Novel system for percutaneous cardiopulmonary bypass

Percutaneous cardiopulmonary bypass (PCPB) has recently come to the forefront of medicine as a technique for resuscitating and supporting patients in various clinical situations. Current systems utilize small-diameter cannulas to aspirate blood under high suction into the cardiopulmonary bypass circuit. Aspiration-based systems have several disadvantages including risk of air embolism, blood hemolysis, and cavitation. Additionally, they are suboptimal for use during open-heart surgical procedures. A system with a venous cannula that employs gravity drainage has been evaluated. Once advanced into position over a guide-wire, the stylet is removed, causing the basket near the end of the cannula to expand. Blood flows into the cannula from side holes and the basket region, which prevents the vessel wall or atrium from collapsing around the catheter and impeding venous drainage. Hemodynamic, hematologic, and histologic examinations were performed on eight anesthetized mongrel dogs during 2 h of PCPB. All animals exhibited adequate tissue perfusion and right and left heart decompression. All animals were successfully weaned from PCPB and after 30 min exhibited normal myocardial function. No ischemic changes were observed in the heart, lung, kidney, or liver by light and electron microscopy. We conclude that full PCPB can be satisfactorily achieved by using a novel percutaneous venous cannula and gravity drainage.     

Cardiopulmonary bypass

The purpose of cardiopulmonary bypass is to maintain perfusion and oxygenation of the vital organs in the absence of heart and lung function, usually to facilitate surgery on the heart, but occasionally in other situations. Although the intricacies of the modern extracorporeal circuit and the conduct of cardiopulmonary bypass are the domain of the clinical perfusion scientist (‘perfusionist’), safe surgery mandates a good understanding of some fundamentals by the anaesthetist and the surgeon. This review is aimed at the anaesthetist. First, we will systematically examine the main components of the extracorporeal circuit, travelling in the direction that blood travels, from the venous cannula to the arterial cannula. Then we will describe the process of preparing for bypass, ‘going on’, conducting a bypass run, and weaning and separation from bypass. It is crucial to have clear communication between the surgeon, perfusionist and anaesthetist. This can be difficult for the novice because a quite specific language has evolved in cardiac operating theatres to signal key events in the cardiopulmonary bypass sequence. As we go through this article, we will highlight commonly used terminology and expressions used.     

Diagnosis of inadvertent cannulation of the azygos vein during cardiopulmonary bypass

Cardiac surgery with cardiopulmonary bypass demands diligence and attention to detail to prevent neurologic injury. Arterial and venous cannulae are used to facilitate cardiopulmonary bypass. The assessment of adequate decompression of the venous circulation is an essential duty of the cardiac surgical team. Modalities for the assessment of adequate regional venous drainage are limited, however communication between the team and increased awareness of certain pathologic states can be useful. These modalities include cerebral oximetry and superior vena caval pressure monitoring, which were employed during a case with bicaval venous cannulation. Malposition of the superior vena cava cannula was detected after a series of events alerted the team that superior vena cava drainage may be compromised.     

Systemic venous drainage: can we help Newton?

In recent years substantial progress occurred in the techniques of cardiopulmonary bypass, but the factor potentially limiting the flexibility of cardiopulmonary bypass remains the drainage of the systemic venous return. In the daily clinical practice of cardiac surgery, the amount of systemic venous return on cardiopulmonary bypass is directly correlated with the amount of the pump flow. As a consequence, the pump flow is limited by the amount of venous return that the pump is receiving. On cardiopulmonary bypass the amount of venous drainage depends upon the central venous pressure, the height differential between patient and inlet of the venous line into the venous reservoir, and the resistance in the venous cannula(s) and circuit. The factors determining the venous return to be taken into consideration in cardiac surgery are the following: (a) characteristics of the individual patient; (b) type of planned surgical procedure; (c) type of venous cannula(s); (d) type of circuit for cardiopulmonary bypass; (e) strategy of cardiopulmonary bypass; (f) use of accessory mechanical systems to increased the systemic venous return. The careful pre-operative evaluation of all the elements affecting the systemic venous drainage, including the characteristics of the individual patient and the type of required surgical procedure, the choice of the best strategy of cardiopulmonary bypass, and the use of the most advanced materials and tools, can provide a systemic venous drainage substantially better than what it would be allowed by the simple ‘Law of universal gravitation’ by Isaac Newton.     

