Intracranial Pressure
Opioids are generally thought to affect ICP minimally. Under
background anesthesia (isoflurane-N2
O), opioids do not cause significant
increases in ICP during craniotomy for supratentorial space-occupying lesions.[104]
[105]
Under stable anesthesia with isoflurane-N2
O,
sufentanil (0.8 µg/kg) or fentanyl (4.5 µg/kg) prior to skull-pin insertion
resulted in stable ICP.[106]
It was also reported
that opioid sedation did not alter ICP in head-injured patients (also see Chapter
53
).[107]
However, it has been reported that opioids may produce increases
in ICP in patients undergoing craniotomy for excision of supratentorial space-occupying
lesions, especially if intracranial compliance is compromised. It was reported that
CSF pressure increased by 90% after sufentanil (1 µg/kg) and 20% after alfentanil
(50 µg/kg), in contrast to no significant change after fentanyl (5 µg/kg),
in patients with brain tumors who were anesthetized with thiopental-N2
O-vecuronium.
[108]
On the other hand, there was no change in
ICP in hydrocephalic children after alfentanil (70 µg/kg).[109]
In patients with severe head injury with preserved and impaired autoregulation,
morphine (0.2 mg/kg) and fentanyl (2 µg/kg) moderately increased ICP, suggesting
that mechanisms other than vasodilatation could be implicated in the opioid-induced
ICP elevation.[110]
It is not clear whether these discrepancies in the effects of
opioids on ICP are due to different pressure assessment methods or to the effects
of other drugs. If opioids do increase ICP, whether cerebrovascular dilatation is
directly induced by opioids or results indirectly from opioid-induced decreases in
blood pressure is not known. Regional increases in CMR and opioid-induced rigidity
may be involved.[111]
Although many studies suggest the possibility of adverse effects
of opioids on regional CMR, CBF, and ICP, opioid-based anesthesia in intracranial
surgery has an extensive and safe clinical record. The significance of reported
opioid-induced changes in CBF and/or ICP and the impact, if any, of such changes
on patient outcome is unknown.
