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Ann Thorac Surg 1996;61:1177-1181
© 1996 The Society of Thoracic Surgeons

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Original Article: Cardiovascular

Autotransfusion After Coronary Artery Bypass Grafting Halves the Number of Patients Needing Blood Transfusion

Departments of Anaesthesiology, Cardio-Thoracic Surgery, and Clinical Chemistry, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark

Accepted for publication December 8, 1995.

	Abstract

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Background. Several randomized studies about autotransfusion of shed mediastinal blood in patients undergoing coronary artery bypass grafting have resulted in divergent findings concerning reduction of the need for homologous blood transfusions. Most of these studies used less strict criteria for homologous blood transfusion than applied in daily clinical practice.

Methods. A prospective, randomized, controlled study involving 120 patients having elective, uncomplicated coronary artery bypass grafting was performed. The autotransfusion group received transfusion of shed mediastinal blood for 18 hours. Criteria for homologous blood transfusion were hemoglobin concentration less than 5.0 mmol/L in the intensive care unit and less than 5.5 mmol/L during the rest of the hospital stay.

Results. Twenty-eight percent of patients in the autotransfusion group received homologous blood transfusion versus 55% in the control group (p= 0.007). Ninety-five percent of the shed mediastinal blood was transfused. In the autotransfusion group, a total of 26 units of homologous blood was used versus 78 units in the control group (p < 0.001).

Conclusions. Autotransfusion of shed mediastinal blood in patients undergoing elective, uncomplicated coronary artery bypass grafting halves the number of patients needing homologous blood and reduces the amount of homologous blood given.

	Introduction

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
See also page 1181.

The need for blood transfusion in patients undergoing coronary artery bypass grafting has decreased during the past 20 years [1, 2]. Several ways of reducing the requirement for homologous blood in cardiac surgery have been actively pursued because of the concern about infections and immunologic reactions from homologous blood transfusions [3–7]. These methods include predonation of blood prior to operation [8], intraoperative withdrawal of blood before cardiopulmonary bypass (CPB) [9], and intraoperative plasma separation with a cell-saving device [10].

The first report on autotransfusion was by Blundell [11] in 1818. The first autotransfusion in a human was reported by Duncan [12] in 1886, and reinfusion of shed mediastinal blood was first described by Schaff and associates [13] in 1978. Randomized, prospective investigations of the benefit of autotransfusion of shed mediastinal blood have yielded conflicting results. Three studies [14–16] showed a decreased requirement of banked blood transfusion and advocated that the method be used routinely in cardiac operations. Only one [16] of these randomized studies reported a reduction in the number of patients receiving blood transfusions, ie, from 92% in the control group to 75% in the autotransfusion group. In that study, there were no fixed criteria for blood transfusion, and the average blood requirement in the autotransfusion group was 2.7 units. In the two other randomized studies [14, 15], autotransfusion did not reduce the number of patients needing homologous blood transfusion. On the other hand, five different randomized studies [17–21] concluded that autotransfusion did not decrease the need for homologous blood transfusion.

The aim of our study was to investigate whether autotransfusion of shed mediastinal blood could reduce the number of patients needing homologous blood transfusion and reduce the amount of transfused homologous blood if fixed transfusion criteria were used.

The present study is part of a larger prospective, randomized, and controlled study concerning autotransfusion of shed mediastinal blood in patients undergoing coronary artery bypass grafting. At the same time, we studied the coagulation system, renal function, oxygen capacity of the blood, and coronary enzymes. These data will be published separately.

	Material and Methods

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Between November 1992 and October 1993, 120 adult patients undergoing primary elective coronary artery bypass grafting entered the study. Accepting a risk of 5% of overlooking a true difference (type I error) and a risk of 10% of accepting a false difference (type II error), this number of patients would allow detection of a difference between the autotransfusion group and the control group of at least 15% in the number of patients receiving homologous blood. The setup was a prospective, randomized, controlled cohort investigation. The study was approved by the regional ethics committee, and all patients gave informed written consent. Not included in the study were patients with a bleeding time of greater than 10 minutes by the method of Ivy, anticoagulation treatment, preoperative left ventricular ejection fraction of less than 0.40, diabetes, and pulmonary or kidney disease.

