Safe use of a continuous infusion with IV PCA

PAIN CARE

Safe Use of a Continuous Infusion With IV PCA Chris Pasero, MS, RN, FAAN Margo McCaffery, MS, RN, FAAN PATIENT-CONTROLLED ANALGESIA (PCA) is an interactive method of pain management that permits patients to manage their pain by self-administering doses of analgesics, usually opioids.1 PCA can be administered by almost any route of administration, including oral, epidural, and the most common in the hospital, intravenous (IV). IV PCA is appropriate for the treatment of moderate to severe postoperative pain in patients who are able to understand the relationships between pain, pressing a button to receive pain medication, and pain relief. The patient must also be able to operate the pump used to administer PCA.1 Basic IV PCA prescriptions include the amount of opioid the patient receives each time the PCA button is pressed (PCA bolus dose), the frequency with which the patient may self-administer a dose (delay or lockout interval), and the total amount the patient may receive in one or more hours (hour limit). Occasionally, a continuous background infusion (also called basal rate) is prescribed. The purpose of a continuous infusion of opioid is to help maintain a stable analgesic level.2 It has the advantage of letting patients sleep without frequent interruptions Chris Pasero, MS, RN, FAAN, is a pain management educator and consultant in El Dorado Hills, CA; Margo McCaffery MS, RN, FAAN, is a consultant in the nursing care of patients with pain in Los Angeles, CA. Address correspondence to Chris Pasero, MS, RN, FAAN, 1252 Clearview Dr, El Dorado Hills, CA 95762; e-mail address: [email protected]. © 2004 by American Society of PeriAnesthesia Nurses. 1089-9472/04/1901-0008$30.00/0 doi:10.1016/j.jopan.2003.11.006 42

by pain.1 If a continuous infusion is not added, patients often wake up in pain and must selfadminister enough PCA doses to achieve pain relief again. Continuous infusions are recommended and commonplace for opioid-tolerant patients with pain. In these patients, the continuous infusion makes up the majority of the opioid dose when IV PCA is used.1 However, the American Pain Society states that continuous opioid infusions may be of limited usefulness in the treatment of acute pain and recommends extreme caution when adding them to IV PCA in opioid naı¨ve patients.2 PCA bolus dose, delay, and hour limit are often described as the safety features that help prevent overdosing during therapy.1 The primary safeguard of PCA therapy is that the patient must be awake to self-administer PCA doses. Patients who are excessively sedated are likely to drop the PCA button, thereby preventing delivery of more opioid and further sedation, which can lead to clinically significant respiratory depression. Herein lies the controversy of adding a continuous background infusion to IV PCA therapy in opioid-naı¨ve patients outside of the ICU. The patient has no control over the delivery of a continuous infusion; thus, the built-in safeguard of the PCA pump is gone. This article reviews the research on the use of continuous infusions with PCA in opioid-naı¨ve patients and suggests tips for ensuring safety in providing this therapy. Journal of PeriAnesthesia Nursing, Vol 19, No 1 (February), 2004: pp 42-45

SAFE USE OF A CONTINUOUS INFUSION WITH IV PCA

Research on Continuous Infusion With PCA Parker et al3 performed one of the first studies evaluating the use of continuous infusion plus PCA. Patients (N ⫽ 230 females) were randomly assigned to one of four morphine groups: 1) PCA bolus doses of 2 mg every 10 minutes on demand with no continuous infusion (control group); 2) PCA bolus doses of 2 mg every 10 minutes on demand with 0.5 mg/hour continuous infusion; 3) PCA bolus doses of 1 mg every 10 minutes on demand with 1 mg/hour continuous infusion; or 4) PCA bolus doses of 1 mg every 10 minutes with 2 mg/hour continuous infusion. Thirty-one of the 230 patients who began the study were unable to complete it because of opioid-induced adverse effects such as nausea, sedation, and respiratory depression. These were comprised of 2 from each of the first three groups and 25 from the group receiving the highest infusion rate (2 mg/hour). However, the majority (84%) of the 199 patients who did complete this study were able to achieve adequate analgesia without experiencing major adverse effects or requiring a change in the PCA prescription. The presence of a continuous infusion did not change the number of demands for PCA doses or decrease pain ratings. Sedation scores were described as similar among the groups despite the fact that 12 patients in the group receiving the highest infusion rate reported excessive sedation and showed signs of oxygen desaturation. Perhaps the most important findings in this study were the percentages of patients in the various groups who required a change in PCA therapy or discontinuation of therapy entirely because of adverse effects.3 The lowest was 10% of those in the group receiving 0.5 mg/ hour infusion followed by 11% of those with no infusion, 14% of those with 1 mg/hour infusion, and 66% of those receiving 2 mg/hour. In addition, continuous infusions had to be added to 5% of the patients in the group without infusions. During the first 2 days of the study, the 0to 100-mm visual analogue pain ratings were

