Difficult laryngoscopy and intubation in the Indian population: An assessment of anatomical and clinical risk factors
Identifieur interne : 000250 ( Pmc/Corpus ); précédent : 000249; suivant : 000251Difficult laryngoscopy and intubation in the Indian population: An assessment of anatomical and clinical risk factors
Auteurs : Smita Prakash ; Amitabh Kumar ; Shyam Bhandari ; Parul Mullick ; Rajvir Singh ; Anoop Raj GogiaSource :
- Indian Journal of Anaesthesia [ 0019-5049 ] ; 2013.
Abstract
Differences in patient characteristics due to race or ethnicity may influence the incidence of difficult airway. Our purpose was to determine the incidence of difficult laryngoscopy and intubation, as well as the anatomical features and clinical risk factors that influence them, in the Indian population.
In 330 adult patients receiving general anaesthesia with tracheal intubation, airway characteristics and clinical factors were determined and their association with difficult laryngoscopy (Cormack and Lehane grade 3 and 4) was analysed. Intubation Difficulty Scale score was used to identify degree of difficult laryngoscopy.
The incidence of difficult laryngoscopy and intubation was 9.7% and 4.5%, respectively. Univariate analysis showed that increasing age and weight, male gender, modified Mallampati class (MMC) 3 and 4 in sitting and supine positions, inter-incisor distance (IID) ≤3.5 cm, thyromental (TMD) and sternomental distance, ratio of height and TMD, short neck, limited mandibular protrusion, decreased range of neck movement, history of snoring, receding mandible and cervical spondylosis were associated with difficult laryngoscopy. Multivariate analysis identified four variables that were independently associated with difficult laryngoscopy: MMC class 3 and 4, range of neck movement <80°, IID ≤ 3.5 cm and snoring.
We found an incidence of 9.7% and 4.5% for difficult laryngoscopy and difficult intubation, respectively, in Indian patients with apparently normal airways. MMC class 3 and 4, range of neck movement <80°, IID ≤ 3.5 cm and snoring were independently related to difficult laryngoscopy. There was a high incidence (48.5%) of minor difficulty in intubation.
Url:
DOI: 10.4103/0019-5049.123329
PubMed: 24403616
PubMed Central: 3883391
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<record><TEI><teiHeader><fileDesc><titleStmt><title xml:lang="en">Difficult laryngoscopy and intubation in the Indian population: An assessment of anatomical and clinical risk factors</title><author><name sortKey="Prakash, Smita" sort="Prakash, Smita" uniqKey="Prakash S" first="Smita" last="Prakash">Smita Prakash</name><affiliation><nlm:aff id="aff1">Department of Anaesthesia and Intensive Care, Vardhman Mahavir Medical College and Safdarjang Hospital, New Delhi, India</nlm:aff></affiliation></author><author><name sortKey="Kumar, Amitabh" sort="Kumar, Amitabh" uniqKey="Kumar A" first="Amitabh" last="Kumar">Amitabh Kumar</name><affiliation><nlm:aff id="aff1">Department of Anaesthesia and Intensive Care, Vardhman Mahavir Medical College and Safdarjang Hospital, New Delhi, India</nlm:aff></affiliation></author><author><name sortKey="Bhandari, Shyam" sort="Bhandari, Shyam" uniqKey="Bhandari S" first="Shyam" last="Bhandari">Shyam Bhandari</name><affiliation><nlm:aff id="aff1">Department of Anaesthesia and Intensive Care, Vardhman Mahavir Medical College and Safdarjang Hospital, New Delhi, India</nlm:aff></affiliation></author><author><name sortKey="Mullick, Parul" sort="Mullick, Parul" uniqKey="Mullick P" first="Parul" last="Mullick">Parul Mullick</name><affiliation><nlm:aff id="aff1">Department of Anaesthesia and Intensive Care, Vardhman Mahavir Medical College and Safdarjang Hospital, New Delhi, India</nlm:aff></affiliation></author><author><name sortKey="Singh, Rajvir" sort="Singh, Rajvir" uniqKey="Singh R" first="Rajvir" last="Singh">Rajvir Singh</name><affiliation><nlm:aff id="aff2">Medical Research Cardiology, HMC, Doha, Qatar</nlm:aff></affiliation></author><author><name sortKey="Gogia, Anoop Raj" sort="Gogia, Anoop Raj" uniqKey="Gogia A" first="Anoop Raj" last="Gogia">Anoop Raj Gogia</name><affiliation><nlm:aff id="aff1">Department of Anaesthesia and Intensive Care, Vardhman Mahavir Medical College and Safdarjang Hospital, New Delhi, India</nlm:aff></affiliation></author></titleStmt><publicationStmt><idno type="wicri:source">PMC</idno><idno type="pmid">24403616</idno><idno type="pmc">3883391</idno><idno type="url">http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3883391</idno><idno type="RBID">PMC:3883391</idno><idno type="doi">10.4103/0019-5049.123329</idno><date when="2013">2013</date><idno type="wicri:Area/Pmc/Corpus">000250</idno><idno type="wicri:explorRef" wicri:stream="Pmc" wicri:step="Corpus" wicri:corpus="PMC">000250</idno></publicationStmt><sourceDesc><biblStruct><analytic><title xml:lang="en" level="a" type="main">Difficult laryngoscopy and intubation in the Indian population: