Perfusion

Introduction: Despite major advances in biomaterial research and blood conservation, bleeding is still a common complication after cardiopulmonary bypass and cardiac surgery remains a major consumer of blood products. Although the underlying mechanisms for these effects are not fully established, two proposed major etiologies are the hemodilution associated with the use of the heart-lung machine and the impact of reinfusion of shed cardiotomy blood. Therapeutic strategies that primarily encompass the use of devices or technologies to overcome these effects may result in improved clinical outcomes.

Objective: To determine the extent to which 1) lipid/leukocyte filtration and centrifugal processing of cardiotomy blood, and 2) modified ultrafiltration (MUF) are currently applied in adult cardiac surgery in Canada.

Methods: A questionnaire was mailed to the chief perfusionist at all adult cardiac surgical centers in Canada, addressing details regarding the frequency of use of cardiotomy blood processing and MUF.

Results: All questionnaires (36, 100%) were completed and returned. With regards to cardiotomy blood management, in 21 centers (58%), no specific processing steps were utilized exclusive of the integrated cardiotomy reservoir filter. Of the remaining centers, two (6%) reported using lipid/leukocyte filtration and 15 (42%) reported washing their cardiotomy blood. Three centers (8%) reported using MUF at the end of CPB.

Conclusions: Despite growing concern about the potential detrimental effects of cardiotomy blood, few centers in Canada routinely manage this blood with additional filtration and/or centrifugal processing prior to reinfusion. Similarly, MUF, demonstrated to be effective in the pediatric population, has not seen popular application in adult cardiac surgical practice.

Introduction: Coronary artery bypass graft surgery (CABG) using cardiopulmonary bypass (CPB) is assumed to be associated with a decline of neurocognitive functions. This study was designed to analyse the neurocognitive function of patients with coronary heart disease before and after CABG and to determine possible protective effects of oxygenator surface coating on neurological outcome.

Methods: Forty patients scheduled for selective CABG were prospectively randomized into two groups of 20 patients each according to the type of hollow-fibre membrane oxygenator used. Non-coated oxygenators (Group A) were compared to phosphorylcholine (PC)- coated oxygenators (Group B). A battery of six neurological tests was administered preoperatively, 7 - 10 days and 4 - 6 months after surgery.

Results: One patient of Group A suffered from a perioperative stroke and died on postoperative day 3, presumably because of sudden heart failure. Two patients of Group A (10%) developed a symptomatic transitory delirious psychotic syndrome (STPT) on postoperative days 3 and 5. None of the patients of Group B had perioperative complications. The test analysis revealed a trend of declined neurocognitive function early after CABG, but did not show any difference in neurocognitive outcome between the two groups.

Discussion: PC coating of the oxygenators did not show any significant benefit on neurocognitive function after CABG using CPB.

Biocompatible cardiopulmonary bypass (CPB) circuits aim to reduce contact activation and its physiological consequences. We investigated the hypothesis that use of Surface Modifying Additive (SMA)-treated circuits (Sorin Group Ltd) compared with non-SMA circuits would be associated with preservation of blood pressure during CPB and modulation of perioperative subclinical renal function (urinary α-1-microglobulin (α-1-m)) and plasma and urinary cytokine changes. In a study of low-risk CABG patients (n=40), randomized to SMA (n=20) versus non-SMA circuits (n=20), we found better preserved blood pressure at CPB initiation in SMA patients (p <0.05), particularly in ACE-inhibited SMA patients (n=11) versus ACE-inhibited non-SMA patients (n=10) (p <0.05). Plasma anti-inflammatory IL-10, as well as urinary α-1-m, were elevated 48 hours postoperatively (p <0.05). SMA patients also had lower blood loss (p <0.05). SMA circuits have some clinical benefit, especially in ACE-inhibited patients.

