When administered intrathecal ketamine shows local anesthetic effects in both animals and humans. Intrathecal ketamine when used as a sole agent (0.7-0.95 mg/kg) with or without epinephrine for intrathecal use, although produces motor and sensory block but the analgesia is inadequate and of short duration along with varied psychomimetic disturbances.
When added to the intrathecal bupivacaine it may reduce the dosage of bupivacaine to be used and thus can avoid the cardiovascular effects of large dose of bupivacaine with shorter duration of motor block. However, this can be helpful in elderly patients and for short surgical procedures like TURP.
Intrathecal ketamine also shortens the onset of motor and sensory block. Intrathecal ketamine may be associated with adverse events, such as sedation, dizziness, nystagmus, ‘strange feelings’ and postoperative nausea and vomiting.
The use of neuraxial intrathecal ketamine to produce analgesia is of limited value. It does not provide extended postoperative analgesia or decrease the postoperative analgesic requirements. Moreover, the central adverse effects of Intrathecal use of ketamine limit its spinal application.
Though ketamine and S(+)-ketamine have been advocated for neuraxial use in the management of postoperative pain and severe intractable pain syndromes unresponsive to opioid escalation, some studies demonstrated the toxic effect on the central nervous system after repeated intrathecal administration of even preservative-free S(+)-ketamine in a clinically relevant concentration and dosage.