The use of allogeneic blood transfusion after coronary artery surgery is still high despite published transfusion guidelines and costly blood conservation strategies [27
]. Readily available patient variables can predict patients at risk for transfusion [29
]. The classification of coronary artery bypass graft patients on the basis of attributes known preoperatively and by conduits used yields subsets of patients with distinctly different transfusion requirements and in-hospital outcomes [30
Prediction models based on preoperative variables may facilitate blood component management and improve the efficiency of ordering blood before operations for patients undergoing CABG surgeries in order to assist blood banks in improving responsiveness to clinical needs [1
Two patterns are usually prevailing for preoperative blood component stocking and preparation in cardiac surgical patients. One practice is the cross-matching of a large number (4 or more) of PRBC units that are usually – at least in part – not utilized, leading to wasting blood bank efforts and resources, including time, space, and reagents. The other is cross-matching a limited number of units (usually 2 units of PRBCs) and typing an extra 2 units to be cross-matched at need. This may lead to a blood bank emergency when a patient is in urgent need for blood component transfusion, putting a considerable stress and time load on the blood bank team. A model to predict patients at risk of requiring more than the standard number of blood components would alleviate plenty of blood bank stress, save time and resources, and allow better utilization of available space and blood resources [1
Blood conservation has become one of the most important issues in cardiac surgery [29
]. Some of blood conservation strategies are cost-efficient and simple to utilize and can be employed in nearly all cardiac surgical patients without adding further risk to the patient or effort to the operating room team, including non-hemic prime of cardiopulmonary bypass machine, salvage of blood from surgical field using cardiotomy suction, hemodilution during CPB, retransfusion of all contents of oxygenator at the end of CPB, and use of ultrafiltration and modified ultrafiltration during and after CPB. Use of other modalities, such as antifibrinolytic therapy, preoperative autologous blood donation, use of cell saving devices, and auto transfusion of shed mediastinal chest tube drainage is still limited owing to doubts about their effectiveness and inappropriateness for use in many patients [8
]. In addition, the routine use of such expensive and sophisticated techniques in all cardiac surgical patients causes higher cost exceeding the benefit obtained. So, these strategies should be utilized more critically [37
The use of predictors of allogeneic PRBC use in CABG patients allows for preoperative risk stratification and may allow for more rational resource allocation of costly blood conservation strategies [28
]. Identifying high-risk patients for transfusion would alter perioperative patient management and allow the employment of a multimodality approach to blood conservation resulting in a lower transfusion rate at a reasonable cost-efficiency [38
In our study, 67.6% (71 patients) of all patients undergoing primary isolated CABG operations either on pump or off-pump received PRBC transfusion, 33.3% of the total number (35 patients) needed more than 2 units, and only 13.3% (14 patients) needed more than 4 units of PRBCs. The mean number of PRBC units received was 2.16 ± 2.25 unit per patient.
The strongest predictors of PRBC use in our study were the use of CPB (P = 0.0001), preoperative hematocrit ≤ 40 (P = 0.0021), body weight ≤ 70 kg (P = 0.0105), serum creatinine > 100 μmol/L (P = 0.0142). Other predictors included female gender, age > 65 years, BSA ≤ 1.75 m2, BMI ≤ 25, hemoglobin ≤ 13 gm/dL, Euro SCORE > 2, radial artery use, and higher number of distal anastomoses (a cut point could not be derived).
Current smoking; associated comorbidities (including diabetes mellitus, hypertension, cerebrovascular disease, COPD and peripheral vascular disease); preoperative platelet count, PT, PTT, and serum albumin; left ventricular EF; type of intervention (elective/emergency); type of conduits used (apart from radial artery); and duration of CPB and aortic cross-clamping were not significant predictors for PRBC transfusion in our patients. Also, preoperative use of heparin or continuation of antiplatelet treatment beyond the last 5 preoperative days didn't prove as significant predictors of PRBC transfusion.
Clinical studies conducted to identify perioperative risk factors and predictors of blood component use in cardiac surgical procedures varied widely regarding study designs, surgical procedure characteristics, study period, and study end points.
