Discussion
postoperative pain, reduction in arterial blood pressure, hypotension, PONV, hypertension
BEZOLD, ADVERSE EVENTS, BLOOD, MOTION SICKNESS, HYPERTENSION
The current study is the first randomized placebo-controlled study that investigates the effect of intravenous granisetron on the ED50 of ephedrine for preventing hypotension after general anesthesia induction in elderly patients. We found that the ED50 of ephedrine for preventing hypotension after general anesthesia induction in elderly patients was about 0.14 mg/kg. Moreover, we demonstrated that prophylactic IV administration of granisetron before general anesthesia induction results in a significantly lower ephedrine requirement to prevent post-induction hypotension which was supported by a significant reduction of ED 50 to 0.08 mg/kg in granisetron group.Induction of general anesthesia often results in a significant reduction in arterial blood pressure, especially in the elderlyNumerous previous studies investigated the effect of 5-HTThe exact mechanism of serotonin 3 receptor antagonists in reducing hypotension and the need of vasopressin is still not fully understood. A possible explanation for this phenomenon is that such drugs block the Bezold–Jarisch reflex which is associated with perioperative hypotensionAmong the receptors involved in Bezold–Jarisch reflex are chemoreceptors responding to 5-hydroxytryptamine3 (5-HT3, serotonin)The simplified risk score for PONV is a tool used to predict the likelihood of a patient experiencing PONV after surgery. It consists of four factors: female gender, non-smoking status, history of PONV or motion sickness, and the use of opioids for postoperative pain management. Each factor is assigned one point, and patients with a score of 2 or higher are considered to be at high risk for PONVOur current study showed no significant differences in adverse events between the two groups. There are two possible reasons for this phenomenon. One possibility is that granisetron at this dose itself has no significant effect on hypotension and hypertension. On the other hand, it could be due to our research protocol. We adopted the sequential up-down method, and the ephedrine dose of the next patient was constantly adjusted according to the blood pressure result of the previous patient, so that the incidence of hypotension and hypertension was not significantly different between the two groups.The present study has several limitations. First, Blood pressure measurements may be affected by the size and location of the cuff and the type of monitor used. Second, the blood pressure measurement was intermittent and hypotension occurring between measurements might not have been detected. Third, the definition of intraoperative hypotension is variable, which significantly limited the comparisons between studies concerning this issue. Forth, different types of surgery included in this study may affected the reliability of this study. However, the inclusion of different types of surgery can better reflect real clinical situation. Fifth, the effect of different doses of granisetron on the prevention of hypotension after general anesthesia remains to be studied.