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Ann Thorac Surg 1996;62:105-108
© 1996 The Society of Thoracic Surgeons

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Original Articles: Cardiovascular

Autotransfused Shed Mediastinal Blood Has Normal Erythrocyte Survival

Department of Anaesthesiology, Gentofte Hospital, and Department of Clinical Physiology and Nuclear Medicine, Gentofte and Herlev Hospitals, University of Copenhagen, Hellerup, Denmark

Accepted for publication February 23, 1996.

	Abstract

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Background. Autotransfusion of shed mediastinal blood may reduce the need for homologous blood transfusions in cardiac surgery. In an earlier study we have shown that the red blood cells (RBCs) of shed mediastinal blood have a normal membrane stability (osmotic fragility) compared with circulating RBCs after coronary artery bypass grafting and better than stored RBCs. This indicates that RBCs in shed mediastinal blood are not damaged further during salvage. It remains to be determined how autotransfusion affects the survival of RBCs from shed mediastinal blood.

Methods. We performed a prospective, randomized, and controlled study involving 26 patients having elective, uncomplicated coronary artery bypass grafting. Dual-isotope labeling technique (chromium 51 and technetium 99m) was used to investigate the 24-hour survival of RBCs from shed mediastinal blood and RBCs from circulating blood, and to estimate the mean survival time of RBCs.

Results. There was no significant difference between the 24-hour survival of shed mediastinal RBCs and circulating RBCs. The estimated mean cell lifespan was 20.5 days (range, 11.6 to 29.0 days) for shed mediastinal RBCs and 22.7 days (range, 14.4 to 36.2 days) for circulating RBCs.

Conclusions. The survival of RBCs from shed mediastinal blood after autotransfusion is comparable with the survival of RBCs in the patients' circulating blood.

	Introduction

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Autotransfusion of shed mediastinal blood has been used to reduce the blood requirement after coronary artery bypass grafting (CABG) [1–4]. During cardiopulmonary bypass the red blood cells (RBCs) are damaged, with an increase in plasma hemoglobin at the end of cardiopulmonary bypass [1, 5, 6]. During salvage shed mediastinal blood has been in contact with various tissue types and exposed to suction, which might damage the blood cells. Several trials have shown that the concentration of free hemoglobin is elevated in shed mediastinal blood [5–8]. Activation of the complement system, which occurs during autotransfusion, may also induce RBC damage [5]. However, in an earlier study [9] we have shown that the membrane stability of RBCs (normal osmotic fragility) collected by a hardshell cardiotomy reservoir is comparable with that of circulating RBCs after CABG and better than that of stored RBCs. This indicates that RBCs saved from shed mediastinal blood may not be damaged further during salvage. The survival of shed mediastinal RBCs, however, has not been thoroughly evaluated.

The aim of the present study was to determine the survival of RBCs from shed mediastinal blood after autotransfusion compared with the survival of normal circulating RBCs in patients undergoing CABG.

	Material and Methods

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Twenty-six adult patients undergoing primary and uncomplicated CABG entered the study. Inclusion criteria were primary CABG and age between 18 and 80 years. The study was approved by the regional ethical committee. Information was given to each patient and written consent was obtained according to the guidelines of the regional ethical committee. The number of patients in the study was calculated to allow detection of a 10% difference in 24-hour survival of RBCs between shed mediastinal RBCs and circulating RBCs, with a risk of overlooking a real difference of 5% (type I error) and a risk of 10% of accepting a false difference (type II error).

Not included in the study were patients with prolonged bleeding time (the Ivy method > 10 minutes), emergency operation, preoperative left ventricular ejection fraction less than 0.40, diabetes mellitus, and pulmonary or kidney diseases. Excluded from the study were patients needing operation for bleeding within the first 18 postoperative hours and patients receiving homologous blood transfusion intraoperatively or within the first 24 hours. If the patients received homologous blood transfusion later during the study, the data after transfusion were not used in the calculations of the lifespan of RBCs.

Anesthesia was induced with fentanyl, midazolam, pancuronium, and enflurane in oxygen. The patients were monitored with radial artery, central venous, and pulmonary artery catheters. All operations were performed through a median sternotomy using standard techniques for cardiopulmonary bypass with a crystalloid prime and a delivery rate of 2.4 L•min^-1•m^-2. At the end of the operation all patients had their mediastinal and, if necessary, pleural tubes attached to the inlet port of a Baxter Cardiotomy/Auto-transfusion reservoir (Baxter Healthcare Corp, Irvine, CA). Mediastinal shed blood was filtered through a 40-µm filter in the cardiotomy reservoir before autotransfusion.

