Short-term inhaled nitric oxide in canine lung transplantation from non-heart-beating donor

Therapeutic benefits of nitric oxide in lung transplantation

Lung transplantation is an evolutionary procedure from its experimental origin in the twentieth century and is now recognized as an established and routine life-saving intervention for a variety of end-stage pulmonary diseases refractory to medical management. Despite the success and continuous refinement in lung transplantation techniques, the widespread application of this important life-saving intervention is severely hampered by poor allograft quality offered from donors-after-brain-death. This has necessitated the use of lung allografts from donors-after-cardiac-death (DCD) as an additional source to expand the pool of donor lungs. Remarkably, the lung exhibits unique properties that may make it ideally suitable for DCD lung transplantation. However, primary graft dysfunction (PGD), allograft rejection and other post-transplant complications arising from unavoidable ischemia-reperfusion injury (IRI) of transplanted lungs, increase morbidity and mortality of lung transplant recipients annually. In the light of this, nitric oxide (NO), a selective pulmonary vasodilator, has been identified as a suitable agent that attenuates lung IRI and prevents PGD when administered directly to lung donors prior to donor lung procurement, or to recipients during and after transplantation, or administered indirectly by supplementing lung preservation solutions. This review presents a historical account of clinical lung transplantation and discusses the lung as an ideal organ for DCD. Next, the author highlights IRI and its clinical effects in lung transplantation. Finally, the author discusses preservation solutions suitable for lung transplantation, and the protective effects and mechanisms of NO in experimental and clinical lung transplantation.

Nitric oxide ventilation of rat lungs from non-heart-beating donors improves posttransplant function

Lungs from non-heart-beating donors (NHBDs) would enhance the donor pool. Ex vivo perfusion and ventilation of NHBD lungs allows functional assessment and treatment. Ventilation of rat NHBD lungs with nitric oxide (NO) during ischemia, ex vivo perfusion and after transplant reduced ischemia-reperfusion injury (IRI) and improved lung function posttransplant. One hour after death, Sprague-Dawley rats were ventilated for another hour with either 60% O2 or 60% O2/40 ppm NO. Lungs were then flushed with 20-mL cold Perfadex, stored cold for 1 h, perfused in an ex vivo circuit with Steen solution and warmed to 37 degrees C, ventilated 15 min, perfusion-cooled to 20 degrees C, then flushed with cold Perfadex and stored cold. The left lung was transplanted and ventilated separately. Recipients were sacrificed after 1 h. NO-ventilation was associated with significantly reduced wet:dry weight ratio in the ex vivo circuit, better oxygenation, reduced pulmonary vascular resistance, increased lung tissue levels of cGMP, maintained endothelial NOS eNOS, and reduced increases in tumor necrosis factor alpha (TNF-alpha) and inducible nitric oxide synthase (iNOS). NO-ventilation had no effect on MAP kinases or NF-kappaB activation. NO administration to NHBDs before and after lung retrieval may improve function of lungs from NHBDs.

Post-ischemic infusion of atrial natriuretic peptide attenuates warm ischemia-reperfusion injury in rat lung

BACKGROUND

The serious shortage of organs for transplantation, especially lungs, has drawn increasing attention to donation after cardiac death and protection of organs against warm ischemic injury. Atrial natriuretic peptide (ANP) activates guanylate cyclase receptors and increases cyclic guanosine monophosphate (cGMP) levels, which decrease in the lung during ischemia. In this study we investigated the effect on lung ischemia-reperfusion injury of administering synthetic ANP (carperitide) at the onset of reperfusion after warm ischemia.

METHODS

An isolated rat lung perfusion model was used. The rats were allocated into three groups: the control group; the ANP group; and the sham group. In the control and ANP groups, the heart-lung block was exposed to 60 minutes of ischemia at 37 degrees C, and subsequently reperfused for 60 minutes. At the onset of reperfusion, either saline or ANP was added to the perfusate. In the sham group, lungs were continuously perfused without ischemia and only saline was added to the perfusate.

