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Endotracheal tubes and the cricoid: Is there a good fit?
International Journal of Pediatric Otorhinolaryngology 85 (2016) 8–11
Contents lists available at ScienceDirect
International Journal of Pediatric Otorhinolaryngology journal homepage: www.elsevier.com/locate/ijporl
Endotracheal tubes and the cricoid: Is there a good fit? Mahmood Rafiq a,*, Tariq M. Wani a,b, Melissa Moore-Clingenpeel c, Joseph D. Tobias a,b a
Department of Anesthesiology and Pain Medicine, Nationwide Children’s Hospital, Columbus, OH, USA Department of Anesthesiology and Pain Medicine, The Ohio State University, Columbus, OH, USA c Biostatistics Core, The Research Institute at Nationwide Children’s Hospital, Columbus, OH, USA b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 27 November 2015 Received in revised form 9 March 2016 Accepted 11 March 2016 Available online 19 March 2016
Background: Choosing an appropriately sized endotracheal tube (ETT) is important in pediatric patients as an inappropriately sized ETT may result in multiple endotracheal intubation attempts or excessive pressure on the tracheal mucosa with the potential for airway damage. Although age-based formulas are generally used with choice of an ETT based on the internal diameter (ID), measurements of the outer diameter (OD) of the ETT would seem to be a more scientific approach to determine the proper size of an ETT. However, the variable OD of the ETT despite the same ID makes the selection of a proper sized ETT more difficult. The current study compares airway dimensions measured using computed tomography (CT) with the OD of ETTs from various manufacturers. Methods: The outer diameter of commonly used ETTs (12 cuffed and 5 uncuffed) were measured and compared with CT-based cricoid measurements obtained from a previous study involving 130 pediatric patients, ranging in age from 1 month to 10 years. These data were used to determine the likelihood of a clinically acceptable match. Results: The differences of the cricoid dimensions between the 5th and the 95th percentile in each group ranged from a minimum of 2.23 mm to a maximum of 6.51 mm. Depending on the manufacturer, there was significant variation in the OD of the ETTs with the same ID. These discrepancies, which varied according to manufacturer and were greater with uncuffed as compared to cuffed ETTs, impacted the chances of an acceptable fit with the cricoid diameters. Conclusion: When choosing an ETT, age-based formulas which use the ID may not be uniformly accurate in ensuring the appropriately-sized ETT given the variation in the OD despite the same ID. These issues further support the use of cuffed ETTs as the variation in fit can be adjusted by inflation of the cuff to provide an adequate tracheal seal. ß 2016 Elsevier Ireland Ltd. All rights reserved.
Keywords: Cricoid diameter Pediatric endotracheal tubes Outer diameter Pediatric airway CT imaging
1. Introduction The cricoid, the only complete cartilaginous ring, is the single fixed dimension in the pediatric airway. It has been defined as the narrowest part of the airway, offering resistance to the passage of an endotracheal tube (ETT), thereby being a key dimension when choosing an ETT. Choosing the correct ETT size is important in pediatric patients because an inappropriately sized ETT may result in multiple intubation attempts or excessive pressure on the tracheal mucosa thereby causing damage to the airway [1–3]. Although, age-based formulas are routinely used to estimate the optimal ETT size, none of these systems is accurate for all patients because of variations of tracheal dimensions among the pediatric population [4–6].
Measurements of the outer diameter (OD) of an ETT would seem to be the most accurate approach to determine the proper size of an ETT. However, in clinical anesthesia practice, the ETT size is generally based on the internal diameter (ID). Variation between the ID and OD exists among manufacturers, further complicating age-based pediatric ETT size selection [7]. In the current study, we compare the diameter of the trachea at the level of the cricoid ring, using CT-based images of pediatric patients, to the OD of cuffed and uncuffed ETTs of different manufacturers. The aim was to evaluate the design of these ETTs, relate it to CT-based anatomical airway measurements of the trachea, and determine the likelihood of a good fit between the ETT and the trachea.
2. Methods * Corresponding author. Tel.: +1 6142540826. E-mail address: [email protected] (M. Rafiq). http://dx.doi.org/10.1016/j.ijporl.2016.03.016 0165-5876/ß 2016 Elsevier Ireland Ltd. All rights reserved.
