Acute post-operative pain causes not only discomfort for the patient, but delays recovery by increasing the morbidity of the circulatory system, respiratory system, and immune system, so pain control is one of the important objectives in peri-operative patient management. Patient controlled analgesia (PCA) is a piece of equipment for which the patient can personally control the administration of an analgesic. It is generally used in postoperative pain management because it is a method which can heighten patient satisfaction by reducing complications and obtaining the appropriate level of pain relief. Usually, it is designed to administer an analgesic at a steady speed, and the patient can administer additional medication by pressing a button when the pain is severe. Here, to prevent complications from excessive administration of an analgesic, repeated administration is not allowed within a certain time interval. The PCA equipment can be categorized as electronic and physical according to the force which operates the drug injection pump. Electronic equipment uses electrical energy to apply vermicular movement to the fluid tube to administer the analgesic. Physical equipment is disposable equipment designed to fill an elastomer reservoir bag expanding the material, and its elasticity returns to the original length used to administer the analgesic. The physical equipment is easy to carry and movement is comfortable because there is no need for additional electronic equipment or devices. There is also no need for special training to operate the equipment, and the action mechanism is simple so there is less opportunity for malfunction. The disposable physical equipment accounts for approximately 70% of the domestic market share and it is preferred over the electronic equipment. On the other hand, contrary to the electronic equipment, the physical PCA equipment has the disadvantage of not providing information regarding the history of the equipment's use. The early physical PCA equipment was very simple and only had the function of continually administering medication at a set speed. Hence, it was not sufficient to function as 'patient controlled' pain control equipment. Then, the function of an additional administration button was added so that the patient can personally decide whether to administer an additional amount of analgesic. At the same time, the physical PCA equipment has improved to prevent excessive administration by setting a lock-out time as a safety measure. The following development was Accufuser Selectuss®, where a function was added to select the administration speed from three options. In this way, the physical PCA equipment has continued to evolve in the direction of enhancing safety, convenience, and clinical effectiveness. The advantage of pain control using PCA equipment is that the patient can personally control additional the administration of an analgesic by pressing a button. In the case of existing or imported products, it is designed to administer a bolus by pressing the button, and the pressure presses the PVC bag filled with medication under the button to administer the bolus. Compared to the intravenous route, using an epidural as a PCA administration route has superior analgesic effect, so it can reduce the amount of opioid analgesic administered. On the other hand, the disadvantage is that it has to pass through a narrow and long epidural catheter to deliver the medication to the epidural space which has a relatively higher resistance. Woo Young Medical experimented with their own product Accufuser plus® (Woo Young Medical, Korea), and the results showed that the time taken to empty the bolus bag was approximately 40-80 seconds depending on the dosage. The pressure when a person presses the bolus button on the PCA equipment was repeatedly measured to obtain a mean value, and this pressure was constantly maintained by a machine to measure the time taken to empty the bolus bag. Clinically, it is not easy to continually press the button for 40-80 seconds, so it is difficult to exclude the possibility that the bolus was not administered properly. In addition, when excessive pressure is applied, there is the possibility that the bolus bag may burst. The domestically developed products and Accufuser Omnibus® (Woo Young Medical, Korea) was developed for the purpose of supplementing bolus failure which can occur when using epidural PCA. Within the bolus module, a second elastomeric balloon is installed behind the first bolus bag so the patient does not have to press the bolus button for a long time.