Accurate prediction of a difficult airway patient remains a challenge among laryngoscopists and anesthesia providers. Despite the lack of sensitivity and specificity of routine preoperative airway tests, many providers still perform them, suggesting they may still guide and influence airway planning. The most commonly used Mallampati exam has a low sensitivity. Our hypothesis was that digital documentation of the airway exam would improve intraobserver reliability between airway exams and provide more consistent information for airway providers. We obtained written informed consent from 250 patients presenting to the UF Health Shands Presurgical Center to participate in an observational cohort study. Their airway exam was photographed and uploaded into the electronic medical record. Data extracted from the electronic medical record were reviewed by three independent investigators. From chi-square analyses, there were significant differences (
Accurate prediction of a difficult airway patient remains a challenge for anyone entrusted to obtain an artificial airway. Many preoperative tests have been studied and validated to assess patients for difficulty, such as observing thyromental distance, degree of mouth opening, neck range of motion (ROM), ability to protrude the lower jaw beyond the upper incisors (prognath), and other characteristics. In the 1980s, Mallampati initially described a correlation between the visualization of oropharyngeal structures and difficult laryngoscopy [
An ideal exam to predict a difficult airway would have a high sensitivity, a high specificity, and a high intraobserver reliability. When studied, the value of the Mallampati score as a single predictor of a difficult airway showed a specificity of 0.84, a positive predictive value of 0.10, and a sensitivity of 0.64 [
Airway examination also involves assessing facial hair, neck mobility, and the patient’s ability to sublux the jaw. Cervical spine limitation has been shown to increase the likelihood of a difficult intubation [
After obtaining Institutional Review Board approval, 250 patients presenting to the University of Florida (UF Health) Shands Presurgical Center from March until April 2015 were approached and gave written informed consent to participate in the study. Since 2015, all patients who have presented for preoperative evaluation at the center in preparation for surgery have undergone a photographical examination of their airway as routine practice. N = 250 would be able to estimate Kappa statistic (agreement) with a 95% confidence interval ± 0.14. Participants 18 years or older were enrolled on days when a designated study team member was present in the clinic. There were no other exclusion criteria.
All patients had their airway exam photographed and uploaded into the electronic medical record. The Mallampati exam was photographed with the patient sitting in a chair with an iPad mini 2 (Apple Inc., Cupertino, CA, USA) level with and within 6 inches of the mouth. Maximal neck ROM without pain was photographed from a profile view. The patient’s ability to prognath was also photographed from profile view. Further description of how the images were obtained has been previously described [
A single investigator, not involved with evaluating the pictures, extracted the following data from the written preassessment documented in the electronic medical record: age, gender, body mass index, Mallampati score, mouth opening greater than 3 finger breadths, thyromental distance greater than 6 cm, whether the patient had full neck ROM, and the presence of dentures or missing teeth. Three investigators (a certified registered nurse anesthetist with 10 years of experience, a junior faculty member, and a senior faculty member) reviewed all the extracted data to determine whether they predicted that there was a reasonable possibility that the patient would be difficult to intubate. The single investigator also extracted the laryngoscopic view and the method of intubation for each patient from the electronic anesthesia record. Correlations between airway exam and anesthetic management were considered secondary outcomes.
All analyses were conducted in JMP Pro 13.0 (SAS Institute Inc., Cary, NC, USA). Categorical measures were summarized by percentages and continuous measures were summarized by means and standard deviations. Associations between categorical measures were assessed with chi-square analyses.
A total of 250 patients were enrolled in the study, none of whom withdrew. Seventeen patients had an incomplete Mallampati exam in the electronic medical record, so those charts were not reviewed for perceived possible difficulty with intubation. One patient did not have a complete set of pictures, so they were not included in the pictures assessed by the reviewers. One hundred and twenty-nine patients out of 131 had a Cormack–Lehane assessment of the laryngeal structures under direct laryngoscopy. Eleven of 13 patients had a Cormack–Lehane assessment recorded after video laryngoscopy.
