Poor prognostic value of the modified Mallampati score: a meta-analysis involving 177 088 patients

[Update Mallampati : Theoretical and practical knowledge of European anesthetists on basic evaluation of airways]

In 1985 Mallampati et al. published a non-invasive score for the evaluation of airways (Mallampati grading scale, MGS), which originally consisted of only three different classes and has been modified several times. At present it is mostly used in the version of Samsoon and Young consisting of four different classes. Class I: soft palate, fauces, uvula, palatopharyngeal arch visible, class II: soft palate, fauces, uvula visible, class III: soft palate, base of the uvula visible and class IV: soft palate not visible. Nevertheless, other versions of MGS still exist, each having different values for sensitivity and specification. The current opinion is therefore that MGS is no longer useful as a stand-alone predictor but in combination with others it is still part of today's most relevant guidelines, such as those of the American Society of Anesthesiologists (ASA), the UK's Difficult Airway Society (DAS), the European Society of Anaesthesiology (ESA) and the German Society for Anesthesiology and Intensive Care Medicine (DGAI) and must therefore be known by anesthetists. Even in times of sophisticated tools for airway management, the procedure remains a high risk, so every anesthetist has to be prepared for and well trained in management of known and unexpected difficult airways. Evaluation of the patient's airway is a part of modern airway management to prevent problems and reduce risk of hypoxia during the procedure. The theoretical knowledge and practical skills of European anesthetists were evaluated at two international congresses, the German Anesthesia Congress (DAC) and Euroanaesthesia 2014. The DAC is an annual meeting of German speaking anesthetists, hosted by the DGAI. The Euroanaesthesia is the annual European pendant hosted by the ESA. Participation was voluntary and only physicians were allowed to take part. Theory was evaluated by a questionnaire containing open and closed questions for MGS that had to be answered by every participant alone. Apart from theory, a practical evaluation was performed. Every participant had to classify the MGS of a human airway model. The model was identical on both congresses. According to the original publication a checklist containing the factors essential for the correct performance was filled out by a supervising experienced anesthetist. During DAC 2014 n = 267 physicians participated in the study, 22 participants were excluded due to inconsistent answers, incomplete questionnaires or missing practical part. A total of 245 data sets were evaluated. During Euroanaesthesia 2014 n = 298 physicians participated in the study, 68 participants were excluded due to inconsistent answers, incomplete questionnaires or missing practical part and 230 data sets were evaluated. At the DAC the mean age (± SD) was 44.5 ± 9.5 years, 157 (64.1%) were male and 88 (35.9%) were female. Working experience was trainee anesthetist in 16.7% and other participants were experienced anesthetists. At the ESA the mean age (± SD) was 42.4 ± 9.5 years, 133 (57.8%) were male and 97 (42.2%) female. Trainee anesthetists were 15.2%, the rest were experienced anesthetists. The DAC participants knew Mallampati classes 1 (65%) and 4 (45%) better than 2 and 3 and there was no relevant differences to the ESA (close to 30% knew the classes 1-4 here). Classification of the airway model was correct in 62% and 67% at DAC and ESA, respectively. Most participants performed the practical evaluation correctly except the sitting position of the model. In agreement with earlier studies, these results show the lack of knowledge in evaluation of airways according to current guidelines of all relevant societies. This is likely to increase preventable risks for patients as unexpected difficult airway management increases the risk for hypoxia and intubation damage.

Do Difficult Airway Techniques Predispose Obese Patients to Bronchospasm?

Objective

The existing evidence separately correlates morbid obesity with difficult intubation and bronchospasm. However, there is a lack of data on whether anaesthesia provider manipulations during difficult intubation contribute to an increased ratio of bronchospasm in these patients.

Methods

This is a retrospective analysis of data prospectively taken from 50 morbidly obese patients involved in a previously published study. A possible difficult intubation was preoperatively investigated by recording the following specific physical examination indices: Mallampati and Cormack-Lehane (CL) classifications, cervical spine mobility (CSM), thyromental distance (Td) and patients' ability to open their mouth (mouth opening). Bronchospasm was clinically detected by auscultation and confirmed by measuring peak airway pressures during mechanical ventilation. The Kruskal-Wallis H test was used for data analysis, followed by the Mann-Whitney U test as applicable.

Results

Different physical examination prognostic indices, including Mallampati and CL scales (p<0.001; the CSM excluded -p=0.790), showed that they are related to difficult intubation. Bronchospasm not attributable to difficult intubation was observed in six obese patients.

Conclusion

Patients with morbid obesity constitute an increased relative risk group as far as difficult intubation is concerned, particularly if preoperative findings support a relationship between the two variables examined. In our study, difficult intubation and the concomitant use of special equipment and manipulations did not contribute to an increased rate of bronchospasm in obese patients, but in view of the lack of data, a large number of more sophisticated studies are required to elucidate such an assumption.

Airway physical examination tests for detection of difficult airway management in apparently normal adult patients

BACKGROUND

The unanticipated difficult airway is a potentially life-threatening event during anaesthesia or acute conditions. An unsuccessfully managed upper airway is associated with serious morbidity and mortality. Several bedside screening tests are used in clinical practice to identify those at high risk of difficult airway. Their accuracy and benefit however, remains unclear.

OBJECTIVES

The objective of this review was to characterize and compare the diagnostic accuracy of the Mallampati classification and other commonly used airway examination tests for assessing the physical status of the airway in adult patients with no apparent anatomical airway abnormalities. We performed this individually for each of the four descriptors of the difficult airway: difficult face mask ventilation, difficult laryngoscopy, difficult tracheal intubation, and failed intubation.

SEARCH METHODS

We searched major electronic databases including CENTRAL, MEDLINE, Embase, ISI Web of Science, CINAHL, as well as regional, subject specific, and dissertation and theses databases from inception to 16 December 2016, without language restrictions. In addition, we searched the Science Citation Index and checked the references of all the relevant studies. We also handsearched selected journals, conference proceedings, and relevant guidelines. We updated this search in March 2018, but we have not yet incorporated these results.

SELECTION CRITERIA

We considered full-text diagnostic test accuracy studies of any individual index test, or a combination of tests, against a reference standard. Participants were adults without obvious airway abnormalities, who were having laryngoscopy performed with a standard laryngoscope and the trachea intubated with a standard tracheal tube. Index tests included the Mallampati test, modified Mallampati test, Wilson risk score, thyromental distance, sternomental distance, mouth opening test, upper lip bite test, or any combination of these. The target condition was difficult airway, with one of the following reference standards: difficult face mask ventilation, difficult laryngoscopy, difficult tracheal intubation, and failed intubation.

