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Ann Thorac Surg 1997;64:801-808
© 1997 The Society of Thoracic Surgeons

Original Article: General Thoracic

Extended Preservation of Ischemic Pulmonary Graft by Postmortem Alveolar Expansion

Dirk E. M. Van Raemdonck, MD, Nicole C. P. Jannis, Filip R. L. Rega, Paul R. J. De Leyn, MD, PhD, Willem J. Flameng, MD, PhD, Toni E. Lerut, MD, PhD

Center for Experimental Surgery and Anesthesiology, Katholieke Universiteit Leuven, Leuven, Belgium


   Abstract
Top
 Footnotes
 Abstract
Introduction
 Material and Methods
 Animal Preparation
 Pulmonary Flush
 Assessment of Graft Function
 Statistical Analysis
 Results
 Comment
 Acknowledgments
 References
 
Background. If lungs could be retrieved for transplantation from non–heart-beating cadavers, the shortage of donors might be significantly alleviated.

Methods. Peak airway pressure, mean pulmonary artery pressure, pulmonary vascular resistance, and wet to dry weight ratio were measured during delayed hypothermic crystalloid flush in rabbit lungs (n = 6) at successive intervals after death comparing cadavers with lungs left deflated (group 1), inflated with room air (group 2) or 100% oxygen (group 4), or ventilated with room air (group 3), or 100% nitrogen (group 5), or 100% oxygen (group 6).

Results. There was a gradual increase in mean pulmonary artery pressure and pulmonary vascular resistance with longer postmortem intervals in all study groups (p = not significant, group 1 versus group 2 versus group 3). There was also a gradual increase in peak airway pressure and wet-to-dry weight ratio over time in all groups, which reflected edema formation during flush (airway pressure, from 14.5 ± 1.0 cm H2O to 53.7 ± 12.2 cm H2O, and wet-to-dry weight ratio, from 3.6 ± 0.1 to 11.5 ± 1.2, in group 1 at 0 and 6 hours postmortem, respectively; p < 0.05). Compared with group 1, however, the increase in groups 2 and 3 was much slower (airway pressure, 20.9 ± 0.5 cm H2O and 18.8 ± 1.2 cm H2O, and wet-to-dry weight ratio, 5.2 ± 0.3 and 4.6 ± 0.4 at 6 hours postmortem, respectively; p < 0.05 versus group 1 and p = not significant, group 2 versus group 3). Airway pressure and wet-to-dry weight ratio did not differ between groups 2 and 4 or between groups 3, 5, and 6.

Conclusions. These data suggest that (1) pulmonary edema will develop in atelectatic lungs if hypothermic flush is delayed for 2 hours after death, (2) postmortem inflation is as good as ventilation in prolonging warm ischemic tolerance, (3) inflation with oxygen or ventilation with nitrogen or oxygen is no different from that with room air, and (4) therefore, prevention of alveolar collapse appears to be the critical factor in protecting the lung from warm ischemic damage independent of continued oxygen delivery.


   Introduction
Top
 Footnotes
 Abstract
 Introduction
Material and Methods
 Animal Preparation
 Pulmonary Flush
 Assessment of Graft Function
 Statistical Analysis
 Results
 Comment
 Acknowledgments
 References
 
See also page 808.

Lung transplantation, like other forms of solid-organ transplantation, is limited by a scarcity of good donor organs. It is estimated that less than 10% of all available multiorgan donors have lungs suitable for transplantation [1]. With continued progress in organ transplantation, the demand for transplants and thus the need for organs have increased markedly. The result is a growing waiting time for a suitable organ and an augmented risk of premature death of patients listed for lung transplantation.

To alleviate this critical organ shortage, there is growing interest in increasing the potential donor pool by turning to alternative sources such as the use of lobar or split transplants [2, 3], living-related donors [4], or organs from circulation-arrested cadavers, so called non–heart-beating donors (NHBDs).

Rapid cooling of perfused organs by in situ flush with a cold crystalloid solution forms the basis of any solid-organ preservation before transplantation. In the NHBD, however, there will always be a certain delay between (unexpected) circulatory arrest and the start of cold in situ flush of the organs.

