A new cardiopulmonary bypass circuit with reduced foreign surface (CorX™): initial clinical experience and implications for anaesthesia management (2004)

EDITOR: Cardiac surgery provokes a vigorous inflammatory response. The direct contact of the patient's blood with the foreign surface of the cardiopulmonary bypass (CPB) circuit plays an important role in triggering this response [1]. The heat exchanger and open hard-shell venous reservoir contribute to the total artificial surface and can initiate blood protein denaturation and damage to cellular elements like erythrocytes and platelets [2]. Beyond that, marked haemodilution by the prime solution of the CPB circuit can trigger significant fluid shifts from the intravascular to the extravascular space [3]. A growing body of evidence suggests that significant cardiodepression may be a consequence of myocardial oedema caused by decreased colloid osmotic pressure and increased capillary permeability as well as the effects of proinflammatory cytokines on the myocardium [1]. Therefore, CPB circuits with restricted foreign surface and smaller priming volume may reduce the inflammatory response and subsequently morbidity and mortality [3,4]. Recently, a new CPB circuit (CorX™; Cardiovention, Santa Clara, CA, USA) was developed which offers a significant reduction of total foreign surface. We present our initial experience with the device and some important issues related to the anaesthetic management. CorX™ is a disposable system consisting of an oxygenator with an integrated centrifugal pump at the bottom (Fig. 1). An air detector (AirVac™; Cardiovention, Santa Clara, CA, USA) at the top senses and evacuates air from the venous line. Following standard cannulation, the negative pressure generated by the centrifugal pump actively drains venous blood. The negative pressure in the venous line enables left ventricular (LV) venting and addition of prime, blood and other fluids. Excess blood in the system can be drained to a reservoir bag by the positive pressure in the arterial line. The reservoir bag is connected to the venous as well as the arterial line and when needed, the stored blood may be reinfused into the venous line. There is no cardiotomy suction, heat exchanger or hard-shell reservoir. The foreign surface, including the compact arterio-venous loop, totals approximately 1.4 m2. Shed blood is retransfused via a cell saver. Temperature homeostasis is achieved with a heated blanket (Bair Hugger 560 Cath Lab™; Augustine Medical, MN, USA). All intravenous fluids are warmed and the operating room temperature is kept at 25°C.Figure 1: CorX™ circuit. Arrows indicate direction of blood flow in the different lines.Following Institutional Review Board approval and written informed consent, nine ASA III patients (six males, three females) scheduled for elective coronary artery bypass surgery were enrolled in the study. Their mean age was 64 ± 13 yr. After oral premedication with midazolam (0.1-0.2 mg kg−1) and clonidine (2 μg kg−1), anaesthesia was induced and maintained with propofol and sufentanil. The patients were ventilated with an air/oxygen mixture (FiO2 0.5). Central venous and arterial catheters were inserted. The arterial line was connected to a cardiac output monitor (PICCO™; Pulsion Systems, Munich, Germany) for determination of haemodynamic variables (cardiac output, intrathoracic blood volume, systemic vascular resistance and extravascular lung water index). These measurements were performed in triplicate immediately before and 5 min after CPB. The operative and CPB techniques were strictly standardized. The crystalloid prime volume was 500 mL. Pump flow rate was 2.5 L min−1 m−2. Normothermia was maintained. All patients were operated on by the same surgeon and anaesthetized by the same anaesthesiologist. A paired t-test was used for comparisons with a P-value <0.05 considered to be statistically significant. Values are reported as mean ± SD. The duration of surgery was 211 ± 50 min, CPB time was 86 ± 15 min, and aortic cross-clamp time was 49 ± 15 min. Total blood loss was 2367 ± 907 mL and 730 ± 534 mL was retransfused from the cell saver. Packed red cells were transfused in three cases (one patient received two units, and two patients, one unit each). There were no significant differences in cardiac output, intrathoracic blood volume, systemic vascular resistance or extravascular lung water index between the measurements before and after CPB (Table 1). In contrast, haematocrit was significantly lower after CPB (P < 0.01, Table 1). Nasopharyngeal temperature was 36.2 ± 0.5°C before and 36.2 ± 0.6°C after CPB (P > 0.05). There were no adverse effects (air entrainment, circulatory arrest) related to the CorX™-use in any patient.Table 1: Haemodynamic parameters, haemoglobin and haematocrit before and after CPB (mean ± SD, n = 9).Our findings regarding cardiac output, intrathoracic blood volume, systemic vascular resistance and extravascular lung water index agree with data from studies using conventional CPB circuits [5]. In a preliminary animal study, Mueller and coworkers compared the CorX™ system with a conventional CPB circuit in a model of prolonged perfusion. They found an improved gas exchange, a stable haematocrit and a limited decrease in platelet count in the CorX™ group [6]. In our patients haematocrit was significantly reduced after CPB, similarly to conventional CPB [7]. The limited transfusion requirements (3/9 patients) despite the low pre-CPB haematocrit in our patients (30.8 ± 3.2%) nevertheless suggests a positive impact of the reduced haemodilution of the CorX™ circuit. At the moment, sparing homologous blood transfusion seems to be an advantage of CorX™ compared to conventional CPB circuits. We found that anaesthesiologist-directed temperature and intravascular volume control can compensate for the absent heat exchanger and reservoir without running the risk of haemodynamic instability or postoperative hypothermia. Temperature management is crucial to avoid hypothermia and enable fast tracking. LV venting cannot be adjusted individually but depends on the negative pressure in the venous part of the circuit, which in turn depends on total pump flow. This may sometimes impede adequate drainage of the left ventricle. The CorX™ system may be used safely provided that the anaesthesiologist is familiar with this special CPB technique. Particular attention is necessary to avoid huge amounts of air entering the venous line of the CPB circuit (i.e. accidental venous decannulation or vent displacement), which could overwhelm the air suction capacity. An interdisciplinary approach including anaesthesiologist, surgeon and perfusionist is necessary for optimal management of cardiac surgery with the CorX™ system. B. Bein D. Caliebe J. Scholz M. Steinfath P. H. Tonner Department of Anaesthesiology and Intensive Care Medicine; University Hospital Schleswig-Holstein Kiel, Germany A. Boening Department of Cardiothoracic and Vascular Surgery; University Hospital Schleswig-Holstein; Kiel, Germany