DATA COLLECTION AND ANALYSIS

We performed screening and selection of the studies, data extraction and assessment of methodological quality (using QUADAS-2) independently and in duplicate. We designed a Microsoft Access database for data collection and used Review Manager 5 and R for data analysis. For each index test and each reference standard, we assessed sensitivity and specificity. We produced forest plots and summary receiver operating characteristic (ROC) plots to summarize the data. Where possible, we performed meta-analyses to calculate pooled estimates and compare test accuracy indirectly using bivariate models. We investigated heterogeneity and performed sensitivity analyses.

MAIN RESULTS

We included 133 (127 cohort type and 6 case-control) studies involving 844,206 participants. We evaluated a total of seven different prespecified index tests in the 133 studies, as well as 69 non-prespecified, and 32 combinations. For the prespecified index tests, we found six studies for the Mallampati test, 105 for the modified Mallampati test, six for the Wilson risk score, 52 for thyromental distance, 18 for sternomental distance, 34 for the mouth opening test, and 30 for the upper lip bite test. Difficult face mask ventilation was the reference standard in seven studies, difficult laryngoscopy in 92 studies, difficult tracheal intubation in 50 studies, and failed intubation in two studies. Across all studies, we judged the risk of bias to be variable for the different domains; we mostly observed low risk of bias for patient selection, flow and timing, and unclear risk of bias for reference standard and index test. Applicability concerns were generally low for all domains. For difficult laryngoscopy, the summary sensitivity ranged from 0.22 (95% confidence interval (CI) 0.13 to 0.33; mouth opening test) to 0.67 (95% CI 0.45 to 0.83; upper lip bite test) and the summary specificity ranged from 0.80 (95% CI 0.74 to 0.85; modified Mallampati test) to 0.95 (95% CI 0.88 to 0.98; Wilson risk score). The upper lip bite test for diagnosing difficult laryngoscopy provided the highest sensitivity compared to the other tests (P < 0.001). For difficult tracheal intubation, summary sensitivity ranged from 0.24 (95% CI 0.12 to 0.43; thyromental distance) to 0.51 (95% CI 0.40 to 0.61; modified Mallampati test) and the summary specificity ranged from 0.87 (95% CI 0.82 to 0.91; modified Mallampati test) to 0.93 (0.87 to 0.96; mouth opening test). The modified Mallampati test had the highest sensitivity for diagnosing difficult tracheal intubation compared to the other tests (P < 0.001). For difficult face mask ventilation, we could only estimate summary sensitivity (0.17, 95% CI 0.06 to 0.39) and specificity (0.90, 95% CI 0.81 to 0.95) for the modified Mallampati test.

AUTHORS' CONCLUSIONS

Bedside airway examination tests, for assessing the physical status of the airway in adults with no apparent anatomical airway abnormalities, are designed as screening tests. Screening tests are expected to have high sensitivities. We found that all investigated index tests had relatively low sensitivities with high variability. In contrast, specificities were consistently and markedly higher than sensitivities across all tests. The standard bedside airway examination tests should be interpreted with caution, as they do not appear to be good screening tests. Among the tests we examined, the upper lip bite test showed the most favourable diagnostic test accuracy properties. Given the paucity of available data, future research is needed to develop tests with high sensitivities to make them useful, and to consider their use for screening difficult face mask ventilation and failed intubation. The 27 studies in 'Studies awaiting classification' may alter the conclusions of the review, once we have assessed them.

Use of ultrasound to predict difficult intubation in Chinese population by assessing the ratio of the pre-epiglottis space distance and the distance between epiglottis and vocal folds

Objective:

To investigate the accuracy of using the ratio of pre-epiglottis space distance (Pre-E) and the distance between the epiglottis and the vocal folds (Pre-E/E-VF) measured by the ultrasound to predict potential difficult airway in the Chinese population.

Design:

A prospective clinical study.

Setting:

The pre-operative assessment service clinic of Tuen Mun Hospital.

Patients:

Patients with age of 18 years or above, who were scheduled for elective surgery requiring general anesthesia with direct laryngoscopy and tracheal intubation.

Results:

A total of 113 patients with direct laryngoscopic assessment during elective operations were included. Thirty-nine (34.5%) patients had potential difficult airway which was defined as documented Cormack–Lehane classification grade 2b, 3, or 4 by the anesthetists. Measurement of the distance from the epiglottis to the anterior vocal folds (Pre-E/aVF) ratio had better inter-rater reliability and accuracy comparing to the measurements of the distances from the epiglottis to the midpoint between the vocal folds and to the posterior vocal folds. The performance of using the Pre-E/aVF ratio to predict potential difficult airway was compared with other clinical tests (the Mallampati classification, the thyromental distance and the neck circumference to thyromental distance ratio). By using the Pre-E/aVF ratio of 1, the sensitivity and specificity to predict a potential difficult airway were 79.5% and 39.2%, respectively (p = 0.044). The ultrasound assessment method had a comparable predictive value as the Mallampati classification (the area under the receiver operator characteristic curves 0.648 vs 0.687). The negative likelihood ratio of the ultrasound assessment method was the lowest among all the other airway assessment methods.

Conclusion:

The ultrasound airway assessment method could serve as a non-invasive test and supplement the currently used clinical assessment methods. A lower cut-off point of the Pre-E/E-VF ratio should be used in the Chinese population.

Radiologic indicators for prediction of difficult laryngoscopy in patients with cervical spondylosis

BACKGROUND

We identified the most useful variables for prediction of difficult laryngoscopy in patients with cervical spondylosis according to physical indicators and preoperative skeletal X-ray and soft tissue MRI measurements. We hypothesized that there was a closer association between difficult laryngoscopy and radiologic indicators.

METHODS

We randomly enroled 315 patients undergoing elective cervical spine surgery and analysed the radiological and physical data in predicting difficult laryngoscopy.

RESULTS

We identified five variables that were most useful in predicting difficult laryngoscopy: the inter-incisor gap (P = 0.006), modified Mallampati test score (P = 0.004), distance from the highest point of the hyoid bone to the mandibular body (P < 0.001), most antero-inferior point of the upper central incisor tooth (P < 0.001), and length of the epiglottis (P = 0.002). Binary multivariate logistic regression analyses identified three factors that were independently associated with difficult laryngoscopy: the Mallampati score, distance from the hyoid bone to the mandibular body, and the anterior-inferior point of the upper central incisor tooth. The odds ratios and 95% confidence intervals were 1.547 (1.029-2.327), 1.222 (1.139-1.310), and 1.224 (1.133-1.322), respectively. The AUC for hyoid bone distance to mandibular body (0.832) was larger than that of anterior-inferior point of the upper central incisor tooth (0.802, P > 0.05) and that of modified Mallampati test (0.602, P < 0.05).

CONCLUSION

Distance from the highest point of the hyoid bone to the mandibular body appears to be the most accurate indicator for difficult laryngoscopy in patients with cervical spondylosis.