In a Japanese study, Isomatsu et al. (2001)
] studied 89 patients undergoing isolated CABG surgery over 2 years, from 1997 to 1999, to determine preoperative predictors of the need for blood transfusions during CABG surgery. Of these, 66 patients (74%) received transfusion during hospitalization. Independent predictors were emergency surgery, lower hematocrit, older age, and presence of peripheral vascular disease. Optimal cutoff of hematocrit was 39% and age 64 years.
Karkouti et al. (2001)
] studied all patients undergoing elective first-time CABG surgery prospectively from January 1997 to September 1998 in Ontario, Canada. Transfusion rate was 29.4 percent. Predictors included preoperative hemoglobin, weight, age, and sex.
In a retrospective analysis of 400 consecutive patients undergoing CABG, including emergency and re-operations, Litmathe et al. (2003)
] found that 132 patients (33%) received PRBC transfusion during hospitalization. On average, 2.2 ± 0.68 units of red cell concentrate were transfused per patient. Predictive parameters were age > 70 years, preoperative hemoglobin < 11 gm/dL, reoperation, and ejection fraction < 0.35. The authors could not find any significantly increased red cell concentrate transfusion in female cases, insulin dependent diabetes mellitus, or impaired renal function.
Scott et al. (2003)
] studied impact of CPB, hematocrit, gender, age, and body weight on blood use in 1235 consecutive patients undergoing primary CABG over a period of 2 years under on-pump or off-pump technique. PRBC transfusion was used in 72.5% of on-pump patients compared with 45.7% of off-pump patients. A lower percentage of males (52.6%) than females (79.4%) received transfusion. Use of CPB, preoperative hematocrit < 35%, female gender, increasing age (≥ 65 years), and decreased body weight (≤ 83 Kg) were significant predictors of transfusion. The strongest predictors of PRBC transfusion were preoperative Hct < 35% and use of CPB.
Arora et al
., in 2004
], studied 3,046 consecutive, isolated CABG patients over 3 years to identify independent predictors of allogeneic blood product transfusion. Allogeneic blood was used in 23% of all patients and 16.9% of isolated, elective, first-time CABG cases. Independent predictors of blood product usage were preoperative hemoglobin 12 gm/dL or less, emergent operation, renal failure, female sex, age 70 years or older, left ventricular ejection fraction 0.40 or less, redo procedure, and low body surface area. The authors validated this model on 2,117 consecutive isolated CABG patients.
Al-Shammari et al. (2005)
] reviewed the medical records of 159 consecutive primary CABG patients retrospectively to determine the perioperative factors associated with intraoperative blood transfusion. Overall, 128 (80.5%) patients received blood product transfusion intraoperatively, 113 (70.5%) of them received PRBCs and the remaining received fresh frozen plasma and platelets. Moreover, 23 patients (12.6%) received more than two PRBC units intraoperatively. Totally, 159 patients consumed 342 units of PRBCs at an average of 2.1 units per patient. Significant factors associated with intraoperative RBC transfusion were: age > 60 years, female gender, preoperative hemoglobin < 12 gm/dL, and 3 or more coronary bypass grafts constructed.
McDonald and McMillan
, in 2005
], utilized the product of BSA (m2
) and preoperative hemoglobin (gm/L) as an index for intraoperative blood transfusion, the Transfusion Predictor Product (TPP). For patients with TPP less than 211.7 units, 46% received blood transfusion intraoperatively. At a TPP greater than 211.7 units, 6% of patients had intraoperative blood transfusion. They suggested that patients with a TPP > 211.7 do not require routine cross-matching of blood.
The role of increased postoperative chest tube drainage should be considered as the cause of lowering postoperative hemoglobin/hematocrit to the level necessitating PRBC transfusion according to the transfusion guidelines employed and not as a predictor.