Interrater agreement was inconsistent and was mostly in fair to good range (
The incidence of difficult intubation varies in the literature, but it is in the range of 1% to 10%. Complications associated with difficult or failed intubation range from mild to serious complications, such as death or brain damage [
Our study demonstrated a range of Mallampati scores similar to those found in other studies, with over 50% of patients having a ranking of Class 1 or 2. The Mallampati class rating did not appear to correlate or predict the view seen at the time of laryngoscopy nor the method of intubation chosen by the provider, supporting its lack of sensitivity for predicting intubation difficulty. Poor interrater reliability has been demonstrated for many of the airway tests used for assessment, so it is not surprising that our study demonstrated this result as well [
Phonation during performance of the Mallampati test has been reported to increase the false negative rate of the test [
There was no agreement between the assessments made using a photograph versus the preoperative airway assessment documented in the electronic medical record. One weakness of the study is that the source of the documented airway assessment in the record is unknown: whether the assessment was made from the photographs alone, by the provider examining the patient in the preoperative clinic, or by the provider consenting the patient on the day of surgery is unclear. The lack of agreement could be due to this uncertainty but it could also support the findings that assessments vary among raters. Other variables that could impact the Mallampati class assessment are patient position or provider level of training. The photographs were taken with patients sitting upright, while day-of-surgery airway assessments are usually performed with the patient lying supine on a stretcher. Several studies have compared Mallampati class in the supine versus upright position and found that differences in position can affect the results. Two studies, one by Khan et al. and another by Singhal et al., found that the upright position improved Mallampati class compared to the supine position [
The level of training may also impact the ability to predict intubation difficulty using preoperative airway assessment tests. A study by Celebi compared difficult airway prediction among anesthesia residents in different years of residency and found significant interobserver variability, especially with the use of the Mallampati test and assessment of mouth opening [
Our study has several other weaknesses. We used a low number of raters and small sample size. It is possible that with a larger number of raters as well as patients, the results might have been different. The electronic medical record documentation of airway assessment as well as airway management was sometimes incomplete, which could have affected our results as well. It is unknown whether the airway assessment documented on the day of surgery was a de novo evaluation by the anesthesia providers caring for the patient or a repeat evaluation of the photographs in the electronic record. There was still significant variability in difficult airway prediction, regardless of whether the assessment was from a preoperative exam versus a photograph.
Is a picture worth a thousand words? Is airway assessment from a photograph as opposed to a dynamic airway assessment via a physical exam superior? This remains unclear. Poor lighting can influence a photographic result, but it can also affect an airway assessment by a physical exam. The fact remains that no single airway assessment test or combination of tests have been proved to be sensitive or specific enough for predicting airway difficulty [
The value of the tests themselves to predict a difficult airway may lie in the focus on clinical examination and the thought process generated by the encounter. In a provocative but still relevant editorial titled “Predicting difficult intubation: worthwhile exercise or pointless ritual?”, Yentis argues that although attempting to predict intubation difficulty is unlikely to be accurate, it does force the anesthesia provider to examine and assess the airway before formulating an airway management plan [
Based on a review of the literature and our findings, it is evident that accurate prediction of airway difficulty is nuanced and remains a challenge. The evidence for photographs of the airway assessment being superior to bedside evaluation is lacking since both demonstrate low specificity, sensitivity, and interrater agreement. However, photographic documentation of airway assessment tests may allow for airway evaluation prior to the day of surgery.
Conceptualization, J.W.S., F.K.E., T.V.; Methodology, J.W.S., F.K.E., T.V.; Formal Analysis, J.W.S., F.K.E., T.V., L.C.B., N.N.A; Data Curation, J.W.S., F.K.E., T.V., L.C.B., N.N.A., D.S.; Writing—Original Draft Preparation, J.W.S., F.K.E., T.V., L.C.B., N.N.A., D.S.; Writing—Review & Editing, J.W.S., F.K.E., T.V., L.C.B., N.N.A.; Supervision, J.W.S., F.K.E.; Project Administration, J.W.S., F.K.E., T.V.
This research received no external funding.
The authors declare no conflict of interest.
Characteristics of study (from preassessment).
