Cellular aggregation and trauma in cardiotomy suction systems

Turbulence in surgical suction heads as detected by MRI

BACKGROUND

Blood loss is common during surgical procedures, especially in open cardiac surgery. Allogenic blood transfusion is associated with increased morbidity and mortality. Blood conservation programs in cardiac surgery recommend re-transfusion of shed blood directly or after processing, as this decreases transfusion rates of allogenic blood. But aspiration of blood from the wound area is often associated with increased hemolysis, due to flow induced forces, mainly through development of turbulence.

METHODS

We evaluated magnetic resonance imaging (MRI) as a qualitative tool for detection of turbulence. MRI is sensitive to flow; this study uses velocity-compensated T1-weighted 3D MRI for turbulence detection in four geometrically different cardiotomy suction heads under comparable flow conditions (0-1250 mL/min).

RESULTS

Our standard control suction head Model A showed pronounced signs of turbulence at all flow rates measured, while turbulence was only detectable in our modified Models 1-3 at higher flow rates (Models 1 and 3) or not at all (Model 2).

CONCLUSIONS

The comparison of flow performance of surgical suction heads with different geometries via acceleration-sensitized 3D MRI revealed significant differences in turbulence development between our standard control Model A and the modified alternatives (Models 1-3). As flow conditions during measurement have been comparable, the specific geometry of the respective suction heads must have been the main factor responsible. The underlying mechanisms and causative factors can only be speculated about, but as other investigations have shown, hemolytic activity is positively associated with degree of turbulence. The turbulence data measured in this study correlate with data from other investigations about hemolysis induced by surgical suction heads. The experimental MRI technique used showed added value for further elucidating the underlying physical phenomena causing blood damage due to non-physiological flow.

Practical conduct of open heart procedures for congenital heart lesions

Open heart surgery on infants with congenital heart lesions can be challenging not only in terms of the surgical procedure itself but also for setting up ideal conditions for safe and smooth conduct of cardiopulmonary bypass (CPB). The surgeon has to deal with a variety of lesions in a subgroup of patients who offer little room for any error. Familiarity with the principles of CPB, check lists and protocols go a long way in improving outcome in this critical group of patients.

Pathophysiological aspects of cardiotomy suction usage

Cardiotomy suction is used for preservation of autologous blood during on-pump cardiac surgery at present. Controversially, the exclusion of cardiotomy suction in some types of operations (coronary artery bypass surgery) is not necessarily associated with an increased transfusion requirement. On the other hand, the use of cardiotomy suction causes an amplification of systemic inflammatory response and a resulting coagulopathy, as well as exacerbation of the microembolic load and hemolysis. This leads to a tendency towards increased blood loss, transfusion requirement and organ dysfunction. On the basis of these facts, it is appropriate to reconsider routine use of cardiotomy suction in on-pump coronary artery surgery.

The relationships between air exposure, negative pressure, and hemolysis

The purpose of this study was to describe the hemolytic effects of both negative pressure and an air-blood interface independently and in combination in an in vitro static blood model. Samples of fresh ovine or human blood (5 ml) were subjected to a bubbling air interface (0-100 ml/min) or negative pressure (0-600 mm Hg) separately, or in combination, for controlled periods of time and analyzed for hemolysis. Neither negative pressure nor an air interface alone increased hemolysis. However, when air and negative pressure were combined, hemolysis increased as a function of negative pressure, the air interface, and time. Moreover, when blood samples were exposed to air before initiating the test, hemolysis was four to five times greater than samples not preexposed to air. When these experiments were repeated using freshly drawn human blood, the same phenomena were observed, but the hemolysis was significantly higher than that observed in sheep blood. In this model, hemolysis is caused by combined air and negative pressure and is unrelated to either factor alone.