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lowest (30-40 mm) in the group receiving 0.5 mg/hour continuous infusion. These findings suggest that infusion rates greater than 1 mg/ hour are not well tolerated and may be unsafe, and no infusion may result in inadequate pain relief; however, a low infusion rate (0.5 mg/ hour) is safe and may improve pain relief. A small study evaluated the addition of continuous infusion to IV PCA morphine in 34 patients undergoing hip replacement.4 The average patient age was 65 years old. Patients were randomized to receive 1 mg PCA bolus doses every 6 minutes on demand without a continuous infusion or with a 0.5 to 1 mg/hour continuous infusion. There were no significant differences in morphine consumption, sedation scores, and loss of sleep secondary to pain between the groups. Although there were no significant differences in pain intensity, a trend was noted toward lower pain intensity on movement at 28 hours in the patients receiving continuous infusion. Therapy was discontinued due to nausea in three patients receiving PCA only and four patients receiving PCA plus infusion; a total of eight patients (44%) in the infusion group required discontinuation of continuous infusion or PCA therapy entirely due to adverse effects. There were no incidences of clinically significant respiratory depression. Another small study (n ⫽ 35) demonstrated similar findings in patients undergoing elective open-heart surgery.5 There were no differences in pain intensity scores or adverse effects between patients who received morphine by PCA only and those who received it by PCA plus continuous infusion. Although the addition of a continuous infusion appeared to be safe, the authors could find no benefit to this approach. Research performed in the early 1990s demonstrated positive effects from the addition of a continuous infusion to IV PCA. One study evaluated IV PCA meperidine in 171 women postcesarean section.6 Patients received either 5 or 10 mg PCA doses on demand every 10 minutes

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without continuous infusion or with a continuous infusion of 10, 20, or 30 mg/hour. The groups receiving continuous infusion reported more immediate and sustained relief with no serious adverse effects, although four patients (10%) in the group receiving the highest infusion rate (30 mg/hour) were observed to have “slurred speech,” which resolved after the meperidine was discontinued. All patients were able to ambulate and care for their babies without difficulty. Researchers in one institution observed that patients who received PCA without a continuous infusion experienced fragmented sleep patterns due to the short duration of small doses of analgesics they self-administered.7 This prompted their study comparing IV PCA morphine with and without continuous infusion in 30 patients undergoing abdominal surgery. PCA was initiated immediately after surgery in all patients; and the continuous infusions of 1 mg/hour were begun on the first postoperative day. There were no statistically significant differences in pain and sedation scores between the two groups, despite the fact that the patients receiving continuous infusion consumed significantly more total morphine. The mean sedation level in both groups was 1 (mild) on a scale of 0 (none) to 4 (severe). There were no incidences of clinically significant respiratory depression or need for antiemetics. The authors concluded that although pain relief was not improved, PCA with continuous infusion is safe and may benefit patients with higher opioid requirements.

Clinical Implications PCA starting prescriptions are always just estimates of what patients will require to control their pain. It is crucial that patients be evaluated regularly and their PCA dose titrated when necessary to maintain adequate analgesia along with tolerable and manageable adverse effects.1 The need for changes in the PCA prescription is signaled by pain ratings above the identified comfort-function goal (often indicating a need

PASERO AND MCCAFFERY

for an increase in dose) or by unmanageable and intolerable adverse effects (perhaps indicating a need to decrease the dose).8 Patients reporting inadequate pain relief with the use of PCA require prompt evaluation and may benefit from the addition of a continuous infusion. Although the studies yield conflicting results and despite the American Pain Society warning, clinical experience indicates that the addition of a continuous infusion to IV PCA for opioid-naı¨ve patients can be done safely and produce excellent results. A cautious approach and one that is supported by research is to begin PCA without a continuous infusion, and then add one later if the patient has difficulty maintaining satisfactory pain control, especially after sleep. Beginning PCA therapy without a continuous infusion may be particularly appropriate in the elderly. In a review of more than 6,000 patients aged 65 and older who had received IV PCA, PCA bolus doses greater than 1 mg/dose and intra-abdominal surgery were cited as risk factors for hypoxemia and respiratory depression during IV PCA therapy.9 However, the decision to add a continuous infusion to IV PCA for any opioid-naı¨ve patient, including children and the elderly, should be based on patient response, rather than a preconceived notion that they cannot tolerate continuous infusions.1 Starting with low initial continuous infusions is another safeguard. Continuous infusions are calculated from the parenteral dosage information found in equianalgesic dose charts (see www3.us.elsevierhealth.com/PAIN to download an equianalgesic chart). The starting continuous infusion for opioid naı¨ve patients should not exceed one half of the projected hourly requirement.1 According to the equianalgesic chart, 10 mg of morphine is required to relieve moderate to severe pain over a 3- to 4-hour period. The approximate hourly requirement is determined by dividing 10 mg by 4 hours, which is 2.5 mg/hour. One half of this is 1.25 mg. Therefore, the starting prescription for a continuous infusion in an opioid-naı¨ve patient

