What is the best method of treating acutely worsened chronic pain?

The Hospitalist. 2008 April;2008(04):

April 1, 2008|The Hospitalist

Case

A 69-year-old female with metastatic ovarian cancer and chronic pain syndrome presented to the hospital with seven days of progressively worsening abdominal pain. The pain had been similar to her chronic cancer pain but more severe. She has acute renal failure secondary to volume depletion from poor intake. A CT scan of the abdomen and pelvis reveal progression of her cancer with acute pathology. What is the best method of treating this patient’s pain?

Overview

Pain is pandemic. It is the most common reason patients seek healthcare.1 Almost one-third of Americans will experience severe chronic pain at some point in their lives. Every year, approximately 25 million Americans experience acute pain and 50 million experience chronic pain. Only one in four patients with pain receives appropriate therapy and control of their pain.

Pain is the most common symptom experienced by hospitalized adults.2 Acute or chronic pain can be particularly challenging to treat because these patients are frequently opioid dependent and have many psychosocial factors. No one method of pain control is superior to another. However, one method to gain rapid control of an acute pain crisis in a patient with chronic pain is to use patient-controlled analgesia (PCA).

How to Initiate and Titrate a PCA

Calculate basal rate (equi-analgesic dose of current opioid):
- Opioid naïve: No basal rate; and
- Chronic opioid use: Use equianalgesic dose of combined 24-hour chronic dose divided by 24 to get hourly rate.
Incremental dose: 50% to 100% of basal rate.
Lockout time: Eight to 10 minutes (use six-minute lockout only for fentanyl).
Loading dose: Twice the incremental dose.
Can change incremental dose at least every 30 to 60 minutes (use for acute pain control; rapid titration):
- For mild to moderate pain: increase dose by 25% to 50%; and
- For moderate to severe pain: increase dose by 50% to 100%.
Can change basal rate every eight hours or greater (do not increase by more than 100% at a time).

Review of the Data

The first commercially available PCA pumps became available in 1976.3 They were created after studies in the 1960s demonstrated that small doses of opioids given intravenously provided more effective pain relief than conventional intramuscular injections.

The majority of studies on PCAs are in the postoperative patient, with cancer pain being next most commonly studied. PCAs utilize microprocessor-controlled infusion pumps that deliver a preprogrammed dose of opioid when the patient pushes the demand button. They allow programming of dose (demand dose), time between doses (lockout interval), background infusion rate (basal rate), and nurse-initiated dose (bolus dose).

The PCA paradigm is based on the opioid pharmacologic concept of minimum effective analgesic concentration (MEAC).4,5 The MEAC is the smallest serum opioid concentration at which pain is relieved. The dose-response curve to opioids is sigmoidal such that minimal analgesia is achieved until the MEAC is reached, after which minute increases in opioid concentrations produce analgesia, until further increases produce no significant increased analgesic effect.

PCAs allow individualized dosing and titration to achieve the MEAC, with small incremental doses administered whenever the serum concentration falls below the MEAC. A major goal of PCA technology is to regulate drug delivery to rapidly achieve and maintain the MEAC.