To evaluate the lung function of donors after circulatory deaths (DCDs),
Lung transplantation continues to be hampered by the number of available donors [
The use of DCD lungs has gained much interest lately. DCDs are classified according to the Maastricht classification and may be subdivided as controlled and uncontrolled [
There are also some issues regarding the optimal preservation of uncontrolled donor lungs such as how long warm ischemic time the lungs can withstand and whether it is better to harvest the lungs after the period of warm ischemia or cool the lungs inside the deceased body. These issues are relevant for the donation team. The formalities of the donation process have to be also managed properly according to the law of each country.
As mentioned above, EVLP is also an excellent tool for reassessing DCD lungs. How to perform the optimal EVLP has also been a focus of the discussion. After the warming phase in EVLP, the lung is 37°C and fully ventilated, and it is ready to be reassessed for transplant suitability. To reassess the lungs adequately, all of the atelectasis has to be eliminated. In conventional EVLP, the atelectasis is eliminated by increasing the PEEP up to 10 cm H2O for 10–15 minutes at the time when the lungs have reached 37°C. The maneuver is performed, while the lung is maximally perfused. All of the lung atelectasis has to be eliminated for the lung to be tested adequately. If the lung is tested with the lung atelectasis present, a shunt will be formed where the blood is not oxygenated. In the present study, we hypothesize that elimination of atelectasis is preferably made under conditions where, the lung is ventilated but not perfused. In the present study the lung perfusion is temporarily shut down during 10 minutes. During that time, the lung is fully ventilated, and the PEEP is increased to 10 cm H2O. According to our knowledge, no such study has been performed previously.
Twelve Swedish landrace pigs were fasted overnight with free access to water. The study was approved by the Ethics Committee for Animal Research, Lund University, Sweden (no. M 172-11). All animals received care according to the European Convention for the Protection of Vertebrate Animals Used for Experimental and Other Scientific Purposes, to the USA Principles of Laboratory Animal Care of the National Society for Medical Research, and to the Guide for the Care and Use of Laboratory Animals.
Premedication was performed with an intramuscular injection of xylazine (Rompun Vet. 20 mg/mL, Bayer AG, Leverkusen, Germany, 2 mg/kg) mixed with ketamine (Ketaminol Vet. 100 mg/mL, Farmaceutici Gellini S.P.A., Aprilia, Italy, 20 mg/kg) while the pig was still in its stable. Peripheral i.v. access was then established in the ear. The pig was then transferred to the laboratory and placed on the operating table in the supine position. Oral intubation was performed using a 7.5 mm endotracheal tube after the induction of anesthesia with sodium thiopental (Pentothal, Abbott Laboratories, North Chicago, IL, USA) and pancuronium bromide (Pavulon, N.V. Organon, Oss, the Netherlands). Anesthesia was maintained by infusions of ketamine (Ketaminol Vet.), midazolam (Midazolam Panpharma, Oslo, Norway), and fentanyl (Leptanal, Lilly, France). Fluid loss was compensated for by continuous infusion of Ringer’s acetate. Mechanical ventilation was established with a Siemens-Elema ventilator (Servo Ventilator 300, Siemens, Solna, Sweden).
Ventricular fibrillation was induced electrically. The tracheal tube was disconnected from the ventilator when circulatory arrest was confirmed. The animals were left untouched for 1.5 hours at room temperature. Thereafter, a median sternotomy was performed. The pulmonary artery was cannulated via the right ventricle with a 28 F cannula secured with a purse string suture placed in the outflow tract of the A. pulmonalis. A clamp was placed on the v. cava superior, and another clamp on the v. cava inferior. A third clamp was then placed on the ascending aorta. The left atrial and the v. cava inferior were then opened. The right and left pleurae were filled with ice slush to cool the lungs.
