The histopathology of the larynx in the neonate following endotracheal intubation

Strategies to Improve Neonatal Intubation Safety by Preventing Endobronchial Placement of the Tracheal Tube-Literature Review and Experience at a Tertiary Center

Unintended endobronchial placement is a common complication of neonatal tracheal intubation and a threat to patient safety, but it has received little attention towards decreasing its incidence and mitigating associated harms. We report on the key aspects of a long-term project in which we applied principles of patient safety to design and implement safeguards and establish a safety culture, aiming to decrease the rate of deep intubation (beyond T3) in neonates to <10%. Results from 5745 consecutive intubations revealed a 47% incidence of deep tube placement at baseline, which decreased to 10-15% after initial interventions and remained in the 9-20% range for the past 15 years; concurrently, rates of deep intubation at referring institutions have remained high. Root cause analyses revealed multiple contributing factors, so countermeasures specifically aimed at improving intubation safety should be applied before, during, and immediately after tube insertion. Extensive literature review, concordant with our experience, suggests that pre-specifying the expected tube depth before intubation is the most effective and simple intervention, although further research is needed to establish accurate and accepted standards for estimating the expected depth. Presently, team training on intubation safety, plus possible technological advances, offer additional options for safer neonatal intubations.

Mucosal injury following short-term tracheal intubation: A novel animal model and composite tracheal injury score

OBJECTIVES

Postintubation laryngotracheal injury is common. Assessment of histopathological changes currently requires animal models. We set about developing a viable, resource effective animal model to study these effects and to develop a detailed tissue injury score.

METHODS

Six pigs were anesthetized using a standard regimen. We intubated the tracheas using a standard endotracheal tube modified to include optical sensors. Animals were anesthetized for a duration of two to four hours, and their lungs were ventilated using a normoxic gas mixture. Following euthanasia, the tracheas were removed and underwent histological assessment by two independent veterinary pathologists. The histological lesions, including controls, were described and quantified, and two pathologists classified tissues according to a novel injury score.

RESULTS

Mean duration of tracheal intubation was 191 minutes (SD ± 41.6). In all except one animal, cuff pressures were maintained in the range of 25-45 cmH20. Histopathological findings in all study animals showed more extensive changes than previously described with short-term intubation. Changes were seen in all mucosal layers consistent with acute, suppurative, and ulcerative tracheitis. The range of scores of the developed composite scoring system among the animals was wider than in earlier descriptions. There was a high percentage of agreement between both pathologists.

CONCLUSIONS

We have described a novel tracheal injury score to assess pathological changes following short term intubation in a viable animal model. The scoring system distinguished between the test animals as well as controls and may be appropriate for continuing study of intubation injury.

LEVEL OF EVIDENCE

3.

Risk factors for laryngeal trauma and granuloma formation in pediatric intubations

OBJECTIVE

Intubation has been associated with laryngeal injury that often resolves spontaneously without complication. We present a case of a child intubated for less than 48 hours, who presented with dysphonia and intermittent dyspnea two months after intubation due to epiglottic and vocal process granulomas. This is unusual in that multiple granulomas were found in the posterior glottis and supraglottis after short-term intubation. Our objective was to determine if there are risk factors for developing persistent post-intubation sequelae, including the delayed presentation and unusual location of post-intubation granulomas in our case.

STUDY DESIGN

Case report and systematic literature review.

METHODS

Pubmed database, which is inclusive of MEDLINE, was used to perform a literature review with the search terms ((pediatric OR children OR neonatal OR infant) AND (laryngeal OR supraglottic) AND intubation AND (granuloma OR injury OR complication)). Only English language results were reviewed. Titles and abstracts from 379 results were reviewed. Full text was reviewed from all original studies which included human pediatric subjects and endoscopic examinations after endotracheal intubation.

RESULTS

In our case, laryngeal granuloma size reduced significantly after starting anti-reflux medications. The remainder was removed with laryngeal microdebrider with no recurrence at 3 weeks and 2.5 years post-operatively. Overall, 28 of the 379 studies reviewed identified evidence of laryngeal trauma due to intubation, however only 6 studies documented any type of supraglottic injury. Risk factors identified for developing post-intubation sequelae included intubation duration greater than 24 h; trauma to the larynx via various mechanisms including traumatic intubation, need for reintubation and tube changes, and increased movement while intubated; and presence of respiratory tract infection during intubation.

CONCLUSION

Trauma to the larynx during intubation should be avoided to minimize post-intubation injury in pediatric patients, by using appropriate intubation protocols, endotracheal tube size, and adequate sedation.

Management of Posterior Glottal Insufficiency With Use of a Buccal Graft

Objective:

Posterior glottal insufficiency manifests as a rough, breathy voice with poor vocal projection, air hunger, and decreased phonatory efficiency. There are limited medical and surgical therapies. This study reports the use of insetting a buccal mucosa graft into the posterior interarytenoid space to close the posterior glottic gap for phonatory rehabilitation.

Methods:

Our study is a retrospective case series of 2 female patients undergoing buccal mucosa graft inset to repair acquired posterior glottic insufficiency as a result of prolonged intubation and laryngeal tuberculosis infection. Patients selected for this procedure had posterior glottal insufficiency due to erosion of posterior glottal tissue. They also had dysphonia refractory to voice therapy and injection augmentation.

