Magnesium is implicated in the activation of NMDA receptors by amino-excitatory acids in the central nervous system [1]. Magnesium deficiency is associated to an increased activation of these receptors, and to an increased sensitivity to pain in animals. Spinal cord is the site of sensitization of pain, mainly mediated by the NMDA receptors, and intrathecal magnesium may have anti-hyperalgesic effect when administered intrathecally [2]. As intrathecal magnesium has already been used in humans for treatment of eclampsia, we stated that it could also improve postoperative analgesia and reduce the need for auto-administered morphine if given (50 mg of magnesium sulfate) with the intrathecal anesthetic drugs (bupivacaine and sufentanil) injected for orthopedic surgery.

Magnesium is implicated in the activation of NMDA receptors by amino-excitatory acids in the central nervous system [1]. Magnesium deficiency is associated to an increased activation of these receptors, and to an increased sensitivity to pain in animals. Spinal cord is the site of sensitization of pain, mainly mediated by the NMDA receptors, and intrathecal magnesium may have anti-hyperalgesic effect when administered intrathecally [2]. As intrathecal magnesium has already been used in humans for treatment of eclampsia, we stated that it could also improve postoperative analgesia and reduce the need for auto-administered morphine if given (50 mg of magnesium sulfate) with the intrathecal anesthetic drugs (bupivacaine and sufentanil) injected for orthopedic surgery.

Inclusion Criteria:

• Total hip replacement under intrathecal anesthesia.

Exclusion Criteria:

• General anesthesia (alone or not)
• Intolerance to morphine
• Misunderstanding of the use of the device for intravenous patient-controlled administration of morphine.