Pediatric airway dimensions-A summary and presentation of existing data

Microbubble-laden aerosols improve post-nasal aerosol penetration efficiency in a preterm neonate model

Nebulized lung surfactant therapy has been a neonatology long-pursued goal. Nevertheless, many clinical trials have yet to show a clear clinical efficacy of nebulized surfactant, which, in part, is due to the technical challenges of delivering aerosols to the lungs of preterm neonates. The study aimed to test microbubbles for improving lung deposition in preterm neonates. An in vitro testing method was developed to replicate the clinical environment; it used a 3D-printed preterm neonate model, connected to a high-flow nasal cannula (HFNC) and a vibrating mesh nebulizer. The flow rate of the HFNC mirrored that used in the clinics (i.e., 4, 6, and 8 L/min). Followingly, the lung penetrations of aerosols with and without microbubbles were compared. The aerodynamic diameter of aerosols with microbubbles (MMAD=1.75 μm) was lower than that of the counterpart (MMAD=2.25 μm). Microbubble-laden aerosols had a significantly higher number of microbubbles that were below 1.0 μm. Microbubble-laden aerosols had dramatically higher lung penetration in the preterm model; lung penetration efficiencies were 30.0, 25.5, and 17.5 % at 4, 6, and 8 L/min, respectively, whereas the lung penetration efficiency for conventionally nebulized aerosols was below 1.25 % in the three flow rates.

Anatomical investigations on the upper airway in premature and newborn babies

Safe intubation of newborns remains a challenge. This investigates the upper airway anatomy of (pre-)term infants was investigated to improve airway management and the development of airway devices. Angles and diameters of both oral and nasal intubation pathways of 22 cadavers of premature and term stillborn infants were measured, relative to their gestational age (GA) and tested for statistical significance. The systematic influence of sex on the distribution of values was examined. Cast models of the oral and nasal intubation pathway were (produced using a silicone dental impression material) 3D-scanned. No significant correlation with GA was seen in the angles studied. However, four distances around the hard and soft palate did show statistically significant positive correlations with GA. Regarding differences between the sexes, only the angle between the entrance of the trachea and the esophagus was greater for male cadavers. The angles of the ventilation pathway of (pre-)term infants do not depend systematically on GA. Anatomically, laryngeal masks might therefore also be well-suited ventilators for preterm infants. Alterations in the size but not the shape of laryngeal masks for small preterm infants is recommended. The data obtained may thus be used as a basis for the development of airway devices and airway simulators for medical education and clinical training.

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.

Determining normal values for lower trachea and bronchi size in children by computed tomography (CT)

BACKGROUND

Normative data for central airway dimensions are a prerequisite to objectively assess large airway pathologies. Studies with computed tomography (CT) measurements of normal trachea and bronchi size in children are scarce.

OBJECTIVE

The purpose of this study is to establish normal values of central airway dimensions in children by CT.

METHODS

The study included chest CT studies from children aged 0-18 years. Any condition that predisposed the patient to have an abnormal tracheal or bronchial size was excluded. Airway diameters and cross-sectional area (CSA) were measured using double oblique reconstructions at five levels: proximal trachea, mid-trachea, distal trachea, right main bronchus, and left main bronchus.

RESULTS

The inclusion criteria were met by 110 subjects (mean age, 10.8 years; SD, 5.2 years). Various regression models that considered the relationship between patient demographics and anteroposterior (AP) diameter, transverse diameter, and CSA at each of the five levels were assessed. R² was utilized to select the best model. Multiple formulae (using patient age) were developed to calculate expected normal dimensions for five levels in the central airways on the natural log scale. Finally, z-scores were obtained for central airway dimensions at these five levels.

CONCLUSION

Normative data in pediatric central airways are crucial to identify large airway pathologies. We propose using the formulae devised in our study to calculate the predicted dimensions of central airways and their z-scores in pediatric patients. Normative data from our study will aid in objective quantification of central airways, increase clinician confidence, and provide appropriate patient care.

