Intrathecal normal saline without preservative does not have a local anesthetic effect

The effects of intrathecally administered normal saline (preservative-free) were studied in patients undergoing differential spinal block anesthesia for evaluation of chronic pain below the waist. The injection of 5 ml saline did not significantly change the sensitivity to pinprick measured in the lower back and both lower extremities. Temperature measurement in both the lower extremities and psycho-galvanic skin reflex did not show evidence of sympathetic block; the psychogalvanic skin reflex was abandoned because of inconsistent results. These findings refute the earlier conclusion of Urban and McKain who found that normal saline acts as a weak local anesthetic when injected intrathecally. We recommend use of normal saline (preservative-free) in 5 ml doses as a placebo for differential spinal block anesthesia.