Conclusions:

Interarytenoid buccal graft for posterior glottal insufficiency is effective with excellent vocal rehabilitation and minimal donor site morbidity.

Innate Immune Response of the Pig Laryngeal Mucosa to Endotracheal Intubation

Objective

The aim of this study was to measure the effects of endotracheal intubation on innate immune response within the pig laryngeal mucosa.

Study Design

Prospective controlled basic science study.

Setting

The animal experiments and analyses were conducted at the University of Bristol.

Samples and Methods

Eighteen pigs, matched at the major histocompatibility complex (MHC), were used in the study. The pigs were divided into 9 pairs. One of each pair (9 pigs in total) was intubated with an endotracheal tube under general anesthesia for 90 minutes. Two days later, pinch biopsies were taken from the supraglottis (specifically the false cords) and subglottis of both pigs. The experiment was repeated 8 more times. Based on quantitative immunohistochemistry, percentage areas of positive staining for CD172a, CD163, MHC class II, CD14, and CD16 were calculated separately for the epithelium and lamina propria of each biopsy.

Results

Total areas of laryngeal mucosa (epithelium and lamina propria) expressing CD172a and coexpressing CD163 and CD172a were significantly reduced at 2 days following endotracheal intubation ( P = .039 and P = .037, respectively). MHC class II expression and MHC class II coexpression with CD172a were similarly reduced following intubation ( P = .003 and P = .005, respectively). In the supraglottis, MHC class II coexpression with CD16 and CD14 was also reduced following endotracheal intubation ( P = .037).

Conclusions

Our results indicate that endotracheal intubation reduces the number of innate immune cells within the upper airway mucosa. This may be an important first step in a cascade leading to chronic wound and scar formation causing airway stenosis.

Predictors of Posterior Glottic Stenosis: A Multi-Institutional Case-Control Study

OBJECTIVE

To assess intrinsic and extrinsic risk factors in the development of posterior glottic stenosis (PGS) in intubated patients.

METHODS

Patients diagnosed with PGS between September 2012 and May 2014 at 3 tertiary care university hospitals were included. Patient demographics, comorbidities, duration of intubation, endotracheal tube (ETT) size, and indication for intubation were recorded. Patients with PGS were compared to control patients represented by patients intubated in intensive care units (ICU).

RESULTS

Thirty-six PGS patients were identified. After exclusion, 28 PGS patients (14 male, 14 female) and 112 (65 male, 47 female) controls were studied. Multivariate analysis demonstrated ischemia (P < .05), diabetes (P < .01), and length of intubation (P < .01) were significant risk factors for the development of PGS. Fourteen of 14 (100%) males were intubated with a size 8 or larger ETT compared to 47 of 65 (72.3%) male controls (P < .05). Posterior glottic stenosis (P < .01), length of intubation (P < .001), and obstructive sleep apnea (P < .05) were significant risk factors for tracheostomy.

CONCLUSION

Duration of intubation, ischemia, diabetes mellitus, and large ETT size (8 or greater) in males were significant risk factors for the development of PGS. Reducing the use of size 8 ETTs and earlier planned tracheostomy in high-risk patients may reduce the incidence of PGS and improve ICU safety.

Comparisons of recursive partitioning analysis and conventional methods for selection of uncuffed endotracheal tubes for pediatric patients

BACKGROUND

Numerous studies have investigated the best method of selecting the appropriate size of endotracheal tube (ETT) for children. However, none of the methods or formulae for selection of ETT size have shown better prediction over another, and they have required complex formulae calculation or even use of cumbersome equipment. Recursive partitioning analysis creates a decision tree that is more likely to enable clearer and easier visualization of decision charts compared to other data mining methods.

OBJECTIVES

The aim of the current study was to develop a clinically practical and intuitive chart for prediction of ETT size.

METHODS

Pediatric patients aged 2-9 years undergoing general anesthesia were intubated with uncuffed ETT. The tube size was considered optimal when a tracheal leak was detected at an inflation pressure between 10 and 25 cmH2 O. The observed ETT size was compared with the predicted ETT size calculated using Cole's formula, multivariate regression analysis, ultrasonographic measurements, and recursive partitioning tree structure analysis. Preference among the prediction methods was also investigated by asking physicians about their preference of methods.

RESULTS

Correct prediction rates were 33.3%, 50%, 61.9%, and 59.5%, and close prediction rates were 61.9%, 83.3%, 88.1%, and 93.7% for Cole's formulae, multivariate regression analysis, ultrasonographic measurements, and recursive partitioning tree model, respectively. Fourteen of 16 physicians prefer to use the easy-to-interpret tree model.

CONCLUSIONS

Analysis of the tree model by recursive partitioning structure analysis accomplished a high correct and close prediction rate for selection of an appropriate ETT size. The intuitive and easy-to-interpret tree model would be a quick and helpful tool for selection of an ETT tube for pediatric patients.

Subglottic injury: a clinically relevant animal model

OBJECTIVES/HYPOTHESIS

To develop a clinically aligned, reproducible model for subglottic injury.

STUDY DESIGN

Prospective randomized control pilot study.