In previous rabbit animal studies from our laboratory, we have investigated the effect of postmortem lung inflation, ventilation, and cooling on catabolism of adenine nucleotides [5] and pulmonary cell viability [6, 7]. We [8] also have looked at the effect of external cadaver cooling on pulmonary temperatures at intervals after death. The current study was undertaken to investigate pulmonary hemodynamic and aerodynamic changes during hypothermic flush at intervals after cardiac arrest. It was our aim to determine the effect of postmortem cadaver lung stretching by inflation and ventilation and to evaluate the effect of different gas mixtures during lung expansion in a rabbit NHBD model.


   Material and Methods
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
Animal Preparation
 Pulmonary Flush
 Assessment of Graft Function
 Statistical Analysis
 Results
 Comment
 Acknowledgments
 References
 
Experimental Groups
One hundred fifty New Zealand white rabbits (mean weight, 2,632 ± 20 g) were sacrificed and left at room temperature (±24°C). Cadavers were assigned to one of six groups of animals. Postmortem condition of the lungs inside the cadaver differed between groups. In group 1 (control NHBD), cadavers were left with lungs deflated (Defl) by disconnecting the endotracheal cannula from the ventilator, thus resulting in progressive atelectasis. In group 2, lungs were fully inflated with room air (Infl-RA) immediately after cardiac arrest by clamping the endotracheal cannula at end-tidal volume with end-expiratory pressure higher than 30 cm H2O. In group 3, the lungs were continuously ventilated with room air (Vent-RA) at a respiratory rate of 30 breaths/min, a tidal volume of 10 mL/kg of body weight, and a positive end-expiratory pressure of 2 cm H2O. In group 4, lungs were inflated with 100% oxygen (Infl-O2). In groups 5 and 6, lungs were ventilated with 100% nitrogen (Vent-N2) and 100% oxygen (Vent-O2), respectively. Cadaver lungs (n = 6 at each time interval) were flushed after 0.5, 1, 1.5, 2, 3, 4, and 6 hours in group 1, after 0.5, 1, 2, 4, 6, and 8 hours in groups 2 and 3, and after 4 and 8 hours in groups 4, 5, and 6. Finally, in nonischemic animals (n = 6), lungs were flushed immediately on insertion of the pulmonary artery catheter reflecting the situation in the heart-beating donor to derive control values at 0 hour (Table 1Go).


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  		Table 1. . Time Intervals Between Cardiac Arrest and Pulmonary Flush in the Six Study Groups
 
The pH of the flush solution was adjusted to 7.4 in all groups. Weight of the animals and temperature of the flush solution in all groups are listed in Table 2Go. Except for the weight in group 4 (Infl-O2) at 8 hours and the temperature of the flush solution at 4 hours in group 3 (Vent-RA) and at 6 hours in group 2 (Infl-RA), there were no significant differences between control and ischemic values at successive intervals after death within a group or between groups at any interval.


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  		Table 2. . Animal Weight and Temperature of Flush Solution in All Study Groupsa
 

   Animal Preparation
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
 Animal Preparation
Pulmonary Flush
 Assessment of Graft Function
 Statistical Analysis
 Results
 Comment
 Acknowledgments
 References
 
All animals received humane care in compliance with the "Guide for the Care and Use of Laboratory Animals" published by the National Institutes of Health (NIH publication 85-23, revised 1985).

Rabbits were premedicated and anesthetized by intramuscular injection with 0.25 mL/kg of Imalgène (50 mg/mL of ketamine hydrochloride; Rhône Mérieux, Lyon, France) and 0.15 mL/kg of Domitor (1 mg/mL of medetomidin-chlorhydrate + 1 mg/mL of paramethylhydroxybenzoate + 0.2 mg/mL of parapropylhydroxybenzoate; Orion Corporation, Farmos, Espoo, Finland). The animals were intubated using a cannula with a 3.5-mm inner diameter (Mallinckrodt Medical, Athlone, Ireland) through a cervical tracheostomy, and the lungs were ventilated using a Harvard rodent ventilator (model 683; Harvard Apparatus, Inc, South Natick, MA) with room air (respiratory rate, 30 breaths/min; tidal volume, 10 mL/kg of body weight; positive end-expiratory pressure, 2 cm H2O).