The present study was performed at Nationwide Children’s Hospital (Columbus, Ohio). As no direct patient involvement was
M. Rafiq et al. / International Journal of Pediatric Otorhinolaryngology 85 (2016) 8–11
needed, there was no IRB approval necessary. The ODs of 12 different cuffed and 5 different uncuffed ETTs were measured. The ETTs involved were manufactured by Rusch, Covidien, Covidien–Mallinckrodt, Portex, Sheriden, and Kimberly–Clark. Anatomical airway measurements were calculated using the data from our previous study, which determined airway dimensions using the antero-posterior (AP) and transverse (T) diameters at the level of cricoid from CT-based images [7]. Data from the previous publication used for the current study included 130 pediatric patients, ranging in age from 1 month to 10 years, who underwent thoracic computed tomography (CT) imaging for pathologies not involving the airway were included in the study. Exclusion criteria included a diagnosis or condition that the investigators felt would cause abnormal laryngeal anatomy or interfere with the measurements obtained during CT imaging. For the current study, the internal diameter of the trachea at the level of the cricoid from the previous study, which is outlined above, was compared with the OD of cuffed and uncuffed ETTs. For cuffed ETTs, the OD was measured at a point immediately above the level of the cuff. Table 1 shows the ETT sizes (cuffed and uncuffed) that were used for the various age ranges for the purpose of the study. The size of the cuffed ETT was derived from commonly used data suggested by references 1, 5, and 6 [1,5,6]. 2.1. Statistical analysis All analyses were performed using SAS 9.3 (SAS Institute, Cary, NC). Two sided p-values <0.05 are considered statistically significant. For each manufacturer, the proportion of patients where the ETT would fit was compared by age using Fisher’s exact tests. The distribution of the AP and the transverse cricoid dimensions were broken down by age group. The 5th, 25th, 50th, 75th, and 95th percentiles of cricoid diameters in each age group were calculated. The 50th percentile represents the median. 3. Results Data from the previous study of Wani et al. included the CT scans of 130 patients, ranging in age from 1 month to 10 year [7]. There were no statistically significant gender differences in any of the cricoid measurements so all data is considered together without reference to gender. For the youngest age group, 5% of the patients in the sample had an AP diameter less than 4.93 mm and 5% of the patients had an AP diameter greater than 9.05 (Table 2). The differences between the 5th percentile and the 95th percentile in each group ranged from a minimum of 2.23 mm to a maximum of 6.51 mm (Table 2). The distribution of transverse and AP cricoid dimensions within each ETT-determined age group is shown in Table 2. Table 3 shows the proportion of the 130 patients from the study of Wani et al. that would have an acceptable fit according to each specific manufacturer when using an age-appropriate cuffed
Table 1 Endotracheal tube size vs. age groups. ETT size (mm):
Cuffed (Age)
Uncuffed (Age)
3.0 3.5 4.0 4.5 5.0 5.5 6
Full-term to 1 year 1 to <2 2 to <4 4 to <6 6 to <8 8 to 10 –
Full-term to 1 year Full-term to 1 year 1 to <2 2 to <4 4 to <6 6 to <8 8 to 10
The choice of endotracheal tube (ETT) used to assess the fit for the current study was based on this table. The size of the cuffed and uncuffed ETT is derived from references [1,5,6]. ETT = endotracheal tube.
9
Table 2 Distribution of cricoid measurements by age. Age (years) <1 1 to 2 to 4 to 6 to 8 to
N
Variable
15 AP Transverse <2 34 AP Transverse <4 24 AP Transverse <6 23 AP Transverse <8 17 AP Transverse <10 17 AP Transverse
5th % 25th % 50th % 75th % 95th % Difference 95th%–5th % 4.9 4.7 6.0 6.1 6.7 7.0 7.6 7.4 8.4 7.4 7.1 7.7
5.8 5.6 6.9 6.5 6.9 7.4 8.5 8.5 9.2 9.0 9.2 9.3
6.6 6.3 7.2 7.2 8.1 8.2 9.3 9.0 9.4 9.7 10.1 9.7
7.2 6.9 8.0 7.7 9.4 8.9 9.8 10.1 10.8 10.7 10.9 10.8
9.1 8.2 8.6 8.5 10.9 9.5 12.0 10.9 13.2 11.9 12.8 11.1
4.1 3.4 2.6 2.4 4.2 2.5 4.4 13.5 4.9 4.5 5.8 3.4
Values are expressed in mm and rounded to the nearest tenth of a millimeter. This information is based on the data from reference [7]. N = number; AP = anterioposterior.
or uncuffed ETT as defined in Table 1. Did not fit was assumed if the outside diameter of the ETT would not fit in either the AP or the transverse dimension as measured in the 130 patients from the study of Wani et al. [7]. Among cuffed ETTs, Mallinckrodt TT Hi-Lo Murphy and Portex TT-Profile Soft Seal Cuff Murphy tubes both fit less than 95% of the time. However, there were no statistically significant differences in fit across the various manufacturers. Among uncuffed ETTs, only Rusch ETTs fit more than 95% of the time. The fit for ETTs (cuffed and uncuffed) across various age ranges and depending on specific manufacturers is listed in Table 4. For all cuffed ETTs, fit was less likely for patients between 8 and 10 years of age. For cuffed ETTs, the fit was 100% for all patients less than 8 years of age with the exception of Mallinckrodt TT Safety Flex ETTs for patients less than 1 year age (97% fit) and Ru¨sch Ruschelit Super Safety Clear Magill ETTs in patients less than 1 year of age (93% fit) and in the 1–2 year age group (97% fit). Fit tended to be worse overall when considering uncuffed ETTs compared to cuffed ETTs. The fit for uncuffed ETTs was best for patients between 2 and 6 years of age.