Preoperative coagulation parameters (platelet count, PT, PTT) couldn't prove to be significant predictors for PRBC use in our study. This can be explained by the very small number of patients in our study with subnormal platelet count or prolonged PT and PTT due to our center's adherence to a strict policy regarding preoperative coagulation status. In elective cases, antiplatelets are stopped for at least 5 days preoperatively except if strongly indicated, highest PT and PTT allowed for CABG surgery is 15 seconds and 44 seconds, respectively, and the lowest platelet count accepted is 150 × 103/L. In emergency cases, patients not fulfilling these criteria are usually postponed for few hours up to 72 hours for control of their coagulation parameters unless earlier/immediate surgical intervention is indicated. This accounts to the narrow range reported in this study for PT (9 – 15 seconds) and PTT (28 – 46 seconds), thus ameliorating the effect of these otherwise important parameters as predictors of bleeding/transfusion.
Although use of CPB and number of distal anastomoses are intraoperative events, rather than preoperative; yet, in the vast majority of cases, both are usually planned from preoperative parameters (including patient's general condition and demographic variables, left ventricular function, and coronary angiography data about number and sites of diseased coronary vessels). Changes from off-pump to on-pump and omitting anastomoses based on intraoperative findings and/or events are usually kept within a narrow range. So, use of CPB and number of distal anastomoses still maintain their validity as preoperative predictors for blood preparation and use of blood conservation modalities.
Radial artery use was found statistically significant as a predictor for PRBC use in the perioperative setting. This could not be explained in light of previous researches or literature. We couldn't determine if this was a mere coincidental association or due to the association of radial artery use with other verified predictors for transfusion, e.g. number of distal anastomoses and use of CPB.
We chose body weight (and not BSA or BMI) for analysis in most models owing to the fact that univariate analysis and multivariate analysis proved that weight is a stronger predictor for PRBC transfusion than BSA and BMI. Also, Hct was used in most multivariate analysis models instead of Hb as it was a stronger predictor for transfusion than Hb by univariate analysis.
The strongest predictor of PRBC use in our study was the use of CPB. Of 48 patients in whom CPB was used, 41 (85.4%) received PRBC transfusion compared with 30 patients (52.6%) of 57 off-pump patients. Off-pump CABG eliminates the risks of cardiopulmonary bypass and the systemic inflammatory response it elicits [42
A retrospective review of 744 patients undergoing multivessel CABG either on-pump (n = 609) or off-pump (n = 135) was carried out by Kshettry et al. (2000)
]. Postoperative blood loss and use of blood transfusions were significantly less in patients operated upon off-pump.
Three other studies were in agreement with our results. Nuttal et al. (2003)
] retrospectively studied charts of 200 adult patients who underwent CABG either on-pump or off-pump. Although heparin was not reversed at the end of OPCAB patients, OPCAB surgery was associated with an overall reduction in allogeneic transfusion requirements.
In a large series, Frankel et al. (2005)
] compared 3646 off-pump CABG patients with a contemporaneous control group of 5197 on-pump CABG patients. Off-pump CABG was associated with a lower need for single and multiple unit postoperative blood transfusions compared to on-pump CABG patients.
On the contrary, Gerola et al. (2004)
], in a multicenter randomized study on 160 selected low-risk patients undergoing CABG on-pump (80 patients) or off-pump (80 patients), did not find any statistical difference in blood component use between on-pump and off-pump patients; 43.7% of on-pump patients and 43% of off-pump patients received blood component transfusion. Number of blood units used in on-pump patients was 2.9 ± 1.8 unit per patient and 2.2 ± 1.3 unit per patient in off-pump patients.
In our study, out of 620 units of PRBCs cross-matched for 105 patients undergoing first-time isolated CABG (4 units for patients) according to our hospital's policy, only 192 units were transfused (30.9%) and another 35 units were cross-matched and transfused in the 14 patients who received > 4 units of PRBCs. This reflects the necessity of developing a blood reservation policy considering patients individually based on their predicted transfusion risks. Such a policy would have saved > 50% of blood bank's efforts and resources.
Among the limitations of this study is the small number of patients included due to the small size of our center's target population. Another limitation is restricting the study to PRBC transfusion predictors only. There is a strong need in our center for determining the predictors of fresh frozen plasma and platelet transfusion in cardiac surgical procedures. The cost-efficiency of application of a blood conservation strategy targeting patients at risk of transfusion needs verification through prospective clinical studies.