The chest was opened through a median sternotomy. Thymic tissue was excised. Pleural cavities were opened. Both superior caval veins, the inferior caval vein, the ascending aorta, and the main pulmonary artery were encircled by individual ligatures. Heparin Novo, 700 IU/kg (sodium heparin, 5,000 IU/mL; Novo Nordisk, Bagsvaerd, Denmark), was administered through a marginal ear vein. The main pulmonary artery was cannulated through the right ventricular outflow tract using a 10-gauge catheter (Angiocath; Becton Dickinson Vascular Access, Sandy, UT). The pulmonary artery was isolated from the right ventricle by a ligature around the tip of the catheter just distal to the pulmonary valve, creating pulmonary ischemia. The animal was then sacrificed by ligating the ascending aorta and caval veins, which resulted in cardiac arrest. Both the endotracheal cannula and the pulmonary artery catheter remained in place until pulmonary flush. The cadaver was left at room temperature with sternal edges reapproximated using towel clips. The whole procedure was carried out under clean but not sterile conditions.

In preliminary experiments, rabbits were sacrificed by intravenous injection through a marginal ear vein with 100 mg/kg of Nembutal (60 mg/mL of sodium pentobarbital; Abbott Laboratories, North Chicago, IL) inducing immediate cardiac arrest. This resulted in massive edema formation during pulmonary flush, even in control animals without ischemia (unpublished results). The edema was attributed to a direct pulmonotoxic effect of pentobarbital on the pulmonary vasculature. This method to sacrifice the animal was therefore abandoned.


   Pulmonary Flush
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
 Animal Preparation
 Pulmonary Flush
Assessment of Graft Function
 Statistical Analysis
 Results
 Comment
 Acknowledgments
 References
 
Both lungs were flushed through the pulmonary artery catheter by gravitational pressure at 30 cm H2O with 200 mL (±80 mL/kg) of cold (3.7° ± 0.1°C) modified Krebs-Henseleit bicarbonate buffer (KHBB) solution (composition in millimoles per liter: NaCl, 118; NaHCO3, 25; KCl, 5.6; CaCl2, 2.9; MgCl2, 0.6; NaH2PO4, 1.2; and D-glucose, 11; pH, 7.4; osmolarity, 321 mOsm/L). The tip of the left atrial appendage was transected to allow free drainage of the flush solution prior to the start of the flush. During the flush, the lungs were ventilated with room air (respiratory rate, 30 breaths/min; tidal volume, 10 mL/kg of body weight; positive end-expiratory pressure, 2 cm H2O).

The temperature and the pH of the KHBB solution were noted at the start of the flush using a rectal probe (type AR 1; Ellab Rødovre, Denmark) connected to a five-channel digital thermometer (Ellab, Copenhagen, Denmark) and a pH electrode (Hamilton Liq-Glass, Bonaduz, Switzerland) connected to a pH meter (WTW pH-91, Weilheim, Germany), respectively. At the end of the flush, the heart-lung block was excised, and the pulmonary artery catheter and endotracheal cannula were removed, collecting the endotracheal edema fluid.


   Assessment of Graft Function
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
 Animal Preparation
 Pulmonary Flush
 Assessment of Graft Function
Statistical Analysis
 Results
 Comment
 Acknowledgments
 References
 
Immediately before the flush, the endotracheal cannula and the pulmonary artery catheter were connected to pressure transducers (Uniflow type 43-600F; Baxter, Uden, the Netherlands) and zeroed at this level. During the flush, peak airway pressure (AwP) and mean pulmonary artery pressure (mPAP) were continuously measured and recorded with an amplifier (Carrier amplifier AP-601G; Nihon Kohden, Tokyo, Japan) on a four-channel recorder (heat writing recorder model WT-645G; Nihon Kohden). Flushing time (306 ± 7 seconds) was recorded using a stopwatch (Hanhart Profile 1; Germany). Pulmonary vascular resistance (PVR) was calculated using the following formula: PVR = mean pulmonary artery flush pressure/(flush volume/flush time). At the end of the flush, the heart-lung block was weighed and dried in an oven (model HT 600; Heraeus, Hanau, Germany) at 150°C overnight to constant weight. Wet-to-dry weight ratio (W/D) was calculated as an estimate of the extent of lung edema.


   Statistical Analysis
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
 Animal Preparation
 Pulmonary Flush
 Assessment of Graft Function
 Statistical Analysis
Results
 Comment
 Acknowledgments
 References
 
Data are presented as the mean ± the standard error of the mean. Differences within a group between control and ischemic values at successive intervals after death were calculated using one-way analysis of variance with repeated measurements followed by Scheffé's multiple comparison test [9]. Differences between groups at the same postmortem interval were compared using analysis of variance with factorial analysis (StatView SE+ Graphics [Abacus Concepts Inc, Berkeley, CA] on a Macintosh Performa 630 computer). Values of p less than 0.05 were accepted as significant.


