This document summarizes research on using sonography (ultrasound) to predict difficult intubations compared to traditional pre-anesthetic airway assessment methods. Several studies found that sublingual ultrasound was more accurate at identifying difficult laryngoscopy grades than individual traditional measures like Mallampati score and thyromental distance. However, the clinical value of screening tests remains limited. More research is needed to validate ultrasound techniques and compare ultrasound to combined traditional methods.

1. Abbreviated Data Sheet
Union University
Sonography In Pre-anesthetic Airway Evaluation: Integrative
Research Review
Scott Awtry, Brad Beckstead, Chris Courtney, Mitch Frank, Cory York
Clinical Question
Results
Discussion
Background
• Airway assessment consists of a compilation of the following:
thyromental distance, inter-incisor gap distance, and mallampati
scores to predict easy or difficult intubations in pre-anesthetic
patients.
• Cormack and Lehane defined difficult intubation “as poor glottic
visualization during direct laryngoscopy, or a high-grade laryngeal
view with no ability to see the vocal cords or the glottic view”
(Cormack & Lehane, 1984).
• Easy intubation is classified as a Cormack and Lehane grade 1 or 2.
Difficult intubation is classified as Cormack and Lehane grade 3 or 4
(Cormack & Lehane, 1984).
• Due to subjectivity in performing these traditional methods, a more
reliable and objective approach is needed.
• The purpose of this IRR is to synthesize evidence to determine the
efficacy of using sonography in accurately predicting a Cormack and
Lehane laryngoscopic grade
In the adult population undergoing general anesthesia, is sonography
more sensitive in identifying an accurate Cormack and Lehane
laryngoscopic grade when compared to traditional methods of pre-
anesthetic airway assessment?
Methods
Inclusion Criteria:
• Any study involving ultrasonography for
airway evaluation prior to intubation
• Adult patients- 18 years of age or older
• Patients of any race or gender
• Patients of any ASA classification
• Experimental research design and
meta-analysis studies conducted from
2005-2014
• Sublingual ultrasound is well-tolerated, simple and efficient method for pre-operative
airway assessment and suggest that sublingual ultrasound alone is sufficiently
effective at identifying possible difficult intubation patients that would otherwise be
identified by laryngoscopy (Hui, et. Al 2014).
• Currently available screening tests for difficult intubation have only poor to moderate
discriminative power when used alone. Combinations of tests add some incremental
diagnostic value in comparison to the value of each test alone. The clinical value of
bedside screening tests for predicting difficult intubation remains limited (Shiga, et. Al
2005)
• Sonographic measurements of anterior neck soft tissue were greater in difficult
laryngoscopy group compared to the easy laryngoscopy group at the level of the
hyoid bone and thyrohyoid membrane. No correlation between sonographic
measurements and clinical screening tests (Srikar, et. Al 2011)
• The non-invasive ultrasonographic modification of invasive Cormack Lehane
classification for pre-anesthetic airway assessment can supplement the presently
available non-invasive modalities of pre-anesthetic airway assessment including the
Mallampati Classification (Gupta, et. Al 2012).
Exclusion Criteria:
• Studies including only pediatric
population
• Studies of surgical procedures that do
not require endotracheal tube intubation
• Studies greater than 10 years old
• Studies not published in English
Results: Airway Evaluation Techniques
Adhikari, S., Zeger, W., Schmier, C., Crum, T., Craven, A., Frrokaj, I., & ... Shostrom, V. (2011). Pilot study to determine the utility of point-of-care ultrasound in the
assessment of difficult laryngoscopy. Academic Emergency Medicine: Official Journal Of The Society For Academic Emergency Medicine, 18(7), 754-758.
doi:10.1111/j.1553-2712.2011.01099.x
Cormack, R. S., & Lehane, J. (1984). Difficult tracheal intubation in obstetrics. Anaesthesia, 39(11), 1105-1111. doi:10.1111/j.1365-2044.1984.tb08932.x
Gupta, D., Srirajakalidindi, A., Ittiara, B., Apple, L., Toshniwal, G., & Haber, H. (2012). Ultrasonographic modification of Cormack Lehane classification for pre-anesthetic
airway assessment. Middle East Journal Of Anaesthesiology, 21(6), 835-842.
Hui, C. M., & Tsui, B. C. (2014). Sublingual ultrasound as an assessment method for predicting difficult intubation: a pilot study. Anaesthesia, 69(4), 314-319.
doi:10.1111/anae.12598
Shiga, T., Inoue, T., Sakamoto, A., & Wajima, Z. (2005). Predicting Difficult Intubation in Apparently Normal Patients: A Meta-analysis of Bedside Screening Test
Performance. Anesthesiology, 103(2), 429-437. doi:10.1097/00000542-200508000-00027
Singh, M., Chin, K. J., Chan, V. W., Wong, D. T., Prasad, G. A., & Yu, E. (2010). Use of Sonography for Airway Assessment. American Institute of Ultrasound in
Medicine, 29, 79-85.
Soyuncu, S., Eken, C., Cete, Y., Bektas, F., & Akcimen, M. (2009). Original Contribution: Determination of difficult intubation in the ED. American Journal Of Emergency
Medicine, 27905-910. doi:10.1016/j.ajem.2008.07.003
Wadhwa, A., Komatsu, R., Sengupta, P., Akca, O., Sessler, D., Ezri, T., & Lenhardt, R. (2007). Ultrasound quantification of anterior soft tissue thickness fails to predict
difficult laryngoscopy in obese patients: A-269. Anesthesia & Intensive Care, 35(1), 32-37.
