Minimally invasive versus conventional extracorporeal circulation circuits in patients undergoing coronary artery bypass surgery: a propensity-matched analysis

Abstract

Objectives:

Minimally invasive extracorporeal circulation circuits provide several advantages compared to conventional extracorporeal circulation circuits. We compared the results of a minimally invasive extracorporeal circulation system with those of conventional extracorporeal circulation system, in patients undergoing isolated coronary artery bypass grafting.

Methods:

We identified 753 consecutive patients who underwent coronary artery bypass grafting at our centre between October 2014 and September 2016. These patients were divided into two groups: a minimally invasive extracorporeal circulation group (M, n = 229) and a conventional extracorporeal circulation group (C, n = 524). Baseline parameters, details of cardiac surgery as well as postoperative complications and outcomes were compared by means of a propensity-matched analysis of 180 matched pairs.

Results:

The median EuroSCORE II was 1.3%. Transfusion requirement of packed red blood cells (p = 0.002) was lower in Group M compared to conventional extracorporeal circulation systems. There were no differences in hospital mortality or in rates of adverse events between the matched groups. Total in-hospital mortality of the cohort was 1.7%.

Conclusion:

The use of minimally invasive extracorporeal circulation is associated with a significantly lower use of blood products after isolated coronary revascularisation. There were no differences concerning duration of surgery, complication rates and mortality between the groups. Therefore, the application of minimally invasive extracorporeal circulation systems should be considered as preferred technique in isolated coronary artery bypass grafting procedures.

Keywords

minimally invasive extracorporeal circulation circuits coronary artery bypass surgery

Introduction

The minimally invasive extracorporeal circulation (MiECC) circuit was designed to attenuate the potentially harmful effects of conventional extracorporeal circulation (CECC) circuits by reducing the blood–air interface, decreasing the surface area of the tubing, optimising the surface coating of components and requiring lower priming volumes.^1,2 They are postulated to attenuate the effects of systemic inflammatory response syndrome (SIRS) by generating lower levels of pro-inflammatory cytokines, neutrophil activation and thrombin deposition. Along with lower levels of inflammatory markers, MiECC circuits have also been reported to be associated with a lower level of myocardial injury, oxidative stress and end organ dysfunction.^3,4 The main components of a MiECC system include a closed cardiopulmonary bypass (CPB) circuit with a centrifugal pump, a membrane oxygenator, a heat exchanger and a cardioplegia system with biologically inert contact surfaces and reduced priming volumes. Additional optional components which can be included in the circuit are a pulmonary artery or vein vent, venous bubble trap, an aortic root vent, an arterial line filtration, a soft-shell reservoir, a hard-shell reservoir and a suction device.⁵ In this study, we review our experience with MiECC and compare it with CECC circuits in patients undergoing isolated coronary artery bypass grafting (CABG).

Patients and methods

Study design and definition of groups

We identified 753 consecutive patients who underwent isolated coronary artery revascularisation at our centre between October 2014 and September 2016. These patients were divided into two groups: the MiECC (M, n = 229) and the CECC group (C, n = 524). All patients consented to the cardiac surgery, postoperative treatment and data acquisition performed as part of routine patient care. All procedures described in this study were in accordance with the institutional research committee, national data safety regulations, and the 1964 Helsinki Declaration and its last amendment by the 64th WMA General Assembly, Fortaleza, Brazil, October 2013. Informed patient consent was not required by the institutional research committee for this retrospective, non-interventional study.

Preoperatively, patients on vitamin K antagonists were bridged with intravenous heparin to achieve a partial thromboplastin time (PTT) ranging from 50 to 60 seconds. Intraoperatively, an activated clotting time (ACT) of 400 seconds was maintained as per our institutional standard. Newer reports suggest that an ACT of 300 seconds may also be safely applied on MiECC procedures.⁶ Postoperatively, all patients received body weight adjusted intravenous low-dose heparin (0.07 IU/kg/min) starting 6 hours after surgery until the first postoperative day. Subsequently, body weight adjusted low molecular weight heparin (<50 kg, 5,000 IU; 50-100 kg, 7,500 IU; >100 kg, 10,000 IU) was administered subcutaneously. Patient blood management was standardised and performed in accordance with the recommendations by Meybohm et al.⁷

Technical characteristics of the MiECC and CECC circuits

In Group M, the ROCsafe mini-HLM system (Terumo Corporation, Ann Arbor, MI, USA) was used. This MiECC circuit was a polymethoxyethylacrylate-coated (PMEA; X-coating; Terumo Corporation) closed-loop system with a centrifugal pump and a microporous polypropylene fibre oxygenator (Capiox FX25; Terumo Corporation) with an integrated bubble filter. The priming volume used in this system was about 950 mL, which consisted of 250 mL of 15% mannitol and 700 mL of lactate-free electrolyte solution. A 24-F arterial cannula (Maquet, Getinge Group, Rastatt, Germany) and a 29-F three-stage venous cannula (Medtronic MC2X^®) for drainage were used. In this group, warm Calafiore blood cardioplegia was used.

