Blood Conservation Methods Research Articles

Living related donor nephrectomy in transfusion refusing donors

Many transplant programs are averse to evaluate potential kidney donors with preferences against accepting human blood products. We examined the donor and graft outcomes between our transfusion-consenting (TC) and transfusion-refusing (TR) live kidney donors to determine whether a functional or survival disadvantage resulted from the disallowance of blood product transfusion during live donor (LD) nephrectomy. From July, 1999 to August, 2005, 82 live donor nephrectomies were performed, eight of who were TR donors (10%). Blood conservation techniques were utilized in TR donors. Demographics, surgical and functional outcomes, admission and discharge hematocrit, and creatinine were compared between TC and TR donors. No donor mortalities occurred. Two TC donors received blood transfusions (2.7%), and each study group experienced a single, <1-year graft loss. Intra-operative blood losses were significantly less in TR donors (298 +/- 412 vs. 121 +/- 91 ml, P < 0.03). No differences were noted between donor demographics, intra-operative events, and graft and patient survival. Successful donor nephrectomy from TR patients has the potential to expand the kidney allograft pool to include the TR donor population. Precautionary blood conservation methods allow the informed and consenting TR individual to donate a kidney with acceptable risk and without compromise to donor or graft outcomes.

P06 Use of Intraoperative Red Cell Salvage During Elective Abdominal Aortic Aneurysm Repair is Safe and Associated with Reduced Need for Allogeneic Blood Transfusion.

Introduction The need for blood transfusion during vascular surgery can be considerable. Concerns regarding the safety and cost of allogeneic blood have demanded scrutiny of alternative methods of blood conservation during these operations, including intraoperative red cell salvage. Autotranfusion is purported to reduce the need for blood transfusion, and therefore its attendant complications.Method We retrospectively collected data on all patients undergoing elective infrarenal abdominal aortic aneurysm repair in our unit, and compared patients in which the cell saver was used to those in which it was not, in terms of operative blood loss, transfusion requirement, length of stay, and postoperative haemoglobin. The Mann Whitney test and Kendall's tau B statistics were used to analyse the dataResults Thirty‐five patients underwent AAA repair with use of the cell saver, and 31 patients underwent repair without the use of this device. We found a significant association between the use of the cell saver and reduced need for allogneic blood in these patients (Table). There was also a significant positive correlation between the volume of blood obtained by the cell saver, and that returned to the patient (t = +0.5, P &lt; 0.00001). The postoperative haemoglobin in the cell saver group was significantly lower, but still within acceptable range. There was no significant difference in mortality between the two groups; Variable Cell Saver Group ‐Mean No‐Cell Saver Group ‐ Mean Significance Age (years) 72.4 (8.1) 74.5 (7.1) 0.11 AAA size (cm) 6.2 (0.9) 6.1 (0.7) 0.94 Preop Hb (g/dL) 13.9 (1.2) 13.9 (1.6) 0.92 Operative blood loss (mL) 986.7 (494.2) 1900.6 (1657.6) 0.02 Intraoperative allogeneic blood used (no. units) 0.5 (1.2) 2.6 (2.8) &lt;0.0001 Total allogeneic blood (7d) 0.9 (1.4) 3.5 (4.3) &lt;0.0001 Post operative Hb 10.9 (1.2) 11.7 (1.7) 0.03 Length of stay (days) 12.5 (4.2) 10.7 (8.1) 0.01 Conclusion Our study indicates that use of the cell saver in elective AAA repair is associated with a reduced need for allogeneic blood transfusion, and therefore, with a reduction in risks of transmitted infection and transfusion reaction. These findings also have important financial implications.

