Objective:To observe the effect of esketamine on cardiac index in patients undergoing lumbar surgery in prone position under general anesthesia.Methods:Forty-five patients with prone lumbar surgery after general anesthesia in Hunan Provincial People′s Hospital from March to July 2021 were divided into observation group (24 cases, group A) and control group (21 cases, group B) according to random number table method. Group A received 0.5 mg/kg esketamine intravenously during induction, and 0.15 mg/(kg·h) esketamine intravenously for 2 h after prone position. Group B received the same amount of normal saline. Both groups were given sevoflurane and remifentanil during operation to maintain anesthesia, and sufentanil was given intermittently during operation. The mean arterial pressure (MAP), systolic blood pressure (SBP), diastolic pressure (DBP), cardiac index (CI), and heart rate (HR) before induction (T 0), during endotracheal intubation (T 1), 5 minutes after intubation (T 2), 5 minutes after prone position (T 3), 10 minutes after prone position (T 4), 30 minutes after prone position (T 5), 45 minutes after prone position (T 6), 60 minutes after prone position (T 7), 90 minutes after prone position (T 8), and 120 minutes after prone position (T 9) were recorded; The total dosage of norepinephrine 2 hours after anesthesia to prone position and extubation time after operation were also recorded. The Visual Analogue Scale (VAS) was performed 15 minutes after extubation, 6 and 24 hours after operation. Results:There was no significant difference in CI between T 3-T 9 and T 2 in group A ( P>0.05); the CI of group B at T 3-T 7 was significantly lower than that at T 2 (all P<0.05); there was no significant difference in CI between T 8-T 9 and T 2 in group B (all P>0.05); There was no significant difference in CI between group A and group B at T 0-T 2 (all P>0.05). The CI of group A at T 3-T 9 was significantly higher than that of group B (all P<0.05); The dosage of norepinephrine in group A was significantly lower than that in group B ( P<0.05); There was no significant difference in HR, MAP, SBP and DBP between the two groups at different time points (all P>0.05); there was also no significant difference in extubation time and VAS scores at 15 minutes, 6 hours and 24 hours after extubation between the two groups (all P>0.05). Conclusions:Intraoperative application of esketamine can increase CI after prone position and reduce the amount of norepinephrine during lumbar surgery.