Study Protocol
Anesthesia was induced and maintained with fentanyl, midazolam hydrochloride, pancuronium bromide, and enflurane in oxygen. Hemodynamic variables were monitored with radial artery, central venous, and pulmonary artery catheters. In all patients, operation was performed through a median sternotomy using standard techniques for CPB with a crystalloid prime. Cardiopulmonary bypass was conducted using an arterial roller pump with a Bard cardiotomy/autotransfusion reservoir and a Bard membrane oxygenator (William Harvey HF-570). St. Thomas' cardioplegic solution (4°C) was used for myocardial protection, and CPB was performed at moderate hypothermia (32° to 36°C). Anticoagulation was established with heparin sodium, 300 IU/kg, and was monitored throughout the operation. After CPB, heparin was neutralized with protamine sulfate. The activated prothrombin time was lower than 40 seconds before the patient entered the study.

At the conclusion of the procedure, blood remaining in the bypass circuit was collected in bags for later transfusion. By the end of the operation, the mediastinal and pleural tubes were attached to the inlet port of the Bard cardiotomy/autotransfusion reservoir. Prior to transfusion, the shed mediastinal blood was filtered through the 40-µm filter in the cardiotomy reservoir.

After arrival in the intensive care unit, the patients were randomly allocated (120 closed envelopes) to autotransfusion of shed mediastinal blood (autotransfusion group) or to the control group. Excluded from the study after randomization were patients who underwent a revisional procedure for bleeding within the first 18 postoperative hours and patients needing inotropic drugs or an intraaortic balloon pump to maintain a cardiac index higher than 2 L•min^-1•m^-2. All the residual blood from the CPB circuit was transfused. In the autotransfusion group, shed mediastinal blood from the cardiotomy reservoir was transfused every hour for the first 18 postoperative hours if more than 20 mL of blood had accumulated. In the control group, the cardiotomy reservoir was used for mediastinal drainage only.

The criteria for postoperative volume replacement were as follows:

1. Cardiac index less than 2.2 L•min^-1•m^-2 and pulmonary capillary wedge pressure less than 18 mm Hg or
   
2. Mean arterial pressure less than 60 mm Hg or
   
3. Urine output less than 1 mL•kg^-1•h^-1.
   

Postoperative volume therapy was performed with crystalloid solutions. Homologous blood transfusion was given in accordance with the following criteria:

1. Hemoglobin concentration less than 5.0 mmol/L during stay in the intensive care unit
   
2. Hemoglobin concentration less than 5.5 mmol/L during stay in the surgical ward.
   

The difference in hemoglobin concentration reflects the clinical practice in our hospital and the state of hemodilution of patients the first day after CPB. The blood used for transfusion was packed red blood cells stored in saline solution, adenine, glucose, and mannitol, 350 mL/U.

Blood samples were drawn preoperatively and 1 hour, 6 hours, 18 hours, 2 days, 6 days, 1 month, and 3 months after operation and analyzed for hemoglobin concentration, hematocrit, platelet count, reticulocyte count, and levels of aspartate aminotransferase, lactate dehydrogenase, and creatine kinase MB activity. The physicians in the intensive care unit prescribed blood products in accordance with these criteria but were not involved in the study. The surgeons prescribing blood products during the stay in the surgical ward were unaware of whether the patients had received autotransfusion or not during the stay in the intensive care unit.

Postoperative bleeding was recorded every hour for 18 hours in all patients. The number of transfusions of packed red blood cells and other blood products was recorded for 3 months after the operation. Infections, number of perioperative infarctions, and mortality within 3 months after the operation were noted.

Statistical Methods
The amount of bleeding and the number of blood transfusions are presented as the median value and the range. All other data are presented as the mean ± the standard deviation. Statistical analysis was performed using the Mann-Whitney test, Kruskal-Wallis test, and Fisher's exact test. The difference between the two groups in the percentage of patients exposed to homologous blood products was calculated and called the therapeutic gain; the 95% confidence interval was calculated. A p value (type I error) of less than 0.05 was considered significant.

	Results

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Of the 120 patients enrolled in the study, 109 completed it according to protocol. Eleven patients were excluded during the study; 7 in the autotransfusion group and 4 in the control group. There was no difference between the groups in the number of patients excluded. Five patients required reoperation for bleeding within the first 18 hours, 3 patients had low cardiac output syndrome, and 3 patients in the autotransfusion group were excluded for technical reasons (air leak in the cardiotomy reservoir). No patient required the use of an intraaortic balloon pump.

There were no differences between the two groups regarding patient age, weight, height, preoperative left ventricular ejection fraction, and sex (Table 1). Duration of CPB, aortic cross-clamp time, number of grafts per patient, operative blood loss, and perioperative weight gain were similar in the two groups (Table 2). None of the patients received homologous blood transfusion during the operation. Before the start of the study period, ie, at the time of randomization, there was no difference in hemoglobin concentration between the two groups.