An assessment of anatomical and clinical risk factors</title><author><name sortKey="Prakash, Smita" sort="Prakash, Smita" uniqKey="Prakash S" first="Smita" last="Prakash">Smita Prakash</name><affiliation><nlm:aff id="aff1">Department of Anaesthesia and Intensive Care, Vardhman Mahavir Medical College and Safdarjang Hospital, New Delhi, India</nlm:aff></affiliation></author><author><name sortKey="Kumar, Amitabh" sort="Kumar, Amitabh" uniqKey="Kumar A" first="Amitabh" last="Kumar">Amitabh Kumar</name><affiliation><nlm:aff id="aff1">Department of Anaesthesia and Intensive Care, Vardhman Mahavir Medical College and Safdarjang Hospital, New Delhi, India</nlm:aff></affiliation></author><author><name sortKey="Bhandari, Shyam" sort="Bhandari, Shyam" uniqKey="Bhandari S" first="Shyam" last="Bhandari">Shyam Bhandari</name><affiliation><nlm:aff id="aff1">Department of Anaesthesia and Intensive Care, Vardhman Mahavir Medical College and Safdarjang Hospital, New Delhi, India</nlm:aff></affiliation></author><author><name sortKey="Mullick, Parul" sort="Mullick, Parul" uniqKey="Mullick P" first="Parul" last="Mullick">Parul Mullick</name><affiliation><nlm:aff id="aff1">Department of Anaesthesia and Intensive Care, Vardhman Mahavir Medical College and Safdarjang Hospital, New Delhi, India</nlm:aff></affiliation></author><author><name sortKey="Singh, Rajvir" sort="Singh, Rajvir" uniqKey="Singh R" first="Rajvir" last="Singh">Rajvir Singh</name><affiliation><nlm:aff id="aff2">Medical Research Cardiology, HMC, Doha, Qatar</nlm:aff></affiliation></author><author><name sortKey="Gogia, Anoop Raj" sort="Gogia, Anoop Raj" uniqKey="Gogia A" first="Anoop Raj" last="Gogia">Anoop Raj Gogia</name><affiliation><nlm:aff id="aff1">Department of Anaesthesia and Intensive Care, Vardhman Mahavir Medical College and Safdarjang Hospital, New Delhi, India</nlm:aff></affiliation></author></analytic><series><title level="j">Indian Journal of Anaesthesia</title><idno type="ISSN">0019-5049</idno><idno type="eISSN">0976-2817</idno><imprint><date when="2013">2013</date></imprint></series></biblStruct></sourceDesc></fileDesc><profileDesc><textClass></textClass></profileDesc></teiHeader><front><div type="abstract" xml:lang="en"><sec id="st1"><title>Background and Aim:</title><p>Differences in patient characteristics due to race or ethnicity may influence the incidence of difficult airway. Our purpose was to determine the incidence of difficult laryngoscopy and intubation, as well as the anatomical features and clinical risk factors that influence them, in the Indian population.</p></sec><sec id="st2"><title>Methods:</title><p>In 330 adult patients receiving general anaesthesia with tracheal intubation, airway characteristics and clinical factors were determined and their association with difficult laryngoscopy (Cormack and Lehane grade 3 and 4) was analysed. Intubation Difficulty Scale score was used to identify degree of difficult laryngoscopy.</p></sec><sec id="st3"><title>Results:</title><p>The incidence of difficult laryngoscopy and intubation was 9.7% and 4.5%, respectively. Univariate analysis showed that increasing age and weight, male gender, modified Mallampati class (MMC) 3 and 4 in sitting and supine positions, inter-incisor distance (IID) ≤3.5 cm, thyromental (TMD) and sternomental distance, ratio of height and TMD, short neck, limited mandibular protrusion, decreased range of neck movement, history of snoring, receding mandible and cervical spondylosis were associated with difficult laryngoscopy. Multivariate analysis identified four variables that were independently associated with difficult laryngoscopy: MMC class 3 and 4, range of neck movement <80°, IID ≤ 3.5 cm and snoring.</p></sec><sec id="st4"><title>Conclusions:</title><p>We found an incidence of 9.7% and 4.5% for difficult laryngoscopy and difficult intubation, respectively, in Indian patients with apparently normal airways. MMC class 3 and 4, range of neck movement <80°, IID ≤ 3.5 cm and snoring were independently related to difficult laryngoscopy. 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<front><journal-meta><journal-id journal-id-type="nlm-ta">Indian J Anaesth</journal-id><journal-id journal-id-type="iso-abbrev">Indian J Anaesth</journal-id><journal-id journal-id-type="publisher-id">IJA</journal-id><journal-title-group><journal-title>Indian Journal of Anaesthesia</journal-title></journal-title-group><issn pub-type="ppub">0019-5049</issn><issn pub-type="epub">0976-2817</issn><publisher><publisher-name>Medknow Publications & Media Pvt Ltd</publisher-name><publisher-loc>India</publisher-loc></publisher></journal-meta><article-meta><article-id pub-id-type="pmid">24403616</article-id><article-id pub-id-type="pmc">3883391</article-id><article-id pub-id-type="publisher-id">IJA-57-569</article-id><article-id pub-id-type="doi">10.4103/0019-5049.123329</article-id><article-categories><subj-group subj-group-type="heading"><subject>Clinical