Environmental Preparation: A quiet, clean, and well-lit room with a comfortable temperature was maintained. Curtains were drawn to ensure privacy and minimize patient exposure.

Equipment Preparation: Ultrasound machine (model: GE LOGIQ E20; catalog number: Not applicable; manufacturer: GE Healthcare Trading Development (Shanghai) Co., Ltd.; location: Shanghai, China); sterile kit (catalog number: Zhejiang NMPA Approval 20212140086; manufacturer: Zhejiang Kanglidi Medical Supplies Co., Ltd.; location: Hangzhou, Zhejiang, China), which includes fenestrated drapes, gauze, cotton balls, and needle holder (all components are of the same brand and sterilized by ethylene oxide); No. 4 suture thread (catalog number: S4006010; manufacturer: Hangzhou Aipu Medical Devices Co., Ltd.; location: Hangzhou, Zhejiang, China); suture needle (catalog number: Zhejiang NMPA Approval 20192020440; model: sterile SW-4; manufacturer: Ningbo Medical Suture Needle Co., Ltd.; location: Ningbo, Zhejiang Province, China); lidocaine (catalog number: F220924B; manufacturer: Shandong Qidu Pharmaceutical Co., Ltd.; location: Zibo, Shandong Province, China); 5 mL and 2 mL syringes (catalog number: National NMPA Approval 20193141951; manufacturer: Zhejiang Longde Pharmaceutical Co., Ltd.; location: Hangzhou, Zhejiang, China); Arrow central venous catheter (model: CS-24301-E; catalog number: CS-24301-E; lot number: 71F21G0685; manufacturer: Arrow International Inc.; location: Zdar Nad Sazavou, Czech Republic; specific address: Jamska 2359/47, 59101); non-antimicrobial central venous catheter (catalog number: 220315B; manufacturer: Weihai Jierui Medical Products Co., Ltd.; location: Weihai, Shandong, China); drainage bag (catalog number: Zhejiang-Taiwan NMPA Filing 20150014; manufacturer: Zhejiang Lingyang Medical Devices Co., Ltd.; location: Linhai, Zhejiang, China); antiseptic swabs (catalog number: Zhejiang-Hangzhou NMPA Filing 20200056; manufacturer: Hangzhou Hualang Medical Technology Co., Ltd.; location: Hangzhou, Zhejiang, China); sterile gloves (catalog number: Jiangxi NMPA Approval 20192140090; manufacturer: Jiangxi Yunge Rubber & Plastic Co., Ltd.; location: Shangrao, Jiangxi, China); and surgical cap (catalog number: Hubei NMPA Approval 20162142405; manufacturer: Winner Medical (Huanggang) Co., Ltd.; location: Huanggang, Hubei, China).

Assessment and Patient Education: The patient’s general condition was evaluated, with inquiries about symptoms such as dizziness or worsening chest tightness. The skin was inspected at the intended puncture site for any lesions, infections, or other abnormalities. Thorough explanations were provided to the patient and their family regarding the principles, steps, and safety profile of the procedure. Patient concerns were addressed to alleviate fear and anxiety, thereby facilitating patient cooperation and smooth implementation of thoracentesis and drainage.

Patient Positioning: The patient was positioned in a seated posture, facing the back of a chair. Both forearms rested on the back of the chair, with the forehead resting on the arms, maintaining relaxed, spontaneous breathing.

Procedural Cooperation: The physician performed puncture site localization under bedside ultrasound guidance and after selecting the most prominent area of pleural effusion on the affected side as the puncture point, most commonly the 7th–8th intercostal space along the posterior axillary line. The puncture site was precisely located at the superior border of the lower rib within the intercostal space. Prior to the procedure, the puncture area was disinfected in a standardized concentric-circle manner using povidone-iodine, with a disinfection radius of no less than 15 cm. A sterile drape was then applied to establish a surgical field. Local anesthesia was administered with 2% lidocaine. Vertical insertion was performed using a central venous catheter puncture needle, with a distinct sensation of break through indicating entry into the pleural cavity. Upon confirming smooth drainage of pleural fluid, a guidewire was gently advanced through the needle for approximately 20 cm, after which the needle was withdrawn. A central venous catheter was then inserted over the guidewire to a depth of 13–15 cm, and the guidewire removed. The distal end of the catheter was firmly connected to the hub of a 2 mL syringe, which was connected to the drainage bag. After catheter placement, the puncture site was sutured for fixation, followed by coverage with a sterile dressing.