A novel device for reducing hemolysis provoked by cardiotomy suction during open heart cardiopulmonary bypass surgery: a randomized prospective study

Since the inception of cardiopulmonary bypass (CPB), little progress has been made concerning the design of cardiotomy suction (CS). Because this is a major source of hemolysis, we decided to test a novel device (Smartsuction [SS]) specifically aimed at minimizing hemolysis during CPB in a clinical setting. Block randomization was carried out on a treated group (SS, n=28) and a control group (CTRL, n=26). Biochemical parameters were taken pre-, peri-, and post CPB and were compared between the two groups using the Student's t-test with statistical significance when P<0.05. No significant differences in patient demographics were observed between the two groups. Lactate dehydrogenase (LDH) and plasma free hemoglobin (PFH) pre-CPB were comparable for the CTRL and SS groups, respectively. LDH peri-CPB was 275+/-100 U/L versus 207+/-83 U/L for the CTRL and SS groups, respectively (P<0.05). PFH was 486+/-204 mg/L versus 351+/-176 mg/L for the CTRL and SS groups, respectively (P<0.05). LDH post CPB was 354+/-116 U/L versus 275+/-89 U/L for the CTRL and SS groups, respectively (P<0.05). PFH was 549+/-271 mg/L versus 460+/-254 mg/L for the CTRL and SS groups, respectively (P<0.05). Preoperative hematocrit (Hct) of 43+/-5% (CTRL) versus 37+/-5% (SS), and hemoglobin (Hb) of 141+/-16 g/L (CTRL) versus 122+/-17 g/L (SS) were significantly lower in the SS group. However, when normalized (N), the SS was capable of conserving Hct, Hb, and erythrocyte count perioperatively. Erythrocytes (N) were 59+/-5% (CTRL) versus 67+/-9% (SS); Hct (N) was 59+/-6% (CTRL) versus 68+/-9% (SS), and Hb (N) was 61+/-6% (CTRL) versus 70+/-10% (SS) (all P<0.05). This novel SS device evokes significantly lowered blood PFH and LDH values peri- and post CPB compared with the CTRL blood using a CS system. The SS may be a valuable alternative compared to traditional CS techniques.

Physiological coagulation can be maintained in extracorporeal circulation by means of shed blood separation and coating

OBJECTIVE

Conventional extracorporeal circulation results in an activation of coagulation cascades. Coating of extracorporeal circulation tubes as well as avoidance of shed blood recirculation have been shown to reduce these phenomena. We evaluated a new shed blood separation system (AVANT D 970) utilizing a coated cardiopulmonary bypass tube system (PHISIO).

METHODS

Forty patients (62 +/- 10 years) underwent isolated coronary revascularization. Four groups (n = 10/group) were defined: no extracorporeal circulation, conventional uncoated extracorporeal circulation, uncoated extracorporeal circulation with shed blood separation, and coated extracorporeal circulation with shed blood separation. Thrombin-antithrombin complex and free Hb were analyzed and statistically compared.

RESULTS

Conventional extracorporeal circulation exhibited the highest intraoperative activation of coagulation (thrombin-antithrombin complex: extracorporeal circulation, 31.1 +/- 15.8 microg/L; uncoated extracorporeal circulation with shed blood separation, 15.3 +/- 7.8 microg/L; coated extracorporeal circulation with shed blood separation, 8.1 +/- 4.8 microg/L; no extracorporeal circulation, 2.4 +/- 0.6 microg/L; P <.05 extracorporeal circulation vs all others) and red blood cell damage (free Hb: extracorporeal circulation, 16.8 +/- 11.4 micromol/L; uncoated extracorporeal circulation with shed blood separation, 10.3 +/- 3.5 micromol/L; coated extracorporeal circulation with shed blood separation, 6.8 +/- 2.9 micromol/L; no extracorporeal circulation, 3.4 +/- 1.1 micromol/L; P <.05 extracorporeal circulation vs no extracorporeal circulation, coated extracorporeal circulation with shed blood separation). Coated extracorporeal circulation with shed blood separation showed only slight activation and cell trauma, which did not differ significantly from no extracorporeal circulation.

