Prediction of difficult mask ventilation and difficult laryngoscopy by pre-operative ultrasound-based measurement of airway parameters

The unanticipated difficult airway is a potentially life-threatening event. Predicting the difficulties with airway management currently remains a challenge and the incidence of death and brain damage related to airway management is about 25% of relevant incidents reported during general anesthesia. Several authors have shown that the described risk factors have low predictability in anticipating difficult airway. Future research is needed to develop tests with high sensitivities and to better screen difficult face mask ventilation and failed intubation.

Pre-operative ultrasound measurement of the anterior neck soft-tissue thickness at different levels, combined with the commonly used screening tests and risk factor assessment for difficult laryngoscopy might improve the ability to predict difficult laryngoscopy. Research regarding difficult mask ventilation combined with difficult laryngoscopy is extremely limited even though these two aspects of airway management are closely related.

The aim of our study is to evaluate the accuracy of preoperative ultrasound assessment of neck anatomy in predicting difficult mask ventilation and difficult laryngoscopy in patients undergoing elective surgery with general anesthesia

Primary objective:

To correlate preoperative upper airway ultrasound measurements to predict difficult mask ventilation and difficult laryngoscopy

Secondary objectives:

·      To correlate findings of upper airway ultrasound measurements with body mass index (BMI) in predicting difficult mask ventilation and difficult laryngoscopy

·      To compare upper airway ultrasound measurements with conventional clinical assessments in predicting difficult mask ventilation and difficult laryngoscopy

·      To evaluate the demographic variables associated with difficult mask ventilation and difficult laryngoscopy

Methods:

This will be a prospective observational study conducted on 114 adult patients of either sex, between 18-65 years undergoing elective surgeries under general anesthesia with muscle relaxation and endotracheal intubation in various surgical specialties at All India Institute of Medical Sciences, Bhopal, India. Institutional human ethics committee approval will be obtained before starting the trial. In the preoperative area, upper airway ultrasound parameters namely, distance from skin to hyoid bone (DSHB), distance from skin to thyroid isthmus (DSTI), thickness of base of the tongue (TBT) will be noted. Then the patient will be shifted inside the operation theatre and given general anesthesia. Han scale grading and Cormack-Lahane grading will be noted during mask ventilation and laryngoscopy respectively. The results will be analyzed to assess upper airway ultrasound measurements to predict difficult mask ventilation and difficult laryngoscopy.

Outcome parameters:

Ultrasound based airway parameters:

1.     Distance from skin to hyoid bone (DSHB)

2.     Distance from skin to thyroid isthmus (DSTI)

3.     Thickness of base of the tongue (TBT)

Conventional clinical assessment:

1.     Modified Mallampati grading (MMP)

2.     Upper lip bite test

Body mass index (BMI) and other demographic variables like age, gender

Han scale grading

Cormack-Lahane grading