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Airway Management in Patients with Subglottic Stenosis

Experience at an Academic Institution

Knights, Richard M., MB, ChB, MRCP, FRCA; Clements, Stephan, BM, BSc, MRCS, FRCA; Jewell, Elizabeth, MS; Tremper, Kevin, MD, PhD; Healy, David, MD

doi: 10.1213/ANE.0b013e3182a6d1ab
Patient Safety: Brief Report
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We describe a pilot study investigating the airway techniques used in the anesthetic management of subglottic stenosis. We searched the electronic clinical information database of the University of Michigan Health System for cases of subglottic stenosis in patients undergoing surgery. Demographics, airway techniques, incidence of hypoxemia, and technique failure were extracted from 159 records. A lower incidence of hypoxemia was found between the 4 most commonly used techniques and the less common techniques. We detected no difference in outcome between individual techniques. This study suggests a larger prospective multicenter study is required to further investigate these outcomes in patients with subglottic stenosis.

From the Department of Anesthesiology, University of Michigan Medical School, Ann Arbor, Michigan.

Richard M. Knights, MB, ChB, MRCP, FRCA, and Stephan Clements, BM, BSc, MRCS, FRCA, are currently affiliated with Betsi Cadwaladr University Health Board, Bangor, United Kingdom.

Funding: Internal funding.

The authors declare no conflicts of interest.

This report was previously presented, in part, at the Difficult Airway Society Conference 2011.

Reprints will not be available from the authors.

Address correspondence to David Healy, MD, Department of Anesthesiology, University Hospital 1H2471500 E Medical Center Dr., SPC 5048 Ann Arbor, MI 48109-5048. Address e-mail to dhealy@med.umich.edu.

Subglottic stenosis presents unique challenges to the anesthesiologist. A variety of airway management techniques have been described, each with perceived risks and benefits.1–4 No studies have examined whether any technique is associated with fewer complications or improved patient outcomes. A prospective randomized controlled trial in 1 institution to investigate the optimal technique would be difficult because subglottic stenosis is relatively rare,5 and any performance difference is slight. Retrospective studies have limitations but are useful when studying such conditions; therefore, we describe a pilot study using the electronic clinical information system of the University of Michigan Health System (Centricity®). Our study describes the techniques in use and any trend in outcome difference associated with use of a particular airway technique.

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METHODS

After receiving IRB approval, the Centricity® database of the University of Michigan Health System was searched from 2006 to 2011 identifying all patients presenting for otolaryngology surgery of subglottic stenosis under general anesthesia. Exclusion criteria were: patients with bronchial, laryngeal, or supraglottic pathology; or presence of a preexisting secure airway. Of the 327 cases that were initially identified, 168 cases failed inclusion criteria, resulting in 159 cases of subglottic stenosis entered into the study. The medical record and intraoperative data were then reviewed for demographic information (Table 1) and the outcomes of interest.

Table 1

Table 1

We chose hypoxemia as our primary outcome (defined as 2 consecutive minutes during the case when the pulse oximeter reading was <90%). Our secondary outcome was the incidence of initial airway technique failure. We also collected data on the grade of stenosis (Myer-Cotton grading) and ease of facemask ventilation recorded (Han grade).6

Descriptive statistics provided summaries of the basic demographic information and surgical procedures. The 4 most common established airway management techniques were compared for differences in incidence of hypoxemia. In addition, the incidence of hypoxemia in the 4 most common established airway management techniques combined was compared with the incidence in all the other techniques combined. The incidence of initial airway management technique failure was calculated. Comparisons between proportions were made using a 95% confidence interval (CI) adjusted for multiple comparisons using the Bonferroni correction.7 CIs not including zero were considered to provide statistical evidence that the true difference within the upper and lower bounds of the CI was not equal to zero.8 The data were analyzed using R version 2.15.2 (R Foundation for Statistical Research, Vienna, Austria).9

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RESULTS

Demographics and surgical procedures for the 159 patient study population are summarized in Table 1 and Table 2. The 4 most common airway techniques combined accounted for 83.0% (n = 132) of the total sample (Table 3). The overall hypoxemia rate for this group was 26.5%. Pairwise comparisons among these 4 airway techniques failed to provide statistical evidence of a difference in incidence of hypoxemia among the techniques. The differences in incidence all had wide CIs that included zero, indicating the possibility of a true difference of zero (Table 4). However, the combined 4 most commonly used airway techniques group had a lower incidence of hypoxemia than the remaining groups combined, with statistical evidence that the true difference was between 7.0% and 73.3% (26.5% vs 66.7%, difference = 40.2%, 95% CI, 7.0%–73.3%). The overall reported failure rate of the initial technique was 7.5% (n = 12). Failures occurred in patients in whom the initial airway technique was either the Hunsaker jet catheter (n = 5 failures of 44 attempts, 11.4%), jet ventilation by bronchoscope (n = 2 failures of 35 attempts, 5.7%), or a plain endotracheal tube (n = 5 failures of 59 attempts, 8.5%). Pairwise comparisons between the incidence of failure in the 3 groups with technique failures showed no evidence of a true difference in incidence between groups (95% CIs, −11.7% to 23.0%, −13.5% to 19.2%, and −17.8% to 12.3%). No information was available on the precise mechanism of failure from direct medical record review.

Table 2

Table 2

Table 3

Table 3

Table 4

Table 4

Ability to facemask ventilate was documented in 91 of the 159 cases (57.2%) and was either not attempted or not recorded in the other 68 cases. The vast majority (n = 84, 92.3%) were recorded as easy to facemask ventilate (Han grade 1) or easy to ventilate with the use of an oral airway (Han grade 2). The majority of patients with tight (Myer-Cotton grade 3) stenosis did not have facemask ventilation attempted or recorded (25 of 40 patients, 62.5%), but in those who did, (15 patients) difficulty was not met during ventilation (Table 5).

Table 5

Table 5

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Conclusion

Our pilot study demonstrated no difference in the occurrence of intraoperative hypoxemia among the 4 most commonly used airway techniques at the University of Michigan Health System during anesthetic provision for patients with subglottic stenosis. The study did show a lower incidence of hypoxemia when clinicians chose one of the 4 most common airway techniques over one of the other less common methods.

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DISCUSSION

Our pilot study has generated some interesting unanswered questions relating to the management of subglottic stenosis. The high overall failure rate of the initial airway management technique (7.5%) demonstrates the importance of a series of defined backup plans as part of the overall airway management strategy in the patient with known subglottic stenosis. A larger, ideally multicentered study is warranted to determine which technique has the best efficacy and safety and to further investigate the relationship between grade of stenosis and ability to facemask ventilate. This type of study would additionally help minimize the contribution of patient selection and nuanced practice. Any future study should also include further investigation into the reasons contributing to technique failure.

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DISCLOSURES

Name: Richard M. Knights, MB, ChB, MRCP, FRCA.

Contribution: This author helped design and conduct the study, analyze the data, and write the manuscript.

Attestation: Richard M. Knights has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Stephan Clements, BM, BSc, MRCS, FRCA.

Contribution: This author helped conduct the study and analyze the data.

Attestation: Stephan Clements has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Elizabeth Jewell, MS.

Contribution: This author helped analyze the data and write the manuscript.

Attestation: Elizabeth Jewell has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Kevin Tremper, MD, PhD.

Contribution: This author helped design the study and write the manuscript.

Attestation: Kevin Tremper has seen the original study data and approved the final manuscript.

Name: David Healy, MD.

Contribution: This author helped design and conduct the study, analyze the data, and write the manuscript.

Attestation: David Healy has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.

This manuscript was handled by: Steven L. Shafer, MD.

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