Hematological advantage of a membrane oxygenator over a bubble oxygenator in long perfusions

Extracorporeal Hyperoxygenation Therapy (EHT) for Carbon Monoxide Poisoning: In-Vitro Proof of Principle

Carbon monoxide (CO) poisoning is the leading cause of poisoning-related deaths globally. The currently available therapy options are normobaric oxygen (NBO) and hyperbaric oxygen (HBO). While NBO lacks in efficacy, HBO is not available in all areas and countries. We present a novel method, extracorporeal hyperoxygenation therapy (EHT), for the treatment of CO poisoning that eliminates the CO by treating blood extracorporeally at elevated oxygen partial pressure. In this study, we proof the principle of the method in vitro using procine blood: Firstly, we investigated the difference in the CO elimination of a hollow fibre membrane oxygenator and a specifically designed batch oxygenator based on the bubble oxygenator principle at elevated pressures (1, 3 bar). Secondly, the batch oxygenator was redesigned and tested for a broader range of pressures (1, 3, 5, 7 bar) and temperatures (23, 30, 37 °C). So far, the shortest measured carboxyhemoglobin half-life in the blood was 21.32 min. In conclusion, EHT has the potential to provide an easily available and effective method for the treatment of CO poisoning.

Platelet damage and haemolysis during bubble oxygenator perfusion with and without arterial line filter, compared to membrane oxygenator perfusion

We determined to what extent a 27 micron depth filter (Bentley Polyfilter bypass blood filter PF427, Bentley Lab., Irvine, California, USA) in the arterial line of a bubble oxygenator (BO) system is responsible for the difference in haemocompatibility between this BO system and a membrane oxygenator (MO) system in which no arterial line filter is used. We studied three groups of patients subjected to long perfusions of approximately three hours: BO perfusion with ( n = 8) and without ( n = 8) the arterial line filter and MO perfusion ( n = 10) without filter. Platelet and erythrocyte damage were evaluated at seven sampling points during perfusion. Also pre- and postoperative bleeding times and postoperative blood loss and blood transfusions up to 18 hours after perfusion were determined.

We found that the 27 micron depth filter in the arterial line impairs the haemocompatibility of the BO only to a small extent; the MO remains haematologically superior over the BO even when the arterial line filter is absent from the BO circuit.

Analysis of cardiopulmonary bypass status in China: eight-year development trends

Objective:

To study the development of cardiopulmonary bypass (CPB) in the past 8 years and to come up with predictions and recommendations for the future in China.

Methods:

Domestic hospitals performing cardiovascular operations were supplied with questionnaires, annually (between 2003 and 2008), upon the number of on-pump and off-pump cardiovascular operations, oxygenators of different types and the number of extracorporeal membrane oxygenation (ECMO). All the hospitals in this study were divided into 8 grades, according to the number of cardiovascular operations. The market share of hospitals in each grade was analyzed.

Results:

The total anumber of cardiovascular operations was 170,547 in 2010, of which 136,753 were performed under CPB. The ratio of imported membrane oxygenators increased from 43.22% in 2003 to 59.75% in 2010, while bubble oxygenator composition decreased from 43.78% in 2003 to 14.59% in 2010. Forty-four hospitals carried out 206 cases of ECMO in 2010. There were 32 hospitals that performed cardiovascular operations of over 1,000 cases and their market share was 43%. There were 255 hospitals that performed cardiovascular operations in less than 50 cases and their market share was only 3%.

Conclusions:

CPB in China has gone through a rapid development in the past eight years. Medical resources for CPB should be concentrated and systematic training regulations should be established in the future.

Modification of Suction-Induced Hemolysis During Cell Salvage

BACKGROUND

The efficiency of red blood cell collection during cell salvage is dictated by multiple variables, including suction pressure. In this study, we attempted to determine the influence of suction pressure on the efficiency of cell salvage and to identify methods for minimizing the impact of suction on salvaged blood.

METHODS

Whole blood was placed in 60-mL aliquots either in a beaker or on a flat surface and suctioned at 100 and 300 mm Hg. The amount of hemolysis was measured and compared under the varying conditions. The experiments were repeated with the blood diluted with normal saline solution in a 1:1 mix.

RESULTS

Hemolysis ranged from 0.21% to 2.29%. Hemolysis was greatest when whole blood was suctioned from a flat surface at 300 mm Hg. It was reduced when the blood was diluted with saline. Blood suctioned from a surgical field during cell salvage should be done with minimal suction pressures and with the goal of minimizing blood-air interfaces.

