Airway Ultrasonography Measurements With Cormack Lehane Classification in Patients With OSA
Condition: Obstructive Sleep Apnea; Difficult Intubation
MeSH terms: Sleep Apnea Syndromes; Sleep Apnea, Obstructive
Study type: Observational

Summary: 
      Airway assessment using ultrasonography can provide an additional information in identifying
      difficult intubation in OSA patients. The main purpose of this study is to find the
      correlation of the ultrasound parameters and the Cormack Lehane Score (CL Score) as well as
      to identify the cut-off point of the ultrasound parameters that would differentiate between
      the easy and difficult intubation.
    

Detailed description: 
      Research design

        1. This is a cross sectional study. Involving face-to-face interview, USG airway assessment
           and Cormack Lehane score assessment. The patient will be identified from locations
           listed below:

             -  Anaesthesia clinic

             -  In the ward, during review by anaesthesia team for elective operation in the
                following day

             -  In the ward, when cases are notified for operations as emergency case

        2. Once consent obtained from the patient, information regarding surgery and date of
           surgery will be recorded in the patient's data collection sheet. Patient's STOPBANG
           score and AHI score will also be recorded.

        3. The airway ultrasonography will be performed by the principal investigator using a
           standardized ultrasound machine (NextGen LOGIC e Ultrasound with 12L-RS wide band linear
           array 5-13 MHz frequency probe) under supervision by a radiologist. The procedure will
           be performed at the recovery bay in the operation theatre. The following measurements
           will be done and recorded for future statistical analysis.

             -  Depth of preepiglottic space (PE)

             -  Distances between epiglottis and midpoint between 2 vocal cords (E-VC)

        4. Cormack Lehane score will be obtained during induction of General Anaesthesia and
           Intubation in OT on the specified OT date. Conventional direct laryngoscope will be used
           for CL score determination. Medical Officer of more than 2 years' experiences in
           anaesthesiology will be requested to intubate the patient to minimize bias. CL scores
           are as described below

      CL 1: Most of glottis Visible CL 2: Half of the glottis seen CL 3: Only epiglottis visible
      CL4: No laryngeal structure visible

      Study area: Hospital Sultanah Nurzahirah, Kuala Terengganu Study population: Adult patient
      age between 18 to 65, diagnosed or suspected OSA, planned for operation under General
      Anaesthesia

      Sample size estimation

        1. st Objective :

             -  To determine the correlation between airway ultrasonography measurements and CL
                score.

             -  Using R package pwr

                  -  For PE

                       -  r: 0.595 (based on Gupta D, 2012), significant level 0.05, power: 0.8

                       -  Number of sample: 19

                  -  For E-VC

                       -  r: -0.966 (based on Gupta D,2012), significant level 0.05, power: 0.8)

                       -  Number of sample: 4

                  -  For ratio PE/E-VC

                       -  r: 0.495 (based on Gupta D, 2012), significant level 0.05, power: 0.8)

                       -  Number of sample: 28

        2. nd and 3rdobjective

             -  2nd objective: To determine the best cut off point of airway ultrasonography
                measurement in predicting the difficulty in intubation using CL (difficult vs less
                difficult)

             -  3rd objective: To determine the accuracy of cut-off point in determining difficult
                intubation. (AUC) )

             -  Receiver Operating characteristics (ROC) curve power calculation using R

                  -  Significance level: 0.05

                  -  Power of study: 0.8

                  -  Kappa: 4

                  -  AUC: 0.7

      Based on previous study, the incidence of difficult intubation in OSA patient is 19.3%. Hence
      kappa: 4. Using pROC package in R, based on the above values and data, the investigators need
      at least 24 cases of difficult intubation and 41 cases of non-difficult intubation (to detect
      AUC of 0.7 from 0.5 null hypothesis). So, total patients required is at least 65

      Sampling method and subject recruitment As mentioned above, this is a cross sectional study.
      Involving face-to-face interview, USG airway assessment and Cormack Lehane score assessment.
      After the samples identified at the specific locations mentioned and they will be approached
      for consent. Once agreed, the patient will be recruited for the study.

      Data analysis

      Statistical Analysis Plan For objective 1

      • Intended statistical analysis: Spearman correlation

      For objective 2 and 3

        -  Using ROC curve

        -  outcome: difficulty status (0 or 1)

        -  test variable: PE, E-VC and ratio PE/E-VC

      AUC in the ROC curve will be calculated accordingly based on the study results
    

Observational model: Case-Control
Time perspective: Cross-Sectional
Sampling method: Non-Probability Sample
Study population: 
        Adult patient age between 18 to 65, diagnosed or suspected OSA, planned for operation under
        General Anaesthesia
      
Keywords: OSA; ultrasound; airway; difficult intubation