Table 3 Proportion of fit by manufacturer for endotracheal tubes. ETT manufacturer (uncuffed)
Did not fit—number and (%)
Fit—number and (%)
Portex clear Portex Ivory Rusch Sheriden Covidien
6 11 4 6 9
124 119 126 124 121
ETT manufacturer (cuffed)
Did not fit—number and (%)
Fit—number and (%)
Kimberly–Clark microcuff Sheridan Murphy Sheridan Magill Mallinckrodt High-Contour Murphy Mallinckrodt High-Contour Mallinckrodt TT Lo-Contour Magill Mallinckrodt TT Lo-Contour Murphy Mallinckrodt TT Hi-Lo Murphy Mallinckrodt TT Safety Flex Portex TT-Profile Soft Seal Cuff, Murphy Ru¨schRuschelit Super Safety Clear Magill Ru¨schRuschelit Super Safety Clear Murphy
1 (1) 2(2) 0 (0) 2(2) 2(2) 2(2) 2(2) 2 (6) 3 (2) 2 (6) 3 (2) 1 (3)
129 (99) 128 (98) 60 (100) 128 (98) 128 (98) 128 (98) 128 (98) 32 (94) 127 (98) 32 (94) 127 (98) 33 (97)
(5) (8) (3) (5) (7)
(95) (92) (97) (95) (93)
The values are listed as the number and (percentage) based on the comparison of the ETT from Table 1 and the measurements from the 130 patients from the previous study of Wani et al. [7]. ETT = endotracheal tube; ID = internal diameter.
10
M. Rafiq et al. / International Journal of Pediatric Otorhinolaryngology 85 (2016) 8–11
Table 4 Proportion of fit by age within manufacturer for endotracheal tubes. Cuffed ETT size (mm)
3
Age (years)
<1
Kimberly–Clark microcuff Sheridan Murphy Sheridan Magill Mallinckrodt High Contour Murphy Mallinckrodt High Contour Mallinckrodt TT Lo-Contour Magill Mallinckrodt TT Lo-Contour Murphy Mallinckrodt TT Hi-Lo Murphy Mallinckrodt TT Safety Flex Portex TT Profile Soft Seal Cuff, Murphy Ru¨schRuschelit Super Safety Clear Magill Ru¨schRuschelit super safety clear murphy
15 15 15 15 15 15 15
3.5
(100) (100) (100) (100) (100) (100) (100)
4
4.5
5
5.5
p-Value
1 to <2
2 to <4
4 to <6
6 to <8
8 to <10
34 (100) 34 (100)
24 24 24 24 24 24 24
23 (100) 23 (100)
17 17 17 17 17 17 17 17 17 17 17 17
16 (94) 15 (88)
34 34 34 34
(100) (100) (100) (100)
(100) (100) (100) (100) (100) (100) (100)
23 23 23 23
(100) (100) (100) (100)
14 (93)
34 (100)
24 (100)
23 (100)
14 (93)
33 (97)
24 (100)
23 (100)
(100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100)
15 15 15 15 15 15 15 16 16
(88) (88) (88) (88) (88) (88) (88) (94) (94)
0.3769 0.045 1 0.045 0.045 0.045 0.045 0.4848 0.0371 0.4848 0.4955 >0.9999
Uncuffed ETT size (mm)
3-3.5
4
4.5
5
5.5
Age (years)
<1
1 to <2
2 to <4
4 to <6
6 to <8
8 to <10
p-value
Portex clear Portex Ivory Rusch Sheriden Covidien
14 14 15 14 14
33 33 33 33 32
24 22 24 24 22
23 21 23 23 23
16 16 17 16 16
14 13 14 14 14
0.0815 0.3046 0.0245 0.0815 0.4120
(93) (93) (100) (93) (93)
(97) (97) (97) (97) (94)
(100) (92) (100) (100) (92)
(100) (91) (100) (100) (100)
6
(94) (94) (100) (94) (94)
(82) (76) (82) (82) (82)
The values are listed as the number and (percentage) based on the comparison of the ETT from Table 1 and the measurements from the 130 patients from the previous study of Wani et al. [7]. If there was no corresponding ETT in a specific size, brand and style, the cell is left blank. ETT = endotracheal tube; ID = internal diameter
4. Discussion Uncuffed ETTs are normally selected using the modified Cole formula, which relates uncuffed ETT size to age (ID in mm = (age/4) + 4) [6]. Formulae for the cuffed ETT size generally subtract 0.5–1 mm from the ID of the ETT when using formulas for uncuffed ETTs to compensate for the presence of the cuff. Various formulae exist for cuffed ETTs such as the one developed by Motoyama ((ID in mm = (age/4) + 3.5) or the one developed by Khine and colleagues (ID in mm = (age/4) + 3)) [1,2,4]. In children less than 2 years of age, these equations are not applicable and ETT sizes are chosen according to specific tables developed from common clinical practice. Airway dimensions increase with age in infants and children with appreciable changes evident over a period of only a few months [7,8]. As noted in our study, the AP and transverse diameters of the cricoid vary considerably even within each specific age group and thus, a particular ETT size selected by a formula cannot be expected to fit all of the patients in any one age group. The variability is demonstrated by the significant differences when comparing the 5th percentile and the 95th percentile of the cricoid dimensions in each age group with differences ranging from a minimum of 2.5 mm to a maximum of 5.8 mm (Table 2). Thus, an ETT chosen on age-based formulas