Effects of spinal anaesthesia and intravenous general anaesthesia on the absorption of normal salinein patients undergoing hysteroscopic endometrial resection: an observational study

Introduction The absorption of uterine distention fluid during hysteroscopic endometrial resection can cause vol- umeoverload, which can lead to coagulation dysfunction, acute left heart failure and pulmonary oedema in patients. The effects of spinal anaesthesia and intravenous general anaesthesia on the absorption of normal saline as uterine distention fluid during hysteroscopic surgery remain unclear. The aim of this clinical trial was toobserve the effects of spinal anaesthesia and intravenous general anaesthesia on the absorption of normal saline in patients undergoing hysteroscopic endometrial resection.

A total of 126 patients undergoing elective hysteroscopic endometrial resection were divided into a spinal anaesthesia group (s group) and a propofol-fentanyl intravenous anaesthesia group (PF group), with 63 cases in each group, and both groups were divided into a short-term group (S1 group and PF1 group) and a long-term group (S2 group and PF2 group) according to the operation time. The primary outcome was the absorption of normal saline, and the secondary outcomes included the perioperative SBP , DBP , HR and SpO2 and postoperative haematocrit val- ues, and the incidence of postoperative complications.

The volume of saline absorbed was significantly increased in the S2 and PF2 groups compared with the S1 and PF1 groups (P < 0.001). There was a significant positive correlation between the amount of normal saline absorbed and the operation time (r = 0.895, P < 0.001). The postoperative haematocrit value was slightly lower than that before the operation in all four groups (P 0.05).

There was no difference in the effects of spinal anaesthesia and intravenous general anaesthesia on the absorption of normal saline during hysteroscopic endometrial resection, and the absorption of normal saline increased accordingly with the extension of operation time. †Wuchang Fu, Xue Li, Hongchun Xu and Ting Zhao contributed equally to this work. *Correspondence: Fangjun Wang [email protected] Full list of author information is available at the end of the article Page 2 of 9Fu et al. BMC Women’s Health (2023) 23:240

Spinal anaesthesia, Intravenous general anaesthesia, Absorption, Uterine distention fluid, Hysteroscopic endometrial resection

Hysteroscopic surgery has become a standard surgical treatment for abnormal uterine bleeding that is ineffec - tive in conservative treatment, and it has been shown to be a safe and effective alternative to hysterectomy [1]. Hysteroscopic surgery requires distention of the uterine cavity with distention medium to fully display the surgi - cal area. However, distention fluid can be absorbed rap - idly through the surgical wound and retained in the body during surgery, which can easily lead to fluid overload. Severe fluid overload can cause coagulation dysfunction, acute left heart failure and pulmonary oedema in patients undergoing surgery [2]. It was found that different anaesthesia methods had different effects on the absorption of glycine as uter - ine distention fluid during hysteroscopic surgery, but the results were inconsistent [3, 4]. Berg et  al. reported that the mean serum sodium level dropped significantly in a monopolar resectoscope using 1.5% glycine with no change in the bipolar resectoscope using 0.9% saline [5], suggesting that bipolar resectoscopes with 0.9% normal saline have a better safety profile. At present, the effects of spinal anaesthesia and intravenous general anaesthesia on the absorption of normal saline during hysteroscopic surgery are unclear. Our objective was to determine whether spinal anaesthesia and intravenous general anaesthesia have different effects on the absorption of normal saline as uterine distention fluid during hystero - scopic endometrial resection.

