|Year : 2016 | Volume
| Issue : 2 | Page : 241-244
Preoperative airway predictive tests: How far are we from the books?
Babatunde B Osinaike
Department of Anaesthesia, College of Medicine, University of Ibadan/University College Hospital, Ibadan, Nigeria
|Date of Web Publication||29-Sep-2016|
Babatunde B Osinaike
University College Hospital, Queen Elizabeth Road, Mokola, Ibadan
Source of Support: None, Conflict of Interest: None
Background: Many preoperative airway assessment tests to predict a difficult intubation (DI) have been developed and documented, but we have no published data on how frequently these tests are used or how useful they are perceived by anesthetists in Nigeria. This survey was done among physician anesthetists in Nigeria to document practices related to the use of bedside airway predictive tests in adults.
Methods: The following tests were compiled into a questionnaire and administered to physician anesthetists in training. Effective mandibular length, inter-incisor gap (IIG), Mallampati classification (MC), sternomental distance, thyromental distance, hyomental distance (HMD), range of neck motion (ROM), upper lip bite test (ULBT), mandibular protrusion test, and prayer sign (PS). A 5 and 4-level Likert item was used to assess the frequency of use and perceived importance of each test during the preoperative period.
Results: A total of 81 (90%) participants completed the questionnaires. Of the 10 predictive tests listed; MC and ROM were "always" and "very often" used in 80 (98.8%) and 67 (82.7%) of participants, while PS, ULBT, and HMD is "rarely" or "never used" in 42 (51.9%), 41 (50.6%), and 39 (48.2%) of participants, respectively. MC, ROM, and IIG assessments were considered "very useful" and "useful" in 76 (93.8%), 69 (85.2%), and 69 (85.2%) of participants respectively in predicting DI, while HMD and PS were considered to be of "little use" by 7 (8.6%) and 7 (8.6%) of participants, respectively. MC, ROM, and IIG measurement (28%) were perceived as the best combination for high predictive value for DI.
Conclusion: There is a tendency towards the use of MC and ROM more frequently than other tests during bedside preoperative airway assessment in adults by physician anesthetists in Nigeria. This practice may be insufficient for the prediction of DI in view of the current evidence.
Keywords: Anesthetists, difficult airway prediction, Nigeria
|How to cite this article:|
Osinaike BB. Preoperative airway predictive tests: How far are we from the books?. Indian J Health Sci Biomed Res 2016;9:241-4
| Introduction|| |
Tracheal intubation is mandatory for achieving airway control during anesthesia; however, there are occasions when one is faced with difficult tracheal intubation and when this occurs; it is often a challenging scenario for anesthetists. The incidence of failed intubation is approximately 1 in 1000 and the incidence of cannot intubate, cannot ventilate is approximately 1 in 2800-20,000. , Depending on the definition, 2-8% of all intubations turn out to be difficult. ,
Correct prediction of the difficult airway alters the potentially dangerous unanticipated airway to an anticipated difficult airway with, predominantly, ample time for proper preparation. Thus, accurate prediction of difficult airway management may reduce potential complications by the allocation of experienced personnel and using relevant equipment and well-planned strategies.  To prevent adverse consequences such as aspiration pneumonitis, hypoxic brain injury, and even death, many preoperative assessment tests have been developed to predict a difficult intubation (DI) and laryngeal view.
Evidence have shown that no single bedside test is reliable enough to prospectively detect all cases of difficult laryngoscopy or intubation, however, the use of a combination of these tests has been shown to be very helpful. , Few studies ,, on difficult airway prediction in Nigeria has been on best predictors of DI; there is no published data of how frequently these bedside predictive tests are used or how useful they are perceived by Nigerian anesthetists. This study is, therefore, to evaluate the use of some predictive airway tests by physician anesthetists in Nigeria for adult patients during preoperative assessment.
| Methods|| |
Physician anesthetists in training from the six geopolitical zones in Nigeria were administered a questionnaire. The questionnaire contained questions on ten airway tests. These included; effective mandibular length (EML), inter-incisor gap (IIG), Mallampati classification (MC), sternomental distance (SMD), thyromental distance (TMD), hyomental distance (HMD), range of neck motion (ROM), upper lip bite test (ULBT), mandibular protrusion test (MPT), and prayer sign (PS).
The following information was requested about each of the bedside tests using a 4 or 5-level Likert item; the frequency of use, perceived importance, and best combination of tests for predicting DI.
| Results|| |
A total of 81 (90%) of the participants completed the questionnaire, all of whom have spent an average of 3 years in training as physician anesthetists. When asked about the frequency of use of predictive tests; MC and ROM were "always" and "very often" used by 80 (98.8.%) and 67 (82.7%) of participants while, PS, ULBT, and HMD is "rarely" or "never used" in 42 (51.9%), 41 (50.6%), and 39 (48.2%) of participants, respectively. However, MPT, SMD, and ULBT were considered "sometimes useful" by 32 (39.5%), 27 (33.3%), and 27 (33.3%) of participants, respectively [Table 1].
