Description

Propofol total intravenous anaesthesia (TIVA) is a preferred technique for providing induction and maintenance of general anaesthesia (GA). As opposed to the conventional inhaled anesthetics for maintaining GA, propofol TIVA has several advantages, such as, lower incidence of postoperative nausea and vomiting (PONV), antinociceptive and anti-inflammatory action, anti-neoplastic activity, and most importantly, its environment disposition (no greenhouse effect); and therefore, has potential to replace inhaled vapors for GA.

The introduction of target-controlled infusion (TCI) pumps has allowed precision control in propofol delivery as compared to the conventional manually operated infusion pumps. In manually operated infusion pumps the clinician regulates the propofol infusion rate to achieve the desired anaesthesia depth, whereas TCI-pumps deliver propofol using inbuilt algorithms based on the pharmacokinetic (PK) and pharmacodynamic (PD) profile of propofol. Two of the most used PK-PD models for propofol delivery are the Marsh model and the Schneider model. Whereas in the Marsh model the user can set the desired target plasma concentration, Schneider model allows the user to set the desired target effect site concentration for achieving adequate depth of GA.

Over the last two decades the evolution and advancement in automated anaesthesia delivery systems, particularly for propofol administration, has made propofol-TIVA delivery more efficient by removing the human interface required for adjusting real-time propofol delivery, both rate and concentration of propofol. Automated anaesthesia delivery systems deliver propofol based on ascertaining frontal cortex electrical activity as determined by the processed electroencephalogram, the bispectral index (BIS) score. These devices regulate propofol delivery based on a feedback loop involving the BIS score (control variable) generated by the patient and the propofol infusion pump (actuator) and attempts to keep the values within a pre-assigned range, consistent with robust GA depth.

Closed loop anaesthesia delivery system (CLADS) is an indigenously developed patented (Patent no.502/DEL/2003 & US 9,108,013 B2) computer-controlled anaesthesia delivery system which works with feedback loop information elicited by BIS monitoring and delivers propofol TIVA to the patient via a non-TCI automated infusion pump. The basic control algorithm is based on the relationship between the infusion rates of propofol and BIS values, taking into consideration the pharmacokinetic variables, such as, drug distribution and clearance. The system updates the EEG data every 5-seconds and calculates the BIS error, a difference between the target BIS and the actual BIS value using the proportional-integral-derivative (PID) controller. During anaesthesia induction the target concentration is achieved in a stepwise manner with BIS feedback received every 5-seconds. During maintenance phase of anaesthesia, the propofol delivery is modified every 1-epoch of 30-seconds duration. In each epoch an average of initial 3-BIS values (of every 5-seconds) and average of last 3-BIS values (of every 5-seconds) are compared, and a trend assessment is made. If the trend indicates increasing BIS values, then higher propofol rate is delivered by the infusion pump (actuator) and vice-versa. The control algorithm is implemented using a personal computer (PC) with a Pentium 4 processor. The PC controls communication with the infusion pump (Pilot-C, Fresenius, Paris, France) and the vital sign monitor (AS5, Datex Ohmeda Division, GE Healthcare, Singapore) through RS 232 serial ports.

CLADS has been extensively used and validated for administering propofol TIVA in patients undergoing both cardiac and non-cardiac surgical procedures. In a multi-centric study on evaluation of anaesthesia delivery by CLADS, it was shown that CLADS maintains depth of anaesthesia with far more precision as compared to manual administration.

A new compact and upgraded version of CLADS (Clarity Medical Private Ltd., Mohali, Punjab Indiais now available. The new version integrates the anaesthetic depth as well as the hemodynamic monitor, the controller, the user interface and the actuator syringe pump into a single, compact and user-friendly module.

The investigators aim to conduct a prospective randomised pilot to compare the multiple connected-unit conventional CLADS with the hermetically unit-integrated CLADS version, with respect to, the adequacy of anaesthesia depth (primary objective); and, performance characteristic, propofol requirement, haemodynamic stability, recovery from anaesthesia and postoperative sedation of the delivery systems (secondary objectives).