Homologous blood transfusion is not required in surgery for adolescent idiopathic scoliosis

We studied 70 consecutive patients with adolescent idiopathic scoliosis who underwent corrective surgery. They were divided into two groups. In the study group of 38 patients one or more modern blood-conservation measures was used peri-operatively. The 32 patients in the control group did not have these measures. Both groups were similar in regard to age, body-weight, the number of levels fused and the type of surgery. Only two patients in the study group were transfused with homologous blood and these transfusions were 'off-protocol'. Wastage of autologous pre-donated units was minimal (6 of 83 units). By contrast, all patients in the control group were transfused with homologous blood. In the study group there was a significant decrease (p = 0.005) in the estimated blood loss when all the blood-conservation methods were used. The use of blood-conservation measures, the lowering of the haemoglobin trigger for transfusion and the education of the entire team involved in the care of the patient can prevent the need for homologous blood transfusion in patients undergoing surgery for adolescent idiopathic scoliosis.

Transfusion in Coronary Artery Bypass Grafting is Associated with Reduced Long-Term Survival

Perioperative red blood cell (PRBC) transfusion has been associated with early risk for morbid outcomes, but risk related to long-term survival has not been thoroughly explored. Therefore, we examined the influence of PRBC transfusion and component therapy on long-term survival after isolated coronary artery bypass grafting after controlling for the effect of demographics, comorbidities, operative factors, and the early hazard for death. The US Social Security Death Index was used to ascertain survival status for 10,289 patients who underwent isolated coronary artery bypass grafting from January 1, 1995 through June 28, 2002. The outcome measure was all-cause mortality during the follow-up period. Unadjusted survival estimates were performed using the Kaplan-Meier techniques. Survival curves for transfusion status were compared with the log-rank test. The parametric decomposition model was used for risk-adjusted survival. A balancing score was calculated for each patient and forced into the final model. Survival among transfused patients was significantly reduced as compared with nontransfused patients. The instantaneous risk of death displayed a biphasic pattern: a declining hazard phase from the time of the operation (early hazard) up until 6 months postoperatively and then a late hazard that continued out until about 10 years. Transfusion of red cells was associated with a risk-adjusted reduction in survival for both the early (0.34 +/- 0.02, p < 0.0001) and late phases (0.074 +/- 0.016, p < 0.0001). Perioperative PRBC transfusion is associated with adverse long-term sequela in isolated CABG. Attention should be directed toward blood conservation methods and a more judicious use of PRBC.

The use of blood conservation methods in addition to erythropoietin allows myeloablative allogeneic stem cell transplantation without the use of blood products

The use of blood conservation methods in addition to erythropoietin allows myeloablative allogeneic stem cell transplantation without the use of blood products

Impact of Extracorporeal Circuit Prime Volume Reduction on Whole Blood Sequestration During Acute Normovolemic Hemodilution for Adult Cardiac Surgery Patients

Acute normovolemic hemodilution (ANH) is a blood-conservation method in which whole blood (WBANH) is sequestered into blood collection bags before the commencement of surgery. However, for cardiac surgery, extracorporeal circuit (ECC) priming techniques limit the amount of blood that may collected prior to the actual initiation of cardiopulmonary bypass (CPB). In this study, computational modeling was used to examine the effect of reducing extracorporeal “pump” prime volume (PPV) on WBANH prior to the CPB. Increments of estimated blood volume (EBV), precardiopulmonary bypass hemoglobin concentration [HbPre-CPB], and PPV volume were manipulated to assess effects on predicted hemoglobin concentration during cardiopulmonary bypass [HbCPB]. Similarly, increments of EBV and preanesthetic hemoglobin concentration [HbPre-Anes] were manipulated to examine the change in WBANH volume. The impact of PPV reduction on the minimum acceptable precardiopulmonary bypass hemoglobin concentration [HbPre-CPB-MA] was then measured by computing PPV, EBV, and the minimum acceptable cardiopulmonary bypass hemoglobin [HbCPB-MA]. Finally, by manipulating EBV and target hemoglobin concentration [HbTarget], the change in [HbPre-CPB] produced by PPV reduction was used to quantify the effect on WBANH volume. The net increase in the [HbCPB] produced by PPV reduction is inversely proportional to EBV. Higher [HbPre-Anes] or lower [HbTarget] facilitates sequestration of larger WBANH volume. Although PPV and [HbPre-CPB-MA] bear a direct relationship, as EBV decreases, proportionally greater increases in [HbPre-CPB-MA] occur. The impact of PPV reduction on precardiopulmonary bypass hemoglobin concentration [HbPre-CPB] is reflected by the “excess hemoglobin” over the minimum hemoglobin threshold (designated as 7 g/dL in this study). For each 100-mL decrement in PPV, “excess hemoglobin” increases from 1% (EBV = 8000 mL) to 2% (EBV = 4000 mL). In turn, increases in “excess hemoglobin” are associated with expansion of WBANH volume. In conclusion, sequential PPV reduction from 2000 mL increases the volume of WBANH that potentially may be sequestered prior to initiation of CPB. Therefore, the combination of PPV reduction with ANH may represent a useful blood conservation approach in adult patients undergoing cardiac surgery with CPB.

