Study of plasma neuropeptide Y and catecholamine levels during high dose fentanyl anesthesia

Ten ASA physical status I-II patients were studied after obtaining institutional approval and informed consent. All patients were free from endocrine and metabolic disease undergoing elective low risk operation. They were premedicated with pethidine 1.0 mg/kg intramuscularly and diazepam 0.1 mg/kg orally one hour before anesthesia. Anesthesia was induced with thiopental 4 mg/kg and succinylcholine 1.5 mg/kg for tracheal intubation. Anesthesia was maintained with intermittent intravenous injection of fentanyl (50-100 micrograms/kg) and inhalation of N2O-O2 (50%). Ventilation was controlled during surgery. Atracurium (0.4 mg/kg iv) was given for muscle relaxation when needed. Blood samples were obtained from the radial artery 15 min before induction of anesthesia and 5 min after intubation, 15 min, 30 min, 60 min, 120 min during operation and 30 min after operation. Neuropeptide Y (NPY) was determined by radioimmunoassay, catecholamines were determined by radioenzymatic method using CAT-A-KIT (Amersham). Statistical analysis was performed using Student's t-test for paired and unpaired samples. P values less than 0.05 were considered significant. Naloxone 0.4 mg was given by iv at the end of operation in all of the patients to establish adequate spontaneous respiration. The results showed that the plasma NPY was significantly decreased under high dose fentanyl as well as catecholamines.