may be either too large or too small in a significant percentage of patients. These issues are further compounded by the variability noted in the OD of ETTs so that ETTs with the same ID may have different ODs [9]. Despite such variability and the common use of the ID to select ETT size, clinical sense would dictate the use of the OD as the deciding feature when selecting an ETT. For the current study, cricoid dimensions from our previous study were used [7]. These dimensions were determined using computed tomography (CT) images. CT delineates the air-tissue interface better than other imaging modalities and is generally considered the current gold standard for airway measurements. As cricoid dimensions varied considerably in each age group, an age-based formula cannot be expected to predict the proper size of ETT in all patients. The OD of the ETT would seem to be the more rational method for choosing the right ETT size. However, the ODs of the cuffed ETTs varied markedly for a given ID, both between tubes from different
manufacturers (0 0.9 mm) and between cuffed and uncuffed ETTs from the same manufacturer (0 1.1 mm) [9,10]. These variations are due to variations in ETT wall thickness, the nature of the material (latex, PCV) used for the ETT as well as the cuff, and variations as a result of manufacturing. The variation in the OD of the uncuffed ETT among the manufacturers makes the selection of the proper ETT size more complicated and may result in the choice of an ETT that does not fit. When using an uncuffed ETT, Khine et al. reported the need to try a different sized ETT in 30% of children younger than 2 years of age and 18% of patients 2 years or older [1]. Standardization of the OD of ETTs based on the ID may eliminate some of these issues and improve the accuracy of ETT selection and perhaps minimize the consequences of a poorly sized ETT in the pediatric population. Most anesthesia providers may not be aware of differences in OD of ETTs among manufacturers given our common clinical practice of using the ID to size ETTs. When using the age-based formulae, there was a better fit with cuffed ETTs. Furthermore, if the cuffed ETT is too small, the fit can be adjusted by inflation of the cuff, which may allow fewer laryngoscopies to replace ill-fitted ETTs. Author’s contribution TMW, MRM: study design and concept; MRM, TMW, MMC: data analysis; MMC, MRM, TMW: revising critically important intellectual content of the paper, preparation of the first draft; MRM, JDT: manuscript revisions, editing, and preparation of the final draft. Conflict of interest None of the authors have conflict of interest to declare. Funding This investigation was performed without funding. References [1] H.H. Khine, D.H. Corddry, R.G. Kettrick, T.M. Martin, J.J. McCloskey, J.B. Rose, Comparison of cuffed and uncuffed tracheal tubes in young children during general anesthesia, Anesthesiology 86 (1997) 627–631.
M. Rafiq et al. / International Journal of Pediatric Otorhinolaryngology 85 (2016) 8–11 [2] J. Holzki, Laryngeal damage from tracheal intubation, Paediatr. Anaesth. 7 (1997) 435–437. [3] I. Murrat, Cuffed tubes in children: a 3-year experience in a single institution, Paediatr. Anaesth. 11 (2001) 748–749. [4] A.A. Vanden Berg, T. Mphanza, Choice of tracheal tube size for children. Finger size or age-related formula, Anaesthesia 52 (1997) 695–703. [5] J.B. Eck, G. De Lisle Dear, B.G. Phillips-Bute, B. Ginsberg, Prediction of tracheal tube size in children using multiple variables, Paediatr. Anaesth. 12 (2002) 495–498. [6] F. Cole, Pediatric formulas for the anaesthesiologists, Am. J. Dis. Child. 94 (1957) 672–673.
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[7] T.M. Wani, B. Bissonnette, M. Rafiq Malik, D. Hayes Jr., A.S. Ramesh, M. Al Sohaibani, et al., Age-based analysis of pediatric upper airway dimensions using computed tomography imaging, Pediatr. Pulmonol. 51 (2016) 267–271. [8] R.S. Litman, E.E. Weissend, D. Shibata, P.L. Westesson, Developmental changes of laryngeal dimensions in unparalyzed, sedated children, Anesthesiology 98 (2003) 41–45. [9] J.K. Park, D.M. Wynne, Review of the variation in the outer diameter of uncuffed neonatal and paediatric endotracheal tubes, Clin. Otolaryngol. 37 (2012) 503–504. [10] M. Weiss, A. Dullenkopf, C. Gysin, C.M. Dillier, A.C. Gerber, Shortcomings of cuffed paediatric tracheal tubes, BJA 92 (2004) 78–88.
