Cerebral hemodynamic effects of morphine and fentanyl in patients with severe head injury - Absence of correlation to cerebral autoregulation

Background: The current study investigates the effects of morphine and fent anyl upon intracranial pressure and cerebral blood now estimated by cerebra l arteriovenous oxygen content difference and transcranial Doppler sonograp hy in 30 consecutive patients with severe head injury in whom cerebrovascul ar autoregulation previously had been assessed. Methods: Patients received morphine (0.2 mg/kg) and fentanyl (2 mu g/kg) in travenously over 1 min but 24 h apart in a randomized fashion. Before study , carbon dioxide reactivity and autoregulation were assessed. Intracranial pressure, mean arterial blood pressure, and cerebral perfusion pressure wer e repeatedly monitored for 1 h after the administration of both opioids, Ce rebral blood flow was estimated from the reciprocal of arteriovenous oxygen content difference and middle cerebral artery mean flow velocity using tra nscranial Doppler sonography, Results: Although carbon dioxide reactivity was preserved in all patients, 18 patients (56.7%) showed impaired or abolished autoregulation to hyperten sive challenge, and only 12 (43.3%) had preserved autoregulation, Both morp hine and fentanyl caused significant increases in intracranial pressure and decreases in mean arterial blood pressure and cerebral perfusion pressure, but estimated cerebral blood flow remain unchanged. In patients with prese rved autoregulation, opioid-induced intracranial pressure increases were no t different than in those with impaired autoregulation, Conclusions: The authors conclude that both morphine and fentanyl moderatel y increase intracranial pressure and decrease mean arterial blood pressure and cerebral perfusion pressure but have no significant effect on arteriove nous oxygen content difference and middle cerebral artery mean flow velocit y in patients with severe brain injury, No differences on intracranial pres sure changes were found between patients with preserved and impaired autore gulation. Our results suggest that other mechanisms, besides the activation of the vasodilatory cascade, also could be implicated in the intracranial pressure increases seen after opioid administration.