Chapter 17: Patient-Controlled Analgesia

INTRODUCTION

Patient-controlled analgesia (PCA) was first introduced into clinical practice in the early 1980s as an alternative way to administer analgesic medications. The basic principle behind PCA is that the patient can self-administer small doses of the drug (usually an opioid) at relatively frequent intervals to provide optimal pain relief.¹ These small doses are typically delivered intravenously or into the spinal canal by some type of machine (i.e., pump) that is controlled by the patient. Patient-controlled analgesia has several advantages over more traditional dosing regimens. In particular, PCA systems allow the patient to better match his or her need for analgesic medication to the dose to treat a specific amount of pain at any given point in time—that is, as pain fluctuates, the patient can self-administer more or less drug to provide the appropriate level of anesthesia. PCA therefore provides equivalent or increased analgesic effects with better patient satisfaction compared to conventional analgesia.^2,3 This has generated increased use of PCA in a variety of clinical situations. For instance, PCA systems are used to help manage acute pain following surgery, and they are used to treat pain in patients with cancer and other conditions associated with chronic pain.^4,5

Because PCA is used extensively to treat acute and chronic pain, rehabilitation specialists should be aware of some of the fundamental principles governing it. This chapter begins by discussing the basic concepts and strategies of PCA, followed by some of its practical aspects, including the types of analgesics used, the types of machines used to administer the drugs, and the possible routes of drug administration. More recently, many prescribers are moving away from PCA due to the risk of infection, potentially longer length of stay, and adverse effects of opioids. Instead, “multimodal” pain control has been used, which utilizing multiple drug classes to control pain. Although the use of PCA may be rarer, it is still a procedure used in the clinical setting.

PHARMACOKINETIC BASIS FOR PCA

To provide optimal management of pain, analgesic drugs should be delivered into the bloodstream or other target tissues (epidural space, within joints, etc.) in a predictable and fairly constant manner. The goal is to maintain drug levels within a fairly well-defined therapeutic window.⁵ Such a therapeutic window for systemic (IV) dosages is represented schematically by the shaded area in Figure 17-1. If drug levels are below this window, the analgesic is below the minimum analgesic concentration, and the patient is in pain. Drug levels above the window may produce adequate analgesia but may also produce side effects such as sedation. The traditional method of administering analgesics is to give relatively large doses with relatively large time intervals between each dosage. For instance, opioid analgesics are sometimes injected intramuscularly every 3 to 4 hours to manage severe pain, thus creating large fluctuations in the amount of drug present in the body. The dark ...