Investigation</subject></subj-group></article-categories><title-group><article-title>Difficult laryngoscopy and intubation in the Indian population: An assessment of anatomical and clinical risk factors</article-title></title-group><contrib-group><contrib contrib-type="author"><name><surname>Prakash</surname><given-names>Smita</given-names></name><xref ref-type="aff" rid="aff1"></xref><xref ref-type="corresp" rid="cor1"></xref></contrib><contrib contrib-type="author"><name><surname>Kumar</surname><given-names>Amitabh</given-names></name><xref ref-type="aff" rid="aff1"></xref></contrib><contrib contrib-type="author"><name><surname>Bhandari</surname><given-names>Shyam</given-names></name><xref ref-type="aff" rid="aff1"></xref></contrib><contrib contrib-type="author"><name><surname>Mullick</surname><given-names>Parul</given-names></name><xref ref-type="aff" rid="aff1"></xref></contrib><contrib contrib-type="author"><name><surname>Singh</surname><given-names>Rajvir</given-names></name><xref ref-type="aff" rid="aff2">1</xref></contrib><contrib contrib-type="author"><name><surname>Gogia</surname><given-names>Anoop Raj</given-names></name><xref ref-type="aff" rid="aff1"></xref></contrib></contrib-group><aff id="aff1">Department of Anaesthesia and Intensive Care, Vardhman Mahavir Medical College and Safdarjang Hospital, New Delhi, India</aff><aff id="aff2"><label>1</label>Medical Research Cardiology, HMC, Doha, Qatar</aff><author-notes><corresp id="cor1"><bold>Address for correspondence:</bold> Dr. Smita Prakash, C 17 HUDCO Place, New Delhi - 110 049, India. E-mail: <email xlink:href="drsunilprakash@gmail.com">drsunilprakash@gmail.com</email></corresp></author-notes><pub-date pub-type="ppub"><season>Nov-Dec</season><year>2013</year></pub-date><volume>57</volume><issue>6</issue><fpage>569</fpage><lpage>575</lpage><permissions><copyright-statement>Copyright: © Indian Journal of Anaesthesia</copyright-statement><copyright-year>2013</copyright-year><license license-type="open-access" xlink:href="http://creativecommons.org/licenses/by-nc-sa/3.0"><license-p>This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.</license-p></license></permissions><abstract><sec id="st1"><title>Background and Aim:</title><p>Differences in patient characteristics due to race or ethnicity may influence the incidence of difficult airway. Our purpose was to determine the incidence of difficult laryngoscopy and intubation, as well as the anatomical features and clinical risk factors that influence them, in the Indian population.</p></sec><sec id="st2"><title>Methods:</title><p>In 330 adult patients receiving general anaesthesia with tracheal intubation, airway characteristics and clinical factors were determined and their association with difficult laryngoscopy (Cormack and Lehane grade 3 and 4) was analysed. Intubation Difficulty Scale score was used to identify degree of difficult laryngoscopy.</p></sec><sec id="st3"><title>Results:</title><p>The incidence of difficult laryngoscopy and intubation was 9.7% and 4.5%, respectively. Univariate analysis showed that increasing age and weight, male gender, modified Mallampati class (MMC) 3 and 4 in sitting and supine positions, inter-incisor distance (IID) ≤3.5 cm, thyromental (TMD) and sternomental distance, ratio of height and TMD, short neck, limited mandibular protrusion, decreased range of neck movement, history of snoring, receding mandible and cervical spondylosis were associated with difficult laryngoscopy. Multivariate analysis identified four variables that were independently associated with difficult laryngoscopy: MMC class 3 and 4, range of neck movement <80°, IID ≤ 3.5 cm and snoring.</p></sec><sec id="st4"><title>Conclusions:</title><p>We found an incidence of 9.7% and 4.5% for difficult laryngoscopy and difficult intubation, respectively, in Indian patients with apparently normal airways. MMC class 3 and 4, range of neck movement <80°, IID ≤ 3.5 cm and snoring were independently related to difficult laryngoscopy. There was a high incidence (48.5%) of minor difficulty in intubation.</p></sec></abstract><kwd-group><kwd>Airway evaluation</kwd><kwd>difficult intubation</kwd><kwd>difficult laryngoscopy</kwd><kwd>intubation difficulty scale</kwd></kwd-group></article-meta></front><body><sec id="sec1-1"><title>INTRODUCTION</title><p>Difficulty in airway management is a major cause of morbidity and mortality in anaesthetic practice. The ability to identify patients at risk of difficult tracheal intubation is important especially in patients with apparently normal airways. Difficult laryngoscopy (poor glottis visualization) is considered a surrogate indicator of difficult intubation. Preoperative assessment of various anatomic and clinical features helps in identifying potentially difficult laryngoscopy. The diagnostic accuracy of these screening tests varies between different studies. This is attributed to difference in incidence of difficult laryngoscopy, inadequate statistical power, different test thresholds and differences in patient characteristics.