The lungs were perfused antegradely with 5 L of cold Perfadex containing 1.0 mL isotonic trometamol (Addex-THAM 3.3 mmol/mL, Fresenius Kabi AB, Uppsala, Sweden), 2 mL calcium chloride (0.45 mmol/mL), and 3 mL nitroglycerine (5 mg/mL, BMM Pharma AB, Stockholm, Sweden) at a low perfusion pressure (<20 mmHg). The cannula was then removed from the pulmonary artery. The lungs were harvested en bloc in a standard fashion and weighed. A segment (
EVLP was performed using the Medtronic
Gas was supplied to the affinity membrane oxygenator (Medtronic, Minneapolis, NJ, USA): first oxygen and CO2 during the reconditioning phase and then 93% nitrogen and 7% CO2 during the testing phase, creating a normal venous blood gas in the perfusate to the pulmonary artery (in other words, the oxygenator was used to deoxygenate the perfusate). Before starting perfusion, the pulmonary artery was extended using the excised segment of the descending aorta to facilitate cannulation. The pulmonary artery cannula was then connected to the corresponding tube of the extracorporeal circuit, the air was removed, and the shunt of the circuit was clamped. An endotracheal tube was secured in the trachea with a cotton band and connected to the ventilator. The remnant of the left atrium was left open, preventing obstruction of the pulmonary outflow since the perfusion solution flowed directly out into the lung reconditioning box. The left atrium pressure was, therefore, 0 mmHg.
Low-flow perfusion at 25°C was initiated through the lungs. The lungs were gradually warmed by increasing the temperature of the perfusate. When the temperature reached 32°C, ventilation was started with an inspired oxygen fraction of 0.5 and a minute volume of 1 L/minute, with no PEEP. The pump flow was gradually increased, but the pulmonary arterial pressure was never allowed to exceed 20 mmHg. With each 1°C increase in temperature, the ventilation was increased by a minute volume of 1 L. When the perfusate from the lung reached 37°C, normal ventilation
In the conventional EVLP group, the lung atelectasis was eliminated by temporarily increasing PEEP to 10 cm H2O for 10 minutes when the perfusate from the lung reached 37°C. The perfusion through the lung (pulmonary artery flow) was kept unchanged during this time. The PEEP was then removed, and the lung was ventilated
In the modified EVLP group, the lung perfusion was shut down (e.g., stopping the circulation) when the perfusate from the lung reached 37°C. During the shutdown time of 10 minutes, the ventilation was kept at
Calculations and statistical analysis were performed using GraphPad 4.0 software. Statistical analysis was performed using one-way ANOVA and Bonferroni’s multiple comparison test, comparing all groups. A level of
No significant differences were observed in animal weight in the two groups (
The time from the initiating of the EVLP circuit and until the perfusate from the lung had reached 37°C was calculated. No significant differences in the EVLP time were observed in the two groups (25 ± 2 minutes in the modified EVLP group and 26 ± 3 minutes in the conventional EVLP group (
Samples of blood were taken before and after passing through the lungs (i.e., venous and arterial blood samples) to measure blood gases after 5-minutes exposure to fractions of inspired oxygen (FiO2) at 1.0. The arterial blood gases and the venous blood gases after 5 minutes of ventilation with FiO2 at 1.0 are presented in Table
Samples of blood were taken before and after passing through the lungs (i.e., venous and arterial blood samples) to measure blood gases after 5-minute exposure to fractions of inspired oxygen (FiO2) at 1.0.
Before & after modified EVLP | Before & after conventional EVLP | Total | |||||
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Before | After |
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Before | After |
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FiO2 1.0 | |||||||
PAP (mmHg) |
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n.s. |
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n.s. | n.s. |
CO (L/min) |
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n.s. |
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n.s. | n.s. |
AP (cm H2O) |
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PvCO2 (kPa) |
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n.s. |
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n.s. | n.s. |
PvO2 (kPa) |
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n.s. |
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n.s. | n.s. |
PaCO2 (kPa) |
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n.s. |
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n.s. | n.s. |
PaO2 (kPa) |
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PVR ((dynes × s)/cm5) |
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Weight (gram) |
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FiO2: inspired oxygen fraction, PAP: pulmonary arterial pressure, CO: cardiac output/pulmonary artery flow, AP: mean airway pressure, PvCO2: venous carbon dioxide partial pressure, PvO2: venous oxygen partial pressure, PaCO2: arterial carbon dioxide partial pressure, PaO2: arterial oxygen partial pressure, and PVR: pulmonary vascular resistance.
Mean arterial oxygen tension (± SEM) before and after modified and conventional EVLP in the aspect of eliminating lung atelectasis after initial EVLP where the lung is warmed up to 37°C and ventilated according to the golden standard for EVLP. Statistical analysis was performed using ANOVA.
