Atropine-induced heart rate changes: a comparison between midazolam-fentanyl-propofol-N2O and midazolam-fentanyl-thiopentone-enflurane-N2O anaesthesia.
Atropine-induced heart rate (HR) changes were studied in 19 patients (ASA physical status I) during anaesthesia-maintained predominantly with propofol-N2O or thiopentone-enflurane-N2O. Ten patients (Group A) received midazolam (0.07 mg.kg-1), fentanyl (1 microgram.kg-1), propofol (2 mg.kg-1) and succinylcholine (1 mg.kg-1). Following tracheal intubation, anaesthesia was maintained with propofol (6 mg.kg-1.hr-1), N2O (67 per cent) and O2 (33 per cent). In nine patients (Group B) thiopentone (4 mg.kg-1) was substituted for propofol and anaesthesia maintained with N2O (67 per cent) O2 (33 per cent), and enflurane (0.5 per cent inspired concentration). The study was non-randomised because Group B patients were only included if HR before administration of atropine less than 90 beats.min-1. IPPV was performed in all patients using a Manley ventilator (minute vol. 85 ml.kg-1; tidal vol. 7 ml.kg-1). Ten minutes after tracheal intubation, incremental doses of atropine (equivalent cumulative doses: 1.8, 3.6, 7.2, 14.4, 28.8 micrograms.kg-1) were administered at two-minute intervals and HR responses calculated during the last 45 sec of each intervening period. No differences were observed between the groups following 1.8 and 3.6 micrograms.kg-1 atropine, but propofol-N2O anaesthesia was associated with reduced responses (P less than 0.01) following 7.2, 14.4 and 28.8 micrograms.kg-1 atropine. These results suggest that there is a predominance of parasympathetic influences during propofol-N2O anaesthesia compared with thiopentone-enflurane-N2O anaesthesia.
Cross
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G
Dept. of Anaesthesia, St. Thomas' Hospital, London, United Kingdom.
Gaylard
D
D
Lim
M
M
D000328:Adult; D000769:Anesthesia, Inhalation; D000771:Anesthesia, Intravenous; D001285:Atropine / Q000008:administration & dosage / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004562:Electrocardiography; D004737:Enflurane / Q000494:pharmacology*; D005260:Female; D005283:Fentanyl / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D008297:Male; D008874:Midazolam / Q000494:pharmacology; D009609:Nitrous Oxide / Q000494:pharmacology*; D015742:Propofol / Q000494:pharmacology*; D011897:Random Allocation; D013268:Stimulation, Chemical; D013874:Thiopental / Q000494:pharmacology*
D001285:Atropine; D004737:Enflurane; D013874:Thiopental; D009609:Nitrous Oxide; D008874:Midazolam; D005283:Fentanyl; D015742:Propofol