Opioids
Patient-Controlled Analgesia
12. T.J., a 52-year-old woman, has had posterior spinal fusion with instrumentation because of severe scoliosis that compromised her respiratory function and quality of life. She has just been transferred to the ward from the postanesthetic recovery critical care unit. She is now crying and complaining of severe pain not relieved by intramuscular meperidine 75 mg every 3 hours. T.J. has no known drug allergies. She has a history of taking acetaminophen 500 mg with hydrocodone 7.5 mg two tablets every 3 hours before admission. Why would a patient-controlled analgesia (PCA) device be useful for T.J.?
The current dose of meperidine is high and carries the risk of CNS side effects. PCA is a technique whereby patients self-administer narcotics by using a preprogrammed mechanical infusion device attached to tubing that delivers the drug to the patient through an IV or subcutaneous needle or catheter. Basically, the patient depresses a button to activate the PCA controller to deliver a preset dose of opiate medication. This prevents the need to call a nurse or other caregiver when pain arises and also obviates the problem of drug doses that are not ordered sufficiently frequently. The controller is preprogrammed to establish “lock-out” periods that prevent the pump from delivering a dose if the patient presses the button too often. Safeguards against accidental overdose are instituted by adjusting the concentration of drug in the controller or the duration of the lock-out period. Either of these variables can be adjusted to fit the patient's analgesic needs. Caution must be taken to instruct parents of children or adolescents appropriately on the use of the PCA device, lest they inadvertently administer an excess amount of medication. In general, family members should not act as “surrogates” in helping patients control their pain with a PCA device.
Numerous programmable PCA devices are available, most of which provide intermittent self-boluses of drug, with or without continuous infusion. Some systems use syringe pump technology and others an IV pump system. Compact devices are convenient for ambulatory use. T.J.'s pain can be managed with a PCA device for as long as she is able to comprehend the operation of the device. Most postoperative patients require a basal continuous IV infusion of opioid in addition to intermittent boluses during the first 24-hour period. The need for continuous basal infusion usually diminishes after 24 to 48 hours. PCA is most useful in the first 3 to 5 postoperative days when the patient has the most severe pain. After this initial critical period, the pain can readily be managed with oral analgesic doses. The PCA allows T.J. to have control over her pain. She will determine how often and when the opioid analgesic is delivered, and she can titrate the dose to a level of comfort or side effects that is acceptable to her.
| Table 8-5 Recommended Doses of Opioid Analgesics | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Opioid Selection for Use in PCA
13. What opioid analgesics could be used in T.J.'s PCA device?
Most of the commonly prescribed parenteral opioids can be used in a PCA, but fentanyl, hydromorphone, and morphine are used most frequently. Meperidine is used less frequently because of the problems with the normeperidine metabolite discussed earlier. (See Table 8-5 for dosing guidelines.) Morphine usually is recommended first, followed by hydromorphone, fentanyl, and meperidine. If the patient has a history of morphine intolerance (e.g., itching or nausea), alternative agents, such as hydromorphone, should be initiated. Most of the opioids used for PCA have a broad range of acceptable doses with the exception of meperidine, which has a narrow dosing range because the active normeperidine metabolite can accumulate, even at normal therapeutic doses. Meperidine also has only a 3-hour half-life and perhaps an even shorter duration of action as an analgesic.81 Therefore, meperidine is unsuitable for treatment of acute severe pain when the analgesic requirement is exceedingly high or when patients have impaired renal function. Fentanyl can be a safer alternative to meperidine.
Patient controlled analgesia is used most commonly for administering opioids IV and, on rare occasions, subcutaneously. Subcutaneous opioid administration is limited by the fluid volume needed to deliver the drug. A subcutaneous infusion of 1 mL/hour is universally accepted; however, slightly larger volumes is acceptable in some patients. Highly concentrated morphine solutions (e.g., 60 mg/mL) must be compounded to permit maximal doses for these patients. Alternatively, hydromorphone (Dilaudid HP) at concentrations of 10 mg/mL can be used. When necessary, hydromorphone powder can be purchased and higher concentrations can be prepared (maximal concentration of 40 mg/mL can be achieved), but it is unknown whether concentrations that exceed those of commercial products increase local tissue irritation or other untoward effects.82,83 Because no contraindications exist, T.J. should be started on IV morphine in her PCA pump.