METHODS

Juvenile (3-month-old) New Zealand White rabbits underwent intubation with a 3-cm length of an endotracheal tube that was chosen so that there would be no air leak below 20 cm of water. This tube was one or two sizes above the appropriate tube for the animal. It was held in situ with a suture placed at the trachea and secured over a button in the neck for a period of 1 week. Animals were sacrificed 1 week postextubation, and larynges were harvested. A range of histological techniques and gross morphology were utilized to examine the injury caused at the level of the subglottis. Unintubated animals constituted controlled specimens.

RESULTS

Intubated animals demonstrated considerable histopathology including evidence of ulceration, inflammation, granulation tissue, perichondritis, and chondritis when compared with control animals. Morphometric analysis demonstrated a significant increase in lamina propria thickness (P = .0013), mucosal thickness (P ≤ .0001), and in goblet cell areal density (P = .014). Analysis of mucin types found a significant decrease in acidic (P = .0001) mucin coinciding with a significant increase in mixed mucin types (P = .0013).

CONCLUSIONS

Our model provides a reliable and reproducible technique for acute/subacute injury to the subglottis secondary to intubation, which is consistent with previous histological findings of early changes associated with acquired subglottic stenosis (SGS). Future uses of this model could include the examination of current adjunctive therapies and their effects on limiting progression to SGS.

An animal model for endotracheal tube-related laryngeal injury using hypoxic ventilation

OBJECTIVES

To explore whether hypoxic ventilation could allow a practical animal model of laryngotracheal injury secondary to endotracheal intubation.

STUDY DESIGN

Randomized controlled animal study.

SETTING

Animal laboratory in a tertiary pediatric hospital.

SUBJECTS AND METHODS

Eight Sus scrofa piglets (15-18 kg) were anesthetized and intubated for 4 hours, with a 6-mm cuffed endotracheal tube. They were randomly assigned to either constant hypoxic ventilation (oxygen saturation under 70%) or nonhypoxic ventilation. Endotracheal tube cuff pressure was manually controlled and maintained at a constant level. After 4 hours, fluorescein dye was administered intravenously to highlight areas of hypoperfusion within the larynx. The animals were euthanized at the end of the procedure, and the larynx and trachea were harvested for gross and histological examination. The pathologist was blinded to the ventilation group. The severity of laryngeal injury was graded between 0 and 4 by a senior pathologist.

RESULTS

The experiment protocol was successfully completed in all animal subjects. The animals undergoing hypoxic ventilation showed a significantly higher median injury grade than the nonhypoxic animals (2 vs 1, respectively; P = .003). Damage was significantly worse in the hypoxic group at all anatomical sublevels.

CONCLUSIONS

Endotracheal tube-related laryngeal injury was demonstrated after only 4 hours of intubation using this animal model, and hypoxic ventilation increased the severity of injury. This study therefore provides an animal model that may be suitable for future investigation and prevention of intubation injury.

Piloting a novel porcine model for endolaryngeal injury following prolonged intubation

OBJECTIVES

(1) To develop a practical animal model of endolaryngeal damage secondary to prolonged endotracheal intubation. (2) To demonstrate the contribution of chronic hypoxia to laryngeal injury in the context of this model.

METHODS

Four Sus scrofa piglets were anaesthetized and intubated for 24h. Two animals were maintained in a state of constant hypoxia (pO(2)<60 mmHg) while two others were ventilated with 100% oxygen. Prior to sacrifice, fluorescein dye was infused intravenously to highlight areas of hypoperfusion. The larynx and trachea were then harvested for gross and histological examination.

RESULTS

All four specimens demonstrated areas of edema, erythema, and ulceration on gross examination. Areas of significant histological inflammation, ulceration, and necrosis involved tube-mucosa contact, in particular, the arytenoids, the interarytenoid area, and the subglottis.

CONCLUSIONS

This animal model represents a practical and novel means for the investigation and treatment of laryngeal injury secondary to prolonged endotracheal intubation. Significant injury to the endolarynx was evident after only 24h of intubation and the injury involved similar areas within the larynx as described in human studies. Although clinical experience suggests that chronic hypoxia is a risk factor for endolaryngeal injury, this model did not provide experimental evidence to support this observation, most likely due to the small study size.

Flexible fiber-optic laryngoscopy in the first hours after extubation for the evaluation of laryngeal lesions due to intubation in the pediatric intensive care unit

OBJECTIVE

To evaluate the feasibility and safety of using fiber-optic laryngoscopy in the first hours after extubation for the early diagnosis of laryngeal lesions in infants and children in the pediatric intensive care unit and describe the findings of such approach.

METHODS

Patients 0-4 years old who had undergone endotracheal intubation for longer than 24h were included in the study. Exclusion criteria were history of laryngeal symptoms, current intubation or tracheostomy, craniofacial malformations, or a poor prognosis according to the medical team responsible for the patient. Exams were performed in the pediatric intensive care unit in the first 8h after extubation; the patient was at the bedside and did not receive sedation. The fiber-optic laryngoscope was used to obtain images of the larynx. Minor complications were: saturation decrease not below 85% and rapid recovery, and minor nasal bleeding. Severe complications were: bradycardia and laryngospasm that required intervention. Images were evaluated by a blinded examiner, and findings were classified as mild and unspecific (edema and hyperemia), or specific, such as laryngomalacia and glottic granulation and subglottic ulceration and granulation. Results were expressed as means and standard deviations when the variable had a normal distribution, and as median and interquartile ranges for asymmetric data.

