Continuous intracisternal infusion of
bupivacaine for the management of
intractable pain of the head and neck is effective in controlling
pain in this patient group. With the
catheter tip being located at the height of the C1 vertebral body, autonomic regulatory information may also be influenced by the infusion of
bupivacaine. By combining direct sampling of cerebrospinal fluid (CSF), via a percutaneously placed
catheter in the cisterna magna, with a
noradrenaline and
adrenaline isotope dilution method for examining sympathetic and adrenal medullary activity, we were able to quantify the release of brain
neurotransmitters and examine efferent sympathetic nervous outflow in patients following intracisternal administration of
bupivacaine. Despite severe
pain, sympathetic and adrenal medullary activities were well within normal range (4.2 +/- 0.6 and 0.7 +/- 0.2 nmol min(-1), respectively, mean +/-S.E.M.). Intracisternal
bupivacaine administration caused an almost instantaneous elevation in mean arterial blood pressure, increasing by 17 +/- 7 mmHg after 10 min (P < 0.01). Heart rate increased in parallel (17 +/- 5 beats min(-1)), and these changes coincided with an increase in sympathetic nervous activity, peaking with an approximately 50% increase over resting level 10 min after injection (P < 0.01). CSF levels of
GABA were reduced following
bupivacaine (P < 0.05). CSF
catecholamines and
serotonin, and EEG, remained unaffected. These results show that acutely administered
bupivacaine in the cisterna magna of
chronic pain sufferers leads to an activation of the sympathetic nervous system. The results suggest that the haemodynamic consequences occur as a result of interference with the neuronal circuitry in the brainstem. Although these effects are transient, they warrant caution at the induction of intracisternal local anaesthesia.