Description

Endotracheal tube (ETT) is the gold standard conduit for providing controlled ventilation during general anesthesia (GA). However, since the introduction of classic laryngeal mask airway (LMA) in the 1980's and serial evolution of supra-glottic airway devices (SGA) thereafter, LMAs have become a reliable alternative to ETT for carrying out controlled ventilation. Interestingly, of the additional advantages that the LMA proffers, including, a lower incidence of postoperative sore throat (POST) and superior hemodyamic profile during surgery; its ability to maintain equivalent depth of anesthesia (in comparison to when ETT-GA) with lower anesthetic requirement, is intriguing.

A handful of studies have demonstrated that the end-tidal isoflurane concentration required for maintenance of GA is 0.2 -0.53% greater with use of ETT as compared to LMA. However, the evidence generated by these studies remains unsubstantiated because in them, anaesthetic gas concentration was titrated to patient's clinical profile like heart rate and blood pressure without the backing of specific protocol for maintaining depth-of-anaesthesia. Therefore, for credible evidence, assessment of quantitative anesthetic requirement for achieving and sustaining a steady anesthesia depth with either LMA or ETT warrants confirmation with the use of an objective depth-of-anesthesia monitor, such as, bispectral index (BIS).

Closed loop anaesthesia delivery system (CLADS) is an indigenously developed patented (502/DEL/2003) computer-controlled and BIS-guided automated anesthesia delivery system. CLADS, which runs on a control algorithm based on the relationship between diverse rates of propofol infusion and the processed EEG variable; delivers propofol infusion at a rate which is continuously adjusted by patient's state of depth of anesthesia as per BIS monitoring input. This automated system maintains anaesthesia depth with high accuracy and objectively determines propofol delivery quantitatively.

Of the several variants of SGA available today, the ProSeal laryngeal mask airway (PLMA) 9 is preferred for controlled ventilation for its unique design that serves dual function of a ventilation tube and an oropharyngeal drainage tube for excluding gastric contents from getting aspirated through the peri-laryngeal cuff seal.

Given that CLADS can help us to accurately quantify anaesthesia, we hypothesize that there is no difference in anesthesia requirement for GA maintained through an ETT or a PLMA. This randomized controlled study aims to compare: anaesthesia requirement as determined by total propofol consumption (primary objective); intraoperative hemodynamic profile and incidence of POST (secondary objectives) in patients undergoing laparoscopic surgery with controlled ventilation via ETT or PLMA.