The prospective, randomized controlled trial was performed at University Hospital Ostrava. All eligible participants were adult patients of both genders aged 18 years or older, and scheduled for elective orthopaedic surgery (THR). The enrolled patients underwent per-protocol randomization into one of two groups (PCEA or non-PCEA group) using the envelopes method. Randomization was performed immediately after ICU admission by an independent physician, who was not involved in the data collection or management of the study subjects. Following randomization, patients were admitted to the ICU. Data for the analyses were collected for 24 hours after THR. The baseline demographic and preoperative characteristics (age, gender, weight, body mass index, and American Society of Anesthesiologists \[ASA\] physical status) were obtained at the time of admission. The degree of motor block was assessed using the modified Bromage Score. The level of sedation due to the residual effect of anaesthetics at the time of admission was assessed using a sedation score. The Visual Analogue Scale (VAS) values were determined at hourly intervals and 30 minutes after administration of analgesics to determine the effect of the analgesic dose. The other parameters evaluated at hourly intervals were: a) the presence of hypotension defined as a decrease in systolic blood pressure below 90 mmHg or a greater than 30% decrease from the baseline value; b) bradypnea measured on a numeric scale; c) bradycardia defined as heart rate ≤ 50/min and tachycardia defined as heart rate ≥ 120/min; d) the presence of postoperative nausea and vomiting (PONV); and e) skin itching. At the time of discharge from the ICU, the total consumption of analgesics was recorded, and patients' satisfaction was evaluated using the Likert scale. All patients were perioperatively treated by the protocol for administration of anesthesia and analgesia: The patients were administered 7.5 mg of midazolam orally one hour before surgery. Patients weighing more than 70 kg received 2 mg of bisulepin. Prior to surgery, a subarachnoid blockade was established with 2-4 ml of levobupivacaine 0.5% at the L2-L3 spinal interspace. Subsequently, a catheter for postoperative analgesia was inserted into the epidural space. If the subarachnoid blockade was insufficient for surgery, epidural levobupivacaine 0.5 % was administered to a maximum dose of 10 ml, after which the patient underwent general anesthesia and was excluded from the study. During surgery, patients were sedated with a target-controlled infusion of propofol (dose of 1-2 mg/kg body weight per hour) so that they were asleep but aroused when spoken to. After surgery, patients received a mixture of levobupivacaine 0.1% and sufentanil 1 µg/ml. Postoperatively, patients were moved to the ICU. Immediately after ICU admission, continuous monitoring of vital functions and pain was initiated. When the pain intensity exceeded ≥ 4 points, analgesic therapy was initiated by the administration of a mixture containing levobupivacaine 0.1% and sufentanil 1 μg/ml. The PCEA group was initially given a bolus of 10 ml of the mixture, and then a basal infusion at the rate of 3 ml/h. The bolus was set on 4 ml, a lockout interval of 20 minutes, and a maximum dose of 40 ml/4 h according to the literature recommendation. The non-PCEA group was initially administered 5 ml of the analgesic mixture followed by a basal infusion at 5 ml/h. If pain developed, a bolus of 8 ml of the mixture was administered according to the physician's prescription. If analgesia was insufficient after 1 hour of maximal dosing in both groups, the patient was given adjunctive analgesic therapy including one or a combination of the following drugs: i.v. paracetamol, i.v. metamizole, or i.v. tramadol. Patients requiring systemic adjunctive medication were excluded from the final analysis.