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Eur J Cardiothorac Surg 2003;23:633-636
© 2003 Elsevier Science NL

A prospective randomised comparison of cardiotomy suction and cell saver for recycling shed blood during cardiac surgery

^a Department of Cardiothoracic Surgery, The Northern General Hospital, Herries Road, Sheffield S5 7AU, UK
^b Department of Histopathology, The Northern General Hospital, Herries Road, Sheffield S5 7AU, UK

Received 9 October 2002; received in revised form 23 November 2002; accepted 27 November 2002.

^* Corresponding author. Tel.: +44-114-271-4954; fax: +44-114-261-0350
e-mail: graham.cooper{at}sth.nhs.uk

	Abstract

Top Abstract 1. Introduction 2. Methods and materials 3. Results 4. Discussion 5. Conclusion References

 
Objective: Post-operative neuropsychological complications correlate with intra-operative microemboli in the middle cerebral artery. When severe neurological complications follow cardiac surgery, diffuse cerebral fat emboli are present at autopsy. Recycling shed blood with cardiotomy suction is an important source of cerebral fat microemboli. A cell saver may reduce this. Methods: Twenty patients were prospectively randomised to assess the amount of fat in blood salvaged from the pericardium and returned to the patient with either cell saver or cardiotomy suction. Blood samples were taken before and after filtration in the cardiotomy suction group or cell saver processing in the cell saver group. After centrifuging samples, fat content was graded on a scale of 0–3 by a blinded independent observer. Fat content was also quantified by weight. Results: Compared with cardiotomy suction, cell saver removed significantly more fat from shed blood. Median fat grading after cell saver was 0 (0–1) compared with 1 (1–2) for cardiotomy suction (P=0.0001). Percentage reduction in fat weight achieved by cell saver or cardiotomy suction was 87% compared to 45% (P=0.007). There was no difference in the post-operative use of blood or blood products, haemoglobin, or bleeding between the two groups. Conclusion: Use of cell saver results in less fat being recycled during cardiopulmonary bypass.

Key Words: Cerebral protection • Cell saver • Cardiotomy suction • Fat emboli

	1. Introduction

Top Abstract 1. Introduction 2. Methods and materials 3. Results 4. Discussion 5. Conclusion References

 
Although major neurological complications occur in only 2–3% of patients following cardiopulmonary bypass, neuropsychological deterioration is almost universal after coronary artery bypass grafting surgery and can persist for at least 6 months after surgery [1,2]. This peri-operative cognitive decline correlates with severity of cognitive impairment 5 years after surgery [3]. This in turn impacts on patients’ quality of life and employment [4].

Diffuse intravascular fat emboli have been observed in the brains of patients who die after post-operative neurological complications early after cardiopulmonary bypass [5]. And fat emboli have therefore been implicated in post-operative neuropsychological impairment [5].

During cardiopulmonary bypass shed blood within the pericardium contains fat from the sternal marrow and other cut surfaces. Traditionally this blood is salvaged by cardiotomy suction and returned to the patient after filtration by a 40 µm arterial line filter. Before arterial line filters were standard, neurological complications were found to be preventable by discarding all blood that overflowed from the heart [6]. The current 40 micron arterial line filters reduce emboli in the middle cerebral artery [2]. However in dogs, even when shed blood salvaged by cardiotomy suction is filtered through 25 µm filters, cardiotomy suction has been identified as a major source of cerebral lipid emboli [7].

Another option for recycling shed blood is a cell saver. Compared with cardiotomy suction, use of a cell saver in dogs undergoing cardiopulmonary bypass decreases cerebral lipid emboli [8]. However there is concern that cell savers cause increased fragmentation of erythrocytes and removal of platelets [9,10].

This prospective randomised control trial compares the efficacy of cell saver with cardiotomy suction for removing fat from shed blood during cardiopulmonary bypass.