In the CECC group, two different CECC systems were used. Both were conventional open ECC circuits, one system with a centrifugal pump (Sorin Group Germany GmbH, Munich) and the second with a roller pump (Terumo Corporation). The first CECC circuit was coated with albumin and heparin (BIOLINE Coating; Maquet, Getinge Group). The priming volume was 1,550 mL, which consisted of 250 mL of 15% mannitol and 1,300 mL of lactate-free electrolyte solution. The second CECC used had a polymethoxyethylacrylate-coated circuit (PMEA; X-coating; Terumo Corporation). The priming volume of this system was 1,250 mL: 250 mL of 15% mannitol and 1,000 mL lactate-free electrolyte solution. In the CECC group, warm Calafiore blood cardioplegia as well cold Buckberg cardioplegia was used.

In all the ECC circuits, 5,000 IU of heparin was added to the priming volume. The ECC was located in the same position relative to the patient in all cases and the length of tubing was comparable in all cases. Equivalent flow rates were observed in all groups. The cardiotomy suction was directly returned into the ECC in the CECC group, while in the MiECC group, auto-transfusion of blood was performed by passing collected blood through a cell-saver (Medtronic autoLog^® Autotransfusion System).

Indication for transfusion of blood products

At our institution, packed red blood cells (PRBC; 300 mL/unit) were transfused when the blood haemoglobin levels fell below 8.0 g/dL. Postoperatively, haemoglobin levels were determined routinely every 2 hours. Platelet concentrates (PC) were transfused only in case of severe bleeding which was defined as a blood loss of more than 200 mL over the chest tubes every hour for at least 2 hours taking into account the patient’s clinical status and haemoglobin values. Fresh frozen plasma (FFP) was used only in case of severe therapy refractory hypovolemic shock and where the blood volume could not be adequately replaced with other volume expanders (i.e. crystalloids and 20% human albumin).

Data collection and statistical analysis

All patients consented to surgery; postoperative treatment and data acquisition were performed as part of routine patient care. Patient details were collected from our institutional database and de-identified. In addition, the EuroSCORE II was calculated, which predicted the total perioperative mortality as well as the Cleveland Clinic Score to predict acute kidney injury after cardiac surgery. Data were analysed using IBM SPSS version 25 (Statistical Package for the Social Sciences). Categorical variables were evaluated using chi-square and Fisher’s exact methods, and continuous variables were evaluated using Mann–Whitney’s U-test. All analyses were two-tailed. The null hypothesis was rejected and significant difference was assumed with p-values < 0.05. Data are presented as medians (interquartile range) or absolute values (percentages) unless otherwise specified. To compensate for the differences in this retrospective, non-randomised study, a propensity score-matching analysis was performed. For this purpose, logistic regression was used to develop a propensity score. A propensity score difference of 0.05 was used as a maximum calliper for matching the two groups. Factors included to compute the propensity score were as follows: age, gender, body mass index, left ventricular ejection fraction, EuroSCORE II coronary artery disease and revascularisation strategy, that is, total arterial revascularisation or use of venous grafts. This resulted in the formation of 180 matched pairs. Due to the matching, 49 patients of the MiECC group and 344 patients of the CECC group have not been considered in the following analysis.

Results

Baseline parameters of the total cohort are listed in Table 1 and the characteristics of the matched populations are listed in Table 2. The median age of the matched cohort was 64 years (p = 0.888), among which, 22.5% of patients were female (p = 0.103). The median EuroSCORE II of our cohort was 1.3% and was comparable among the groups (p = 0.700). A total of 6.1% of patients presented with single vessel disease (p = 0.122), 20.8% with two vessel disease (p = 0.194) and 84.7% with three vessel disease (p = 0.812). In the matched patient cohort, we did not observe any differences in the baseline characteristics.

Table 1.

Baseline parameters.