   Results
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
 Animal Preparation
 Pulmonary Flush
 Assessment of Graft Function
 Statistical Analysis
 Results
Comment
 Acknowledgments
 References
 
Values for mPAP, PVR, AwP, and W/D in all study groups are presented in Table 3Go. There was a gradual increase in both mPAP and PVR with longer ischemic intervals in all groups (mPAP, from 9.5 ± 0.6 mm Hg to 15.2 ± 1.7 mm Hg, and PVR, from 16.7 ± 1.2 mm Hg • mL-1 • s-1 to 25.2 ± 5.4 mm Hg • mL-1 • s-1, in group 1 [Defl] at 0 and 6 hours postmortem, respectively; p < 0.05). No significant differences were observed at any interval between groups 1 (Defl), 2 (Infl-RA), and 3 (Vent-RA), between groups 2 and 4 (Infl-O2), or between groups 3, 5 (Vent-N2), and 6 (Vent-O2) (see Table 3Go).


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  		Table 3. . Graft Variables at End of Cold Flush in All Study Groupsa
 
Figure 1Go shows AwP in groups 1 (Defl), 2 (Infl-RA), and 3 (Vent-RA). There was a sharp and constant increase in AwP in group 1 starting 2 hours after circulatory arrest (from 14.5 ± 1.0 cm H2O [control value] to 53.7 ± 12.2 cm H2O at 6 hours postmortem; p < 0.05). In contrast, the increase in AwP in groups 2 and 3 was much slower (20.9 ± 0.5 cm H2O and 18.8 ± 1.2 cm H2O at 6 hours after death, respectively; p < 0.01 for group 2 and p = not significant for group 3 versus control value). The difference between groups 1 and 3 was significant starting at 1 hour and between groups 1 and 2, at 2 hours (see Fig 1Go). No significant differences were observed between groups 2 and 3 at any interval. In group 4 (Infl-O2), AwP was lower at 4 hours compared with group 2 (p < 0.05), but no significant difference was seen between groups 2 and 4 at 8 hours or between groups 3, 5 (Vent-N2), and 6 (Vent-O2) at 4 and 8 hours (Fig 2Go).



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  		Fig 1. . Peak airway pressure (mean ± standard error of the mean) in rabbit lungs (n = 6) at end of cold (±4°C) crystalloid flush at intervals after death comparing lungs left deflated (Defl) versus lungs inflated with room air (Infl-RA), versus lungs ventilated with room air (Vent-RA). (* = p < 0.05, Infl-RA [except 60 minutes] and Vent-RA versus Defl by analysis of variance; ^ = p < 0.05 versus control value; ^^ = p < 0.01 versus control value.)

 


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  		Fig 2. . Peak airway pressure (mean ± standard error of the mean) in rabbit lungs (n = 6) at end of cold (±4°C) crystalloid flush 4 and 8 hours after death comparing lungs inflated with room air (Infl-RA) versus lungs inflated with 100% oxygen (Infl-O2) and lungs ventilated with room air (Vent-RA), versus lungs ventilated with 100% nitrogen (Vent-N2), versus lungs ventilated with 100% oxygen (Vent-O2). (N.S. = not significant by analysis of variance; * = p < 0.05.)

 
Figure 3Go shows the W/D in groups 1 (Defl), 2 (Infl-RA), and 3 (Vent-RA). There was a sharp and constant increase in W/D in group 1 starting 2 hours after cessation of circulation (from 3.6 ± 0.1 [control value] to 11.5 ± 1.2 at 6 hours postmortem; p < 0.001). In contrast, the increase in W/D in groups 2 and 3 was much slower (5.2 ± 0.3 and 4.6 ± 0.4 at 6 hours postmortem, respectively; p < 0.01 for group 2 and p = not significant for group 3 versus control value). The differences between group 1 and groups 2 and 3 were highly significant (p < 0.01 at 4 hours and p < 0.001 at 6 hours) (see Fig 3Go). No significant differences were observed between groups 2 and 3 at any interval, between groups 2 and 4 (Infl-O2), or between groups 3, 5 (Vent-N2), and 6 (Vent-O2) at 4 and 8 hours (Fig 4Go).



