Advantages of PCAs
- More individual dosing and titration of pain medications to account for inter-individual and intra-individual variability in the response to opioids;
- Negative feedback control system, an added safety measure to avoid respiratory depression. As patients become too sedated from opioids, they are no longer able to push the button to receive further opioids;
- Higher patient satisfaction with pain control, a major determinant being personal control over the delivery of pain relief;6-8 and
- Greater analgesic efficacy vs. conventional analgesia.
Disadvantages of PCAs
Select patient populations: Not all patients are able to understand and retain the required instructions necessary to safely or effectively use self-administered opioids (e.g., cognitively impaired patients).
Potential for opioid dosing errors: These are related to equipment factors, medical personnel prescribing or programming errors.
Increased cost: PCAs have been shown to be more expensive in comparison with intramuscular (IM) injections, the prior standard of care.9-10
PCA Prescribing
The parameters programmed into the PCA machine include the basal rate, demand (or incremental) dose, lockout interval, nurse-initiated bolus dose, and choice of opioid.
Basal rate: The continuous infusion of opioid set at an hourly rate. Most studies that compare PCA use with and without basal rates (in postoperative patients) do not show improved pain relief or sleep with basal rates.11 Basal rates have been associated with increased risk of sedation and respiratory depression.12
The routine use of basal rates is not recommended initially, unless a patient is opioid-tolerant (i.e., on chronic opioid therapy). For patients on chronic opioids, their 24-hour total opioid requirement is converted by equianalgesic dosing to the basal rate. Steady state is not achieved for eight to 12 hours of continuous infusion; therefore, it is not recommended to change the basal rate more frequently than every eight hours.13
Demand dose: The dose patients provide themselves by pushing the button. Studies on opioid-naïve patients using morphine PCAs have shown that 1 mg IV morphine was the optimal starting dose, based on good pain relief without respiratory depression. Lower doses, such as 0.5 mg IV morphine, are generally used in the elderly as opioid requirements are known to decrease with patient age.14
For patients with a basal rate, the demand dose is often set at 50% to 100% of the basal rate. The demand dose is the parameter that should be titrated up for acute pain control. World Health Organization guidelines recommend increasing the dose by 25% to 50% for mild to moderate pain, and 50% to 100% for moderate to severe pain.15
Lockout interval: Minimal allowable time between demand doses. This time is based on the time to peak effect of IV opioids and can vary from five to 15 minutes. The effects of varying lockout intervals—seven to 11 minutes for morphine and five to eight minutes for fentanyl—had no effect on pain levels or side effects.16 Ten minutes is a standard lockout interval.
Bolus dose: The nurse-initiated dose that may be given initially to achieve pain control and later to counteract incidental pain (e.g., that caused by physical therapy, dressing changes, or radiology tests). A recommended dose is equivalent to the basal rate or twice the demand dose.
Choice of opioid: Morphine is the standard opioid because of its familiarity, cost, and years of study. Although inter-individual variability exists, there are no major differences in side effects among the different opioids. Renal and hepatic insufficiency can increase the effects of opioids. Morphine is especially troublesome in renal failure because it has an active metabolite—morphine-6-glucuronide—that can accumulate and increase the risk of sedation and respiratory depression.