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Stridor in Neonates After Using the Microcuff® and Uncuffed Tracheal Tubes: A Retrospective Review

Sathyamoorthy, Madhankumar MBBS, MS*; Lerman, Jerrold MD, FRCPC, FANZCA*†; Asariparampil, Rajeshri MD*; Penman, Alan D. MBChB, PhD, MPH; Lakshminrusimha, Satyan MD§

doi: 10.1213/ANE.0000000000000918
Pediatric Anesthesiology: Research Report

BACKGROUND: We conducted a retrospective chart review to determine the frequency of stridor and contributing factors after the use of Microcuff® and uncuffed tracheal tubes (TTs) in neonates.

METHODS: All neonates in our neonatal intensive care unit whose airways were intubated between May 2011 and June 2012 were included. Data were collected from the neonatal intensive care unit database and from the electronic anesthesia record. Extracted data included postmenstrual age (PMA) at birth, birth weight, TT size and type, duration of tracheal intubation, and number of reintubations. The use of racemic epinephrine, heliox, and/or dexamethasone postextubation was considered diagnostic of stridor.

RESULTS: Of the 324 neonates whose data were reviewed, 27 (8.3%) developed postextubation stridor. Neonates who developed stridor were more premature (PMA at birth, 29.9 ± 5.8 vs 33.0 ± 4.8 weeks, P = 0.001), had a lower birth weight (1.56 ± 1.07 vs 2.02 ± 0.96 kg, P = 0.005), greater duration of intubation (median: 20 vs 3 days, P < 0.0001), and multiple reintubations (median: 2 vs 0, P < 0.0001). The frequency of stridor was 17.2% after using Microcuff TT and 7.5% after using uncuffed TTs (Fisher exact test, 2-sided P = 0.08 [95% confidence interval for difference in proportions: −9.4% to 28.7%]). In a multivariable logistic regression model, after adjusting for PMA, birth weight, duration of intubation, and number of reintubations, the use of a Microcuff TT was associated with increased odds of stridor (adjusted odds ratio = 9.27 [95% confidence interval: 1.88–45.67], P = 0.006).

CONCLUSIONS: The use of the Microcuff TT is associated with increased odds of postextubation stridor in neonates compared with the use of uncuffed TT.

Published ahead of print August 13, 2015

From the *Department of Anesthesiology, Women and Children’s Hospital of Buffalo, Buffalo, New York, and SUNY at Buffalo, Buffalo, New York; Department of Anesthesiology, University of Rochester, Rochester, New York; Department of Medicine and Biostatistics, University of Mississippi Medical Center, Jackson, Mississippi; and §Department of Pediatrics, SUNY at Buffalo, Buffalo, New York.

Madhankumar Sathyamoorthy, MBBS, MS, is currently affiliated with the Department of Anesthesiology, University of Mississippi Medical Center, Jackson, Mississippi.

Accepted for publication May 8, 2015.

Published ahead of print August 13, 2015

Funding: None.

The authors declare no conflicts of interest.

Presented, in part, at the annual meeting of the American Society of Anesthesiologists, October 2013, San Francisco, CA.

Reprints will not be available from the authors.

Address correspondence to Madhankumar Sathyamoorthy, MBBS, MS, Department of Anesthesiology, University of Mississippi Medical Center, 2500 N State St., Jackson, MS 39216. Address e-mail to msathyamoorthy@umc.edu.