RESULTS

ANP significantly reduced pulmonary vascular resistance and pulmonary edema, and improved oxygenation. It also significantly increased cGMP levels in reperfused lungs. Histologically, lungs in the ANP group showed significantly fewer signs of injury and fewer cells demonstrated apoptotic changes or single-stranded DNA than lungs in the control group.

CONCLUSIONS

Our results indicate that ANP administered at the onset of reperfusion increases cGMP in lung tissue and attenuates warm ischemia-reperfusion injury in isolated perfused rat lung.

Evaluation of techniques for lung transplantation following donation after cardiac death

BACKGROUND

Lung transplantation using "donation after cardiac death" donors is a potential means to alleviate the shortage of suitable donor lungs for transplantation, but the practicality and utility of the various possible techniques need to be clarified.

METHODS

Using a dog model, we explored seven variations of standoff (ischemic) time (50 to 240 minutes), topical cooling (60 to 120 minutes), and flush cooling and cold storage (30 to 140 minutes) to mimic different human donor lung retrieval scenarios that can follow donation after cardiac death. The functional status of donation after cardiac death donor lungs was assessed initially with a 250 mL pulmonary arterial blood flush while ventilating with 100% oxygen and then on an ex-vivo perfusion rig for 120 minutes after retrieval.

RESULTS

All lungs achieved an excellent pO2/FiO2 ratio ranging from 472 to 586 with stable pulmonary artery pressures and pulmonary vascular resistance and no net weight gain (952 +/- 221 g versus 1,006 +/- 235 g) during the 120-minute evaluation period. Initial blood flush correlated well with measured perfusion rig pO2 at 30 minutes (R2 = 0.63).

CONCLUSIONS

This canine study suggests that lungs donated after cardiac death are reproducibly useable for transplantation with ischemic times of as long as 60 minutes. Although more study is needed, a blood flush evaluation is simple and may have a role as a secondary allograft assessment tool. The existing techniques of donor lung evaluation and preservation after donation following cardiac death thus appear both feasible and practical.

Canine Bilateral Lung Transplantation After 18-hour Preservation Using Non–heart-beating Donors

BACKGROUND

We previously reported that lung inflation with oxygen, EPC-K1 (a diester alpha-tocopherol and ascorbic acid), urokinase and low-potassium dextran glucose (LPDG) solution can be beneficial in lung preservation. In the present study, a canine bilateral lung transplantation (BLT) model was used to evaluate long-term lung preservation of non-heart-beating donors (NHBDs).

METHODS

Animals were euthanized without heparinization and left at room temperature for 2 hours until lung extraction. After cardiac arrest, the lungs were kept inflated with 100% oxygen. After extraction, the donor lungs were flushed with LPDG solution containing EPC-K1 (1.0 mg/liter), followed by injection of urokinase (120,000 IU) into the pulmonary artery. Eighteen BLTs were performed after preservation at 4 degrees C. Total ischemic time was scheduled for 12 hours in Group 1 (n = 6), 18 hours in Group 2 (n = 6) and 24 hours in Group 3 (n = 6). After BLT, recipients were followed up for 6 hours. An additional 6 BLTs were performed as a chronic study in the same setting as for Group 2.

RESULTS

All animals in Groups 1 and 2 showed excellent pulmonary function during the 6-hour post-transplant assessment time, in contrast to only 2 dogs from Group 3. In the chronic study, all 6 animals showed excellent pulmonary function for 24 hours (PaO2 = 528 +/- 8 mm Hg with 100% oxygen) and 2 of them survived for >1 week.

CONCLUSION

Successful chronic lung preservation (18 hours) using NHBDs is achievable in a canine BLT model.