Venoarterial air embolus: a complication of vacuum-assisted venous drainage

Minimal access techniques with cardiopulmonary bypass use smaller cannula systems for management of cardiopulmonary bypass. To augment flow rates through the smaller cannula, the technique of vacuum-assisted venous drainage has been used. We describe a complication of vacuum-assisted venous drainage by inadvertent positive pressurization of the venous circuit resulting in a paradoxic air embolus across a patent atrial septal defect. Hazards of the current cardiopulmonary bypass systems and techniques for avoiding this potential complication are discussed.     

An In Vitro Evaluation of Venous Cannula in a Simulated Partial (Femoro-Femoral) Cardiopulmonary Bypass Circuit

Abstract: We designed a study to evaluate three factors (siphon gradient [PH], the right atrial pressure [RAP], and the inferior vena caval flow [IVCF]) to be optimized to maximize the venous drainage flow (DF) during partial cardiopulmonary bypass using eight venous cannulas of three different types and an original model circuit. The relationship between venous DF and the three factors is indicated by the multiple regression equation DF² = a PH + βRAP + γIVCF² + C, where α, β, and γ are regression estimates and C is a constant. Multiple regression analysis results showed that DF was positively correlated with PH and RAP and negatively correlated with IVCF. A long cannula with 12 side holes and 60 cm long was considered to be useful to yield the optimal venous drainage flow under the condition of maintenance of the flow balance (DF and ICVF) and the pressure balance (RAP and IVCP) at the zero point. Moreover, this model may allow extensive research in flow dynamics of venous cannula without involving human subjects.     

Open inferior vena caval anastomosis during bicaval heart transplantation

Performing a precise inferior vena caval (IVC) anastomosis during bicaval orthotopic heart transplantation can sometimes be challenging because of crowding of the operative field by the venous cannula and tourniquet. We performed bicaval orthotopic heart transplantation in 10 patients using an open IVC anastomotic technique with vacuum-assisted venous drainage. A long venous cannula was passed into the IVC through the femoral vein. The IVC anastomosis was performed after removing the IVC tourniquet under vacuum-assisted venous drainage. A precise edge-to-edge IVC anastomosis was successfully performed in all patients. This technique may result in greater anastomotic precision and improved outcomes.     

Cannulae and Cell Saver Design: Do They Make a Difference?

In the evolution of cardiopulmonary bypass (CPB), it is becoming increasing obvious that minimizing microembolization is critical in protecting the brain. Every component of the CPB circuit and ancillary apparatus must be evaluated and, if necessary, re-engineered with the reduction of microemboli a major focus. Cardiotomy suction has been identified as a major source of lipid microemboli. However, is the alternative blood treatment apparatus, the cell saver, capable of reducing the lipid embolic load and are all cell savers equally efficient? In the event that microemboli do make it to the aorta, is it possible to divert them away from the brain to more robust vascular beds through clever design of the aortic cannula? Is the venous cannula a source of microgaseous emboli? The answer is yes to both questions. Emboli can be directed away from the brain by the positioning and design of the aortic cannula and the venous cannulae may be a source of gaseous microemboli delivered to the oxygenator by the venous line but careful practice will prevent this type of embolic formation.     

Immediate post-LVAD implant support: two approaches

Increased use of left ventricular assist devices (LVAD) as bridges to transplant has revealed the need for short-term right heart support for deairing and right ventricular recovery. The two approaches described are implemented as the patient is weaned from regular cardiopulmonary bypass. Dependent on patient needs, the surgeon may select a high-flow or low-flow approach to what is essentially right heart bypass. Both methods use the existing venous drainage from the right side of the heart. The higher flow returns blood through a 0.25-in tube connected to a modified adult vent (AV) to the pulmonary artery (PA). This provides flows as high as 3.5 L/min. The low-flow method uses the cardioplegia line, which goes unused during LVAD insertion. It is attached to the same modified AV cannula, placed into the PA, with flows between 400 and 600 ml/min. Each method has its advantages, disadvantages, and quirks. The results are functionally successful in allowing support of the right heart and deairing of the ventricular device.     

