"Assessment of perioperative difficult airway using STOP-BANG questionnaire among undiagnosed obstructive sleep apnea patients undergoing elective surgery under general anaesthesia": A hospital based case series study.

Obstructive sleep apnea is a condition in which upper airway becomes obstructed during sleep causing hypoxia, hypercarbia, fragmented sleep.  Without proper sleep, the patient may experience excessive daytime sleepiness ,headache, change in behavior, reduced intelligence and even personality change . It is associated with complications like increased risk of hypertension , diabetes, myocardial infarction, stroke, diabetic neuropathy, as well as cognitive dysfunction. The perioperative period is a time of particularly high risk for patients with OSA. Inducing general anaesthesia and maintenance of mask ventilation may be difficult due to airway obstruction from reduced pharyngeal muscle tension, and intubation may be difficult due to the abnormalities of the face or upper airway. Such a difficult intubation can be the main factor leading to increased morbidity and increased death rate  Unfortunately >80% of patients with OSA are undiagnosed before surgery, putting them at risk of complications2 . Gold standard for diagnosing OSA is polysomnography. However it is expensive and not widely available. Therefore anaesthesiologist need a practical pre-operative screening tool to identify patients more likely to have true OSA5 . The aim of the study is to estimate the occurrence and compare utility of OSA screening parameters in predicting difficult mask ventilation and difficult intubation in patients with undiagnosed OSA.

Ethical clearance will be taken from ethics committee . Written informed consent will be taken from all the study subjects before enrolment in the study. It is a prospective observational study of patients posted for elective surgery under general anaesthesia. Patients will be identified from daily OT list that satisfy the inclusion criteria. Brief medical history related to study will be taken. Airway assessment using modified mallampatti score, anthropometric data like height, weight, BMI, neck circumference, thyromental distance, sternomental distance will be measured2,6. Along with routine preoperative investigations the patient will be screened based on STOP BANG questionnaire to determine the risk of OSA.

STOP BANG questionnaire: Snoring? Do you snore loudly(loud enough to be heard through closed doors or your bed partner elbows you for snoring at night)?. Yes/No.  Tired? Do you often feel tired, fatigue, or sleepy, during the daytime( such as falling asleep during driving or talking to someone?. Yes/No.   Observed? Has anyone observed you stop breathing risk of OSA.  or choking/gasping during your sleep?. Yes/No.  Pressure. Do you have or are being treated for high blood pressure?. Yes/No.  Body Mass Index more than 35 kg/m2?. Yes/No.  Age older than 50?. Yes/No.  Neck size large?(measured around adams apple)  For male, is your shirt collar 17 inches/43cm or large?Yes/No  For female, is your shirt collar 16 inches/41cm or large?Yes/No . Gender= male? Yes/No.

For each question, the patient receives one point for a YES response. Sum of each score is taken as the total score. Patients scoring >3 in STOP BANG are taken as patients having OSA .

In the operating theatre, standard ASA monitors like pulse oximeter, non-invasive blood pressure device, Etco2 and ECG leads will be connected to all the patients. Preoxygenation for 3min will be done. Premedication given with inj midazolam(0.05mg/kg) and inj glycoprrolate (0.01mg/kg) will be given. Patients are induced with inj propofol(2mg/kg). Adequacy of mask ventilation will be confirmed and any difficulty in mask ventilation will be recorded. Patients relaxed with inj succinyl choline(2mg/kg), laryngoscopy done using macintosh blade of proper size, and Cormack- Lehane grading will be recorded. Use of additional maneuver, bougie, stylet, external pressure, need of additional or change of operator and ease of intubation are also noted.  Occurrence of difficult mask ventilation , difficult laryngoscopy and difficult intubation are noted using DMV score , Cormack-Lehane grading.

Difficult Mask Ventilation score:  Mask ventilation, did not attempt - 0 , Easy mask ventilation -1 ,Mask ventilation with oral airway device -2 , Difficult mask ventilation ,unstable or requiring -3 , 2 persons , Unable /impossible mask ventilation -4 .

Cormack-Lehane Difficult intubation score:

Able to visualize entire larynx, arytenoids, chords, true and false, epiglottis superior to chords 1

Chords partially obstructed from view with epiglottis, arytenoids visible 2

Epiglottis visible only 3

Soft palate visible only 4

With the above score visualization will be classified as below:

Difficult visualization is described as grade 3&4

Easy visualization is described as grade 1&2.