Ultrasound evaluation of the airway in the ED: a feasibility study

Background

Recognition of the difficult airway is a critical element of emergency practice. Mallampati score and body mass index (BMI) are not always predictive and they may be unavailable in critically ill patients. Ultrasonography provides high-resolution images that are rapidly obtainable, mobile, and non-invasive. Studies have shown correlation of ultrasound measurements with difficult laryngoscopy; however, none have been performed in the Emergency Department (ED) using a consistent scanning protocol.

Objectives

This study seeks to determine the feasibility of ultrasound measurements of the upper airway performed in the ED by emergency physicians, the inter-rater reliability of such measurements, and their relationship with Mallampati score and BMI.

Methods

A convenience sample of volunteer ED patients and healthy volunteers with no known airway issues, aged > 18 years, had images taken of their airway using a standardized ultrasound scanning protocol by two EM ultrasound fellowship trained physicians. Measurements consisted of tongue base, tongue base-to-skin, epiglottic width and thickness, and pre-epiglottic space. Mean and standard deviation (SD) were used to summarize measurements. Inter-rater reliability was assessed by intraclass correlation coefficients (ICCs). Analysis of variance with linear contrasts was used to compare measurements with Mallampati scores and linear regression with BMI.

Results

Of 39 participants, 50% were female, 50% white, 42% black, with median age 32.5 years (range 19–90), and BMI 26.0 (range 19–47). Mean ± SD for each measurement (mm) was as follows: tongue base (44.6 ± 5.1), tongue base-to-skin (60.9 ± 5.3), epiglottic width (15.0 ± 2.8) and thickness (2.0 ± 0.37), and pre-epiglottic space (11.4 ± 2.4). ICCs ranged from 0.76 to 0.88 for all measurements except epiglottis thickness (ICC = 0.57). Tongue base and tongue base-to-skin thickness were found to increase with increasing Mallampati score (p = .04, .01), whereas only tongue-to-skin thickness was loosely correlated with BMI (r = .38).

Conclusions

A standardized ultrasound scanning protocol demonstrates that the airway can be measured by emergency sonologists with good inter-operator reliability in all but epiglottic thickness. The measurements correlate with Mallampati score but not with BMI. Future investigation might focus on ultrasound evaluation of the airway in patients receiving airway management to determine whether ultrasound can predict challenging or abnormal airway anatomy prior to laryngoscopy.

Does Body Mass Index Reduction by Bariatric Surgery Affect Laryngoscopy Difficulty During Subsequent Anesthesia?

BACKGROUND

The effect of body mass index (BMI) reduction following bariatric surgery on subsequent airway management has not been investigated. This study aimed to investigate the association between BMI reduction and airway assessment and management measured by Mallampati class (MC) and laryngoscopy grade (LG).

METHODS

We conducted a retrospective study over 6 years to compare the BMI changes, MC and LG in patients having weight reduction bariatric surgery followed by subsequent surgery. Data was extracted from the anesthesia records of patients undergoing laparoscopic band insertion (LBI) and laparoscopic sleeve gastrectomy (LSG). Difficult airway was defined as Malampati class 3 and 4 on a 1-4 difficulty scale or laryngoscopy grade >2 on a 1-4 difficulty scale and need for unplanned fiberoptic intubation. Changes in these variables were correlated with weight reduction. Statistical analysis included t test, univariante, and multivariant logistic regression.

RESULTS

Five hundred forty-six patients underwent LSG and 83 patients had LBI during the study period. Of those patients, 65 patients had subsequent surgical procedures after the bariatric procedure. Of the 65 patients identified, 62 were eligible. BMI decreased by approximately13 kg/m² (p = 0.000) which roughly represents a 30 % reduction between the two surgical procedures. Mallampati class decreased significantly (p = 0.000) while laryngoscopy grade did not (p = 0.419).

CONCLUSION

Our study revealed that a significant reduction in BMI was associated with a significant decrease in Mallampati class. There was no significant decrease in laryngoscopy grade, and there was no case of unplanned fiberoptic intubation.

Enhancing airway assessment of patients with head and neck pathology using virtual endoscopy

Studies have demonstrated that poor assessment and planning contribute to airway complications and that current airway assessment strategies have a poor diagnostic accuracy in predicting difficult intubation in the general population. Patients with head and neck pathology are at higher risk for difficulties during airway management and are more likely to need emergency surgical access. Therefore, thorough assessment of this group of patients is mandatory. The addition of virtual endoscopy (VE) to clinical history and computerised tomography imaging has been shown to improve diagnostic accuracy for supraglottic, glottic and infraglottic lesions and has a positive influence in formulating a more cautious and thorough airway management strategy in this high-risk group of patients. This article reviews whether VE can enhance airway assessment in patients with head and neck pathology and help reduce airway complications.

Clinical Experiences with the FRONT Formula for Pre-Operative Airway Assessment and Documentation: a Multi-Centre Study

OBJECTIVE

The prediction of difficult airway is one of the most important challenges before general anaesthesia. This study aimed to assess the clinical usefulness of the FRONT score, a recently developed scoring system to predict and document airway difficulties.

METHODS

This multi-centre, inter-observer, prospective and double-blinded study included 976 patients from two university centres. The pre-operative evaluation of the patients was performed by a pre-operative team of anaesthesiologists (team A) who evaluated and scored the expected difficulty of airway management. An intra-operative team of evaluators (team B) working independently of team A, performed the actual instrumentation of the airway and scored the actual findings. Both teams used the FRONT scoring system and worked independently of each other to ensure blinded assessments. The statistical analysis of the pre- and intra-operative FRONT scores was performed in an off-line blinded manner.

RESULTS

Our results show a fair and promising association between pre-operative composite FRONT score and that observed at the induction phase (Spearman=0.43). Among the score components, the best correlation was observed for the F and R components (kappa=0.44 and 0.36, respectively), and the worse correlation was observed for the O and T components (kappa=0.25 and 0.24, respectively).

CONCLUSION

The FRONT formula for the prediction and documentation of the airway status is a simple and effective method for assessing and defining airway management difficulties. Further prospective studies are required to assess the sensitivity and specificity of the system.

Avoidance versus use of neuromuscular blocking agents for improving conditions during tracheal intubation or direct laryngoscopy in adults and adolescents

BACKGROUND

Tracheal intubation during induction of general anaesthesia is a vital procedure performed to secure a patient's airway. Several studies have identified difficult tracheal intubation (DTI) or failed tracheal intubation as one of the major contributors to anaesthesia-related mortality and morbidity. Use of neuromuscular blocking agents (NMBA) to facilitate tracheal intubation is a widely accepted practice. However, because of adverse effects, NMBA may be undesirable. Cohort studies have indicated that avoiding NMBA is an independent risk factor for difficult and failed tracheal intubation. However, no systematic review of randomized trials has evaluated conditions for tracheal intubation, possible adverse effects, and postoperative discomfort.

