Assessment of sensory block in epidural anaesthesia by electric stimulation

Abstract

The onset of sensory block in lumbar epidural anesthesia was investigated in 26 patients, aged 18 to 84 years, employing the loss of discrimination to cold and pinprick, as well as by determining threshold electric stimulation (threshold intensities). A standard dose of 2% mepivacaine with adrenaline, 5 micrograms.ml-1, (0.1 ml per cm body height) was given and the patients' ability to discriminate stimuli within dermatomes T8, T10, T12, L2, L4 and S1 was investigated at five min intervals for 30 min after injection. From the results of the study it is concluded that i) The interval to peak analgesic efficacy of the anaesthetic solution used is < 30 min when assessments are based on the patients' ability to discriminate cold or pinprick but > 30 min when determinations of threshold intensities are employed. ii) Cold discrimination is lost earlier than discrimination to pinprick and at lower threshold intensities. iii) Threshold intensities describe the time course of onset of sensory block more precisely than results of testing by cold or pinprick. iv) The onset of sensory block was found to be positively correlated to the age of patients in the following respects: a) Threshold intensities during early onset in all investigated dermatomes except L2. b) Intensity of block in T8, T10, and S1 at the end of the study period. c) Time to loss of discrimination to cold and pinprick in T12, L2 and S1, and d) Threshold intensities at loss of discrimination to cold and pinprick. We propose that determinations of threshold intensities offer distinct advantages over conventional testing by cold and pinprick discrimination, especially when detailed analyses of the sensory blocking effects of local anaesthetic drugs are being investigated.

Temporal summation during extradural anaesthesia

“…1). Dyhre, Renck and Andersson found that single electrical stimulation is superior to pinprick and cold for assessing extradural analgesia [6]. Our results confirm these findings, but show also that false negatives may be expected with single electrical stimulation, as this test does not evoke temporal summation ( fig.…”

Intrathecal drug spread

“…Loss of vibration and proprioceptive sensation have also been used. 101 More definitive assessment of pain sensation has been attempted with tetanic stimulation using peripheral nerve stimulators, 44 87 and transcutaneous electrical nerve stimulation, 36 both of which correlate well with surgical incision, 116 and assessment of somatosensory evoked potentials. 82 Chemical stimulation with capsaicin, mustard oil, hypertonic saline, bradykinin, serotonin or substance Pinduceexperimental pain but are ineffective on intact skin.…”

Warming the Epidural Injectate Improves First Sacral Segment Block: A Randomised Double-Blind Study

“…This test was chosen because it enables a reproducible quantification of epidural block and induces temporal summation 9,10 . In contrast, evaluation by pinprick or cold testing may not necessarily predict pain-free skin incision 11 . Despite the presence of a sensory block of L4-S1 segments tested by pinprick, in one study 13 of 45 patients complained of pain and a burning sensation during epidural anaesthesia for foot or ankle surgery 12 .…”