[<xref ref-type="bibr" rid="ref1">1</xref>]</p><p>Differences in patient characteristics due to race or ethnicity may influence the incidence of difficult laryngoscopy and difficult intubation. The majority of studies of difficult laryngoscopy and intubation have been performed in the American or European population.[<xref ref-type="bibr" rid="ref1">1</xref><xref ref-type="bibr" rid="ref2">2</xref><xref ref-type="bibr" rid="ref3">3</xref><xref ref-type="bibr" rid="ref4">4</xref><xref ref-type="bibr" rid="ref5">5</xref><xref ref-type="bibr" rid="ref6">6</xref>] Anthropometrically, Indians are different compared to the Americans or Europeans. Adequate data of normal values in a given population may help the clinician to identify patients who are outside the range and therefore potentially challenging. Moreover, most studies do not provide a ‘measure’ of difficult intubation in patients with difficult laryngoscopy. To address this issue, we undertook a prospective study to determine: (1) the incidence of difficult laryngoscopy and difficult intubation; (2) the anatomic and clinical risk factors associated with difficult laryngoscopy; (3) to characterise the degree of difficulty in tracheal intubation in the Indian patient population.</p></sec><sec sec-type="methods" id="sec1-2"><title>METHODS</title><p>After obtaining approval from the local ethics committee and written informed consent from patients, 330 adult ASA physical status I and II adult patients scheduled for elective surgery under general anaesthesia requiring tracheal intubation were included in this prospective study. Patients with obvious abnormality of the airway where intubation under general anaesthesia would be contraindicated, those at increased risk of aspiration, inter-incisor distance <2.5 cm and unstable cervical spine were excluded from the study.</p><p>The following airway characteristics were assessed preoperatively by one investigator to reduce inter-observer variability: (1) modified Mallampati class (MMC)[<xref ref-type="bibr" rid="ref2">2</xref>] of oropharyngeal view obtained with the patient sitting and also in the supine position (tongue protruding, without phonation); (2) inter-incisor distance (IID) < or > 3.5 cm with the mouth fully open (inter-gingival distance in edentulous patients); (3) thyromental distance (TMD) and sternomental distance (SMD) obtained by measuring the straight distance from thyroid notch and sternal notch to the inner mentum, respectively, with the head in extension; (4) range of head and neck movement < or > 80° as described by Wilson <italic>et al</italic>.;[<xref ref-type="bibr" rid="ref3">3</xref>] (5) mandibular protrusion limitation; the lower incisors can be brought in front of the upper incisors or the lower incisors can be advanced only to the level of upper incisors or cannot reach the level of the upper incisors; (6) ratio of height (cm) and TMD (cm) [RHTMD] and body mass index (BMI), kg/m<sup>2</sup> was calculated; (7) dentition: Loose, missing, protruding teeth or edentulous; (8) other features such as history of snoring, hypertension or diabetes, short muscular neck, beard or cervical spondylosis were noted. All patients fasted overnight and received oral alprazolam 0.25 mg/0.5 mg (< or > 50 kg body weight, respectively) the night before and on the morning of surgery.</p><p>In the operating room, standard monitoring was established (electrocardiogram, non-invasive blood pressure, pulse oximetry, capnography). A difficult airway cart was kept at hand.</p><p>The height of the operating table was adjusted such that the plane of the patient's face was at the level of xiphisternum of the anaesthesiologist performing laryngoscopy and intubation. Anaesthesia was induced with fentanyl 2 μg/kg and propofol 2-2.5 mg/kg until loss of verbal contact. Intubation was facilitated by vecuronium 0.1 mg/kg. The lungs were ventilated with O<sub>2</sub>, N<sub>2</sub>O and isoflurane 0.6% for 3 minutes. Degree of difficulty with mask ventilation was graded as easy, difficult or impossible.[<xref ref-type="bibr" rid="ref4">4</xref>]</p><p>Intubation was performed using Macintosh size 3 blade with the patients’ head in sniffing position by anaesthesiologists with more than five years experience in anaesthesia who were unaware of the airway measurements. Tracheal tubes size 7 and 8 were used in female and male patients, respectively. Laryngoscopic view was graded by Cormack and Lehane grading[<xref ref-type="bibr" rid="ref5">5</xref>] without external laryngeal pressure (ELP). Cormack grade 3 and 4 were regarded as difficult laryngoscopy. ELP was permitted to facilitate intubation and the Cormack grade obtained following ELP was also noted. Intubation difficulty was assessed by the Intubation Difficulty Scale (IDS) score.