OBJECTIVES

To evaluate the effects of avoiding neuromuscular blocking agents (NMBA) versus using NMBA on difficult tracheal intubation (DTI) for adults and adolescents allocated to tracheal intubation with direct laryngoscopy. To look at various outcomes, conduct subgroup and sensitivity analyses, examine the role of bias, and apply trial sequential analysis (TSA) to examine the level of available evidence for this intervention.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, BIOSIS, International Web of Science, LILACS, advanced Google, CINAHL, and the following trial registries: Current Controlled Trials; ClinicalTrials.gov; and www.centerwatch.com, up to January 2017. We checked the reference lists of included trials and reviews to look for unidentified trials.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) that compared the effects of avoiding versus using NMBA in participants 14 years of age or older.

DATA COLLECTION AND ANALYSIS

Two review authors extracted data independently. We conducted random-effects and fixed-effect meta-analyses and calculated risk ratios (RRs) and their 95% confidence intervals (CIs). We used published data and data obtained by contacting trial authors. To minimize the risk of systematic error, we assessed the risk of bias of included trials. To reduce the risk of random errors caused by sparse data and repetitive updating of cumulative meta-analyses, we applied TSA.

MAIN RESULTS

We identified 34 RCTs with 3565 participants that met our inclusion criteria. All trials reported on conditions for tracheal intubation; seven trials with 846 participants described 'events of upper airway discomfort or injury', and 13 trials with 1308 participants reported on direct laryngoscopy. All trials used a parallel design. We identified 18 dose-finding studies that included more interventions or control groups or both. All trials except three included only American Society of Anesthesiologists (ASA) class I and II participants, 25 trials excluded participants with anticipated DTI, and obesity or overweight was an excluding factor in 13 studies. Eighteen trials used suxamethonium, and 18 trials used non-depolarizing NMBA.Trials with an overall low risk of bias reported significantly increased risk of DTI with no use of NMBA (random-effects model) (RR 13.27, 95% CI 8.19 to 21.49; P < 0.00001; 508 participants; four trials; number needed to treat for an additional harmful outcome (NNTH) = 1.9, I² = 0%, D² = 0%, GRADE = moderate). The TSA-adjusted CI for the RR was 1.85 to 95.04. Inclusion of all trials resulted in confirmation of results and of significantly increased risk of DTI when an NMBA was avoided (random-effects model) (RR 5.00, 95% CI 3.49 to 7.15; P < 0.00001; 3565 participants; 34 trials; NNTH = 6.3, I² = 70%, D² = 82%, GRADE = low). Again the cumulative z-curve crossed the TSA monitoring boundary, demonstrating harmful effects of avoiding NMBA on the proportion of DTI with minimal risk of random error. We categorized only one trial reporting on upper airway discomfort or injury as having overall low risk of bias. Inclusion of all trials revealed significant risk of upper airway discomfort or injury when an NMBA was avoided (random-effects model) (RR 1.37, 95% CI 1.09 to 1.74; P = 0.008; 846 participants; seven trials; NNTH = 9.1, I² = 13%, GRADE = moderate). The TSA-adjusted CI for the RR was 1.00 to 1.85. None of these trials reported mortality. In terms of our secondary outcome 'difficult laryngoscopy', we categorized only one trial as having overall low risk of bias. All trials avoiding NMBA were significantly associated with difficult laryngoscopy (random-effects model) (RR 2.54, 95% CI 1.53 to 4.21; P = 0.0003; 1308 participants; 13 trials; NNTH = 25.6, I² = 0%, D²= 0%, GRADE = low); however, TSA showed that only 6% of the information size required to detect or reject a 20% relative risk reduction (RRR) was accrued, and the trial sequential monitoring boundary was not crossed.

AUTHORS' CONCLUSIONS

This review supports that use of an NMBA may create the best conditions for tracheal intubation and may reduce the risk of upper airway discomfort or injury following tracheal intubation. Study results were characterized by indirectness, heterogeneity, and high or uncertain risk of bias concerning our primary outcome describing difficult tracheal intubation. Therefore, we categorized the GRADE classification of quality of evidence as moderate to low. In light of defined outcomes of individual included trials, our primary outcomes may not reflect a situation that many clinicians consider to be an actual difficult tracheal intubation by which the patient's life or health may be threatened.

Neck circumference to inter-incisor gap ratio: a new predictor of difficult laryngoscopy in cervical spondylosis patients

Background

Preoperative airway assessment help anticipate a difficult airway. We hypothesized that a close association existed between difficult laryngoscopy and the neck circumference/inter-incisor gap ratio (RNIIG). Our aim was to determine its utility in predicting difficult laryngoscopy in cervical spondylosis patients.

Methods

Two hundred thirteen consecutive patients, aged 20–70 years, scheduled to undergo cervical spine surgery under general anesthesia, were recruited. Preoperative assessments included inter-incisor gap (IIG), thyromental distance (TMD), neck circumference (NC), NC/IIG ratio (RNIIG), NC/TMD ratio (RNTMD) and modified Mallampati test (MMT). Cormack–Lehane scales were assessed during intubation. The anesthesiologist was blinded to the airway assessments. RNIIG’s ability to predict difficult laryngoscopy was compared with that of established predictors.

Results

Difficult laryngoscopy incidence was 16.4%. Univariate analysis showed that male gender, increased age, weight, NC, RNIIG and RNTMD, decreased IIG and TMD, and MMT 3 and 4 were associated with difficult laryngoscopy. Binary multivariate logistic regression analyses identified only one factor that was independently associated with difficult laryngoscopy: RNIIG. The odds ratio and 95% confidence interval (95% CI) were 1.932 (1.504–2.482). RNIIG (≥9.5) exhibited the largest area under the curve (0.80; 95% CI 0.73–0.86) and the highest sensitivity (88.6%; 95% CI 78.1–99.1) and negative predictive value (96.6%; 95% CI 94.0–99.2), confirming its better predictive ability.

Conclusions

RNIIG is a new and simple predictor with a higher level of efficacy, and could help anesthetists plan for difficult laryngoscopy management in cervical spondylosis patients.

Trial registration

ChiCTR-OON-16008320 (April 19th, 2016).

Ethnicity and upper airway measurements: A study in South Indian population

Background and Aims:

Most studies on upper airway are conducted based on airway measurements in the western population. We set out to find the normal values of upper airway measurements in South Indian population. The aim of this study was to perform various upper airway examinations and to set standards for normal measurements in the South Indian population as well as to analyse the data for predictors of difficult intubation.

Methods:

This prospective observational study was conducted in a tertiary cancer hospital in Southern India. Airway assessment parameters, including modified Mallampati classification (MPC), upper lip bite test (ULBT), sternomental distance, thyromental distance (TMD), and the inter-incisor distance were documented for 2004 patients meeting the inclusion criteria. Laryngoscopic view after induction was graded as per Cormack and Lehane's (CL) classification. Any CL ≥3 was considered to be difficult laryngoscopy. The collected data (2004 cases) was analyed with SPSS software version 17. Receiver operating characteristics (ROC) curve was used to determine cut-offs in the population. Sensitivity, specificity, positive and negative predictive value were computed.

