A comparative analysis of carbon dioxide versus nitrous oxide as the pressurised gas driving a retinal cryotherapy...

To evaluate the relative performance of carbon dioxide and nitrous oxide as the cryogenic gas in an ophthalmic cryotherapy machine.

We performed a benchtop analysis of CO₂- and N2O-driven cryotherapy delivery systems in the Keeler laboratory, UK. For each gas, 10 cryotherapy probes were tested in terms of the internal and external tip temperatures, when applied to a simulated tissue sample.

Using CO₂, the external and internal tip temperatures were on average 2.07°C and 2.12°C colder, respectively, than those achieved using N₂O as the cryogenic gas. These diff erences were statistically significant (p<0.05 for both external and internal tip temperatures).

CO₂ delivers a deeper freeze than N₂O to a simulated tissue sample. A strong case can be made for switching ophthalmic cryotherapy units from N₂O to CO₂ in order to reduce greenhouse gas emissions.