Introduction
Lung transplantation is a well-known surgery for patients with advanced or end-stage lung disorders. Based on the research done by the International Society of Heart and Lung Transplantation, the number of operated cases of lung transplant surgery has achieved a sudden hike since 2012. Due to the increase in the demand for lung transplant patients, various patients are not able to get the matching donor on time, and sometimes the requirements cannot be fulfilled. All these factors have resulted in an increase in the mortality ratio. Lack of reliable lung preservation methods and poor control rejection has resulted in the failure of lung transplantation procedures. The shortage of donor lungs and limited viability of the harvested organs has posed significant challenges in this field. This article explores some of the recent advances in lung preservation techniques which have provided hope for improved patient outcomes and have proven as a boon in the field of organ transplantation.
What Are the Different Criteria That Define Successful Lung Preservation?
Different criteria that define successful lung preservation include:
-
Maintenance of morphological integrity of the lungs (especially the alveolar-capillary barrier).
-
Prevent depression of lung functions even for a shorter period of time.
-
Inhibition of the metabolism process prevents metabolic end-products accumulation or breaks down the stored energy.
-
Preservation of immune function of the lungs is crucial to prevent any risk of organ rejection.
-
Prevent any kind of injury while preserving the donor lung.
-
Prevent any kind of fluid accumulation (edema) within the lungs as it can result in impaired lung function.
-
Maintain the correct temperature while preserving the donor lung. Temperature optimization is needed to prevent any kind of cellular damage to the lungs.
-
Maintaining adequate oxygenation and ventilation during preservation of the lungs to prevent lung hypoxia and meet the metabolic needs of the lungs.
What Are the Different Methods of Lung Preservation?
Different methods of lung preservation are:
1. Lung Preservation by Metabolic Inhibition: Lung preservation by metabolic inhibition is achieved by hypothermia and pharmacological agents.
-
Hypothermia: Hypothermia was achieved by freezing the lungs below zero (subzero) temperatures or by using fluorocarbons. The drawback of this method is excessive morphological and functional damage to the organ.
-
Pharmacological Agent: Pharmacological, metabolic inhibition is achieved by using magnesium ions. This technique also did not give good results, so was no longer accepted.
Based on different research studies done by Crane and his associates, lungs stored in Collin-sacks solution with quick ligation of the pulmonary artery on the contralateral side for 24 hours have shown successful and compatible results after lung transplantation surgery.
2. Lung Preservation by Metabolic Maintenance: Lung preservation by metabolic maintenance is achieved by in vivo or in vitro perfusion or by hyperbaria.
-
Hyperbaric Method: In this method low -molecular weight Dextran is used to flush the lungs, and the lungs are then placed in a hyperbaric chamber with 100 percent oxygen, 30 pascals pressure, and 39.3 degree Fahrenheit temperature for about 24 hours.
-
Perfusion Technique: Pulsatile perfusion is one of the most successful methods of lung preservation. Almost 48 hours of safe preservation can be achieved using this method. The drawback of non-pulsatile perfusion is pulmonary edema. Histological alterations are also present in the case of longer perfusion time.
3. EVLP (Ex-Vivo Lung Perfusion Technique): It is the most promising and advanced lung preservation technique. The use of EVLP was first described by Steen for preserving the donor lungs using the external machine as a specific normothermic condition. This method involves the use of the Steen solution (extracellular solution consisting of dextran 40 and human albumin).
The albumin in the solution helps to maintain the colloidal osmotic pressure and also prevents edema. The dextran in the solution helps to protect the lungs from cell-mediated injury and inhibits aggregation of platelets.
Components of EVLP (Ex-Vivo Lung Perfusion) Circuit: The EVLP circuit is composed of:
-
Centrifugal pump.
-
Leukocyte filter.
-
Heat exchanger.
-
Hardshell reservoir.
Steady State Ventilation Settings of EVLP: It involves a tidal volume of 7 milliliters per kg, a rate of 7 cycles per minute, a fraction of inspired oxygen of 21 percent, and positive end-expiratory pressure of 5 cm of water (H2O).
Assessment State Ventilation Settings of EVLP: It involves a tidal volume of 10 milliliters per kg, a rate of 10 cycles per minute, a fraction of inspired oxygen of 100 percent, and positive end-expiratory pressure of 5 cm of water (H2O).
Advantages of Ex-Vivo Lung Perfusion procedure:
-
Helps in the assessment of marginal donor lungs before the lung transplantation procedure.
-
Preservation time can be extended safely.
-
It helps to maintain and improve standard grafts by targeted administration of therapeutics.
4. Biotechnology and Regenerative Medicine: It has shown great promise in the lung preservation method. Methods such as decellularization and bioengineering allow the formation of lung scaffolds that can be populated with autografts (patients' own cells) which reduces the risk of rejection. These advances provide patients with readily available organs, eliminating the need for a long waiting list and immunosuppressive medications.
What Are the Future Of EVLP Centers for Lung Preservation?
The EVLP (Ex-Vivo Lung Perfusion) method of assessing and preserving the donor's lungs requires complex and multiple technologies as well as infrastructure along with trained expertise. The efforts are ongoing for setting up a few EVLP centers to perform the assessment of the organ and then sending it to the satellite hospitals when required. These centers would help patients who need emergency lung transplantation procedures and are on the waiting list for lung transplantation surgeries.
Conclusion
Advances in lung preservation methods have been revolutionizing the field of organ transplantation and offering new hope for patients in urgent need of lung transplants. The EVLP (Ex-Vivo Lung Perfusion) and normothermic machine perfusion techniques have shown excellent results when compared to the conventional techniques in terms of donor lung preservation and assessment. These advanced techniques have helped to decrease the failure rates of lung transplantation, thereby decreasing the mortality ratios by saving more lives. With ongoing advances and research, the future of lung transplantation will become brighter with the organization of EVLP centers at different locations in the near future.