High-flow endobronchial cooled humidified air protects non-heart-beating donor rat lungs against warm ischemia

OBJECTIVE

Lungs from non-heart-beating donors for transplantation require protection against warm ischemic damage. Minimally invasive techniques are required to reduce organ damage during the warm ischemic period because invasive surgical procedures are often not feasible at this time. This study investigated the preservative effect of high-flow endobronchial cooled humidified air during warm ischemia in non-heart-beating donor rat lungs.

METHODS

Fourteen animals were divided into a Cooling group (n = 7), which received cooled air/saline spray during a 2-hour warm ischemic period, and a Control group (n = 7), which received no cooling. After ischemia the lungs were reperfused on an isolated lung perfusion apparatus.

RESULTS

Endobronchial temperatures in the Cooling and Control groups were 8 degrees C and 36 degrees C at 10 minutes, and 5 degrees C and 35 degrees C at 20 minutes, respectively (P < .0001). Lung core and surface temperatures in the Cooling group were also lower than those in the corresponding Control group (P < .0001). After reperfusion, pulmonary arterial pressure (P = .003) and peak airway pressure (P = .002) were lower in the Cooling group than in the Control group. Higher pulmonary venous PO2 (P = .02), higher adenosine triphosphate levels (P = .01), and lower wet/dry lung weight ratio (P = .003) were seen in the Cooling group compared with the Control group.

CONCLUSIONS

High-flow endobronchial cooled humidified air can decrease lung temperature and improve post-ischemic pulmonary function and adenosine triphosphate levels in non-heart-beating donor lungs.

Inhaled nitric oxide reduces ischemia-reperfusion injury in rat lungs from non-heart-beating donors

OBJECTIVE

If lungs could be retrieved from non-heart-beating donors, the critical shortage of lungs for transplantation could be alleviated. However, lungs subjected to warm ischemia develop edema when reperfused. We hypothesized that ventilation of rat lungs from non-heart-beating donors with nitric oxide during the period of warm ischemia alone, with reperfusion, or both might reduce ischemia-reperfusion injury.

METHODS

An isolated perfused rat lung model measured the filtration coefficient and accumulation of lung water by the wet/dry weight ratio. Donor rats were euthanized, and then lungs were retrieved immediately after death or 2 or 3 hours postmortem. Lungs retrieved postmortem were either not ventilated or ventilated with 100% oxygen alone or 40 ppm nitric oxide in oxygen. In the circuit, lungs were ventilated with alveolar gas with or without 40 ppm nitric oxide.

RESULTS

Nitric oxide administration to the non-heart-beating donor or in the perfusion circuit reduced filtration coefficient and wet/dry weight ratio. Lungs retrieved 2 hours postmortem ventilated with nitric oxide or treated with nitric oxide on reperfusion had filtration coefficients and wet/dry weight ratios similar to those of lungs retrieved immediately after death. Nitric oxide was most beneficial when administered both during warm ischemia and at reperfusion in lungs retrieved 3 hours postmortem. Nitric oxide administration in the circuit was associated with increased lung levels of lung cyclic guanosine monophosphate, determined by enzyme-linked immunosorbent assay.

CONCLUSIONS

Administration of nitric oxide to non-heart-beating donors during warm ischemia and with reperfusion might facilitate transplantation of lungs from non-heart-beating donors by reducing ischemia-reperfusion injury and capillary leak.

Optimal time for post-mortem heparinization in canine lung transplantation with non-heart-beating donors

BACKGROUND

We previously reported that post-mortem heparinization by closed-chest cardiac massage is beneficial in lung transplantation from non-heart-beating donors by preventing formation of microthrombi. In this study, we evaluated the optimal time for post-mortem heparinization in canine lung transplantation from non-heart-beating donors.

METHODS

Left lung transplantation was performed in 25 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 cadaver donors were assigned randomly to one of five study groups. In Group H0, heparin sodium (1,000 U/kg) was given intravenously before cardiac arrest. In Groups H10, H30, H45 and H60, heparin sodium (1,000 U/kg) was given intravenously 10, 30, 45 and 60 minutes after cardiac arrest, respectively, followed by closed-chest cardiac massage 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 allotransplantation, the right pulmonary artery was ligated, and recipient animals were followed up for 3 hours. Uni- and multivariate repeat analyses were utilized for statistical assessment.