RESULTS

Forty-one patients, mean age 2.7 months (interquartile range 1.5-6.1), were included in the study. Fiber-optic laryngoscopy was performed between 40 min and 8h after extubation, and mean time was 4.9h (standard deviation=2.4h). Mean exam duration was 4.16 min (2.41-7.12 min; standard deviation=1 min). One patient (2.4%) had mild desaturation, a minor complication. No other complications were found. Thirty-five patients were available to 6-month follow-up and subglottic stenosis was found in 11.4%.

CONCLUSIONS

Fiber-optic laryngoscopy may be safely performed in the first hours after extubation, with few minor complications. It does not take long, but provides accurate information about the conditions of the supraglottic and glottic larynx. The subglottic region can also be visualized in most patients. This easily performed exam seems to be useful for the diagnosis of pediatric patients with acute laryngeal lesions due to intubation.

Incidence of severe acquired subglottic stenosis in newborns

OBJECTIVE

To determine the change in the statewide incidence of severe acquired subglottic stenosis (SGS) in newborns over the past decade.

METHODS

Multicenter, statewide retrospective study of all patients under the age of 12 months who were diagnosed with acquired SGS that required surgical intervention by anterior cricoid split (ACS) or tracheostomy between 1993 and 2003.

RESULTS

There were 34 patients (19 male; 15 female) with a median age of 4 months at the time of surgery. The primary surgical intervention performed was ACS 20, and tracheostomy 14 (incidence rate of 41%). Subsequently, 11 patients who failed decannulation following ACS underwent tracheostomy. Five patients died due to reasons unrelated to their SGS, and among the 29 survivors, 8 remain cannulated. The overall success rate for ACS was 35%. The mean annual statewide incidence of severe acquired SGS over the 10-year period was 4.95 per 100,000 live births.

CONCLUSION

The annual incidence of acquired SGS in newborns requiring open surgical intervention is in the order of 0.005%. The incidence of acquired SGS provides us with a benchmark figure that reflects the quality and standard of obstetric, neonatal and pediatric care across the state.

The Respiratory System

One of the most critical events of birth is the conversion of the fluid-filled lung, unimportant to fetal intrauterine existence, into a hollow organ distended with air and capable of gaseous exchange sufficient to support life. Indeed, it has been argued that the major determinant of perinatal survival is respiratory function (Wigglesworth and Desai 1982).

The failure to make this conversion adequately may lead, directly or indirectly, to infant death, and the pathologist often needs to assess the contribution made by respiratory inadequacy to the sequence of events leading to death. In the preterm infant, problems are mainly related to pulmonary immaturity and associated therapy. In the mature infant, birth asphyxia primarily results in cerebral damage but can engender significant respiratory complications when associated with aspiration of meconium. Even in stillbirths, where primary pulmonary pathology is rarely a cause of death, lung pathology may provide clues to antecedent events. Poor lung growth and maturation may point to the presence of pathology elsewhere. Consequently, adequate pathological investigation of the fetal or infant respiratory system is critical in any perinatal autopsy.

Shortcomings of cuffed paediatric tracheal tubes

BACKGROUND

The goal of this investigation was to evaluate adequacy of the design of readily available paediatric cuffed tracheal tubes (CPTT).

METHODS

In 15 series of cuffed (11) and uncuffed (four) paediatric tracheal tubes (ID: 2.5-7.0 mm) from four different manufacturers the following dimensions were measured: outer diameter of the tube, position and largest diameter of the tube cuff inflated at 20 cm H(2)O and position of depth markings and compared with age-related dimensions.

RESULTS

Outer diameters for tubes with similar IDs varied markedly between manufacturers and between cuffed and uncuffed tracheal tubes from the same manufacturer. Cuff diameters at 20 cm H(2)O cuff pressure and cross-sectional cuff area at 20 cm H(2)O cuff pressure did not always cover maximal internal age-related tracheal diameters and cross-sectional areas. Placing the tube tip in the mid-trachea, the cuffs of cuffed tubes with ID 3.0, 4.0, or 5.0 mm would become positioned within the larynx. If the cuffs were placed 1 cm below the cricoid level, many of the tube tips would be dangerously deep within the trachea. Only five of the 11 cuffed tubes had a depth marking. In many of these tubes the distances from depth marking to tube tip were greater than the age-related minimal tracheal length.

CONCLUSION

Most cuffed paediatric tracheal tubes are poorly designed, in particular the smaller sizes. A better design of cuffed tubes with a short high-volume, low-pressure cuff, cuff-free subglottic space and adequately placed depth markings are urgently needed.

Laryngeal damage due to an unexpectedly large and inappropriately designed cuffed pediatric tracheal tube in a 13-month-old child

PURPOSE

To present a case of laryngeal damage in an infant caused by a too large and inappropriately designed cuffed tracheal tube.

