Common terms of patient-controlled analgesia

⑴ Load dose: Load dose (LD) refers to the first dose administered at the beginning of PCA. The purpose of the load is to make the patient quickly reach the minimum effective analgesic concentration (MEAC) required for analgesia, so that the patient can quickly eliminate the pain. The load is usually managed by medical personnel. The injection speed of loading dose should be controlled to avoid transient high blood concentration caused by too fast injection speed. LD and LD pumping speed of drugs are determined by their pharmacological characteristics. The calculation formula is as follows: load = minimum effective analgesic concentration × initial distribution volume.

⑵ Single dose: Push injection refers to the additional drug dose when the patient's pain does not disappear or the pain recurs. Its purpose is to maintain a certain blood concentration without excessive sedation. Push injection is the main means for PCA to overcome the individual differences of analgesic drugs. According to the degree of pain and the patient's sedation, adjust the dose by 25-50% each time. Every time the blood concentration is increased, the additional dose is divided by the initial distribution volume of the drug. Pill dosage is one of the important parameters to determine the effect of PCA on pain treatment. If the bolus dose is too large and the blood concentration is too high, the probability of side effects will increase; If the dose is too small, it will increase the frequency of medication and reduce the compliance of patients with PCA.

⑶ Locking time: Locking time (LT) refers to the interval between two single-dose PCA devices. Locking time is one of the security protection methods of PCA. The purpose of locking time is to prevent patients from taking drugs again after the previous single dose failed to take effect, and to prevent drug overdose. The locking time is determined by the drug onset speed and PCA administration route. It reflects the time required for the drug to reach sufficient analgesic concentration at the site of action. For example, the locking time of morphine intravenous analgesia is generally 5- 15 minutes, and the locking time of epidural analgesia is mostly 10-30 minutes.

⑷ Continuous infusion rate: The purpose of continuous infusion rate or background infusion rate is to maintain a relatively stable blood drug concentration and reduce the number of times of instruction medication. The steady-state blood drug concentration during constant-speed infusion is equal to the pumping speed divided by the drug clearance rate. Theoretically, the minimum pumping speed of PCA is equal to the product of CI and MEAC.

5. Maximum dose: The maximum dose is another safety protection device of PCA. There are 1 hour dose limit (1 hour limit) and 4-hour dose limit (4-hour limit). Its purpose is to attract attention and limit the situation of exceeding the average dose. The setting of the maximum dose should vary from person to person. Such as morphine 0.4-5.25mg.h- 1, fentanyl 0.15-0.18mg.h-1.