The development of the cricoid cartilage and its implications for the use of endotracheal tubes in the pediatric population

The accuracy of the ultrasound measured transverse cricoid diameter and the epiphyseal transverse diameter of the distal radius in predicting the pediatric endotracheal tube size

BACKGROUND

In everyday pediatric anesthesia practice, clinicians frequently exchange an already inserted endotracheal tube because of a leak or resistance causing significant morbidity. We investigated the accuracy of two ultrasound measurements; the transverse cricoid diameter and epiphyseal diameter of the distal radius in the prediction of endotracheal tube size that best fits in children compared to age-based formulas.

PATIENTS

One hundred children (1-6 years) who underwent elective surgery with endotracheal tube whether cuffed (n = 50) or uncuffed (n = 50) were enrolled. The primary endpoint was the agreement between the reference tube size for which its outer diameter was selected based on transverse cricoid diameter and the final best-fit-ETT. The Correlation and Bland Altman agreement tests were conducted between best-fit-ETT outer diameter and ultrasound-measured outer diameter, and between best-fit-ETT inner diameter and inner diameter calculated by age-based formulas.

RESULTS

The agreement rate between transverse cricoid diameter-based endotracheal tube size and best-fit-ETT size was 88% in cuffed group compared to 90% in uncuffed group. A significant positive correlation was reported between the outer diameter of best-fit-ETT and the outer diameter measured by the two ultrasound methods. A lower degree of positive correlation was reported between the inner diameter of best-fit-ETT, and the inner diameter calculated by age-based formulas. Bland Altman's analysis showed agreement between best-fit-ETT outer diameter and epiphyseal diameter of the distal radius in both groups and with transverse cricoid diameter in the cuffed group, with no agreement with age-based formulas in either group.

CONCLUSIONS

Both transverse cricoid diameter and epiphyseal diameter of the distal radius are reliable predictors of the size of best-fit-ETT pediatric endotracheal tube compared to age-based formulas. To save time and effort, we recommend the US measurement of the epiphyseal diameter of distal radius in the preoperative visit and documenting the predicted tube size with the preoperative assessments.

Anatomic development of the upper airway during the first five years of life: A three-dimensional imaging study

Purpose

Normative data on the growth and development of the upper airway across the sexes is needed for the diagnosis and treatment of congenital and acquired respiratory anomalies and to gain insight on developmental changes in speech acoustics and disorders with craniofacial anomalies.

Methods

The growth of the upper airway in children ages birth to 5 years, as compared to adults, was quantified using an imaging database with computed tomography studies from typically developing individuals. Methodological criteria for scan inclusion and airway measurements included: head position, histogram-based airway segmentation, anatomic landmark placement, and development of a semi-automatic centerline for data extraction. A comprehensive set of 2D and 3D supra- and sub-glottal measurements from the choanae to tracheal opening were obtained including: naso-oro-laryngo-pharynx subregion volume and length, each subregion’s superior and inferior cross-sectional-area, and antero-posterior and transverse/width distances.

Results

Growth of the upper airway during the first 5 years of life was more pronounced in the vertical and transverse/lateral dimensions than in the antero-posterior dimension. By age 5 years, females have larger pharyngeal measurement than males. Prepubertal sex-differences were identified in the subglottal region.

Conclusions

Our findings demonstrate the importance of studying the growth of the upper airway in 3D. As the lumen length increases, its shape changes, becoming increasingly elliptical during the first 5 years of life. This study also emphasizes the importance of methodological considerations for both image acquisition and data extraction, as well as the use of consistent anatomic structures in defining pharyngeal regions.

Dimensional compatibility of rigid ventilating bronchoscopes with pediatric airway anatomy using different recommendations for age-related sizing-A bench study

BACKGROUND

Appropriate size selection of pediatric rigid bronchoscopes is fundamental to avoidance of airway trauma and to a high success rate with the first intubation attempt. The aim of the present study was to compare the outer diameters of pediatric rigid bronchoscopes with the anatomical data on the pediatric airway.

METHODS

Outer diameters (OD) of pediatric rigid ventilating bronchoscopes as given by the manufacturer were compared with published computed tomography internal diameters (ID) of the cricoid outlet, the trachea as well as the left and right proximal mainstem bronchus, using six published recommendations for age-related size selection. The ratios between a specific OD and ID were calculated and given as percentage values (%) for lower and upper age ranges.

RESULTS

Nominal sized 2.5, 3, 3.5, 3.7, 4, 4.5, 5, and 6 rigid bronchoscopes were included. In five recommendations, the rigid bronchoscopes' OD was larger than the internal cricoid diameter in the upper age range, whereas in one recommendation the ratio (OD rigid bronchoscope to ID of cricoid) ranged between 77% and 90% for the upper age and between 95% and 109% for the lower age range. In only one of the six recommendations was the rigid bronchoscope OD larger than the tracheal ID. Ratios for the left and right proximal mainstem bronchus ranged from 70% to 146% for the upper and from 78% to 156% for the lower age range, with the highest ratios for the left proximal mainstem bronchus.

CONCLUSION

Based on this in vitro study, most of the recommendations analyzed result in a balanced fit of rigid bronchoscopes within the cricoid. Since the left mainstem bronchus is considerably smaller than the cricoid, any insertion on this level will require careful endoscopic guidance to avoid damage to the left mainstem bronchus.

