Block of pinprick and cold sensation poorly correlate with relief of postoperative pain during epidural analgesia

Objective: To test the following hypotheses: there is a correlation between spread of epidural analgesia as assessed postoperatively by pinprick/cold test and postoperative pain intensity; block of pinprick/cold sensation is associated with absence of postoperative pain. Design: Correlation analysis on prospectively collected data Setting: University hospital. Patients: One hundred patients undergoing major surgery. Consecutive sample . Interventions: Patients received an epidural infusion of bupivacaine 1 mg/m l, fentanyl 2 mu g/ml, and epinephrine 2 mu g/ml for at least 48 hours post operatively. The infusion rate was adjusted according to pain intensity, oc currence of hypotension, or motor block. Outcome Measures: Assessments were made on three time points: 20-24 hours, 32-36 hours, and 42-48 hours after extubation. Assessments included pinpric k and cold sensitivity from C2 to S5, pain intensity (visual analogue scale , VAS) at rest, after cough, and after mobilization. Data were analyzed by multiple regression. Results: VAS significantly decreased with increasing spread (number of derm atomes for which hyposensitivity to pinprick or cold was observed). Spread could explain only 2-5% of the variability of VAS. Absence of both pinprick and cold sensation at all dermatomes corresponding to the surgical wound w as frequently associated with pain. A high proportion of patients manifesti ng an upper level of block above T5 had pain after abdominal surgery. Conclusions: Spread and efficacy of epidural analgesia. as assessed by pinp rick and cold stimulation correlate poorly with postoperative pain. These m ethods are of limited value both as clinical indicators of the efficacy of postoperative pain control and for investigating the effect of epidural dru gs and techniques.