[Patient-controlled analgesia].
Patient controlled analgesia (PCA) is a drug delivery system aimed to control acute pain using negative feedback technology in a closed loop system in which the patient plays an active role. It overcomes the inadequacies of traditional analgesic protocols due to marked differences in pharmacokinetic and dynamy of analgesis between patients. Moreover, doctors and nurses frequently underprescribe opioids in patients with severe pain for fear of dangerous side-effects. A safe and effective delivery of these drugs on patient demand can be achieved using various delivery systems, modes and dosing parameters. Most devices provide both demand dosing, where a constant predetermined dose is self administered, and constant rate infusion plus demand dosing, where the minimum administration rate is determined by the doctor, but can be supplemented by patient demand. Morphine sulphate remains the drug most commonly used in PCA therapy, but meperidine hydrochloride, alfentanil, nalbuphine and buprenorphine are also sometimes administered. The doctor determines the incremental dose per demand, the lockout interval, and the maximum dose per time unit, possibly also the loading dose and the minimum dose rate when a continuous flow is used. PCA provides improved analgesia, which is immediate and independent of nurse availability. This technique decreases opioid requirements, and the required total amounts are lowered. PCA gives patients both behavioural and decisional control. They can titrate the analgesic dose in such a way as to balance pain relief with the degree of side-effects, the patient is willing to tolerate. Patients often choose less than the available total dose of analgesic. The risks consists in the usual opioid side-effects, mainly respiratory depression. These may be due to mechanical problems, machine failure, or user incidents (misprogramming, or miscalculation of doses). Standards help to ensure consistent care and avoid errors that can occur even with handwritten orders. The principles of demand analgesia are now being investigated using other agents, such as local anaesthetics, and other routes of administration, mainly epidural injection. In most patients, even in children, PCA can replace intramuscular injections, which are the standard route for opioid administration. Today PCA and spinal opioids are the two main methods of analgesia for postoperative pain management.