Incidence and predictors of difficult mask ventilation and intubation in patients scheduled for coronary artery bypass surgery – a prospective observational study

Difficult airway is defined as ‘’the clinical situation in which a conventionally trained anesthesiologist experiences difficulty with face mask ventilation of the upper airway, difficulty with tracheal intubation or both.’’ Predictors of difficult airway include age, sex, BMI, ASA classification, external signs like, facies, facial hair, body habitus, head and neck pathology, airway examination including cervical spine mobility ,dentition, thyromental distance, sternomental distance, jaw protrusion, mallampatti classification, neck circumference, history of snoring.

 Patients undergoing coronary artery bypass grafting invariably have physiologically low cardiac reserve. They are also mostly associated with obesity, diabetes mellitus, hypertension, metabolic syndrome making them difficult airways. Duration of successful intubation (DSI) in these high risk patients should be less in order to prevent adverse events on myocardial oxygenation while securing the airway. Therefore it is essential to preoperatively clinically assess the airway and determine the predictors of difficult mask ventilation and intubation. In  this study we also assess the correlation of our clinical prediction with real time mask ventilation and intubation.

 The ASA originally defined difficult intubation as requiring more than 3 attempts or taking  longer than 10 minutes to complete using conventional laryngoscopy.

In order to assess difficult tracheal intubation and difficult mask ventilation there are scales of difficulty. Difficult mask ventilation grading includes usage of airway adjuncts, 2 hand technique, usage of muscle relaxant. Intubation difficulty scale includes 7 contributors namely, number of supplementary attempts, number of supplementary operators, alternative techniques used, glottic exposure (Cormack and lehane grading), lifting force applied during laryngoscopy, necessity of external laryngeal pressure and position of the vocal cords. Duration of successful intubation is also taken into account.

Patients undergoing coronary artery bypass graft surgery can have higher incidence of difficult airway. Awareness about the incidence and predictors of difficult airway in CABG patients will help the anesthesia provider in being adequately prepared for management of a difficult airway situation thereby reducing the laryngoscopy related adverse events on myocardial oxygenation.

 Hence in this observational study we will be clinically assessing the airway of patients undergoing coronary artery bypass surgery preoperatively and determine the difficulty of mask ventilation and intubation.