Cerebral protection during extracorporeal circulation

Influence of anesthesia protocol in experimental traumatic brain injury

Most pharmacologic studies on brain trauma in animals are performed while the animals are under general anesthesia, which can interfere with brain metabolism and modify the experimental results. This study investigates the effects of three anesthetic drugs (halothane 2% and 4%, propofol at 10 mg/kg, and chloral hydrate at 400 mg/kg) on the traumatic brain injury-induced neurologic deficit in mice. Trauma was induced with a weight-drop device. For each drug, animals were divided into four groups; the first did not receive either anesthesia or trauma, the second received anesthesia but no trauma, the third received a trauma without anesthesia, and the fourth received anesthesia before the trauma. A neurologic examination using two different scorings (string and grip test) was performed 1 hour and 24 hours after the trauma. Mortality after trauma was increased for halothane 4% (48% versus 20% in unanesthetized mice), propofol (80% versus 30%), and chloral hydrate (70% versus 44%). Halothane 2% did not increase the mortality in traumatized mice. Halothane 2% or 4% anesthesia did not modify the string score after the trauma. Grip score after the trauma was better in mice anesthetized with halothane at either 2% or 4%. Mice injured under anesthesia with chloral hydrate had worse grip and string scores (P < .05) than unanesthetized mice. These results lead us to question the influence of anesthesia on the results obtained in experimental neuropharmacologic studies, particularly when there are discrepancies between two studies on the same pharmacologic treatment, which differ in their anesthesia protocols.

Brain protection: physiological and pharmacological considerations. Part II: The pharmacology of brain protection

Neuroprotective agents may exert their effect by reducing cerebral oxygen demand (CMRO2), increasing cerebral oxygen delivery, or by altering ongoing pathological processes. Barbiturates provide neuroprotection by reducing the CMRO2 necessary for synaptic transmission while leaving the component necessary for cellular metabolism intact. Isoflurane may exert a neuroprotective effect by a similar mechanism but its efficacy is likely less than that of barbiturates due to adverse effects on cerebral blood flow. Lidocaine reduces CMRO2 by affecting both cellular metabolic processes and synaptic transmission and thus resembles hypothermia in its mechanism of action. Benzodiazepines reduce CMRO2 by reducing synaptic transmission and their use as neuroprotectants produces less haemodynamic compromise than barbiturates. The mechanism of protection by calcium entry blocking agents appears to be due to improved blood flow as opposed to altering abnormal Ca++ fluxes. In contrast, agents such as ketamine and MK-801 may prevent abnormal Ca++ fluxes through their competitive interaction with N-methyl-D-aspartate receptors. Phenytoin prevents K(+)-mediated ischaemic events from progressing. Agents worthy of further investigation include corticosteroids, free radical scavengers, prostaglandin inhibitors and iron chelators.