This observational clinical study was performed from February 2022 to August2022, and a total of 126 patients who underwent elective hysteroscopic endometrial resection were included in the study. These women, who had previously been treated with various combinations of progestin, antifibrinolytic drugs, gonadotropin releas - ing hormone analogues, nonsteroidal anti-inflammatory drugs, and oral contraceptives, underwent endome - trial resection due to symptomatic menorrhagia. The inclusion criteria for this study were American Soci - ety of Anaesthesiologists (ASA) classification I or II, 18.5 ≤ BMI ≤ 24  kg/m2, personal consent of the patient and age 18 to 60 years. The exclusion criteria were coag - ulation dysfunction, hypertension, diabetes mellitus, deformity in the spinal anatomyor skin infection on the back, history of allergies to local anaesthetics or propo - fol, submucosal fibroids, uterine prolapse, endometrial hyperplasia, uterine polyps, and cervical or endometrial precancerous lesions. Withdrawal criteria included a change in the surgical plan, refusal by the patient or rela - tives to continue the study, and incomplete data collec - tion. All patients underwent preoperative transvaginal pelvic ultrasonography, cervical smear and coagulation tests. Patients were grouped according to the anaesthe - sia methods. If the patients underwent propofol-fenta - nyl intravenous anaesthesia during surgery, they were included in the propofol-fentanyl intravenous anaesthe - sia group (PF group). If the patients underwent spinal anaesthesia during surgery, they were included in the spinal anaesthesia group (S group), with 63 cases in each group. According to the operation time, both groups were divided into a short-term group (operation time less than or equal to 30 min) (S1 group and PF1 group) and a long-term group (operation time more than 30 min) (S2 group and PF2 group). The patients fasted for 8 h without any preanaesthetic medication. After arriving in the operating room, all patients were routinely monitored noninvasively for sys - tolic and diastolic blood pressure, electrocardiography, capnography for end-tidal carbon dioxide, pulse oxime - try, and heart rate. After good IV access to the upper limb was secured, Ringer’s lactic acidsolution was used for IV hydration during surgery. In both groups, the intravenous fluids were adjusted for fluid maintenance requirements after a bolus of 6 to 8  ml/kg. For patients in the spinal anaesthesia group, a spinal neuraxial block was performed at the L3-4 interspace with ropivacaine 15.0  mg (mg) by the anaesthesiologist under an aseptic technique. For patients in the propofol-fentanyl intrave - nous anaesthesia group, general anaesthesia was induced with intravenous administration of midazolam 0.04 mg/ kg, fentanyl  2 µg/kg, propofol 2  mg/kg and cisatracu - rium 0.15  mg/kg. After tracheal intubation, controlled mechanical ventilation was adjusted to maintain an end- tidal carbon dioxide concentration of 40 to 45  mmHg. Anaesthesia was maintained with propofol 4 ~ 6  mg/ kg•h and fentanyl 2 ug/kg•h to maintain a BIS value of 40–60 during surgery. All hysteroscopic procedures were performed by an experienced gynaecologic endoscopist with a bipolar resectoscope (Karl Storz SE & Co.KG, Tut- tlingen, Germany). Patients were placed in the lithotomy position during the operation, a 0.9% sodium chloride solution was used as the uterine distention medium, and an automatic surgical irrigator (Tonglu Jingrui Medi - cal Instruments Co., Ltd., Zhejiang, China) was used to Page 3 of 9 Fu et al. BMC Women’s Health (2023) 23:240 control the pressure outflow. The uterine distention fluid was irrigated at a variable flow rate under continuous pressure of 100  mmHg. Hypotension (defined assystolic blood pressure falling more than 20% before anaesthesia or systolic blood pressure values lower than 80  mmHg) was immediately treated with an ephedrine 6  mg intra - venous bolus. Bradycardia (defined as a heart rate < 55 beats/minute) was treated with 0.5  mg of injected atropine. The primary outcome was the amount of uterine dis - tention fluid absorbed in each group during the opera - tion. The amount of uterine fluid absorbed was equal to the amount of fluid irrigated into the uterine