Isoflurane and hypothermic cardiopulmonary bypass: vasodilation without metabolic effects

During cardiopulmonary bypass, isoflurane may have beneficial effects on systemic oxygen uptake and vascular resistance. For this reason, the effects of isoflurane during low-flow (1.6 L/min/m2), hypothermic (27 degrees to 29 degrees C) cardiopulmonary bypass on systemic hemodynamics and oxygen uptake were studied in 20 patients in a cross-over experiment. Mean arterial and central venous pressures were measured during two consecutive periods of 10 minutes' duration. Blood samples were aspirated at the end of each period from the arterial and venous lines and analyzed for oxygen content. The concentration of isoflurane in the arterial samples was also determined. Systemic oxygen uptake and vascular resistance were calculated. Isoflurane had no significant effect on systemic oxygen uptake. Significant inverse relationships between blood isoflurane concentration and both mean arterial pressure and systemic vascular resistance were found. It is concluded that isoflurane is a vasodilator under the abnormal conditions of hypothermic cardiopulmonary bypass, but has no effect on systemic oxygen uptake.     

Comparative effects of propofol versus fentanyl on cerebral oxygenation state during normothermic cardiopulmonary bypass and postoperative cognitive dysfunction

BACKGROUND: The purpose of this study was to examine the comparative effects of propofol and fentanyl on cerebral oxygenation during normothermic cardiopulmonary bypass and postoperative cognitive dysfunction. METHODS: One hundred eighty patients scheduled for elective coronary artery bypass grafting were randomly divided into two groups: propofol group (n = 90) and fentanyl group (n = 90). After induction of anesthesia, a fiberoptic oximetry oxygen saturation catheter was inserted into the right jugular bulb to monitor jugular venous oxygen hemoglobin saturation continuously. Hemodynamic measurements and arterial and jugular venous blood gases were measured at seven time points. All patients underwent a battery of neurologic and neuropsychological tests on the day before the operation and at 6 months after the operation. RESULTS: Cerebral desaturation (defined as a jugular venous oxygen hemoglobin saturation value less than 50%) during cardiopulmonary bypass was more frequent in the fentanyl group than in the propofol group. Cerebral desaturation time (duration when jugular venous oxygen hemoglobin saturation was less than 50%) and the ratio of cerebral desaturation time to total cardiopulmonary bypass time in the fentanyl group differed significantly from those in the propofol group (fentanyl group: 27 +/- 14 minutes, 20% +/- 9%; propofol group: 18 +/- 11 minutes, 14% +/- 7%, respectively, p < 0.05). There was no significant difference in postoperative cognitive dysfunction at 6 months after operation between the two groups (propofol group: 5 of 77, 6%; fentanyl group: 5 of 75, 7%). CONCLUSIONS: Propofol preserved cerebral oxygenation state estimated by jugular venous oxygenation during cardiopulmonary bypass compared with the fentanyl group. However, propofol did not affect postoperative cognitive dysfunction.     

Venous air in the bypass circuit: a source of arterial line emboli exacerbated by vacuum-assisted drainage.

BACKGROUND: Arterial emboli cause neurocognitive deficits in cardiac surgical patients. Carotid artery emboli, detected ultrasonically, have been observed after venous air entrainment into the cardiopulmonary bypass circuit. We investigated in vitro the extent to which venous air affected emboli detected in the arterial line downstream from a 40-microm filter. METHODS: Using salvaged clinical cardiopulmonary bypass circuits, fixed volumes of air were introduced into the venous return line at unrestricted rates and at fixed rates using gravity venous drainage and vacuum-assisted venous drainage. Emboli counts were recorded distal to the arterial line filter using a 2-MHz pulsed-wave Doppler monitor. Emboli counts were similarly recorded after the introduction of carbon dioxide into the venous return line instead of air. RESULTS: The number of emboli rose with increasing volumes of entrained venous air (p < 0.001), and there was an almost tenfold increase with vacuum-assisted venous drainage (p < 0.0001) compared with gravity venous drainage. Venous air was entrained at a significantly faster rate under vacuum-assisted venous drainage (p < 0.0001). When the entrainment rate of venous air was fixed, the difference in emboli numbers recorded for gravity and assisted venous drainage was not significant. There was a significant reduction in arterial line emboli when carbon dioxide rather than air was entrained under both vacuum-assisted and gravity drainage (p < 0.001). CONCLUSIONS: Entrained venous air during cardiopulmonary bypass is a potential hazard, particularly during vacuum-assisted venous drainage. Every effort should be made to avoid venous air entrainment.     

