Postoperative nausea: inhalational agents
Basic, Clinical Sciences: Anesthesia Procedures, Methods, and Techniques
Volatile agents are a well-known cause of PONV and are the leading risk factor for vomiting in the early postoperative period (0-2 hours). After this period, other risk factors, such as childhood, early PONV, and use of postoperative opioids become the main predictors . Modern volatile anesthetics do not appear to differ significantly in their emetogenic potency, despite major differences in their pharmacokinetic properties. Multiple studies have shown similar incidences of PONV with isoflurane, enflurane, sevoflurane, and desflurane, and an increased incidence of PONV with volatile agents when compared to total intravenous anesthesia (TIVA) with propofol (19% reduction in early PONV), or regional techniques alone (patients receiving general anesthesia have been shown to be up to 11 times more likely to experience PONV) [3,6,7,8]. There appears to be a dose-dependent relationship between volatile agents and PONV, with longer duration of use being associated with increased incidence of PONV (however, duration of surgery itself – regardless of anesthetic technique used – is an independent risk factor for PONV) .
Nitrous oxide (N2O) is also a contributor to PONV, although early studies likely overemphasized its effect. Subsequent studies have shown that the emetogenic effects of N2O are less than that of volatile anesthetics; however, its emetogenic properties are additive, meaning that adding N2O to a volatile anesthetic further increases the chances of PONV . Furthermore, this risk likely increases with an increased inspiratory concentration of N2O, as well as increased duration of N2O exposure [14,15]. However, a more recent study showed that there was no difference in the incidence of PONV when 70% N2O was added during the last 30 minutes of an isoflurane-based anesthetic for laparoscopic vaginal hysterectomy (the rescue antiemetic was actually required less frequently in the N2O group, and there was reduced time to extubation, eye opening, and orientation) . Other studies have shown that any increased risk of PONV with N2O is eliminated by pretreatment with one or more common antiemetics, such as dexamethasone or ondansetron . Thus, although there is broad agreement that N2O contributes to PONV, there remains some controversy as to the extent of its effect.
In sum, inhalational agents remain an important contributor to PONV, particularly in the early postoperative period. Alternative techniques, such as TIVA and regional anesthesia, as well as multi-agent antiemetic prophylaxis, should be considered in high-risk patients.