cavity minus the amount of fluid that passed through the cer - vix into the container bottle and onto the surgical drapes and the operating room floor. The amount of uterine dis- tention liquid spilled on the floor of the operating room was completely absorbed by the preweighed dry surgical drapes, and then the volume was calculated according to the weight of the liquid absorbed by the surgical drapes and the density of normal saline. The blood pressure (SBP and DBP), heart rate and pulse oxygen saturation of patients in each group were recorded from a Centricity Anaesthesia system and electronic medical records when the patients entered the operation room (T0), 5 min after anaesthesia induc - tion or subarachnoid injection (T1), at the beginning of the operation (T2), during the operation (T3), at the end of the operation (T4), and 3 h after the operation (T5). A total of 2 ml of arterial blood samples were collected at T0, T4 and T5 to measure the arterial blood gas analysis and haematocrit (HCT) of patients. For each patient, age, body weight, ASA physical status, uterine size, operation time, and intraoperative and postoperative complications such as bradycardia, hypotension, nausea and vomiting, and urinary retention were recorded from electronic medical records using a standardized form. Statistical analysis We calculated that a sample size of 28 patients would be needed in each group (type I error of 0.05, power of 0.9) based on a previous study [6] using PASS 15. Considering a 20% dropout rate, a total of 135 patients were necessary. The following formula was used to compute the sample size: Where nij represents the sample size of each group, T represents the number of comparisons between the two groups, and σ 1 and σ 2 represent the standard deviations nij = ( Z1−α/(2T ) + Z1−β )2 × ( σ12 + σ22) δij 2 n = max nij , pairs(i, j) of Group 1 and Group 2, respectively. δ ij represents the value of the difference between any two groups with clin- ical significance. Furthermore, σ was 62 in all groups, μ 1 and μ 2 were 100 in the S1 and S2 groups, and μ 3 and μ 4 were 145 in the PF1 and PF2 groups, respectively. Data were statistically processed using the SPSS 24.0program. The results were expressed as the mean ± standard deviation (SD) unless otherwise indi - cated. One-way analysis of variance (ANOVA) with Bonferroni’s post hoc test was used to compare mean differences between groups for demographic data (age, weight, and uterine size), the amount of normal saline irrigated and absorbed, intraoperative intravenous infu - sion volume and urine volume, and operation time. SBP , DBP , HR, SpO2 and HCT were analysed by repeated measures analysis of variance, and the SNK post hoc test was performed if the comparison between groups was positive.  X2 or Fisher’s exact tests were used to compare differences between groups for ASA physical status clas - sification and the incidence of bradycardia, nausea and vomiting, hypotension, and urinary retention. A P value of < 0.05 was considered statistically significant.

A total of 135 patients who underwent thysteroscopic endometrial resection were enrolled in this study; three patients with hypertension were excluded (one patient in the PF group and two patients in the S group), two patients in the S group had incomplete data collection, and two patients in the PF group cancelled the surgical procedure due to drug allergies. During the operation, two patients underwent changes in the surgical plan because of intraoperative uterine perforation. Finally, the data of 126 patients were included. There were 36 patients in the S group and 33 patients in the PF group with operation times ≤ 30  min, so 36, 27, 33, and 30 patients in the S1, S2, PF1 and PF2 groups, respectively, were analysed (Fig.  1). The demographic data of the patients in all groups were comparable in regard to age, weight, uterine size and ASA physical status classifica - tion, as shown in Table 1 (P > 0.05). The volume of normal saline irrigated and absorbed, intraoperative intrave - nous infusion volume, urine volume, and operation time were significantly increased in the S2 and PF2 groups compared with the S1 and PF1 groups ( p < 0.05). The absorption of normal saline was significantly positively correlated with the