	2. Methods and materials

Top Abstract 1. Introduction 2. Methods and materials 3. Results 4. Discussion 5. Conclusion References

 
Twenty consecutive patients having elective, first time coronary artery bypass graft surgery were prospectively randomised to have shed blood salvaged by either cell saver or cardiotomy suction. The study was approved by North Sheffield Research Ethics Committee and all patients provided informed written consent pre-operatively.

A Haemonetics Cell Saver 5 was used, with a 3-l capacity cell saver collection reservoir and a 125 ml wash bowl. The centrifuge speed was 5650 rpm. The washing solution was 500 ml of normal saline and the wash cycle lasted 1 min. The cell saver circuit was heparinised with 30 000 units of heparin in 1litre of normal saline.

A Polystan softshell cardiotomy reservoir with a 30 µm filter was connected into the cardiotomy suction line after the roller pump and before the main venous reservoir. The exit port of the cardiotomy reservoir was clamped to enable samples to accumulate for sampling. This allowed sampling before and after the filter, prior to dilution of salvaged blood by venous return in the main venous reservoir.

For the cell saver group, samples were taken before blood entered the cell saver reservoir. The post-cell saver sample was collected from an exit port of the cell saver blood bag. Prior to collection of the post process sample, the cardiotomy reservoir or cell saver blood bag was agitated to overcome any possible settling of blood.

Eight ml of blood was removed before and after the cardiotomy filter or cell saver process. All samples were centrifuged at 3000 rpm at 4°C for 15 min. The presence of visual fat on the surface was graded from 0 to 3 by an observer blinded to the source of samples (0=no fat, 1=fat visible, 2=a distinct layer of fat, 3=a thick layer of fat).

The top 1 ml of supernatant including the visible fat layer was removed from each sample. It was filtered under suction through a 25 mm diameter Whatman cellulose nitrate membrane filter with 5 µm pores and flushed through with 0.5 ml of water. Filters were dried on glass slides in boxes half full of desiccant at 4°C until constant weight. Filters were weighed to calculate the weight of fat per 8 ml blood sample. For each patient the percentage reduction in fat weight achieved by cardiotomy filter or cell saver was calculated.

For two random patients in each group an additional 6 ml was taken before and after the cardiotomy filter or cell saver and decanted into a separate test tube for observation by a histopathologist. After centrifugation of these histopathology samples, cytology slides of the fat layer were prepared and stained with Oil Red O and Sudan Black to confirm that it was indeed fat.

Chest drains were removed on the 1st post-operative day, when drainage was less than 20 ml an hour for 3 consecutive h.

Analysis of data was performed using Microsoft Excel and the SPSS 11 statistical package. Proportions were compared with a ² test. Continuous normally distributed data was compared with a student t test and non-parametric data with a Mann–Whitney U-test. Actual P-values are reported.

	3. Results

Top Abstract 1. Introduction 2. Methods and materials 3. Results 4. Discussion 5. Conclusion References

 
There was no difference between the two groups regarding pre-operative, intra-operative or post-operative variables (Table 1).

View larger version (80K): [in this window] [in a new window]   Fig. 1. Photograph of blood samples after centrifugation. Two samples were taken before and one after processing. After cell saver all samples appear virtually free of fat.

The median weight of fat after cell saver process was 0.5 mg (0.1–0.9 mg) compared to 2.9 mg (1.3–4.5 mg) in the cardiotomy suction group (P<0.0001). For each patient the percentage reduction in fat weight achieved by cardiotomy suction or cell saver was calculated. Cell saver resulted in an 87% reduction compared to 45% with cardiotomy suction (P=0.007) (Fig. 2) .

View larger version (17K): [in this window] [in a new window]   Fig. 2. Percentage reductions in the weight of fat in samples after cardiotomy filter or cell saver compared with before cardiotomy filter or cell saver. Cell saver leads to a greater reduction in the weight of fat. The bar represents the median value; the box represents the interquartile range; the whiskers represent the range.