CLINICAL FEATURES

A 13-month-old child undergoing cardiac surgery was intubated with an uncuffed endotracheal tube with an internal diameter (ID) of 4.0 mm. Because of an important air leak around the tracheal tube during mechanical ventilation, a cuffed endotracheal tube ID 4.0 mm was inserted. The air leak with the tube cuff not inflated was acceptable at 25 cm H2O airway pressure. After extubation on the third postoperative day, the patient showed increasing stridor and respiratory deterioration. Fibreoptic laryngoscopy of the spontaneously breathing patient showed a large intra-laryngeal web. After surgical removal of the web, the child rapidly recovered and was discharged from the hospital on the 12th postoperative day. Inspection of the 4.0 mm (ID) cuffed tracheal tube revealed a cuff positioned inappropriately high and an increase of 0.7 mm in outer tube diameter compared to the 4.0 mm (ID) uncuffed tracheal tube from the same manufacturer. The tube cuff is likely to be situated within the larynx when placed in accordance to insertion depth formulas or radiological criteria, as used for uncuffed tracheal tubes in children.

CONCLUSION

The larger than expected tracheal tube with its intra-laryngeal cuff position in a 13-month-old child likely caused mucosal damage and an inflammatory reaction within the larynx resulting in granulation tissue formation and fibrous healing around the tracheal tube.

Subglottic stenosis after endolaryngeal intubation in infants and children: result of wound healing processes

OBJECTIVE

To study the histopathology of subglottic stenosis in children of different ages after treatment during different periods of time, with or without laser application. Partial resection of the anterior cricoid with adhering stenotic subglottic area in the live young patient provides unique material for studying wound healing and scarring processes.

METHODS

25 specimens obtained from partial cricotracheal resection (PCTR) in children, were histologically processed and stained with Haematoxylin and Eosin, Resorcin and Fuchsin (for elastic fibers), and immunohistochemical staining (for the presence of macrophages).

RESULTS

All specimens were found to have severe and sclerotic scarring with squamous metaplasia of the epithelium, loss of glands and elastic mantle fibers (tunica elastica), and dilation of the remaining glands with formation of cysts. Also, the cricoid cartilage was affected on the internal and external side, with irreversible loss of perichondrium on the inside and resorption by macrophages of cartilage on both sides. Detrimental effects of laser therapy were demonstrated in four cases. The normal intercellular matrix was completely destroyed and the number of chondrocytes in the cartilage structure diminished.

CONCLUSION

Wound healing after laryngeal injury is a process of intense restoration and reorganization of the various tissues involved. This process, however, does not guarantee complete repair. In the severe cases irreversible scarring has replaced normal tissues. There seems to be no direct relationship between the length of the post-lesional period, the age of the patient and the severity of the stenosis. When subglottic stenosis has developed and the majority of the tissues is replaced by dense fibrous tissue, PCTR is strongly indicated to achieve renewed patency of the airway.

Acquired subglottic stenosis caused by methicillin resistant Staphylococcus aureus that produce epidermal cell differentiation inhibitor

Local infection of the trachea in intubated neonates is one of the main risk factors for development of acquired subglottic stenosis, although its role in the pathogenesis is unclear. Methicillin resistant Staphylococcus aureus (MRSA) is often the cause of critical illness in neonatal patients. Two cases are reported of acquired subglottic stenosis following bacterial infection of the trachea, suggesting an association with the staphylococcal exotoxin, epidermal cell differentiation inhibitor (EDIN). EDIN-producing MRSA were isolated from purulent tracheal secretions from both infants. Acquired subglottic stenosis in both cases was probably caused by delayed wound healing as the result of EDIN inhibition of epithelial cell migration.

Pseudopolyp of the right laryngeal ventricle following atraumatic intubation: a diagnostic dilemma

The traumatic effects of tracheal intubation are well recognized. Whilst these usually follow prolonged intubation, acute lesions have been described, usually following a traumatic intubation technique. We present a case of acute, localized swelling of the right laryngeal ventricle which followed an entirely atraumatic intubation by an experienced paediatric anaesthetist. The lesion was not present at the time of intubation, but developed subsequently during the surgical procedure. Although previously observed at our institution, such lesions have not been described in the literature. The potential for a diagnostic pitfall, by mistaking the lesion for a laryngeal cyst or nodule, is discussed.

Role of infection in the development of acquired subglottic stenosis in neonates with prolonged intubation

OBJECTIVE

To examine whether clinically diagnosed infection correlates with subsequent development of subglottic stenosis in intubated neonates.

METHODS

Sixty-two neonatal infants intubated for more than 14 days were examined. Several risk factors for subglottic stenosis, including infection, duration of intubation, frequency of intubation, the size of the endotracheal tube etc., were evaluated by multiple logistic regression analysis.

RESULTS

Infection that occurred within 14 days of intubation showed a positive correlation with subsequent subglottic stenosis. The duration of intubation, frequency of intubation and the size of the endotracheal tube did not affect the development of subglottic stenosis. The majority of infections were considered to be respiratory tract infections, including pneumonia.

CONCLUSIONS

Infection occurring within 14 days of intubation is considered to be a risk factor for acquired subglottic stenosis in neonates intubated for more than 14 days. Prevention of infection within 14 days of intubation may reduce the incidence of subglottic stenosis in neonates.