[<xref ref-type="bibr" rid="ref6">6</xref>] The number of attempts and operators, alternate intubation techniques used, Cormack grade, lifting force used, need for external laryngeal pressure and vocal cord position were noted. Alternative techniques included patient repositioning, change of blade or tracheal tube, use of stylet, laryngeal mask airway (LMA), intubating LMA, fibreoptic intubation or intubation through LMA. IDS score = 0 represented easy intubation, IDS score = 1-5 represented slight difficulty and IDS score >5 represented moderate to major difficulty in intubation.[<xref ref-type="bibr" rid="ref6">6</xref>] Duration of laryngoscopy was recorded. The stance of the anaesthesiologist performing laryngoscopy and intubation (upright or leaning backwards, bending at the knee or stooping) was also noted. The study ended after successful tracheal intubation was confirmed by assessment of chest movement, auscultation and capnography.</p><p>Assuming an incidence of difficult laryngoscopy of 8%[<xref ref-type="bibr" rid="ref7">7</xref>] and an error of 3%, a sample size of 327 patients would be required to find significant differences between patients with easy and difficult laryngoscopy. We included 330 patients. Descriptive statistics in the form of mean, standard deviation for interval variables and frequency and percentage for categorical variables have been performed. Student's <italic>t</italic>-test was performed to see significant differences between easy and difficult laryngoscopy for interval variables. Chi-square tests with Yates correction factor were used to see association between the two groups for categorical variables. All significant and important variables were selected for multivariate logistic regression analysis. Stepwise forward multivariate logistic regression analysis was performed to see important risk factors for difficult laryngoscopy. Adjusted odds ratio and 95% confidence interval were presented. A <italic>P</italic> value 0.05 (two-tailed) was considered to be of statistically significant level. SPSS 19.0 statistical package was used for the analysis.</p></sec><sec sec-type="results" id="sec1-3"><title>RESULTS</title><p>A total of 330 patients were included in the study. The demographic and airway characteristics of the study population are presented in <xref ref-type="table" rid="T1">Table 1</xref>. Mask ventilation was easy in 293 (88.8%), difficult in 36 (10.9%) and impossible in 1 (0.3%) of 330 patients. There was no significant difference between the Easy and Difficult laryngoscopy groups with regard to difficulty in mask ventilation (<italic>P</italic> = 0.312). The incidence of difficult laryngoscopy was 9.7%. The duration of laryngoscopy was 13.4 ± 5.5 and 28.2 ± 21.5 s in patients with easy and difficult laryngoscopy, respectively (<italic>P</italic> = 0.000). There were no failed intubations.</p><table-wrap id="T1" position="float"><label>Table 1</label><caption><p>Overall patient data</p></caption><graphic xlink:href="IJA-57-569-g001"></graphic></table-wrap><p>The distribution of airway characteristics between the Easy (Cormack grade 1 and 2) and Difficult (Cormack grade 3 and 4) laryngoscopy groups are shown in Tables <xref ref-type="table" rid="T2">2</xref> and <xref ref-type="table" rid="T3">3</xref>. The incidence of MMC zero airway was 1.7% (5 of 330 patients; 3 females and 2 males). The supine position worsened the MMC view [<xref ref-type="table" rid="T1">Table 1</xref>]. Both MMC in the sitting position and supine position were statistically significantly related to difficult laryngoscopy (<italic>P</italic> = 0.000 and 0.004, respectively).</p><table-wrap id="T2" position="float"><label>Table 2</label><caption><p>Demographic data of patients in the easy and difficult laryngoscopy groups</p></caption><graphic xlink:href="IJA-57-569-g002"></graphic></table-wrap><table-wrap id="T3" position="float"><label>Table 3</label><caption><p>Airway characteristics in the easy and difficult laryngoscopy groups</p></caption><graphic xlink:href="IJA-57-569-g003"></graphic></table-wrap><p>Univariate analysis demonstrated several risk factors that were associated with difficult laryngoscopy: increasing age, weight, male gender, modified Mallampati class 3 and 4 in sitting and supine positions, TMD, RHTMD, SMD, short neck, limited mandibular protrusion, decreased range of neck movement, history of snoring, receding mandible and cervical spondylosis [Tables <xref ref-type="table" rid="T2">2</xref> and <xref ref-type="table" rid="T3">3</xref>]. Multivariate analysis identified four variables that were independently associated with difficult laryngoscopy [<xref ref-type="table" rid="T4">Table 4</xref>]. These were modified Mallampati class 3 and 4, range of neck movement <80°, IID ≤ 3.5 cm and a history of snoring.