Neonatologists and pediatric anesthesiologists have traditionally used uncuffed tracheal tubes (TTs) to intubate the tracheas in neonates and infants. However, with the introduction of Microcuff® TTs (Halyard Health—formerly Kimberly-Clark Health Care Inc., Roswell, GA) into clinical practice in 2008, and evidence of their safe use in children, pediatric anesthesiologists have embraced their use.1,2 Several studies have demonstrated that cuffed TTs may be used in children <8 years of age without increasing morbidity,3,4 prompting an editorial that recommended these tubes for all infants (beyond the neonatal period) and children who require tracheal intubation.5

Despite the widespread use of Microcuff TTs in pediatric anesthesia, their safe use in neonates and young infants has not been established.5 We recently reported 3 instances of postextubation stridor after the use of Microcuff TTs in full-term and preterm neonates, which prompted us to evaluate whether there was an association between Microcuff TT and postextubation stridor.6

We designed this retrospective chart review to determine whether the frequency of postextubation stridor in neonates after the use of the Microcuff TT was greater than that after uncuffed TT and to identify those factors that may contribute to postextubation stridor.

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METHODS

This study was approved by the IRB at State University of New York at Buffalo. The need for written informed consent was waived. The study was not registered at clinicaltrials.gov.

All neonates whose airways were intubated with a TT and who were in the neonatal intensive care unit (NICU) at our institution (Women and Children’s Hospital of Buffalo, Buffalo, NY) between May 2011 and June 2012 were included in the study. This time period was selected because Microcuff TTs were the only cuffed TTs used to intubate the tracheae in neonates in the operating room (OR) during this period. Neonates whose airways were intubated for a surgical procedure in the OR and who were subsequently transferred intubated to the NICU postoperatively were also included. Neonates whose airways were extubated at the end of their surgical procedures and who were transferred to the recovery room were excluded because follow-up records (pertaining to stridor and other airway events) were unavailable. The demographic and airway data were extracted from both the NICU database (Neodata®; Isoprime Corporation, Lisle, IL) and the electronic anesthesia record.

The following data were recorded for each neonate: postmenstrual age (PMA) at birth, birth weight, type of TT and size, duration of tracheal intubation, and number of repeat tracheal intubations. The use of any one or combination of racemic epinephrine, heliox, and/or dexamethasone postextubation with clinical signs of stridor was deemed to be diagnostic for stridor. The duration of intubation was defined as the total number of days with a TT in situ. The number of reintubations, including both elective and emergency intubations, was recorded, although the number of attempts at each tracheal intubation was not recorded. Posthospital discharge follow-up data were not collected for any of the neonates.

Neonates were divided into 2 groups based on the presence or the absence of postextubation stridor (“stridor” or “no stridor,” respectively). Demographic data were compared using the Student t test. Because the data for “intubation days” and “number of reintubations” were skewed, the Wilcoxon 2-sample test was used to compare these values between the stridor and no stridor groups. Birth weight was log-transformed before testing.

Multivariable logistic regression was done to identify significant covariates for stridor. Interaction between the significant covariates was tested. For the regression model, the number of reintubations was categorized into 5 groups (0, 1, 2, 3, 4 or more), and the duration of intubation was categorized into 4 groups (<2, 2–6, 7–13, 14 or more days). We chose these arbitrary cutoff points to distinguish between short-term and long-term intubations using a reasonable number of groups for statistical analysis.

The association between stridor and the use of Microcuff TTs was estimated and adjusted for the effects of covariates (birth weight, PMA, duration of intubation, number of reintubations) using multivariable logistic regression. Adjusted odds ratio with 95% confidence interval (CI) limits was reported.

Neonates whose airways were intubated with incorrect-sized TTs based on their age/weight and according to guidelines and manufacturer’s recommendation were also analyzed. In this separate group, the frequency of stridor after the Microcuff TT was compared with that after uncuffed TT.

Statistical analysis was performed using SAS (version 9.3; SAS Institute, Inc., Cary, NC). Contingency tables were analyzed using the Fisher exact test. Two-sided P values are reported, and P < 0.05 was considered significant. Exact unconditional confidence limits for differences in proportions are presented.

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RESULTS

A total of 324 neonates were included from the database. The study data set was complete for every neonate, and no neonate was excluded from the analysis. The mean PMA of the neonates was 32.6 weeks at birth with a mean birth weight of 2.0 kg. Tracheal intubation was performed in 274 neonates in the NICU only with uncuffed TTs and in 50 neonates (21 with uncuffed TTs and 29 with Microcuff TTs) in the OR (Fig. 1).