The airway pressure (AP) is also presented in Table
Mean airway pressure (± SEM) before and after modified and conventional EVLP in the aspect of eliminating lung atelectasis after initial EVLP where the lung is warmed up to 37°C. Statistical analysis was performed using ANOVA.
Pulmonary vascular resistance (PVR) was calculated using the following formula: PVR (dyne × s/cm5) = [(80 * PAP) – LAP]/CO, where PAP is the mean pulmonary artery pressure, LAP is the left atrium pressure, and CO is the cardiac output (CO is equivalent to pulmonary artery flow in the EVLP method).
The pulmonary vascular resistance was calculated after ventilation with FiO2 at 1.0 and is also presented in Table
Mean pulmonary vascular resistance (PVR) (± SEM) before and after modified and conventional EVLP in the aspect of eliminating lung atelectasis after initial EVLP where the lung is warmed up to 37°C and ventilated according to the golden standard for EVLP. Statistical analysis was performed using ANOVA.
The lungs were weighed after harvesting and after EVLP to assess the degree of lung edema.
The time from disconnecting the EVLP circuit and until the lungs were weighed was calculated. No significant differences in the EVLP time were observed in the two groups (3 ± 0.3 minutes in the modified EVLP group and 3 ± 0.5 minutes in the conventional EVLP group (n.s.)).
The results are shown in Figure
Mean lung weight (± SEM) before and after modified and conventional EVLP in the aspect of eliminating lung atelectasis after initial EVLP where the lung is warmed up to 37°C and ventilated according to the golden standard for EVLP. Statistical analysis was performed using ANOVA.
In the modified EVLP group, the pulmonary graft weight was
Pulmonary artery flow (L/min), that is, cardiac output (CO), in the
After completing the lung evaluation, the pulmonary arterial branches were macroscopically studied for thrombotic material by opening the arteries distally as far as possible. No thrombotic material was observed in either of the groups.
Lung transplantation is used to treat patients with a variety of end-stage pulmonary diseases [
Some years ago, we reported the results of the first six double-lung transplantations performed in the world with donor lungs from HBDs that were rejected for transplantation by the Scandiatransplant, the Eurotransplant, and the UK Transplant organizations after
In the present study, we present a modified form of EVLP for eliminating atelectasis. In conventional EVLP, the golden standard to eliminate the atelectasis is to increase PEEP up to 10 cm H2O for 10–15 minutes after the lung has reached 37°C. The perfusion of the lung is kept on maximum flow, while the lungs are ventilated with increased PEEP. We have noticed in earlier studies (work in progress) that during this maneuver it is very easy to harm the lung and create a slight edema while eliminating the atelectasis. However, it is crucial to eliminate the atelectasis to be able to perform an adequate validation of the lungs. If there is atelectasis, a shunt will be formed in this part of the lung resulting in nonfunctional lung parenchyma. This may lead to false low blood gas values and, in the worst case, failure to meet the criteria for lung transplantation. In the present study, we hypothesize that lung injury could be minimized by shutting down the perfusion without disconnecting the EVLP circuit, ventilating the lung with increased PEEP for 10 minutes. We refer to this maneuver as modified EVLP. As expected, both groups had significant higher blood gases after eliminating the atelectasis, but the lungs from the modified EVLP group had significant higher blood gases compared with the conventional EVLP group. Both groups, however, met the criteria for acceptance for lung transplantation. Interestingly, the lungs receiving modified EVLP had a significant lower lung weight compared with the conventional EVLP lungs indicating less lung injury and lung edema with the modified EVLP. There were also significantly higher airway pressure and PVR in the conventional EVLP group compared with the modified EVLP group, also indicating lung injury in the conventional EVLP group. Clinically, it is preferable to transplant a dry lung compared with a slightly heavier lung due to interstitial lung edema. The recipient who receives the dry lung with less lung injury will likely experience shorter time on a ventilator and shorter time at the ICU after the transplantation. The signs of primary graft dysfunction will probably be also less, which will affect the recipient’s morbidity and longtime mortality. Limitations in our study are the rather small study groups, the use of the EVLP and not a transplant model, and being assessed
Modified EVLP with normoventilation of the lungs without ongoing lung perfusion for 10 minutes may eliminate atelectasis almost completely without harming the lungs, thereby making it possible to evaluate blood gases properly in order to decide whether to transplant.
This study was supported by foundations from Region Skane and Lunds University.