LMA- Spontaneous respirations with a little PS and PEEP. This diminishes reduction in preload compared to SIMV which leads to better hemodynamics. In addition, it is easier to run a patient lighter (less volatile agent) and titrate opioids with spontaneous ventilation compared to SIMV which again leads to better hemodynamics.
ASA4 patients tolerate GAs better (IMHO) with LMAs combined with Spontaneous respirations.
I emphasized the difference. PSV is not SV, and I was talking about (unsupported) SV. Hunting for spontaneous ventilations, at any price, regardless of anesthetic depth and EtCO2, and running the entire case without pressure support, are typically CRNA-ish, in my experience. I am talking about LMA cases, to be more precise.
If the patient is not breathing, I use pressure control post-induction. I get good respiratory volumes, a well-controlled anesthetic level, with low inspiratory pressures and little cardiovascular impact. Especially pre-incision, until I reach a proper anesthetic depth, PCV is better than PSV for me. Not only that, but PCV allows overbreathing, hence I can look for spontaneous breathing (without bucking) and switch to PSV when I feel we are in calm waters. By the way, kazuma, I used to be a big SIMV fan until I discovered the much more natural PCV (look at their flow curves and compare both to negative pressure spontaneous breathing).
Of course, if I get spontaneous breathing after induction, it makes me happy and I run PSV at a level that provides good tidal volumes and ventilation. I will go up to 10-15 cmH20, if needed, as if I was running PCV, to keep the patient deep and prevent atelectasis. But I don't go hunting for spontaneous ventilations
at any price, especially pre-incision. That's recipe for laryngospasm and possibly recall, on incision. Later during the surgery, it can be recipe for significant respiratory acidosis. (Have you never walked in on a CRNA running the patient at EtCO2 of 60-70 and 1.5 MAC, waiting for him to start breathing? They just don't feel comfortable blowing off the gas and waking up the patient on controlled ventilation.)
Getting the patient breathing spontaneously is the best way to a fast extubation at the end of the case, but not "at any price".
Of course, there is an art to using the right amount of propofol that allows rapid recovery of spontaneous breathing, right after LMA placement. That's not what I was criticizing here.