Alteration of the Traditional Extracorporeal Bypass Circuit to Accommodate Port-Access Minimally Invasive Cardiac Procedures Using Endovascular Based Cardiopulmonary Bypass

Port-Access minimally invasive cardiac surgery systems (Heartport, Inc., Redwood City, CA, U.S.A.) enable surgeons to perform many procedures including valve surgery and complete coronary artery revascularization of all surfaces of the heart through small anterior thoracotomies. The endovascular based EndoCPB (Heartport, Inc.) cardiopulmonary bypass system uses a modified extracorporeal circuit to afford the same level of myocardial protection through cardioplegic cardiac arrest and bypass as is provided in traditional open chest surgery. We describe the changes required to convert a conventional CPB pump circuit to perform Port-Access procedures and make recommendations based on clinical experience to facilitate establishing a Port-Access surgical team and interpreting EndoCPB pressure and flow data. Specific emphasis is placed on the expanded role of the perfusionist in these cases.     

Occupational exposure to desflurane and isoflurane during cardiopulmonary bypass: is the gas outlet of the membrane oxygenator an operating theatre pollution hazard?

We have compared occupational exposure to isoflurane and desflurane during cardiopulmonary bypass, with and without a scavenging system at the membrane oxygenator outlet. Trace concentrations of volatile anaesthetics were measured by a direct reading instrument in 40 elective heart surgery procedures. Measurements were obtained in the breathing zones of the anaesthetist and perfusionist. When a scavenging system was used, median desflurane values were less than 0.3 ppm and isoflurane values less than 0.2 ppm. Without a scavenging system values were, in general, three- (isoflurane) to five- (desflurane) fold higher. We conclude that the use of a scavenging system at the membrane oxygenator outlet can reduce occupational exposure to volatile anaesthetics. We therefore recommend routine use of scavenging devices during cardiopulmonary bypass.      

Cerebral emboli during cardiopulmonary bypass: effect of perfusionist interventions and aortic cannulas

Neuropsychological impairment is a very common complication of cardiopulmonary bypass (CPB). The principal cause of postoperative cognitive impairment is thought to be cerebral microemboli during CPB. We recently investigated the effects of perfusionist interventions and aortic cannulation techniques on cerebral emboli production during coronary bypass (CABG) surgery. Patients undergoing isolated CABG were monitored with continuous transcranial Doppler ultrasonography of the middle cerebral artery. Perfusionist interventions were defined as injections of drugs into the CPB circuit or acquisition of blood samples from the CPB circuit. Patients were randomized to receive either standard cannulation of the ascending aorta or cannulation of the distal aortic arch. Cerebral emboli were detected in all patients. The number of emboli per minute was markedly higher during perfusionist interventions than during other time periods. Patients with increased perfusionist interventions had worse neuropsychological outcomes. Cannulation of the distal aortic arch, with placement of the cannula tip beyond the cerebral vessels, resulted in significantly less cerebral emboli than cannulation of the ascending aorta. Perfusionist interventions are a common source of cerebral microemboli during CPB, and may contribute to postoperative neuropsychological impairment. Care should be taken to minimize the introduction of air into the bypass circuit during CPB. Provided it is performed safely, distal aortic arch cannulation is a useful technique for reducing cerebral emboli during cardiac surgery.     

Clear prime for infant cardiopulmonary bypass: a miniaturized circuit

The extracorporeal circuit used clinically to perform cardiopulmonary bypass (CPB) in small infants is relatively large requiring blood to prime the circuit to reduce hemodilution. To study the merits of clear prime also in infants, we did experiments in rabbits with two extracorporeal circuits: one employing traditional venous gravity drainage (priming volume 330 ml) and the other employing vacuum drainage (priming volume 90 ml). The first circuit still had to be primed with blood, whereas the second circuit could be primed with a clear solution. Both circuits were automatically controlled to lighten the task of the perfusionist to operate the CPB safely and accurately. We demonstrated that the clear priming solution in the second circuit eliminates the hemodynamic deterioration caused by blood prime in the first circuit. Studying the effect of various modes of regulation, we showed that automatic control of CPB based on venous return is similar to autoregulation of the heart according to Starling's law, and maintains not only normal hemodynamics, but also an optimal microcirculation.     