Figure 1

Figure 1

The median duration of intubation was 4 days (interquartile range, 1–13 days). The duration of tracheal intubation was 1 day or less in 116 (35.8%) neonates, 2 days in 31 (9.6%), 3 to 7 days in 69 (21.3%), and 8 days or more in 108 (33.3%). One hundred nine (33.6%) neonates required reintubation: 45 once, 26 twice, 13 three times, and 25 four or more times.

The overall frequency of postextubation stridor was 27 of 324 neonates (8.3%). The frequency of stridor was 17.2% after using the Microcuff TT and 7.5% after using uncuffed TTs (Fisher exact test, 2-sided P = 0.08; 95% CI for difference in proportions: −9.4% to 28.7%; Table 1). When all intubations in the OR were considered, the overall frequency of stridor was 14%.

Table 1

Table 1

Ninety percent (26 of 29) of neonates had a larger than recommended size Microcuff TT for their age and weight according to the published criteria.7 The frequency of stridor was 19.2% after using incorrectly sized Microcuff TTs (based on textbook guidelines8) and 8.0% after using incorrectly sized uncuffed TTs (Fisher exact test, 2-sided P = 0.14; 95% CI for difference in proportions: −9.8% to 31.9%; Table 2).

Table 2

Table 2

In a univariable analysis, the factors associated with postextubation stridor included greater prematurity (PMA, 29.9 ± 5.8 vs 33.0 ± 4.8 weeks, P = 0.001), low birth weight (1.56 ± 1.07 vs 2.02 ± 0.96 kg, P = 0.005), prolonged duration of intubation (median: 20 vs 3 days, P < 0.0001), and the number of tracheal reintubation (median: 2 vs 0, P < 0.0001; Table 1).

The frequency of stridor after zero reintubations was 1.9%, after 1 reintubation was 6.7%, after 2 reintubations was 26.9%, after 3 reintubations was 23%, and after 4 or more reintubations was 40% (Fig. 2).

Figure 2

Figure 2

Table 3

Table 3

In a multivariable logistic regression model, we found that the TT type and the number of reintubations were significantly associated with stridor. After adjusting for PMA, birth weight, duration of intubation, and number of reintubations, the odds ratio for developing stridor after tracheal intubation with a Microcuff TT was 9.27 (95% CI: 1.88–45.67; P = 0.006). The interaction between TT type and the number of reintubations was not significant (P = 0.99; Table 3).

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DISCUSSION

In this study, we found that the use of the Microcuff TT was associated with increased odds of stridor in neonates. Interestingly, 90% of the Microcuff TTs were placed in premature and low-birth-weight neonates (<3 kg), infants in whom these TTs are not recommended. In those premature and low-birth-weight neonates with the Microcuff TT, the incidence of stridor was the greatest of all subgroups (19.2%). In addition, we determined that multiple reintubations contributed to postextubation stridor.

In a previous study, the frequencies of postextubation stridor in children after Microcuff and uncuffed TTs were similar.3 However, only 10% of the subjects in that study were neonates. In a carefully conducted study using the 3.0-mm ID Microcuff TT in full-term neonates ≥3 kg and the 3.5-mm ID TT in infants 6 to 18 months of age that included monitoring for both a suitable air leak before cuff inflation and the cuff pressure during anesthesia, the frequency of postextubation stridor for the 2 sizes of Microcuff TT was small (2.3%–3%).7 The frequency of stridor with the Microcuff TT in that study was one-fifth that reported in the current study, 17.2%, with identical size Microcuff TTs. Plausible reasons for the increased frequency of postextubation stridor in the present study include the placement of TTs that were too large for the airways in these premature and low-birth-weight neonates, that the TTs themselves are not suitable for use in such small neonates, that the cuff pressures were not monitored in the current study, and that the neonates were sicker and required multiple and prolonged intubations.