CONCLUSIONS

Combination of coating and avoidance of shed blood recirculation maintained physiological coagulation levels and markedly reduced red blood cell trauma in extracorporeal circulation procedures. These combined modalities may therefore offer an alternative for off-pump procedures in patients with contraindications for conventional extracorporeal circulation.

Smart suction device for less blood trauma: a comparison with Cell Saver

OBJECTIVE

The major source of hemolysis during cardiopulmonary bypass remains the cardiotomy suction and is primarily due to the interaction between air and blood. The Smart suction system involves an automatically controlled aspiration designed to avoid the mixture of blood with air. This study was set-up to compare this recently designed suction system to a Cell Saver system in order to investigate their effects on blood elements during prolonged intrathoracic aspiration.

METHODS

In a calf model (n=10; mean weight, 69.3+/-4.5 kg), a standardized hole was created in the right atrium allowing a blood loss of 100 ml/min, with a suction cannula placed into the chest cavity into a fixed position during 6 h. The blood was continuously aspirated either with the Smart suction system (five animals) or the Cell Saver system (five animals). Blood samples were taken hourly for blood cell counts and biochemistry.

RESULTS

In the Smart suction group, red cell count, plasma protein and free hemoglobin levels remained stable, while platelet count exhibited a significant drop from the fifth hour onwards (prebypass: 683+/-201*10(9)/l, 5 h: 280+/-142*10(9)/l, P=0.046). In the Cell Saver group, there was a significant drop of the red cell count from the third hour onwards (prebypass: 8.6+/-0.9*10(12)/l, 6 h: 6.3+/-0.4*10(12)/l, P=0.02), of the platelet count from the first hour onwards (prebypass: 630+/-97*10(9)/l, 1 h: 224+/-75*10(9)/l, P<0.01), and of the plasma protein level from the first hour onwards (prebypass: 61.7+/-0.6 g/l, 1 h: 29.3+/-9.1 g/l, P<0.01).

CONCLUSIONS

In this experimental set-up, the Smart suction system avoids damage to red cells and affects platelet count less than the Cell Saver system which induces important blood cell destruction, as any suction device mixing air and blood, as well as severe hypoproteinemia with its metabolic, clotting and hemodynamic consequences.

Investigation and quantification of the blood trauma caused by the combined dynamic forces experienced during cardiopulmonary bypass

Blood is exposed to various dynamic forces during cardiopulmonary bypass (CPB). Understanding the damaging nature of these forces is paramount for research and development of the CPB circuit. The object of this study was to identify the most damaging dynamic non-physiological forces and then quantify this damage. A series of in vitro experiments simulated the different combinations of dynamic forces experienced during CPB while damage to the blood was closely monitored. A combination of air interface (a) and negative pressure (P) caused the greatest rate of change in plasma Hb (deltap Hb) (4.94 x 10(-3) mg/dl/s) followed by negative pressure and then an air interface. Shear stresses, positive pressures, wall impact forces and a blood-nonendothelial surface caused the least damage (0.26 x 10(-3) mg/dl/s). An air interface showed no threshold value for blood damage, with the relationship between the size of the interface and the blood damage modelled by a second-order polynomial. However, negative pressure did exhibit a threshold value at -120 mm Hg, beyond which point there was a linear relationship. Investigating the reasons for the increased blood trauma caused by the low-pressure suction (LPS) system makes it clear how research into minimizing or completely avoiding certain forces must be the next step to advancing extracorporeal technology.