	Group M (n = 229)	Group C (n = 524)	Overall (n = 753)	p-value
Baseline parameters
Age (years)	66 (57-75)	70 (61-76)	69 (60-76)	0.003
Female (%)	47 (20.5)	90 (17.2)	137 (18.2)	0.160
Body mass index (kg/m²)	28.3 (25.9-31.8)	28.1 (25.3-31.6)	28.1 (25.4-31.6)	0.498
LVEF (%)	55 (45-60)	55 (45-60)	55 (45-60)	0.275
EuroSCORE II (%)	1.4 (1.0-2.3)	1.6 (1.1-2.5)	1.6 (1.1-2.5)	0.014
Cleveland Clinic Score (%)	0.4 (0.4-0.4)	0.4 (0.4-0.4)	0.4 (0.4-0.4)	0.391
Cleveland Clinic Score (mean ± SD)	0.6 ± 0.5	0.8 ± 1.5	0.8 ± 1.3	0.391
Comorbidities
Arterial hypertension (%)	195 (85.2)	456 (87.0)	651 (86.5)	0.489
Atrial fibrillation (%)	28 (12.2)	54 (10.3)	82 (10.9)	0.447
Insulin-dependent diabetes (%)	46 (20.1)	80 (15.3)	126 (16.7)	0.112
Chronic kidney disease (%)	51 (22.3)	112 (21.4)	163 (21.6)	0.774
Hyerlipidemia (%)	115 (50.2)	264 (50.4)	379 (50.3)	1.000
Hyperuricemia (%)	21 (9.2)	51 (9.7)	72 (9.6)	0.893
COPD (%)	21 (9.2)	38 (7.3)	59 (7.8)	0.378
Pulmonary hypertension (%)	0 (0.0)	2 (0.4)	2 (0.3)	1.000
Coronary artery disease
Single vessel disease (%)	15 (6.6)	7 (1.3)	22 (2.9)	0.000
Two vessel disease (%)	34 (14.8)	59 (11.3)	93 (12.4)	0.186
Three vessel disease (%)	180 (78.6)	458 (87.4)	638 (84.7)	0.003

COPD: chronic obstructive pulmonary disease; EuroSCORE: European System for Cardiac Operative Risk Evaluation; LVEF: left ventricular ejection fraction; SD: standard deviation.

Data are presented as medians (25th-75th percentiles) or absolute values (percentages).

Table 2.

Baseline parameters matched.

	Group M (n = 180)	Group C (n = 180)	Overall (n = 360)	p-value
Baseline parameters
Age (years)	63 (56-74)	64 (57-72)	64 (56-72)	0.888
Female (%)	35 (19.4)	46 (25.6)	81 (22.5)	0.103
Body mass index (kg/m²)	28.7 (26.0-31.7)	28.5 (25.0-32.0)	28.6 (25.6-31.9)	0.708
EuroSCORE II (%)	1.3 (0.9-2.0)	1.4 (0.9-2.0)	1.3 (0.9-2.0)	0.700
Cleveland Score (median)	0.4 (0.4-0.4)	0.4 (0.4-0.4)	0.4 (0.4-0.4)	0.207
Cleveland Score (mean ± SD)	0.6 ± 0.5	0.5 ± 0.4	0.6 ± 0.5	0.207
LVEF (%)	55 (45-60)	55 (50-60)	55 (50-60)	0.505
Comorbidities
Arterial hypertension (%)	150 (83.3)	151 (83.9)	301 (83.6)	1.000
Atrial fibrillation (%)	27 (15.0)	25 (13.9)	52 (14.4)	0.881
Insulin-dependent diabetes (%)	42 (23.3)	49 (27.2)	91 (25.3)	0.467
Chronic kidney disease (%)	40 (22.2)	37 (20.6)	77 (21.4)	0.797
Hyerlipidemia (%)	92 (51.1)	91 (50.6)	183 (50.8)	1.000
Hyperuricemia (%)	18 (10.0)	16 (8.9)	34 (9.4)	0.857
COPD (%)	19 (10.6)	21 (5.8)	40 (11.1)	0.867
Pulmonary hypertension (%)	0 (0.0)	0 (0.0)	0 (0.0)	−
Coronary artery disease
Single vessel disease (%)	15 (8.3)	7 (3.9)	22 (6.1)	0.122
Two vessel disease (%)	32 (17.8)	43 (23.9)	75 (20.8)	0.194
Three vessel disease (%)	133 (73.9)	130 (72.2)	263 (73.1)	0.812

COPD: chronic obstructive pulmonary disease; EuroSCORE: European System for Cardiac Operative Risk Evaluation; LVEF: left ventricular ejection fraction; SD: standard deviation.