References
Study Sample Size Variables of
interest
Study
Design
Statistics Results Limitations
C.M. Hui & B.C. Tsui,
2014
100 adult patients
>17 years old
• Sublingual ultrasound
• Mallampati score
• Thyromental distance
• Inter-incisor gap
• Neck extension
• Pilot study
• Quantitative
analysis
• P = <.0001
• Sensitivity 70%
• Specificity 97%
Sublingual ultrasound was more
sensitive than mallampati score,
thyromental distance, inter-incisor gap,
and neck extension.
Different physicians performed subjective
airway assessment and also graded
laryngoscopic view.
T. Shiga, Z. Wajima,
T. Inoue, A.
Sakamoto, 2005
50,760 adult
patients
• Difficult intubation
• Mallampati
Classification
• Thyromental distance
• Combination
(Mallampati and
thyromental)
• Inter-incisor gap
Meta-analysis • Mallampati classification:
• Sensitivity 49%
• Specificity 86%
• Thyromental distance:
• Sensitivity 20%
• Specificity 94%
• Combination
• Sensitivity 36%
• Specificity 87%
• Inter-incisor gap:
• Sensitivity 22%
• Specificity 97%
Currently available screening tests for
difficult intubation have only poor to
moderate discriminative power when
used alone.
• Studies differed in defining Cormack and
Lehane difficult intubation grades
• Studies did not define whether cricoid
pressure was used
S. Adhikari, W.
Zeger, C. Schmier,
T. Crum, A. Craven,
I. Frrokaj, H. Pang,
V. Shostrom, 2011
51 adult patients
with average age of
53.1 years
Anterior neck soft tissue
measurements at the level
of hyoid bone and
thyrohyoid membrane
Perspective
observational study
P < 0.5 Sonographic measurements of
anterior neck soft tissue were greater
in difficult laryngoscopy group
compared to the easy laryngoscopy
group at the level of the hyoid bone
and thyrohyoid membrane.
• Small sample size
• Only 6 patients in difficult laryngoscopy
group
• Investigators not blinded to the study
hypothesis
• Uncontrollable variables: experience of
anesthesia providers, laryngoscopy
equipment used, number of intubation
attempts, external laryngeal maneuvers
during intubation
D. Gupta, A.
Srirajakalidindi, B.
Ittiara, L. Apple, G.
Toshniwal, H. Haber,
2012
49 adult patients • Distance from the
epiglottis to the midpoint
of the distance between
the vocal folds
• Depth of the pre-
epiglottic space
• Total time taken by the
operator to achieve the
final ultrasonic image.
• Pilot study
• Quantitative
analysis
• P < 0.5
• Sensitivity 67%
• It was observed that there was a
correlation of the distance between
the epiglottis and the vocal cords
with the Cormack Lehane Grading.
• The average time taken to
complete the ultrasound
examination of airway in the
preoperative area was 31.7 ± 12.4
seconds
• Small sample size
• No Cormack Lehane grade IV patients in
study
• Only Cormack Lehane grade III patients
were included in the study
Conclusion
Search Process:
• Sources: Google Scholar, Pubmed, CINAHL, Medline, Ebsco Host
• Search terms: Ultrasound, Difficult airway, Difficult laryngoscopy, Sonography, and
Cormack Lehane
• Fifteen studies were found
• Eleven studies were excluded due to duplicated information, small sample sizes, or not
meeting inclusion criteria
• Four articles met inclusion criteria and therefore reviewed
• Search methodology used to retrieve articles
• Each reviewer or investigator was responsible for finding a minimum of three articles
related to the studied topic.
• A ranking sheet was used to determine appropriateness of articles.
• Difference between reviewers were handled with respect . Majority vote was used
for handling of disputes between data included.
Strengths of this systemic review:
• Provides strong statistical data through all articles reviewed
• All studies are based on same airway classification criteria
Limitations of this systemic review.
• Few ultrasonography studies available for review
• Studies do not distinguish between different patient populations (e.g. Obesity)
Implications (clinical, administration, or education)
• Use of ultrasonography in airway classification implicates the necessity for competence training
• Introduction of ultrasonography into pre-anesthetic airway assessment could improve patient safety
Recommendations for future studies
• Further study is needed to confirm the validity of results already produced
• Study comparing ultrasonography and the combined use of traditional methods
• Study comparing effectiveness of different ultrasonography techniques
After reviewing the literature, sublingual ultrasound was found to be the most
effective and objective individual method for determining the correct Cormack
Lehane airway grade. In addition, other ultrasonography techniques prove to
be superior to traditional methods of airway classification.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Mallampati Thyromental Distance Incisor Gap Mallampati &
Thyromental Distance
Sublingual Ultrasound Epiglottic Measurement
49%
20% 22%
36%
73%
67%
86%
94%
97%
87%
97%
Sensitivity: If a person has a difficult airway, how often will the assessment technique relfect a difficult laryngoscopy and intubation (True positive rate)?
Specificity: If a person does not have a difficult airway, how often will the assessment technique reflect an easy laryngoscopy and intubation (True negative rate)?