Comparison of Mini-Cardiopulmonary Bypass System With Air-Purge Device to Conventional Bypass System

'Goal-directed extracorporeal circulation: transferring the knowledge and experience from daily cardiac surgery to extracorporeal membrane oxygenation'

Metabolism management plays an essential role in extracorporeal technologies. There are different metabolic management devices integrated to extracorporeal devices; the most commonly used and accepted metabolic target in adult patients is indexed oxygen delivery (280 mL/min/m²) and cardiac index (2.4 L/min/m²), which can be managed independently or according to other metabolic parameters. Extracorporeal membrane oxygenation (ECMO) is a temporary form of life support providing a prolonged biventricular circulatory and pulmonary support for patients experiencing both pulmonary and cardiac failure unresponsive to conventional therapy. The goal-directed perfusion initiative during cardiopulmonary bypass (CPB) reduced the incidence of acute kidney injury after cardiac surgery. On the basis of the available literature, the identified goals to achieve during CPB include maintenance of oxygen delivery > 300 mL O₂/min/m² and reduction in vasopressor use. ECMO and CPB are conceptually similar but differ in many aspects and finality; in particular, they differ in the scientific evidence for metabolic management nadirs. As for CPB, predictive target parameters have been found and consolidated, particularly in terms of acute renal injury and the prevention of anaerobic metabolism, while for ECMO management, a blurred path remains. In this context, we review the strategies for optimal goal-directed therapy during CPB and ECMO, trying to transfer the knowledge and experience from daily cardiac surgery to veno-arterial ECMO.

Modular minimally invasive extracorporeal circulation ensures perfusion safety and technical feasibility in cardiac surgery; a systematic review of the literature

INTRODUCTION

Despite extensive evidence that shows clinical of superiority of MiECC, worldwide penetration remains low due to concerns regarding air handling and volume management in the context of a closed system. The purpose of this study is to thoroughly investigate perfusion safety and technical feasibility of performing all cardiac surgical procedures with modular (hybrid) MiECC, as experienced from the perfusionist's perspective.

METHODS

We retrospectively reviewed perfusion charts of consecutive adult patients undergoing all types of elective, urgent, and emergency cardiac surgery under modular MiECC. The primary outcome measure was perfusion safety and technical feasibility, as evidenced in the need for conversion from a closed to an open circuit. A systematic review of the literature was conducted aiming to ultimately clarify whether there are any safety issues regarding MiECC technology.

RESULTS

We challenged modular MiECC use in a series of 403 consecutive patients of whom a significant proportion (111/403; 28%) underwent complex surgery including reoperations (4%), emergency repair of acute type A aortic dissection and composite aortic surgery (1.7%). Technical success rate was 100%. Conversion to an open circuit was required in 18/396 patients (4.5%), excluding procedures performed under circulatory arrest. Open configuration accounted for 40% ± 21% of total procedural perfusion time and was related to significant hemodilution and increase in peak lactate levels. Systematic review revealed that safety of the procedure challenged originated from a single report, while no clinical adverse event related to MiECC was identified.

CONCLUSIONS

Use of modular MiECC secures safety and ensures technical feasibility in all cardiac surgical procedures. It represents a type III active closed system, while its stand-by component is reserved for a small (<5%) proportion of procedures and for a partial procedural time. Thus, it eliminates any safety concern regarding air handling and volume management, while it overcomes any unexpected intraoperative scenario.

Can venous cannula design influence venous return and negative pressure with a minimally invasive extracorporeal circulation?

INTRODUCTION

Recent advances to make cardiopulmonary bypass more physiological include the use of kinetic-assisted venous drainage but without a venous reservoir. Despite manipulation of intravascular volume and patient positioning, arterial flow is frequently reduced. Negative venous line pressures can be generated, which may elicit gaseous microemboli. We investigated the influence of venous cannula design on venous return and negative venous line pressures.

METHODS

In a single-centre, single-surgeon, prospective, randomized, double-blind trial, 48 patients undergoing isolated coronary artery, aortic valve or combined coronary artery and aortic valve surgery, with a minimally invasive circuit, were randomized to a conventional two-stage (2S) or three-stage venous cannula (3S), or to a three-stage venous cannula with additional 'fenestrated' ridges (F3S). Blood flow, venous line pressures and gaseous microemboli number and size were measured.

RESULTS

The pump flow achieved was the same between groups, but in each case fell below the target range of 2.2-2.4 L min^-1 m^-2. The three-stage cannula recorded significantly lower negative pressure than the other cannulae. The total count and volume of gaseous emboli detected with the F3S cannulae was very high in some cases, with wide heterogeneity.

DISCUSSION

The low negative pressures recorded with three-stage cannula, despite having a larger drainage orifice area, suggest that negative pressure may be more influenced by lumen diameter and vena cava collapse rather than drainage hole size. The additional fenestrations resulted in flow characteristics and negative pressures similar to the larger two-stage cannula but are associated with generation of gaseous microemboli.