Contents lists available at ScienceDirect
International Journal of Pediatric Otorhinolaryngology journal homepage: www.elsevier.com/locate/ijporl
Endotracheal tubes and the cricoid: Is there a good fit? Mahmood Rafiq a,*, Tariq M. Wani a,b, Melissa Moore-Clingenpeel c, Joseph D. Tobias a,b a
Department of Anesthesiology and Pain Medicine, Nationwide Children’s Hospital, Columbus, OH, USA Department of Anesthesiology and Pain Medicine, The Ohio State University, Columbus, OH, USA c Biostatistics Core, The Research Institute at Nationwide Children’s Hospital, Columbus, OH, USA b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 27 November 2015 Received in revised form 9 March 2016 Accepted 11 March 2016 Available online 19 March 2016
Background: Choosing an appropriately sized endotracheal tube (ETT) is important in pediatric patients as an inappropriately sized ETT may result in multiple endotracheal intubation attempts or excessive pressure on the tracheal mucosa with the potential for airway damage. Although age-based formulas are generally used with choice of an ETT based on the internal diameter (ID), measurements of the outer diameter (OD) of the ETT would seem to be a more scientific approach to determine the proper size of an ETT. However, the variable OD of the ETT despite the same ID makes the selection of a proper sized ETT more difficult. The current study compares airway dimensions measured using computed tomography (CT) with the OD of ETTs from various manufacturers. Methods: The outer diameter of commonly used ETTs (12 cuffed and 5 uncuffed) were measured and compared with CT-based cricoid measurements obtained from a previous study involving 130 pediatric patients, ranging in age from 1 month to 10 years. These data were used to determine the likelihood of a clinically acceptable match. Results: The differences of the cricoid dimensions between the 5th and the 95th percentile in each group ranged from a minimum of 2.23 mm to a maximum of 6.51 mm. Depending on the manufacturer, there was significant variation in the OD of the ETTs with the same ID. These discrepancies, which varied according to manufacturer and were greater with uncuffed as compared to cuffed ETTs, impacted the chances of an acceptable fit with the cricoid diameters. Conclusion: When choosing an ETT, age-based formulas which use the ID may not be uniformly accurate in ensuring the appropriately-sized ETT given the variation in the OD despite the same ID. These issues further support the use of cuffed ETTs as the variation in fit can be adjusted by inflation of the cuff to provide an adequate tracheal seal. ß 2016 Elsevier Ireland Ltd. All rights reserved.
Keywords: Cricoid diameter Pediatric endotracheal tubes Outer diameter Pediatric airway CT imaging
1. Introduction The cricoid, the only complete cartilaginous ring, is the single fixed dimension in the pediatric airway. It has been defined as the narrowest part of the airway, offering resistance to the passage of an endotracheal tube (ETT), thereby being a key dimension when choosing an ETT. Choosing the correct ETT size is important in pediatric patients because an inappropriately sized ETT may result in multiple intubation attempts or excessive pressure on the tracheal mucosa thereby causing damage to the airway [1–3]. Although, age-based formulas are routinely used to estimate the optimal ETT size, none of these systems is accurate for all patients because of variations of tracheal dimensions among the pediatric population [4–6].
Measurements of the outer diameter (OD) of an ETT would seem to be the most accurate approach to determine the proper size of an ETT. However, in clinical anesthesia practice, the ETT size is generally based on the internal diameter (ID). Variation between the ID and OD exists among manufacturers, further complicating age-based pediatric ETT size selection [7]. In the current study, we compare the diameter of the trachea at the level of the cricoid ring, using CT-based images of pediatric patients, to the OD of cuffed and uncuffed ETTs of different manufacturers. The aim was to evaluate the design of these ETTs, relate it to CT-based anatomical airway measurements of the trachea, and determine the likelihood of a good fit between the ETT and the trachea.
2. Methods * Corresponding author. Tel.: +1 6142540826. E-mail address: [email protected] (M. Rafiq). http://dx.doi.org/10.1016/j.ijporl.2016.03.016 0165-5876/ß 2016 Elsevier Ireland Ltd. All rights reserved.
