Inhalation anaesthetic were backbone of general anaesthesia (GA) practice till the time
an intravenous anaesthetic, propofol was introduced in early 1970's and its commercial
availability in 1980's, which led to the resurgence in the practice of total intravenous
anaesthesia (TIVA). TIVA is now being adopted as a preferred technique for providing GA
because of scores of inherent advantages, like, reduced PONV incidence, improved quality
of post-anaesthesia recovery, anti-inflammatory and anti-oxidant action, anti-neoplastic
activity, analgesic action, and absence of greenhouse effect among many others.Over the
years propofol-TIVA delivery has become more methodical and precise owing to the use of
target controlled infusion (TCI) systems. TCI systems use propofol pharmacokinetic (PK)
or pharmacodynamics (PD) models which predict either the plasma or the effect-site
propofol concentration required for maintenance of GA steady-state during surgery. The
'Diprifusor' TCI-system was the first commercially available propofol TCI-system. The
'Diprifusor' TCI-system was a 'closed' TCI-system which required a special electronically
tagged pre-filled propofol syringe to be attached to the TCI-pump. The current TCI
technology has evolved with the introduction of the 'open' TCI concept wherein syringes
of any configuration can be attached to the TCI-pumps having pre-programmed propofol
PK-PD models. Currently, the two most commonly used PK-PD models that drive TCI systems
to deliver TIVA are the 'Marsh' and 'Schneider' models. Whereas Marsh model targets blood
plasma concentration of propofol for anaesthesia maintenance, the Schneider model targets
effect-site concentration in the brain. A recent advance in propofol TIVA delivery has
been the development of automated closed loop anaesthesia delivery system. These devices
deliver propofol based ascertaining patient's frontal cortex electrical activity as
determined by bispectral index (BIS) score and then keeping the values within a
pre-assigned range consistent with robust GA depth. Closed loop anaesthesia delivery
system (CLADS) is an indigenously developed patented (502/DEL/2003) computer-controlled
anaesthesia delivery system. CLADS typically works with feedback loop information
elicited by BIS monitoring and delivers propofol TIVA to the patient via a non-TCI
automated infusion pump. This basis of CLADS is the control algorithm based on the
relationship between diverse rates of propofol infusion and the processed EEG variable.
Although propofol delivery by CLADS is based on pharmacokinetic model but for greater
precision and efficient administration, its delivery trigger is directly linked with
feedback mechanism involving patient's EEG profile as monitored by the BIS scores. In a
multicentre 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. Queerly while TCI & CLADS technology evolved over a period of time; there
is no data available comparing the efficacy of TCI delivered propofol-TIVA versus
automated propofol delivery systems. Based on additional feedback loop incorporated to
the PK-PD model the investigators contend that automated propofol TIVA as administered by
CLADS is likely to be superior to TCI system in achieving and sustaining anaesthesia
depth. This randomized controlled study aims to compare the efficacy of CLADS-driven
propofol TIVA versus TCI administered propofol TIVA in adult patients undergoing
non-cardiac surgery with respect to: adequacy of anaesthesia depth maintenance (primary
objective), performance characteristic of propofol delivery system, propofol requirement,
hemodynamic stability, recovery from anaesthesia and postoperative sedation (secondary
objectives).