Comparison of the Efficiency of Anesthetic Depth Control Using Closed Loop Anesthesia Delivery System vs. Manual Control Using Target Controlled Infusion in Patients With Moderate to Severe Left Ventricular Systolic Dysfunction

MATERIALS AND METHODS:

Patient will be pre-medicated with oral tablet alprazolam 0.25 mg the night before and on the morning of surgery. In the anesthetic room, 16 G i.v. cannula will be inserted and following monitors will be attached: continuous pulse-oximetry (SpO2), electrocardiogram (ECG), periodic non-invasive blood pressure (S/Anesthesia monitor, Datex Ohmeda Inc., Madison, WI) , and continuous BIS (BIS XP, Aspect Medical Systems, Newton, MA in the S/5 Anesthesia monitor). Pre-induction arterial line and central line will be inserted in all patients and continuous arterial blood pressure and central venous pressure measurements will be recorded. Pulmonary artery catheter will also be inserted in all patients for monitoring of cardiac output. All invasive lines will be inserted under local anesthesia. NIBP measurements will be stopped after transducing arterial line, because it may interfere with the assessment of MOAA/S score.

All the patients will receive i.v. fentanyl at a dose of 3µg.kg-1 over a period 3 minutes, followed by propofol administration either by CLADS or TCI.

Group 1:

Propofol will be administered with the Diprifusor (Marsh Pharmacokinetic model, Master TCI pump, Fresenius Kabi; Bad Homburg; Germany) starting at a predetermined target plasma propofol concentration (Cp) of 1.8µg.ml-1 based on a previous study. Further target concentrations were set according to the Dixon up and down method. A failure will be followed by an increase in the target plasma concentration in the next patient by 0.2µg.ml-1 and a success will be followed by a decrease in the target plasma concentration in the next patient by 0.2µg.ml-1. TCI pump will be controlled manually and all the data including BIS and vitals will be recorded through CLADS into a laptop. MOAA/S will be assessed every 15 second for assessing time to loss of consciousness; BIS and HR will be recorded every 5 seconds and MAP and PAP every 10 seconds. Thus, the anesthetic depth control will be assessed based on time to achieve loss of consciousness and by comparing the dose of propofol required for induction and maintenance. BIS overshoots and hemodynamic stability will be noted. In case the patient achieves loss of consciousness within 5 minutes, a 2 minutes observation period will be allowed for achieving target BIS. If the patient does not achieve target BIS after this period, the case will be considered a failure. On the other hand, if the patient achieves target BIS within this period it will be considered a success. In cases where neither LOC nor target BIS will be achieved within 5 minutes will also be considered a failure Vecuronium will be administered at a dose of 0.1 mg.kg-1 after the LOC and the patient will be intubated after 4 minutes. Patients will be ventilated through face mask to maintain normocapnia administering air-oxygen mixture with FiO2 of 0.6 during the period of induction till intubation. Fentanyl infusion 1µg.kg.h-1 will provide analgesia with additional boluses of 1µg.kg-1 before skin incision, sternotomy and at the commencement of CPB. Additional bolus of analgesic supplements (fentanyl 1µg.kg-1) will be given when the mean arterial pressure (MAP) or heart rate exceeds 25% of the baseline <50. If hypertension or tachycardia persists with a BIS≤50, either nitroglycerine infusion or esmolol will be used. In conditions of hypotension, inotropic support and/or vasopressor will be initiated after ensuring normovolaemia. Atropine sulphate will be used to treat bradycardia (heart rate <45b.p.m.) after excluding other treatable causes. The MAP on CPB will be maintained between 50 and 80 mmHg using phenylephrine / nitroglycerine as required. Systemic hypothermia up to 28ºC will be practiced during CPB and patients will be actively re-warmed to 36ºC before separation from CPB.