Data are presented as medians (25th-75th percentiles) or absolute numbers (percentages).

Details of the surgical procedures performed are presented in Table 3 and in the matched patient cohort in Table 4. Indications for surgery were elective in 92.8% of the cases (p = 0.839) and urgent in 5.6% (p = 0.819), and emergency surgery was performed in 1.7% of patients (p = 0.215). There were neither differences concerning CPB time nor aortic cross-clamp times in the matched cohort. A total of 31.7% of the patients underwent total arterial coronary revascularisation using the left internal mammary artery and the radial artery from the non-dominant hand as bypass grafts. Concomitant closure of the left atrial appendage and modified MAZE procedure for atrial fibrillation was performed in 1.1% (p = 1.000) and 1.9% (p = 0.449) of the patients, respectively.

Table 3.

Details of cardiac surgery.

	Group M (n = 229)	Group C (n = 524)	Overall (n = 753)	p-value
Median duration of surgery (minutes)	205 (185-230)	195 (175-230)	200 (175-230)	0.012
Median duration of cardiopulmonary bypass (minutes)	90 (73-107)	87 (72-103)	88 (72-104)	0.255
Median duration of aortic cross-clamping (minutes)	51 (42-63)	50 (41-62)	51 (41-62)	0.198
TAR (%)	58 (25.3)	96 (18.3)	154 (20.5)	0.031
CABG (%)	171 (74.7)	428 (81.7)	599 (79.5)	0.031
MAZE procedure (%)	2 (0.9)	4 (0.8)	6 (0.8)	1.000
LAA closure	5 (2.2)	18 (3.4)	23 (3.1)	0.491
Number of bypass grafts (median)	3 (2-4)	3 (3-4)	3 (3-4)	0.000
Number of bypass grafts (mean ± SD)	3.1 ± 0.9	3.4 ± 0.9	3.3 ± 0.8	0.000
Elective surgery (%)	194 (84.7)	404 (77.1)	598 (79.4)	0.019
Urgent surgery (%)	23 (10.0)	57 (10.9)	80 (10.6)	0.798
Emergency surgery (%)	12 (5.2)	63 (12.0)	75 (10.0)	0.004
Re-operation (%)	0 (0.0)	6 (1.1)	6 (0.8)	0.186

CABG: coronary artery bypass grafting; LAA: left atrial appendage; SD: standard deviation; TAR: total arterial revascularisation.

Data are presented as medians (25th-75th percentiles) or absolute values (percentages).

Table 4.

Details of cardiac surgery matched.

	Group M (n = 180)	Group C (n = 180)	Overall (n = 360)	p-value
Median duration of surgery (minutes)	200 (185-235)	198 (175-230)	200 (180-234)	0.070
Median duration of cardiopulmonary bypass (minutes)	89 (73-107)	86 (71-103)	87 (72-104)	0.308
Median duration of aortic cross-clamping (minutes)	52 (43-65)	51 (41-62)	52 (42-63)	0.218
TAR (%)	56 (31.1)	58 (32.2)	114 (31.7)	0.910
CABG (%)	124 (68.9)	122 (67.8)	246 (68.3)	0.910
MAZE procedure (%)	2 (1.1)	2 (1.1)	4 (1.1)	1.000
LAA closure (%)	5 (2.8)	2 (1.1)	7 (1.9)	0.449
Number of bypass grafts (median)	3 (2-4)	3 (3-4)	3 (3-4)	0.016
Number of bypass grafts (mean ± SD)	3.1 ± 0.9	3.2 ± 0.9	3.2 ± 0.9	0.016
Elective surgery (%)	168 (93.3)	166 (92.2)	334 (92.8)	0.839
Urgent surgery (%)	11 (6.1)	9 (5.0)	20 (5.6)	0.819
Emergency surgery (%)	1 (0.6)	5 (2.8)	6 (1.7)	0.215
Re-operation (%)	0 (0.0)	0 (0.0)	0 (0.0)	−

CABG: coronary artery bypass grafting; LAA: left atrial appendage; SD: standard deviation; TAR: total arterial revascularisation.

Data are presented as medians (25th-75th percentiles) or absolute numbers (percentages).