Air removal capacity of two different minimal invasive ECC systems: an in vitro comparison

Minimally invasive extracorporeal circulation systems are developed to decrease the deleterious effects of cardiopulmonary bypass. For instance, prime volume and foreign surface area are decreased in these systems. However, because of the lack of a venous reservoir in minimized systems, air handling properties of these minimally invasive extracorporeal circulation systems may be decreased as compared to conventional cardiopulmonary bypass systems. The aim of this in vitro study is to compare the air handling properties of two complete minimized cardiopulmonary bypass systems of two manufacturers, of which one system is provided with the air purge control. In an in vitro study, two minimally invasive extracorporeal circulation systems, Inspire Min.I manufactured by Sorin Group Italia, Mirandola, Italy (LivaNova, London, United Kingdom) and minimized extracorporeal circulation manufactured by Maquet, Rastatt, Germany (Getinge, Germany), were challenged with two types of air challenges; a bolus air challenge and a gaseous microemboli challenge. The air removal characteristics of the venous bubble traps and of the complete minimally invasive extracorporeal circulation systems were assessed by measuring the gaseous microemboli volume and number downstream of the venous bubble traps in the arterial line with a bubble counter. No significant differences were observed in air reduction between the venous bubble traps of Getinge (venous bubble traps) and LivaNova (Inspire venous bubble traps 8 in conjunction with the air purge control). Similarly, no significant differences were observed in volume and number of gaseous microemboli in the arterial line of both complete minimally invasive extracorporeal circulation systems. However, the gaseous microemboli load of the Inspire Min.I system was marginally lower after both the bolus air and the gaseous microemboli challenges. Both minimally invasive extracorporeal circulation systems assessed in this study, the LivaNova Inspire Min.I and the Getinge minimized extracorporeal circulation, showed comparable air removal properties, after both bolus and gaseous microemboli air challenges. Besides, air purge control automatic air removal system provided with the LivaNova Inspire Min.I. system may enhance patient's safety with the use of a minimally invasive extracorporeal circulation system. We consider both systems equally safe for clinical use.

Miniaturized versus conventional cardiopulmonary bypass and acute kidney injury after cardiac surgery

Introduction:

Acute kidney injury (AKI) is a serious complication after coronary artery bypass grafting (CABG). There are conflicting reports whether a miniaturized cardiopulmonary bypass (MCPB) system is associated with a lower AKI incidence compared with conventional cardiopulmonary bypass (CCPB). It is unknown if AKI risk factors differ between the two groups. We assessed if MCPB decreases AKI after CABG and compared the risk factors between both groups.

Methods:

Sixty-eight Asian patients presenting for elective CABG at a tertiary heart centre were enrolled. They were randomly assigned to MCPB (n=34) or CCPB group (n=34) and followed up in a single-blinded, prospective, randomized, controlled trial. The primary outcome was Acute Kidney Injury Network stage 1 AKI.

Results:

The AKI incidence was 21.5% and was not significantly different between patients undergoing MCPB versus CCPB (21.9% versus 21.2%, p=0.948). The first CPB haematocrit was independently associated with AKI in the MCPB group (Relative Risk [RR]=0.484, 95% Confidence Interval [CI]=0.268-0.876, p=0.016); post-operative blood loss and inflammation were independently associated with AKI in the CCPB group (RR=1.005, 95%CI=1.003-1.007, p<0.001; RR=1.018, 95%CI=1.010-1.028, p<0.001).

Conclusion:

The MCPB system is not associated with a lower incidence of AKI in Asian patients undergoing CABG. Risk factors for AKI differed between patients using the MCPB and CCPB systems.

The inflammatory response between miniaturised and conventional cardiopulmonary bypass after cardiac surgery in an Asian population

INTRODUCTION

We compared the systemic inflammatory response of the MCPB system to the CCPB system with cell salvage and phosphorylcholine-coated tubing amongst Asian patients undergoing coronary artery bypass grafting.

METHODS

Seventy-eight patients were randomly assigned to the MCPB or the CCPB groups equally and followed up in a prospective, single-blinded, randomised, controlled trial. Levels of TNF-α, IL-6, CRP and LDH were measured peri-operatively.

RESULTS

The systemic inflammatory response was similar in both groups (TNF-α: p=0.222; IL-6: p=0.991; CRP: p=0.258). Only haemolysis was significantly higher in the CCPB group (LDH: p=0.011). The MCPB system was twice more expensive, but had a near 4-fold cost saving in tranfusions. Overall, the MCPB system cost 20% more than the modified CCPB system.

CONCLUSION

These results corroborate with studies that demonstrated the avoidance of cardiotomy suction rather than the MCPB system, itself, leads to an attenuated inflammatory response. The absence of obvious clinical benefit and the higher costs involved with the MCPB system would preclude its routine use.

