Treatment efficacy is not an index of pain intensity

To determine if the efficacy of pain treatment assessed by the patient is a valid indicator to evaluate pain management.

Three hundred and ninety one adult patients were investigated on the day of surgery and on the two following days after intraperitoneal or orthopedic surgery. Pain scores and efficacy of pain treatment were evaluated using ungraduated visual analog scales (VAS). According to the evolution of pain between two consecutive days, patients were classified as having "worse pain", "same pain" or "lower pain".

During the first time interval, pain treatment was considered effective by 42% of patients with worse pain, compared with 55% with less pain (OR= 1.9, 95% CI=1.1-3.7) and to 58% of patients with the same pain (OR =2.0, 95%CI=1.2-3.0). During the second time interval, these proportions were: 46% (worse pain), 63% (lower pain vs worse: OR= 1.8, 95%CI= 1.0-3.2) and 66% (same pain vs worse: OR=2.1, 95%CI=1.1-4.1). Using pain evolution as a"gold standard", patient assessment of pain treatment efficacy had sensitivity of 0.55 and specificity 0.5 during the first time interval, and of 0.63 and 0.43 during the second time interval.

Patient evaluation of the efficacy of pain treatment can mislead the clinician about the severity of pain. Patients tend to be satisfied with pain treatment, even when pain is not relieved. The relation of intensity of pain to patient perception of treatment efficacy is weak.