Pediatric airway management

PURPOSE OF REVIEW

Children are at risk of severe hypoxemia in the perioperative period owing to their unique anatomy and physiology. Safe and effective airway management strategies are therefore key to the practice of pediatric anesthesia. The goal of this review is to highlight recent publications (2019-2021) aimed to advance pediatric airway safety and to highlight a proposed simple, pediatric-specific, universal framework to guide clinical practice.

RECENT FINDINGS

Recent investigations demonstrate that infants with normal and difficult airways experience high incidences of multiple laryngoscopy attempts and resulting hypoxemia. Video laryngoscopy may improve tracheal intubation first attempt success rate in infants with normal airways. In infants with difficult airways, standard blade video laryngoscopy is associated with higher first attempt success rates over non-standard blade video laryngoscopy. Recent studies in children with Pierre Robin sequence and mucopolysaccharidoses help guide airway equipment and technique selection. Department airway leads and hospital difficult airway services are necessary to disseminate knowledge, lead quality improvement initiatives, and promote evidence-based practice guidelines.

SUMMARY

Pediatric airway management morbidity is a common problem in pediatric anesthesia. Improvements in individual practitioner preparation and management strategies as well as systems-based policies are required. A simple, pediatric-specific, universal airway management framework can be adopted for safe pediatric anesthesia practice.

Anatomical In Vitro Investigations of the Pediatric Larynx: A Call for Manufacturer Redesign of Tracheal Tube Cuff Location and Perhaps a Call to Reconsider the Use of Uncuffed Tracheal Tubes

BACKGROUND

Some in vivo studies question the traditional "funnel-shaped" infant larynx; further anatomic examinations were warranted. Examination of fixative free fresh autopsy laryngeal and upper tracheal specimens and multiple measurements was needed to determine consistency between current tracheal tube designs and anatomic observations.

METHODS

Larynges from 19 males and 11 females (Caucasian term newborn to 126 months) were examined by the same forensic pathologist. Measurements included anterior/posterior (A/P) and transverse (T) diameters of the cricoid outlet (CO), interarytenoid diameter (IAD), cricothyroid membrane (CTM), distance from the vocal cords (VC) to CO (VC-CO), and calibration of the larynx lumen with uncuffed tracheal tubes as measuring rods. Assessment of "safe tracheal tube placement" was assessed using manufacturer recommended cuffed Microcuff (Kimberly-Clark, Koblenz, Germany) tubes.

RESULTS

In 77% (95% confidence interval [CI], 58-90) of specimens, the proximal end of the cuff was within the CO and in 23% even with or close to the CO. The VC-CO varied from 9.1 to 13.17 mm in infants, 11.55 to 15.17 mm in toddlers, and 13.19 to 18.34 mm in children. The AP/T ratio of the CO was nearly 0.99 in most larynges; the IAD was greater than CO in all specimens. The CTM could be minimally distended in all specimens.

CONCLUSIONS

First, despite being marketed as a safer tracheal tube design, the proximal end of the Microcuff cuff rested within or close to the cricoid cartilage theoretically increasing potential cuff-induced injury when using the VC markings for positioning. Our data suggest that the optimal cuff free distance (VC-CO) would be ~13.5 mm for a Microcuff internal diameter (ID) size 3.0, ~15 mm for size 3.5, and ~16 to 19 mm for greater sizes.Second, the CO was virtually circular in all specimens, suggesting that appropriately sized uncuffed tubes should provide an adequate seal in most neonates and toddlers, thus avoiding the potential for cuff-related necrosis injury.Third, the IAD was always greater than CO confirming that the narrowest point of the infant larynx is the nondistensible cricoid cartilage and not the easily distended glottis.Fourth, appropriately sized Microcuff tubes with the cuff deflated completely filled the lumen of the CO and proximal trachea in all specimens. Our data suggest the need for all manufacturers to further evaluate tracheal tube cuff locations and lengths in relation to the VC safe insertion markings, particularly for neonates and toddlers.Fifth, the CTM is minimally distensible, thus having important implications for emergency surgical airway access with most currently available emergency airway devices.

Age-related Change of the Dimensions of the Cricoid Cartilage in Adults

OBJECTIVES

To measure the dimensions of the cricoid cartilage in adults and to investigate the age-related change of the dimensions of the cricoid cartilage.

METHODS

After performing the multiplanar reconstruction and correcting the slant of the cervical computed tomography scans, the transverse and anteroposterior internal diameters of the inlet (TD-in and APD-in) and outlet (TD-out and APD-out) of the cricoid cartilage were measured, respectively. The angle between the arch and lamina of the cricoid cartilage in the middle sagittal plane was measured. The ratios of transverse to anteroposterior diameter for the inlet (Ratio-in) and outlet (Ratio-out) of the cricoid cartilage were calculated, respectively.

RESULTS

A total of 1200 adults were included in this study, with 600 males and 600 females. The TD-in is the smallest cricoid diameter and the APD-in is the largest cricoid diameter. The mean cricoid diameters and the cricoid angle in males were larger than those in females. The cricoid inlet is oval shaped and the cricoid cartilage is "funnel-shaped" in the middle sagittal plane. The shape of the outlet of the cricoid cartilage varies greatly among individuals. In males, the APD-in and APD-out were negatively correlated with age while the Ratio-in and Ratio-out was positively correlated with age. In females, the APD-out were negatively correlated with age while the Ratio-out was negatively correlated with age.

CONCLUSIONS

The dimensions of the cricoid cartilage change as age advances in adult population and the sexual dimorphism of the cricoid outlet occurs after 50 years old.