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J Thorac Cardiovasc Surg 2005;129:429-434
© 2005 The American Association for Thoracic Surgery
Cardiothoracic Transplantation |
Department of Cancer and Thoracic Surgery (Surgery II), Okayama University Graduate School of Medicine and Dentistry, Okayama, Japan
Received for publication February 3, 2004; revisions received May 2, 2004; accepted for publication May 6, 2004. * Address for reprints: Hiroshi Date, MD, Department of Cancer and Thoracic Surgery (Surgery II), Okayama University Graduate School of Medicine and Dentistry, 2-5-1 Shikata Cho, Okayama 700-8558, Japan (E-mail: hdate{at}nigeka2.hospital.okayama-u.ac.jp).
| Abstract |
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METHODS: Left lung transplantation was performed in 18 weight-matched pairs of mongrel dogs. Donors were killed with an intravenous injection of potassium chloride and left at room temperature for 2 hours. The cadaveric donors were assigned randomly to one of the three groups. In group 1 (n = 6), no heparin was given as a control. In group 2 (n = 6), heparin sodium (1000 U/kg) was administered intravenously before cardiac arrest. In group 3 (n = 6), heparin sodium (1000 U/kg) was administered intravenously 10 minutes after death, then closed-chest cardiac massage was performed for 2 minutes. After 2 hours of cardiac arrest, donor lungs were flushed with low-potassium dextran-glucose solution and preserved for 60 minutes. After left lung transplantation, the right pulmonary artery was ligated, and recipient animals were followed up for 3 hours. Univariate and multivariate repeated analyses were used for statistics.
RESULTS: Both groups 2 and 3 had significantly better gas exchange and lower pulmonary vascular resistance than group 1. Changes in thrombin-antithrombin III complex concentration during the warm ischemia indicated that postmortem heparinization suppressed clotting activation in the donor.
CONCLUSIONS: Postmortem heparinization by cardiac massage is beneficial in lung transplantation from nonheart beating donors by preventing microthrombus formation.
Previous experimental studies have shown that a safe period of ischemia for the lungs at normothermia is less than 2 hours without heparinization,2 but this could be extended to 4 hours when the lungs were fully heparinized and ventilated before cardiac arrest.3 However, heparinizing the donor before death for the purpose of organ donation requires consensus on ethics. With uncontrolled nonheart-beating donors, heparinization before death is practically impossible. In this study, we have evaluated the effects of postmortem heparinization by closed-chest cardiac massage in a canine model of left single-lung allotransplantation from nonheart-beating donors.
| Material and methods |
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The cadaveric donors were assigned randomly to one of the three groups. In group 1 (n = 6), no heparin was given, for control. In group 2 (n = 6), heparin sodium (1,000 U/kg) was administered intravenously before cardiac arrest. In group 3 (n = 6), heparin sodium (1,000 U/kg) was administered intravenously 10 minutes after death, then closed chest cardiac massage was performed for 2 minutes to distribute the heparin around the circulatory system. Chest compressions were provided 30 times per minute to maintain the systolic arterial pressure around 50 to 60 mm Hg.
To measure the degree of clotting activation, the concentration of the clotting marker thrombinantithrombin III (TAT) complex was measured in citrate-anticoagulated plasma by enzyme-linked immunosorbent assay.4 Serial blood samples were taken from donors before death and 30, 60, 90, and 120 minutes after death through a femoral arterial catheter. In group 3, activated coagulation time (ACT) was measured after cardiac massage.
After 2 hours of cardiac arrest, a median sternotomy was performed. The main pulmonary artery was opened, and the left atrial appendage was incised. Postmortem thrombus in the pulmonary artery and left atrium was evacuated as much as possible. A 20F catheter was inserted into the main pulmonary artery and secured. Ventilation was established at a tidal volume of 20 mL/kg, a respiratory rate of 15 breaths/min, and a positive end-expiratory pressure of 5 cm H2O. The heart-lung block, ventilated with 100% oxygen, was perfused with 50-mL/kg low-potassium dextran-glucose solution5 stored at 4°C from a bag that was hung 50 cm above the chest. Semi-inflated lung block was excised, submerged in cold saline solution, and stored at 4°C for 60 minutes.
The recipient animals were sedated in the same manner as the donors. Anesthesia was maintained with a 50:50 mixture of nitrous oxide and oxygen and 0.3% to 1.0% halothane. A thermodilution catheter was placed in the main pulmonary artery from the right external jugular vein to measure pulmonary arterial pressure, central venous pressure, and cardiac output. Aortic pressure was measured by a femoral artery line. With the animal in the right lateral decubitus position, a thoracotomy was performed in the left fifth intercostal space, followed by a left pneumonectomy. The right pulmonary artery was encircled with 1-0 silk string. A 5F catheter was inserted into the left atrial appendage to measure left atrial pressure.
On a back table, the left lung, which was to be used for implantation, was trimmed from the donor lung block. The donor right lung was used for histologic study.
Left lung implantation was then performed in the usual fashion. After transplantation, both lungs were ventilated with a tidal volume of 20 mL/kg and a positive end-expiratory pressure of 5 cm H2O at a respiratory rate of 15 breaths/min and an inspired oxygen concentration of 1.0. The baseline measurement was done. Then the right pulmonary artery was ligated 15 minutes after reperfusion so that we could measure the function of the transplanted left lung. Aortic pressure, pulmonary arterial pressure, central venous pressure, left atrial pressure, and airway pressure were continuously recorded. Cardiac output and arterial blood gas values were measured periodically (30 minutes, 60 minutes, 90 minutes, 120 minutes, 150 minutes, and 180 minutes after ligation of the right pulmonary artery).