A versatile extracorporeal circuit for use during repair of descending and thoracoabdominal aortic aneurysms in high-risk patients with cardiac and/or pulmonary dysfunction: a novel approach to a significant perfusion management dilemma

The incidence of ischemic complications associated with repair of descending and thoracoabdominal aortic aneurysms has been significantly reduced by the use of distal aortic perfusion with moderate hypothermia, cerebral spinal fluid drainage, and segmental sequential clamping techniques. However, because the maintenance of proximal perfusion, the adequacy of left heart bypass (LHB), and the ability to ventilate patients on only one lung are all dependent on ventricular and pulmonary function, high-risk patients with descending and/or thoracoabdominal aortic aneurysms in the presence of cardiopulmonary insufficiency or instability present a difficult challenge for the surgical team. Traditional closed LHB circuits become nonfunctional in the event of cardiac arrest or refractory arrhythmias that create hemodynamic instability and are unable to provide necessary pulmonary support if the patient fails to ventilate adequately on one lung during thoracotomy. Furthermore, converting a patient from closed LHB to traditional venoarterial cardiopulmonary bypass (CPB) is frequently difficult, especially when the perfusionist works without the benefit of extra personnel to assist during such crises. Consequently, a modified extracorporeal circuit was designed to provide closed LHB with desired therapeutic adjuncts while also satisfying the additional need for a rapid infusion device, a source of supplemental ventilation/oxygenation, and, if necessary, the ability to convert the patient to venoarterial CPB conveniently in the event of cardiac and/or pulmonary failure during surgery to repair descending and/or thoracoabdominal aortic aneurysms.     

Administration of vancomycin during cardiopulmonary bypass

Vancomycin was given during cardiopulmonary bypass to 12 anaesthetised patients undergoing open heart surgery. Injection of vancomycin 1 g within 60 s via the venous inlet of the oxygenator resulted in a moderate and transient decrease of mean arterial pressure. This minimal reaction may be attributed to dilution of vancomycin by the extracorporeal circuit volume, to the bypassing of the lungs which are a major site of storage of vasoactive substances, or to the maintenance of adequate perfusion flow during cardiopulmonary bypass. The results suggest that the haemodynamic adverse reactions to vancomycin, given as antibiotic prophylaxis, may be decreased by its administration after initiation of cardiopulmonary bypass.     

Use of bivalirudin as an anticoagulant during cardiopulmonary bypass

Bivalirudin is a short-acting direct thrombin inhibitor that has been used in cardiac surgical patients with heparin-induced thrombocytopenia (HIT) or suspected HIT. Although no direct thrombin inhibitor is indicated for anticoagulation during cardiac surgery in patients with heparin-induced thrombocytopenia (HIT) or suspected HIT, use of heparin-alternatives are increasing as the awareness of HIT increases. Reports of anticoagulation with bivalirudin are sporadic, however, with variable dosing and management strategies. In this report, we describe our management techniques for cardiopulmonary bypass with bivalirudin based upon our personal experience. Although the reported clinical experience with bivalirudin in cardiac surgery is reviewed, operative techniques for the perfusionist/surgeon team are discussed in detail. We recognize that the use of bivalirudin during cardiopulmonary bypass is evolving and modifications of technique will undoubtedly occur as further data and experience accumulate.     

Simultaneous Automatic Control of Oxygen and Carbon Dioxide Blood Gases During Cardiopulmonary Bypass

In this work an automatic control strategy is presented for the simultaneous control of oxygen and carbon dioxide blood gas partial pressures to be used during cardiopulmonary bypass surgery with heart–lung machine support. As the exchange of blood gases in the artificial extracorporeal lung is a highly nonlinear process comprising varying time delays, uncertainties, and time‐varying parameters, it is currently being controlled manually by specially trained perfusionist staff. The new control strategy includes a feedback linearization routine with augmented time‐delay compensation and two external linear gain‐scheduled controllers, for partial oxygen and carbon dioxide pressures. The controllers were robustly tuned and tested in simulations with a detailed artificial lung (oxygenator) model in cardiopulmonary bypass conditions. Furthermore, the controllers were implemented in an ex vivo experiment using fresh porcine blood as a substitute fluid and a special deoxygenation technique to simulate a patient undergoing cardiopulmonary bypass. Both controllers showed robust stability during the experiments and a good disturbance rejection to extracorporeal blood flow changes. This automatic control strategy is proposed to improve patient's safety by fast control reference tracking and good disturbance rejection under varying conditions.     