operation time ( r = 0.895, P < 0.001) (Table  2). After anaesthesia induction or subarachnoid injection, the SBP and DBP values decreased significantly in all four groups ( P < 0.05). Although oxygen saturation increased significantly from anaesthesia induction to 3 h after the operation in the PF1 and PF2 groups (P < 0.05), it was not clinically significant. The heart rate at T1~3 was Page 4 of 9Fu et al. BMC Women’s Health (2023) 23:240 significantly decreased in the PF1 and PF2 groups com - pared with the S1and S2groups (P 0.05) (Figs.  2, 3, 4 and 5). The haematocrit values decreased significantly at the end of the operation (P < 0.05) and returned to Fig. 1 Study flow diagram Table 1 Demographic data Values are mean ± SD, number of patients. S1: spinal anesthesia with operation time ≤ 30 min; S2: spinal anesthesia with operation time > 30 min; PF1: propofol-fentanyl intravenous anesthesia with operation time ≤ 30 min; PF2: propofol-fentanyl intravenous anesthesia with operation time > 30 min ASA American Society of Anesthesiologists Groups n Age(y) Weight(kg) ASA(I/II) Uterine size(cm) vertical diameter anteroposterior diameter transverse diameter S1 36 37.6 ± 4.3 54.7 ± 3.9 22/14 6.8 ± 0.5 3.7 ± 0.3 4.7 ± 0.4 S2 27 35.8 ± 4.6 56.3 ± 4.2 18/9 6.6 ± 0.3 3.6 ± 0.2 5.0 ± 0.5 PF1 33 36.6 ± 5.2 54.3 ± 4.3 20/13 6.9 ± 0.5 3.8 ± 0.3 4.9 ± 0.4 PF2 30 37.2 ± 4.8 55.1 ± 3.7 19/11 6.8 ± 0.4 3.7 ± 0.3 4.8 ± 0.4 F/x2 values 0.549 0.912 0.875 1.308 1.276 0.779 P values 0.946 0.437 0.831 0.275 0.286 0.508 Page 5 of 9 Fu et al. BMC Women’s Health (2023) 23:240 Table 2 The amount of normal saline irrigated and absorbed, intraoperative intravenous infusion volume, urine volume and operation time Values are mean ± SD. S1: spinal anesthesia with operation time ≤ 30 min; S2: spinal anesthesia with operation time > 30 min; PF1: propofol-fentanyl intravenous anesthesia with operation time ≤ 30 min; PF2: propofol-fentanyl intravenous anesthesia with operation time > 30 min *p < 0.001 vs. S1 group, #p < 0.05 vs. PF1 group Groups n Absorption of normal saline(ml) Irrigation of normal saline (ml) Intravenous infusion(ml) Operation time(min) Urine volume(ml) S1 36 317.8 ± 16.8 4118.6 ± 287.5 428.7 ± 78.3 25.8 ± 1.6 224.8 ± 43.4 S2 27 415.8 ± 14.7*# 6215.8 ± 496.6*# 514.1 ± 66.4*# 53.6 ± 4.4*# 316.5 ± 48.8*# PF1 33 307.2 ± 11.2 4087.2 ± 356.6 436.2 ± 50.0 26.3 ± 2.0 231.4 ± 50..7 PF2 30 421.2 ± 13.7*# 6186.2 ± 467.9*# 523.6 ± 56.8*# 52.5 ± 5.4*# 323.7 ± 57.7*# F values 338.280 171.743 13.177 413.790 24.313 P values 0.000 0.000 0.000 0.000 0.000 Fig. 2 The values of systolic blood pressure in four groups at different time points Fig. 3 The values of diastolic blood pressure in four groups at different time points Page 6 of 9Fu et al. BMC Women’s Health (2023) 23:240 almost baseline levels3 h after the operation in all four groups. There were no differences in the haematocrit values between groups at different time points (P > 0.05) (Table  3). The incidence of postoperative nausea and vomiting was higher in the PF1and PF2groups than in the S1 and S2 groups (P < 0.05). There was no difference in the Fig. 4 The values of heart rate in four groups at different time points Fig. 5 The values of pulse oxygen saturation in four groups at different time points Table 3 The values of hematocrit at different time points Values are mean ± SD. T0: before operation; T4: the end of operation; T5: 3 h after operation. S1: spinal anesthesia with operation time ≤ 30 min; S2: spinal anesthesia with operation time > 30 min; PF1: propofol-fentanyl intravenous anesthesia with operation time ≤ 30 min; PF2: propofol-fentanyl intravenous anesthesia with operation time > 30 min * P < 0.05 vs. T0 Groups n T0 T4 T5 F values P values S1 36 39.6 ± 2.4 35.8 ± 1.9* 38.6 ± 2.3 15.808 0.000 S2 27 38.5. ± 2.3 34.9 ± 2.0* 37.6 ± 2.4 11.541 0.000 PF1 33 39.0 ± 2.6 35.2 ± 1.8* 38.1 ± 2.3 15.624 0.000 PF2 30 38.8 ± 2.8 36.1 ± 2.4* 37.9 ± 2.5 4.626 0.012 F values 0.556 1.174 0.429 - - P values 0.645 0.323 0.733 - - Page 7 of 9 Fu et al. BMC Women’s Health (2023) 23:240 incidence of intraoperative or postoperative bradycardia or hypotension (P > 0.05). There were two patients with postoperative urinary retention in the S1  and S2  groups and none in the PF1 and PF2 groups (Table 4).