Subglottic stenosis associated with transesophageal echocardiography

Transesophageal echocardiography (TEE) is used extensively to assess cardiac function and anatomical relationships in both adults and children. Although considered a noninvasive procedure, TEE in infants and small children may result in airway complications. A patient who developed subglottic stenosis after the use of TEE during a cardiac procedure is reported.

Changing trends in neonatal subglottic stenosis

OBJECTIVES

To determine whether there are any changes in the incidence and management of neonatal subglottic stenosis (SGS).

METHODS

A retrospective chart review of 416 infants who were admitted to the neonatal intensive care unit of the Children's National Medical Center between July 1, 1995, and June 30, 1996, was carried out. The incidence of airway obstruction requiring anterior cricoid split or placement of tracheotomy tube was determined and compared with the incidence studied 10 years ago at the same institution.

RESULTS

One of 416 neonates required surgical intervention for airway obstruction caused by SGS, for an overall neonatal SGS incidence of 0.24%. When only the neonates who were intubated for 48 hours or longer were considered, the incidence of SGS was 0.49% (1/204). In neonates who were intubated for 48 hours or longer and survived, the incidence of SGS was 0.63% (1/160). This is in comparison with the incidences of 0.65% (3/462), 1.5% (3/195), and 1.9% (3/159), respectively, seen in a study done at the Children's National Medical Center 10 years ago. Five infants in this current study required placement of a tracheotomy tube for reasons other than SGS. Two infants needed tracheotomy tube placement for micrognathia, and 3 others for central hypotonia, an omphalocele that required multiple surgical procedures, and choanal atresia with a serious heart anomaly, which was a manifestation of CHARGE association. None of these 5 infants had evidence of SGS at rigid endoscopy preceding the tracheotomy tube placement.

CONCLUSION

The incidence and management of neonatal SGS remain unchanged during this study period when compared with those of 10 years ago.

Expression of vascular endothelial growth factor in exuberant tracheal granulation tissue in children

Prolonged tracheotomy and endotracheal intubation often induce symptoms of airway obstruction and delay decannulation and extubation. Bronchoscopic examination of patients undergoing these treatments usually shows the presence of exuberant (pseudopapillary or nodular) granulation tissue occupying the airway lumen. An immunohistochemical analysis was undertaken of vascular endothelial growth factor (VEGF) expression in exuberant tracheal granulation tissue (n=17) obtained from children treated with prolonged tracheotomy or endotracheal intubation. Increased levels of VEGF protein and mRNA were expressed mainly by tracheal epithelial cells that migrated to cover the granulation tissue and partly by pericapillary macrophages in this tissue, whereas normal tracheal epithelium did not express VEGF. The VEGF expression level correlated significantly with the severity of the exuberant granulation tissue response (p=0.0018). As VEGF induces angiogenesis and vascular permeability, characteristics of granulation tissue, and plays a pivotal role in granulation tissue development, enhanced VEGF expression may be involved in the development of exuberant tracheal granulation tissue.

Acquired subglottic stenosis--depth and not extent of the insult is key

In contrast to skin, mucosal wound healing has not been extensively studied. Subglottic stenosis (SGS) is an excellent model for such investigation. The main objective of this pilot study was to develop a chronic model of SGS in a small animal (i.e. rabbit). In so doing, a serendipitous observation was made that the development of SGS is directly related to depth of the injury and is independent of circumferential extent. Animals with deep injury (i.e. deep to the lamina propria, reaching the perichondrium), independent of age and circumferential extent, experienced respiratory obstruction resulting from edema and granulation tissue formation and died or had to be sacrificed in the acute period. This was in contrast to no risk of mortality in the more superficially injured group. Histology was used to characterize this model of SGS. In the mucosal epithelium, or mucosa, changes of inflammation, squamous metaplasia, basal cell hyperplasia, necrosis and ulceration were only seen acutely and total regeneration of the epithelium was achieved by the end of the study period. In contrast, changes within the lamina propria, including chronic inflammatory cellular infiltrates and fibroplasia, were lasting and resulted in fibrotic repair, not regeneration. These findings are quite similar to the healing events in skin and suggest that SGS is the mucosal equivalent of a 'keloid' or, perhaps more appropriately, a 'hypertrophic scar.' Likewise, cartilage degeneration and deformation were persistent markers of the chronic phase of healing. Like the lamina propria, the response to injury was reparative. Therefore, injury to the connective tissue is a critical component of development of SGS.

Posterior glottic stenosis: a canine model

Posterior glottic stenosis is a disabling disease in which the vocal folds are fixed near the midline. This allows adequate vocal fold adduction for voicing, but does not permit useful abduction for ventilation. The most common cause is prolonged endotracheal intubation for mechanical ventilation, and the incidence is estimated at 4% for intubations between 5 and 10 days. Currently, our understanding and treatment modalities are based on retrospective reviews of small, nonrandomized clinical experiences. The purpose of this project was to develop an animal model that would improve our understanding of histologic changes and allow future prospective randomized trials for therapeutic intervention. Twelve dogs, 15 to 25 kg, were randomly divided into three groups. Animals in group I had a superficial injury produced in the tissue over the right cricoarytenoid joint; animals in group 2 had a deep soft tissue injury produced; and animals in group 3 underwent joint opening. The animals were allowed to recover for 2 months. Morphometric analysis of the harvested larynges demonstrated clinically significant limitation in motion in the animals with deep soft tissue injury and in animals with joint disruption. Histologic analysis revealed various degrees of injury, from loss of subepithelial soft tissue to cartilaginous resorption and fusion of the arytenoid to the cricoid. These findings were directly related to the depth of the initial injury. It is possible to produce posterior glottic stenosis in the canine species. This will serve as a reliable animal model for future study.