Results:

MPC, ULBT, and ratio of height to TMD (RHTMD) predicted difficult intubation with sensitivity of 40.86%, 45.53% and 64.60%, respectively and these were statistically significant with P < 0.001. Using the area under the curve of the ROC curve and discrimination analysis normal RHTMD in our population had a cut off value of 17.1.

Conclusion:

The cut off value for RHTMD to predict difficult laryngoscopy in the South Indian population is 17.1.

Soft Palate Injuries During Orotracheal Intubation With the Videolaryngoscope

OBJECTIVE

The videolaryngoscope has gained popularity for providing superior visualization in intubations. A rare complication of this technology is soft palate injury. Through a literature review and case series, we highlight the risks associated with the Glidescope and McGrath videolaryngoscopes and the management of soft palate injuries.

METHOD

A case series of multi-institutional review of medical records was performed to identify patients with soft palate injuries from the videolaryngoscope. A literature review was also performed to analyze risk factors, mechanism of injury, complications, and management of palate injuries.

RESULTS

Of 9 cases, 3 resulted in soft palate perforations, which required primary closure. The remaining 6 patients sustained a soft palate laceration, which was treated conservatively. This injury commonly occurs when the intubator is focused on the video monitor and blindly inserts the Glidescope into the oropharynx. The rigid stylet used with the Glidescope increases the propensity for oropharyngeal injuries during blind insertions.

CONCLUSION

Proper training, an awareness of this potential complication, and direct oral cavity visualization are recommended while inserting the videolaryngoscope. Repair is recommended for through-and-through perforations or if a large hanging flap is present. Antibiotics should be considered for lacerations greater than 1 to 2 cm.

Usefulness of Ultrasound View of Larynx in Pre-Anesthetic Airway Assessment: A Comparison With Cormack-Lehane Classification During Direct Laryngoscopy

Background

One of the main challenges in anesthesiology is difficult intubation. There are many anatomical parameters for evaluating the feasibility of tracheal intubation; one that can reliably predict a difficult intubation is the Cormack-Lehane classification obtained during direct laryngoscopy. This is an invasive procedure that cannot be performed in an awake patient or for pre-anesthetic airway assessments in patients with no prior history of tracheal intubation. Recently, ultrasound has been successfully used for several airway-related applications.

Objectives

The aim of this study was to compare and correlate the ultrasound view of the larynx with the Mallampati classification before anesthesia and the Cormack-Lehane classification during direct laryngoscopy under general anesthesia.

Methods

This cross-sectional descriptive-analytic study included 53 ASA class I - III patients aged 18 - 70 years who were scheduled for tracheal intubation under general anesthesia. Before anesthesia, an oblique transverse ultrasound view of the airway was obtained; in addition, the total time taken to achieve the final plane, the depth of the pre-epiglottic space, and the distance from the epiglottis to the mid-point between the vocal cords were all recorded. The ultrasound measurements were then compared with the Mallampati class on the preoperative evaluation and with the Cormack-Lehane grade during direct laryngoscopy under general anesthesia.

Results

It was observed that correlations between the pre-epiglottic space (PE) and Cormack-Lehane grades I, II, and III were weak. Correlations between the distance from the epiglottis to the vocal cords (E-VC) and Cormack-Lehane grades I, II, and III were also weak. The PE/E-VC ratio for correlations between the sonographic view and laryngoscopy had 87.5% sensitivity and 30% specificity. There was no correlation between Mallampati class and the PE/E-VC ratio (P = 0.566).

Conclusions

Our study revealed weak correlation between PE/E-VC and Cormack-Lehane grade, with 87% sensitivity and 30% specificity. Therefore, we concluded that sonographic measurement criteria are not accurate in airway evaluations before anesthesia.

Hyomental distance in the different head positions and hyomental distance ratio in predicting difficult intubation

The hyomental distance ratio (HMDR) is the ratio between the hyomental distance (HMD) (the distance between the hyoid bone and the tip of the chin) at the extreme of head extension (HMDe) and the one in the neutral position (HMDn). The objective of the study was to examine the predictive value, sensitivity, and specificity of HMDe, HMDn, and HMDR in predicting difficult endotracheal intubation (DI). A prospective study included 262 patients that underwent elective surgical operations. The following parameters were observed as possible predictors of DI: HMDR, HMDe, HMDn, Mallampati score, and body mass index (BMI). The cut-off points for the DI predictors were HMDe <5.3 cm, HMDn ≤5.5 cm, and HMDR ≤1.2. The assessment that DI existed was made by the anesthesiologist while performing laryngoscopy by applying the Cormack-Lehane classification. DI was present in 13 patients (5%). No significant difference was observed in the frequency of DI with regard to the sex, age, and BMI of the patients. Our research indicated HMDR as the best predictor of DI with a sensitivity of 95.6% and specificity of 69.2%. HMDR can be used in the everyday work of anesthesiologists because HMDR values ≤1.2 may reliably predict DI.

Bedside tests to predict laryngoscopic difficulty in pediatric patients

BACKGROUND AND OBJECTIVES

Pediatric airway management is a priority during anesthesia, critical care and emergency medicine. The purpose of this study is to validate bedside tests that predict airway management difficulty in anesthetized children.

METHODS

Children under 12 years of age were recruited in a cross-sectional study to assess the value of some anthropometric measures as predictors of laryngoscopic difficulty. The patients were divided into three groups by age. Weight, height, neck circumference, BMI (body mass index), inter incisors distance thyromental distance, sternomental distance, frontal plane to chin distance (FPCD) and the Mallampati index were determined and were correlated with the CML (Cormack & Lehane classification).

RESULTS

The incidence of difficult laryngoscopy (CML 3 or 4) was 3.58%. Factors that were significantly associated with laryngoscopic difficulty included short inter incisors distance, high FPCD, thyromental distance, sternomental distance and the Mallampati index. The FPCD/weight index exhibited a higher area under the ROC curve than any other variable considered.

CONCLUSIONS

This study confirms that the FPCD and the FPCD/weight ratio are the most consistent predictors of laryngoscopic difficulty in pediatric patients. For patients over 6 months of age, the IID also correlated with laryngoscopic difficulty. For children who were capable of obeying simple orders, the Mallampati test correlated better with laryngoscopic difficulty than did the Mallampati test with phonation. Our results strongly suggest that skilled professionals should perform airway management in children, especially in patients with a high FPCD or a high FPCD/weight ratio.