CONCLUSIONS

Significant reduction of blood damage can be obtained by diluting blood with normal saline while suctioning it from the surgical field. Although immediate hemolysis due to suctioning was not very high, the red blood cell damage from suctioning produced by a dynamic blood-air interface might adversely affect the efficiency of cell salvage.

Vacuum assisted venous drainage does not increase trauma to blood cells

Although gravity drainage has been the standard technique for cardiopulmonary bypass (CPB), the development of min imally invasive techniques for cardiac surgery has renewed interest in using vacuum assisted venous drainage (VAVD) Dideco (Mirandola, Italy) has modified the D903 Avant oxygenator to apply a vacuum to its venous reservoir. The impact of VAVD on blood damage with this device is analyzed. Six calves (mean body weight, 71.3 +/- 4.1 kg) were con nected to CPB by jugular venous and carotid arterial cannu lation, with a flow rate of 4-4.51 L/min for 6 h. They were assigned to gravity drainage (standard D903 Avant oxygen ator, n = 3) or VAVD (modified D903 Avant oxygenator, n = 3). The animals were allowed to survive for 7 days. A standard battery of blood samples was taken before bypass, throughout bypass, and 24 h, 48 h, and 7 days after bypass. Analysis of variance was used for repeated measurements. Thrombocyte and white blood cell counts, corrected by hematocrit and normalized by prebypass values, were not significantly different between groups throughout all study periods. The same holds true for hemolytic parameters (lactate dehydrogenase [LDH] and plasma hemoglobin). Both peaked at 24 hr in the standard and VAVD groups: LDH, 2,845 +/- 974 IU/L vs. 2,537 +/- 476 IU/L (p = 0.65), respectively; and plasma hemoglobin, 115 +/- 31 mg/L vs. 89 +/- 455 mg/L (p = 0.45), respectively. In this experimental setup with prolonged perfusion time, VAVD does not increase trauma to blood cells in comparison with standard gravity drainage.

Pressure drop, shear stress, and activation of leukocytes during cardiopulmonary bypass: a comparison between hollow fiber and flat sheet membrane oxygenators

The membrane oxygenator is known to be superior to the bubble oxygenator, but little information is available about the difference between the hollow fiber and flat sheet membrane oxygenators with regard to pressure drop, shear stress, and leukocyte activation. In this study, we compared these 2 types of membrane oxygenators in patients undergoing cardiopulmonary bypass (CPB) surgery with special focus on leukocyte activation and pressure drop across the oxygenators. Plasma concentration of elastase, a marker indicating leukocyte activation, increased to 593+/-68% in the flat sheet oxygenator group versus 197+/-42% in the hollow fiber oxygenator group (p<0.01) at the end of CPB compared to their respective baseline concentrations before CPB. Pressure drop across the oxygenator was significantly higher in the flat sheet group than in the hollow fiber group throughout the entire period of CPB (p<0.01). High pressure drop across the oxygenator as well as the calculated shear stress was positively correlated with the release of elastase at the end of CPB (r = 0.760, p<0.01, r = 0.692, p<0.01). However, this positive correlation existed in the flat sheet oxygenator but not in the hollow fiber oxygenator. Clinically, both membrane oxygenators have satisfactory performance in O2 and CO2 transfer. These results suggest that a higher pressure drop across the flat sheet oxygenator is associated with more pronounced activation of leukocytes in patients undergoing cardiopulmonary bypass.

A study of the effects of extracorporeal circulation on the immunologic system of humans

OBJECTIVES

The objectives of this study were to quantify the immunosuppressive effects of cardiopulmonary bypass (CPB) and to identify mechanisms responsible for the postoperative immunosuppression of patients undergoing cardiac surgery.

DESIGN

A prospective study from 20 consecutive patients.

SETTING

The same team operated on all patients in a major teaching hospital, and the immunologic tests were performed in the hospital's hematology laboratory.

PARTICIPANTS

Twenty patients were studied who had consented to participate in the study.

INTERVENTIONS

All patients underwent valve replacement under general anesthesia.

