Cormack RS & Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia 1984; 39: 1105-1111.
RHH Journal Club. February 23rd, 2012. Dr Ashok Elayaperumal
No free full-text available
How can we prepare for difficult tracheal intubations in obstetric patients?
Introduction:-Difficult intubation is a factor most commonly associated with disasters in obstetric anaesthesia .
Cormack and Lehane classification:- Forward displacement of larynx or the upper teeth, and backward displacement of tongue can make intubation difficult. Size and mobility of the tongue are not easy to see and a normal looking patient can have unpredictable difficult airway . Difficult intubation has been classified into four grades, according to the view obtainable at laryngoscopy. Grade 1. If most of the glottis is visible thenthere is no difficulty. Grade 2. If only the posterior extremity of the glottis is visible then there may be slight difficulty. Grade 3. If no part of the glottis can be seen, but only the epiglottis, then there may be fairly severe difficulty. Grade 4. If not even the epiglottis can be exposed then intubation is impossible except by special methods.
Relevance to obstetrics:- Grade 4 are probably not the cause of maternal death since severe neck pathologies are rare and if so will be known early. This leave grade 3 as a main cause
Statistical argument:- If the grade 3 case occurs about once every 2 years in routine work and if it takes about 8 years to become a consultant then each person can anticipate meeting this problem about four times before he is a consultant.
Possible Solutions :- However the problem can be simulated in routine anaesthesia, so that a drill for managing it can be practised. Laryngoscopy is carried out as usual, then the blade is lowered so that the epiglottis descends and hides the cords. Intubation has to be done blind using the Macintosh method, where introducer is inserted well anterior, up against the epiglottis . This ensures that it does not enter the oesophagus. There are then only three places it can go, namely the trachea, or left or right pyriform fossae. If it is kept in the mid-line then it will enter the trachea the first time, but if it deviates then it will stick in one of the pyriform fossae. It should then be withdrawn and shifted to the left or right. This can be helpful as part of the training before starting in the maternity department, supplementing the Aberdeen drill. Most common cause of difficulty for a beginner is not putting the patient’s head in Magill’s position “ Neck should be flexed , which may require the insertion of a pillow , whilst the head is extended on the atlas”
Guidelines:- It is always worth attempting to intubate in grade 3 cases, but never worth it for grade 4 cases , in obstetric practice. Grade 3 cases Most , if not all should be fairly easy to intubate provided Macintosh method has been practiced. If tube enters oesophagus ,take out , re-apply cricoid , Suck out pharynx ,oxygen if needed and try again . 3 attempts are reasonable before failed intubation Grade 4 cases Macintosh method not suitable , because success depends on using epiglottis as a guide. Introducer if kept forward will stick to epiglottis and moving it backward will enter oesophagus. Success is only a matter of luck. Failed intubation drill should be started . Options are GA without tube, Local infiltration, Spinal or Epidural
Sellick’s Manoeuvre:- Even the correctly applied cricoid pressure may not be fully effective. But it will convert a flood into a trickle. Intubation is impossible in a flood, but a trickle is manageable . Releasing cricoid pressure must be a last resort , if done patient must be put head down on her side
Conclusions:- Grade 3 cases are rare, almost like serious problems in routine air travel . Pilots carry out emergency drills in a flight simulator. So how can we train anaesthetists on grade 3 cases except simulating on routine lists?
“ Using an unfamiliar method in an emergency is a recipe for disaster. Even one preventable death is one too many.”