Assessment before airway management

It is wise to plan and prepare for the unexpected difficult airway. Although it is essential to take a history and examine every patient prior to airway management, preoperative anticipation of a difficult airway occurs in only 50% of patients subsequently found to have a difficult airway. Bedside screening tests lack accuracy. The modified Mallampati test and the measurement of thyromental distance are unreliable for prediction of difficult tracheal intubation. Knowledge of risk factors for various airway management techniques may help when devising an airway management plan.

Facial Image Analysis for Fully Automatic Prediction of Difficult Endotracheal Intubation

GOAL

Difficult tracheal intubation is a major cause of anesthesia-related injuries with potential life threatening complications. Detection and anticipation of difficult airway in the preoperative period is, thus, crucial for the patients' safety. We propose an automatic face-analysis approach to detect morphological traits related to difficult intubation and improve its prediction.

METHODS

For this purpose, we have collected a database of 970 patients including photos, videos, and ground truth data. Specific statistical face models have been learned using the faces in our database providing an automated parametrization of the facial morphology. The most discriminative morphological features are selected through the importance ranking provided by the random forest algorithm. The random forest approach has also been used to train a classifier on these selected features. We compare a threshold tuning method based on class prior with two methods, which learn an optimal threshold on a training set for tackling the inherent imbalanced nature of the database.

RESULTS

Our fully automated method achieves an AUC of 81.0% in a simplified experimental setup, where only easy and difficult patients are considered. A further validation on the entire database has proven that our method is applicable for real-world difficult intubation prediction, with AUC = 77.9%.

CONCLUSION

The system performance is in line with the state-of-the-art medical diagnosis, based on ratings provided by trained anesthesiologists, whose assessment is guided by an extensive set of criteria.

SIGNIFICANCE

We present the first completely automatic and noninvasive difficult intubation detection system that is suitable for use in clinical settings.

Indirect laryngoscopic assessment for the diagnosis of difficult intubation in patients undergoing microlaryngeal surgery

BACKGROUND

The aim of this study is to investigate the feasibility of using indirect laryngoscopy for the diagnosis of difficult intubations in patients who are undergoing microlaryngeal surgery.

METHODS

In the pre-anesthetic examination the thyromental distance, sternomental distance, interincisor distance, neck circumference, modified Mallampati scores, and Wilson risk scores were measured. An otolaryngologist conducted an indirect laryngoscopic assessment. Direct laryngoscopic profiles were classified according to their Cormack-Lehane scores.

RESULTS

Forty patients underwent microlaryngeal surgery. Their mean ages, neck circumferences, Cormack-Lehane scores of the patients who had intubation difficulties were statistically significantly higher than those who did not have intubation difficulties (p < 0.05). The significant differences between the indirect laryngoscopic assessment distributions of patients who either had or did not have intubation difficulty were assessed (p < 0.05).

CONCLUSIONS

Indirect laryngoscopic assessment is a simple and valuable technique that can be used for the diagnosis of difficult intubation in patients who are undergoing microlaryngeal surgery.

Predicting outcomes: Is there utility in risk scores?

PURPOSE

This review discusses the utility of risk scores, specifically, the role of preoperative risk scores in guiding the management of surgical patients, approaches to evaluate the quality of risk scores, and limitations to consider when applying risk scores in clinical practice.

PRINCIPAL FINDINGS

This review shows how accurate predictions of perioperative risk can help inform patients and clinicians with respect to decision-making around surgery; identify patients who warrant further specialized investigations, new interventions intended to decrease risk, modifications in planned operative procedures, or intensification of postoperative monitoring; and facilitate fairer comparisons of outcomes between providers and hospitals. A preoperative risk score formally integrates several pieces of clinical information (e.g., age, comorbid disease, laboratory tests) to arrive at an overall estimate of an individual patient's expected risk for specific postoperative adverse events. A good risk score should be simple to incorporate in clinical practice, reliable when applied by different raters, and accurate at predicting postoperative risk. Several analytical methods (e.g., receiver operating characteristic curves, likelihood ratios, risk reclassification tables, observed vs predicted plots) are required to characterize the relevant domains that encompass the prognostic accuracy of a risk score. External validation is critical in determining whether the predictive accuracy of a risk score is preserved when applied to new settings, populations, or outcome events.

CONCLUSIONS

Preoperative risk scores help inform perioperative clinical decision-making. Future research must determine how estimates of preoperative risk can be updated with information from the intraoperative period, how risk information should be communicated to patients, and which interventions can improve outcomes among patients within newly identified risk strata.

Comparison between different tests and their combination for prediction of difficult intubation: An analytical study

CONTEXT

There is an impelling need for accurate tests to predict difficult intubation, as failure to achieve endotracheal intubation causes significant morbidity and mortality in anesthetic practice.

AIM

To calculate the validity of the different tests along with their combination and agreement when compared with endotracheal intubation in predicting difficult intubation.

SETTINGS AND DESIGN

Operation theaters, analytical study.

MATERIALS AND METHODS

Three hundred patients aged between 16 and 60 years of American society of anesthesiologist (ASA) physical status I and II, scheduled for elective surgical procedures requiring endotracheal intubation were studied during January-July 2012. Mallampati grade (MP), sternomental distance (SMD), thyromental distance (TMD), and Delilkan and Calder test were recorded for every patient. Endotracheal intubation was performed by an experienced anesthesiologist blinded to the measurements and recorded grading of intubation. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), likelihood ratio (LR), odds ratio (OR), and kappa coefficient of tests individually and in combination were calculated.

STATISTICAL ANALYSIS USED

IBM SPSS software (version 16.0) and Epi-info software (version 3.2).

RESULTS

Difficult and failed intubation was 13.3% and 0.6%, respectively. Difficult intubation increased with age. TMD and Calder test showed highest sensitivity individually and Dellilkan's test showed least sensitivity. Among the combination of tests, MP with SMD and MP with Calder test had the highest sensitivity.

CONCLUSION

Among individual test TMD and Calder are better predictive tests in terms of sensitivity. Combination of tests increases the chance of prediction of difficult intubation.

[Correlation between oro and hypopharynx shape and position with endotracheal intubation difficulty]

BACKGROUND AND OBJECTIVE

Prediction of intubation difficulty can save patients from major preoperative morbidity or mortality. The purpose of this paper is to assess the correlation between oro-hypo pharynx position, neck size, and length with endotracheal intubation difficulty. The study also explored the diagnostic value of Friedman Staging System in prediction cases with difficult intubation.

METHOD

The consecutive 500 ASA (I, II) adult patients undergoing elective surgery were evaluated for oro and hypopharynx shape and position by modified Mallampati, Cormack and Lehane score as well as Friedman obstructive sleep apnea classification systems. Neck circumference and length were also measured. All cases were intubated by a single anesthesiologist who was uninformed of the above evaluation and graded intubation difficulty in visual analog score. Correlation between these findings and difficulty of intubation was assessed. Sensitivity, Specificity, Positive and Negative Predictive Values were also reported.

