Strategies to optimize the use of currently available lung donors

Ex Vivo Evaluation of Nonacceptable Donor Lungs

BACKGROUND

Only a minority of the potential candidates for lung donation are considered suitable, using current evaluation methods. A new method for ex vivo evaluation, with the potential for reconditioning of marginal and nonacceptable lungs, has been developed. This is a report of the ex vivo evaluation of six donor lungs deemed nonacceptable (arterial oxygen pressure less than 40 kPa) by the Scandiatransplant, Eurotransplant, and UK transplant organizations.

METHODS

The lungs are perfused ex vivo with Steen solution, a lung evaluation-preservation solution, mixed with red blood cells to a hematocrit of 15%. This extracellular solution is designed to have an optimal colloid osmotic pressure so that physiologic pressure and flow can be maintained without development of pulmonary edema. An oxygenator connected to the extracorporeal circuit maintains a normal mixed venous blood gas level in the perfusate. The lungs are ventilated and evaluated through analyses of pulmonary vascular resistance, oxygenation capacity, and arterial carbon dioxide pressure minus end-tidal carbon dioxide difference.

RESULTS

The arterial oxygen pressure (inspired oxygen fraction, 1.0) increased from 27 kPa (range, 17 to 34 kPa) in situ in the organ donor at the referring hospital to 57 kPa (range, 39 to 66 kPa) during the ex vivo evaluation. The pulmonary vascular resistance varied from 3.2 to 5.7 Wood units, and the arterial carbon dioxide pressure minus end-tidal carbon dioxide difference was in the range of 1 to 2.5 kPa.

CONCLUSIONS

The arterial oxygen pressure improves significantly in this model. This ex vivo evaluation model is a valuable addition to the armamentarium in finding acceptable lungs in a donor population with inferior arterial oxygen pressure values.

Unexpected donor pulmonary embolism affects early outcomes after lung transplantation: A major mechanism of primary graft failure?

OBJECTIVE

Primary graft failure remains a significant cause of morbidity and mortality after lung transplantation, and its mechanism is not understood. Previously 2 case reports described fatal primary graft failure due to donor-related unexpected pulmonary embolism. This study investigated the incidence, early outcome, and risk factors of unexpected pulmonary embolism in lung transplantation.

METHODS

An exploratory retrograde donor lung flush before implantation to diagnose pulmonary embolism (emboli group) or no pulmonary embolism (no-emboli group) was performed in 74 of 122 consecutive lung transplantations.

RESULTS

The incidence of macroscopic unexpected pulmonary embolism was 38% (28% clot and 9% fat). In the emboli group, significantly decreased oxygenation (P < .05), increased pulmonary vascular resistance (P < .001), an increased proportion of opacity on chest radiograph (P = .03), prolonged intubation (P < .001) and intensive care unit stay (P < .01), and decreased 1-year survival (P = .03) were seen after transplantation. In multivariate analysis, pulmonary embolism was an independent risk factor for prolonged intubation (hazard ratio, 2.42; P < .01). In logistic regression, death due to trauma with fracture and a smoking history of more than 20 pack-years were significant donor risk factors for pulmonary embolism (adjusted odds ratio, 8.77 and 5.64; P = .02 and .04, respectively). No deleterious effects of the exploratory flush were seen.

CONCLUSIONS

Unexpected pulmonary embolism is relatively common, is potentially predicted by donor history (but not by arterial blood gas analysis or chest radiograph), and is associated with primary graft failure. Donor lungs with risk factors of pulmonary embolism should undergo an exploratory flush. When pulmonary embolism is diagnosed, further therapeutic strategies must be considered.

High Prevalence of Pulmonary Arterial Thrombi in Donor Lungs Rejected for Transplantation

BACKGROUND

Donor hypoxemia is a common reason for the rejection of lungs for transplantation. Organ donors are at high risk for venous thromboembolism. Pulmonary arterial thrombosis could contribute to donor hypoxemia. The primary objective of this study was to prospectively quantify the incidence of pulmonary arterial thrombosis in organ donors whose lungs were rejected for transplantation. The secondary objective was to better define the spectrum of histologic abnormalities in the same group of lungs.

METHODS

A complete gross pathologic and histologic analysis of whole lung specimens was done on lungs from 17 donors whose lungs were rejected for transplantation. Lungs had not been flushed with a pulmonary preservation solution.

RESULTS

Overall, 35% of the donors had gross or microscopic evidence of either pulmonary arterial thrombosis, pulmonary infarction, or both. Clinical characteristics, including oxygenation, were not significantly different between donors who had thrombi or infarction and donors who did not. Other pathologic findings included bronchopneumonia (focal or early in 4/17, moderate or severe in 8/17), respiratory bronchiolitis (7/17) and centriacinar emphysema (7/17).

CONCLUSIONS

Pulmonary arterial thrombosis and/or pulmonary infarction are very common in organ donors whose lungs are rejected for transplantation and might contribute to lung dysfunction both in lung donors and lung recipients. Further studies are needed to define the incidence of pulmonary arterial thrombosis in organ donors whose lungs are used for transplantation and to better assess the adverse clinical consequences of donor pulmonary arterial thrombosis in lung recipients.

Lung transplantation: donor and recipient critical care aspects

PURPOSE OF REVIEW

The purpose of this paper is to highlight new developments in donor and recipient lung transplant issues for the critical care physician.

RECENT FINDINGS

A shortage of suitable lung donors has led to the use of extended donors and the development of novel techniques such as live-donor lung transplantation and the use of non-heart-beating donors. The increased experience and success with lung transplantation has also resulted in the extension of this therapy to patients previously considered unsuitable for transplantation. Postoperative outcomes can be affected by many of these recent donor and recipient changes. Improved preservation solutions and techniques to reduce reperfusion injury may be able to ameliorate some of the new perioperative graft dysfunction, but morbidity is still potentially significant, and extraordinary interventions such as extracorporeal membrane oxygenation may be required in selected cases.

SUMMARY

Patients undergoing lung transplantation continue to be very challenging in the intensive care unit. A multidisciplinary approach to care, and early recognition of serious problems, will help improve outcomes.

Lung preservation

Better understanding of the mechanisms of ischemia-reperfusion injury, improvement in the technique of lung preservation, and the recent introduction of a new preservation solution specifically developed for the lungs have helped to reduce the incidence of primary graft dysfunction after lung transplantation. Currently, the limitation in extending the ischemic time is more often related to the increasing use of non-ideal lung donors rather than to poor lung preservation. In this review, we have focused our attention on the experimental and clinical work performed to optimize the methods of lung preservation from the time of retrieval to the period of reperfusion after graft implantation.