Preoperative acute normovolemic hemodilution: a meta-analysis.

Acute normovolemic hemodilution (ANH) involves withdrawal of whole blood with concurrent infusion of fluids to maintain normovolemia. The aim of this study was to quantify the efficacy and safety of preoperative ANH with a systematic review and meta-analysis. Randomized controlled trials were identified through MEDLINE (1966-2002) and the Cochrane Controlled Trials Database and with hand searching of journals. All trials of preoperative ANH reporting on allogeneic transfusion, bleeding, or adverse outcomes were included. Paired reviewers independently abstracted data. Outcomes were pooled using random-effects models. A total of 42 trials compared hemodilution to usual care or to another blood conservation method. The risk of allogeneic transfusion was similar among patients receiving ANH and those receiving usual care (relative risk [RR], 0.96; 95% CI, 0.90-1.01), or another blood conservation method (RR, 1.11; 95% CI, 0.96-1.28). Hemodiluted patients, however, were transfused from 1 to 2 fewer units of allogeneic blood. They had less total bleeding than patients receiving usual care (91 mL; 95% CI, 25-158 mL), although more intraoperative bleeding. Only one-third of studies reported on adverse events. The literature supports only modest benefits from preoperative ANH. The safety of the procedure is unproven. Widespread adoption of ANH cannot be encouraged.

Haemodilutional Effect of Standard Fluid Management Limits the Effectiveness of Acute Normovolaemic Haemodilution in AAA Surgery—Results of a Pilot Trial

Objective: To evaluate the impact of standard fluid management on the effectiveness of ANH as a blood conservation method in elective open AAA repair.Design: Prospective randomised controlled study.Methods: Thirty-four patients undergoing elective AAA repair were randomised to have ANH (16) or act as controls (18). Intra-operative cell salvage was permitted in both groups. Haemoglobin (Hb) concentrations were determined at variable intervals peri-operatively. Blood loss and the use of heterologous blood were recorded.Results: The pre- and post-operative Hb concentrations, surgical blood loss and the use of cell salvage were similar in both groups. Hb concentration (median, range) decreased significantly from pre-operative to aortic clamping (with blood loss <100 ml) in ANH patients from 8.8 (7.5–10.2) to 5.7 (4.2–6.6)mmol/l following ANH but also in controls from 8.6 (7.5–9.7) to 7.0 (4.5–9.0)mmol/l due to fluid infusion (P<0.01 for every comparison). Bank blood requirements were similar: median 2 units in ANH and 2.5 units in control patients (P=0.68).Conclusions: Large volumes of fluids infused during AAA repair already conserve blood by the mechanism of hypervolaemic haemodilution. When cell salvage is used with standard fluid management during AAA repair, additional ANH is ineffective in saving blood.

