2.1 General information

This study was approved by the Ethics Committee of Wenzhou Medical University (clinical trial number: ChiCTR2000036066; Registry URL: YJLCYJ-2020-051). This manuscript adheres to the applicable Equator guidelines. A total of 58 women ASA ⅠandⅡ aged 18 to 60 years old, 3-7 days following the last day of menstruation and were subjected to diagnostic hysteroscopy or treatment. Patients were divided into two groups: patients with dysmenorrhea (Group A) and patients without dysmenorrhea (Group B). Informed consent was obtained from all study subjects and the Institutional Review Board approval was obtained for data collection. In this study, diagnostic hysteroscopy was used to investigate abnormal uterine bleeding, endometrial thickening, infertility, fibroids, polyps, recurring miscarriage and uterine malformation. Women with a history of previous diagnostic hysteroscopy procedures were excluded from the study. Patients with an ongoing pregnancy, cervical carcinoma, pelvic inflammatory disease, excessive uterine bleeding and the need for performing an endometrial biopsy during the procedure were excluded from the study.

2.2 Anesthesia process

All patients were monitored using electrocardiography (ECG), noninvasive blood pressure cuff (NBP) and peripheral arterial blood oxygen saturation (SpO2). A non-rebreather oxygen mask was utilized. After obtaining baseline measurements, 7.5 $\mu$g of sufentanil was administered by intravenous injection followed by a propofol infusion using a target-controlled infusion pump (Master TCI, Fresenius Vial SA, Berzins, France). The target effect-site concentration was initially set at 2 $\mu$g/mL. Degrees of sedation were evaluated by using a bispectral index monitor (BIS XP, A-2000, Aspect Medical Systems, Newton, MA). The target concentration of propofol was increased by 0.5 $\mu$g/mL if the BIS went above 80 and decreased by 0.5 $\mu$g/mL when the BIS decreased below 60 to maintain a BIS of 60 to 80. Concurrently remifentanil was administered as a continuous infusion at 0.05 $\mu$g/kg per minute. The infusion rate was increased if signs of insufficient analgesia (facial grimace, movement, a sudden increase in heart rate [HR] or BP, complaint of discomfort or pain) were present or decreased with signs of excessive analgesia (respiratory depression, hypotension, or bradycardia) (Fig. 1).

Fig. 1.Study flow diagram.

Adverse hemodynamic events were present when the systolic BP (SBP) was higher than 150 mmHg (hypertension), less than 90 mmHg (hypotension), HR greater than 110 bpm (tachycardia), HR less than 45 bpm (bradycardia); respiratory depression with a SpO2 of 90% or lower for more than 30 seconds or a respiratory rate (RR) less than 8 breaths/min for more than one minute. These adverse events were treated by titration of the propofol and opioid infusion and if necessary ephedrine, atropine, or assisted ventilation with jaw thrust.

2.3 Curative effect observation and recovery

After all the hysteroscopic procedures were completed, the anesthesiologist calculated the total dose of propofol and remifentanil utilized. When patients were transferred to post-anesthesia care unit (PACU), a PACU nurse evaluated the patient by using a modified Aldrete scoring system. The criterion used for patient discharge was the achievement of a modified Aldrete score of 9.

2.4 Numerical rating scale

Fifteen minutes after the procedure, a PACU nurse, who was unaware of the amount of opioid given to each patient, assisted patients to evaluate their pain level by using a numerical rating scale (VAS: 0 = none, 10 = most severe, 1-3 mild pain, 4-6 moderate pain, 7-10 severe pain) [12].

2.5 Statistical analysis

Continuous values were expressed by mean $\pm$ SD and compared using Student’s t-test. Categorical values were described by count and proportions and compared by the $\chi$2 test. All calculations were carried out with SPSS with the statistical significance level at 0.05. Multivariate logistic was utilized used to evaluate the relationship between dysmenorrhea and the incidence of pain.

3.1 Characteristic between patients with or without dysmenorrhea

As shown in Table 1, there was no statistical significance in age, weight, height, length of the procedure and the total amount of propofol and remifentanil given. The operating methods used in the two groups were not statistically significant, P = 0.75 (Table 2).

3.2 Incidence of pain after operation between patients with or without dysmenorrhea

The incidence of pain after the procedure in patients with dysmenorrhea was higher than that of patients without dysmenorrhea (77.8% vs. 45.2%, P = 0.011) (Table 3). A comparison of pain severity in two groups was significant (P = 0.038) (Table 4). Multiple logistic regression analysis revealed that dysmenorrhea was an independent predictor of pain in patients with diagnostic hysteroscopy after adjusting for age, BMI, length of operation and doses of propofol and sufentanil (OR: 3.28, 95% CI = 1.14-9.42, P = 0.027).