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By: Michael Reines
Published: 8/6/2015
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).
The basics
Here's the basic procedure I've used, with great results:
The technique is most easily mastered in non-obese, ASA I and II patients, and with surgeons who are reliable in their pace. Bookending can then be tailored, based on BMI and/or case duration — that is, transitioning earlier to allow more complete elimination of gas. In general, the parameters to consider when transitioning include the timing of the transition, the dose and frequency of propofol boluses, the oxygen flow rate used to eliminate gas, and establishing a reversible depth of paralysis that allows for rapid reversal at the very end. Intuitively, it may seem preferable to avoid paralysis and mechanical ventilation until the end, but it's the best way to effectively drive out the anesthetic gas.
Augmenting the technique
I also incorporate other practices to help minimize PONV. To manage pain, I give narcotics mostly toward the beginning of a case, and use ketolorac when transitioning. In longer cases and/or those with greater patient exposure, I use a forced-air warmer to maintain normothermia. You should also optimize fluid balance and avoid nitrous oxide, especially in long cases.
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