Haemolysis during cardiopulmonary bypass: an in vivo comparison of standard roller pumps, nonocclusive roller pumps and centrifugal pumps

Cardiopulmonary bypass (CPB) involves the use of either an occlusive roller pump or centrifugal pump. Damage to blood elements, including haemolysis, may arise from occlusion when using a roller pump; the appropriate degree of occlusion has not yet been determined scientifically. Centrifugal and nonocclusive roller pumps are reputed to reduce haemolysis. The objective of this study was to compare haemolysis caused by a standard roller pump with a dynamically set nonocclusive roller pump and with a centrifugal pump. We prospectively randomized 60 patients undergoing routine coronary artery surgery into three groups: standard roller pump (STD, n = 20), dynamically set roller pump (DYN, n = 20), or centrifugal pump (CEN, n = 20). The level of plasma free haemoglobin (FHb) was measured preoperatively, and the rate of formation of FHb (in mg/dl/min) was determined at the end of the ischaemic phase and at the end of CPB. Cardiotomy suction blood was isolated for the ischaemic phase and returned before the end of CPB. It was found that there were no differences between the groups in demographic or operative variables. The rate of formation of FHb at the end of the ischaemic phase was similar for all groups (STD 0.108 +/- 0.10, DYN 0.117 +/- 0.08, CEN 0.129 +/- 0.07). At the end of CPB, after return of the cardiotomy suction blood, there was a significant (< 0.001) increase in the rate of formation of FHb in all groups. The increase was similar for each of the groups (STD 0.424 +/- 0.17, DYN 0.481 +/- 0.20, CEN 0.471 +/- 0.18). We conclude that the rates of haemolysis are similar for each of the pump types, and no benefit is conferred by the use of either a dynamically set roller pump or a centrifugal pump compared with the standard roller pump. The return of the cardiotomy suction blood to the circulation is the principal source of plasma free haemoglobin.

Clinical study of totally roller pumpless cardiopulmonary bypass system

We have developed a low negative pressure vacuum suction system in which cardiotomy suction is performed by the negative pressure of the venous reservoir controlled by a vacuum controller. We have employed this vacuum suction system with a centrifugal pump as a totally roller pumpless cardiopulmonary bypass (CPB) system. In this study, the clinical availability and hemocompatibility of our totally roller pumpless CPB system were evaluated by a randomized prospective study. Thirty patients undergoing aortocoronary bypass grafting were assigned to the study. Data from seventeen patients treated with a totally roller pumpless CPB system were compared with data from 13 treated with a conventional roller pump CPB system. Totally roller pumpless CPB reduces hemolysis, showing lower plasma free hemoglobin levels (81.8 +/- 25.0 versus 42.0 +/- 16.3 at 30 min after CPB initiation, p < 0.05), higher plasma haptoglobin levels (37.8 +/- 36.6 versus 77.2 +/- 31.3 at 120 min after CPB, p < 0.05), and lower blood lactate dehydrogenase (LDH) levels (1391 +/- 497 versus 972 +/- 187, p < 0.01) than those of CPB with a roller pump suction with no significant difference between platelet counts. Arterial blood oxygen tension after using a totally roller pumpless CPB system was slightly better than that with a roller pump (396 +/- 48 versus 437 +/- 43, p = 0.069); however, there was no significant difference in intubation times between groups. A totally roller pumpless CPB system provides sufficient biocompatibility for the blood to reduce hemolysis significantly and simplifies and miniaturizes the entire CPB system to achieve good visuality and handling for control as well.

Mechanical simulation of cardiac function by means of pulsatile blood pumps

After a review of the theoretical and experimental background, a history of the development of pulsatile blood pumps is presented with an attempt to understand the underlying rationale. The case for the use of pumps that simulate normal cardiac function is made by considering cardiovascular hemodynamics, the function of arterial baro-receptors, hemodynamic energy and power, tissue fluid movement, and lymph formation and flow. The pulsatile output of the heart and mechanical pumps is described in units of power and the load that they work against as a complex impedance. Many pulsatile pumps have been designed and developed for research, but few have been used during cardiac operations on human patients. The evidence in favor of using pulsatile flow for cardiopulmonary bypass is strong, but major problems have been identified such as the lack of a satisfactory definition of pulsatile flow and technical difficulties resulting from impedance mismatches in clinical applications.