Comparison of ease of insertion of two different types of second generation Laryngeal mask airways in aural surgeries under total intravenous anaesthesia

Inhalational anaesthetic agents have remained the main stay in the conduct of anaesthesia. This is primarily because of their ability to produce surgical anaesthesia without the need of hepatic or renal metabolism for their elimination. However, many side effects of inhalational agents have been noticed like sensitization of myocardium by halothane and nephrotoxicity of methoxyflurane and operation theatre pollution. In addition, nitrous oxide which is used as a carrier gas with inhalational agents, can cause ozone layer depletion. To overcome these side effects of inhalational anaesthetic agents and nitrous oxide; an alternative technique was thought of. One such alternative technique is total intravenous anaesthesia (TIVA) where in there is total avoidance of nitrous oxide and inhalational anaesthetic agent and operative anaesthetic depth is maintained by continuous infusion of intravenous anaesthetic agent.

Advantages of TIVA are1

1. Simplicity of technique and readily acceptance by patients.

2. Produces high quality anaesthetic condition

3. Minimal cardiovascular depression.

4. Avoidance of deleterious effect of volatile anaesthetics eg., hepatotoxicity

5. Speedy and complete recovery.

6. Avoids malignant hyperthermia.

7. Reduction in theatre pollution

8. Avoids distention of air-filled spaces within patient’s body, which is due to nitrous oxide.

9. Avoids postoperative diffusion hypoxemia

10. Decreases the incidence of PONV

 Propofol is currently the most suitable anaesthetic agent for total intravenous anaesthesia (TIVA); it allows for rapid changes in anaesthetic depth and a rapid, clear-headed recovery. Also, low context sensitive half-time 2 makes it theoretically the best available agent for long procedures under TIVA.

Furthermore, propofol attenuates airway reflexes to the extent that the laryngeal mask airway (LMA) may be positioned easily without neuromuscular block 3

The Laryngeal Mask Airway (LMA) is a supraglottic airway device designed to maintain a clear airway, which sits outside of and creates a seal around the larynx. Compared with the face mask, the LMA allows for a more "handsfree approach" to airway management 4. In difficult airway management, LMA can bypass obstruction at supraglottic level and allow rescue oxygenation and ventilation, provided that mouth opening is sufficient 5.

The LMA-ProSeal is a second generation supraglottic airway device with modified cuff and drainage tube, designed for better seal with both the respiratory and gastrointestinal tracts, not compromising the access to the alimentary tract. 6,7,8

The I-gel airway is a new supraglottic airway device with a non-inflatable cuff, composed of soft gel like, transparent thermoplastic elastomer. It is designed to achieve a mirror impression of pharyngeal and laryngeal structures and to provide a peri laryngeal seal without cuff inflation. A drain tube is placed lateral to the airway tube, which allows insertion of gastric tube.9 It has the potential advantages of easier insertion, minimal risk of tissue compression, stability after insertion and an inbuilt bite block.10

Patients undergoing surgery under general anesthesia require an adequate level of hypnosis to protect them from stress of awareness and recall of traumatic interventions. Conventionally, the hypnotic state is assessed by observing changes in the respiratory and cardiovascular system.

However, in recent times, the hypnotic state is assessed by monitoring the electrical activity of the brain which directly indicates the depth of anesthesia. This has been made possible by the introduction of newer and more sophisticated delivery system for total intravenous anesthesia (TIVA) and the Bispectral index monitor, which allows a computed analysis of real time EEG to assess the depth of anesthesia continuously.