THE EFFECT OF THE DURATION OF ELECTRICAL STIMULATION ON THE ANALGESIC RESPONSE (1999)

S211 INTRODUCTION: Percutaneous electrical nerve stimulation (PENS) has recently been reported to be an effective non-pharmacologic therapy for the management of acute [1] and chronic pain syndromes [2]. However, the effect of the duration of electrical stimulation on the analgesic response has not been previously studied. Therefore, we designed a randomized, sham-controlled, cross-over study to compare the efficacy of differing durations of electrical stimulation on the analgesic response, physical activity and quality of sleep in patients with chronic low back pain (LBP). METHODS: 65 consenting patients with LBP secondary to degenerative disc disease were studied. All patients had been maintained on a stable oral non-opioid analgesic regimen prior to entering this IRB-approved study. 10 acupuncture-like needles (32 ga) were inserted in a standardized dermatomal pattern in the low back region. Three different durations of PENS therapy (namely, 15, 30 and 45 min) were administered using a low-output electrical generator at alternating 15 Hz and 30 Hz frequencies, as well as a sham treatment (no stimulation of the needles during the 30 min treatment sessions). Each treatment was administered 3 times per week for 2 consecutive weeks in a random sequence, with one week off between each 2-week block according to a randomized, cross-over study design. The pretreatment assessments included visual analog scales (VAS) for pain, physical activity and quality of sleep. The pain VAS was repeated before and after each treatment session. The daily usage of analgesic medications was recorded in the patient's diary. After receiving the all four treatment modalities, the patient completed a global assessment questionnaire. Data (means +/- SD) were analyzed using ANOVA and Chi-square tests, with p-value <0.05 considered statistically significant. RESULTS: All three durations of electrical stimulation were more effective than the sham treatments in improving VAS scores for pain, physical activity and quality of sleep (* vs sham, p-value < 0.05). However, the 30 min and 45 min durations of stimulation were also significantly more effective than the 15 min interval ([dagger] vs 15 min, p-value < 0.05). The daily oral analgesic requirements were also significantly decreased after all three intervals of electrical stimulation compared with the sham treatment. Similarly, the decreases in daily oral analgesic medications after the 30 min and 45 min stimulation intervals were significantly greater than with a 15 min interval of stimulation. Finally, the global assessment of the four modalities indicated that the 30 min and 45 min treatment periods were the therapies preferred by the patients. There were no statistical differences between 30 min and 45 min of electrical stimulation with respect to patient outcome after PENS therapy. (Table 1)Table 1DISCUSSION: Use of non-pharmacologic modalities like PENS for the management of pain syndromes has been limited, in part, by a lack of scientific information regarding their optimal use. This sham-controlled, cross-over study suggests that the duration of electrical stimulation should be at least 30 min in order to achieve a maximal analgesic response in patients with LBP.