Fragmented, distorted cricoid cartilage: an acquired abnormality

This paper reports the identification of the fragmented, distorted cricoid cartilage. The laryngeal findings in four patients with this acquired abnormality are presented. The postmortem whole organ serial section of their larynges is described and illustrated with horizontal sections from the Laryngeal Development Laboratory in Chicago. The histopathologic sequence, pathogenesis, and clinical relevance are elucidated.

Histopathologic fundamentals of acquired laryngeal stenosis

Acquired laryngeal stenosis is the most serious long-term complication of endotracheal intubation in children. Employing the whole-organ serial section technique, the sequence of histopathologic changes leading to stenosis was studied. Ulceration occurs when an endotracheal tube causes mechanical abrasion and/or induces pressure necrosis on the laryngeal mucosa. Secondary healing of ulceration produces granulation tissue and subsequent fibrous scar tissue. Most exuberant granulation tissue resolves without sequelae, but some becomes firm, almost avascular fibrous scar tissue. The accumulation of submucosal fibrous tissue may decrease the size of the glottic or subglottic lumen. Contraction of scar tissue causes a distortion of glottic and subglottic laryngeal complex, leaving a reduced and irregularly shaped glottic and subglottic lumen. Submucosal mucous gland hyperplasia directly reduces the inner diameter of the airway. Finally, compromise of the laryngeal lumen may occur when the duct of a mucous gland is obstructed by scarring resulting from intubation: mucus accumulates in the dilated duct, producing a ductal cyst.

Formal reintubation for incipient neonatal subglottic stenosis

In a small prospective series of 10 children who presented with incipient subglottic stenosis following neonatal intubation a protocol of formal reintubation for two weeks, with sedation, enabled six of the children to avoid tracheostomy or other forms of surgery and in the remaining four it is unlikely that the trial of reintubation made the degree of laryngeal and subglottic damage worse.

Respiratory failure in congenital heart disease

Infants and children with congenital heart disease (CHD) present unique difficulties when they develop respiratory failure, either as a consequence of their heart disease, in relation to cardiac surgery, or from infectious causes. Extensive cardiac surgical repairs are now being performed on younger infants with complex anatomy and physiology. The evolution of cardiac surgical technique and perioperative management has revealed the importance of subtle interactions between respiratory physiology and hemodynamic performance.

Subglottic ulceration and healing following endotracheal intubation in the neonate: a morphometric study

In neonates, acquired subglottic stenosis is the most serious long-term complication of endotracheal intubation and is due primarily to posttraumatic fibrosis of the infant larynx. We have examined 78 larynges, 75 of which were intubated, from infants ranging in gestation from 22 to 40 weeks, and who survived from a few hours to up to 300 days. Each larynx was morphometrically assessed for the extent of acute injury, indicated by the percentage of epithelial loss, and healing, indicated by the percentage of a subglottic ulcer covered by metaplastic squamous epithelium. Results show that acute injury is almost invariable, and up to 100% of the subglottic epithelium may be lost within a few hours of intubation, but that progression of injury is relatively short-lived. Ulcer healing starts after a few days, rapidly progresses from day 10, and in the majority of cases is complete after 30 days. This study suggests that long-standing acute injury in the subglottis is the exception rather than the rule, even with the endotracheal tube remaining in place.

Intrinsic laryngeal muscle regeneration following endotracheal intubation

The larynges of 33 premature and term neonates who were intubated for the management of respiratory difficulties were studied. In addition to the changes commonly associated with endotracheal intubation (epithelial erosion, ulceration, squamous metaplasia, edema, inflammation, and perichondritis), the intrinsic laryngeal muscles were damaged in 26 of the 33 cases and, in 4 cases, oriented striated skeletal muscle regeneration was found. The active synthetic nature of the myotube formations in the latter cases was confirmed by the demonstration of concentrated vimentin intermediate-filament immunoreactivity. In view of the frequency of neonatal intubation, the probability of muscle damage, and the generally infrequent critical sequelae of this procedure, regeneration of the intrinsic muscles may help to explain the excellent functional recovery of the neonatal larynx. This phenomenon also occurs in the postintubated adult larynx and is therefore not limited to the neonatal period. In addition, these findings support the fact that skeletal muscle regeneration occurs in nonmyopathic human skeletal muscles following injury, as has been shown in experimental animal models.