Advancement of the Infant Air-Jet Dry Powder Inhaler (DPI): Evaluation of Different Positive-Pressure Air Sources and Flow Rates

PURPOSE

In order to improve the delivery of dry powder aerosol formulations to the lungs of infants, this study implemented an infant air-jet platform and explored the effects of different air sources, flow rates, and pulmonary mechanics on aerosolization performance and aerosol delivery through a preterm nose-throat (NT) in vitro model.

METHODS

The infant air-jet platform was actuated with a positive-pressure air source that delivered the aerosol and provided a full inhalation breath. Three different air sources were developed to provide highly controllable positive-pressure air actuations (using actuation volumes of ~10 mL for the preterm model). While providing different flow waveform shapes, the three air sources were calibrated to produce the same flow rate magnitude (Q90: 90th percentile of flow rate). Multiple air-jet DPI designs were coupled with the air sources and evaluated with a model spray-dried excipient enhanced growth formulation.

RESULTS

Compared to other designs, the D1-Single air-jet DPI provided improved performance with low variability across all three air sources. With the tested D1-Single air-jet and Timer air source, reducing the flow rate from 4 to 1.7 L/min marginally decreased the aerosol size and significantly increased the lung delivery efficiency above 50% of the loaded dose. These results were not impacted by the presence of downstream pulmonary mechanics (resistance and compliance model).

CONCLUSIONS

The selected design was capable of providing an estimated >50% lung delivery efficiency of a model spray-dried formulation and was not influenced by the air source, thereby enabling greater flexibility for platform deployment in different environments.

Length of the Cricoid and Trachea in Children: Predicting Intubation Depth to Prevent Subglottic Stenosis

OBJECTIVE

Define the length of the subglottis and trachea in children to predict a safe intubation depth.

METHODS

Patients <18 years undergoing rigid bronchoscopy from 2013 to 2020 were included. The carina and inferior borders of the cricoid and true vocal folds were marked on a bronchoscope and distances were measured. Patient age, weight, height, and chest height were recorded. Four styles of cuffed pediatric endotracheal tubes (ETT) were measured and potential positions of each cuff and tip were calculated within each trachea using five depth of intubation scenarios. Multivariate linear regression was performed to identify predictors of subglottic and tracheal length.

RESULTS

Measurements were obtained from 210 children (141 male, 69 female), mean (SD) age 3.21 (3.66) years. Patient height was the best predictor of subglottic length (R² : 0.418): Length_sg (mm) = 0.058 * height (cm) + 2.8, and tracheal length (R² : 0.733): Length_t (mm) = 0.485 * height (cm) + 21.3. None of the depth of intubation scenarios maintained a cuff-free subglottis for all ETT styles investigated. A formula for depth of intubation: Length_di (mm) = 0.06 * height (cm) + 8.8 found that no ETT cuffs would be in the subglottis and all tips would be above the carina.

CONCLUSION

Current strategies for determining appropriate depth of intubation pose a high risk of subglottic ETT cuff placement. Placing the inferior border of the vocal cords 0.06 * height (cm) + 8.8 from the superior border of the inflated ETT cuff may prevent subglottic cuff placement and endobronchial intubation.

LEVEL OF EVIDENCE

4 Laryngoscope, 2021.

Inflation volume-balloon diameter and inflation pressure-balloon diameter characteristics of commonly used bronchial blocker balloons for single-lung ventilation in children

BACKGROUND

Balloon-tipped bronchial blocker catheters are widely used in pediatric thoracic anesthesia to establish single-lung ventilation. In clinical practice, their balloons demonstrate sudden expansion when inflated with air. In addition, there are concerns related to the high inflation pressures required to expand the balloons.