Cardiopulmonary bypass

The primary function of the cardiopulmonary bypass (CPB) machine is to provide oxygenated blood flow to the systemic circulation while providing the surgeon with a motionless, bloodless surgical field. The CPB circuit consists of a reservoir, blood pump, oxygenator, heat exchanger, arterial filter, cardioplegia delivery device and cannulae, interconnected by various sized tubing. The venous cannula directs blood away from the heart and lungs via the CBP circuit and the arterial cannula returns the oxygenated blood to the systemic circulation. A blood pump propels the blood volume forward through a membrane oxygenator and allows rapid transfusion of oxygenated blood back into the systemic circulation. The CPB flow needs to be enough to maintain an adequate cardiac output, therefore a flow of 1.8–2.2 litres/minute/m² is recommended when at normothermia, although these flows can be reduced if the temperature is less than 28°C. The mortality and neurological complications after cardiac surgery are similar using either normothermic or hypothermic CPB. Maintenance of anaesthesia on CPB is often achieved with a propofol infusion (sometimes with the addition of remifentanil), but the use of volatile anaesthetic is also possible through the CPB machine. A vaporizer can be attached to the CPB circuit and volatile anaesthetic delivered into the sweep gas passing through the oxygenator. A safety checklist before separation from bypass is essential, and it may include: optimal temperature, heart rhythm, de-airing, acid-base status, ventilation, electrolytes and patient position. If heparin was used to maintain anticoagulation, it should be reversed with protamine after the patient is stable off-CPB. Some patients require inotropic or mechanical support to facilitate ‘weaning’ from CPB.     

Neuropsychologic impairment after coronary bypass surgery: effect of gaseous microemboli during perfusionist interventions

OBJECTIVE: Neuropsychologic impairment is a common complication of coronary bypass surgery. Cerebral microemboli during cardiopulmonary bypass are the principal cause of cognitive deficits after coronary bypass grafting. We have previously demonstrated that the majority of cerebral emboli occur during perfusionist interventions (ie, during the injection of air into the venous side of the cardiopulmonary bypass circuit). The purpose of this study was to determine whether an increase in perfusionist interventions is associated with an increased risk of postoperative cognitive impairment. METHODS: Patients undergoing elective coronary artery bypass grafting (n = 83) underwent a battery of neuropsychologic tests preoperatively and 3 months postoperatively. Patients were divided into 2 groups according to the median value of perfusionist interventions during cardiopulmonary bypass. Group 1 patients (n = 42) had fewer than 10 perfusionist interventions, and group 2 patients (n = 41) had 10 or more interventions. RESULTS: The 2 groups of patients were similar for all preoperative, intraoperative, and postoperative variables, with the exception of longer cardiopulmonary bypass times in group 2 patients (P <.001). Group 2 patients had lower mean scores on 9 of 10 neuropsychologic tests, with 3 (Rey Auditory Verbal Learning, Digit Span, and Visual Span) being statistically significant. Group 2 patients had worse cognitive test scores, even when controlling for increased bypass times. Group 2 patients had a nonsignificant trend toward an increased prevalence of neuropsychologic impairment 3 months postoperatively. CONCLUSIONS: Introduction of air into the cardiopulmonary bypass circuit by perfusionists, resulting in cerebral microembolization, may contribute to postoperative cognitive impairment.     

Spinal cord infarction due to aortic dissection during coronary artery bypass grafting under percutaneous cardiopulmonary support

We report a case of aortic dissection due to improper position of a percutaneous cardiopulmonary support (PCPS) cannula into the femoral artery during coronary artery bypass grafting (CABG). A 77-year-old man with 3-vessel disease underwent off-pump CABG (OPCAB). Blood pressure suddenly lowered during bypass grafting to the right coronary artery. PCPS was performed between the left femoral artery and the right atrium. Bradycardia occurred 37 min after initiation of PCPS, and transesophageal echocardiography revealed Stanford type A aortic dissection. By converting the perfusion site from the femoral artery to the right axillar artery, the false lumen disappeared and did not reccur after cessation of PCPS. Therefore, the aorta was not replaced. He had however, bilateral leg paralysis after surgery. Magnetic resonance imaging (MRI) revealed spinal cord infarction caused by aortic dissection. Computed tomography (CT) confirmed disappearance of the false lumen and no expansion of the aorta 1 month after surgery. Meticulous care should be taken of the site and size of the arterial cannula in the extracorporeal circuit in such cases.     

