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).