Animal care
All dogs received humane care in compliance with the "Principles of Laboratory Animal Care" formulated by the National Society for Medical Research and the "Guide for the Care and Use of Laboratory Animals" (http://www.nap.edu/catalog/5140.html).
Statistics
Univariate and multivariate repeated analyses were used to determine whether an overall difference existed in lung function and in TAT complex data among the three groups during the 3-hour assessment period. Multiple group comparisons were made with contrasts. Results are expressed as mean ± SEM.
| Results |
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Lung function study
The results of gas exchange and hemodynamic evaluation of the recipients during the 3-hour assessment period are shown in Table 1. Among the various functional indicators, three valuables (PaO2, PaCO2, and pulmonary vascular resistance) had a significant group effect (P < .001, P = .01, and P = .03, respectively). Regarding these three valuables, all three comparisons (group 1 vs group 2, group 1 vs group 3, and group 2 vs group 3) for each time point were performed. PaO2 was significantly better in groups 2 and 3 than in group 1. PaCO2 was significantly lower in groups 2 and 3 than in group 1. Pulmonary vascular resistance was significantly lower in groups 2 and 3 than in group 1. There were no significant differences between groups 2 and 3 in these three functional indicators. There were no significant group effects in mean aortic pressure, mean pulmonary arterial pressure, mean central venous pressure, mean left atrial pressure, cardiac output, and mean airway pressure.
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| Discussion |
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Several investigators2,3,9 have conducted examinations of the lung's tolerance of warm ischemia. It has been proved that lung cells remain viable by metabolizing the oxygen in the alveoli for a certain period even at warm temperatures without circulation.10 A safe period for the lungs at normothermia is less than 2 hours without heparinization.2 Ulicny and colleagues3 demonstrated that the acceptable warm ischemic time could be extended to 4 hours when the lungs were fully heparinized before cardiac arrest and kept ventilated after death. A number of strategies have been developed in an attempt to reduce warm ischemic injury: oxygen radical scavengers,11 topical cooling,12 leukocyte depletion,13 inhaled nitric oxide,14 fibrinolytic drugs,15 and retrograde pulmonary flush.16
Because cardiac arrest occurs under very different conditions, two classes of nonheart-beating donors, controlled and uncontrolled, have been distinguished.17 Controlled nonheart-beating donors undergo circulatory arrest after planned withdrawal of life support with a retrieval team standing by. Heparin is usually administered before cardiac arrest to prevent microthrombus formation. Successful transplants from controlled nonheart beating donors have been reported for the kidney,18 pancreas,19 liver,19,20 and lung.19 However, heparinizing the donor before death for the purpose of organ donation requires consensus on the ethics, because it could hasten death in donors with brain injury. In fact, the practice is strictly restricted in Japan.
The first successful human lung transplantation from an uncontrolled nonheart beating donor was reported by Steen and colleagues1 in 2001, and it is gathering much attention. The donor was a 54-year-old man who had an acute myocardial infarction. After unsuccessful resuscitation, the patient was declared dead. Heparin was given into a central venous catheter 10 minutes after declaration of death, followed by 20 chest compressions. With an intrapleural cooling technique, the right lung was transplanted successfully into a 54-year-old woman with chronic obstructive pulmonary disease.
Postmortem heparinization by closed-chest cardiac massage is potentially problematic because it could cause pulmonary contusion and could deliver microthrombi and toxic cytokines to the lungs from venous blood. We hypothesized that postmortem heparinization by cardiac massage would improve overall lung function by preventing microthrombus formation in lung transplantation from nonheart-beating donors.
In this study, heparin was given intravenously 10 minutes after cardiac arrest in group 3. Equivalent pulmonary functions were obtained in groups 2 (premortem heparinization) and 3 (postmortem heparinization), whereas group 1 (no heparinization) showed worse pulmonary function. It was clearly shown that postmortem heparinization by closed-chest cardiac massage improved gas exchange and lowered pulmonary vascular resistance (Table 1). Prevention of microthrombus formation by postmortem heparinization was confirmed macroscopically (Figure 1, A-C) and microscopically (Figure 2, A-C). Prolonged ACT in group 3 demonstrated that systemic heparinization could be achieved by closed-chest cardiac massage for 2 minutes. Significant inhibition of the clotting system was also demonstrated by the changes in TAT complex in group 3 (Figure 3).
Postmortem heparinization by closed-chest compression can be achieved easily by anyone, anywhere, without special equipment. It should be also emphasized that no skin incision is required. It therefore can be readily applied to uncontrolled nonheart-beating donors, including those dead on arrival at the hospital. However, it would be essential to administer heparin shortly after cardiac arrest. Further study is needed to determine the optimal time for postmortem heparinization in lung transplantation from nonheart-beating donors.
| Acknowledgments |
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This article has been cited by other articles:
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C. Van De Wauwer, A. P. Neyrinck, N. Geudens, F. R. Rega, G. M. Verleden, E. Verbeken, T. E. Lerut, and D. E.M. Van Raemdonck Retrograde flush following topical cooling is superior to preserve the non-heart-beating donor lung Eur. J. Cardiothorac. Surg., June 1, 2007; 31(6): 1125 - 1133. [Abstract] [Full Text] [PDF] |
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