Characteristic | Mean ± Standard Deviation or n (%) |
---|---|
Age (years) | 60.7±14.0 |
Gender | |
Female | 137 (54.8%) |
Male | 113 (45.2%) |
Body mass index | 31.0±7.5 |
Mallampati score | |
Class 1: Entire tonsil clearly visible | 59 (23.6%) |
Class 2: Upper half of tonsillar fossa visible | 113 (45.2%) |
Class 3: Soft and hard palate clearly visible | 52 (20.8%) |
Class 4: Only hard palate visible | 9 (3.6%) |
Class not recorded | 17 (6.8%) |
Mouth opening | |
<3 finger breadths | 17 (6.8%) |
>3 finger breadths | 219 (87.6%) |
Not recorded | 14 (5.6%) |
Thyromental distance | |
<6 cm | 30 (12.0%) |
>6 cm | 194 (77.6%) |
Not recorded | 26 (10.4%) |
Neck range of motion | |
Full range of motion | 205 (82.0%) |
Limited | 28 (11.2%) |
Not recorded | 17 (6.8%) |
Presence of dentures or missing teeth | |
Dentures—lower | 2 (0.8%) |
Dentures—upper | 16 (6.4%) |
Dentures—upper & lower | 4 (1.6%) |
Edentulous | 32 (12.8%) |
Other | 196 (78.4%) |
Laryngoscopic view | |
Visualization Class 1: supraglottic structures, laryngeal inlet, vocal cords | 107 (42.8%) |
Visualization Class 2: epiglottis, laryngeal inlet, posterior aryepiglottic folds | 26 (10.4%) |
Visualization Class 3: epiglottis only | 7 (2.8%) |
Visualization Class 4: cannot see epiglottis | 2 (0.8%) |
Not recorded | 108 (43.2%) |
Method of intubation | |
Direct laryngoscopy | 131 (52.4%) |
Laryngeal mask airway | 25 (10.0%) |
Natural airway | 64 (25.6%) |
Video laryngoscopy | 13 (5.2%) |
Not recorded | 17 (6.8%) |
Differences among raters in Mallampati scores, neck range of motion, and rater prediction of difficulty with intubation.
Variable | Reviewer 1 | Reviewer 2 | Reviewer 3 | |
---|---|---|---|---|
Mallampati (%) (from photographs) | 0.002 | |||
Class 1: Entire tonsil clearly visible | 19.1% | 32.1% | 19.0% | |
Class 2: Upper half of tonsil fossa visible | 34.7% | 24.1% | 27.0% | |
Class 3: Soft and hard palate clearly visible | 39.1% | 31.2% | 41.9% | |
Class 4: Only hard palate visible | 7.1% | 12.6% | 12.1% | |
Neck ROM (%) (from photographs) | 0.012 | |||
Full range of motion | 82.2% | 81.6% | 71.0% | |
Limited | 17.8% | 18.4% | 29.0% | |
Difficult intubation prediction (%) (from photographs) | 0.001 | |||
No | 66.7% | 85.7% | 83.1% | |
Yes | 33.3% | 14.3% | 16.9% | |
Difficult intubation prediction (%) (from preassessments) | 0.001 | |||
No | 78.4% | 66.4% | 90.6% | |
Yes | 21.6% | 33.6% | 9.4% |
*
Association between Mallampati scores and method of intubation.
Mallampati Score | Method of Intubation (from Preassessment) | ||||
---|---|---|---|---|---|
Direct Laryngoscopy | Laryngeal Mask Airway | Natural Airway | Video Laryngoscopy | ||
Preassessment | 0.296 | ||||
Class 1 | 26.6% | 30.4% | 27.6% | 0.0% | |
Class 2 | 50.0% | 30.4% | 50.0% | 58.3% | |
Class 3 | 20.3% | 34.8% | 17.2% | 33.3% | |
Class 4 | 3.1% | 4.3% | 5.2% | 8.3% | |
Reviewer 1 (from photographs) | 0.559 | ||||
Class 1 | 16.2% | 33.3% | 23.3% | 9.1% | |
Class 2 | 41.0% | 19.0% | 31.7% | 36.4% | |
Class 3 | 37.6% | 38.1% | 41.7% | 45.5% | |
Class 4 | 5.1% | 9.5% | 3.3% | 9.1% | |
Reviewer 2 (from photographs) | 0.957 | ||||
Class 1 | 33.9% | 30.4% | 35.5% | 33.3% | |
Class 2 | 21.8% | 30.4% | 22.6% | 25.0% | |
Class 3 | 32.3% | 26.1% | 30.6% | 16.7% | |
Class 4 | 12.1% | 13.0% | 11.3% | 25.0% | |
Reviewer 3 (from photographs) | 0.559 | ||||
Class 1 | 16.8% | 25.0% | 25.0% | 7.7% | |
Class 2 | 30.5% | 12.5% | 28.1% | 38.5% | |
Class 3 | 42.0% | 41.7% | 37.5% | 38.5% | |
Class 4 | 10.7% | 20.8% | 7.8% | 15.4% |
Mallampati Class 1: Entire tonsil clearly visible; Class 2: Upper half of tonsillar fossa visible; Class 3: Soft and hard palate clearly visible; Class 4: Only hard palate visible.
