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LUNG TRANSPLANTATION

NO MAGIC NUMBER

Preservation temperature is often framed as a single number to achieve, yet the science of thermodynamics tells a more nuanced story. So, the question stands: can a single number be achieved?
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DOES A MAGIC NUMBER EXIST?

THE CURRENT STATE OF AFFAIRS

Static controlled hypothermia with FDA-cleared preservation systems remains an effective approach for donor lung storage because of its reliability, ease of use, and safe failure modes. All currently available FDA-cleared hypothermic preservation systems rely on phase-change material to maintain donor organ temperature within a safe range over a defined period of time. This range is reflected both in the engineering constraints and in regulatory filings.

WHAT'S REGULATED?

In the United States, only 3 portable preservation devices are FDA-cleared for static controlled moderate hypothermia of donor lungs intended for transplantation:

BAROguard Lung Preservation System

Designed to store, preserve, and transport human lungs donated for transplantation at 4°C-8°C with additional automated airway pressure control at 12-15 cm H20.

LUNGGUARD SYSTEM

PREDICATE DEVICE

 

The Paragonix LUNGguard System was the first passive hypothermic system indicated to store, preserve, and transport donor lungs at a range of 4°C-8°C.

x°port LUNG PRESERVATION SYSTEM

Designed to store, preserve, and transport human lungs donated for transplantation at 4°C-10°C.

 X°PORT is a trademark of Traferox Technologies Inc.

Each of these systems were FDA-cleared through the 510(k) pathway, requiring a legally marketed predicate device to which the new (subject) device can be deemed substantially equivalent. Both the BAROguard and X°Port® Systems were determined by the FDA to be substantially equivalent to the LUNGguard System.1-3
 
In other words, the FDA has cleared static preservation devices to hold temperature ranges: specifically 4–8°C or 4–10°C.

 

HOW DO PASSIVE SYSTEMS COOL?

 
All FDA-cleared portable static moderate hypothermic preservation devices are labeled for a temperature range, each achieving this through passive cooling. Passive cooling systems utilize phase change material (PCM), which operates over a temperature range.
magic number no temps

 

Real PCMs experience a gradual melting or solidifying of the material across several degrees, in comparison to an idealized, theoretical PCM, which would undergo an isothermal phase transition at a single temperature and does not exist in practice.

This temperature range can be further understood in terms of finite heat transfer and spatial temperature gradients within the PCM. This means that different regions of the material absorb or release heat at different rates, causing segments of the material to transition at slightly different temperatures causing a spatial temperature gradient.9,10

THE ENGINEERING PERSPECTIVE:

 

Variation in lung size, in-situ flush temperature, technique, and time between final breath and the start of preservation are significant contributors to the actual preservation temperature of a donor lung. These variables, combined with a consistent energy capacity in the PCM, inevitably result in variable temperature.

Reporting a single characteristic temperature is insufficient, and it is recommended that all PCMs in passive thermal systems be described with temperature ranges for the greatest level of accuracy and transparency.

thermodynamics-1

DID YOU KNOW?

THE USE OF UNREGULATED STORAGE DEVICES


Thermoelectric systems have not received FDA clearance or approval for organ preservation and transport.4-7 Their thermostat control mechanisms have not been validated to meet the rigorous standards applied to FDA cleared or approved medical devices and may subject the contents to cyclic variations in temperature. They have not been recommended by any professional societies for donor organ storage.

SO WHAT'S THE OPTIMAL PRESERVATION CONDITION?

Recent clinical findings have begun to indicate that the conversation extends beyond mere temperature control.

Control the Conditions. Not Just the Temperature.

EXPANDING THE SCOPE. NARROWING THE PRECISION.
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View References List
  1. LUNGguard 510k Premarket Notification. https://www.accessdata.fda.gov/CDRH510K/K192869.pdf.
  2. BAROguard 510k Premarket Notification. https://www.accessdata.fda.gov/cdrh_docs/pdf22/K223874.pdf.
  3. X°Port 510k Premarket Notification. https://www.accessdata.fda.gov/cdrh_docs/pdf24/K243870.pdf.
  4. MYTEMP 65HC: https://www.gohcl.com/assets/d9/b6/d9b6b613-100d-4f53-8576-b90aa36e3108/21088_Instructions.pdf
  5. Ryobi https://556aa8d9de68ea9c4f29-0a8acad11a4df5016d26cc39a7429843.ssl.cf1.rackcdn.com/2/Pi1824BQT_015_trilingual_03.pdf
  6. Lion Cooler: https://cdn.shopify.com/s/files/1/0095/7431/8146/files/PX30A_PX40A_PX50A_User_Manual.pdf?v=1689665989
  7. Dometic: https://www.dometic.com/externalassets/07-0703-070328-070328002_97000050754_123574.pdf?ref=-1684432367.
  8. Fatahi et al., Thermal Characterization of Phase Change Materials by Differential Scanning Calorimetry: A Review. Appl. Sci. 2022, 12(23), 12019; https://doi.org/10.3390/app122312019.
  9. Ye et al., Improved Performance of Latent Heat Energy Storage Systems in Response to Utilization of High Thermal Conductivity Fins. Energies 2023, 16(3), 1277; https://doi.org/10.3390/en16031277.
  10. Günther et al., Measurement of the enthalpy of PCM. Conference: 11th International Conference on Thermal Energy Storage At: Stockholm, Sweden. 2009.