Blood conservation strategies in Jehovah’s Witness patients undergoing complex aortic surgery: a report of three cases

Thoracic aortic surgery in Jehovah’s Witness (JW) patients presents a unique challenge to the surgeon and anesthesiologist because the patient’s religious-based objection to the use of allogeneic blood products impacts surgical technique and intraoperative fluid management methodology. Successful thoracic aortic repair without the transfusion of allogeneic blood products is especially difficult because the outcome of this type of surgery usually depends on the transfusion of relatively large amounts of allogeneic blood products. 1 Svensson L.G. Crawford E.S. Hess K.R. et al. Experience with 1509 patients undergoing thoracoabdominal aortic operations. J Vasc Surg. 1993; 17: 357-368 Abstract Full Text Full Text PDF PubMed Scopus (1091) Google Scholar To maintain a treatment course congruent with the JW patient’s religious beliefs, alternative methods of blood conservation should be used by the anesthesiologist. 2 Dupuis J.F. Nguyen D.T. Anesthetic management of the patient who refuses blood transfusions. Int Anesthesiol Clin. 1998; 36: 117-131 Crossref PubMed Scopus (2) Google Scholar Two cases are presented in which a JW patient underwent repair of a thoracoabdominal aneurysm (TAA), and a third case of a JW patient who underwent repair of an aortic root and arch aneurysm. All cases used acute normovolemic hemodilution (ANH) and underwent successful surgical repair without the use of allogeneic blood products.

Influence of transfusions on perioperative and long-term outcome in patients following hepatic resection for colorectal metastases.

To determine if transfusion affected perioperative and long-term outcome in patients undergoing liver resection for metastatic colorectal cancer. Blood transfusion produces host immunosuppression and has been postulated to result in adverse outcome for patients undergoing surgical resection of malignancies. Blood transfusion records and clinical outcomes for 1,351 patients undergoing liver resection at a tertiary cancer referral center were analyzed. Blood transfusion was associated with adverse outcome after liver resection. The greatest effect was in the perioperative course, where transfusion was an independent predictor of operative mortality, complications, major complications, and length of hospital stay. This effect was dose-related. Patients receiving one or two units or more than two units had an operative mortality of 2.5% and 11.1%, respectively, compared to 1.2% for patients not requiring transfusions. Transfusion was also associated with adverse long-term survival by univariate analysis, but this factor was not significant on multivariate analysis. Even patients receiving only one or two units had a more adverse outcome. Perioperative blood transfusion is a risk factor for poor outcome after liver resection. Blood conservation methods should be used to avoid transfusion, especially in patents currently requiring limited amounts of transfused blood products.

Survey of anesthesia practice in spine surgery patients in the United States.

There is a wide range of anesthetic practice in spine surgery with respect to anesthetic choice, blood conservation, and monitoring. There is no ideal technique with respect to each of these choices. This study was designed to determine the usual practice for members of the Society of Neurosurgical Anesthesia and Critical Care (SNACC), with regard to the use of anesthetic technique, the type of monitoring used (and the person responsible for its application and interpretation), and the blood conservation strategies most often utilized for the management of patients undergoing spinal surgery. A total of 415 questionnaires were mailed to all current members of the SNACC. Of these, 85 (23%) were completed and returned. The majority of the respondents administer general anesthesia for lumbar laminectomy. Somatosensory evoked potential (SSEP) monitoring is available at most of the institutions (94%) but only utilized in 75% of patients undergoing a Harrington rod placement. Motor evoked potential monitoring is available at 50% of the institutions, but utilized 25% of the time for these surgeries. The two most frequent blood conservation strategies utilized are intraoperative salvage and autologous donation. The most frequent monitoring utilized for major spinal surgeries is SSEP. Autologous donation and intraoperative salvage are the most frequent blood conservation methods utilized.

Preoperative autologous plateletpheresis in patients undergoing open heart surgery.