On the question about the perceived usefulness of the bedside tests; MC, ROM, and IIG assessments were considered "very useful" and "useful" by 76 (93.8%), 69 (85.2%), 69 (85.2%) and of little use by 0, 0 and 2 (2.5%) of the participants, respectively. HMD and PS were considered to be of "little use" by 7 (8.6%) and 7 (8.6%) of participants, respectively [Table 2].
Considering the perceived best combination of tests; the most common combination of tests likely to offer high predictive value for DI among the participants was; MC, ROM, IIG measurement 23 (28%) and MC, ROM, TMD 13 (16%). The least common combinations as perceived by the participants were MC, ULBT, IIG 1 (0.01%), MC, ULBT, PS 1 (0.01%) and MC, EML, TMD 1 (0.01%) [Figure 1].
| Discussion|| |
Most participants in this survey make more use of MC and ROM to assess for DI and rely on a combination of MC, IIG, and ROM as the best predictor of DI.
Evidence suggest that combination of bedside airway tests better predict DI compared to single tests. , The poor predictive value of MC alone is supported by the systematic review involving 34,523 patients, that showed that MC, when used alone, has limited accuracy for predicting the difficult airway and thus is not useful as a single screening test.  Currently, available screening tests for DI is said to have poor to moderate discriminative power when used alone, and combinations of tests add some incremental diagnostic value in comparison to the value of each test alone. 
ROM is useful as a predictive test often because it may affect SMD and TMD. Some studies have reported fairly good predictive value with ROM for difficult laryngoscopy, , however, another recent study showed a poor sensitivity with the ROM and IIG. 
The ability of a combination of tests to adequately predict DI usually depends on the composite tests. Shiga et al.  in a well-quoted meta-analysis conducted on some bedside airway screening tests-Mallampati oropharyngeal classification, TMD, SMD, mouth opening, and Wilson risk score, opined that each test yielded poor to moderate sensitivity (20-62%) and moderate to fair specificity (82-97%). They found the most useful bedside test for prediction of DI to be a combination of the MC and TMD (positive likelihood ratio, 9.9; 95% confidence interval, 3.1-31.9).  Merah et al.  also found the best combination of predictors for difficult laryngoscopy to be modified MC with the TMD and IIG with sensitivity, specificity, and positive predictive value (PPV) of 84.6%, 94.6%, and 35.5%, respectively. This combination is the third most preferred in our survey.
Many participants in this survey perceived some airway tests to be of little or no use. These include the ULBT, MPT, HMD, and PS. This perception is possibly related to the infrequent or nonapplication of these tests during routine airway assessment. Recently, many authors have reported good predictive values when some of these tests are employed alone or in combination with other tests. Bhat et al. in a study that compared ULBT and modified MC in predicting DI concluded that a combination of ULBT and modified Mallampati test is more sensitive, specific and has a higher discriminative power.  Furthermore, Khan et al.  in a study on the diagnostic value of the ULBT combined with SMD, TMD, and interincisor distance for prediction of easy laryngoscopy and intubation found that the specificity and accuracy of ULBT is significantly higher than other single tests and ULBT combined with the other tests could more reliably predict easy laryngoscopy or intubation. Infarct Seo et al.  concluded that the ULBT (Class III) is a very useful stand-alone test for predicting difficult endotracheal intubation
In a study by Ali et al.,  the accuracy (91.9%), sensitivity (87.5%), PPV (71.6%), and negative predictive value (NPV) (97.3%) of ULBT were higher than the Mallampati test, while specificity of both tests was similar. With regard to the MPT, it was observed that the MPT had higher sensitivity (95.9% vs. 27.1%), NPV (98.7% vs. 82.0%), and accuracy (90.1% vs. 80.3%) when compared to MC in predicting difficult laryngoscopy and intubation. 
The HMD is a valuable test in assessing the length of the lower jaw. Airway tests like the ULBT and MPT are directly or indirectly dependent on the HMD, and a reduced HMD is likely to be associated with failed ULBT and MPT. Furthermore, the highly predictive value of the HMD is responsible for it being recommended as one of the tests to employ when using the "LEMON" method during airway assessment in the emergency department.  The major limitation of this study is that expressed opinions of participants may not reflect true practice.
| Conclusion|| |
Our survey revealed that Anaesthesia Registrars in Nigeria are more familiar with the use of MC, IIG measurement, and ROM for preoperative airway assessment in adults. However, this preferred combination of tests may not always sufficiently predict DI. Adoption of a standard protocol for preoperative airway assessment will encourage the use of other important airway tests for better prediction of DI. A study demonstrated that using a comprehensive airway assessment form that included all 11 of the American Society of Anesthesiologist's proposed airway risk predictors improved documentation of airway assessment, though not always the accuracy.  A prospective observational study among senior anesthetists will help provide an objective assessment of current practices regarding preoperative airway assessment in Nigeria.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Cooper GM, McClure JH. Anaesthesia chapter from saving mothers' lives; reviewing maternal deaths to make pregnancy safer. Br J Anaesth 2008;100:17-22.