The Aachen Miniaturized Heart‐Lung Machine—First Results in a Small Animal Model

Congenital heart surgery most often incorporates extracorporeal circulation. Due to foreign surface contact and the administration of foreign blood in many children, inflammatory response and hemolysis are important matters of debate. This is particularly an issue in premature and low birth‐weight newborns. Taking these considerations into account, the Aachen miniaturized heart‐lung machine (MiniHLM) with a total static priming volume of 102 mL (including tubing) was developed and tested in a small animal model. Fourteen female Chinchilla Bastard rabbits were operated on using two different kinds of circuits. In eight animals, a conventional HLM with Dideco Kids oxygenator and Stöckert roller pump (Sorin group, Milan, Italy) was used, and the Aachen MiniHLM was employed in six animals. Outcome parameters were hemolysis and blood gas analysis including lactate. The rabbits were anesthetized, and a standard median sternotomy was performed. The ascending aorta and the right atrium were cannulated. After initiating cardiopulmonary bypass, the aorta was cross‐clamped, and cardiac arrest was induced by blood cardioplegia. Blood samples for hemolysis and blood gas analysis were drawn before, during, and after cardiopulmonary bypass. After 1 h aortic clamp time, all animals were weaned from cardiopulmonary bypass. Blood gas analysis revealed adequate oxygenation and perfusion during cardiopulmonary bypass, irrespective of the employed perfusion system. The use of the Aachen MiniHLM resulted in a statistically significant reduced decrease in fibrinogen during cardiopulmonary bypass. A trend revealing a reduced increase in free hemoglobin during bypass in the MiniHLM group could also be observed. This newly developed Aachen MiniHLM with low priming volume, reduced hemolysis, and excellent gas transfer (O₂ and CO₂) may reduce circuit‐induced complications during heart surgery in neonates.     

Pulsatile Augmentation Device for Extracorporeal Circulation

Abstract: A device has been designed, constructed, and tested to provide pulsatile pressure/flow to a standard extracorporeal bypass circuit. The pulsatile augmentation device is pneumatically driven similar to an artificial heart ventricle except that there are no valves. It is constructed of polyurethane by vacuum forming and high frequency welding. Drivers used are a modified Arrow-Kontron in-traaortic balloon pump or the Utah artificial heart driver. In vitro testing with fresh bovine blood demonstrated acceptable blood compatibility and hemodynamic function. In vivo testing for 4 h in a right and left heart extracorporeal bypass circuit showed good pulse augmentation in pulmonary and systemic bypass circuits. The device shows promise for adding pulse to standard cardiopulmonary bypass and to extracorporeal right heart circulatory assist circuits.     

Regional blood flow distribution during extracorporeal membrane oxygenation in rabbits

To study regional blood distribution during extracorporeal membrane oxygenation, we stabilized three groups of five rabbits each (3 to 5 kg) on venoarterial bypass at a flow rate of 30 ml/kg/min. Albumin aggregates (15 to 30 microns) labeled with technetium 99m were injected into the left ventricle during bypass (ventricle), the perfusion cannula during bypass (cannula), and the left ventricle with no bypass (control). Animals were put to death, organs were removed, and the percent distribution was determined with a gamma camera. The Student Newman-Keuls test was used for statistical comparisons. Distribution to both the heart and brain in the cannula group were decreased from control by 55% and 35%, respectively. Distribution to the brain in the ventricle group was also decreased from control by 39%. Intestinal distribution was elevated above control in the ventricle group by 37%, whereas musculoskeletal distribution was elevated 33% above control in the cannula group. No significant changes were noted for the kidneys, stomach, or liver. These data suggest that overall perfusion of some vital organs may be significantly reduced during low-flow extracorporeal membrane oxygenation, specifically in the case of the heart and brain, which may be deprived of oxygenated blood.     

Transapical Aortic Perfusion with a Double-Barreled Cannula

The transapical aortic perfusion method is a new approach to cardiopulmonary bypass and is performed with an infusion cannula placed in the ascending aorta through the left ventricular apex. The technique is applicable to almost all varieties of open-heart surgery, and is the most efficient method in infants and small children. A double-barreled forked cannula performs the two functions of aortic infusion and left ventricular decompression. With a Bakelite obturator, its cannulation to the aorta is very quick and easy.The transapical aortic perfusion method with a double-barreled cannula has been utilized in 156 open-heart operations with 17 perioperative fatalities and 1 late death. The 138 surviving patients have done well for periods up to four years.The perfusion method was developed from the left heart bypass and assisted circulation technique independently invented by Chardack's group and by us in 1966 and 1969, respectively.     