RESULTS

After transplantation, gas exchange was significantly worse in Groups H45 and H60 than in Groups H0, H10 and H30. Thrombin/anti-thrombin III complex concentration during warm ischemia was significantly higher in Groups H30, H45 and H60 than in Groups H0 and H10.

CONCLUSIONS

The optimal time for post-mortem heparinization in lung transplantation from non-heart-beating donors is approximately 30 minutes after cardiac arrest.

Effects of postmortem heparinization in canine lung transplantation with non–heart-beating donors

OBJECTIVE

Microthrombus formation appears to be one of the major detrimental factors in lung transplantation from non-heart-beating donors. The purpose of this study was to evaluate the effects of postmortem heparinization by closed-chest cardiac massage in a canine model of left single-lung allotransplantation from non-heart-beating donors.

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 non-heart beating donors by preventing microthrombus formation.

Non-heart-beating donors

The widespread application of lung transplantation is limited by the shortage of suitable donor organs resulting in longer waiting times for listed patients with a substantial risk of dying before transplantation. To overcome this critical organ shortage, some transplant programs have now begun to explore the use of lungs from circulation-arrested donors, so called non-heart-beating donors (NHBDs). This review outlines the different categories of NHBDs, the relevant published experimental data that support the use of lungs coming from these donors and the clinical experience worldwide so far. Techniques for NHBD lung preservation and pretransplant functional assessment are reviewed. Ethical issues involved in transplanting lungs from asystolic donors are discussed.

CONTINUOUS INFUSION OF NITROGLYCERIN IMPROVES PULMONARY GRAFT FUNCTION OF NON???HEART-BEATING DONOR LUNGS

BACKGROUND

The warm ischemic period of lungs harvested from a non-heart-beating donor (NHBD) results in an increased ischemia-reperfusion injury after transplantation. The intravenous application of nitroglycerin (NTG), a nitric oxide (NO) donor, proved to be beneficial during reperfusion of lung grafts from heart-beating donors. The objective of the present study was to investigate the effect of nitroglycerin on ischemia-reperfusion injury after transplantation of long-term preserved NHBD-lungs.

METHODS

Sixteen pigs (body weight, 20-30 kg) underwent left lung transplantation. In the control group (n=5), lungs were flushed (Perfadex, 60 mL/kg) and harvested immediately after cardiac arrest. In the NHBD group (n=5) and the NHBD-NTG group (n=6), lungs were flushed 90 min (warm ischemia) after cardiac arrest. After a total ischemia time of 19 hr, lungs were reperfused and graft function was observed for 5 hr. Recipient animals in the NHBD-NTG group received 2 microg/kg/min of NTG administered intravenously during the observation period starting 5 min before reperfusion. Tissue specimens and bronchoalveolar lavage fluid (BALF) were obtained at the end of the observation period.

RESULTS

Compared with the control group, pulmonary gas exchange was significantly impaired in the NHBD group, whereas graft function in the NHBD-NTG group did not change. Leukocyte fraction and protein concentration in the BALF and histologic alteration of the NHBD-NTG group were not different from controls.

CONCLUSIONS

Continuous infusion of NTG in the early reperfusion period improves pulmonary graft function of NHBD lungs after long-term preservation. The administration of an NO donor during reperfusion may favor the use of NHBD lungs to alleviate the critical organ shortage in lung transplantation.