Lundstrøm LH, Vester-Andersen M, Møller AM, Charuluxananan S, L'hermite J, Wetterslev J. Poor prognostic value of the modified Mallampati score: A meta-analysis involving 177 088 patients. Br J Anaesth 2011;107:659-67.
Lundstrøm LH, Møller AM, Rosenstock C, Astrup G, Wetterslev J. High body mass index is a weak predictor for difficult and failed tracheal intubation: A cohort study of 91,332 consecutive patients scheduled for direct laryngoscopy registered in the Danish Anesthesia Database. Anesthesiology 2009;110:266-74.
Lundstrøm LH, Møller AM, Rosenstock C, Astrup G, Gätke MR, Wetterslev J. A documented previous difficult tracheal intubation as a prognostic test for a subsequent difficult tracheal intubation in adults. Anaesthesia 2009;64:1081-8.
Kahan BC, Morris TP. Reporting and analysis of trials using stratified randomisation in leading medical journals: Review and reanalysis. BMJ 2012;345:e5840.
Lee A, Fan LT, Gin T, Karmakar MK, Ngan Kee WD. A systematic review (meta-analysis) of the accuracy of the Mallampati tests to predict the difficult airway. Anesth Analg 2006;102:1867-78.
Law JA. Relying on just a few predictors of easy airway management may bite back! Anesth Analg 2008;106:668.
Merah NA, Wong DT, Ffoulkes-Crabbe DJ, Kushimo OT, Bode CO. Modified Mallampati test, thyromental distance and inter-incisor gap are the best predictors of difficult laryngoscopy in West Africans. Can J Anaesth 2005;52:291-6.
Amadasun FE, Adudu OP, Sadiq A. Effects of position and phonation on oropharyngeal view and correlation with laryngoscpic view. Niger J Clin Pract 2010;13:417-20.
Etta OE, Edentekhe TA, Akpan SG. Prediction of difficult laryngoscopy in a homogenous population: The role of height. Afr J Anaesth Intensive Care 2015;15:6-9.
Shiga T, Wajima Z, Inoue T, Sakamoto A. Predicting difficult intubation in apparently normal patients: A meta-analysis of bedside screening test performance. Anesthesiology 2005;103:429-37.
Gupta AK, Ommid M, Nengroo S, Naqash I, Mehta A. Predictors of difficult intubation: Study in Kashmiri population. Br J Med Pract 2010;3:307-12.
Farzi F, Mirmansouri A, Forghanparast K, Abdolahzade M, Nahvi H. Difficult laryngoscopy; the predictive value of ratio of height to thyromental distance versus other common predictive tests of upper airway. Prof Med J 2012;19:6.
Seo SH, Lee JG, Yu SB, Kim DS, Ryu SJ, Kim KH. Predictors of difficult intubation defined by the intubation difficulty scale (IDS): Predictive value of 7 airway assessment factors. Korean J Anesthesiol 2012;63:491-7.
Bhat R, Mishra S, Badhe A. Comparison of upper lip bite test and modified Mallampati classification in predicting difficult intubation. Int J Anesthesiol 2007;13:1.
Khan ZH, Mohammadi M, Rasouli MR, Farrokhnia F, Khan RH. The diagnostic value of the upper lip bite test combined with sternomental distance, thyromental distance, and interincisor distance for prediction of easy laryngoscopy and intubation: A prospective study. Anesth Analg 2009;109:822-4.
Ali MA, Qamar-ul-Hoda M, Samad K. Comparison of upper lip bite test with Mallampati test in the prediction of difficult intubation at a tertiary care hospital of Pakistan. J Pak Med Assoc 2012;62:1012-5.
Ul Haq MI, Ullah H. Comparison of Mallampati test with lower jaw protrusion maneuver in predicting difficult laryngoscopy and intubation. J Anaesthesiol Clin Pharmacol 2013;29:313-7.
Reed MJ, Dunn MJ, McKeown DW. Can an airway assessment score predict difficulty at intubation in the emergency department? Emerg Med J 2005;22:99-102.
Cattano D, Killoran PV, Iannucci D, Maddukuri V, Altamirano AV, Sridhar S, et al.
Anticipation of the difficult airway: Preoperative airway assessment, an educational and quality improvement tool. Br J Anaesth 2013;111:276-85.
[Table 1], [Table 2]