MEASUREMENT AND MAIN RESULTS

The changes in the white blood cell count (WBC), in the B, T, T4, T8 lymphocytes, the concentrations of C-reactive protein (CRP), a1-antitrypsin (A1AT), a2-macroglobulin (A2MG), C3, C4 immunoglobulin A (IgA), IgM, IgG, Kappa (K), and lambda (L) chains were studied. The postoperative immune response was expressed with (1) increased mean axillary temperature (37.5 degrees +/- 0.62 degrees) in the first postoperative 24 hours; (2) increase of WBC (p < 0.001) and T8 (p < 0.01); (3) reduction of C3 (p = 0.01) and A2MG (p < 0.01); (4) reduction of IgA (p < 0.001) and IgG, K, L chains (p < 0.01); and (5) reduction of T (p < 0.01) and T4 (p < 0.01). In the first 24 hours postoperatively, B cells were increased (81%) together with CRP (p < 0.01) and A1AT.

CONCLUSIONS

The observed immune alterations were mostly of no immunologic origin and were related to hemodilution and inflammation together with an immunosuppressive effect of trauma and stress.

Clinical comparison of blood oxygenators: a retrospective study

The results for platelet count (PC), activated clotting time (ACT), postoperative bleeding, and hemoderivatives usage in cardiac surgeries were crossed against the type of oxygenator used. These were two bubble and one membrane type. A sample of the surgery population for each type was selected at random. Thus, the patients in this study were divided into 3 groups: BA: 87 patients, bubble oxygenator; BB: 87 patients, bubble oxygenator; M: 73 patients, membrane oxygenator. The groups were statistically similar (p > 0.05) for age, body surface area, cardiopulmonary bypass (CPB) time, and prevalence of cardiac disease. The rate of PC 15 min after CPB end and before its beginning was BA, 0.48 +/- 0.02; BB, 0.49 +/- 0.02; M, 0.55 +/- 0.03. The rate of ACT after protamine administration and before CPB was BA, 1.22 +/- 0.03; BB, 1.16 +/- 0.03; M, 1.16 +/- 0.03. Volume (ml) of total postoperative bleeding (POB) was BA, 904 +/- 72; BB, 963 +/- 73; M, 867 +/- 83. Patient percentage that used hemoderivatives (HD) was BA, 86.3%; BB, 88.5%; M, 90.0%. No statistical difference was found between groups (p > 0.05). This study indicates that although membrane oxygenators have better theoretic and experimental biocompatibility, no significant difference in PC, ACT, POB, and HD usage was observed in the clinical setting. All values are expressed as the mean +/- standard error of the mean.

Respiratory function after cardiopulmonary bypass: a comparison of bubble and membrane oxygenators

A consecutive sample of 500 adults undergoing cardiac surgery was randomly allocated to extracorporeal circulation with either a Bard bubble oxygenator H1700 or a Bard membrane oxygenator HF5700 (Bard Ltd, Crawley, UK). Alveolar-arterial oxygen tension gradient (AaDO2) was calculated prebypass, then 20, 90, 180, and 420 minutes postbypass. Preoperative, initial postoperative, and first-day postoperative chest x-rays were assigned an extravascular lung water (EVLW) score and an atelectasis score. There was a comparable increase in AaDO2 after bypass in each group. The increase in EVLW score was significantly greater in the bubble group (mean 2.91, 95% CI 2.28-3.54) than the membrane group (mean 2.06, 95% CI 1.43-2.69) for the initial postoperative x-rays (P < 0.01) and also for the x-rays on the first postoperative day (P < 0.01). The increase in atelectasis score was significantly greater in the bubble group (mean 1.06, 95% CI 0.94-1.18) than the membrane group (mean 0.86, 95% CI 0.74-0.98) for the initial postoperative x-rays (P < 0.01) but not for the x-rays on the first postoperative day. There was no difference in duration of ventilation, intensive care, hospital stay, or hospital mortality between bubble and membrane groups. Although there was a statistically significant difference in x-ray scores between oxygenator groups, neither intrapulmonary shunting nor clinical outcome was influenced by the type of oxygenator used during bypass.

Cardiopulmonary bypass and cellular immunity: changes in lymphocyte subsets and natural killer cell activity

To investigate whether cell-mediated immunity responses are suppressed or activated by the effect of cardiopulmonary bypass (CPB), we studied peripheral blood lymphocyte subsets and antibody-dependent cell-mediated cytotoxicity in 52 adult patients who had undergone open heart operations. Lymphocyte function also was studied with regard to mixed lymphocyte reaction, which indicates the amount of DNA synthesis of lymphocytes, and natural killer (NK) cytotoxicity, which represents the killing activity of NK cells on the tumor cells (K-562), in 11 patients. The total T lymphocyte (OKT3+ and OKT11+) number showed no significant change during CPB. Suppressor/cytotoxic T cell (OKT8+) and NK cell (Leu7+ and Leu11+) numbers were found to be remarkably increased. However, helper/inducer T cell (OKT4+) and B cell (Leu12+) numbers were decreased during CPB. Antibody-dependent cell-mediated cytotoxicity was elevated during CPB. All of these changes were almost returned to the preoperative levels by the seventh day after operation. Mixed lymphocyte reaction and NK cytotoxicity were also activated during CPB. The results show that heart operations in which cardiopulmonary bypass is used are associated with activation of cytotoxic cell-mediated immunity.