At arrival in the intensive care unit the patients were randomly allocated to three groups before the start of autotransfusion: Group A (10 patients) had circulating RBCs labeled with technetium 99m (^99mTc) and shed mediastinal RBCs labeled with chromium 51 (⁵¹Cr). Group B (10 patients) had circulating RBCs labeled with ⁵¹Cr and shed mediastinal RBCs labeled with ^99mTc. Group C (6 patients) served to compare the behavior of the two radionuclides as RBC markers. Three patients had RBCs from circulating blood labeled with both ^99mTc and ⁵¹Cr and 3 patients had RBCs from shed mediastinal blood labeled with ^99mTc as well as ⁵¹Cr.

Before the start of autotransfusion a 20-mL sample of arterial blood (circulating blood) and a 20-mL sample from the cardiotomy reservoir (shed mediastinal blood) were collected in heparinized syringes.

For ^99mTc labeling, 2 mL of blood was incubated in a vial with pyrophosphate and stannochloride (CIS TCK-11, CIS Bio International, France) for 10 minutes. Sodium hypochlorite 0.1%, 0.2 mL, and EDTA 4.4%, 0.05 mL, were added, followed by 800 MBq of a fresh eluate of ^99mTc-pertechnetate. The labeling efficiency was measured, and if it was less than 95% erythrocytes were washed in isotonic saline solution. For ⁵¹Cr labeling, erythrocytes from 10 mL of blood were isolated by centrifugation at 1,500 rpm and washed two times in isotonic saline solution. Five MBq ⁵¹Cr-sodium chromate was added and cells were incubated for 30 minutes at 37°C during repeated mixing. After three washings in isotonic saline solution the erythrocytes were ready for injection.

The two labeled samples of ^99mTc-labeled and ⁵¹Cr-labeled erythrocytes were injected into the patient and the autotransfusion of shed mediastinal blood was stopped (4 hours after the salvage procedure was started). Five-milliliter samples of whole blood were collected in heparinized tubes at 15, 30, 45, and 60 minutes and 3, 6, 18, and 24 hours and daily thereafter for approximately 4 days.

Three milliliters of each sample was lysed by cooling to -20°C and counted in a dual-channel automatic gamma counter (COBRA II Autogamma; Packard) along with standards. The count rate for each radionuclide was corrected for background, overlap of the gamma ray spectra, decay during elapsed time for counting, and RBC volume using standard techniques.

We used the 15-minute value as the 100% value (early time values averaged method [10]), and a log regression line was calculated for each patient for ^99mTc-labeled as well as ⁵¹Cr-labeled erythrocytes. From the regression line the 24-hour survival fraction was calculated. The mean cell life span for the ⁵¹Cr-labeled RBCs was estimated from the 4-day samples.

The data from group C were used to calculate a correction factor for ^99mTc release from the erythrocytes using the following formula: correction factor = 24-hour survival of ⁵¹Cr-labeled erythrocytes/24-hour survival of ^99mTc-labeled erythrocytes. A corrected 24-hour survival fraction of ^99mTc-labeled erythrocytes in groups A and B was calculated by multiplying the percentage survival at 24 hours by the correction factor.

Data are expressed as medians with ranges in parentheses. Statistical analysis was performed using the Mann-Whitney test, Wilcoxon paired test, and Kruskal-Wallis test where appropriate. A p value less than 0.05 was regarded as significant (two-sided tests).

	Results

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
There were no differences between the groups regarding demographic characteristics and operative data before entering the study (Table 1). None of the patients were excluded due to reoperation for bleeding or blood transfusion within the first 24 hours. Three patients in group A (1 on postoperative day 3 and 2 on postoperative day 4), 1 patient in group B (postoperative day 4), and none in group C received homologous blood transfusion later during the study period.

The 24-hour survival of labeled RBCs in group C (Table 2) shows, however, a low in vivo stability for ^99mTc-labeled RBCs. The 24-hour correction factor to adjust ^99mTc-labeled RBC survival was estimated at 1.55 (1.42 to 1.67).

The survival of ⁵¹Cr-labeled shed mediastinal RBCs and circulating RBCs throughout the study are shown in Figure 1. There were no significant differences between the groups. The estimated mean cell lifespan had a median of 20.5 days and a range of 11.6 to 29.0 days for shed mediastinal RBCs and median of 22.7 days and a range of 14.4 to 36.2 days for circulating RBCs (p = 0.15).