Non-heart-beating donors in thoracic transplantation

Access to lung transplantation is severely limited by a scarcity of suitable donors, resulting in increasing numbers of deaths on the heart and lung transplant waiting lists, and strict selection criteria for recipients. Unlike some other solid organs, the lung may be ideally suited to retrieval for transplant following substantial intervals after circulatory arrest. This may be because lung parenchymal cells do not rely on perfusion for cellular respiration. This review outlines the relevant published experimental data that addresses the concept that lungs might be suitable for transplant even if retrieved from non-heart-beating donors (NHBDs), and the small published clinical experience with NHBDs as lung donors. Aspects of reperfusion injury in this setting are reviewed. The prospect of heart transplant from NHBDs is addressed. The impact of the routine use of NHBDs on lung transplantation is discussed.

Nitric oxide during perfusion improves posttransplantation function of non- heart-beating donor lungs

BACKGROUND

We attempted to determine in a pig model whether 20 ppm of nitric oxide (NO) during perfusion ameliorates warm ischemic lung injury in the non-heart-beating donor (NHBD), thereby improving function with longer warm ischemia.

METHODS

Lungs were retrieved from three groups (n=6): 1 hr (NHBD(1)) and 2 hr with and without NO (NHBD(2)NO, NHBD(2)) after hypoxic death. For assessment and preservation, left lungs were ventilated with 100% oxygen (NHBD(2)NO with added NO) and perfused for 20 min with neutrophil-depleted, deoxygenated blood in Perfadex solution. Pulmonary vascular and airway pressures and blood flow were measured with pulmonary venous blood gases. Perfusion temperature was reduced to 18 degrees C prior to storage at 4 degrees C before transplantation.

RESULTS

NO during perfusion significantly improved posttransplantation pulmonary venous oxygenation (NHBD(1) [mean +/- SD] 51+/-14 kPa, NHBD(2) 54+/-16 kPa, and NHBD(2)NO 61+/-6 kPa; P=0.01) and airway pressures (NHBD(1) 30.8+/-3.5, NHBD(2) 32.5+/-5.6, NHDB(2)NO 29.4+/-5.3; P=0.0001). NO significantly improved pulmonary vascular resistance (excluding the initial cold-induced vasoconstricted reperfusion period): NHBD(1) 19+/-9 Wood units, NHBD(2) 28+/-25 Wood units, NHDB(2)NO 16+/-10 Wood units, P=0.029. Neutrophil uptake was significantly lowered by NO: NHBD(1) 0.6+/-1.4*10(9) minute-1, NHBD(2) 1.2+/-1.0*10(9) minute-1, NHBD(2)NO 0.4+/-0.9*10(9) minute-1 (P=0.029).

CONCLUSIONS

This technique satisfactorily assesses and preserves the non-heart-beating lung. NO during preservation reverses the slight deterioration seen when increasing warm ischemia from 1 to 2 hr, significantly improving transplant oxygenation, vascular resistance, and airway pressures. This may be a result of the observed significant reduction in neutrophil sequestration.

Improved lung function by means of retrograde flush in canine lung transplantation with non-heart-beating donors

OBJECTIVE

Use of lungs from non-heart-beating donors would increase the pulmonary donor pool. The aim of this study was to evaluate the effects of retrograde flush in canine lung transplantation from non-heart-beating donors.

METHODS

Left lung transplantation was performed in 12 weight-matched pairs of dogs. Donors were killed without heparinization, left at room temperature for 2 hours, and then randomized into 2 groups. In group AF (n = 6) lung retrieval was performed after flushing the lung block with low potassium dextran glucose (50 mL/kg) solution through the pulmonary artery. In group AF+RF (n = 6) additional retrograde flushing (low potassium dextran glucose, 25 mL/kg) was performed through the left atrium before retrieval. Flushed solution was sampled at intervals to measure hemoglobin concentrations. The lungs were preserved at 4 degrees C for 2 hours, and the left lung was implanted to the recipient being subjected to a total ischemic time of 5 hours. After left lung transplantation, the right pulmonary artery and main bronchus were ligated. Lung function, including arterial blood gas and pulmonary hemodynamics, was measured for 3 hours. For lung function study, statistical analyses were performed by using 1-way analysis of variance with repeated measures.