Endoscopic examination of the neonatal larynx at extubation: a prospective study of variables associated with laryngeal damage

Despite postmortem and clinical studies, the etiological factors that determine why only a proportion of intubated neonates develop subglottic stenosis remain unclear. This prospective study was initiated to identify factors that were associated with laryngeal abnormalities secondary to intubation. Thirty neonates were examined at extubation by two independent observers blinded to the neonate's ventilatory history. Thirty-six possible prognostic indicators were recorded for each neonate. After screening by univariate (chi 2) analysis, 10 indicators were selected for further analysis. Of these 10 selected only two indicators showed an association with the laryngeal appearance. Active neonates had significantly more abnormalities in the supraglottis (P = 0.004) than those who were quiescent. Younger neonates had more abnormalities in the glottis though the significance level was marginal (P = 0.056). Other prognostic indicators, including birthweight, gestational age, duration of intubation and frequency of intubation, were not significantly related to laryngeal appearance. This study supports the hypothesis that the etiology of laryngotracheal stenosis is multifactorial, and has identified two possible etiological factors: age and neonatal activity. Neonatal activity has not been identified previously as an etiological factor. The contribution of individual factors may vary from one neonatal unit to another, as a result of variation in intubation, ventilation and extubation policy. This could explain the inconsistency in etiological factors identified by previous studies. It is therefore not yet possible to recommend a standard technique for the ventilation of premature neonates that would further reduce the incidence of laryngotracheal stenosis.

Long term pathological sequelae of neonatal endotracheal intubation

In neonates, acquired subglottic stenosis (SGS) is the most serious long term complication of endotracheal intubation. In this case report, we describe the pathological changes in the larynx of a child who died two years after successful treatment, involving corrective surgery, for neonatally acquired SGS. Stenosis, due to dense fibrous connective tissue, was still present at death. However, there was evidence that there had been growth of the laryngeal cartilages. Disruption of the laryngeal cartilages was present anteriorly due to the antecedent surgery but major cricoid cartilage injury secondary to intubation was not seen. The crico-arytenoid joints demonstrated ankylosis and to this was attributed the abnormal quality of voice noted in the child at follow-up. The pathological changes are considered in relation to the pathology of endotracheal intubation and pathogenesis of acquired subglottic stenosis.

The histopathology of the upper airway in the neonate following mechanical ventilation

Laryngotracheobronchial lesions were carefully documented in 26 neonatal autopsies and were classified into two main types. Type I lesions were focal desquamative or ulcerative, asynchronous, and variable in severity involving areas exposed to contact with endotracheal tube or suction catheter. These lesions are most likely due to trauma of artificial ventilation. Type II lesions were diffuse, necrotizing, more synchronous and uniform in severity involving tissues distal to the endotracheal tube and extending to second or third generation bronchi. The early or mild type II lesions consisted of coagulative necrosis of epithelial cells and mucosal oedema. The late or severe type II lesions showed features similar to those of necrotizing tracheobronchitis described by Metley et al. All the cases with type II lesions had been ventilated with 100 per cent oxygen continuously for at least 3 h during life. The use of pure oxygen may be an important factor leading to necrotizing tracheobronchitis.

Differential effects of endolaryngeal trauma upon the growth of the subglottis

In young rabbits (4-week-old) the growth of the subglottis was studied after an endolaryngeal soft tissue trauma. The injury induced the formation of a subglottic stenosis. In contrast to earlier observations on endolaryngeal trauma extending into the cricoid cartilage, the cricoid developed normally to the adult size and shape at 24 weeks. Similar to the earlier findings, the subepithelial layer showed considerable thickening as the result of formation of scar tissue, ectopic cartilage and fatty tissue with interruption of the elastic tunica (= conus elasticus). It was concluded that after endolaryngeal trauma in rabbits two types of subglottic stenosis can develop, determined by the depth of the injury.

Laryngotracheal stenosis

Laryngotracheal stenosis is a nonspecific term implying the presence of airway compromise involving the larynx, trachea, or both. This is usually the result of scar formation with the associated morbidity dependent on the location, extent, and thickness of the tissue. Because of this variability, a single treatment protocol cannot be recommended. The procedure used to correct the stenosis must be tailored to the case in question. This paper reviews the treatment of laryngotracheal stenosis, specifically focusing on the variables in the preoperative assessment that must be considered in selecting an appropriate treatment plan.

Management of subglottic stenosis: experience from two centres

The incidence of subglottic stenosis in children has risen rapidly in the last 20 years as more advanced techniques enable younger preterm neonates to survive. There has been a similar rise in the number of different surgical methods devised to alleviate the stenosis; success has been claimed for each technique. The importance of normal laryngeal growth throughout an often protracted period of surgical intervention may, however, have been underestimated. This study analyses the data from two units in London over the last five years and assesses retrospectively the benefit of different surgical approaches.

Subglottic stenosis: a clinicopathological study

Subglottic stenosis is the most common serious long-term complication of endotracheal intubation in neonates and its pathogenesis is poorly understood. We describe the experience of one unit with 15 cases of subglottic stenosis requiring operative intervention seen over a 3-year period and review the pathology and pathogenesis of the condition. In 1 instance operative intervention was successful in treatment and avoided the need for long-term tracheostomy. A possible aetiological factor in at least 2 of the cases of subglottic stenosis was insertion of the wide shoulder of the endotracheal tube through the vocal cords. It is suggested that subglottic stenosis is due to reparative fibrosis following particularly severe acute intubation injury. Another factor may be delayed healing of the subglottic mucosa possibly exacerbated by full thickness cricoid cartilage necrosis. Although severe subglottic injury may occur at any time that the endotracheal tube is in situ, the most critical period is the first week of intubation.