Establishment of an animal model of non-transthoracic cardiopulmonary bypass in rats

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Modified aortic cannulation for cardiopulmonary bypass in neonatal piglet model

Abstract   Animal models are still essential for studying effects of cardiopulmonary bypass. We describe modifications in cannulation technique for a neonatal piglet model, which may also serve as an "everyday" technique in congenital cardiac surgery (age of animals <7 days; mean body weight 2.9 ± 0.5 kg). Surgical approach through median sternotomy and cardiopulmonary bypass was established by cannulating right atrium and ascending aorta with a modified aortic root cannula. Left ventricular venting was performed placing a cannula into the apex and connecting this to the venous drainage line. The described technique has been applied in 19 cases, all but one were without technical problems.     

Detection of lower torso ischemia by near-infrared spectroscopy during cardiopulmonary bypass in a 6.8-kg infant with complex aortic anatomy

Neonates and small infants with congenital heart disease and complex cardiac and vascular anatomy are particularly prone to episodes of complete or incomplete regional ischemia during cardiopulmonary bypass. These episodes may result either from inhomogeneous distribution of arterial blood flow via the aortic cannula or from impaired drainage of blood via the venous cannulae. However, techniques for continuous routine monitoring of regional perfusion in neonates or small infants undergoing cardiopulmonary bypass are extremely limited. Over recent years, transcranial near-infrared spectroscopy has become established as a useful technique for the non-invasive monitoring of cerebral oxygenation. Here we present a case in which simultaneous near-infrared spectroscopic monitoring of the oxygenation status in the brain and the right upper thigh revealed lower torso ischemia due to accidental cross-clamping of a hypoplastic descending aorta which would otherwise have been unnoticed. This shows that parallel near-infrared spectroscopy of the brain and the lower extremities may represent a novel non-invasive monitoring technique to ensure adequate cerebral and extracerebral perfusion during cardiopulmonary bypass.     

Blood management issues: getting clots together when you want them

Coagulation is a complex process that allows whole blood to form clots at tissue and vessel sites where damage has occurred. Activation of the hemostasis system causes platelets and fibrin-containing clot to stop the bleeding. Perfusionists must find ways to preserve the coagulation system if we are to avoid bleeding in the cardiopulmonary bypass patient. It is still unclear what techniques are best to continue maintaining hemostasis and avoiding transfusion in patients requiring cardiopulmonary bypass (CPB). There are numerous factors that come into play with the use of CPB including deactivating the coagulation system with anticoagulants, hemodilution of the circulating blood volume, inflammatory response, and a possible pro-coagulant response from protamine with heparin reversal once the surgical procedure has been completed and CPB terminated. All these factors make achieving hemostasis post CPB extremely difficult. This review attempts to assess what is currently being discussed in the literature, which may improve hemostasis with cardiopulmonary bypass. There is still no one technique that will improve hemostasis post CPB. Perhaps the answer may lie in a combination of reported techniques that may in some way lead to the preserving of coagulation factors during CPB.     

A Novel Technique for Cardiopulmonary Bypass Using Vacuum System for Venous Drainage with Pressure Relief Valve: An Experimental Study

To decrease the circuit priming volume, develop safety, and simplify the equipment, a cardiopulmonary bypass (CPB) circuit using a vacuum suction venous drainage system with a pressure relief valve was developed. The efficacy of this vacuum system was compared to that of a conventional siphon system. The system contains a powerful vacuum generator and a pressure relief valve to keep the negative pressure constant when blood suction is used. Using 8 mongrel dogs, the feasibility and the efficacy of this CPB system was tested. The changes in the negative pressure in the reservoir were within 5 mm Hg whether the suction lines were switched on or off. In all animals the amount of blood in the venous reservoir was stable throughout bypass. The decrease of priming volume was from 725 ml (siphon system) to 250 ml (vacuum system). At the end of CPB, the levels of hemoglobin in the vacuum system were significantly higher than those in the siphon system. These results demonstrated that this vacuum drainage system can provide simplification and a miniaturization of the cardiopulmonary bypass circuit resulting in low hemodilution during CPB.     

