by Michael Wong
Patient-controlled analgesia (PCA) allows patients to “control” the amount of pain medication they receive. Although there are many benefits to the use of PCA, I discussed with Dr. Jason McKeown (Associate Professor, Medical Director – Inpatient Pain Service, University of Alabama School of Medicine), who is a member of the Anesthesia History Association and was the recipient of the Bullough Prize at the International Symposium on the History of Anesthesia in Cambridge, UK, in 2005, about the history of PCA and role of technology in ensuring patient safety when using PCA.
Who first thought of PCA?
Dr. Philip H. Sechzer is considered one of the pioneers of PCA. Because of the chief conclusions of his 1970 paper, “Studies in Pain With Analgesic-Demand System”—improved analgesia and patient satisfaction with lower total opioid dose—PCA has become the gold standard in postoperative pain treatment.
Why is PCA more effective than IM injections?
To understand why PCA is generally more effective than IM (Intramuscular) injection, one must first understand the term “minimum effective analgesic concentration” (MEAC), which is the smallest concentration of analgesia, when given by constant infusion, at which pain is relieved. Patients receiving IM or IV bolus injections of opioids may experience more fluctuations in their pain because of “overshoots” in optimal plasma concentration leading to oversedation, sleep and possibly respiratory depression. During these “overshoot” episodes the patient may sleep until opioid concentration finally drops below MEAC; the awake patient then experiences severe pain again. The best-managed PCA allows the patient to self-titrate to achieve a plasma opioid level above MEAC but below the level at which oversedation and side effects occur. The graph below “compares analgesia achieved with two different analgesic regimens: intermittent bolus administration (nurse administered analgesia) or frequent small doses (patient-controlled analgesia, PCA). The shaded area represents the target analgesic concentration. With intermittent bolus administration, there are frequent periods with concentrations more than and less than the target range. In contrast, PCA results in the opioid concentration being in the target range for a large percentage of the time.”
Nurse administered “rescue” boluses are occasionally needed to re-establish the target range after periods of sleep, but patients generally are more satisfied with the enhanced quality of analgesia and the autonomy afforded by PCA.
Is PCA safer?
PCA has become part of accepted medical practice and is generally considered more effective and safer than conventional IM injections of opioids. The most catastrophic events of overdose related to PCA systems have been linked to misprogramming or mechanical problems. While PCA may be the safest mode of opioid delivery it is true that regardless of the route of administration, respiratory depression may still occur.
To help prevent such incidents from happening, it should be remembered that some of the most significant strides in medicine and surgery are directly attributable to anesthesiology’s advances in patient monitoring. The charting of patient vital signs at the bedside began with William Halsted in the 19th century. Harvey Cushing is credited with introducing the written anesthetic record in the early 20th century.
The end of the 20th century brought electronic monitoring like pulse oximetry which tells us the amount oxygen in a patient’s blood and capnography which measures in real-time the adequacy of ventilation.
Electronic monitoring has dramatically improved patient safety. I believe the 21st century will see the adoption of these modes of electronic monitoring at the bedside along with PCA techniques to provide the safest means of pain treatment possible. To have these tools and not use them would ignore anesthesiologists’ historic dedication to patient safety.