ENCORE 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).

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 approximately the equivalent of the induction dose, which I split into thirds and deliver every 5 to 10 minutes.

• Maintain paralysis to the end, so I can mechanically ventilate the patient with 100% oxygen to an end tidal concentration near zero (0% to 0.3%). This way, I know propofol is the only remaining agent sedating the patient.

• At the very end, reverse the partial paralysis. The remaining propofol is metabolized, resulting in a gentle, peaceful emergence, similar to that of a sedation case.

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.

Anesthesia Notebook

• Dexamethasone may improve blocks. Perineural dexamethasone when given as an adjunct to brachial plexus blocks appears to significantly extend the duration of blocks and improve post-op pain outcomes, according to a recent study (osmag.net/xqVED3). Researchers at Northwestern University conducted a meta-analysis of 9 randomized trials involving 760 patients and found that patients given dexamethasone also consumed fewer opioids. Additionally, there were no reports of persistent nerve injury related to the perineural administration, say the authors.
• Regional safer for tots. Regional anesthesia is safer than general for infants, say researchers who measured the presence of apnea after hernia surgery. There was little difference in late apnea, but regional reduced the risk of significant apnea in the first 30 minutes after surgery, a study of 722 infants found. Andrew Davidson, MD, author and associate professor at the Royal Children's Hospital in Melbourne, Australia, calls the study "the strongest evidence to date on how babies should have anesthesia for hernia repair."
• Different needles don't help. Researchers following up on a manufacturer's claim that using a larger needle bore reduces the pain of injection were disappointed to find little to no difference in the levels of pain experienced by patients, according to a recent study (osmag.net/ATrN4k) published in Anesthesia Progress. Patients were given dental injections on each side of their mouths, one side with a standard-bore 27-gauge needle, the other side with an enlarged-bore (43% wider) 27-gauge needle. Half of the patients were given the standard needle first; the other half the enlarged-bore needle first. Patients reported nearly identical pain scores (based on the visual analogue scale) for the 2 needles.