MAC-sparing effect of nitrous oxide in sevoflurane anesthetized sheep and its reversal with systemic atipamezole administration

Abstract

IntroductionNitrous oxide (N2O) is an anesthetic gas with antinociceptive properties and reduces the minimum alveolar concentration (MAC) for volatile anesthetic agents, potentially through mechanisms involving central alpha2-adrenoceptors. We hypothesized that 70% N2O in the inspired gas will significantly reduce the MAC of sevoflurane (MACSEVO) in sheep, and that this effect can be reversed by systemic atipamezole.Materials and methodsAnimals were initially anesthetized with SEVO in oxygen (O2) and exposed to an electrical current as supramaximal noxious stimulus in order to determine MACSEVO (in duplicates). Thereafter, 70% N2O was added to the inspired gas and the MAC re-determined in the presence of N2O (MACSN). A subgroup of sheep were anesthetized a second time with SEVO/N2O for re-determination of MACSN, after which atipamezole (0.2 mg kg-1, IV) was administered for MACSNA determinations. Sheep were anesthetized a third time, initially with only SEVO/O2 to re-determine MACSEVO, after which atipamezole (0.2 mg kg-1, IV) was administered for determination of MACSA.ResultsMACSEVO was 2.7 (0.3)% [mean (standard deviation)]. Addition of N2O resulted in a 37% reduction of MACSEVO to MACSN of 1.7 (0.2)% (p <0.0001). Atipamezole reversed this effect, producing a MACSNA of 3.1 (0.7)%, which did not differ from MACSEVO (p = 0.12). MACSEVO did not differ from MACSA (p = 0.69). Cardiorespiratory variables were not different among experimental groups except a lower ETCO2 in animals exposed to SEVO/N2O.ConclusionsN2O produces significant MACSEVO-reduction in sheep; this effect is completely reversed by IV atipamezole confirming the involvement of alpha2-adrenoreceptors in the MAC-sparing action of N2O.

Safety of Nitrous Oxide Anesthesia in a Selected Group of Patients Undergoing Neurosurgery: An Exploratory Subgroup Analysis of the ENIGMA Trials

“…The primary strength of our analysis is that it is based on randomized data from the ENIGMA trials, which minimizes the effects of confounding on our results. Nitrous oxide has a number of advantages that make it a convenient option in contemporary anesthesia, including analgesic properties,1 rapid onset and termination of anesthetic effects, reduction of anesthetic awareness,2,3 and synergy with other anesthetic agents 33. Our findings do not highlight any negative safety signals that would preclude the use of nitrous oxide is modern neuroanesthesia practice.…”

Effect of real-time oxygen consumption versus fixed flow-based low flow anesthesia on oxygenation and perfusion: a randomized, single-blind study

“… 5 Nevertheless, N 2 O allows a dose reduction of potent volatile anesthetics and opioids owing to intense analgesic activity. 6 7 However, there are concerns about hypoxia when used in LFA. Therefore, the need of the hour is the scope for further research for cost containment within N 2 O-based LFA without compromising patient safety.…”

Time to oxygenation for cannula and scalpel‐based techniques for emergency front‐of‐neck access: a wet lab simulation using an ovine model: a reply

“…He mentions the lack of analgesia, while also questioning our use of nitrous oxide (a potent analgesic agent, which also has MAC‐sparing effects) . We acknowledge the potential difficulties regarding the use of nitrous oxide in ruminants, but have not found it to greatly increase ruminal tympany.…”