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  		Fig 3. . Wet-to-dry weight ratio (mean ± standard error of the mean) in rabbit lungs (n = 6) after cold (±4°C) crystalloid flush at intervals after death comparing lungs left deflated (Defl) versus lungs inflated with room air (Infl-RA) versus lungs ventilated with room air (Vent-RA). (** = p < 0.01, Infl-RA and Vent-RA versus Defl by analysis of variance; *** = p < 0.001, Infl-RA and Vent-RA versus Defl by analysis of variance; ^ = p < 0.05 versus control value; ^^ = p < 0.01 versus control value; ^^^ = p < 0.001 versus control value.)

 


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  		Fig 4. . Wet-to-dry weight ratio (mean ± standard error of the mean) in rabbit lungs (n = 6) after cold (±4°C) crystalloid flush 4 and 8 hours after death comparing lungs inflated with room air (Infl-RA) versus lungs inflated with 100% oxygen (Infl-O2) and lungs ventilated with room air (Vent-RA) versus lungs ventilated with 100% nitrogen (Vent-N2) versus lungs ventilated with 100% oxygen (Vent-O2). (N.S. = not significant by analysis of variance.)

 

   Comment
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
 Animal Preparation
 Pulmonary Flush
 Assessment of Graft Function
 Statistical Analysis
 Results
 Comment
Acknowledgments
 References
 
Rapid cooling of perfused organs by in situ flush with a cold crystalloid solution forms the basis of any solid-organ preservation prior to transplantation. Lungs preserved in this way can be transplanted safely after up to 6 to 8 hours of cold ischemia. In the NHBD, however, there will always be a certain delay between (unexpected) circulatory arrest and the start of cold in situ flush of the organs. This critical interval, so-called warm ischemia, will rapidly lead to tissue and cellular damage [10, 11]. This might result in organ dysfunction jeopardizing the transplant recipient and remains the most difficult factor to overcome, especially after lung transplantation. Indeed, besides extracorporeal membrane oxygenation, no valid alternative organ replacement therapy is available today in case of primary nonfunction of the pulmonary allograft.

The period of inevitable warm ischemia in the NHBD, therefore, should be kept as short as possible. However, organizing organ retrieval and obtaining family consent for organ donation consume precious time. During this interval, organs have to be protected against cellular autolysis by preservation inside the dead body. The clinical use of lungs from NHBDs is still anecdotal [12, 13]. Nevertheless, transplantation of lungs retrieved from cadavers after cardiac arrest has been investigated in an increasing number of animal transplant experiments during recent years [14–19].

In the present study, we wanted to investigate graft function during delayed hypothermic crystalloid pulmonary flush at intervals after death. A gradual increase in mPAP and PVR over time was seen in all study groups. No intergroup differences were observed. It is well known that PVR is increased on reperfusion of the allograft after a period of pulmonary ischemia [20]. The exact mechanism remains unclear. Hypoxic vasoconstriction, mediator-induced vasospasm, and microvascular plugging of blood elements have all been recognized as possible causes of increased resistance. Increased microvascular hydrostatic pressure and postischemic endothelial damage may then lead to permeability pulmonary edema and clinically apparent acute graft dysfunction after reperfusion [21]. In fact, these delayed flush experiments after a period of warm ischemia could be seen as blood-free reperfusion experiments, and therefore the findings could be interpreted in the same way.

We observed a significant difference in AwP and W/D after hypothermic flush of lungs already subjected to a period of warm ischemia when comparing postmortem expanded versus nonexpanded lungs. The increase in group 1 (Defl) became evident as early as 2 hours after circulatory arrest. This suggests that warm ischemic tolerance in the atelectatic lung is limited to ±90 minutes. Tolerance to warm ischemia could be extended to 4 hours if the lungs remained inflated or ventilated.

No differences in W/D were found at 4 and 8 hours after death between postmortem inflation with room air (group 2 [Infl-RA]) versus oxygen (group 4 [Infl-O2]) and ventilation with room air (group 3 [Vent-RA]) versus nitrogen (group 5 [Vent-N2]) and oxygen (group 6 [Vent-O2]). In a study conducted by Ulicny and co-workers [15], no difference in early gas exchange was seen after canine single-lung transplantation and hilar occlusion of the native lung after a 4-hour period of postmortem donor ventilation with either 100% oxygen or 100% nitrogen. The authors therefore concluded, as we did in the present study, that the mechanics of ventilation after cessation of circulation appear to confer a functional advantage independent of a continued supply of oxygen. However, in a subsequent identical transplant study [19], postmortem ventilation with alveolar gas was inferior to ventilation with 100% oxygen.