In our study, there was no difference in the absorption of uterine distention fluid during hysteroscopic endome - trial resection using normal saline as the uterine disten - tion fluid between patients undergoing spinal anaesthesia and those with intravenous general anaesthesia. With the extension of operation time, the absorption of uterine distention fluid in patients undergoing spinal anaesthesia or intravenous general anaesthesia increased accordingly. The perioperative haemodynamics in patients during spinal anaesthesia and general anaesthesia were stable. The incidence of postoperativenausea and vomiting was higher in patients with intravenous anaesthesia than in those with spinal anaesthesia. Because of its low trauma, short operation time and rapid postoperative recovery, hysteroscopic surgery is widely used in the clinic [7]. Different dilatation media are often selected according to the electrodes used in the operation. Fluid overload caused by the absorption of uterineirrigation fluid is the main source of compli - cations during hysteroscopic procedures [8]. At pre - sent, there are few studies on the absorption of uterine distention fluid during hysteroscopic surgery. A clini - cal studyshowed thatthe amount of glycine absorbed with epidural anaesthesia (648.3 ± 157.1  ml) was sig - nificantly higher than that with intravenous anaesthesia (380.8 ± 158.2  ml) during endometrial resection. This is mainly due to the expansion of peripheral blood vessels during epidural block, which is more likely to promote the absorption of glycine [3]. Bergeron et al. reported that the absorption of glycine under cervical local block com - bined with intravenous sedation in endometrial resection (33 ~ 45 ml) was significantly lower than that under intra- venous anaesthesia (125 ~ 300 ml). The relaxation of arte- riole muscles under general anaesthesia may result in the expansion of systemic arterial blood vessels and acceler - ate the absorption of glycine [9]. Darwish AM et al. found that there was no difference in the absorbed fluid vol - umes of glycine and normal saline during hysteroscopic myomectomy under general anesthesia [10]. It was sug - gested that different anaesthesia had significant effects on the absorption of uterine distention fluid during hyst - eroscopic surgery, while different dilatation media had no effects on the absorption of uterine dilatation fluid. In our study, we found that there was no difference in the effects of spinal anaesthesia and intravenous general anaesthe - sia on the absorption of normal saline as uterine disten - tion fluid in either the short-term group or the long-term group, which was inconsistent with the above research conclusions. The reason for this inconsistency may be that the body’s blood vessels were expanded under spi - nal anaesthesia and general anaesthesia [9], which may have the same effect on the absorption of normal saline during hysteroscopic endometrial resection. In our study, the absorption of normal saline under spinal anaesthesia and intravenous anaesthesia was significantly increased in the long-term group compared with the short-term group. This result indicated that the absorption of dis - tention fluid increasedaccordingly with the extension of operation time [11]. Therefore, the absorption of uterine dilatation fluid should be monitored during long-term hysteroscopic surgery to avoid fluid overload [12]. The clinical study found that the amount of glycine absorbed under spinal anaesthesia combined with oxy - tocin infusion in hysteroscopic surgery was signifi - cantly less than that under intravenous anaesthesia, but the MAP of the two groups was 87.0 ± 10.0  mmHg and 87.8 ± 12.7 mmHg (P > 0.05), indicating that there was no difference in blood pressure between the two groups [6]. In the present study, we also found that there was no dif - ference in SBP or DBP between groups at different times, and the incidence of hypotension and bradycardia was similar among all groups. It was suggested that there was almost no difference in the effect of general anaesthesia and spinal anaesthesia on the blood pressure of patients during hysteroscopic