A.K. Nørskov

Diagnostic accuracy of anaesthesiologists’ prediction of difficult airway management in daily clinical practice: a cohort study of 188 064 patients registered in the Danish Anaesthesia Database

Both the American Society of Anesthesiologists and the UK NAP4 project recommend that an unspecified pre‐operative airway assessment be made. However, the choice of assessment is ultimately at the discretion of the individual anaesthesiologist. We retrieved a cohort of 188 064 cases from the Danish Anaesthesia Database, and investigated the diagnostic accuracy of the anaesthesiologists’ predictions of difficult tracheal intubation and difficult mask ventilation. Of 3391 difficult intubations, 3154 (93%) were unanticipated. When difficult intubation was anticipated, 229 of 929 (25%) had an actual difficult intubation. Likewise, difficult mask ventilation was unanticipated in 808 of 857 (94%) cases, and when anticipated (218 cases), difficult mask ventilation actually occurred in 49 (22%) cases. We present a previously unpublished estimate of the accuracy of anaesthesiologists’ prediction of airway management difficulties in daily routine practice. Prediction of airway difficulties remains a challenging task, and our results underline the importance of being constantly prepared for unexpected difficulties.

Prediction of difficult mask ventilation using a systematic assessment of risk factors vs. existing practice - a cluster randomised clinical trial in 94,006 patients.

We compared implementation of systematic airway assessment with existing practice of airway assessment on prediction of difficult mask ventilation. Twenty‐six departments were cluster‐randomised to assess eleven risk factors for difficult airway management (intervention) or to continue with their existing airway assessment (control). In both groups, patients predicted as a difficult mask ventilation and/or difficult intubation were registered in the Danish Anaesthesia Database, with a notational summary of airway management. The trials primary outcome was the respective incidence of unpredicted difficult and easy mask ventilation in the two groups. Among 94,006 patients undergoing mask ventilation, the incidence of unpredicted difficult mask ventilation in the intervention group was 0.91% and 0.88% in the control group; (OR) 0.98 (95% CI 0.66–1.44), p = 0.90. The incidence of patients predicted difficult to mask ventilate, but in fact found to be easy (‘falsely predicted difficult’) was 0.64% vs. 0.35% (intervention vs. control); OR 1.56 (1.01–2.42), p = 0.045. In the intervention group, 86.3% of all difficult mask ventilations were not predicted, compared with a higher proportion 91.2% in the control group, OR 0.61 (0.41–0.91), p = 0.016. The systematic intervention did not alter the overall incidence of unpredicted difficult mask ventilations, but of the patients who were found to be difficult to mask ventilate, the proportion predicted was higher in the intervention group than in the control group. However, this was at a ‘cost’ of increasing the number of mask ventilations falsely predicted to be difficult.

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

BackgroundPre-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/DesignWe 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.DiscussionIt 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)

Effects of avoidance or use of neuromuscular blocking agents on outcomes in tracheal intubation: a Cochrane systematic review

Abstract Cohort studies have indicated that avoidance of neuromuscular blocking agents (NMBA) is a risk factor for difficult tracheal intubation. However, the impact of avoiding NMBA on tracheal intubation, possible adverse effects, and postoperative discomfort has not been evaluated in a systematic review of randomised trials. We searched several databases for trials published until January 2017. We included randomised controlled trials comparing the effect of avoiding vs using NMBA. Two independent authors assessed risk of bias and extracted data. The risk of random errors was assessed by trial sequential analysis (TSA). We included 34 trials (3565 participants). In the four trials judged to have low risk of bias, there was an increased risk of difficult tracheal intubation with no use of NMBA [random‐effects model, risk ratio (RR) 13.27, 95% confidence interval (CI) 8.19–21.49, P<0.00001, TSA‐adjusted CI 1.85–95.04]. The result was confirmed when including all trials, (RR 5.00, 95% CI 3.49–7.15, P<0.00001, TSA‐adjusted CI 1.20–20.77). There was a significant risk of upper airway discomfort or injury by avoiding NMBA (RR=1.37, 95% CI 1.09–1.74, P=0.008, TSA‐adjusted CI 1.00–1.86). None of the trials reported mortality. Avoiding NMBA was significantly associated with difficult laryngoscopy, (RR 2.54, 95% CI 1.53–4.21, P=0.0003, TSA‐adjusted CI 0.27–21.75). In a clinical context, one must balance arguments for using NMBA when performing tracheal intubation.

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

BackgroundPreoperative 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/DesignThe 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.ConclusionWe intend to increase the transparency of the data analyses regarding the DIFFICAIR trial by an a priori publication of a statistical analysis plan.Trial registrationClinicalTrials.gov: NCT01718561.

