The effects of nitrous oxide on controlled hypotension during low flow anesthesia

We investigated the effect of Nitrous Oxide (N2O) on controlled hypotension in low-flow isoflurane-dexmedetomidine anesthesia in terms of hemodynamics, anesthetic consumption, and costs.

We allocated forty patients randomly into two equal groups. We then maintained dexmedetomidine infusion (0.1 μg.kg(-1).min(-1)) for 10 minutes. Next, we continued it until the last 30 minutes of the operation at a dose of 0.7 μg.kg(-1).hour(-1). We administered thiopental (4-6 mg. kg(-1)) and 0.08-0.12 mg.kg(-1) vecuronium bromide at induction for both groups. We used isoflurane (2%) for anesthesia maintenance. Group N received a 50% O2-N2O mixture and Group A received 50% O2-air mixture as carrier gas. We started low-flow anesthesia (1L.min(-1)) after a 10-minute period of initial high flow (4.4L.min(-1)). We recorded values for blood pressure, heart rate, peripheral O2 saturation, inspiratory isoflurane, expiratory isoflurane, inspiratory O2, expiratory O2, inspiratory N2O, expiratory N2O, inspiratory CO2, CO2 concentration after expiration, Minimum Alveolar Concentration. In addition, we determined the total consumption rate of fentanyl, dexmedetomidine and isoflurane as well as bleeding.

In each group the heart rate decreased after dexmedetomidine loading. After intubation, values were higher for Group A at one, three, five, 10, and 15 minutes. After intubation, the patients reached desired hypotension values at minute five for Group N and at minute 20 for group A. MAC values were higher for Group N at minute one, three, five, 10, and 15 (p<0.05). FiO2 values were high between minute five and 60 for Group A, while at minute 90 Group N values were higher (p<0.05). FiIso (inspiratuvar isofluran) values were lower in Group N at minute 15 and 30 (p<0.05).

By using dexmedetomidine instead of nitrous oxide in low flow isoflurane anesthesia, we attained desired MAP levels, sufficient anesthesia depth, hemodynamic stability and safe inspiration parameters. Dexmedetomidine infusion with medical air-oxygen as a carrier gas represents an alternative anesthetic technique.