24, 16, 27
The post-oxygenator sample is not a proxy for the carbon dioxide the brainstem is exposed to, and the divergence is largest exactly when the test is being read. Take both radial samples simultaneously; if the mixing point is unknown, the test result is unknown.
Simultaneous right radial and post-oxygenator circuit sampling
DOI 10.1016/j.jcrc.2024.154545
Simultaneous right and left radial arterial sampling during apnoea testing
27 patients, single centre; the mixing point varies with native ejection and flow and was not independently characterised. Structured abstract only. [VERIFICATION REQUIRED]
Right-versus-left radial carbon dioxide difference was 0.90 mmHg (95% CI 0.7-1.3) at the start of the test and 1.1 mmHg (0.9-1.8) at the end. Right radial versus post-oxygenator was 3.3 mmHg (1.5-6.0) at the start (P = 0.001) and rose to 9.9 mmHg (3.5-19.2) at the end (P = 0.002). The authors conclude that simultaneous right and left distal arterial sampling is the method of choice.
27 venoarterial ECMO patients undergoing brain-death determination