Postoperative complications and outcome are listed in Table 5 and of the matched population in Table 6. In the matched patient cohort, differences were observed in terms of postoperative complications, length of total hospital stay and postoperative mechanical ventilation (PMV) time. The total rate of re-explorative surgery was 1.7% (p = 0.0.685) and the rate of adverse cerebrovascular events was 1.7% (p = 0.685). Renal replacement therapy was required in 3.1% (p = 1.000) of patients. Overall in-hospital mortality was 1.7% (p = 1.000).

Table 5.

Postoperative adverse events and outcomes.

	Group M (n = 229)	Group C (n = 524)	Overall (n = 753)	p-value
Postoperative adverse events
Adverse cerebrovascular events (%)	2 (0.9)	7 (1.3)	9 (1.9)	0.730
Re-explorative surgery (%)	4 (1.7)	13 (2.5)	17 (2.3)	0.790
Pacemaker implantation (%)	8 (3.5)	4 (0.8)	12 (1.6)	0.010
Surgical site infection (%)	14 (6.1)	22 (4.2)	36 (4.8)	0.268
Nosocomial pneumonia (%)	8 (3.5)	16 (3.1)	24 (3.2)	0.822
New onset atrial fibrillation (%)	7 (3.1)	26 (5.0)	33 (4.4)	0.333
Renal replacement therapy (%)	8 (3.5)	17 (3.2)	25 (3.3)	0.828
Outcomes
In-hospital mortality (%)	3 (1.3)	6 (1.1)	9 (1.2)	1.000
Length of in-hospital stay (days)	8 (7-11)	9 (7-11)	9 (7-11)	0.538
Length of ICU stay (days)	2 (1-3)	2 (1-3)	2 (1-3)	0.018
Length of ICU stay (days) (mean ± SD)	2.5 ± 2.1	3.6 ± 7.5	3.2 ± 6.3	0.018
Length of PMV (hours)	18 (8-21)	18 (9-20)	18 (9-20)	0.165
Length of PMV > 20 hours (%)	64 (27.9)	107 (20.4)	171 (22.7)	0.029
Length of ICU stay > 7 days (%)	6 (2.6)	34 (6.5)	40 (5.3)	0.033
Length of in-hospital stay > 13 days (%)	26 (11.4)	66 (12.6)	92 (12.2)	0.717

ICU: intensive care unit; PMV: postoperative mechanical ventilation; SD: standard deviation.

Data are presented as medians (25th-75th percentiles) or absolute numbers (percentages).

Table 6.

Postoperative adverse events and outcomes matched.

	Group M (n = 180)	Group C (n = 180)	Overall (n = 360)	p-value
Postoperative adverse events
Adverse cerebrovascular events (%)	2 (1.1)	4 (2.2)	6 (1.7)	0.685
Re-explorative surgery (%)	4 (2.2)	2 (1.1)	6 (1.7)	0.685
Pacemaker implantation (%)	6 (3.3)	1 (0.6)	7 (1.9)	0.121
Surgical site infection (%)	14 (7.8)	12 (6.7)	26 (7.2)	0.839
Nosocomial pneumonia (%)	5 (2.8)	3 (1.7)	8 (2.2)	0.723
New onset atrial fibrillation (%)	4 (2.2)	7 (3.9)	11 (3.1)	0.542
Renal replacement therapy (%)	6 (3.3)	5 (2.8)	11 (3.1)	1.000
Outcomes
In-hospital mortality (%)	2 (1.1)	1 (0.6)	3 (1.7)	1.000
Length of hospital stay (days)	9 (7-11)	9 (8-11)	9 (7-11)	0.138
Length of ICU stay (days)	2 (1-3)	2 (1-3)	2 (1-3)	0.143
Length of PMV (days)	19 (10-21)	19 (11-20)	19 (11-21)	0.873
Length of PMV > 20 hours (%)	49 (27.2)	36 (20.0)	85 (23.6)	0.136
Length of ICU stay > 7 days (%)	3 (1.6)	11 (6.1)	14 (3.9)	0.053
Length of hospital stay > 13 days (%)	19 (10.6)	24 (13.3)	43 (11.9)	0.516

ICU: intensive care unit; PMV: postoperative mechanical ventilation.

Data are presented as medians (25th-75th percentiles) or absolute numbers (percentages).

With regard to the postoperative use of blood products (Table 8), the mean number of PRBC transfused was significantly lower in the MiECC group (p = 0.002), whereas there was no difference concerning the postoperative transfusion of PC or the FFP. Postoperative use of blood products matched is shown in Table 8.

Table 7.