Cardiac surgery with cardiopulmonary bypass (CPB) elicits an inflammatory response and has a multitude of biological consequences, ranging from subclinical organ dysfunction to severe multiorgan failure. Pediatric patients are more prone to have a reaction that can jeopardize their outcome. Cytokines are supposed to be important mediators in this response: limiting their circulating levels is, therefore, appealing. We investigated the pattern of cytokine release during pediatric operation for congenital heart anomalies in 20 patients, and the effect of hemofiltration. Tumor necrosis factor a (TNF-α) was elevated after anesthesia induction and showed significant decrease during CPB. Hemofiltration reduced its concentration, but the effect disappeared on the following day. Interleukin-1 (IL-1) increased slowly at the end of CPB and hemofiltration had no effect. Interleukin-6 (IL-6) showed a tendency toward augmentation during rewarming and hemofiltration did not significantly affect the course. Soluble interleukin-6 receptor (sIL-6r) had a pattern similar to TNF-α, but hemofiltration had no effect. On the other hand, interleukin-8 (IL-8) behaved like IL-6. Our findings suggest that baseline clinical status, anesthetic drugs, and maneuvers before incision may elicit a cytokine response, whereas rewarming is a critical phase of CPB. Hemofiltration is effective in removal of TNF-α, but its role is debatable for the control of IL-1, IL-6, sIL-6r and IL-8 levels.

Delays in initiating extracorporeal membrane oxygenation (ECMO) in the critically ill pediatric patient may lead to adverse outcomes. Maintaining a primed ECMO circuit can considerably reduce the initiation time. The predominant concerns precluding this practice are a decrease in oxygenator efficiency due to the saturation of microporous hollow fibers and compromised sterility when the oxygenator has been primed for 30 days. For institutions using a hollow-fiber oxygenator for ECMO, there are no data reporting pre-primed hollow-fiber oxygenator viability. This study reports the efficiency of oxygen transfer and the sterility of the Carmeda Minimax Plus (Medtronic, Inc, Minneapolis, MN) oxygenator after being crystalloid primed for 30 days. A total of 10 Minimax Plus oxygenators were tested for oxygen transfer in a laboratory setting utilizing fresh whole bovine blood. The control group (n=5) were tested immediately after priming. The test group (n=5) were oxygenators primed for 30 days with crystalloid solution and left stagnant until tested. Prior to testing, all oxygenators were circulated for 5 min and samples drawn to test for circuit sterility. Venous inlet saturations were manipulated to achieve three levels of testing: venous saturation (SvO₂) of 55% for an oxygen challenge, SvO₂ of 65% to comply with AAMI standards, and SvO₂ of 75% to assess oxygen transfer rates and peak PaO₂ achievement. Blood flow for all tests was maintained at 2 L/min with 1:1 blood to gas flow ratio and 100% FiO₂. Samples were drawn pre- and postoxygenator at 1- and 6-hour time intervals to compute actual oxygen transfer values. All cultures from the test group priming solution produced no microbial growth after 30 days of stagnant prime. Average oxygen transfer values (ml/O₂/min) for the control group after 1 hour of continuous use were 130.1±15.5 (@55% SvO₂), 113.7±10.4 (@65% SvO₂),97.7±8.9 (@75% SvO₂). After 6 hours, the average transfer values increased to 134.2±13.2 (@55% SvO₂), 118.76±6.6 (@65% SvO₂) and 98.9±8.3 (@75% SvO₂). The average oxygen transfer values after 1 hour for oxygenators primed for 30 days were 114.9±10.0 (@55% SvO₂), 112.4±8.2 (@65% SvO₂) and 89.6±16.0 (@75% SvO₂). After 6 hours of use, the average transfer values all decreased to 111.4±2.1 (@55% SvO₂, p <0.05 versus control), 104.0±5.6 (@65% SvO₂, p<0.05 versus control) and 88.4±3.2 (@75% SvO₂, p<0.05 versus control). In conclusion, there was a decrease in the average oxygen transfer values for the test group after 6 hours versus the control. The modest loss of oxygen transfer ability observed can be considered acceptable due to the amount of surface area of the Minimax Plus oxygenator when used on a neonate, making it feasible to adopt the practice of prepriming the Minimax oxygenator for neonatal ECMO.