	4. Discussion

Top Abstract 1. Introduction 2. Methods and materials 3. Results 4. Discussion 5. Conclusion References

There is concern that cell saver suction may result in increased haemolysis and removal of platelets compared with cardiotomy suction. Reents et al found increased levels of free haemoglobin and less platelets with cell saver suction compared with cardiotomy suction [10]. However Reents does not discuss any clinical significance of these findings. We found no difference between the two groups regarding post-operative haemoglobin, post operative blood loss, requirement for blood transfusions, or blood products, or the need for re-exploration for bleeding.

Cell saver use has other advantages including the removal of leukocytes activated by cardiopulmonary bypass which contribute to whole body inflammation.

The main limitation of cell saver use is that unlike cardiotomy suction, rapid return of shed blood to patients is not possible. However use of cell saver does not preclude use of cardiotomy suction if required. Other disadvantages include increasing cost of the procedure, and loss of platelets. This may be particularly important in patients with lower than normal platelet counts in whom may coagulation may be impaired.

The main limitation of this study is that the neurological outcome of the two groups were not assessed. However, this was a proof of concept study. A larger study addressing clinical outcomes is required.

	5. Conclusion

Top Abstract 1. Introduction 2. Methods and materials 3. Results 4. Discussion 5. Conclusion References

 
Compared with cardiotomy suction cell saver reduces the lipid burden retuned to patients. Cell saver use as an alternative to cardiotomy suction may lead to less lipid microemboli and therefore reduce cognitive impairment after cardiopulmonary bypass.

	Acknowledgments

 
We thank the perfusionists at The Northern General Hospital who helped with this work.

	Footnotes

 
Presented at the 16th Annual Meeting of the European Association of Cardio-thoracic Surgery, Monte Carlo, Monaco, September 22–25, 2002.

	References

Top Abstract 1. Introduction 2. Methods and materials 3. Results 4. Discussion 5. Conclusion References

 

1. Fearn S.J., Pole R., Wesnes K., Faragher E.B., Hooper T.L., McCollum C.N. Cerebral injury during cardiopulmonary bypass: emboli impair memory. J Thorac Cardiovasc Surg 2001;121:1150-1160.[Abstract/Free Full Text]
2. Pugsley W., Klinger L., Paschalis C., Treasure T., Harrison M., Newman S. The impact of microemboli during cardiopulmonary bypass on neuropsyschological functioning. Stroke 1994;25(7):1393-1399.[Abstract]
3. Newman M.F., Kirchner J.L., Phillips-Bute B., Gave V., Grocott H., Jones R.H., Mark D.B., Reves J.G., Blumenthar J.A. Longitudinal assessment of neurocognitive function after coronary artery bypass surgery. N Eng J Med 2001;344:395-402.[Abstract/Free Full Text]
4. Newman M.F., Grocott H.P., Mathew J.P. Report of the substudy assessing the impact of neurocognitive function on quality of life 5 years after cardiac surgery. Stroke 2001;32:2874-2881.[Abstract/Free Full Text]
5. Ghatak N.R., Sinnenberg R.J., DeBlois G.G. Cerebral fat embolism following cardiac surgery. Stroke 1983;14(4):619-621.[Abstract]
6. Caguin F., Carter M.G. Fat embolization with cardiotomy with the use of cardiopulmonary bypass. J Thorac Cardiovasc Surg 1963;46(5):665-672.
7. Brooker R.F., Brown W.R., Moody D.M., Hammon J.W., Reboussin D.M., Deal D.D., Ghazi-Birry H.S. Cardiotomy suction: a major source of brain lipid emboli during cardiopulmonary bypass. Ann Thorac Surg 1998;65:1651-1655.[Abstract/Free Full Text]
8. Kincaid E., Jones T., Stump D., Brown W., Moody D., Deal D., Hammon J. Processing of scavenged blood with a cell saver reduces cerebral lipid microembolization. Ann Thorac Surg 2000;70:1296-1300.[Abstract/Free Full Text]
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10. Reents W., Babin-Ebell J., Misoph M.R., Schwarzkopf A., Elert O. Influence of different autotransfusion devices on the quality of salvaged blood. Ann Thorac Surg 1999;68:58-62.[Abstract/Free Full Text]
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