Supraglottic airway devices in difficult airway management: a retrospective cohort study of 658,104 general anaesthetics registered in the Danish Anaesthesia Database

Indications for using supraglottic airway devices have widened over time and they now hold a prominent role in guidelines for difficult airway management. We aimed to describe the use of supraglottic airway devices in difficult airway management. We included adult patients undergoing general anaesthesia registered in the Danish Anaesthesia Database from 2008 to 2012 whose airway management had been recorded as difficult, defined as: ≥ 3 tracheal intubation attempts; failed tracheal intubation; or difficult facemask ventilation. In the Danish Anaesthesia Database, a separate difficult airway management module requires the technique used in each successive airway management attempt to be recorded. The primary aim of the study was to describe the use of supraglottic airway devices in cases of difficult airway management. Secondary aims were to examine success rates of supraglottic airway devices in difficult airway management cases, and specifically in the cases of ‘cannot intubate, cannot facemask ventilate’. Difficult airway management occurred in 4898 (0.74% (95%CI 0.72–0.76%)) of 658,104 records of general anaesthesia. Supraglottic airway devices were used or use was attempted in 607 cases of difficult airway management (12.4% (95%CI 11.5–13.3%)), and were successful in 395 (65.1% (95%CI 61.2–68.8%)) cases. In ‘cannot intubate, cannot facemask ventilate’ situations, supraglottic airway devices were used in 86 (18.9% (95%CI 15.6–22.8%)) of 455 records and were successful in 54 (62.8% (95%CI 52.2–72.3%)) cases. We found that supraglottic airway devices are not widely used in the management of the difficult airway despite their prominent role in difficult airway management guidelines.

Avoidance vs use of neuromuscular blocking agent for improving conditions during tracheal intubation: a Cochrane systematic review

Abstract Cohort studies have indicated that avoidance of neuromuscular blocking agents (NMBA) is a risk factor for difficult tracheal intubation. However, the impact of avoiding NMBA on tracheal intubation, possible adverse effects, and postoperative discomfort has not been evaluated in a systematic review of randomised trials. We searched several databases for trials published until January 2017. We included randomised controlled trials comparing the effect of avoiding vs using NMBA. Two independent authors assessed risk of bias and extracted data. The risk of random errors was assessed by trial sequential analysis (TSA). We included 34 trials (3565 participants). In the four trials judged to have low risk of bias, there was an increased risk of difficult tracheal intubation with no use of NMBA [random‐effects model, risk ratio (RR) 13.27, 95% confidence interval (CI) 8.19–21.49, P<0.00001, TSA‐adjusted CI 1.85–95.04]. The result was confirmed when including all trials, (RR 5.00, 95% CI 3.49–7.15, P<0.00001, TSA‐adjusted CI 1.20–20.77). There was a significant risk of upper airway discomfort or injury by avoiding NMBA (RR=1.37, 95% CI 1.09–1.74, P=0.008, TSA‐adjusted CI 1.00–1.86). None of the trials reported mortality. Avoiding NMBA was significantly associated with difficult laryngoscopy, (RR 2.54, 95% CI 1.53–4.21, P=0.0003, TSA‐adjusted CI 0.27–21.75). In a clinical context, one must balance arguments for using NMBA when performing tracheal intubation.

Predictive accuracy of difficult mask ventilation assessment methods – a reply

tion remains a challenge [1, 2]. We have previously suggested possible solutions to this challenge [3, 4]. Nørskov et al. reported a higher prediction rate in the intervention group, ascribed to a higher operator sensitisation to detecting DMV. However, only the proportion of false positives increased (0.64% vs. 0.35%), suggesting that systematic assessment did not improve the accuracy of the diagnostic test but prompted the operators to make more predictive mistakes. Would the authors agree with this? The authors added four more predictors of DMV to the original Simplified Airway Risk Index [4] and removed the predictors’ statistical weight from their assessment. This distorted the Simplified Airway Risk Index tool, and its inter-observer objectivity. High quality assessment of DMV was recorded in the control group, but this group was also prone to subjective bias. Do the authors consider that the increased rate of false positives in the SARI group might simply reflect operator bias, preferring to make a wrong prediction of DMV rather than having the contend with the consequences of a falsely negatives prediction, when in fact the possibility of subjective bias in both groups might have accounted for the apparent equivalence observed between the two assessment methods used?

A Comment on "Airway Assessment Before Intervention: What We Know and What We Do".

To create a dialogue for submission for publication, we recommend the following approach. The parties define beforehand an important patient-centered issue to be addressed. Then, they independently acquire a sound base of knowledge from evidence within their field. Furthermore, they determine the aspects to be discussed and questions to be answered in a structured conversation. Once they meet, the dialogue can be recorded and/or notes can be taken. Finally, they review the material, structure it in a logical order, and link the arguments to the respective literature citations. An introduction, for example, the presentation of a patient, and a conclusion will complement the dialogue. We call for patient-centered dialogues in medical journals, both within and especially among medical specialties, to advance medicine in its smallest interactions as well as on a scale of global health.