surgery, regardless of the different absorption of glycine or the same absorption of normal saline. The main reason for this result is that the differ - ence in the absorption of glycine between the two groups was only approximately 560 ml in previous studies [13]. Most of the hypotonic glycine solution absorbed into the vascular system was quickly transferred into the tissue and cells in the body, and the amount of glycine left in Table 4 Intraoperative and postoperative bradycardia and hypotension, and postoperative nausea and vomiting and urinary retention Values are number of patients. S1: spinal anesthesia with operation time ≤ 30min; S2: spinal anesthesia with operation time > 30 min; PF1: propofol- fentanyl intravenous anesthesia with operation time ≤ 30min; PF2: propofol- fentanyl intravenous anesthesia with operation time > 30 min Groups n Nausea and vomiting Bradycardia Hypotension Urinary retention S1 36 3 6 4 2 S2 27 3 4 3 2 PF1 33 7 5 5 0 PF2 30 7 6 4 0 X2 values 3.896 0.361 0.333 4.303 P values 0.043 0.948 0.954 0.231 Page 8 of 9Fu et al. BMC Women’s Health (2023) 23:240 the circulatory system was relatively small, which had lit - tle effect on the circulation. In our study, the absorption of normal saline during spinal anaesthesia and intrave - nous anaesthesia was similar, so the effect of the absorp - tion of uterine dilatation fluid on circulation was also the same in both types of anaesthesia. The absorption of uterine dilatation fluid was primarily studied in the present study, while changes in blood pressure were less frequently observed during hysteroscopic surgery. The operation time was within 60 min in our study, and the effects of the absorption of normal saline on blood pres - sure in long-term hysteroscopic surgery under different types of anaesthesia were not clear. A previous study showed that the haematocrit was decreased slightly after hysteroscopic surgery [2]. In this study, the haematocrit of patients after surgery was also slightly lower than that before the operation, but the haematocrit returned to the preoperative level 3  h after the operation. This result indicated that the absorption of uterine dilatation fluid during hysteroscopic surgery had little effect on the haematocrit and that the haematocrit recovered rapidly after surgery. There was no difference in the incidence of postoperative nausea and vomit - ing between the long-term group and short-term group under spinal anaesthesia or intravenous general anaes - thesia. However, the incidence of postoperative nausea and vomiting during spinal anaesthesia was 9.5%, while that during intravenous general anaesthesia was 20.6%, which showed that the time of hysteroscopic surgery had no effect on postoperative nausea and vomiting, while the different types of anaesthesia had a significant effect on postoperative nausea and vomiting [14]. There were several limitations in our study. First, the amount of uterine distention fluid that evaporated dur - ing the operation was not included in this study. Because all of the patients included in the study were in the same operating room with the same temperature and humid - ity, the amount of uterine distention fluid lost during the operation due to evaporation should be consistent for each patient. Second, in our preliminary study, we found that the hysteroscopic surgery time of approximately half of the patients was less than 30  min. Therefore, all patients were divided into a long-term group and a short-term group according to operation times less than or equal to 30 min and more than 30 min in the S group and PF group, respectively. The time of hysteroscopic surgery in this study was within 60  min. The effects of spinal anaesthesia and general anaesthesia on the absorption of uterine distention fluid in long-term hys - teroscopic surgery remain unclear and need to be stud - ied in the future. Third, the absorption of no electrolytic solution in transurethral prostatectomy damaged the cascade of blood coagulation, resulting in the inhibition of coagulation factor activity or the reduction of coagu - lation factor concentration through blood haemodilu - tion. In this study, changes