Blood conservation is an important aspect of care provided to the patients undergoing cardiac operations with cardiopulmonary bypass (CPB). It is even more important in patients with anticipated prolonged CPB, redo cardiac surgery, patients having negative blood group and in patients undergoing emergency cardiac surgery. In prolonged CPB the blood is subjected to more destruction of important coagulation factors, in redo surgery the separation of adhesions leads to increased bleeding and difficulty in achieving the haemostasis and in patients with negative blood group and emergency operations, the availability of sufficient blood can be a problem. Harvesting the autologous platelet rich plasma (PRP) can be a useful method of blood conservation in these patients. The above four categories of patients were prospectively studied, using either autologous whole blood donation or autologous platelet rich plasma (PRP) harvest in the immediate pre-bypass period. Forty two patients were included in the study and randomly divided into two equal groups of 21 each, control group (Group I) in which one unit of whole blood was withdrawn, and PRP group (Group II) where autologous plateletpheresis was utilised. After reversal of heparin, autologous whole blood was transfused in the control group and autologous PRP was transfused in the PRP group. The chest tube drainage and the requirement of homologous blood and blood products were recorded. Average PRP harvest was 643.33 +/- 133.51 mL in PRP group and the mean whole blood donation was 333.75 +/- 79.58 mL in the control group. Demographic, preoperative and intra operative data showed no statistically significant differences between the two groups. The PRP group patients drained 26.44% less (p<0.001) and required 38.5% less homologous blood and blood products (p<0.05), in the postoperative period. Haemoglobin levels on day zero (day of operation) and day three were statistically not different between the two groups. We conclude that autologous plateletpheresis is a better method of blood conservation in terms of better haemostasis, and less requirement of blood and blood products in the postoperative period as compared with the autologous whole blood donation. This technique can be especially useful in the above-mentioned categories of patients.

A mathematical model of cell salvage efficiency.

Cell salvage (CS) is one of the modalities that can be used during surgery to decrease the use of allogeneic blood. Unlike acute normovolemic hemodilution, the efficiency of CS has not been mathematically modeled. In this article, we hypothesized that a mathematical model could predict the decline of hematocrit during CS. The model that was developed accounts for both the effect of decreasing the hematocrit because of blood loss and the effect of increasing hematocrit because of the readministration of washed blood in an isovolemic patient. The efficiency of CS is defined to be the maximum allowable blood loss (MABL) for a fixed blood volume and a fixed transfusion trigger. For demonstration purposes, variables used for a hypothetical patient included an estimated blood volume of 5000 mL, a presurgery hematocrit of 45%, and a transfusion trigger of 21%. The MABL in a typical case was 9600 mL, with a CS red cell recovery rate of 60%. Patient records from a convenience sample showed an average recovery rate of 57% with 20% variability. This mathematical model suggests that CS can be a highly effective blood conservation method when red blood cell collection is optimal. In this study, a mathematical model of cell salvage was developed. The model was then matched against real clinical cases to gain an understanding of the variables that modify cell salvage efficiency. The model illustrates that cell salvage can be a highly effective method of avoiding blood transfusion.

Progress in ascending and aortic arch surgery: minimally invasive surgery, blood conservation, and neurological deficit prevention

Background Herein are described recent developments in aortic surgery techniques and the improved results. Methods Of 403 ascending and aortic arch operations, 68 patients underwent minimally invasive aortic surgery including 23 for aortic dissection, 5 for Marfan syndrome, 29 reoperations, and 39 with hypothermic arrest. Blood conservation methods were used in 187 of the 403 patients (46.5%). Aortic valve procedures were used in 267 (66.2%), including 51 (12.7%) valve-preserving operations. A protocol for stroke and neurocognitive deficit prevention was used in an attempt to prevent neurologic deficits. Data were prospectively collected and included new neurocognitive events either by formal testing (n = 35) or by informal questioning. Results Stroke occurred in 2.0% (8 of 403); clinical gross neurocognitive deficits in 2.5% (10 of 403) with a 98% 30-day survival. For those patients undergoing the minimally invasive operation 1 hospital death occurred (98.5% survival). Homologous operative transfusions were required in only 12% of blood conservation patients (23 of 187) and their postoperative intubation time, intensive care unit (ICU) stay, and hospital stay were significantly shorter ( p < 0.04). Conclusions Minimally invasive surgery is particularly useful for reoperations. The blood conservation methods appear to be beneficial and the number of neurologic deficits is low with the current protocol.