Postoperative use of blood products.

	Group M(n = 229)	Group C(n = 524)	Overall(n = 753)	p-value
Use of PRBC
Number of units of PRBC transfused (median)	0 (0-0)	0 (0-0)	0 (0-2)	0.000
Units of PRBC transfused (mean ± SD)	0.9 ± 2.8	1.7 ± 4.7	1.4 ± 4.2	0.000
0 units of PRBC transfused (%)	177 (77.3)	323 (61.6)	500 (66.4)	0.000
1-4 units of PRBC transfused (%)	41 (17.9)	157 (30.0)	198 (26.3)	0.000
5-10 units of PRBC transfused (%)	9 (3.9)	33 (6.3)	42 (5.6)	0.229
More than 10 units of PRBC transfused (%)	2 (0.9)	11 (2.1)	13 (1.7)	0.363
Use of PC
Number of units of PC transfused (median)	0 (0-1)	0 (0-0)	0 (0-1)	0.450
Units of PC transfused (mean ± SD)	0.6 ± 1.1	0.7 ± 1.5	0.7 ± 1.4	0.450
0 PC transfused (%)	168 (73.4)	372 (71.0)	540 (71.7)	0.539
1-4 PC transfused (%)	59 (25.8)	147 (28.1)	206 (27.4)	0.535
5-10 PC transfused (%)	2 (0.9)	3 (0.6)	5 (0.7)	0.643
More than 10 PC transfused (%)	0 (0.0)	2 (0.4)	2 (0.3)	1.000
Use of FFP
Number of units of FFP transfused (median)	0 (0-0)	0 (0-0)	0 (0-0)	0.530
Units of FFP transfused (mean ± SD)	0.4 ± 2.5	0.4 ± 3.4	0.4 ± 3.1	0.530
0 units of FFP transfused (%)	218 (95.2)	504 (96.2)	722 (95.9)	0.552
1-4 units of FFP transfused (%)	6 (2.6)	10 (1.9)	16 (2.1)	0.585
5-10 units of FFP transfused (%)	2 (0.9)	4 (0.8)	6 (0.8)	0.705
More than 10 units of FFP transfused (%)	3 (1.3)	6 (1.1)	9 (1.2)	1.000

FFP: fresh frozen; PC: platelet concentrates; plasma; PRBC: packed red blood cells; SD: standard deviation.

Data are presented as medians (25th-75th percentiles) unless otherwise mentioned.

Table 8.

Postoperative use of blood products matched.

	Group M(n = 180)	Group C(n = 180)	Overall(n = 360)	p-value
Use of packed red blood cells
Units of PRBC transfused (median)	0 (0-0)	0 (0-2)	0 (0-1)	0.002
Units of PRBC transfused (mean ± SD)	0.8 ± 3.0	1.2 ± 4.2	1.0 ± 3.7	0.002
0 units of PRBC transfused (%)	146 (81.1)	119 (66.1)	265 (73.6)	0.002
1-4 units of PRBC transfused (%)	28 (15.6)	53 (29.4)	81 (22.5)	0.002
5-10 units of PRBC transfused (%)	4 (2.2)	6 (3.3)	10 (2.8)	0.750
More than 10 units of PRBC transfused (%)	2 (1.1)	2 (1.1)	4 (1.1)	1.000
Use of thrombocyte concentrates
Use of PC transfused (median)	0 (0-1)	0 (0-0)	0 (0-1)	0.687
Use of PC transfused (mean ± SD)	0.6 ± 1.0	0.6 ± 1.8	0.6 ± 1.5	0.687
0 PC transfused (%)	132 (73.3)	136 (75.6)	268 (74.4)	0.717
1-4 PC transfused (%)	46 (25.6)	43 (23.9)	89 (24.7)	0.807
5-10 PC transfused (%)	2 (1.1)	0 (0.0)	2 (0.6)	0.499
More than 10 PC transfused (%)	0 (0.0)	1 (0.6)	1 (0.3)	1.000
Use of FFP
Units of FFPs transfused (median)	0 (0-0)	0 (0-0)	0 (0-0)	0.058
Units of FFPs transfused (mean ± SD)	0.4 ± 2.6	0.2 ± 3.3	0.3 ± 3.0	0.058
0 units of FFPs transfused (%)	174 (96.7)	179 (99.4)	353 (98.1)	0.121
1-4 units of FFPs transfused (%)	3 (1.7)	0 (0.0)	3 (0.8)	0.248
5-10 units of FFPs transfused (%)	1 (0.6)	0 (0.0)	1 (0.3)	1.000
More than 10 units of FFPs transfused (%)	2 (1.1)	1 (0.6)	3 (0.8)	1.000

FFP: fresh frozen plasma; PC: platelet concentrates; PRBC: packed red blood cells; SD: standard deviation.

