This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anaesthesia
[{'content': 'Least effect on myocardial contractility \nSelect and explain. \nA. Ether, B. Halothane, C. Trilene, D. Isoflurane', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans:D i.e. Isoflurane. CARDIAC EFFECTS OF ANESTHETIC AGENTS :Anticholinergic agents - Atropine/glycopyrrolate: will cause an increase in hea rate, contractility, cardiac output and myocardial oxygen consumption. Often there will be no changein blood pressure and a decrease in right atrial pressure.Thiopental - BarbiturateReduction in blood pressure - peripheral vasodilation is the main action. Compensatory rise in hea rate - barorecptor response. Commonly associated with ventricular arrhythmias .BenzodiazepinesMidazolam and diazepam: Cause little or no direct myocardial depressant effects.Hypnotics- Etomidate: no direct myocardial depression. Safe to use with cardiac, critical and septic patients. .Mu opioids- Fentanyl is a pure mu agonist causes dose dependant bradycardia (increase in vagal tone). Mixed agonist/antagonist agents= Buprenorphine: a paial mu agonist/antagonist. Slow onset of action, duration of 6-8 hours. Cardiovascular depression and respiratory depression not as profound as pure mu agonists. Butorphanol: paial agonist/antagonist. Similar to buprenorphine in cardiovascular/respiratory effects. Dissociative Agents:Ketamine- Hea rate and aerial pressure increase due to an increase in sympathetic tone .Inhalational Anesthetics: Isoflurane and sevoflurane preserved cardiac index, and isoflurane and fentanyl-midazolam preserved myocardial contractility at baseline levels in this group of patients with congenital hea disease. Halothane depressed cardiac index and myocardial contractility.', 'role': 'assistant'}]