male Sprague-Dawley rats were subjected to 60 min of coronary artery occlusion and 120 min of reperfusion. Prior to ischemia, the animals were randomized for the different narcotic regimes (0.6 vol% isoflurane, 70 vol% xenon, or intraperitoneal injection of s-ketamine). Acute injury was quantified by echocardiography and troponin I. After 4 weeks, left ventricular function was assessed by conductance catheter to quantify hemodynamic compromise. Cardiac remodeling was characterized by quantification of dilatation, hypertrophy, fibrosis, capillary density, apoptosis, and expression of fetal genes (α/ß myosin heavy chains, α-skeletal actin, periostin, and sarco/endoplasmic reticulum Ca2+-ATPase). RESULTS: Whereas xenon and isoflurane impeded the acute effects of ischemia-reperfusion on hemodynamics and myocardial injury at a comparable level, differences were found after 4 weeks. Xenon in contrast to isoflurane or ketamine anesthetized animals demonstrated a lower remodeling index (0.7 ± 0.1 vs. 0.9 ± 0.3 and 1.0 ± 0.3g/ml), better ejection fraction (62 ± 9 vs. 49 ± 7 and 35 ± 6%), and reduced expression of ß-myosin heavy chain and periostin. The effects on hypertrophy, fibrosis, capillary density, and apoptosis were comparable. CONCLUSIONS: Compared to isoflurane and s-ketamine, xenon limited progressive adverse cardiac remodeling and contractile dysfunction 28 days after perioperative myocardial infarction.

The effects of levosimendan on brain metabolism during initial recovery from global transient ischaemia/hypoxia.

BACKGROUND: Neuroprotective strategies after cardiopulmonary resuscitation are currently the focus of experimental and clinical research. Levosimendan has been proposed as a promising drug candidate because of its cardioprotective properties, improved haemodynamic effects in vivo and reduced traumatic brain injury in vitro. The effects of levosimendan on brain metabolism during and after ischaemia/hypoxia are unknown. METHODS: Transient cerebral ischaemia/hypoxia was induced in 30 male Wistar rats by bilateral common carotid artery clamping for 15 min and concomitant ventilation with 6% O2 during general anaesthesia with urethane. After 10 min of global ischaemia/hypoxia, the rats were treated with an i.v. bolus of 24 µg kg-1 levosimendan followed by a continuous infusion of 0.2 µg kg-1 min-1. The changes in the energy-related metabolites lactate, the lactate/pyruvate ratio, glucose and glutamate were monitored by microdialysis. In addition, the effects on global haemodynamics, cerebral perfusion and autoregulation, oedema and expression of proinflammatory genes in the neocortex were assessed. RESULTS: Levosimendan reduced blood pressure during initial reperfusion (72 ± 14 vs. 109 ± 2 mmHg, p = 0.03) and delayed flow maximum by 5 minutes (p = 0.002). Whereas no effects on time course of lactate, glucose, pyruvate and glutamate concentrations in the dialysate could be observed, the lactate/pyruvate ratio during initial reperfusion (144 ± 31 vs. 77 ± 8, p = 0.017) and the glutamate release during 90 minutes of reperfusion (75 ± 19 vs. 24 ± 28 µmol·L-1) were higher in the levosimendan group. The increased expression of IL-6, IL-1ß TNFα and ICAM-1, extend of cerebral edema and cerebral autoregulation was not influenced by levosimendan. CONCLUSION: Although levosimendan has neuroprotective actions in vitro and on the spinal cord in vivo and has been shown to cross the blood-brain barrier, the present results showed that levosimendan did not reduce the initial neuronal injury after transient ischaemia/hypoxia.

Neuroprotective properties of levosimendan in an in vitro model of traumatic brain injury.

BACKGROUND: We investigated the neuroprotective properties of levosimendan, a novel inodilator, in an in vitro model of traumatic brain injury. METHODS: Organotypic hippocampal brain slices from mouse pups were subjected to a focal mechanical trauma. Slices were treated after the injury with three different concentrations of levosimendan (0.001, 0.01 and 0.1 µM) and compared to vehicle-treated slices. After 72 hrs, the trauma was quantified using propidium iodide to mark the injured cells. RESULTS: A significant dose-dependent reduction of both total and secondary tissue injury was observed in cells treated with either 0.01 or 0.1 µM levosimendan compared to vehicle-treated slices. CONCLUSION: Levosimendan represents a promising new pharmacological tool for neuroprotection after brain injury and warrants further investigation in an in vivo model.

A practical rule for optimal flows for xenon anaesthesia in a semi-closed anaesthesia circuit.