RESULTS

Cormack-Lehane grade had the strongest correlation with difficulty of intubation followed by Friedman palate position. Friedman palate position was the most sensitive and had higher positive and negative predictive values than modified Mallampati classification. Cormack-Lehane grade was found to be the most specific with the highest negative predictive value among the four studied classifications.

CONCLUSION

Friedman palate position is a more useful, valuable and sensitive test compared to the modified Mallampati screening test for pre-anesthetic prediction of difficult intubation where its involvement in Multivariate model may raise the accuracy and diagnostic value of preoperative assessment of difficult airway.

Role of anterior neck soft tissue quantifications by ultrasound in predicting difficult laryngoscopy

Background

The aim of this study was to determine if ultrasound (US) measurements of anterior neck soft tissue thickness at hyoid bone (DSHB), thyrohyoid membrane (DSEM), and anterior commissure (DSAC) levels can be used to predict difficult laryngoscopy.

Material/Methods

We included 203 patients age 20–65 years scheduled to undergo general anesthesia in this prospective observational study. Correlation analysis and receiver operating characteristic curve (ROC) analysis were used to determine the roles of screening tests [interincisor gap (IIG), thyromental distance (TMD), modified Mallampati score (MMS)] and US measurements (DSHB, DSEM, DSAC) in predicting difficult laryngoscopy.

Results

There were 28 out of 203 patients categorized as difficult laryngoscopy. DSHB, DSEM, DSAC, and MMS were greater in the difficult laryngoscopy group (P<0.0001). There was a strong positive correlation between DSEM and DSHB (r=0.74); moderate positive correlations between DSEM and DSAC (r=0.60), DSHB and DSAC (r=0.69); small positive correlations between MMS and DSHB (r=0.32), MMS and DSEM (r=0.27), MMS and DSAC (r=0.32), all P values ≤0.0001; very small positive correlation between TMD and IIG (r=0.18, P=0.0089); small negative correlation between IIG and MMS (r=−0.27, P=0.0001); and very small negative correlations between MMS and TMD (r=−0.20, P=0.004), IIG and DSAC (r=−0.18, P=0.011), IIG and DSHB (r=−0.15, P=0.034). The areas under the ROC curve (AUCs) of MMS, DSHB, DSEM, and DSAC were significantly larger compared with the reference line (P<0.0001).

Conclusions

Anterior neck soft tissue thicknesses measured by US at hyoid bone, thyrohyoid membrane, and anterior commissure levels are independent predictors of difficult laryngoscopy. Combinations of those screening tests or risk factors with US measurements might increase the ability to predict difficult laryngoscopy.

Investigation of publication bias in meta-analyses of diagnostic test accuracy: a meta-epidemiological study

Background

The validity of a meta-analysis can be understood better in light of the possible impact of publication bias. The majority of the methods to investigate publication bias in terms of small study-effects are developed for meta-analyses of intervention studies, leaving authors of diagnostic test accuracy (DTA) systematic reviews with limited guidance. The aim of this study was to evaluate if and how publication bias was assessed in meta-analyses of DTA, and to compare the results of various statistical methods used to assess publication bias.

Methods

A systematic search was initiated to identify DTA reviews with a meta-analysis published between September 2011 and January 2012. We extracted all information about publication bias from the reviews and the two-by-two tables. Existing statistical methods for the detection of publication bias were applied on data from the included studies.

Results

Out of 1,335 references, 114 reviews could be included. Publication bias was explicitly mentioned in 75 reviews (65.8%) and 47 of these had performed statistical methods to investigate publication bias in terms of small study-effects: 6 by drawing funnel plots, 16 by statistical testing and 25 by applying both methods. The applied tests were Egger’s test (n = 18), Deeks’ test (n = 12), Begg’s test (n = 5), both the Egger and Begg tests (n = 4), and other tests (n = 2). Our own comparison of the results of Begg’s, Egger’s and Deeks’ test for 92 meta-analyses indicated that up to 34% of the results did not correspond with one another.

Conclusions

The majority of DTA review authors mention or investigate publication bias. They mainly use suboptimal methods like the Begg and Egger tests that are not developed for DTA meta-analyses. Our comparison of the Begg, Egger and Deeks tests indicated that these tests do give different results and thus are not interchangeable. Deeks’ test is recommended for DTA meta-analyses and should be preferred.

Detailed statistical analysis plan for the difficult airway management (DIFFICAIR) trial

Background

Preoperative airway assessment in Denmark is based on a non-specific clinical assessment left to the discretion of the responsible anesthesiologist. The DIFFICAIR trial compares the effect of using a systematic and consistent airway assessment versus a non-specific clinical assessment on the frequency of unanticipated difficult airway management.

To prevent outcome bias and selective reporting, we hereby present a detailed statistical analysis plan as an amendment (update) to the previously published protocol for the DIFFICAIR trial.

Method/Design

The DIFFICAIR trial is a stratified, parallel group, cluster (cluster = department) randomized multicenter trial involving 28 departments of anesthesia in Denmark randomized to airway assessment either by the Simplified Airway Risk Index (SARI) or by a usual non-specific assessment. Data from patients’ preoperative airway assessment are registered in the Danish Anesthesia Database. An objective score for intubation grading the severity, that is the severity of the intubations, as well as the frequency of unanticipated difficult intubation, is measured for each group.

Primary outcome measures are the fraction of unanticipated difficult and easy intubations.

The database is programmed so that the registration of the SARI is mandatory for the intervention group but invisible to controls.

Data recruitment was commenced in October 2012 and ended in ultimo December 2013.

Conclusion

We intend to increase the transparency of the data analyses regarding the DIFFICAIR trial by an a priori publication of a statistical analysis plan.

Trial registration

ClinicalTrials.gov: NCT01718561.

Management of the anticipated and unanticipated difficult airway in anesthesia outside the operating room

PURPOSE OF REVIEW

The number of diagnostic and interventional procedures outside the operating room has dramatically increased over the last years. However, providing well tolerated anesthesia with the same standard of care in these locations is often challenging to the anesthesiologist. The remote locations include different organizational aspects and hazards. Airway management in general is still confronted with scenarios of difficult intubation and ventilation and often leads to significant morbidity and mortality. Continuous awareness of the potential complications is urged when providing anesthesia for remote procedures.

RECENT FINDINGS

Recent studies have poorly addressed the issue of airway management by trained anesthesiologists outside the operating room. The majority of evidence is provided in the field of emergency medicine and intensive care settings. However, when dealing with difficult airway management in the remote setting, careful assessment and preparation is even more important than in the operating room. New evidence concerning prediction of ventilation and intubation must be incorporated in algorithms of airway management. Different anesthetic regimens using remifentanil and avoiding the use of neuromuscular blockers have to be carefully considered since they might change the scenario of intubation conditions. The new era of video laryngoscopes offers important potential to increase the tools for airway management. These new devices have the perfect design to be incorporated in remote settings. However, studies mainly focus on the emergency department and ICU. Also, there is currently a lack of consensus among professionals about their use and the large number of different devices seems to avoid careful comparisons.