Clinical application of the M-numbers of aortic cannulas during hypothermic cardiopulmonary bypass in pediatric patients

A standardized system to describe the pressure-flow characteristics of a given cannula has recently been proposed and has been termed the M-number system. Using 3 different sizes of aortic cannulas in 50 pediatric cardiac patients on hypothermic cardiopulmonary bypass, we analyzed the correlation between experimentally and clinically derived M-numbers and found it to be positive. Clinical M-numbers were typically 0.35 to 0.55 greater than experimental M-numbers and correlated inversely with a patient's temperature change; this was most probably due to increased blood viscosity arising from hypothermia. This inverse relationship was more marked in higher M-number cannulas. The clinical data obtained in this study suggest that the experimentally derived M-number correlates strongly with the clinical performance of the cannula and that the influence of temperature is significant.     

Critical values of hematocrit and mixed venous oxygen saturation as parameters for a safe cardiopulmonary bypass

Objective: Mixed venous oxygen saturation (SvO₂) is high despite a low hematocrit implies that the relationship between oxygen demand and supply is in a safe state. This study was sought to determine the critical values for hematocrit and SvO₂ for safe cardiopulmonary bypass. Methods: Study 1: To evaluate the limit of hemodilution without cardiopulmonary bypass, normovolemic hemodilution with Dextran 40 (10%) was performed in 14 rabbits. SvO₂ was monitored from the right atrium, and the hemodynamic parameters were recorded continuously. Study 2: To determine the critical values for hematocrit and SvO₂ during cardiopulmonary bypass, normothermic and hypothermic cardiopulmonary bypass were performed in 13 rabbits and hemodynamic parameters were corrected. Results: Study 1: The heart rate decreased to unsafe levels abruptly, when the SvO₂ was ≦43% or the hematocrit was ≦10%. The lactate concentration increased when the SvO₂ was ≦46% or the hematocrit was ≦12%. Study 2: When the hematocrit was ≦12%, the SvO₂ decreased gradually. Even when weaning was possible, the animals with a hematocrit ≦12% collapsed hemodynamically within 40 minutes after cardiopulmonary bypass. Most of the animals could not be weaned from cardiopulmonary bypass during either normothermic or hypothermic cardiopulmonary bypass when the SvO₂ was ≦46%. Conclusions: Continuous monitoring of hematocrit and SvO₂ provides evidence-based guidelines for safe cardiopulmonary bypass. The lower limits of critical range for a safer cardiopulmonary bypass are hematocrit of 12% and SvO₂ of 46%.     

The Brain Uses Mostly Dissolved Oxygen During Profoundly Hypothermic Cardiopulmonary Bypass

Background. During profoundly hypothermic cardiopulmonary bypass, cerebral venous oxygen saturation increases (eg, to 98% at 15°C). We reanalyzed results of clinical studies to learn why.

Methods. One hundred sixty-eight cerebral oxygen transport measurements were available from 96 infants and children undergoing profoundly hypothermic cardiopulmonary bypass during repair of congenital heart defects.

Results. Dissolved oxygen accounted for 2% to 17% of arterial oxygen content, depending on the arterial oxygen partial pressure and hemoglobin concentration. The fraction of the cerebral metabolic rate for oxygen obtained from dissolved oxygen depended on pump flow, temperature, hemoglobin concentration, and arterial oxygen partial pressure (all p < 10⁻³). For “full-flow” cardiopulmonary bypass, temperatures less than 18°C, and arterial oxygen partial pressure measurements more than 180 mm Hg, the mean ± standard deviation of the fraction of cerebral metabolic rate for oxygen obtained from dissolved oxygen equaled 77% ± 19%.

Conclusions. Dissolved oxygen satisfies most of the brain's oxygen requirements during profound hypothermic cardiopulmonary bypass. This result reflects four properties of profound hypothermic cardiopulmonary bypass: (1) increases in hemoglobin's oxygen affinity due to profound hypothermia (which impairs oxygen transfer from hemoglobin to cerebral tissue), (2) use of hemodilution, (3) use of high arterial oxygen partial pressure, and (4) low cerebral metabolic rate of oxygen.