Low dose epidural morphine does not affect non-nociceptive spinal reflexes in patients with postoperative pain

Publisher Website
Google Scholar
Abstract
In order to determine the selectivity of the antinociceptive effect of epidural morphine, the electrophysiological features of a monosynaptic reflex were investigated before and after epidural morphine (2–3 mg) required for pain relief, in 4 patients suffering from postoperative pain. The reflex tested was the H reflex from the soleus muscle. Not only the classical Hmax/Mmax ratio, but also the threshold and the slope of the rising phase of the recruitment curve of H and M responses were analyzed. It was found that epidural morphine did not change significantly any of these parameters, at least during the 60 min post-injection period. By contrast, as usually observed clinically, epidural morphine produced an onset of pain relief by the 25th–30th min following injection. These data support the hypothesis that epidural morphine produced a ‘selective spinal analgesia in man.’