SUMMARY

Airway management outside the operating room is challenging and needs the implementation of algorithms including the new airway devices. The recent update of the practice guidelines about difficult airway management of the American Society of Anesthesiologists remains the standard reference guide.

Endoscopic removal of a self-expanding metallic airway stent: A case report

Self-expanding metallic stents are sometimes placed for the management of obstructing airway lesions or conditions such as airway wall malacia or tracheal stenosis. However, endoscopic removal of these devices from the airway can pose extreme challenges for both clinical airway management as well as for the administration of general anesthesia. We report on a 61-year-old man with a complex cardiac history presenting for endoscopic stent removal necessitated by the formation of extensive granulation tissue. Comorbidities included a history of myocardial infarction, an ischemic cardiomyopathy with severe left heart failure (ejection fraction of 25%), mild right heart failure, 2+ tricuspid regurgitation status post tricuspid valve repair, and atrial fibrillation. An automatic external (wearable) cardiac defibrillator (Zoll Life Vest) was also in place. Induction of anesthesia was carried out using etomidate, with maintenance of anesthesia carried out with a propofol infusion (total intravenous anesthesia). Rocuronium was used for neuromuscular blockade. A size 4 iGel supraglottic airway and, later, rigid bronchoscopy formed the basis for airway management. Stable conditions were met through the 2-h procedure, and the patient recovered uneventfully. Our successful experience in this case leads us to propose further use of a supraglottic airway in conjunction with total intravenous anesthesia for these procedures.

Incidence of unanticipated difficult airway using an objective airway score versus a standard clinical airway assessment: the DIFFICAIR trial - trial protocol for a cluster randomized clinical trial

BACKGROUND

Pre-operative airway assessment in Denmark is based on a non-specific clinical assessment. Systematic, evidence-based and consistent airway assessment may reduce the incidence of unanticipated difficult airway management. By assessing multiple predictors for difficult airway management, the predictive value of the assessment increases. The Simplified Airway Risk Index (SARI) is a multivariate risk score for predicting difficult intubation.This study aims to compare the use of the SARI with a non-specified clinical airway assessment on predicting difficult intubation. Further, to compare the examination and registration of predictors for difficult mask ventilation with a non-specified clinical airway assessment on prediction of difficult mask ventilation.

METHOD/DESIGN

We cluster-randomized 28 Danish departments of anaesthesia to airway assessment either by the SARI or by usual non-specific assessment. Data from patients' pre-operative airway assessment are registered in the Danish Anaesthesia Database. Objective scores for intubation and mask ventilation grade the severity of airway managements. The accuracy of predicting difficult intubation and mask ventilation is measured for each group. The primary outcome measure is the fraction of unanticipated difficult and easy intubation.The fraction of unanticipated difficult intubation in Denmark is 1.87%. With a stratified randomization, type 1 error risk of 5% and a power of 80%, 30 departments are required to detect or reject a 30% relative risk reduction equalling a number needed to treat of 180. Sample size estimation is adjusted for the study design and based on standards for randomization on cluster-level. With an average cluster size of 2,500 patients, 70,000 patients will be enrolled over a 1-year trial period. The database is programmed so that registration of the SARI and predictors for difficult mask ventilation are mandatory for the intervention group but invisible to controls.

DISCUSSION

It is innovative to use a national clinical database as the basis for a randomized clinical trial. The method can serve as a precedent for implementation of evidence-based recommendations and database registration.The trial will forward understanding of how to predict and reduce unanticipated difficult airways and how to produce evidence-based recommendations for airway assessment and clinical database development.

TRIAL REGISTRATION

(NCT01718561).

The prediction of difficult intubation in obese patients using mirror indirect laryngoscopy: A prospective pilot study

Background:

The incidence of difficult laryngoscopy and intubation in obese patients is higher than in the general population. Classical predictors of difficult laryngoscopy and intubation have been shown to be unreliable. We prospectively evaluated indirect mirror laryngoscopy as a predictor of difficult laryngoscopy in obese patients.

Materials and Methods:

60 patients with a body mass index (BMI) greater than 30, scheduled to undergo general anesthesia, were enrolled. Indirect mirror laryngoscopy was performed and was graded 1-4 according to Cormack and Lehane. A view of grade 3-4 was classified as predicting difficult laryngoscopy. Additional assessments for comparison were the Samsoon and Young modification of the Mallampati airway classification, Wilson Risk Sum Score, neck circumference, and BMI. The view obtained upon direct laryngoscopy after induction of general anesthesia was classified according to Cormack and Lehane as grade 1-4.

Results:

Sixty patients met the inclusion criteria; however, 8 (13.3%) patients had an excessive gag reflex, and examination of the larynx was not possible. 15.4% of patients who underwent direct laryngoscopy had a Cormack and Lehane grade 3 or 4 view and were classified as difficult. Mirror laryngoscopy had a tendency toward statistical significance in predicting difficult laryngoscopy in these patients.

Conclusions:

This study is consistent with previous studies, which have demonstrated that no one individual traditional test has proven to be adequate in predicting difficult airways in the obese population. However, the new application of an old test - indirect mirror laryngoscopy - could be a useful additional test to predict difficult laryngoscopy in obese patients.

Incidences and predictors of difficult laryngoscopy in adult patients undergoing general anesthesia : a single-center analysis of 102,305 cases

BACKGROUND

Hypoxemia caused by difficulties in airway management presents a major cause for perioperative morbidity and mortality. The ability to predict difficult laryngoscopy more accurately would enable anesthesiologists to take specific precautions to reduce airway risks and prevent patient-threatening events.

METHODS

Over a 6-year period of time, all anesthesia records with a documented direct laryngoscopic view were retrieved from the electronic data management system and statistically processed. The Cormack-Lehane four-point scale of grading laryngoscopy was used to assess visibility of the vocal cords.

RESULTS

Of 102,306 cases, the overall rate of difficult laryngoscopy was 4.9 %. Male gender (6.5 %), Mallampati score III and IV (17.3 %), obesity with a BMI ≥35 kg/m(2) (6.1 %), as well as physical status ASA III or IV (6.2 %), were identified as risk factors for difficult laryngoscopy. Patients undergoing surgery in the departments of oromaxillofacial (8.9 %), ear nose throat surgery (ENT) (7.4 %), and cardiac surgery (7.0 %) showed the highest rates of difficult laryngoscopy.

CONCLUSIONS

The results indicate that the risk for difficult airway situations might substantially differ between surgical patient groups. In hospitals with departmental structures and spatially separated operating rooms, the deduction might be increased awareness and particular structural preparation for difficult airway situations in the respective subspecialties.