In order to perform a valid apnea test it is generally accepted that the patient’s CO2 must rise above 60 mm Hg (or increase by 20 mmHg above baseline) with a correlating decrease in pH before the body has a chance to compensate metabolically. This can be challenging on ECMO, especially V-A ECMO.
The suggested way to accomplish this on VV ECMO is simply to turn down the ECMO Sweep flow until the CO2 rises to the desired level. The ventilator rate can also be turned down to 0 as applicable. This can often be obtained while still maintaining adequate oxygenation levels. VA ECMO can be a little more challenging as cardiac output and oxygenation may be more dependent upon the VA ECMO flow. In either VV or VA, if there is difficulty getting CO2 to rise without severely impacting oxygenation, then supplemental CO2 may be bled into the ECMO Sweep flow to drive the CO2 up while still maintaining adequate oxygenation to the patient.
The Apnea test on ECMO is a test that you never want to have to do, but it’s important to be able to achieve this assessment on ECMO when needed.