The present study was performed at Nationwide Children’s Hospital (Columbus, Ohio). As no direct patient involvement was
M. Rafiq et al. / International Journal of Pediatric Otorhinolaryngology 85 (2016) 8–11
needed, there was no IRB approval necessary. The ODs of 12 different cuffed and 5 different uncuffed ETTs were measured. The ETTs involved were manufactured by Rusch, Covidien, Covidien–Mallinckrodt, Portex, Sheriden, and Kimberly–Clark. Anatomical airway measurements were calculated using the data from our previous study, which determined airway dimensions using the antero-posterior (AP) and transverse (T) diameters at the level of cricoid from CT-based images [7]. Data from the previous publication used for the current study included 130 pediatric patients, ranging in age from 1 month to 10 years, who underwent thoracic computed tomography (CT) imaging for pathologies not involving the airway were included in the study. Exclusion criteria included a diagnosis or condition that the investigators felt would cause abnormal laryngeal anatomy or interfere with the measurements obtained during CT imaging. For the current study, the internal diameter of the trachea at the level of the cricoid from the previous study, which is outlined above, was compared with the OD of cuffed and uncuffed ETTs. For cuffed ETTs, the OD was measured at a point immediately above the level of the cuff. Table 1 shows the ETT sizes (cuffed and uncuffed) that were used for the various age ranges for the purpose of the study. The size of the cuffed ETT was derived from commonly used data suggested by references 1, 5, and 6 [1,5,6]. 2.1. Statistical analysis All analyses were performed using SAS 9.3 (SAS Institute, Cary, NC). Two sided p-values <0.05 are considered statistically significant. For each manufacturer, the proportion of patients where the ETT would fit was compared by age using Fisher’s exact tests. The distribution of the AP and the transverse cricoid dimensions were broken down by age group. The 5th, 25th, 50th, 75th, and 95th percentiles of cricoid diameters in each age group were calculated. The 50th percentile represents the median. 3. Results Data from the previous study of Wani et al. included the CT scans of 130 patients, ranging in age from 1 month to 10 year [7]. There were no statistically significant gender differences in any of the cricoid measurements so all data is considered together without reference to gender. For the youngest age group, 5% of the patients in the sample had an AP diameter less than 4.93 mm and 5% of the patients had an AP diameter greater than 9.05 (Table 2). The differences between the 5th percentile and the 95th percentile in each group ranged from a minimum of 2.23 mm to a maximum of 6.51 mm (Table 2). The distribution of transverse and AP cricoid dimensions within each ETT-determined age group is shown in Table 2. Table 3 shows the proportion of the 130 patients from the study of Wani et al. that would have an acceptable fit according to each specific manufacturer when using an age-appropriate cuffed
Table 1 Endotracheal tube size vs. age groups. ETT size (mm):
Cuffed (Age)
Uncuffed (Age)
3.0 3.5 4.0 4.5 5.0 5.5 6
Full-term to 1 year 1 to <2 2 to <4 4 to <6 6 to <8 8 to 10 –
Full-term to 1 year Full-term to 1 year 1 to <2 2 to <4 4 to <6 6 to <8 8 to 10
The choice of endotracheal tube (ETT) used to assess the fit for the current study was based on this table. The size of the cuffed and uncuffed ETT is derived from references [1,5,6]. ETT = endotracheal tube.
9
Table 2 Distribution of cricoid measurements by age. Age (years) <1 1 to 2 to 4 to 6 to 8 to
N
Variable
15 AP Transverse <2 34 AP Transverse <4 24 AP Transverse <6 23 AP Transverse <8 17 AP Transverse <10 17 AP Transverse
5th % 25th % 50th % 75th % 95th % Difference 95th%–5th % 4.9 4.7 6.0 6.1 6.7 7.0 7.6 7.4 8.4 7.4 7.1 7.7
5.8 5.6 6.9 6.5 6.9 7.4 8.5 8.5 9.2 9.0 9.2 9.3
6.6 6.3 7.2 7.2 8.1 8.2 9.3 9.0 9.4 9.7 10.1 9.7
7.2 6.9 8.0 7.7 9.4 8.9 9.8 10.1 10.8 10.7 10.9 10.8
9.1 8.2 8.6 8.5 10.9 9.5 12.0 10.9 13.2 11.9 12.8 11.1
4.1 3.4 2.6 2.4 4.2 2.5 4.4 13.5 4.9 4.5 5.8 3.4
Values are expressed in mm and rounded to the nearest tenth of a millimeter. This information is based on the data from reference [7]. N = number; AP = anterioposterior.
or uncuffed ETT as defined in Table 1. Did not fit was assumed if the outside diameter of the ETT would not fit in either the AP or the transverse dimension as measured in the 130 patients from the study of Wani et al. [7]. Among cuffed ETTs, Mallinckrodt TT Hi-Lo Murphy and Portex TT-Profile Soft Seal Cuff Murphy tubes both fit less than 95% of the time. However, there were no statistically significant differences in fit across the various manufacturers. Among uncuffed ETTs, only Rusch ETTs fit more than 95% of the time. The fit for ETTs (cuffed and uncuffed) across various age ranges and depending on specific manufacturers is listed in Table 4. For all cuffed ETTs, fit was less likely for patients between 8 and 10 years of age. For cuffed ETTs, the fit was 100% for all patients less than 8 years of age with the exception of Mallinckrodt TT Safety Flex ETTs for patients less than 1 year age (97% fit) and Ru¨sch Ruschelit Super Safety Clear Magill ETTs in patients less than 1 year of age (93% fit) and in the 1–2 year age group (97% fit). Fit tended to be worse overall when considering uncuffed ETTs compared to cuffed ETTs. The fit for uncuffed ETTs was best for patients between 2 and 6 years of age.
