Non-neurological surgery results in a neurochemical stress response

There is a paucity of studies assessing changes in measures of human neurotransmission during stressful events, such as surgery. Thirty-five patients without any neurological disorders undergoing knee replacements with spinal bupivacaine anaesthesia and propofol sedation had cerebrospinal fluid (CSF) drawn from a spinal catheter before, three hours after and the morning after surgery. The CSF concentrations of the dopamine metabolite homovanillinic acid (HVA) and the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA), which are related to the activity of the dopaminergic and serotonergic systems of the brain, increased sharply during surgery and reached 188% and 166% of their initial concentrations on the morning after the intervention (p < 0.0001). The CSF concentrations of the norepinephrine metabolite 3-methoxy-4-hydroxyphenylglucol (MHPG) increased modestly (non-significantly) during and after surgery. The HVA/5-HIAA ratios initially increased but returned to the initial level during the night after surgery. We conclude that non-neurological surgery, in this case to the lower limb, is accompanied by a marked central nervous stress response in spite of a spinal blockade.