TEMPORAL SUMMATION DURING EXTRADURAL ANESTHESIA

We have investigated in 10 patients the effect of extradural anaesthes ia on temporal summation by comparing pain thresholds to single and re peated (five impulses at 2 Hz) electrical stimuli and compared these t ests with pinprick and cold stimulation. Bupivacaine 0.5% (20 ml) was injected at L2-3. After extradural anaesthesia the threshold to repeat ed stimuli was significantly lower than the threshold to single stimul i (P = 0.0007). Nine patients lost cold sensation and 10 patients pinp rick sensation. Pain to single electrical stimulation disappeared in s ix patients and pain to repeated electrical stimulation in one. Pain m ay be evoked by temporal summation of repeated electrical stimuli even when pinprick sensation, cold sensation and pain to single electrical stimuli are inhibited. Thus temporal summation should be taken into c onsideration when extradural analgesia is assessed.