The effects of intrathecal midazolam on sympathetic nervous system reflexes in man--a pilot study.

Nine patients were given intrathecal injections of midazolam (dose 0.3-2 mg dissolved in 3 ml 5% dextrose). No changes in motor power or general sensation were produced. Resting heart rate and blood pressure were unchanged and normal valsalva manoeuvres were elicited 30 min post-injection. Cardiovascular responses were provoked at a light plane of anaesthesia by intubation of the trachea and manipulation of peritoneum and bowel but not by surgical incision of the skin. Intrathecal administration of midazolam relieved post-operative pain of somatic origin but not of visceral origin. It is concluded that intrathecal midazolam in the dosage used interrupts somatic nociceptive afferent pathways but not abdominal visceral nociceptive afferent pathways.