Data are presented as medians (25th-75th percentiles) or absolute numbers (percentages).

Discussion

A major concern in the implementation of CPB has been the blood–surface interface, especially the blood–air interface. This has led to the development of closed ECC systems, among them the MiECC systems. Nishida et al.⁸ investigated the biocompatibility of open and closed circuits and found lower levels of C3a (by-product of cleavage of complement component 3), lower amounts of protein adsorbed and lower deposition of fibrinogen bands. They concluded that the open circuit was less biocompatible than a closed one. Another measure to attenuate the inflammatory response associated with exposure to foreign surfaces and thus to increase bio-compatibility is ECC coating. PMEA, applied in the MiECC circuits, forms a molecular mesh, composed of a hydrophobic polyethylene backbone (that adheres to the surface of the ECC) and a hydrophilic blood-contacting layer which helps to prevent activation of a systemic inflammatory reaction and maintain protein conformity.⁹ PMEA has been reported to be more physiologically biocompatible and exhibit lower levels of platelet absorption and fibrinolysis as well as complement activation.^9,10

A crucial difference is the use of cardiotomy suction versus the use of cell salvage since MiECC systems depend solely on the use of cell salvage. A study by Lau et al.¹¹ reports that the use of cardiotomy suction in patients undergoing coronary revascularisation was associated with pronounced systemic inflammatory response resulting in coagulopathy and an increased micro-embolic load. Cell salvage, however, allows conservation of red blood cells while at the same time reduces the re-transfusion of fat micro-emboli and activated coagulation and inflammatory agents. In case of severe haemorrhage, an additional hard-shell reservoir can be added to the MiECC as an additional safety feature.¹²

With regard to the issue of blood transfusions, our results are consistent with those of other authors, who report lower rates of blood transfusions in patients operated with the use of MiECC systems.^2,13,14 The issue of blood transfusion after cardiac surgery has been extensively discussed in literature. Low haemoglobin levels have been shown to be associated with myocardial injury, increased inotrope requirements, neurologic dysfunction and stroke, renal dysfunction and postoperative dialysis, prolonged ventilation, and increased perioperative mortality.¹⁵ Therefore, transfusion of PRBC is an indispensable component of cardiac surgical procedures. However, during the last years, concerns have raised that a liberal transfusion threshold may have negative effects on patient outcome: blood transfusions have been reported to elicit increased infection and postoperative morbidity, hospital stay, increased early and late mortality, and hospital costs.^16–18 A more recently published multi-centre trial by Murphy et al.¹⁹ investigated the outcome of a liberal versus a more restrictive transfusion of PRBC after cardiac surgery. They did not find any significant differences and concluded that a restrictive transfusion threshold (<7.5 g/dL) was neither superior to a more liberal one (<9.0 g/dL) nor did the hospital costs differ significantly between the two groups. All-cause mortality at 90 days was lower in the liberal group when compared to the restrictive group (2.6% vs. 4.2%, p = 0.045). However, based on the aforementioned studies, we tended to apply a more restrictive transfusion threshold in our patients.

In addition to reduced haemodilution and lower rates of blood transfusions, MiECC systems have been reported to have several other benefits such as lower incidence of postoperative atrial fibrillation, improved myocardial protection and preservation of renal function.⁵ Other benefits include an attenuated inflammatory response, reduced cerebral gaseous micro-emboli and a protective effect on end-organ function.⁵ Finally, mortality rates after CABG procedures using MiECC and CECC circuits have been reported to be comparable. A meta-analysis by Anastasiadis et al.²⁰ found that the mortality rate in patients operated with the use of MiECC circuits was lower, however, not statistically significant. This was comparable to our results.

Conclusion

In this study, the use of MiECC is associated with a significantly lower use of blood products after isolated coronary revascularisation compared to CECC, whereas there were no differences concerning duration of surgery, complication rates and mortality between the groups. Therefore, the application of MiECC systems should be considered as preferred technique in isolated CABG procedures.