Evaluation of high-frequency jet ventilation in oxygenation through an artificial membrane lung

The membrane oxygenator often develops impaired gas exchange after prolonged use because plasma proteins adhere to the membrane's surface and leak through its micropores. This study was performed to examine the efficacy of high-frequency jet ventilation (HFJV) in minimizing these problems in a "flat plate" type of membrane oxygenator. We first vibrated the membrane of the oxygenator by HFJV from 1 to 10 Hz to find the frequency most effective for optimal gas exchange in animals with partial extracorporeal circulation. These studies suggested that 6 Hz HFJV was preferable in our model. We subsequently performed in vivo extracorporeal oxygenation in dogs for 8 h using the membrane oxygenator with or without 6 Hz HFJV. Although the gas exchange capacity within the first 8 h was similar in the two groups, after 6 h a significant decrease in the red blood cell count and in the hematocrit was found in the group not receiving HFJV. Scanning electron microscopic examination of the membranes after 8 h of use disclosed that the membrane from the group receiving HFJV had less plasma protein and fibrin adhesion than that from the group not receiving HFJV. Moreover, it appears that with prolonged extracorporeal oxygenation, 6 Hz HFJV also protects against a decrease in the hematocrit of the passed blood and might lead to enhanced gas exchange. Our data suggest that good gas exchange can be maintained for periods even longer than 8 h if HFJV is used in conjunction with the membrane oxygenator.

Qualitative and quantitative changes in platelets after coronary-artery bypass surgery may help identify thrombotic complications and infections

We studied the effect of coronary-artery bypass surgery on blood cells and platelets. Hematological parameters of eighty-three patients were measured by an automated cell counting and sizing analyzer. Sampling time was from 24 h prior to 10 days after surgery. During this time leukocytes and platelets showed characteristic changes in numbers and size, whereas red blood cells revealed no typical modifications. Even though it seems clear that changes of hematological parameters occur after bypass surgery, it is important to be aware of the actual extent of such changes. Therefore the data of 50 patients who had had no post-operative clinical complications were combined to generate diagrams of those parameters that had changed in a characteristic fashion. The diagrams showing average changes, and 99% confidence intervals in mean platelet volume and platelet count were able to identify seven (out of 7) cases with complications up to 48 h before clinical signs were apparent. Complications ranged from mild (3 cases with infections) to severe (4 cases with thrombosis, embolic thrombosis and/or reinfarction). Diagrams showing changes in leukocyte parameters were able to identify only two cases with infections. Even though the number of cases is yet small, the results suggest that surveillance of platelet parameters may be useful in postoperative care. Furthermore, this study was able to confirm the recent findings of Trowbridge and Martin that an abnormal increase in platelet volume distribution width and low platelet counts found in patients with coronary heart disease may serve as good indicators for the prethrombotic state and the risk of myocardial infarction.

Effects of aprotinin on hemostatic mechanisms during cardiopulmonary bypass

Cardiopulmonary bypass (CPB) is associated with activation of humoral systems, which results in the release of proteases. These proteases may affect platelets and stimulate granulocytes. In the present study, the protease inhibitor aprotinin was given in high doses to 11 patients to achieve plasma concentrations of more than 150 kallikrein inactivator units per milliliter during CPB. At such concentrations, kallikrein and plasmin are effectively inhibited. This treatment resulted in platelet preservation during CPB. Platelet numbers were virtually unaffected, and thromboxane release was prevented in the aprotinin-treated group in contrast to the control group. Postoperatively, hemostasis was significantly better preserved after aprotinin treatment (blood loss of 357 ml in the treated group versus 674 ml in the untreated group; p less than 0.01). Since tissue-plasminogen activator activity was similar in both groups, the improved hemostasis most likely should be attributed to platelet preservation. Furthermore, aprotinin lessened neutrophilic elastase release, which might contribute to decreased pulmonary dysfunction in patients at risk.