</p><table-wrap id="T4" position="float"><label>Table 4</label><caption><p>Predictors of difficult laryngoscopy through multivariate logistic regression with forward selection</p></caption><graphic xlink:href="IJA-57-569-g004"></graphic></table-wrap><p>The distribution of Cormack and Lehane grades without and with external laryngeal pressure (ELP) are presented in <xref ref-type="table" rid="T5">Table 5</xref>. IDS scores ranged between 0 and 16. Intubation was judged to be easy (IDS score = 0) in 155 (47%) and minor difficulty (IDS score 1-5) was experienced in 160 (48.5%) of 330 patients. Moderate to major difficulty (IDS score >5) was seen in 15 of 330 patients (4.5%). The distribution of IDS scores and its variables between the two groups are depicted in <xref ref-type="table" rid="T6">Table 6</xref>. Use of stylet was the most commonly employed alternative technique (13.6%), followed by change in patient position (0.9%) and laryngoscope blade (0.9%).</p><table-wrap id="T5" position="float"><label>Table 5</label><caption><p>Distribution of Cormack and Lehane grades without and with external laryngeal manipulation between the easy and difficult laryngoscopy groups</p></caption><graphic xlink:href="IJA-57-569-g005"></graphic></table-wrap><table-wrap id="T6" position="float"><label>Table 6</label><caption><p>Intubation difficulty scale score and variables of IDS</p></caption><graphic xlink:href="IJA-57-569-g006"></graphic></table-wrap><p>There was a statistically significant difference between the two groups in the stance adopted by the anaesthesiologists performing laryngoscopy and intubation; in 50% (16 of 32 patients) of cases in the difficult laryngoscopy group, the anaesthesiologist leaned backwards, bent at the knee or stooped to bring the face closer to the patient during laryngoscopy and intubation to obtain the best laryngeal view compared with 18.9% (56 of 278 patients) in the easy laryngoscopy group (<italic>P</italic> <0.001).</p></sec><sec sec-type="discussion" id="sec1-4"><title>DISCUSSION</title><p>We found an incidence of 9.7% and 4.5% for difficult laryngoscopy and difficult tracheal intubation (IDS score >5), respectively. Difficult laryngoscopy was independent of degree of difficulty in mask ventilation. We identified four risk factors associated with difficult laryngoscopy: Mallampati class 3-4, range of head and neck movement <80°, IID ≤ 3.5 cm and history of snoring. There was a high incidence of minor (IDS score1-5) intubation difficulty (48.5%). External laryngeal pressure (ELP) and use of alternative techniques (stylet, change in patient position or blade) were used in decreasing frequency to facilitate intubation.</p><p>Our data demonstrate that increasing age, weight and male gender were associated with difficult laryngoscopy. An association between difficult laryngoscopy and older[<xref ref-type="bibr" rid="ref8">8</xref><xref ref-type="bibr" rid="ref9">9</xref><xref ref-type="bibr" rid="ref10">10</xref>] and heavier patients has been reported.[<xref ref-type="bibr" rid="ref10">10</xref>] Osteoarthritic changes and poor dentition may be responsible for the age-related increase in difficult laryngoscopy.[<xref ref-type="bibr" rid="ref11">11</xref>] A significant proportion of difficult tracheal intubations has been found in males,[<xref ref-type="bibr" rid="ref11">11</xref>] attributed to differences in neck fat deposition between the sexes.[<xref ref-type="bibr" rid="ref12">12</xref>] Obesity has been found to be a risk factor for difficult intubation.[<xref ref-type="bibr" rid="ref8">8</xref><xref ref-type="bibr" rid="ref11">11</xref>] while other investigators[<xref ref-type="bibr" rid="ref13">13</xref>] found no such association. Though patients in difficult laryngoscopy group were heavier than those in the easy laryngoscopy group, we did not find BMI to be a risk factor for difficult laryngoscopy. Savva[<xref ref-type="bibr" rid="ref14">14</xref>] did not report any difference in age, sex, weight or height between easy and difficult laryngoscopy groups.</p><p>TMD in the difficult laryngoscopy group was significantly shorter (6.0 ± 1.0 cm) compared with that in the easy (6.6 ± 0.9 cm) laryngoscopy group. A positive correlation between short TMD and difficult laryngoscopy has been reported[<xref ref-type="bibr" rid="ref9">9</xref><xref ref-type="bibr" rid="ref15">15</xref><xref ref-type="bibr" rid="ref16">16</xref><xref ref-type="bibr" rid="ref17">17</xref><xref ref-type="bibr" rid="ref18">18</xref>] while others have found no such correlation.[<xref ref-type="bibr" rid="ref11">11</xref><xref ref-type="bibr" rid="ref19">19</xref>] Cut-off values of TMD for predicting difficult laryngoscopy range from 5.5 to 7.0 cm.[<xref ref-type="bibr" rid="ref18">18</xref>] Mean TMD in our patients was 6.5 ± 0.9 cm in contrast to 7.9 ± 1.2 cm reported by Schmitt <italic>et al</italic>.[<xref ref-type="bibr" rid="ref18">18</xref>] TMD is related to body size and proportion. The mean height of our patients (159 ± 12 cm) is shorter than that reported in the study by Schmitt <italic>et al</italic>. (171 ± 9 cm).