Our ECMO patients are always 1:1. From the time they come in to the time they leave. We've even had some be so sick we staffed them 2:1 ( 2 nurses for 1 patient). Even if they are "stable", they are 1:1.
Always 1:1 along with a ECMO tech (who is a specially trained RN or RT).
A few months ago we ran into some serious staffing issues when our 24 bed unit had 6 ecmo patients and an additional 2 CRRT patients (in my hospital CRRT is 1:1 with an additional pump nurse). That was 8 patients total who needed 2:1 care along with the rest who were pretty high acuity, we don't usually staff for that many nurses, it was rough going for a bit.
At my current unit our ECMO patients are always 1:1 in my current job. If paged, profusion shows up in minutes. It was a big change from my last unit where we were often 2:1 with profusion at the bedside 24 hours.