View larger version (29K): [in this window] [in a new window]   Fig 1. . Survival of chromium 51-labeled red blood cells (RBC) of retransfused shed mediastinal blood (group A and 3 patients from group C, n = 10) and circulating blood (group B and 3 patients from group C, n = 12) during the study (median with range).

	Comment

Top Footnotes Abstract Introduction Material and Methods Results Comment References

The demand for blood products has increased with the increasing frequency of heart operations. Transfusion of autologous blood is one approach to reduce the requirements for homologous blood transfusion. Autotransfusion of shed mediastinal blood was first investigated by Schaff and associates in 1978 [1]. Our group has previously shown, with clearly defined criteria for transfusion and volume therapy, that postoperative autotransfusion of shed mediastinal blood after elective uncomplicated primary CABG reduces the number of patients needing homologous blood transfusion from 54% to 28% [5].

It is important to ensure that the quality of shed mediastinal blood is acceptable. Transfused RBCs that survive the first 24 hours are believed to have a normal lifespan distribution [11, 12], and measurement of 24-hour survival fraction is a valid indicator of RBC survival after transfusion. The use of a dual-isotope labeling technique enabled us to study the 24-hour survival fraction of two populations of RBCs in the same individual. This technique is well accepted [13, 14]. The calculation of 24-hour survival fraction by the early time values averaged method has been evaluated by Marcus and colleagues [10]. They showed that this method was equal with the double-isotope methods and the extrapolation methods. In the study by Marcus and colleagues [10] a correction factor of 1.23 was found compared with 1.55 found in the present study. This difference can be explained by the different source of RBCs for ^99mTc-labeling. Marcus and colleagues [10] used autologous RBCs stored for 42 to 49 days, whereas we used autologous mediastinal shed blood and circulating autologous blood without storage. Stored RBCs have low values of adenosine triphosphate and are deprived of 2,3-diphosphoglycerate whereas shed mediastinal blood has normal values of adenosine triphosphate and 2,3-diphosphoglycerate [9, 15]. Heaton [16] showed that posttransfusion recovery of ^99mTc/⁵¹Cr-labeled RBCs was positively correlated to red cell adenosine triphosphate level (r = 0.6). This could explain the difference between our findings and the findings of Marcus and colleagues [10].

When we used the correction factor each patient served as his or her own control. We were unable to detect a difference between survival of shed mediastinal RBCs used for autotransfusion and survival of circulating RBCs postoperatively after cardiopulmonary bypass. The long-term survival of ⁵¹Cr-labeled RBCs from the two sources after cardiopulmonary bypass also showed no significant differences.

The survival of autotransfused RBCs harvested by various methods has been studied by others. Four studies [17–20] compared the survival of RBCs collected during aortic reconstructive procedures with matched controls using cell-saving techniques and ⁵¹Cr-labeled RBCs. However, these studies suffered from a number of methodologic drawbacks. Most important is that the survival of saved RBCs was not compared with the survival of nonsaved RBCs in the same patient or under the same conditions. The dual-isotope labeling technique has been used in two other studies. In an elegant study of 20 patients, Ansell and associates [21] found no significant difference between survival of RBCs saved intraoperatively with a cell-saving device and blood collected preoperatively by venipuncture. In that study [21] the 24-hour survival was not calculated, but the long-term survival results are comparable with our findings. In the study by Kent and associates [22] on 6 patients the 24-hour survival percentage of salvaged RBCs was 81% with a range of 48% to 94%, which was not different from that of preoperatively collected RBCs. Our finding of a 92% (range, 81% to 97%) 24-hour survival of RBCs from shed mediastinal blood suggests that blood collection by the cardiotomy reservoir is less damaging than use of the cell-saving technique.

The alternative to autotransfusion is transfusion of autologous stored blood. The 24-hour survival of RBCs stored for 4 to 5 weeks is about 80% [10, 16, 23, 24]. Autologous RBCs stored for 1 to 5 days have a 92% to 94% 24-hour survival [10, 12], which is comparable with the results of our findings.

It may be considered a limitation of the present study that the RBCs from the cardiotomy reservoir were harvested approximately 1 hour after the start of salvage and before the start of autotransfusion. We did not investigate the survival of RBCs salvaged later during the autotransfusion period. However, in an earlier study we have shown that the membrane stability of RBCs (osmotic fragility) from shed mediastinal blood was comparable after 1 and 6 hours of autotransfusion [9].

The data from our study show that RBCs saved from shed mediastinal blood have not been damaged by collection with the cardiotomy reservoir. The survival of RBCs from shed mediastinal blood is comparable with the survival of fresh autologous blood.

	Footnotes

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
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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