[<xref ref-type="bibr" rid="ref18">18</xref>] Therefore, RHTMD is considered a better indicator of difficult intubation than TMD.[<xref ref-type="bibr" rid="ref18">18</xref><xref ref-type="bibr" rid="ref20">20</xref><xref ref-type="bibr" rid="ref21">21</xref>] Mean RHTMD in our study was 24.9 ± 4 that compares with 22.1 ± 3.0 reported by Schmitt <italic>et al</italic>.[<xref ref-type="bibr" rid="ref18">18</xref>] Cut-off values for RHTMD recommended for predicting difficult laryngoscopy are 25 in Caucasians,[<xref ref-type="bibr" rid="ref18">18</xref>] 24 in Iranian patients[<xref ref-type="bibr" rid="ref19">19</xref>] and 23.5 in Thai patients.[<xref ref-type="bibr" rid="ref20">20</xref>] Krishna <italic>et al</italic>.[<xref ref-type="bibr" rid="ref21">21</xref>] used a cut-off value suggested by Schmitt <italic>et al</italic>.[<xref ref-type="bibr" rid="ref18">18</xref>] (≥25) in their study. In our study RHTMD was significantly higher in patients in the difficult laryngoscopy group (27.5 ± 5.2) compared with that in the easy laryngoscopy group (24.6 ± 3.8).</p><p>Sternomental distance (SMD) is an indicator of head and neck mobility.[<xref ref-type="bibr" rid="ref10">10</xref>] No study has addressed the correlation between SMD and difficult laryngoscopy in the Indian population. There was a statistically significant difference between SMD in the easy and difficult laryngoscopy groups (14.6 ± 1.7 cm and 13.8 ± 2.1 cm, respectively). The cut-off point of SMD suggested for predicting difficult laryngoscopy is 12.5 cm[<xref ref-type="bibr" rid="ref14">14</xref>] and 13.5 cm.[<xref ref-type="bibr" rid="ref10">10</xref>] Our aim was to evaluate anatomical measurements commonly used to predict a difficult airway in the Indian population, thereby revealing differences with measurement values obtained in non-Indian patients. We did not attempt to define cut-off values for TMD, SMD or RHTMD in this study as the sample size was not large enough to determine the cut-off threshold values. It is important to note that no single anatomical factor determines the ease of difficult laryngoscopy and therefore no single anatomic factor can be used to predict a difficult intubation.</p><p>The incidence of difficult laryngoscopy (Cormack grade 3-4) differs in various studies; it was reported to be 3.4% in West African population,[<xref ref-type="bibr" rid="ref17">17</xref>] 8.2% in a predominantly Chinese population[<xref ref-type="bibr" rid="ref22">22</xref>] and 23.1% in Iranian population.[<xref ref-type="bibr" rid="ref19">19</xref>] Amongst studies in the Indian population, Krishna <italic>et al</italic>.[<xref ref-type="bibr" rid="ref21">21</xref>] reported an incidence of 8.5%. However, they graded Cormack scores as the best view obtained with optimal laryngeal manipulation. In contrast, in a predominantly Kashmiri population, the incidence of difficult laryngoscopy was only 3.3%.[<xref ref-type="bibr" rid="ref16">16</xref>] In our study, the incidence of difficult laryngoscopy was 9.7% without ELP; the incidence decreased to 2.1% following ELP application.</p><p>On multivariate analysis, Mallampati class 3 and 4, range of neck movement <80°, IID ≤ 3.5 cm and snoring were independently related to difficult laryngoscopy. Previous studies have identified Mallampati class 3 and 4,[<xref ref-type="bibr" rid="ref11">11</xref><xref ref-type="bibr" rid="ref15">15</xref><xref ref-type="bibr" rid="ref16">16</xref><xref ref-type="bibr" rid="ref20">20</xref>] decreased range of neck movement,[<xref ref-type="bibr" rid="ref9">9</xref><xref ref-type="bibr" rid="ref16">16</xref><xref ref-type="bibr" rid="ref19">19</xref><xref ref-type="bibr" rid="ref20">20</xref>] decreased IID[<xref ref-type="bibr" rid="ref3">3</xref><xref ref-type="bibr" rid="ref15">15</xref><xref ref-type="bibr" rid="ref17">17</xref><xref ref-type="bibr" rid="ref18">18</xref><xref ref-type="bibr" rid="ref19">19</xref>] and snoring[<xref ref-type="bibr" rid="ref23">23</xref>] as predictors of difficult laryngoscopy.</p><p>The incidence of modified Mallampati class zero was 1.7% in our study which is comparable with that reported by Ezri <italic>et al</italic>.[<xref ref-type="bibr" rid="ref11">11</xref>] (1.8%) and Hegde <italic>et al</italic>.[<xref ref-type="bibr" rid="ref24">24</xref>] (1.7%). All patients with class zero airway had a Cormack grade 1laryngoscopic view. MMC zero per se is not associated with difficult laryngoscopy.[<xref ref-type="bibr" rid="ref24">24</xref>] While Mallampati class obtained in the sitting position is standard, at times airway examination in the sitting position may not be convenient, possible or advisable. Elderly, very sick and bed-ridden patients, those requiring emergency tracheal intubation or patients with prolapsed disc and fracture spine may not be able to sit up for assessment.[<xref ref-type="bibr" rid="ref25">25</xref>] MMC class 3-4 was observed in more patients in the supine position compared with sitting position (24.5% versus 16.1%, respectively) as has been reported previously.