Getting the best out of donor lungs: Prone or supine positioning?

A couple of recent studies have thrown further new light on the question of optimal positioning of the donor lung (prone or supine?), both during the warm ischemic period following cardiac arrest in DCD lung donors, and later during ex-vivo perfusion (EVLP) of the donor lung.

Prone positioning of DCD donor after cardiac arrest

There is extensive literature on the oxygenation benefits of positioning ventilated patients with lung injury prone. This concept has not previously been explored in lung donors.

The Toronto group(1) therefore devised a study to determine the effect of donor positioning on the quality of lung preservation after cardiac arrest in a cDCD pig model. After asystole, animals were divided into two groups based on body positioning (supine or prone). All animals were subjected to three hours of warm ischemia. Donor lungs were then explanted and preserved at 4°C for six hours, followed by six hours of assessment under warm ex-vivo lung perfusion (EVLP). The group found that, “Donor lungs from the prone group displayed significantly greater quality as reflected by better function during EVLP, less oedema formation, less cell death, and decreased inflammation compared with the supine group”. They concluded, “A simple manoeuvre of donor prone positioning after cardiac arrest significantly improves lung graft preservation and function”.

Prone or supine positioning during ex-vivo lung perfusion?

Another related study from the Leuven group(2) studied the impact of prone positioning on graft function during warm EVLP, confirming findings first published by Niikawa et al, Cleveland (3) a year previously. Normally, lungs undergoing EVLP are mounted supine, with the risk of fluid accumulation in the dorsal regions. The Leuven group therefore compared two groups of porcine lungs mounted supine or prone during warm EVLP for six hours.

Physiological parameters were similar between both groups, despite a higher pulmonary vascular resistance in the prone group. In the supine group, as expected, wet/dry ratios and CT density of dorsal areas were higher compared to ventral areas. By comparison, in the prone group, these parameters were essentially similar, indicating a more homogeneous distribution of interstitial fluid/oedema throughout the lung. The group conclude, “Prone positioning during EVLP is feasible and leads to more homogenous distribution of interstitial fluid”. Given that interstitial fluid contributes to both impaired gas exchange and poorer compliance, more uniform distribution might lead to better overall function at the end of EVLP. Indeed the earlier Cleveland study had in addition also reported a significant reduction in Ischemia-Reperfusion Injury after only 2 hours of warm EVLP in a similar porcine model.

References:

  1. Watanabe Y et al, Donor prone positioning protects lungs from injury during warm ischemia. Am J Transplant. 2019 Mar 19. doi: 10.1111/ajt.15363. [Epub ahead of print] (link to abstract)
  2. Ordies S et al, Prone Positioning During Ex Vivo Lung Perfusion Influences Regional Edema Accumulation. J Surg Res. 2019 Jul;239:300-308. doi: 10.1016/j.jss.2019.02.003. Epub 2019 Mar 19 (link to abstract)
  3. Niikawa H et al, The protective effect of prone lung position on ischemia-reperfusion injury and lung function in an ex-vivo porcine lung model. J.Thorac Cardiovasc Surg. 2019 Jan;157(1):425-433. doi: 10.1016/j.jtcvs.2018.08.101 (Epub 2018 Sep 29.)

Xvivo Insights PB-2019-06-27