Modifiers of patient-controlled analgesia efficacy. II. Chronic pain.

Fifty-eight gynecologic surgical patients using patient-controlled analgesia (PCA) were given several psychological questionnaires and their pain was monitored postoperatively. Pain scores were recorded hourly on postoperative day 1. In addition, patients were asked to score retrospectively their overall pain experience while using PCA (Patient Overall Evaluation). Patients having had a history of pain for at least 6 months were considered to have 'chronic pain,' while those who had no history of chronic pain were grouped as 'acute pain' patients. Chronic pain patients spent more time in 'moderate' pain than did acute pain patients. While patients with a history of chronic pain had higher scores on the hourly pain scale compared to acute pain patients, there were no differences between the two groups on the Patient Overall Evaluation. In addition, chronic pain patients reported the same pain levels after completion of PCA as they did during its use, in contrast to acute pain patients whose retrospective pain levels were higher than during PCA use. Compared to acute pain patients, chronic pain patients had higher scores on both the Hypochondriasis and the Hysteria scales of the MMPI. A history of chronic pain may affect the use of patient-controlled analgesia since chronic pain patients may accommodate to a 'moderate' pain level which approximates their preoperative perception of pain. By contrast, acute pain patients who have no 'chronic pain experience' may self-administer pain medication so as to attain a predominately 'mild' level of pain.