Because the adoption of the lung allocation scoring system, lung transplantation has been offered to more critically ill end-stage lung disease patients.1,2 Historically, these patients would not have been listed as they would be expected to die on the waiting list. In the current era, we have pushed the envelope in terms of listing and successfully transplanting patients with profound levels of respiratory failure requiring mechanical ventilator support and more recently venovenous extracorporeal membrane oxygenation (ECMO) support.3,4 Indeed, it is now possible and likely preferable to bridge patients with respiratory failure with ECMO alone rather than mechanical ventilation.5
One of the key barriers to successful lung transplant with these bridging strategies is the ability to maintain sufficient levels of conditioning and rehabilitation potential in the candidate recipient as they wait for appropriate donor lungs. Strategies for ambulatory ECMO have been described but are limited in a practical sense by the cumbersome nature of the tenuous attachment that the patient must maintain with the mechanical pump, oxygenator, gas source, and power input via the cannulas and tubing.6 In many cases, these patients wait on ECMO support in a mostly bedridden state, which negatively impacts their rehabilitation potential. Many improvements have been made over the years to simplify and minimize the footprint of these devices as well as cannulation strategies, but progress toward a long-term, truly integrated or wearable unit lags behind the technology available for mechanical circulatory support devices for heart failure.
In the article “Month-long respiratory support by a wearable pumping artificial lung in an ovine model” by Orizondo et al,7 the authors address these 2 main concerns of wearability and long-term function. This article describes and evaluates a compact and wearable pumping artificial lung in a sheep model. The technology involves an integrated centrifugal pump and gas exchanger perfusing normal sheep via a dual-lumen cannula at the internal jugular vein position. In the study, pump and gas exchange performance parameters as well as hematologic physiology were continuously measured over a period of 1 month. The authors describe modifying and trialing different pump designs, which ultimately allowed them to achieve durability and sustainable hematologic stability. The limitations in their study were primarily limited to cannulation in the sheep model. The flow rates and gas exchange appeared adequate in this sheep model with normal lungs. It will be interesting to see the performance in a lung injury model.
The take home message here is that integrated and wearable ECMO support is likely to be achievable in the near future. While this technology is still in the development phase, the possibility of being able to bridge profoundly critical, end-stage lung disease patients to lung transplantation with a long-term, wearable ECMO unit is intriguing. It has the potential to make the process of maintaining rehabilitation potential and conditioning in these patients much more feasible. This would in turn increase the number of patients who can be helped with lung transplantation and improve recipient outcomes due to improved perioperative conditioning in these critically ill patients. Hopefully, future studies will continue in this field to bring us closer to making this a clinical reality.
1. Kozower BD, Meyers BF, Smith MA, et al. The impact of the lung allocation score on short-term transplantation outcomes: a multicenter study. J Thorac Cardiovasc Surg. 2008;135:166–171.
2. Maxwell BG, Levitt JE, Goldstein BA, et al. Impact of the lung allocation score on survival beyond 1 year. Am J Transplant. 2014;14:2288–2294.
3. Tipograf Y, Salna M, Minko E, et al. Outcomes of extracorporeal membrane oxygenation as a bridge to lung transplantation. Ann Thorac Surg. 2019;107:1456–1463.
4. Todd EM, Biswas Roy S, Hashimi AS, et al. Extracorporeal membrane oxygenation as a bridge to lung transplantation: a single-center experience in the present era. J Thorac Cardiovasc Surg. 2017;154:1798–1809.
5. Nosotti M, Rosso L, Tosi D, et al. Extracorporeal membrane oxygenation with spontaneous breathing as a bridge to lung transplantation. Interact Cardiovasc Thorac Surg. 2013;16:55–59.
6. Garcia JP, Kon ZN, Evans C, et al. Ambulatory veno-venous extracorporeal membrane oxygenation: innovation and pitfalls. J Thorac Cardiovasc Surg. 2011;142:755–761.
7. Orizondo RA, Omecinski KS, May AG. Month-long respiratory support by a wearable pumping artificial lung in an ovine model. Transplantation. 2021;105:999–1007.