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588studies investigating the effect of the reversal agent on PONV included only small numbers of patients (mostly < 100 patients)9, 10), whereas the present study included a number of patients large enough to detect its effect (n = 1221). Although neostigmine is used to counteract residual neuro-muscular block, co-administration of anticholiner-gics, such as atropine, are required because neostig-mine given alone exerts cholinergic effects on the gastrointestinal tract (increased motility) and on the heart (bradycardia)10). Reportedly, intrathecal neostigmine in doses ranging from 0.15 to 0.75 mg in human volunteers causes nausea and vomiting in a dose-dependent manner, probably via action on the brainstem11), whereas intrathecal atropine in a small dose (0.1 mg) quite effectively prevents PONV induced by intrathecal morphine in patients undergoing cesarean section12). Further, it is known that intravenous atropine can cross the blood-brain barrier to cause central effects13). In addition, an anticholinergic agent scopolamine is well known to exert a potent antiemetic effect and is used to prevent PONV1). In the present study, we used atropine 1 mg to prevent cholinergic effects of neostigmine 2 mg. Taken together, it seemed plau-sible that the antiemetic effect of atropine outweighed the emetic effect of neostigmine, thereby reducing the incidence of PONV in the present study, although a prospective large-scale study is required to verify our finding.In the present study, we could learn historical changes in our anesthesia practice for LGS. During the study period (2007-2009), only a small number of patients were anesthetized with TIVA that could reduce the incidence of PONV, compared with inha-lation anesthesia1), whereas recently, all patients are anesthetized with TIVA4). Ultrashort-acting remifentanil is used in all patients recently4), while it was used less frequently (865/1221 [70.8%]) during the study period. After our previous study4), prophylactic antiemetics using both droperidol and dexamethasone are given routinely, whereas prophy-lactic antiemetics, droperidol (n = 40) or less effec-tive metoclopramide (n = 96)1) were given only in 136 patients (11.1%) during the study period. Previously, the Japanese Ministry of Health, Labour, and Welfare approved the use of droperidol solely for sedation before and during anesthesia. However, it approved the off-label use of droperidol for treat-ment of PONV in September, 2009. Further, it approved the use of serotonin receptor antagonists, ondansetron and granisetron, for treatment of PONV in August, 2021, which would contribute to a further reduction of the incidence of PONV1). After our previous study4), a disposable PCA pump was exchanged from Baxter Infusor with a 30-min lockout time to a better adjustable disposable PCA pump with a 10-minute lockout time (COOPDECH® PCA Syrinjector®; Daiken Medical, Osaka, Japan)14). After the previous study4), droperidol is routinely added to the PCA pump infusate, while the PCA infusate containing droperidol were used in only 384 patients (31.4%) during the study period. Multi-modal analgesia was not used during the study period, whereas multimodal analgesia, e.g. employing rectus abdominis sheath block as well as trans-versus abdominis plane block15), and intravenous acetaminophen16), is now commonly used to reduce postoperative requirements of opioids and thus to reduce the incidence of PONV. During the study period, vecuronium was commonly used as a muscle relaxant, whereas recently, shorter-acting rocuronium is commonly used. At present, sugam-madex for reversal of rocuronium-induced neuro-muscular blockade is more commonly used than neostigmine because of the faster and more reliable reversal effect of sugammadex, although sugam-madex may not reduce the incidence of PONV, compared with neostigmine17).This study had some limitations. First, the design of retrospective data analysis is clearly inferior to a prospective randomized and blinded investigation. A retrospective study design always has a substan-tial risk of bias. Therefore, we should be cautious in interpreting the data. Second, we could follow up the presence/absence of PONV only for nine hours after the return to the ward due to the follow-up period in the ward during the study period, which could underestimate the incidence of PONV, compared with a 24-hour follow-up time in our previous prospective study4). Further studies are required to confirm the data shown in the present study.In conclusion, longer duration of anesthesia was associated with the increased incidence of PONV. Addition of droperidol to the infusate of intrave-nous fentanyl PCA and the use of the reversal agent neostigmine co-administrated with atropine were effective in reducing the incidence of PONV,