Use of the Hemobag for modified ultrafiltration in a Jehovah's Witness patient undergoing cardiac surgery

Modified ultrafiltration is an important technique to concentrate the patient's circulating blood volume and the residual whole blood in the extracorporeal circuit post-cardiopulmonary bypass. The Hemobag system is a device cleared by the US Food and Drug Administration and represents a novel and safe modification of traditional modified ultrafiltration systems. It is quick and easy to operate by the perfusionist during the hemoconcentration process. Hemoconcentration is accomplished by having the Hemobag "recovery loop" circuit separate from the extracorporeal circuit. This allows the surgeons to continue with surgery, decannulate, and administer protamine simultaneously while the Hemobag is in use. The successful use of the Hemobag in a Jehovah's Witness patient has not been previously described in the literature. This case report describes how to set up and operate the Hemobag in a Jehovah's Witness patient undergoing cardiac surgery that requires an extracorporeal circuit.     

A failure mode effect analysis on extracorporeal circuits for cardiopulmonary bypass

Although many refinements in perfusion methodology and devices have been made, extracorporeal circulation remains a contributor to neurological complications, bleeding coagulopathies, use of blood products, as well as systemic inflammatory response. With the exposure of these adverse effects of cardiopulmonary bypass, the necessity to re-examine the safety of extracorporeal circuits is vital. A failure mode effect analysis (FMEA) is a proven proactive technique developed to evaluate system effect or equipment failure. FMEA was used to evaluate the six different types of extracorporeal circuits based on feedback from five clinical experts. Cardiovascular device manufacturers, the Veteran's Administration National Center for Patient Safety, and the Joint Commission on Accreditation of Healthcare Organizations recommend the use of FMEA to assess and manage risks in current and developing technologies and therapies. This analysis investigates the safety of six types of extracorporeal circuits used in coronary revascularization, including the newer miniaturized extracorporeal circuits. The FMEA lists and ranks the hazards associated with the use of each cardiopulmonary bypass extracorporeal circuit type. To increase the safety of extracorporeal circuits and minimize the effects associated with cardiopulmonary bypass, perfusionists must incorporate FMEA into their clinical practice.     

An ultrafiltration technique for directly reinfusing residual cardiopulmonary bypass blood

Given the shortages of banked blood, the risks of transfusion reactions, disease transmissions, and transfusion errors, we perfusionists must find ways to avoid blood transfusions. At the end of any given bypass run, there is residual blood left in the bypass circuit, the perfusionist must get this blood back to the patient. Most commonly either a cell saver or a hemoconcentrator (HC) has been used, in some fashion, to reinfuse residual circuit blood. The ideal method should: 1) be simple; 2) raise the hematocrit (HCT); 3) allow for changes in the patient's volume status; and 4) not compromise the integrity of the cardiopulmonary bypass (CPB) circuit allowing for rapid re-institution of CPB. We describe a technique in which residual CPB circuit blood is pumped through an HC directly to the patient via a 3/16-inch diameter line into a 16-gauge intravenous needle positioned in a peripheral or central vein. This allows the perfusionist to give back concentrated blood that is protein-rich while maintaining the above criteria.     

A Newly Designed Arterial Monitoring/Perfusion Cannula for Cardiac Operations

A newly designed arterial monitoring and perfusion cannula for cardiopulmonary bypass eliminates the need for cannulation of a peripheral artery for pressure monitoring. The double-lumen cannula is designed as follows: the large central lumen (12 to 26F) acts as the arterial inflow conduit from the pump oxygenator, while a second, smaller lumen (18 gauge) constructed in the wall of the first cannula acts as the pressure-monitoring port and the source for blood sampling and drug infusion. This monitoring/perfusion cannula has been used successfully in more than 250 clinical patients in a variety of settings—total cardiopulmonary bypass, left heart bypass, and when multiple arterial inflow lines were necessary (as in aortic arch replacement). Use of this cannula is advantageous in the infant and pediatric patient or in the emergency setting, when insertion of a peripheral arterial line can be difficult. Used in conjunction with a Doppler system, the cannula provides accurate, dependable blood pressure monitoring.