The key is to get gas out of the patient’s system.
Michael Reines, MD
Take advantage of propofol’s antiemetic properties by reintroducing it toward the end of the procedure.
I‘ve developed an anesthetic technique that significantly reduces PONV and costs, and improves patient, surgeon and nurse satisfaction. I call it “bookending,” because it involves using propofol both at the beginning and at the end of a given procedure.
Most general anesthetics use gas for maintenance, but it’s been proven that propofol infusions without gas significantly reduce the incidence of PONV. My technique uses gas, but transitions back to propofol at the end of the procedure, after the gas is discontinued.
The idea comes from a 1996 study (osmag.net/JuY6Vd) that ostensibly found that the technique doesn’t work. I believe it does work, and I think I know what was wrong with that initial study.
The authors gave one group of patients propofol for induction, anesthetic gas for maintenance, then propofol again for about the last 30 minutes of the case, after the gas was turned off. For a second group of patients, they infused propofol for the entire case, to avoid gases altogether.
They found that the “bookended” group had a greater incidence of PONV than the continuous-infusion group. They concluded that the idea that PONV can be reduced, despite gas use, by bookending propofol (which at the time was an expensive alternative to gases) was an intriguing — but incorrect — hypothesis.
An overlooked factor
Why didn’t it work? I think because the study failed to measure and consider the amount of anesthetic gas that still remained in patients after they woke up, even though they’d been switched from gas to propofol near the end of their cases. Since anesthetic gases can cause PONV if appreciable amounts remain in patients, they can override the antiemetic effects of propofol the authors hoped to see.
Therefore, a crucial part of my technique involves maximizing the gas elimination from the patient. Since most monitors today can measure end tidal (expired) gas concentration, we can objectively ensure that anesthetic gases are virtually gone from a patient by the end of a case. In addition, improvements in anesthetic gases now allow for a more rapid elimination (for example, you can eliminate sevoflurane faster than isoflurane).
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