14. What dosing regimen should be recommended for use for T.J.'s PCA pump?
An appropriate order for PCA must include the name of the drug, solution concentration, dose for self-bolus, lock-out period, continuous basal dose, hourly maximal dose limit, and dose and frequency for breakthrough pain. An example of a PCA order for T.J. would include the following:
| Morphine sulfate | 1 mg/mL |
| Self-dose | 1 mg (1 mL) IV |
| Lock-out time | 6 minutes |
| Basal dose | 1 mg/hour (1 mL/hour) IV |
| Dose for breakthrough | 1 mg IV every 20 minutes as needed for pain |
| 1-hour limit total | 12 mg IV |
15. How often should monitoring occur for T.J.'s PCA therapy?
Although T.J. has a history of opiate use, it is imperative that appropriate monitoring tools be in place to assess her response to therapy. Even at therapeutic doses, opiate analgesics can depress respiration, alter heart rate, and lower blood pressure. Therapeutic monitoring should be more frequent within the first 24 hours, when opioid effects are less predictable. Typical assessments include blood pressure, pulse, respiratory rate, oxygen saturation, and visual analog and sedation scale scores. An appropriate monitoring pattern for T.J. may include the following:
| Holding parameters for PCA: |
| Respiratory rate <10 breaths/minute, OR |
| Systolic blood pressure <90 mmHg |
T.J. should be assessed at the initiation of the PCA dose and then at regular intervals (every 30 minutes, twice; every hour, twice; then every 4 hours) unless she becomes unstable or pain increases.
Dose Conversion Between Opioid Analgesics
16. T.J. has requested another analgesic agent because of excessive sedation. She currently needs 10 mg of morphine per hour from her PCA. How should T.J. be converted to another PCA opioid analgesic?
The IV equivalent of morphine 10 mg/hour is approximately equal to hydromorphone 2 mg/hour, meperidine 100 mg/hour, or fentanyl 100 mcg/hour (Table 8-3). Meperidine is not a viable alternative for T.J. because the equivalent meperidine dose of 100 mg/hour exceeds the maximal recommended dose of 60 mg/hour. The remaining options are either hydromorphone or fentanyl PCA. Examples of options for PCA orders include either of the following:
| Fentanyl | 10 mcg/mL |
| Self-dose | 10 mcg (1 mL) IV |
| Lock-out dose | 6 minutes |
| Basal dose | 10 mcg/hour (1 mL/hour) IV |
| Breakthrough pain | 10 mcg intravenously every 20 minutes as needed for pain |
| 1-hour limit total | 120 mcg IV |
| Hold parameters for PCA: Respiratory rate <10 breaths/minute or, systolic blood pressure <90 mmHg | |
| OR | |
| Hydromorphone | 0.2 mg/mL |
| Self-dose | 0.2 mg (1 mL) IV |
| Lock-out dose | 6 minute |
| Basal dose | 0.2 mg/hour (1 mL/hour) IV |
| Breakthrough pain | 0.2 mg IV every 20 minutes as needed for pain |
| 1-hour limit total | 2.4 mg IV |
| Hold parameters for PCA: Respiratory rate <10 breaths/minute or systolic blood pressure <90 mmHg | |
As always, T.J. should be re-evaluated in 2 hours after changing the PCA, and doses should be adjusted at that time.
Conversion From PCA to Oral Opioids
17. Forty-eight hours later, T.J.'s requirement for hydromorphone has decreased significantly. Her requirement has averaged 0.5 mg hydromorphone/hour in the last 12 hours. How should T.J. be converted to oral opioid analgesics?
Patient controlled analgesia is rarely used beyond 72 hours postoperatively,84 and continuous basal infusions frequently are discontinued after the first 24 hours. Transition to oral opioid analgesics from PCA should occur as soon as the patient is able to tolerate oral intake of solids. Oral opioid analgesia usually is given every 3 to 4 hours for convenience, as well as allowing time for drug absorption. Conversion to oral from parenteral opioids is best achieved based on the total opioid requirement during the previous 24-hour period. For T.J., the total 24-hour IV hydromorphone (0.5 mg/hour) required was 12 mg, which is roughly equivalent to IV morphine 60 mg, methadone 18 mg, or levorphanol 12 mg. Alternatively, the 24-hour oral equivalent doses are as follows: morphine 180 mg, methadone 18 mg, levorphanol 24 mg, or hydromorphone 48 mg. Levorphanol, with its long duration of action and a lower incidence of GI side effects, would be a good oral agent to use for T.J. The levorphanol dose for T.J. would be 4 mg every 4 hours. A period of 4 to 6 hours of PCA overlapping dosing of oral opioids is recommended to allow equilibration of the oral medicines, but the PCA's continuous basal infusion should be stopped as soon as the oral dose is given.
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