The anaesthetist’s most important task during a general anaesthetic is to insure the patient’s breathing and oxygenation are maintained at all times. In some procedures, generally of short duration and of a minor surgical nature, this can be accomplished by allowing the patient to maintain his own natural respiratory rhythm and administering the oxygen and anaesthetic vapours through a hand-held facemask. In longer procedures, and those of a major surgical nature, it is usually necessary to insert a tubular conduit through the mouth or nose directly into the respiratory passage to assure a patent airway under these conditions as well as allowing mechanically-assisted ventilation when a patient is either too deeply anaesthetised to adequately breathe on his own or deliberately paralysed by drugs to provide optimal conditions for the surgeon.
In 1981 when I got my first introduction to anaesthesia as a medical student ‘clinical clerk’, the only method used directly to secure the respiratory passage involved inserting a long, narrow plastic tube into the upper trachea, and was referred to as tracheal intubation. This generally required the patient to be deeply asleep with the muscles paralysed so that the anaesthetist, using an instrument called a laryngoscope, could insert a blunt steel blade with a bright light at its tip through the mouth and deep into the throat to expose the often well-hidden tracheal opening into view and allow the tube to be passed into the trachea through the vocal cords. Even in experienced hands this could on occasion be a quite difficult manoeuvre. Failing to insert the tube quickly and establishing ventilation or mistakenly inserting it into the oesophagus could result in hypoxic brain injury if not cardiac arrest. Even successful tracheal intubations by this technique have on the rare occasions been associated with injuries to the teeth, the soft tissues of the pharynx as well as the vocal cords, larynx and trachea and the forceful extension of the neck that may be required has in a few individuals resulted in serious neck spine injury.
In the early 1990s a new method of securing the airway under anaesthesia arrived on the Canadian anaesthetic scene. We were told of a new airway device called the laryngeal mask airway (LMA) recently imported from England where it was known as the ‘brain airway’ in honour of its inventor Dr. Archie Brain. Like the older tracheal airway, it consisted of a tube inserted via the mouth in order to assure a safe conduit for oxygen and vapour anaesthetics into and out of the lungs. However, unlike the tracheal tube, it only needed to be inserted into the proximal pharynx so that the wide oval inflatable cuff covers to outer borders of the laryngeal opening without needing to pass the vocal cords or enter the trachea at all. The LMA can be inserted simply by opening the patient’s mouth and sliding in manually without need of a laryngoscope, although in some situations an anaesthetist may prefer using one. Smaller ‘induction’ doses of anaesthesia are needed compared to tracheal intubations using the laryngoscope and muscle paralysis is generally not required.
The patient can either breathe on his own via this airway device or his breathing can be mechanically assisted at deeper planes of anaesthesia. However, The LMA isn’t just an airway conduit, but also an airway instrument in its own right. Once in place, the lumen of the LMA is aligned closely to the tracheal opening and a narrower tracheal tube can be passed through the LMA and advanced into the trachea either ‘blindly’ or with the aid of a flexible fibre optic bronchoscope. Many anaesthetists employ such combined techniques in situations where conventional direct laryngoscopic intubation is deemed difficult due to anatomical restrictions or dangerous due to pathological derangements.
In my own anaesthetic practice LMA insertion has by no means supplanted direct laryngoscopic tracheal intubation, but certainly has reduced the percentage of patients undergoing the latter technique in general anaesthesia. Even when I’m planning a tracheal intubation, I make sure I’ve got several sizes of LMA available. I can count several cases these last 15 years when an LMA has enabled me to secure an airway in which the only other alternative would have been an emergency tracheotomy.
Most physicians in Canada are members of the Canadian Medical Protective Association, a medical-legal organisation that deals with any legal problems members may encounter in their practices. Premiums are assessed according to the risk of each speciality. A generation ago anaesthesiology was grouped amongst the higher risk specialities such as neurosurgery and obstetrics. With continual improvements in resident (registrar) training, monitoring and technical developments, anaesthesiology liability risk has dropped well down into the middle ranks of the specialities. No disrespect to the marvellous new computerised monitors and the countless pharmacological improvements in anaesthesia, but I consider the laryngeal mask airway (LMA) the single greatest innovation in the field not only because of its great utility, but because of its simplicity...just a hollow, single piece of silicon plastic with no electronics or moving parts, relatively cheap and reusable 100 or more times, easy to explain to and teach to the greenest of novices.
A final note of interest is the story relating to how Dr. Brain developed the LMA. He made plaster casts of the throats of cadavers to visualise the actual form of the upper human airway and devised the LMA based on the morphology of these casts.
Dr. Alan H Tallmeister is a consultant anaesthetist, member of anaesthesia department Scarborough Hospital in Toronto