Comparison of three methods of blood conservation in expected bleeders in OPCAB (off pump coronary artery bypass surgery)

Background. Blood conservation has remained a challenge in the field of cardiac surgery, especially since the advent of OPCAB. This has led us to conduct this study to compare the efficacy of desmopressin, aprotinin bolus doses and aprotinin continuous infusion in controlling the periorative bleeding.

Mechanical methods of reducing blood transfusion in cardiac surgery: randomised controlled trial

Objective: To assess the effectiveness of two mechanical methods of blood conservation in reducing the need for allogeneic red blood cells or coagulation products during cardiac surgery.Design: Randomised controlled trial.Setting:...

Utility and cost-effectiveness of preoperative autologous blood donation in gynecologic and gynecologic oncology patients

OBJECTIVE: To evaluate utility and cost-effectiveness of preoperative autologous blood donation in gynecologic and gynecologic oncology patients. METHODS: Pheresis unit records were retrospectively reviewed to identify all women who performed autologous blood donation. Clinical charts were abstracted. Use rate (number of units used/number of units donated) and quality-adjusted life years were calculated. Statistical analysis consisted of χ 2, Student t, and Fisher exact tests. RESULTS: A total of 106 women with benign ( n = 63) and malignant disease ( n = 43) donated 143 units (1.4 units per patient) of which 126 (88%) were discarded. Fifteen patients (14%) were transfused a total of 24 units, 17 autologous (71%) and seven allogeneic (29%). Those transfused had a significantly higher estimated blood loss (700 mL versus 275 mL, P < .001), lower nadir hemoglobin (7.9 versus 9.6, P < .001), and longer hospital stay (4.9 days versus 4.0 days, P = .05). Despite similar estimated blood loss (370 mL versus 310 mL), the use rate for malignant versus benign disease was significantly greater (0.31 versus 0.07, P = .005). Radical versus nonradical surgery had a significantly higher estimated blood loss (620 mL versus 250 mL, P = .001) and use rate (0.26 versus 0.11, P = .001) as well. Estimated cost per quality-adjusted life years for autologous blood donation for each category exceeded $1,000,000. CONCLUSION: Autologous blood donation is an expensive medical practice and does not guarantee that exposure to allogeneic blood will not occur. If pursued, it should be directed towards those who have a known malignancy or those for whom radical surgery is anticipated. Other methods of blood conservation may be safer and more cost-effective.

Utility and Cost-Effectiveness of Preoperative Autologous Blood Donation in Gynecologic and Gynecologic Oncology Patients

In Brief OBJECTIVE To evaluate utility and cost-effectiveness of preoperative autologous blood donation in gynecologic and gynecologic oncology patients. METHODS Pheresis unit records were retrospectively reviewed to identify all women who performed autologous blood donation. Clinical charts were abstracted. Use rate (number of units used/number of units donated) and quality-adjusted life years were calculated. Statistical analysis consisted of χ2, Student t, and Fisher exact tests. RESULTS A total of 106 women with benign (n = 63) and malignant disease (n = 43) donated 143 units (1.4 units per patient) of which 126 (88%) were discarded. Fifteen patients (14%) were transfused a total of 24 units, 17 autologous (71%) and seven allogeneic (29%). Those transfused had a significantly higher estimated blood loss (700 mL versus 275 mL, P < .001), lower nadir hemoglobin (7.9 versus 9.6, P < .001), and longer hospital stay (4.9 days versus 4.0 days, P = .05). Despite similar estimated blood loss (370 mL versus 310 mL), the use rate for malignant versus benign disease was significantly greater (0.31 versus 0.07, P = .005). Radical versus nonradical surgery had a significantly higher estimated blood loss (620 mL versus 250 mL, P = .001) and use rate (0.26 versus 0.11, P = .001) as well. Estimated cost per quality-adjusted life years for autologous blood donation for each category exceeded $1,000,000. CONCLUSION Autologous blood donation is an expensive medical practice and does not guarantee that exposure to allogeneic blood will not occur. If pursued, it should be directed towards those who have a known malignancy or those for whom radical surgery is anticipated. Other methods of blood conservation may be safer and more cost-effective. The use of preoperative autologous blood donation in gynecologic patients is not cost-effective.