Fifteen patients (28%) in the autotransfusion group received homologous blood transfusion compared with 31 patients (55%) in the control group (p = 0.007) (Fig 1). The therapeutic gain was 27% (95% confidence interval, 10% to 46%). The total amount of homologous blood used in the control group was about triple that in the autotransfusion group (78 versus 26 units). There was no significant difference between the groups in the number of patients receiving homologous blood during the stay in the surgical ward. One patient in both groups received fresh frozen plasma and platelet transfusion. There were no significant differences between the two groups in hemoglobin concentrations and hematocrit values during the 3-month follow-up, and all the hemoglobin concentrations had normalized 1 month postoperatively (Fig 2).

View larger version (18K): [in this window] [in a new window]   Fig 1. . Number of homologous blood units used postoperatively.

View larger version (38K): [in this window] [in a new window]   Fig 2. . Hematologic data during 3-month follow-up. There were no significant differences between the groups. (Pre = preoperative; 0h = before start of autotransfusion; 1h = 1 hour postoperative before start of autotransfusion; 6h, 18h = hours after start of autotransfusion; 2 day, 7 day, 1 month, 3 month = postoperative time.)

There were no differences between groups in the number of acute myocardial infarctions (autotransfusion group, four; control group, five) or sternal infections (autotransfusion group, one; control group, three). Sepsis did not develop in any patient.

	Comment

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
This is among the first prospective, randomized studies using clearly defined criteria for transfusion and volume replacement that demonstrate that postoperative autotransfusion of shed mediastinal blood after elective, uncomplicated primary coronary artery bypass grafting reduces the number of patients needing homologous blood. We reinfused 95% of the shed mediastinal blood, which resulted in a 50% reduction in the risk of exposure to homologous blood (from 55% of patients in the control group to 28% in the autotransfusion group). In two other studies [14, 15] showing that autotransfusion reduced homologous blood requirements, this did not lead to a reduction in the number of patients receiving blood transfusion. The risk of receiving homologous blood was 70% to 85% in both the autotransfusion and control groups [14, 15]. Schaff and associates [14] were able to transfuse only 50% of the shed mediastinal blood, and their criterion for transfusion was a hematocrit of less than 35% (hemoglobin concentration less than 7.3 mmol/L). Eng and co-workers [15] transfused only 40% of the shed mediastinal blood and used the same transfusion criteria we did in this study. However, their use of homologous blood was much higher than ours, which may be explained by the lower amount of autotransfusion.

Only one randomized study [16], involving 130 patients, has previously shown a reduction in the number of patients receiving homologous blood transfusion (from 95% in the control group to 75% in the autotransfusion group). No fixed criteria for transfusion and no information about hemoglobin values (or hematocrit values) before, during, and after autotransfusion were reported. The period of autotransfusion was 6 hours, and the amount of autotransfusion was 336 mL per patient (65% of the postoperative bleeding). The average homologous blood requirement per patient (2.7 units and 3.3 units in the control group) was much higher than in our study (0.5 unit and 1.4 units in the control group).

Comparing our results with randomized studies [17–21] showing no reduction in the need of homologous blood transfusion, three main reasons could explain the differing results: the smaller number of patients in the studies [19, 20], higher or no criteria for transfusion [17, 18, 20, 21], and transfusion of smaller proportions of the shed mediastinal blood [17–21].

As there was no difference in postoperative hemoglobin or hematocrit levels during our study, it is evident that the transfusion practice was the same in both groups. We believe that because we could transfuse almost all the shed mediastinal blood over the first 18 postoperative hours and because the transfusion protocol was strictly respected, the patients receiving autotransfusion were at distinctly less risk for homologous blood transfusion. The autotransfusion of shed mediastinal blood with fixed criteria for blood transfusion reduced the average use of homologous blood by 1 unit per patient at a price of approximately $125 US (Danish price). The cost of the accessories to the Bard cardiotomy reservoir needed for autotransfusion is about $20 US.

Like others [14, 16], we found no clinical or laboratory signs of coagulopathy. There were no septic reactions, and the number of sternal infections was similar in the two groups. The occurrence of perioperative acute myocardial infarctions was also similar.

In conclusion, autotransfusion of shed mediastinal blood in patients undergoing elective, uncomplicated coronary artery bypass grafting halves the number of patients needing homologous blood and reduces the amount of homologous blood given.

	Footnotes

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Presented at the Forty-third Annual Meeting of the Scandinavian Association for Thoracic Surgery, Aug 24–26, 1994.

Address reprint requests to Dr Schmidt, Department of Anaesthesiology, Gentofte Hospital, Niels Andersensvej 65, DK-2900 Hellerup, Denmark.

	References

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 

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