Minimal extracorporeal circulation (MECC) does not result in less hypertrophic scar formation as compared to conventional extracorporeal circulation (CECC) with dexamethasone

INTRODUCTION

Cardiopulmonary bypass surgery is associated with a systemic inflammatory response through the interaction of air, blood and synthetic components in the bypass system and the physical trauma of surgery. An alternative cardiopulmonary bypass system, minimal extracorporeal circulation (MECC), has shown promising results in terms of reducing the inflammatory response. We hypothesized that this system may reduce pathological excessive scarring. To study this assumption, the effects of MECC and the effects of conventional extracorporeal circulation (CECC) with dexamethasone on skin scarring were compared in a standardized wound-healing model.

METHODS AND RESULTS

Pre-sternal scars were evaluated prospectively at four and 12 months postoperatively. The height and width of the scars were measured, using a slide caliper and sonography. The scars were scored using the validated Patient and Observer Scar Assessment Scale. Additional risk factors for hypertrophic scar formation were identified by means of a questionnaire. During surgery, MECC was used in 45 patients and CECC/dexamethasone in 42 patients. Four months postoperatively, 22 patients of the MECC group (49%) and 18 patients in the CECC/dexamethasone group (43%) had developed hypertrophic scars. Twelve months postoperatively, the hypertrophic scars in four patients of the MECC group and in two patients of the CECC/dexamethasone group had become normotrophic. In 18 patients of the MECC group (38%) and 16 patients of the CECC group (41%) the scars remained hypertrophic at 12 months. These differences between the two groups were not statistically significant.

CONCLUSION

MECC does not reduce hypertrophic scar formation compared with CECC with dexamethasone, but its use is more beneficial than the use of CECC/dexamethasone because of the circulatory and immunological advantages and because treatment with dexamethasone can be omitted.

Miniaturized cardiopulmonary bypass: the Hammersmith technique

Background

Conventional Cardiopulmonary Bypass (cCPB) is a trigger of systemic inflammatory reactions, hemodilution, coagulopathy, and organ failure. Miniaturised Cardiopulmonary Bypass (mCPB) has the potential to reduce these deleterious effects. Here, we describe our standardised ‘Hammersmith’ mCPB technique, used in all types of adult cardiac operations including major aortic surgery.

Methods

The use of mCPB remains limited by the diversity of technologies which range from extremely complex, micro systems to ones very similar to cCPB. Our approach is designed around the principle of balancing the benefits of miniaturisation; reducing foreign surface area while maintaining patient safety.

Results

From January 2010 to March 2011, a single surgeon performed 184 consecutive operations (Euro score Logistic 8.4+/-9.9): 61 aortic valve replacements, 78 CABGs, 25 aortic valve replacement and CABG and 17 other procedures (major aortic surgery, re-do operations or double/triple valve replacements).

Our clinical experience suggests that:

i. Venous drainage is optimally maintained using kinetic energy.

ii. Venous collapse pressure depends on the patient’s anatomy and cannula size, but most importantly on the negative pressure generated by venous drainage.

iii. The patient-prime interaction is optimised with antegrade and retrograde autologous priming, which mixes the blood and prime away from the tissues and results in a reduced oncotic destabilization.

iv. mCPB is a safe and reproducible technique

Conclusion

The Hammersmith mCPB is a “next generation” system which uses standard commercially available components. It aims to maintain safety margin and the benefit of miniaturised system whilst reducing the human factor demands.

Oxygen delivery during cardiopulmonary bypass (and renal outcome) using two systems of extracorporeal circulation: a retrospective review

OBJECTIVES

To investigate the combined influence of blood flow and haemodilution with either a miniaturized (Mini-CPB) or a conventional cardiopulmonary bypass (C-CPB) circuit on average oxygen delivery during bypass. The influence of this on clinical outcome, particularly renal dysfunction after routine coronary artery bypass surgery (CABG), was measured.

METHODS

Retrospective analysis in two groups of 160 patients based on the surgeon's preference for bypass circuit. We compared consecutive patients undergoing isolated CABG surgery by two surgeons using Mini-CPB with a matched cohort of patients, from the same period, undergoing isolated CABG surgery by four other surgeons using a C-CPB. No trial-related intervention occurred. Data on bypass circuit parameters and clinical outcomes were acquired from routinely collected data sources.

RESULTS

Average cardiopulmonary bypass pump flow was significantly lower with Mini-CPB compared with C-CPB. Mini-CPB resulted in significantly less haemodilution. The resultant calculated average oxygen delivery provided by the two systems was the same. Percentage change in plasma creatinine was significantly and inversely related to the oxygen delivery during CPB. There was no difference in percentage change in plasma creatinine between groups. The risk of having Acute Kidney Injury Network (AKIN) score ≥ 1 increased 1% for every 1 ml min(-1) m(-2) decrease in oxygen delivery (P = 0.0001, OR 0.990, 95% CI 0.984-0.995).

CONCLUSIONS

Despite aiming for the same target pump flow, periodic limitations of venous return to the pump resulted in a significant reduction in average flow delivered to the patient by Mini-CPB. Less haemodilution compensated for this reduction, so that the average oxygen delivery was the same. The association between oxygen delivery and postoperative change in plasma creatinine was evident in both groups. Further work to understand whether there is a particular cohort of patients who benefit (or are put at risk) by one method of CPB vs the other is warranted.