Allogeneic transfusion requirements after autologous donations in posterior lumbar surgeries.

A retrospective study of blood transfusion practices after posterior lumbar spine surgery was performed. To determine the overall use rate of autologous blood donations for different spine surgeries, and to identify the risk of requiring additional allogeneic blood transfusions. In an attempt to avoid allogeneic blood transfusions and its associated risks, patients frequently are asked to donate autologous blood before many elective spine surgeries. There is a lack of published data on the use rate for these autologous blood donations, and on their ability to prevent allogeneic blood exposure. A retrospective review of hospital charts and blood bank records was conducted on 191 consecutive patients who had undergone three categories of lumbar spine surgery: laminectomy alone, laminectomy with a noninstrumented posterolateral fusion, and laminectomy with an instrumented posterolateral fusion. Nearly 80% of the autologous blood donated by patients who underwent simple laminectomies was wasted. However, the vast majority (70-90%) of patients who underwent fusion used their autologous blood. In the patients who underwent fusion, autologous blood donations decreased the risk of allogenic blood transfusions by 75% in noninstrumented fusions and 50% in instrumented fusions, as compared with the patients who elected not to donate blood before the fusion (P < 0.05). A substantial number of patients who underwent instrumented fusions (nearly 40%) required additional allogeneic blood transfusions despite predonation of blood. Autologous blood donations are indeed advantageous in decreasing allogeneic blood usage of patients undergoing fusion, but additional methods of blood conservation (intraoperative salvage and preoperative erythropoietin) seem necessary to diminish the allogeneic blood requirements further, especially in those patients undergoing instrumented lumbar fusion.

Hemostatic Abnormalities in Cardiopulmonary Bypass: Pathophysiologic and Transfusion Considerations

Cardiac surgical procedures typically use cardiopulmo nary bypass (CPB), a technique that diverts blood from the heart and lungs, where it is oxygenated and pumped back into the circulation. CPB is associated with significant pathophysiologic changes leading to an increased bleeding risk. Bleeding during CPB occurs for multiple reasons; the primary reason is the expo sure of blood to the material components of the CPB system, with intense systemic coagulation and platelet, fibrinolytic, and endothelial activation. To counteract the coagulation activation, extremely high levels of heparin anticoagulation are required to prevent sys temic thrombosis. Thrombin generation through tissue factor pathway activation is now thought to be the predominant mechanism of coagulation activation in CPB. The stimulus for tissue factor exposure to blood is thought to be a systemic activation of tissue factor on monocytes and endothelial cells caused by comple ment activation by the CPB materials and circulating inflammatory mediators. Despite improvements in the CPB system, surgical techniques, and blood conserva tion methods, the demand for blood in such procedures remains sustantial. Optimal blood use can be achieved by combining blood conservation measures with the transfusion of blood components according to strict guidelines. Blood is a limited resource and must be used wisely and cautiously. The risks and costs associ ated with transfusion are compelling reasons to mini mize unnecessary exposure to blood. However, the bene fits of transfusion are well established, and the risks are reasonably low. New developments in the surfaces of the CPB system, use of established and new protease inhibitors, and new blood conservation measures offer promise in decreasing the bleeding risk associated with CPB.