Table 3 Proportion of fit by manufacturer for endotracheal tubes. ETT manufacturer (uncuffed)
Did not fit—number and (%)
Fit—number and (%)
Portex clear Portex Ivory Rusch Sheriden Covidien
6 11 4 6 9
124 119 126 124 121
ETT manufacturer (cuffed)
Did not fit—number and (%)
Fit—number and (%)
Kimberly–Clark microcuff Sheridan Murphy Sheridan Magill Mallinckrodt High-Contour Murphy Mallinckrodt High-Contour Mallinckrodt TT Lo-Contour Magill Mallinckrodt TT Lo-Contour Murphy Mallinckrodt TT Hi-Lo Murphy Mallinckrodt TT Safety Flex Portex TT-Profile Soft Seal Cuff, Murphy Ru¨schRuschelit Super Safety Clear Magill Ru¨schRuschelit Super Safety Clear Murphy
1 (1) 2(2) 0 (0) 2(2) 2(2) 2(2) 2(2) 2 (6) 3 (2) 2 (6) 3 (2) 1 (3)
129 (99) 128 (98) 60 (100) 128 (98) 128 (98) 128 (98) 128 (98) 32 (94) 127 (98) 32 (94) 127 (98) 33 (97)
(5) (8) (3) (5) (7)
(95) (92) (97) (95) (93)
The values are listed as the number and (percentage) based on the comparison of the ETT from Table 1 and the measurements from the 130 patients from the previous study of Wani et al. [7]. ETT = endotracheal tube; ID = internal diameter.
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M. Rafiq et al. / International Journal of Pediatric Otorhinolaryngology 85 (2016) 8–11
Table 4 Proportion of fit by age within manufacturer for endotracheal tubes. Cuffed ETT size (mm)
3
Age (years)
<1
Kimberly–Clark microcuff Sheridan Murphy Sheridan Magill Mallinckrodt High Contour Murphy Mallinckrodt High Contour Mallinckrodt TT Lo-Contour Magill Mallinckrodt TT Lo-Contour Murphy Mallinckrodt TT Hi-Lo Murphy Mallinckrodt TT Safety Flex Portex TT Profile Soft Seal Cuff, Murphy Ru¨schRuschelit Super Safety Clear Magill Ru¨schRuschelit super safety clear murphy
15 15 15 15 15 15 15
3.5
(100) (100) (100) (100) (100) (100) (100)
4
4.5
5
5.5
p-Value
1 to <2
2 to <4
4 to <6
6 to <8
8 to <10
34 (100) 34 (100)
24 24 24 24 24 24 24
23 (100) 23 (100)
17 17 17 17 17 17 17 17 17 17 17 17
16 (94) 15 (88)
34 34 34 34
(100) (100) (100) (100)
(100) (100) (100) (100) (100) (100) (100)
23 23 23 23
(100) (100) (100) (100)
14 (93)
34 (100)
24 (100)
23 (100)
14 (93)
33 (97)
24 (100)
23 (100)
(100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100)
15 15 15 15 15 15 15 16 16
(88) (88) (88) (88) (88) (88) (88) (94) (94)
0.3769 0.045 1 0.045 0.045 0.045 0.045 0.4848 0.0371 0.4848 0.4955 >0.9999
Uncuffed ETT size (mm)
3-3.5
4
4.5
5
5.5
Age (years)
<1
1 to <2
2 to <4
4 to <6
6 to <8
8 to <10
p-value
Portex clear Portex Ivory Rusch Sheriden Covidien
14 14 15 14 14
33 33 33 33 32
24 22 24 24 22
23 21 23 23 23
16 16 17 16 16
14 13 14 14 14
0.0815 0.3046 0.0245 0.0815 0.4120
(93) (93) (100) (93) (93)
(97) (97) (97) (97) (94)
(100) (92) (100) (100) (92)
(100) (91) (100) (100) (100)
6
(94) (94) (100) (94) (94)
(82) (76) (82) (82) (82)
The values are listed as the number and (percentage) based on the comparison of the ETT from Table 1 and the measurements from the 130 patients from the previous study of Wani et al. [7]. If there was no corresponding ETT in a specific size, brand and style, the cell is left blank. ETT = endotracheal tube; ID = internal diameter
4. Discussion Uncuffed ETTs are normally selected using the modified Cole formula, which relates uncuffed ETT size to age (ID in mm = (age/4) + 4) [6]. Formulae for the cuffed ETT size generally subtract 0.5–1 mm from the ID of the ETT when using formulas for uncuffed ETTs to compensate for the presence of the cuff. Various formulae exist for cuffed ETTs such as the one developed by Motoyama ((ID in mm = (age/4) + 3.5) or the one developed by Khine and colleagues (ID in mm = (age/4) + 3)) [1,2,4]. In children less than 2 years of age, these equations are not applicable and ETT sizes are chosen according to specific tables developed from common clinical practice. Airway dimensions increase with age in infants and children with appreciable changes evident over a period of only a few months [7,8]. As noted in our study, the AP and transverse diameters of the cricoid vary considerably even within each specific age group and thus, a particular ETT size selected by a formula cannot be expected to fit all of the patients in any one age group. The variability is demonstrated by the significant differences when comparing the 5th percentile and the 95th percentile of the cricoid dimensions in each age group with differences ranging from a minimum of 2.5 mm to a maximum of 5.8 mm (Table 2). Thus, an ETT