Patient-controlled analgesia

Published on 07/02/2015 by admin

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Patient-controlled analgesia

Martin L. De Ruyter, MD

As many as 50% of patients who receive conventional therapy for their postoperative pain do not have adequate analgesia. In a report by Sommer et al, 41% of 1490 surgical patients under the care of an acute pain protocol reported having moderate to severe pain on the day of surgery, 30% on their first postoperative day, and 19% on postoperative day 2.

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.

Intravenous patient-controlled analgesia

Advantages

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.

Box 211-1   Advantages of Intravenously Administered Opioids via Patient-Controlled Analgesia

• Compared with other forms of analgesia, IV PCA provides superior pain relief with less medication.

• The use of IV PCA decreases the potential delay between patients’ requests for analgesics and the administration of the drug.

• Postoperative pulmonary function is improved in patients receiving IV PCA.

• IV PCA allows for accommodation for diurnal changes in drug requirements and variable range of analgesic needs.

• Less daytime sedation occurs with the use of IV PCA.

• Patients who receive IV PCA are able to mobilize sooner after surgery.

• Patients report high levels of acceptance and satisfaction with IV PCA.

• Less inappropriate “screening” by nursing staff occurs with the use of IV PCA.

• Patients receiving IV PCA experience fewer postoperative pulmonary complications.

• The potential for overdose is low when small doses per activation are prescribed.

• Patients’ sleep patterns improve when IV PCA is used.

• The use of IV PCA is cost effective.

IV PCA; Intravenously administered patient-controlled analgesia.

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Figure 211-1 Serum levels of analgesic drugs comparing intravenously administered patient-controlled analgesia (solid lines) versus intramuscular administration (dashed lines). (Adapted from White PF. Use of patient-controlled analgesia for management of acute pain. JAMA. 1988;259:243.)

Choice of opioids

Morphine, hydromorphone, and fentanyl are the opioids commonly administered via IV PCA. Meperidine, in the past an often used agent, is less frequently used because of the potential adverse effects (i.e., seizures) associated with its active metabolite, normeperidine, and the recognition of better alternative agents. (Table 211-1).

Table 211-1

Suggested Dosing Regimens for Opioid-Naïve Patients* Receiving Opioids via Intravenous Patient-Controlled Analgesia

Drug Concentration, mg/mL Loading Dose†, mg maximum Demand Dose, mg Lockout Interval, min Basal Infusion‡, mg/h 1-h Limit, mg 4-h Limit, mg
Morphine 1 2-4 1-2 6-10 0-1.0 7.5 30
Hydromorphone 0.2 0.4 0.2-0.4 6-10 0-0.2 1.5 6
Fentanyl 0.01 0.02-0.04 0.01-0.03 6-10 0-0.02 0.1-0.2 0.4-0.8

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*Elderly patients (>65 y) and patients on chronic opioids may need adjustment of these guidelines.

†The loading dose is given as a bolus every 5 min until the patient is comfortable and then the patient-controlled analgesia is started.

‡Most practitioners do not recommend a continuous infusion for most patients.

Initial setup

When prescribing IV PCA with opioids, the anesthesia provider must determine the loading dose, the demand dose, the lockout interval, and the maximum dose limit. The loading dose administered at the initiation of IV PCA is intended to quickly establish an effective serum concentration of drug. The loading dose of the opioid is typically administered over five minutes until satisfactory analgesia is achieved. Satisfactory analgesia is maintained with subsequent demand doses delivered in a predetermined window or frequency. The demand dose of the drug should be adjusted for the patient’s age, comorbid conditions, and concomitant medications. Smaller loading and demand doses of opioids should be prescribed for patients who are elderly, have pulmonary disease (i.e., chronic obstructive pulmonary disease or obstructive sleep apnea), whose hemodynamic status is tenuous, or who are receiving drugs that may act synergistically with opioids, whereas patients with chronic pain and opioid tolerance will likely need higher or more frequent doses. The maximum dose allowed is usually the cumulative dose allowed at 1 or 4 h as a safety measure to ensure that patients do not exceed a total cumulative dose of opioids. Bolus doses are similar to loading doses that can be administered to a patient by a health care provider if the patient does not have adequate analgesia achieved with the initial settings.

Most clinicians do not routinely prescribe a continuous or basal infusion of an opioid that is delivered independent of patient demand unless the patient is opioid tolerant and now has acute pain superimposed on chronic pain. By monitoring the number of patient demands relative to the number of doses delivered, clinicians can tailor and adjust the demand dose and lockout interval to better meet the analgesic needs of the patient. For example, 15 attempts per hour by a patient with a PCA setting of 1 delivery every 10 min implies that the patient’s analgesic needs are not being met. Appropriate responses include decreasing the lockout interval, increasing the demand dose, adding a basal infusion, or using a combination of these strategies.

Adverse effects and outcomes

IV PCA with opioids is not without side effects and adverse outcomes (Box 211-2). Nausea, vomiting, and pruritus are not uncommon, and excessive somnolence has been observed. In a group of patients who underwent total hip arthroplasty and received an IV PCA for postoperative analgesia, investigators observed that, on postoperative day 2, more than 50% of patients experienced episodes of desaturation (SpO2 < 90%) and one patient experienced a respiratory arrest. To improve the safety of IV PCA, many hospitals have guidelines that recommend staff members have regular interaction with patients and measure and document the patient’s pain scores (using a metric such as numeric or visual analog scores), respiratory rate, O2 saturation via pulse oximetry, state of arousal, and level of sedation. In opioid-related respiratory depression, O2 desaturation is a delayed observation. With the advancement of technology and recent more widespread availability, end-tidal CO2 monitors are used more often. As these devices become more accepted in clinical practice, it is hoped that IV PCA will become a safer modality for analgesic administration.

Box 211-2   Disadvantages of Intravenously Administered Opioids via Patient-Controlled Analgesia

• Patients using patient-controlled analgesia must be mentally alert, physically able to push the button, and able to understand the concept of IV PCA and follow instructions.

• IV PCA should be used with caution in patients with significant liver, renal, or pulmonary disease.

• Patients with obstructive sleep apnea are at increased risk of experiencing opioid-induced respiratory depression.

• Pruritus is more common with IV PCA than with intramuscular administration but less common than with epidural administration.

• Surrogate (nonpatient, i.e., family members or nursing staff) “pushers” of the button may subject patients to overdosing levels of opioids.

• Some anesthesia providers consider opioid addiction to be relatively contraindicated.

• Hypovolemia is associated with excessive rates of opioid-induced respiratory depression.

• Direct costs are increased because of the need for special equipment, setup, and staff training.

IV PCA; Intravenously administered patient-controlled analgesia.

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