[<xref ref-type="bibr" rid="ref25">25</xref><xref ref-type="bibr" rid="ref26">26</xref><xref ref-type="bibr" rid="ref27">27</xref>] There was a statistically significant association between MMC in the supine position with difficult laryngoscopy (<italic>P</italic> = 0.004), but less so than MMC in the sitting position (<italic>P</italic> = 0.000). Airway evaluation in both the positions almost equally predicts for difficult laryngoscopy.[<xref ref-type="bibr" rid="ref25">25</xref><xref ref-type="bibr" rid="ref26">26</xref>]</p><p>We found snoring to be an independent risk factor for difficult laryngoscopy. Snoring occurs more frequently in males, overweight patients, worsens with age and is associated with obstructive sleep apnoea which possibly explains its association with difficult laryngoscopy.[<xref ref-type="bibr" rid="ref23">23</xref>] Diabetes is known to be associated with difficult laryngoscopy as was also seen in this study. An interesting finding of our study is that hypertensive patients were found to have a significant association with difficult laryngoscopy on univariate analysis.</p><p>There are anthropometric differences between the Indian population and the American or European population. The average height of an American adult male and female (1.776 m and 1.632 m, respectively)[<xref ref-type="bibr" rid="ref28">28</xref>] is considerably greater than that of an Indian male and female (1.612 m and 1.521 m, respectively).[<xref ref-type="bibr" rid="ref29">29</xref>] This probably translates into differences in the anatomical indices that are commonly used to predict difficult laryngoscopy. Naguib <italic>et al</italic>.[<xref ref-type="bibr" rid="ref30">30</xref>] found the mean TMD of patients in the easy and difficult laryngoscopy groups of 7.6 ± 0.9 and 6.45 ± 1.6 cm, respectively, that is greater compared to that found in our study (6.6 ± 0.9 and 6.0 ± 1.0, respectively). Likewise, the mean TMD in European patients with easy and difficult mask ventilation reported by Langeron <italic>et al</italic>.[<xref ref-type="bibr" rid="ref4">4</xref>] is 8.9 ± 1.6 and 8.5 ± 1.3 cm, respectively, considerably greater than TMD in our study. Safavi <italic>et al</italic>.[<xref ref-type="bibr" rid="ref31">31</xref>] concluded that the cut-off point for RHTMD for prediction of direct laryngoscopy is race dependent and recommend calculating cut-off point for each population separately.</p><p>Most previous studies in the Indian population have considered difficult laryngoscopy as indicative of difficult intubation.[<xref ref-type="bibr" rid="ref16">16</xref><xref ref-type="bibr" rid="ref21">21</xref><xref ref-type="bibr" rid="ref32">32</xref>] Although, difficult laryngoscopy is an important component of difficult intubation, the two may not always be necessarily correlated.[<xref ref-type="bibr" rid="ref33">33</xref>] The incidence of moderate to major difficult tracheal intubation (IDS >5) was 4.5% in our study. We found a high incidence of minor difficulty in intubation (48.5%). Similarly, Adnet <italic>et al</italic>.[<xref ref-type="bibr" rid="ref15">15</xref>] reported minor intubation difficulty in 37% and moderate to major difficulty in 8% of patients. Likewise, Schmitt <italic>et al</italic>.[<xref ref-type="bibr" rid="ref18">18</xref>] found 55% of patients to have no difficulty, 37.3% minor difficulty and 7.7% to have major difficulty in intubation.</p><p>Few studies have used the IDS score to assess tracheal intubation in the Indian population. Prakash <italic>et al</italic>.[<xref ref-type="bibr" rid="ref7">7</xref>] reported an 8% incidence of difficult laryngoscopy and found easy intubation in 60.4%, minor difficulty in 38.2% and moderate to major difficulty in 1.5% patients. In contrast, Ambardekar <italic>et al</italic>.[<xref ref-type="bibr" rid="ref34">34</xref>] reported difficult laryngoscopy in only 1.67% and moderate to major intubation difficulty in 0.67% patients. Gangadhar <italic>et al</italic>.[<xref ref-type="bibr" rid="ref35">35</xref>] reported a positive correlation between MMC class 1/2 and easy intubation, an incidence of Cormack grade 3/4 of 8.3% and difficulty in 35% of intubations in 60 patients undergoing tracheal intubation with cricoid pressure in the emergency department.</p><p>The anaesthesiologists in the easy laryngoscopy group adopted an erect posture in 81.1% of cases. In contrast, in 50% of cases in the difficult laryngoscopy group, the anaesthesiologists bent at their knees, stooped or leaned their upper body backwards to align the line of vision and the laryngeal axis.</p></sec><sec sec-type="conclusion" id="sec1-5"><title>CONCLUSION</title><p>We found an incidence of 9.7% and 4.5% for difficult laryngoscopy and difficult intubation, respectively, in Indian patients with apparently normal airways. 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