Development and application of patient-controlled analgesia

In 1968, Sechzer first described patient-controlled analgesia (PCA) with intermittent intravenous (IV) doses of opioids delivered “on-demand” by the patient, which gave patients the ability to better control their level of analgesia, balanced against their level of sedation and, therefore, the risks of side effects such as respiratory depression. In current practice, an infusion pump is programmed to provide a preset dose of an analgesic agent when the patient presses a button on a handheld controller; the “lockout” time—the interval before the next dose can be delivered—is also preset. Although IV PCA with opioids is the most widely used modality to treat postoperative pain, cancer-related pain, and pain associated with nonmalignant conditions (e.g., acute nephrolithiasis and pancreatitis), other PCA modes have been developed. These other PCA modes include patient-controlled epidural analgesia and patient-controlled peripheral nerve catheter analgesia. Unlike IV PCA, patient-controlled epidural analgesia is not limited to infusion of opioids and often includes the coadministration of a local anesthetic agent, whereas patient-controlled peripheral nerve catheter analgesia primarily involves delivery of only local anesthetic agents. A complete discussion of the various types of PCA is beyond the scope of this section; therefore this chapter will be limited to IV PCA with opioids.

The main advantage of IV PCA with opioids is that it is “patient-controlled.” Traditional intermittent nurse-administered parenteral analgesia is inherently labor intensive and fraught with problems. Patients receive a “scheduled” or an “as-needed” dose of an analgesic drug, one that is targeted for a broad patient population, with little thought given to the pharmacokinetics and pharmacodynamics of a drug in an individual patient. Doses of analgesic drugs are relatively large, sometimes exceeding the minimal effective dose, to achieve a more sustained effect. The time to redosing is often prolonged, resulting in low serum drug concentrations and the recurrence of pain. The “as-needed” administration of analgesic drugs is an even less favorable regimen because patients often wait until their pain is significant before calling the nursing staff, nurses must be able to respond to the call, the analgesic drug must be obtained from the pharmacy or the medication-dispensing device, and then, after the elapse of some time, patients receive their pain medication. With both regimens, patients can experience “peaks” of supratherapeutic analgesia, which can increase the risk of complications such as respiratory depression, nausea, and emesis, followed by “valleys” of low serum opioid levels, during which patients experience “breakthrough” pain. These subtherapeutic levels, with their associated inadequate analgesia, may limit patients’ progress, as evidenced by inadequate pulmonary hygiene, an unwillingness to get out of bed, and refusal to participate in postoperative rehabilitation. In a study of patients administered opioid analgesic agents intramuscularly every 3 to 4 h, the subsequent serum drug concentration met (or exceeded) the minimal analgesic concentration only 35% of the time (Figure 211-1). The other 65% of the time, the dose was inadequate for the patient to achieve adequate analgesia, which, in turn, was associated with adverse perioperative outcomes and patient dissatisfaction. Because the dose of analgesic agent and lockout interval are better individualized, and because it eliminates a second person as a decision maker (i.e., the nurse), IV PCA maintains more effective serum analgesic drug concentrations, minimizes adverse effects, and improves patient satisfaction. Other reported advantages of IV PCA are listed in Box 211-1.