METHODS

This in vitro study assessed inflation volume- and inflation pressure-balloon diameter characteristics of the Fogarty arterial embolectomy catheters and Arndt endobronchial blockers. Balloon diameters were photographically assessed during unrestricted volume- and pressure-guided inflation, using air up to the maximum allowed inflation volume as indicated by the manufacturers. Inflation pressures required to open the blocker balloons and inflation pressures needed to expand them to maximum indicated diameter were measured.

RESULTS

Volume-guided inflation demonstrated a late acute rise in diameter in Fogarty blocker balloons, whereas in the Arndt endobronchial blocker balloons almost linear inflation volume-to-diameter characteristics were observed. Pressure-guided inflation on the other hand demonstrated low-volume, high-pressure characteristics in the Fogarty blocker balloons, with inflation pressures required to expand the balloons to maximum diameters ranging from (mean (SD)) 636 (75) to 947 (152) cmH₂ O. The inflation pressures required to open the Fogarty blocker balloons were even >1000 cmH₂ O. Inflation pressures required to expand the 5 F, 7 F, and 9 F Arndt endobronchial blocker balloons to maximum indicated diameter were much lower, namely at 218 (15), 252 (28), and 163 (8) cmH₂ O.

CONCLUSION

Based on these study findings, the balloons of Fogarty arterial embolectomy catheters represent high-pressure devices and do not permit stepwise controlled bronchial blockage. The Arndt endobronchial blockers have some advantages over the Fogarty blocker devices, but also represent high-pressure equipment and must be used with caution and limited duration. Manufacturers are asked to design pediatric endobronchial blocker catheters with truly high-volume, low-pressure balloons in accordance to age-related pediatric airway dimensions.

Pediatric airway: What is new in approaches and treatments?

Perioperative morbidity and mortality are high among patients in the extremes of life undergoing anesthesia. Complications in children occur mainly as a result of airway management-related events such as difficult approach, laryngospasm, bronchospasm and severe hypoxemia, which may result in cardiac arrest, neurological deficit or death. Reports and new considerations that have changed clinical practice in pediatric airway management have emerged in recent years. This narrative literature review seeks to summarize and detail the findings on the primary cause of morbidity and mortality in pediatric anesthesia and to highlight those things that anesthetists need to be aware of, according to the scientific reports that have been changing practice in pediatric anesthesia. This review focuses on the identification of “new” and specific practices that have emerged over the past 10 years and have helped reduce complications associated with pediatric airway management. At least 9 practices grouped into 4 groups are described: assessment, approach techniques, devices, and algorithms. The same devices used in adults are essentially all available for the management of the pediatric airway, and anesthesia-related morbidity and mortality can be reduced through improved quality of care in pediatrics.

Longer upper airway lengths in Robin Sequence: A case-control study using computed tomography

BACKGROUND

Direct laryngoscopy and intubation are often difficult in children with Robin Sequence. Previous research characterizing anatomic airway differences has focused on parameters influencing airway patency; there is a paucity of data pertaining to intubation trajectories and depth. Such information could impact airway management approaches and decrease the incidence of endotracheal tube malpositioning.

AIM

The study goal was to examine whether longitudinal airway parameters pertaining to intubation are different in children with Robin Sequence compared with age-matched controls.

METHOD

This case-control study compared patients with RS <4 years of age who had computed tomography scans of the head and neck to age- and sex-matched controls. Measurements were made of the nasopharynx, oropharynx, hypopharynx, tongue, hyoid, and the front teeth to vocal cord, nares to vocal cord, and nasion-basion distances. Statistical analysis was performed using multiple ANCOVA models with the categorical predictor of Robin Sequence vs control and potential covariates including subject height/length, weight, and age.