Association between Mallampati scores and type of view.
Mallampati Score | Type of View (from Intraoperative Record) | |||
---|---|---|---|---|
Cormack–Lehane: Class 1 | Cormack–Lehane: Class 2 | Cormack–Lehane: Class 3 or 4 | ||
Preassessment | 0.135 | |||
Class 1 | 26.0% | 24.0% | 0.0% | |
Class 2 | 51.9% | 44.0% | 55.6% | |
Class 3 | 17.3% | 32.0% | 44.4% | |
Class 4 | 4.8% | 0.0% | 0.0% | |
Reviewer 1 (from photographs) | 0.559 | |||
Class 1 | 15.6% | 14.3% | 12.5% | |
Class 2 | 43.8% | 23.8% | 50.0% | |
Class 3 | 34.4% | 57.1% | 37.5% | |
Class 4 | 6.3% | 4.8% | 0.0% | |
Reviewer 2 (from photographs) | 0.072 | |||
Class 1 | 34.7% | 20.0% | 42.9% | |
Class 2 | 23.8% | 12.0% | 42.9% | |
Class 3 | 32.7% | 40.0% | 0.0% | |
Class 4 | 8.9% | 28.0% | 14.3% | |
Reviewer 3 (from photographs) | 0.100 | |||
Class 1 | 17.8% | 3.8% | 22.2% | |
Class 2 | 34.6% | 23.1% | 11.1% | |
Class 3 | 40.2% | 46.2% | 44.4% | |
Class 4 | 7.5% | 26.9% | 22.2% |
108 patients did not have a laryngoscopic view recorded. Visualization Class 1: supraglottic structures, laryngeal inlet, vocal cords; Visualization Class 2: epiglottis, laryngeal inlet, posterior aryepiglottic folds; Visualization Class 3: epiglottis only; Visualization Class 4: cannot see epiglottis.
Interrater agreement for Mallampati scores, neck range of motion and rater prediction of difficulty with intubation.
Variable | Reviewer 1 & Reviewer 2 | Reviewer 1 & Reviewer 3 | Reviewer 2 & Reviewer 3 |
---|---|---|---|
Mallampati (%) (from photographs) | |||
Kappa | 0.47 | 0.64 | 0.47 |
95%CI | 0.38–0.56 | 0.56–0.72 | 0.39–0.56 |
Neck ROM (%) (from photographs) | |||
Kappa | 0.43 | 0.45 | 0.44 |
95%CI | 0.29–0.58 | 0.32–0.57 | 0.32–0.57 |
Difficult intubation prediction (%) (from photographs) | |||
Kappa | 0.41 | 0.39 | 0.64 |
95%CI | 0.30–0.53 | 0.27–0.51 | 0.50–0.77 |
Difficult intubation prediction (%) (from preassessments) | |||
Kappa | 0.69 | 0.48 | 0.35 |
95%CI | 0.59–0.79 | 0.34–0.62 | 0.24–0.47 |
ROM—range of motion, CI—confidence interval.
Agreement between reviewers based on photographs and the information from preassessment: Mallampati scores, range of motion, prediction of difficult intubation.
Variable | Reviewer 1 | Reviewer 2 | Reviewer 3 |
---|---|---|---|
Mallampati | |||
Kappa | 0.17 | 0.11 | 0.13 |
95%CI | 0.07–0.26 | 0.02–0.19 | 0.05–0.21 |
Neck range of motion | |||
Kappa | 0.20 | 0.25 | 0.20 |
95%CI | 0.04–0.35 | 0.09–0.41 | 0.07–0.33 |
Difficult intubation prediction (intrarater) | |||
Kappa | 0.19 | 0.23 | 0.20 |
95%CI | 0.06–0.32 | 0.10–0.36 | 0.04–0.35 |
CI—confidence interval.