Further rat experiments by the same group showed that adenine nucleotides were well preserved after postmortem oxygen but not nitrogen ventilation [22], and this correlated well with light microscopy pulmonary cell viability quantified by pulmonary artery infusion with trypan blue vital dye [10]. This latter study suggested that a continued oxygen supply, not ventilation itself, is important to maintain aerobic metabolism and prevent cellular damage. We [6] also looked at rabbit pulmonary cell viability using trypan blue dye exclusion and came to the same conclusions. On the other hand, Koyama and colleagues [23] compared the effect of postmortem ventilation with room air versus oxygen versus nitrogen in a canine isolated reperfusion model and reported superior function in lungs ventilated with nitrogen. The authors concluded that reperfusion injury seen in oxygen-ventilated animals was mediated by oxygen free radicals. Briefly, conflicting data have been reported from metabolic, morphologic, and functional studies. The ideal gas mixture for delivery to ischemic pulmonary grafts during cadaveric storage remains an open question.

We prefer to use KHBB as flush solution, a crystalloid with electrolytes of extracellular composition, without the addition of a prostanoid as vasodilator to examine solely the effect of increasing periods of warm ischemia on vascular resistance during pulmonary flush. It is well known that the high potassium concentration of an intracellular type of flush solution such as Euro-Collins [24] or University of Wisconsin [25] induces pulmonary vasoconstriction. In preliminary experiments, we also observed higher PVR in control animals (n = 8) during flush with Euro-Collins solution compared with KHBB solution (52.2 ± 7.6 mm Hg • mL-1 • s-1 versus 13.2 ± 1.0 mm Hg • mL-1 • s-1, respectively; p < 0.0001). The absence of a high-molecular-weight osmotic-impermeant component in KHBB solution might have aggravated pulmonary edema in ischemic lungs. However, no significant difference in W/D was observed in an additional group of cadavers (n = 7) with deflated lungs flushed 4 hours postmortem with low-potassium–dextran solution, a crystalloid with similar electrolyte composition as KHBB but with dextran 40 as an impermeant, compared with KHBB (6.0 ± 0.6 versus 6.9 ± 0.6, respectively; p = not significant). D'Armini and co-workers [26] investigated W/D in rat lungs ventilated postmortem with 100% oxygen for 4 hours followed by flush with modified Euro-Collins, University of Wisconsin, or Carolina rinse solution. The lungs were then fully expanded and stored in the same cold solution for another 4 hours. The W/D in lungs flushed with and stored in University of Wisconsin solution was significantly lower, with a value similar to that of fresh tissue.

Another potential criticism of this NHBD model is the use of heparin in the donors before sacrifice [17]. We elected to heparinize the animals to exclude intravascular thrombosis as a cause of poor lung function during delayed hypothermic flush. In a supplemental group of nonheparinized animals (n = 6), deflated lungs were flushed in an identical manner 4 hours after death. The PVR at the end of flush was significantly higher compared with that in heparinized animals (23.4 ± 0.7 mm Hg • mL-1 • s-1 versus 17.6 ± 1.6 mm Hg • mL-1 • s-1; p < 0.05). No significant differences, however, were observed in mPAP, AwP, and W/D between both groups.

Finally, we also compared the effect of cold (3.5° ± 0.2°C) versus warm (22.5° ± 0.1°C) flush with KHBB solution in deflated lungs (n = 6) 4 hours postmortem. No significant differences in mPAP, AwP, and W/D were found between groups. However, PVR was significantly higher after hypothermic flush (17.6 ± 1.6 mm Hg • mL-1 • s-1 versus 12.1 ± 1.2 mm Hg • mL-1 • s-1; p < 0.05).

