Effects of naloxone on systemic and cerebral responses to experimental concussive brain injury in cats

This study examined the effects of bolus injections of naloxone hydrochloride, a specific narcotic antagonist, on systemic cardiovascular function, intracranial and cerebral perfusion pressures, blood gas status, and cortical encephalograms (EEG's) in 38 cats after two different grades of experimental brain injury. Naloxone had no prolonged effects on uninjured control animals. However, as compared to a saline-injected control group, naloxone significantly reversed the hypotension and reduction in pulse pressure seen after higher grades of injury. These changes persisted for at least 60 minutes after injection and were accompanied by increased intracranial and perfusion pressures. More severely injured hypotensive cats injected with naloxone also had higher values of arterial pO2 and pH, lower pCO2, as well as higher EEG amplitudes. In less severely injured normotensive cats, naloxone produced greater effects on cardiovascular variables and intracranial pressure when injected 15 minutes rather than 45 minutes after injury. These data suggest that endogenous opiates may contribute to some instances of hypotension seen after concussive brain injury. Levels of endogenous opiates may also increase transiently even with lesser degrees of injury not associated with hypotension. The possible clinical application of narcotic antagonists to the treatment of head injury is discussed.