Correlation Between Pain Threshold and Analgesic Consumption in Transvaginal Oocyte Aspiration Patients

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In vitro fertilization (IVF) is a promising treatment modality that provides infertile couples with the opportunity to conceive, and its success rates have continued to increase with technological advancements. The IVF treatment process consists of four fundamental stages: ovarian stimulation, oocyte retrieval, fertilization, and embryo transfer. Ultrasound-guided transvaginal oocyte aspiration is considered the gold standard for oocyte retrieval.

Pain is commonly experienced during transvaginal oocyte aspiration, necessitating the use of anesthesia. IVF procedures are typically performed in outpatient settings within assisted reproduction centers. The ideal anesthetic technique in IVF should have minimal side effects, ensure a rapid recovery, provide high pregnancy rates, and offer both patient and surgical team comfort and safety. Many anesthetic agents used during IVF have been detected in follicular fluid. These agents may potentially influence fertilization, implantation, and embryo quality, thereby affecting treatment success. However, studies investigating the effects of anesthetics on fertilization and embryo quality have yielded inconsistent and inconclusive results.

A variety of anesthesia techniques can be employed during transvaginal oocyte aspiration, including general anesthesia, regional/local anesthesia, neuraxial anesthesia, patient-controlled analgesia, sedation, acupuncture, or combinations of these modalities.

A study published in 2023 that reviewed literature from 1987 to 2022 reported that conscious sedation was the most frequently preferred anesthetic technique for women undergoing transvaginal oocyte aspiration. This approach was associated with fewer side effects, faster recovery, higher patient and physician satisfaction, and fewer adverse effects on oocyte and embryo quality. High levels of patient satisfaction have been reported with this method.

During oocyte retrieval, patients experience pain due to needle puncture of the vaginal wall and ovaries and due to manipulation of the aspiration needle. Various opinions exist regarding the nature of this pain. In a study by Wicke et al. involving 277 patients, analgesic administration significantly reduced pain severity during the procedure (mean pain score was 1.21 in patients receiving analgesia vs. 9.26 in those who did not). Younger patients and those with a history of dysmenorrhea reported higher pain scores compared to others.

The IVF treatment process is also associated with considerable psychological stress. Most patients undergoing IVF are over the age of 30 and may have chronic medical conditions, experience familial pressure, and be predisposed to depression or psychosis. Hormonal treatments administered during the process can further exacerbate these symptoms. These medical and psychological factors collectively increase patient anxiety. Therefore, anesthesiologists must be capable of managing preoperative anxiety, which can be assessed using validated questionnaires.

With the approval of Erciyes University Faculty of Medicine Clinical Research Ethics Committee (approval number: 2024/275), the study entitled "Correlation between Pain Threshold and Analgesic Consumption during Oocyte Retrieval: An Open-label, Single-arm, Non-randomized Study" will be conducted at Erciyes University Department of Obstetrics and Gynecology. Exclusion criteria include a history of dyspareunia, major medical or psychiatric disorders, and vaginismus.

Before the procedure, patients will be informed by an anesthesiologist about the process, conscious sedation, and the patient-controlled analgesia (PCA) device. The State-Trait Anxiety Inventory (STAI) will be administered to evaluate pre-procedural stress and anxiety levels. Patients will complete the questionnaire either independently or with assistance from the anesthesiologist. Written informed consent will be obtained.

Pain threshold will be measured using a digital algometer routinely used in clinical settings (Commander Echo Algometer, JTECH Medical, Midvale, UT, USA), which allows measurements in kilograms, pounds, or Newtons. The device has been validated in previous studies. The examiner will hold the algometer with the right hand while supporting the device with the left hand. To familiarize patients with the sensation of pressure, an initial application will be performed on a non-test area (thenar region). Patients will be instructed to say "stop" when the pressure sensation turns into pain. Pressure will be applied at a constant rate of 1 kg/s and a 90° angle until the patient gives the stop command. This familiarization will be performed three times per patient. All measurements will be conducted by the same operator, in the same room, at a consistent ambient temperature, using the same equipment. A 1 cm² probe will be used, and measurements will be recorded in kg/cm². Each anatomical region will be measured bilaterally in a fixed order, with three measurements taken at 5-second intervals. The average of the three values will be recorded as the pain threshold for each site. Measurements will be taken from one muscular site (deltoid) and two bony sites (thumb and mid-tibia). For deltoid measurements, the patient will be seated with the arm resting beside the torso and the elbow in extension; measurements will be taken 2 cm distal to the acromion. For thumb measurements, the thumb will rest volar side down on a table, excluding MCP and IP joints, with the wrist in neutral position. For tibia measurements, patients will sit with feet flat and knees flexed to 60°, and pressure will be applied 6 cm distal to the tibial tuberosity. The average of the three values from each site will be calculated, and a global pressure pain threshold will be derived.

In the operating room, routine monitoring will include electrocardiography (ECG), peripheral oxygen saturation (SpO₂), and noninvasive blood pressure. Patients will be placed in the lithotomy position, and oxygen will be delivered via nasal cannula at 2-4 L/min. Demographic data (height, weight, education level), ASA classification, procedure duration, and intraoperative hemodynamic parameters will be recorded. Hemodynamic parameters including systolic, diastolic, and mean arterial pressures (SAP, DAP, MAP), heart rate (HR), and SpO₂ will be recorded at baseline and at 5, 10, 15, and 20 minutes.

Facial Scale (FS) scores ranging from 0 (no pain) to 5 (very severe pain) will be used by the anesthesiologist to assess facial expressions at 5, 10, 15, and 20 minutes. Ramsay Sedation Scale (RSS) scores will be recorded at the same intervals, ranging from 1 (anxious, agitated) to 6 (no response to painful stimuli).

Five minutes prior to the procedure, 1.5 mg IV midazolam (Sedever®) will be administered. Conscious sedation will be provided via PCA, prepared using 150 mg (15 ml) propofol 1% (Propofol-PF®) and 250 µg (5 ml) fentanyl (Fentanyl-PF®), diluted to 20 ml. Each bolus will contain 2 ml (15 mg propofol + 25 µg fentanyl), without a lock-out interval. Patients will be instructed to press the PCA button upon feeling pain, allowing self-titration of anesthesia to avoid excessive anesthetic exposure and potential harm to oocyte quality.

Desaturation is defined as SpO₂ \<92% for more than 10 seconds. Bradycardia is defined as HR \<50 bpm; tachycardia as a >20% increase from baseline. Hypotension and hypertension are defined as MAP values 20% below or above baseline, respectively.

Postoperatively, patients will be monitored in the recovery unit for nausea, vomiting, and respiratory depression. Complications will be recorded. Once discharge criteria are met, both patient and surgeon satisfaction will be assessed. Pregnancy status, total number of follicles, and number of embryos will also be recorded post-procedure