Effect of Intravenous Ketamine Combined With Spinal Anesthesia on Sensory Block Duration Compared to Spinal Anesthesia Alone in Lower Limb Surgeries in Geriatrics.

Spinal anesthesia is a potent anesthetic procedure and is widely used as it has a number of advantages compared to general anesthesia especially in the geriatric population. It is used for both emergency and elective surgeries and involves the injection of a local anesthetic agent into the cerebrospinal fluid, thereby blocking nerve transmission . Regional anesthesia has been suggested as an alternative to general anesthesia in order to evade or decrease general anesthetic exposure . Neuraxial anesthesia offers numerous benefits as it minimizes the surgical stress, reduces the pulmonary compromise (atelectasis, prolonged mechanical ventilation), provides a superior postoperative pain control and reduction of perioperative opioids consumption, hence minimizing opioid side effects. Neuraxial anesthesia results in better peripheral vascular circulation and reduces total blood loss. Finding adjuvants for spinal anesthesia in geriatric patients is crucial because it allows for the use of lower doses of local anesthetics, which helps minimize potential side effects like hypotension and respiratory depression, while still providing effective pain relief during and after surgery. Adjuvants can also improve the quality and duration of the block, leading to better patient outcomes and faster recovery. Hyperbaric bupivacaine 0.5% is widely used in spinal anesthesia. Main disadvantage of spinal anesthesia with bupivacaine 0.5% is it won't prolong duration of post-operative analgesia . Therefore, research for a drug that may decrease the severity of post-operative pain with minimal side effects seems mandatory. A number of adjuvants have been used to improve post-operative analgesia, along with the bupivacaine. These are opioids, epinephrine, clonidine, dexmedetomidine, midazolam, neostigmine and ketamine . While no study to date has directly assessed the effect of intravenous ketamine infusion on two-segment sensory regression time under spinal anesthesia in elderly patients, related literature provides strong indirect support. For instance, Kathirvel et al. (2000) compared intravenous ketamine versus dexmedetomidine as adjuvants to bupivacaine for spinal anesthesia and reported on onset and duration of sensory and motor block, though not specifically two-segment regression Moreover, a recent 2024 meta-analysis found that ketamine added to regional anesthetic techniques significantly prolongs sensory block by an average of 29.1 minutes. While these studies do not exactly mirror our protocol, they support the hypothesis that IV ketamine may enhance block duration. This underscores the novelty and importance of the current trial, which directly evaluates two-segment regression in a geriatric population undergoing lower-limb surgery.

Ketamine, an N-methyl-D-aspartate (NMDA) receptor blocker, has an anesthetic effect and is synergic with bupivacaine . Its beneficial effects on the cardiovascular system and respiratory functions may be combined with the analgesic effects of spinal anesthesia. Ketamine's impact on cognitive function is largely attributed to its noncompetitive antagonism of NMDA receptors, which disrupts excitatory glutamatergic neurotransmission. Additionally, ketamine increases dopamine release in the prefrontal cortex, which contributes to its psychotomimetic effects such as hallucinations or perceptual disturbances. On the other hand, subanesthetic doses of ketamine have been shown to exert anti-inflammatory and neuroprotective properties, particularly by inhibiting microglial activation and reducing pro inflammatory cytokines implicated in postoperative cognitive dysfunction (POCD). These dual and dose-dependent mechanisms highlight why ketamine may induce cognitive disturbances in some elderly patients while potentially protecting against neuroinflammation-induced cognitive decline in others.