Intravenous clonidine decreases the required end-tidal isoflurane for the maintenance of surgical anaesthesia

Abstract

O-4 Introduction: The aim of this study is to prove that i.v. clonidine, given pre-operatively, decreases the end-tidal isoflurane (ETISO) required for the maintenance of a satisfactory depth of anaesthesia during skin incision. Methods: Twenty-three, ASA grade I or II patients (men and women), scheduled for elective orthopaedic surgery were randomly allocated to two groups in a double-blind study. Patients with medication affecting the cardiovascular system were excluded. All received i.v. midazolam 2 mg for sedation. Patients in group A (clonidine group) received i.v. clonidine 3 μg kg−1 in 100 mL saline infusion over 15 min prior to induction; patients in group B received i.v. saline solution 100 mL (saline group). Anaesthesia was induced with propofol (2.5 mg kg−1) followed by succinylcholine (1 mg kg−1); oral intubation and IPPV achieved stable ETCO2 concentrations (4-4.5%); ETISO was 0.8% for over 15 min before skin incision. Anaesthesia was maintained with isoflurane in 66% N2O/O2. Heart rate (HR), non-invasive systolic (SAP), diastolic (DAP) and mean arterial pressure were recorded before intubation, after intubation, before skin incision and 3 min after skin incision. Oxygen saturation (SaO2) and ECG were monitored by means of Datex cardiocap. ETISO and ETCO2 were monitored using an Engstrom EAS 9010 ventilator. Results: Patients in group A did not react to skin incision, nor present a significant change (>10%) in the HR, SAP, DAP or ETCO2, and we did not observe movement of the extremities or the head. Conclusion: Intravenous clonidine given 15 min preoperatively decreases minimal alveolar concentration (MAC) of isoflurane.