BACKGROUND AND OBJECTIVE: Stable haemodynamics and its cardioprotective and neuroprotective properties favour xenon as an ideal but expensive anaesthetic agent. The aim of this study was to optimize a semi-closed anaesthesia circuit for xenon anaesthesia with respect to economics and patient safety. METHODS: A semi-closed nonrebreathing circuit was compared with a closed anaesthesia circuit. In 12 landrace pigs, we compared eight different wash-in procedures affecting xenon consumption. Additionally, the maintenance of anaesthesia was analysed with regard to minimizing xenon consumption. RESULTS: The current study showed that, by optimization of the electronic regulation of the wash-in procedure for xenon anaesthesia, the consumption of the valuable gas can be reduced by up to 75% in a semi-closed circuit. The additional maintenance of anaesthesia under low flow conditions by coupling the xenon flow to the oxygen consumption is the most effective way to technically reduce the amount of xenon needed for anaesthesia.

Continuous right ventricular volumetry by fast-response thermodilution during right ventricular ischemia: head-to-head comparison with conductance catheter measurements.

OBJECTIVE: To evaluate the accuracy of right ventricular ejection fraction and right ventricular end-diastolic volume obtained by volumetric pulmonary artery catheter, using the conductance catheter as reference method. DESIGN: Prospective, comparative study. SETTING: Research laboratory of a university hospital. SUBJECTS: Seven young female German landrace pigs. INTERVENTIONS: Ligation of the distal right coronary artery to induce temporary acute ischemia. MEASUREMENTS AND MAIN RESULTS: Right ventricular ejection fraction and right ventricular end-diastolic volume were measured simultaneously with a volumetric pulmonary artery catheter and the conductance catheter technique (reference method), in an animal model of acute right ventricular ischemia. Measurements were performed at baseline, during ischemia, and during reperfusion. The methods were compared with Bland-Altman analyses and their diagnostic accuracy to detect ischemia was quantified by receiver operating characteristic curve analysis. For right ventricular ejection fraction measurements, Bland-Altman analysis indicated a bias of -9.9% indicating underestimation by pulmonary artery catheter with limits of agreement ranging from -26% to 6.1%. The data showed a trend for more underestimation at higher right ventricular ejection fraction values. For right ventricular end-diastolic volume, a bias of 31 mL, indicating overestimation by pulmonary artery catheter was found. Limits of agreement ranged from -25 mL to 88 mL. Ischemia induced a decrease in right ventricular ejection fraction and an increase in right ventricular end-diastolic volume, as expected, which was detected by conductance catheter with a significant higher diagnostic accuracy indicated by a receiver operating characteristic area under the curve of 0.98 (p < .001) and 0.92 (p < .001), respectively. Corresponding sensitivity and specificity were 100% and 86%, respectively, for right ventricular ejection fraction conductance catheter (cutoff value = <40%), and 86% and 100% for right ventricular end-diastolic volume conductance catheter (cutoff value = >94 mL). However, diagnostic accuracy for right ventricular ejection fraction pulmonary artery catheter and end-diastolic volume pulmonary artery catheter to detect ischemia was limited with area under the curve 0.76 (p = .06) and 0.57 (p = .65), respectively. CONCLUSIONS: Accuracy of volumetric pulmonary artery catheter in conditions of right ventricular ischemia is low and inadequate for diagnosis of right ventricular ischemia and failure.

Comparison of 3 methods to induce acute pulmonary hypertension in pigs.

Large animal models for acute pulmonary hypertension (PHT) show distinct differences between species and underlying mechanisms. Two embolic procedures and continuous infusion of a stable thromboxane A(2) analogue (U46619) were explored for their ability to induce PHT and their effects on right ventricular function and pulmonary and systemic circulation in 9 pigs. Injection of small (100 to 200 microm) or large (355 to 425 microm) polystyrene beads and incremental dosage (0.2 to 0.8 microg kg(-1) min(-1)) of U46619 all induced PHT. However, infusion of U46619 resulted in stable PHT, whereas that after bead injection demonstrated a gradual continuous decline in pressure. This instability was most pronounced with small beads, due to right ventricular failure and consecutive circulatory collapse. Furthermore, cardiac output decreased during U46619 infusion but increased after embolization with no relevant differences in systemic pressure. This result was likely due to the more pronounced effect of U46619 on pulmonary resistance and impedance in combination with limited effects on pulmonary gas exchange. Coronary autoregulation and adaption of contractility to afterload increase was not impaired by U46619. All parameters returned to baseline values after infusion was discontinued. Continuous infusion of a thromboxane A2 analogue is an excellent method for induction of stable, acute PHT in large animal hemodynamic studies.