Limitations

This study has several limitations. Cardioplegia protocols were different in both groups. A standard protocol of perioperative management of anticoagulation has been applied; however, individual effects of the anticoagulants have not been investigated. In addition, the presence of mitral regurgitation has not been included in the propensity matching. Finally, the amount of cell-saved blood transfused has been included in the intraoperative fluid management and has not been investigated separately.

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship and/or publication of this article.

ORCID iD

Shekhar Saha

References

Wippermann

Albes

Hartrumpf

et al. Comparison of minimally invasive closed circuit extracorporeal circulation with conventional cardiopulmonary bypass and with off-pump technique in CABG patients: selected parameters of coagulation and inflammatory system. Eur J Cardiothorac Surg 2005; 28: 127–132.

Curtis

Vohra

Ohri

SK.

Mini extracorporeal circuit cardiopulmonary bypass system: a review. Perfusion 2010; 25: 115–124.

Vohra

Whistance

Modi

et al. The inflammatory response to miniaturised extracorporeal circulation: a review of the literature. Mediators Inflamm 2009; 2009: 707042.

Fromes

Gaillard

Ponzio

et al. Reduction of the inflammatory response following coronary bypass grafting with total minimal extracorporeal circulation. Eur J Cardiothorac Surg 2002; 22: 527–533.

Anastasiadis

Murkin

Antonitsis

et al. Use of minimal invasive extracorporeal circulation in cardiac surgery: principles, definitions and potential benefits. A position paper from the Minimal invasive Extra-Corporeal Technologies international Society (MiECTiS). Interact Cardiovasc Thorac Surg 2016; 22: 647–662.

Bauer

Hausmann

Schaarschmidt

et al. Is 300 seconds ACT Safe and efficient during MiECC procedures. Thorac Cardiovasc Surg 2019; 67: 191–202.

Meybohm

Muellenbach

Keller

et al. Patient blood management in der Herzchirurgie. Zeitschrift Herz Thorax Gefasschirurgie 2017; 31: 247–265.

Nishida

Aomi

Tomizawa

et al. Comparative study of biocompatibility between the open circuit and closed circuit in cardiopulmonary bypass. Artif Organs 1999; 23: 547–551.

Ask

Holt

Smith

In vivo comparison study of FDA-approved surface-modifying additives and poly-2-methoxyethylacrylate circuit surfaces coatings during cardiopulmonary bypass. J Extra Corpor Technol 2006; 38: 27–32.

10.

Tanaka

Motomura

Kawada

et al. Blood compatible aspects of poly(2-methoxyethylacrylate) (PMEA)-relationship between protein adsorption and platelet adhesion on PMEA surface. Biomaterials 2000; 21: 1471–1481.

11.

Lau

Shah

Kelleher

et al. Coronary artery surgery: cardiotomy suction or cell salvage? J Cardiothorac Surg 2007; 2: 46.

12.

El-Essawi

Hajek

Skorpil

et al. A prospective randomised multicentre clinical comparison of a minimised perfusion circuit versus conventional cardiopulmonary bypass. Eur J Cardiothorac Surg 2017; 38: 91–97.

13.

Pereira

Zumba

Batista

et al. Comparison of two technics of extracorporeal circulation (Conventional and Mini ECC), in the trans and post-operative periods of cardiac surgery. Rev Bras Cir Cardiovasc 2015: 433–442.

14.

Alsatli

Mini cardiopulmonary bypass: anesthetic considerations. Anesth Essays Res 2012; 6: 10.

15.

Murphy

Angelini

GD.

Indications for blood transfusion in cardiac surgery. Ann Thorac Surg 2006; 82: 2323–2334.

16.

LaPar

Crosby

Ailawadi

et al. Blood product conservation is associated with improved outcomes and reduced costs after cardiac surgery. J Thorac Cardiovasc Surg 2013; 145: 796–803.

17.

Koch

Duncan

et al. Transfusion in coronary artery bypass grafting is associated with reduced long-term survival. Ann Thorac Surg 2006; 81: 1650–1657.

18.

Murphy

Reeves

Rogers

et al. Increased mortality, postoperative morbidity, and cost after red blood cell transfusion in patients having cardiac surgery. Circulation 2007; 116: 2544–2552.

19.

Murphy

Pike

Rogers

et al. Liberal or restrictive transfusion after cardiac surgery. N Engl J Med 2015; 372: 997–1008.

20.

Anastasiadis

Antonitsis

Haidich

A-B

et al. Use of minimal extracorporeal circulation improves outcome after heart surgery; a systematic review and meta-analysis of randomized controlled trials. Int J Cardiol 2013; 164: 158–169.