SAFE USE OF A CONTINUOUS INFUSION WITH IV PCA

should not exceed 1.25 mg/hour of morphine or its equivalent.1 A conservative starting continuous infusion and one that has been shown to be safe in opioid naı¨ve patients is 0.5 mg/ hour of morphine.3,7 Another safeguard would be to prescribe starting PCA bolus doses of 1 mg or less per dose.9 Perhaps the most important factor in using continuous infusions with IV PCA for opioid-naı¨ve patients is ensuring that nurses closely monitor sedation and respiratory status (every 1-2 hours for the first 24 hours of therapy) and decrease the opioid dose if increased sedation is detected.1,10 If this level of monitoring is not possible, the use of continuous opioid infusions in opioid-naı¨ve patients is discouraged. Table 1 provides an example of a simple sedation scale that can be used to assess opioid-induced sedation and prevent respiratory depression. It includes actions required at each level of sedation. Finally, each day after the day of surgery as the patient recovers and experiences less pain, the opioid dose should be decreased, beginning with a 25% to 50% reduction in the continuous infusion.1

Conclusion There is controversy over the use of a continuous infusion with IV PCA. The American Pain Society cautions against using continuous infusions in opioid-naı¨ve patients. However, research and clinical practice demonstrate that this practice is both effective and safe when the

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Table 1. Scale for Assessing Opioid-Induced Sedation to Prevent Respiratory Depression* Sedation Scale S ⫽ Sleep, easy to arouse (acceptable; no action necessary) 1 ⫽ Awake and alert (acceptable; no action necessary) 2 ⫽ Slightly drowsy, easily aroused (acceptable; no action necessary) 3 ⫽ Frequently drowsy, arousable, drifts off to sleep during conversation (unacceptable; decrease the opioid dose by 25% to 50%, add an opioidsparing analgesic, such as a COX-2 inhibitor or ketorolac, and monitor the patient’s level of sedation and respiratory status closely) 4 ⫽ Somnolent, minimal or no response to physical stimulation (unacceptable; stop opioid, consider administering naloxone to reverse sedation and a COX-2 inhibitor or ketorolac to control pain). *Appropriate action is given in parentheses at each level of sedation. Source: Pasero C: Acute pain service: policy and procedure guideline manual. Los Angeles, CA, Academy Medical Systems, 1994.

starting infusion rate is low (0.5 mg/hour), PCA bolus doses are 1 mg or less per dose, nurses monitor sedation and respiratory status every 1 to 2 hours for the first 24 hours, and the opioid dose is decreased when excessive sedation is noted and as the patient recovers and pain lessens. If careful nurse monitoring of sedation and respiratory status is not possible, the use of continuous opioid infusions in opioid-naı¨ve patients is discouraged.

References 1. Pasero C, Portenoy RK, McCaffery M: Opioid analgesics, in McCaffery M, Pasero C: Pain: Clinical Manual. (ed 2). St. Louis, Mosby, 1999, pp 161-299 2. American Pain Society (APS): Principles of Analgesic Use in the Treatment of Acute Pain and Cancer Pain (ed 4). Glenview, IL, APS, 2003 3. Parker RK, Holtmann B, White PF: Patient-controlled analgesia. Does a concurrent opioid infusion improve pain management after surgery? J Am Med Assoc 266:1947-1952, 1991 4. Smythe MA, Zak MB, O’Donnell MP, et al: Patient-controlled analgesia versus patient-controlled analgesia plus continuous infusion after hip replacement. Ann Pharmacother 30:224-227, 1996 5. Dal D, Canbak M, Cagler M, et al: A background infusion of morphine does not enhance postoperative analgesia after cardiac surgery. Can J Anaesth 50:476-479, 2003

6. Rayburn WF, Smith CV, Leuschen MP, et al: Combined continuous and demand narcotic dosing for patient-controlled analgesia after cesarean section. Anesthesiol Rev 17:58-62, 1990 7. Hansen LA, Noyes MA, Lehman ME: Evaluation of patientcontrolled analgesia (PCA) versus PCA plus continuous infusion in postoperative cancer patients. J Pain Symptom Manage 6:4-14, 1991 8. Pasero C, McCaffery M: Accountability for pain relief: Use of comfort-function goals. J PeriAnesth Nurs 18:50-52, 2003 9. Sidebotham D, Dijkhuizen MRJ, Schug SA: The safety and utilization of patient-controlled analgesia. J Pain Symptom Manage 14:202-209, 1997 10. Pasero C, McCaffery M: Avoiding opioid-induced respiratory depression. Am J Nurs 94:25-30, 1994