Clinical Monitoring: Throughout the thoracentesis procedure, the patient’s vital signs—including heart rate, blood pressure, respiratory rate, and oxygen saturation—were closely monitored. If any abnormalities such as sudden hypotension or tachypnea occured, the physician immediately ordered suspension of the procedure. If necessary, low-flow continuous oxygen was administered.

Drainage Management: The frequency of pleural fluid drainage was adjusted according to the rate of pleural effusion production and the patient’s clinical symptoms. Prior to each drainage session, information on the patient’s vital signs were obtained, including heart rate, blood pressure, respiratory rate, and oxygen saturation, as well as any changes in symptoms such as chest tightness and dyspnea. Vital signs were closely monitored during drainage. If abnormalities such as hypotension or tachycardia occurred, the procedure was immediately suspended and appropriate interventions implemented. Drainage speed was strictly controlled, and the volume from a single-session, unilateral drainage did not exceed 700 mL. If necessary, drainage was repeated at 2-h intervals, with the total daily unilateral drainage volume not exceeding 1000 mL. This precaution was aimed at preventing sudden drops in intrathoracic pressure, pulmonary vasodilation, increased fluid exudation, and the occurrence of acute pulmonary edema. Continuous daily drainage may be performed until no further effusion is drained while the catheter remains patent [8]. Patient complaints were carefully listened to, and if symptoms such as stabbing chest pain, subclavian discomfort, or poor drainage were reported to the physician, adjustment of catheter depth was considered. In the present cohort, four patients experienced pain beneath the costal margin or in the thoracic cavity during drainage. The Visual Analogue Scale (VAS) score was 3.50 $\pm$ 0.58 (range: 3.00–4.00, 95% CI: 3.00–4.00). Symptoms resolved in three patients after temporarily suspending drainage and clamping the catheter. In the remaining patient, symptoms persisted after clamping, but resolved following the adjustment of catheter depth. One patient developed stabbing thoracic pain during catheter clamping, which was alleviated after a change in body position.

Catheter Maintenance: The catheter was kept tightly connected to the drainage system. When replacing the drainage bag, the stopcock was clamped to prevent air entry that could lead to pneumothorax. After the completion of drainage, a heparin cap was used to seal the catheter and maintain its airtightness. The risk of catheter blockage is elevated due to the high protein content and viscosity of pleural effusion. The patency of the catheter was assessed during each nursing shift, along with observations of drainage fluid color, consistency, and flow rate. If poor drainage was noted, pulse irrigation of the catheter with normal saline was employed. The puncture site was inspected each shift for signs of redness, induration, or exudation, and sterile dressings changed regularly to reduce the risk of infection [9]. The depth of catheter fixation was recorded to prevent displacement or accidental removal.

Prevention of Complications: Following catheterization, patients were guided to perform effective pulmonary expansion breathing—inhale through the nose and exhale through pursed lips—to reduce the risk of atelectasis. Regular monitoring was performed of laboratory parameters and pleural ultrasonography. If clinical symptoms improved and ultrasound findings indicated no significant or only minimal pleural effusion, the catheter was removed promptly to minimize infection risk. Catheter retention in this cohort ranged from 2 to 8 days, with an average duration of 4.2 days.

Patients with severe OHSS complicated by pleural effusion often experience rapid disease progression, accompanied by significant negative emotions such as fear and anxiety. This is particularly evident among those undergoing fresh embryo transfer, who tend to be more concerned about the potential adverse effects of OHSS medications on the fetus [10]. Ten patients in our cohort had undergone embryo transfer. In light of this, a strong nurse–patient relationship must be established to enable psychological support through verbal communication, facial expressions, attitude, and behavior. It is essential to explain in detail the pathogenesis and characteristics of OHSS, provide timely treatment-related information, alleviate the patient’s concerns, and help them build confidence in overcoming the disease. Effective communication with the patient’s family is also crucial to gain their support and cooperation.

Patients with severe OHSS are at increased risk of life-threatening thromboembolic events. Hemoconcentration, reduced plasma volume, and high estrogen levels may contribute to an elevated incidence of thromboembolic disorders. In this case series, all 14 hospitalized patients received heparin for thromboprophylaxis. In addition, patients were instructed to wear compression stockings and perform ankle pump exercises. The patient’s condition was closely monitored, as clinical manifestations of thrombosis may include oliguria, anuria, hematuria and proteinuria, as well as headache, seizures, cyanosis, chest pain, dyspnea, and coma.