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A U G U S T 2 0 1 5 | O U T P A T I E N TS U R G E R Y. N E T
The authors gave one group of patients propofol for induction, anes-
thetic 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).
The basics
Here's the basic procedure I've used, with great results:
• Discontinue gas and start propofol bolusing 15 to 30 minutes
before the expected conclusion of the case. The bolus is approximate-