Objective: We assessed the causes of imbalance of oxygen transport by continuously measuring oxygen consumption (VO₂) during hypothermic cardiopulmonary bypass (CPB) in pigs.

Methods: Six pigs (17.2±1.6 kg) underwent hypothermic (328C) CPB for 180 min with 120 min of aortic crossclamping (ACC). An AMIS 2000 mass spectrometer was adapted for the on-line measurement of VO₂. Arterial lactate was measured at the beginning of CPB, the end of hypothermia, before and 10 min after ACC release, 20 min later, and at the end of CPB.

Results: Arterial lactate increased from 1.8±0.7 to 5.1±1.8 mmol/L during CPB. Hypothermia reduced VO₂by 0.63±0.29 ml/min/kg per 8C, but lactate increased to 4.2±1.5 mmol/L (p <0.05). The most rapid rise of VO₂and lactate occurred during the first 10 min after ACC removal, accounting for 26% and 68%, respectively, of the total rise during rewarming.

Conclusions: Inadequate tissue oxygenation persists throughout hypothermic CPB. The rise in systemic VO₂ and lactate immediately after ACC release may reflect inadequate oxygen transport within the myocardium during ischemia and manifest on reperfusion. This simple technique may be used to provide important information regarding the dynamic balance of systemic and myocardial oxygen transport during ischemia - reperfusion.

Cardiac surgery with cardiopulmonary bypass (CPB) leads to a powerful activation of the hemostatic system. We assessed to what extent this activation can be attenuated by comparing three different perfusion regimens for on-pump coronary artery bypass grafting (CABG): 1) use of a closed CPB system with aspiration of blood from the operation field via the cardiotomy suction line and active venting of the heart via a roller pump; 2) use of a closed CPB system avoiding aspiration of blood from the operation field via the cardiotomy suction line, but with active venting of the heart; and 3) use of a closed system, avoidance of aspiration of blood from the operation field via the cardiotomy suction line and with passive venting of the heart into the collapsible venous reservoir. Our data show that avoidance of aspiration of blood via the cardiotomy suction line significantly reduces hemostatic activation during on-pump CABG. However, further attenuation of hemostatic activation can be achieved by further closing the system and minimizing the blood/air interface by passive venting of the heart.

In recent years, modern medicine has changed considerably. At maximum care centers, in particular, the use of state-of-the-art medical equipment has become an essential part of patient care. However, using such high-tech products also means a considerable burden on the financial resources available, because additional financing is rare. Consequently, there is a need for approaches that allow the use of state-of-the-art equipment without straining the budget unduly. The question now is whether economic strategies that have long since been established in other industries, e.g., the outsourcing of certain services, represent a potential solution for the economic problems of modern clinics. The fundamentals of outsourcing and its pros and cons are outlined and discussed, taking cardiovascular perfusion as an example, a cost-intensive field of heart surgery that is responsible for attending to heart ^/ lung machines, artificial hearts and circulatory support systems.

Due to the short supply of donor organs available, many patients decompensate or die while waiting for transplantation. Options for mechanical support for infants and pediatrics with congenital heart disease are limited because of the patient’s size and device availability. Extracorporeal membrane oxygenation (ECMO) is the most common means of cardiac and respiratory support for these patients. One of the many indications for ECMO use in cardiac patients is as a bridge to transplantation, with patients being transported to the operating room (OR) on ECMO support. Converting the ECMO circuit to an open cardiopulmonary bypass system in the OR minimizes the patient’s exposure to new circuitry, decreases further donor exposures and provides continuous support for patients in cardiac and/or respiratory failure. In addition, the ability to use modified ultrafiltration post-bypass aids in reducing extracellular fluid, increasing the hematocrit and improving hemodynamic stability following an extended duration of ECMO and bypass support. The integrity of the ECMO circuit is maintained and can be converted back to ECMO for support postoperatively if needed.