chosen on age-based formulas may be either too large or too small in a significant percentage of patients. These issues are further compounded by the variability noted in the OD of ETTs so that ETTs with the same ID may have different ODs [9]. Despite such variability and the common use of the ID to select ETT size, clinical sense would dictate the use of the OD as the deciding feature when selecting an ETT. For the current study, cricoid dimensions from our previous study were used [7]. These dimensions were determined using computed tomography (CT) images. CT delineates the air-tissue interface better than other imaging modalities and is generally considered the current gold standard for airway measurements. As cricoid dimensions varied considerably in each age group, an age-based formula cannot be expected to predict the proper size of ETT in all patients. The OD of the ETT would seem to be the more rational method for choosing the right ETT size. However, the ODs of the cuffed ETTs varied markedly for a given ID, both between tubes from different
manufacturers (0 0.9 mm) and between cuffed and uncuffed ETTs from the same manufacturer (0 1.1 mm) [9,10]. These variations are due to variations in ETT wall thickness, the nature of the material (latex, PCV) used for the ETT as well as the cuff, and variations as a result of manufacturing. The variation in the OD of the uncuffed ETT among the manufacturers makes the selection of the proper ETT size more complicated and may result in the choice of an ETT that does not fit. When using an uncuffed ETT, Khine et al. reported the need to try a different sized ETT in 30% of children younger than 2 years of age and 18% of patients 2 years or older [1]. Standardization of the OD of ETTs based on the ID may eliminate some of these issues and improve the accuracy of ETT selection and perhaps minimize the consequences of a poorly sized ETT in the pediatric population. Most anesthesia providers may not be aware of differences in OD of ETTs among manufacturers given our common clinical practice of using the ID to size ETTs. When using the age-based formulae, there was a better fit with cuffed ETTs. Furthermore, if the cuffed ETT is too small, the fit can be adjusted by inflation of the cuff, which may allow fewer laryngoscopies to replace ill-fitted ETTs. Author’s contribution TMW, MRM: study design and concept; MRM, TMW, MMC: data analysis; MMC, MRM, TMW: revising critically important intellectual content of the paper, preparation of the first draft; MRM, JDT: manuscript revisions, editing, and preparation of the final draft. Conflict of interest None of the authors have conflict of interest to declare. Funding This investigation was performed without funding. References [1] H.H. Khine, D.H. Corddry, R.G. Kettrick, T.M. Martin, J.J. McCloskey, J.B. Rose, Comparison of cuffed and uncuffed tracheal tubes in young children during general anesthesia, Anesthesiology 86 (1997) 627–631.
M. Rafiq et al. / International Journal of Pediatric Otorhinolaryngology 85 (2016) 8–11 [2] J. Holzki, Laryngeal damage from tracheal intubation, Paediatr. Anaesth. 7 (1997) 435–437. [3] I. Murrat, Cuffed tubes in children: a 3-year experience in a single institution, Paediatr. Anaesth. 11 (2001) 748–749. [4] A.A. Vanden Berg, T. Mphanza, Choice of tracheal tube size for children. Finger size or age-related formula, Anaesthesia 52 (1997) 695–703. [5] J.B. Eck, G. De Lisle Dear, B.G. Phillips-Bute, B. Ginsberg, Prediction of tracheal tube size in children using multiple variables, Paediatr. Anaesth. 12 (2002) 495–498. [6] F. Cole, Pediatric formulas for the anaesthesiologists, Am. J. Dis. Child. 94 (1957) 672–673.
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[7] T.M. Wani, B. Bissonnette, M. Rafiq Malik, D. Hayes Jr., A.S. Ramesh, M. Al Sohaibani, et al., Age-based analysis of pediatric upper airway dimensions using computed tomography imaging, Pediatr. Pulmonol. 51 (2016) 267–271. [8] R.S. Litman, E.E. Weissend, D. Shibata, P.L. Westesson, Developmental changes of laryngeal dimensions in unparalyzed, sedated children, Anesthesiology 98 (2003) 41–45. [9] J.K. Park, D.M. Wynne, Review of the variation in the outer diameter of uncuffed neonatal and paediatric endotracheal tubes, Clin. Otolaryngol. 37 (2012) 503–504. [10] M. Weiss, A. Dullenkopf, C. Gysin, C.M. Dillier, A.C. Gerber, Shortcomings of cuffed paediatric tracheal tubes, BJA 92 (2004) 78–88.