Two surveys undertaken in the United Kingdom (2008)9 and France (2001)10 confirmed that cuffed TTs were used infrequently to secure the airway in infants and children during anesthesia. Many clinicians were concerned that a cuffed TT led to airway trauma and postextubation stridor. However, a recent survey of the members of the Society of Pediatric Anesthesia confirmed that 65% of respondents use cuffed TTs in children >2 years of age. Furthermore, those who used these TTs most often were young practitioners (<5 years in practice) and those with fellowship training.a We believe that the shift in practice toward the use of cuffed TTs may be attributed, in part, to the introduction of these newly designed, ultrathin cuffed Microcuff TTs since 2008. In addition, the survey reported that 25% of respondents used Microcuff TTs in preterm neonates and 30% used them in full-term neonates (>2 kg) 50% to 90% of the time.a The practice of using TTs in neonates in whom the TTs were not approved, and in sizes larger than those recommended based on their ages and weights, may be more widespread a practice.

There are several limitations to this study. First, we used clinical signs of stridor and the need for specific treatment such as the need for racemic epinephrine, dexamethasone, and/or heliox in the immediate postextubation period to diagnose postextubation stridor. Some argue that stridor is a sign, not a diagnosis,11,12 and that endoscopic evaluation of the glottic and subglottic regions is required to differentiate mucosal injury and/or edema of the airway mucosa from a congenital or acquired defect.13 However, that was not done in the current study. Second, data regarding the actual number of attempts at tracheal intubation, difficult or traumatic intubation, use of sedation and muscle relaxants for tracheal intubation and mechanical ventilation, and elective or accidental extubation, all of which may have affected the frequency of postextubation stridor, were not available from NICU records. Although we are certain of the details associated with postextubation stridor after Microcuff TTs (because they were inserted only once in the OR), we are much less certain about the timing of the postextubation stridor in the nonsurgical neonates, because many neonates experienced multiple intubations during their NICU stay. Similarly, it was easy to identify those neonates whose airways were intubated with incorrectly sized Microcuff TTs, but much more difficult to identify those with incorrectly sized uncuffed TTs in the NICU. In many of the latter cases, larger uncuffed TTs were inserted over time, because the airway dimensions may have increased during their stay in NICU, particularly when compared with the neonate’s birth weight. Third, this was a single-institution, retrospective study in which the allocation of TTs was not randomized. Fourth, the disparate sample sizes (between the Microcuff and the uncuffed TT groups) limited the power to detect a statistically significant difference in the frequency of stridor between the 2 groups. Together, these factors may limit the external validity of the results.

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CONCLUSIONS

We conclude that postextubation stridor may occur more frequently after the use of Microcuff TTs in neonates than after uncuffed TTs. We cannot establish whether the stridor after Microcuff TT is attributable to these TTs or to using a TT that was too large in the premature and low-birth-weight neonates. On the basis of the current observations, we recommend uncuffed TTs for premature infants and those neonates who weigh <3 kg to minimize the risk of postextubation stridor.

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DISCLOSURES

Name: Madhankumar Sathyamoorthy, MBBS, MS.

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

Attestation: Madhankumar Sathyamoorthy 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.

Name: Jerrold Lerman, MD, FRCPC, FANZCA.

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

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

Name: Rajeshri Asariparampil, MD.

Contribution: This author helped conduct the study.

Attestation: Rajeshri Asariparampil 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.

Name: Alan D. Penman, MBChB, PhD, MPH.

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

Attestation: Alan D. Penman has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Satyan Lakshminrusimha, MD.

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

Attestation: Satyan Lakshminrusimha 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: James DiNardo, MD, FAAP.

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FOOTNOTE

a Presented as an abstract at the American Society of Anesthesiologists Annual meeting, New Orleans, Louisiana, October 12–16, 2014 (A3058).
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