In PCS, patients are clearly instructed preoperatively on the proper use of the infusion device as well as the purpose of sedation. Sedation is carried out via an infusion pump with a reservoir, which is connected to a handheld button that only the patient can control. When the button is pressed, the pump delivers a bolus of a predetermined dosage of medication. A lockout period, or a time interval in which another dose cannot be administered, may or may not be programmed. When present, it appears to offer a safety mechanism by preventing excessive drug administration and subsequent oversedation and loss of consciousness.7 The patients are instructed to press the button until they reach the desired level of sedation to allow them to be able to tolerate the procedure. In this way, the patients themselves can control and determine the end point of sedation.
In a prospective, randomized, controlled study, Mazanikov et al compared PCS using propofol and remifentanil with anesthesiologist-controlled patient sedation using propofol for ERCP procedures.9 Between the 2 groups, patient and endoscopist satisfaction were comparable. However, the study found markedly less propofol consumption and faster recovery in the PCS group. Similar results were obtained in a study conducted by Girdler et al on dental patients, with the PCS group requiring a lighter level of sedation compared to a clinician-controlled group.10 This suggests that anesthesiologist-controlled sedation may result in unnecessary deep sedation while PCS is well-accepted because patients appreciate the ability to maintain control of their sedation.
Due to the short duration of action of sedative agents, particularly propofol, a potential drawback of self-administration in bolus increments is the volatility of plasma concentrations and subsequent varying levels of sedation. Target-controlled infusion (TCI) overcomes this problem of varying blood concentrations. This method of administration utilizes a computer-controlled infusion system that can calculate and maintain target blood concentrations of propofol with great accuracy. TCI uses a pharmacokinetic model to predict the initial bolus dose and infusion rates necessary to achieve and maintain a given target concentration, avoiding peaks and troughs in plasma concentration. The target concentration can then be adjusted accordingly by the patient to achieve the optimal level of sedation.
In a study by Irwin et al, the benefits of TCI were used in combination with patient-controlled feedback11 in a technique referred to as patient-maintained sedation (PMS). Based on each patient’s age and weight, a TCI system calculated the dose necessary to achieve and maintain a selected target concentration of propofol. In this case, an initial target concentration of 1 mcg/mL was chosen. The patient also had control of a handset that when pressed, increased the target concentration by 0.2 mcg/mL increments with a lockout interval of 2 minutes. When no demand boluses were required for several minutes, the system gradually decreased until a baseline target concentration of 0.2 mcg/mL was reached. Although there was wide variability amongst individuals in total consumption of propofol, optimal sedation was found to be achieved at median target concentrations of 0.8 to 0.9 mcg/mL. Following cessation of the infusion at the end of the procedure, recovery was rapid and no delays were reported in meeting discharge criteria from the recovery room. Patients expressed overall satisfaction with the technique and reported interest in using the technique again in the future.
Rodrigo et al performed a randomized study comparing outcomes between PCS and PMS using a TCI of propofol.12 The study found no significant differences in depth of sedation, operating conditions and patient satisfaction. However, a majority of patients preferred PMS likely because it produces more stable blood concentrations and possibly less oversedation. The main disadvantage of PMS is relatively slower onset in achieving adequate sedation. The time required for adequate sedation was 8.6 minutes in the PMS group, compared to 5.7 minutes in the PCS group.