Ketamine is an anesthetic agent known for its unique ability to produce dissociative anesthesia while maintaining respiratory drive. It is commonly administered intravenously or intramuscularly and has a complex pharmacological profile. Ketamine’s anesthetic properties arise primarily from NMDA receptor inhibition, though it interacts with a variety of molecular targets. Ketamine is distinct in that it induces a release of endogenous catecholamines, which helps counterbalance its myocardial depressant effects, particularly in patients with adequate catecholamine stores.
Earlier preclinical studies raised concerns about ketamine’s use in neurologically compromised patients, as it was shown to increase CMRO₂ and intracranial pressure (ICP). Small case series and anecdotal reports also noted elevated ICP, making ketamine less favorable in neurosurgical settings. However, more recent studies conducted in humans indicate that ketamine, when used in conjunction with modern anesthetic practices, does not result in increased ICP. The early rises were recorded largely in spontaneously breathing patients, where ketamine-related hypoventilation raised PaCO₂; with controlled ventilation, normocapnia and a GABAergic co-agent such as propofol or midazolam, systematic reviews of brain-injured patients find ICP unchanged or lower. Ketamine is therefore no longer regarded as contraindicated in patients with raised ICP, and this has led to a reconsideration of its safety profile in patients with neurological vulnerabilities.
Ketamine’s Effect on CBF and CMRO₂
While early studies suggested that ketamine might increase CMRO₂, more recent research suggests that this increase is minimal and likely reflects enhanced metabolite supply rather than elevated oxygen consumption. This distinction is crucial, as it suggests that ketamine does not significantly increase metabolic demand despite its effect on blood flow. A recent meta-analysis of available human studies further demonstrated that ketamine administration leads to an increase in CBF. This increase appears to be due to direct vasodilation of medium-sized cerebral vessels, making it distinct from other anesthetics such as propofol, which typically reduces CBF and CMRO₂.
Neuroprotective Potential of Ketamine
Ketamine’s ability to increase CBF while minimally affecting CMRO₂ has renewed interest in its potential neuroprotective properties. Ketamine’s modulation of the NMDA receptor, along with its complex effects on cerebral perfusion, suggests it may offer protection against ischemic brain injury. Preclinical studies support its role in neuroprotection, but further research is necessary to fully understand the clinical applications of ketamine in neurologically compromised patients. For a detailed discussion of ketamine's neuroprotective properties, interested readers can consult additional literature on the topic.