In this study, we measured relatively gross estimates of lung function during a very short period (±5 minutes). Assessment of gas exchange at reperfusion with deoxygenated blood is probably the most reliable variable to evaluate the quality of lung preservation and permits clear differentiation between well-preserved and poorly preserved lungs. We have used these flush experiments as a rapid screening method to define the length of tolerable warm ischemia in all study groups. In later experiments (unpublished results) comparing the same study groups, we have investigated the effect of 4 hours' in situ warm ischemia in a rabbit isolated, pressure-limited, homologous blood reperfusion and room air–ventilated model (n = 4 in each group). Arteriovenous oxygen pressure gradient after 1 hour of reperfusion was only 9 ± 5 mm Hg in cadaver lungs that were left deflated during the ischemic interval versus 95 ± 13 mm Hg in lungs that were inflated with room air, 96 ± 7 mm Hg in lungs that were ventilated with room air, and 96 ± 4 mm Hg in lungs ventilated with 100% nitrogen (p < 0.05, Defl versus all other groups; p = not significant, Infl-RA versus Vent-RA versus Vent-N2). This study therefore validates the conclusion of the present study that the prevention of postmortem alveolar collapse itself will confer a functional advantage independent of continued supply of oxygen.

The exact mechanism of extended warm ischemic tolerance of the lung by preventing the alveolar space to collapse remains unclear. Release of surfactant from type II pneumocytes is known to be stimulated by inflation [27] and ventilation of lungs [28] and by mechanical stretch of isolated pneumocytes in culture [29]. Alveolar surfactant activity is reduced in the atelectatic lung [30]. Although no measurements of surfactant or surfactant activity were made in the present study, it is reasonable to speculate that repetitive or continuous alveolar expansion during warm ischemia in our study groups may have stimulated the release of pulmonary surfactant, thereby decreasing the alveolar surface tension, preventing damage to the alveolar-capillary membrane, and protecting against permeability pulmonary edema during flush [21].

From this study, we can conclude that in the NHBD (1) pulmonary edema will develop in atelectatic lungs if hypothermic flush is delayed for 2 hours after death, (2) postmortem inflation is as good as ventilation in protecting the lung against edema formation, thereby prolonging warm ischemic tolerance up to 4 hours, (3) postmortem inflation with oxygen or ventilation with nitrogen or oxygen is no different from that with room air, and (4) therefore, prevention of alveolar collapse appears to be the critical factor in protecting the lung from warm ischemic damage independent of continued oxygen delivery. Further studies are necessary to investigate whether lungs from human NHBDs will become a realistic alternative to expand the pulmonary donor pool.


   Acknowledgments
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
 Animal Preparation
 Pulmonary Flush
 Assessment of Graft Function
 Statistical Analysis
 Results
 Comment
 Acknowledgments
References
 
This work is supported by grant 7.0036.94 from the Nationaal Fonds voor Wetenschappelijk onderzoek—Levenslijn 1994.

We thank Peter Lemmens, Magda Mathys, Kanigula Mubagwa, MD, and Anne Vancauwenbergh for expert technical and secretarial assistance.


   Footnotes
Top
 Footnotes
Abstract
 Introduction
 Material and Methods
 Animal Preparation
 Pulmonary Flush
 Assessment of Graft Function
 Statistical Analysis
 Results
 Comment
 Acknowledgments
 References
 
Presented at the Thirty-third Annual Meeting of The Society of Thoracic Surgeons, San Diego, CA, Feb 3-5, 1997.

Address reprint requests to Dr Van Raemdonck, Department of Thoracic Surgery, University Hospital Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium (e-mail: dirk.vanraemdonck{at}uz.kuleuven.ac.be).


   References
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
 Animal Preparation
 Pulmonary Flush
 Assessment of Graft Function
 Statistical Analysis
 Results
 Comment
 Acknowledgments
 References
 

  1. Van Raemdonck D, Roels L, Verleden G, et al. Whence the lungs? Assessment of the use of lungs for transplantation from 156 consecutive donors. In: Cooper JD, Weder W, eds. Proceedings of the third international lung transplant symposium (Zurich, Switzerland, June 24–25, 1993). 1993:40.
  2. Starnes VA, Barr ML, Cohen RG. Lobar transplantation. Indications, technique, and outcome. J Thorac Cardiovasc Surg 1994;108:403–11.[Abstract/Free Full Text]
  3. Couetil JPA, Tolan MJ, Loulmet DF, et al. Pulmonary bipartitioning and lobar transplantation. A new approach to donor organ shortage. J Thorac Cardiovasc Surg 1997;113:529–37.[Abstract/Free Full Text]
  4. Starnes VA, Barr ML, Cohen RG, et al. Living-donor lobar lung transplantation experience. Intermediate results. J Thorac Cardiovasc Surg 1996;112:1284–91.[Abstract/Free Full Text]
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Discussion
Ann. Thorac. Surg. 1997 64: 808. [Extract] [Full Text]



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