RESULTS

Group AF+RF had significantly better gas exchange and lower wet/dry weight ratio of the transplanted lung than group AF. Changes of hemoglobin concentration in the flushed solution indicated that additional retrograde flush could remove residual microthrombi after antegrade flush.

CONCLUSIONS

This study supports the theory that additional retrograde flush improves lung function after lung transplantation by removing residual pulmonary microthrombi in the lungs of non-heart-beating donors.

Novel protection strategy for pulmonary transplantation

BACKGROUND

Ischemia-reperfusion injury continues to represent a significant challenge to successful lung transplantation. Traditional pulmonary ischemic protection is performed using hypothermic hyperkalemic depolarizing solutions to reduce the metabolic demands of the ischemic organ. Measures to further reduce the effects of ischemic injury have focused on the reperfusion period. We tested the hypothesis that novel physiologic hyperpolarizing solutions-using ATP-dependent potassium channel (K(ATP)) openers-given at the induction of ischemia, will reduce cellular injury and provide superior graft function even after prolonged periods of ischemia.

METHODS

An isolated blood-perfused ventilated rabbit lung model was used to study lung injury. Airway, left atrial, and pulmonary artery pressures were measured continuously during the 2-h reperfusion period. Oxygenation, as a surrogate of graft function, was measured using intermittent blood gas analysis of paired left atrial and pulmonary artery blood samples. Graft function was measured by oxygen challenge technique (F(i)O(2) = 1.0). Wet-to-dry ratio was measured at the conclusion of the 2-h reperfusion period. Control (Group I) lungs were perfused with modified Euro-Collins solution (depolarizing) and reperfused immediately (no ischemia). Traditional protection lungs were perfused with modified Euro-Collins flush solution and stored for 4 h (Group II) or 18 h (Group III) at 4 degrees C before reperfusion. Novel protection (Group IV) lungs were protected with a hyperpolarizing solution containing 100 nM Aprikalim, a specific K(ATP) channel opener, added to the modified Euro-Collins flush solution and underwent 18 h of ischemic storage at 4 degrees C before reperfusion.

RESULTS

Profound graft failure was measured after 18 h of ischemic storage with traditional protection strategies (Group III). Graft function was preserved by protection with hyperpolarizing solutions even for prolonged ischemic periods (Group IV). Wet-to-dry weight ratio, airway, left atrial, and pulmonary artery pressures were not significantly different between the groups.

CONCLUSIONS

We have created a model of predictable lung injury. Membrane hyperpolarization with a K(ATP) channel opener (PCO) provides superior prolonged protection from ischemia-reperfusion injury in an in vitro model of pulmonary transplantation.

Inhaled NO and prostacyclin during porcine single lung transplantation

BACKGROUND

Increased pulmonary vascular resistance (PVR) and decreased arterial oxygenation frequently complicate lung transplantation. Inhaled nitric oxide (NO) and aerosolized prostacyclin (PGI2) both dilate the pulmonary vasculature and improve oxygenation in adult respiratory distress syndrome. We investigated whether similar effects would occur during early reperfusion of a lung graft.

METHODS

Eighteen pigs underwent left lung transplantation. We measured blood flow distribution, mean pulmonary artery pressure, PVR, and gas exchange in each lung separately. Animals were randomized into three groups to receive NO (10 ppm/30 minutes, 40 ppm/30 minutes), nebulized PGI2 (25 microg/mL/30 minutes, 50 microg/mL/30 minutes), or no drugs (control).

RESULTS

In the transplanted lung, PVR was significantly higher than in the native lung. Pulmonary vascular resistance of the transplanted lung was lower in the NO and PGI2 groups in comparison with the control group. During the first hour of inhalation, NO decreased PVR more than PGI2. Neither drug improved oxygenation in the graft.

CONCLUSIONS

Nitric oxide and PGI2 decreased PVR of the transplanted lung slightly, but the effect did not produce a normal pressure in pulmonary vasculature.