in the coagulation system were not studied, but no patients had coagulation dys - function during or after the operation. The absorption of normal saline under intravenous anaesthesia and spi - nal anaesthesia had no significant effect on coagulation function in patients undergoing hysteroscopic endome - trial resection. Fourth, the administration of oxytocin during hysteroscopic surgery can significantly reduce the absorption of uterine distention fluid [14, 15]. In our study, oxytocin was not administered during hyst - eroscopic endometrial resection. Because of the short operation time and low absorption of uterine distention fluid, the patients in this study did not have correspond - ing complications. Considering that the absorption of uterine dilatation fluid was significantly related to the duration of hysteroscopic surgery, oxytocin should be administered appropriately in clinical practice to reduce the absorption of uterine dilatation fluid and avoid the corresponding complications of fluid overload. In conclusion, there was no difference in the effect of spinal anaesthesia and intravenous general anaes - thesia on the absorption of normal saline during hyst - eroscopic endometrial resection, and the absorption of normal saline increased accordingly with the extension of operation time.

The authors thank the participants for their enthusiastic collaboration, the laboratory physician of the Affiliated Hospital of North Sichuan Medical Col- lege who helped test the haematocrit, and the gynaecological surgeons and nurses who assisted with specimen collection. Authors’ contributions WC.F. and FJ.W. designed and supervised the clinic study, WC.F., X.L. and HC.X. analysed and interpreted the data. X.L. and T.Z. performed clinical data acquisi- tion. HC.X. and T.Z. processed all the samples and detected the hematocrit. WC.F., T.Z. and FJ.W. wrote the manuscript. All authors contributed to discuss the results and to research directions. All authors approved the manuscript. Funding This work was supported by the Sichuan Provincial Health Commission (2017, 17PJ215). Availability of data and materials The datasets used and/or analysed during the current study are available from the corresponding author upon reasonable request. Due to ethical reasons, to protect the integrity of the participants, the study data are not publicly available. Declarations Ethics approval and consent to participate This observational clinical study was approved by the ethics committee of Nan- chong Central Hospital Affiliated to North Sichuan Medical College (IRB2022.002) and registered with the Chinese Clinical Trial Registry (http:// www. chictr. org. cn/; Principal investigator: Wuchang Fu, Date of registration: 09/02/2022, Registration number: ChiCTR2200056605) prior to patient enrolment. All procedures per- formed in this study followed ethical standards of research and the Declaration of Helsinki. Participants received oral and written information about the observa- tional study prior to inclusion and signed informed consent. Page 9 of 9 Fu et al. BMC Women’s Health (2023) 23:240 • fast, convenient online submission • thorough peer review by experienced researchers in your field • rapid publication on acceptance • support for research data, including large and complex data types • gold Open Access which fosters wider collaboration and increased citations maximum visibility for your research: over 100M website views per year • At BMC, research is always in progress. Learn more biomedcentral.com/submissions Ready to submit y our researc hReady to submit y our researc h ? Choose BMC and benefit fr om: ? Choose BMC and benefit fr om: Consent for publication Not applicable. Competing interests The authors declare no competing interests. Author details 1 From the Second Clinical Medical College of North Sichuan Medical College (Nanchong Central Hospital), Nanchong 637000, China. 2 From the Affiliated Hospital, North Sichuan Medical College, Nanchong 637000, China. 3 From North Sichuan Medical College, Nanchong 637000, China. Received: 19 January 2023 Accepted: 30 April 2023

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