I am guessing that if an elderly person (not me) has copd & a pleural effusion (even if the person doesn't have a lung infection) then this would make it harder to survive sepsis. but if so, would either be likely to make a significant difference?

COPD is diagnosis.: The pleural effusion is a SIGN or a symptom, not a "condition". In fact, by draining the effusion, doctors can run tests & perhaps figure out what is causing the problem. But it doesn't portend anything with regards to survival unless it becomes large. COPD is a DIAGNOSIS. It means that the lungs don't function properly. It makes surviving sepsis tougher, as lung problems can easily develop. TTYD.

Sadly, yes and yes: COPD hampers the ability to fight infection, and pleural effusion limits the ability to oxygenate which is already much reduced by the COPD. This further reduces the ability to fight infection. Sepsis is the most serious type of infection. So sadly, all of these things work against the ability to survive. You can't cure COPD, and presumably, total removal of the pleural effusion has failed.