RESULTS

Thirty-three patients with Robin Sequence and 33 control subjects were included. After controlling for subject height/length, mean front teeth to vocal cord distance was 1.2 cm longer (95% CI: 0.9 to 1.6 cm, P < .001) and mean nares to vocal cord distance was 0.8 cm longer (95% CI: 0.4 to 1.2 cm, P < .001) in patients with Robin Sequence than in controls. The tongue was positioned on average 0.5 cm higher (95% CI: 0.3 to 0.8, P < .001) and 0.9 cm more posterior (95% CI: 0.6 to 1.0 cm, P < .001) in cases than in controls. Moreover, in patients with Robin Sequence, the hyoid was positioned on average 0.5 cm more inferiorly (95% CI: 0.2 to 0.8 cm, P < .001) and 0.2 cm more posteriorly (95% CI: 0.1 to 0.4 cm, P < .01) than controls.

CONCLUSION

In patients with Robin Sequence under 4 years of age, the mean front teeth to vocal cord distance was found to be 1.2 cm longer while the mean nares to vocal cord distance was found to be 0.8 cm longer controlling for subject length. Clinicians should account for these differences when selecting and placing endotracheal tubes, particularly those with a preformed bend.

Cuffed pediatric endotracheal tubes-Outer cuff diameters compared to age-related airway dimensions

BACKGROUND

Reliable sealing of the pediatric airway requires appropriately sized tracheal tube cuffs. The aim of this study was to compare residual cuff diameters of pediatric tracheal tubes with pediatric airway dimensions.

METHODS

Cuff diameters of five different brands of locally marketed pediatric cuffed tracheal tubes with internal diameters of 3.0-7.0 mm were measured at a cuff pressure of 20 cm H₂ O and compared with cuff diameters indicated by their manufacturers. The latter values were compared to tracheal dimensions using the Motoyama and Khine formulas for cuffed tracheal tube size selection.

RESULTS

There is considerable heterogeneity in cuff diameters among pediatric tracheal tube brands, except for two brands from different manufacturers (Halyard and Parker Medical) which were identically designed. Cuffs made from polyurethane revealed fewer differences (91%-118%) between measured and manufacturer-indicated values for outer cuff diameters than did those made from polyvinylchloride (91%-146%). Particularly in smaller sized tracheal tubes, cuffs did not reach 100% of the tracheal lateral diameter, while others were oversized in larger tracheal tubes, independent of the two formulas used for cuffed tracheal tube size selection. Cuff diameters indicated by the manufacturer corresponded to 86%-188% of the median and 68%-157% of the maximum mid-tracheal lateral diameter of the corresponding upper age range.

CONCLUSION

Our findings show that many of the cuff diameters of currently marketed tracheal tube brands lack an age-related anatomical rationale. A proposal for age-related anatomically based cuff diameters is provided for both recommendations for cuffed tracheal tube size selection in children.

Airway ultrasound: Point of care in children-The time is now

BACKGROUND

Point-of-care ultrasonography of the airway is becoming a first-line noninvasive adjunct assessment tool of the pediatric airway. It is defined as a focused and goal-directed portable ultrasonography brought to the patient and performed and interpreted on the spot by the provider. Successful use requires a thorough understanding of airway anatomy and ultrasound experience.

AIMS

To outline the many benefits, and some limitations, of airway ultrasonography in the clinical and perioperative setting.

MATERIALS AND METHODS

Expert review of the recent literature.

RESULTS

Ultrasound assessment of the airway may provide the clinician with valuable information that is specific to the individual airway static and dynamic anatomy of the patient. Ultrasound can help identify vocal cord dysfunction and pathology, assess airway size, predict the appropriate diameter of endotracheal and tracheostomy tubes, differentiate tracheal from esophageal intubation, localize the cricothyroid membrane for emergency airway access and identify tracheal rings for US-guided tracheostomy. Ultrasonography is also a great tool for the intraoperative diagnosis of a pneumothorax, the visualization of the movement of the diaphragms, and quantifying the amount of gastric content. Ultrasonography signs, tips, and pearls that allow these diagnoses are highlighted. The major disadvantage of ultrasonography remains interobserver variability, and operator dependence, as it requires specific training and experience.

CONCLUSION

Although it is not standard of care yet, there is significant potential for the integration of ultrasound technology into the routine care of the airway.