Ultrasound and a new videobronchoscopic technique to measure the subglottic diameter

OBJECTIVE: The aim of this study was to evaluate ultrasound (US) and a new videobronchoscopic (VB) technique in the measurement of the subglottic lumen diameter. DESIGN: This blind prospective animal study of 62 recently sacrificed rabbits was conducted at the Montreal Children's Hospital. METHODS: Three different diameter measurements of the subglottis were assessed using B-mode US on each intact animal. The same diameter measurements, as well as a fourth, were estimated with a VB measuring technique. Finally, the subglottic area was surgically exposed allowing for direct caliper measurements of all four corresponding diameters. All three US measurements on each of the 62 rabbits and all four VB measurements on each of the 60 rabbits were compared with the gold standard corresponding caliper measurements. RESULTS: Statistical analysis revealed strikingly convergent values in subglottic lumen diameter measurements using US and calipers. The mean difference between these methods for all 186 observations was 0.11 mm. With 95% confidence, the maximum discordance was less than 0.30 mm on the smallest evaluated lumen. Convergent values were also demonstrated in subglottic lumen diameter measurements using VB and calipers. The mean difference between these methods for all 240 observations was 0.16 mm. With 95% confidence, the maximum discordance was less than 0.37 mm on the smallest evaluated lumen. Pearson's correlation coefficient supported a strong and positive relationship between US and caliper measurements as well as VB and caliper measurements. Simple linear regression model indicated that the subglottic lumen diameter could be predicted by both US and our VB technique. CONCLUSION: This work represents the first attempt to validate B-mode US and a VB technique as measuring tools for the subglottic lumen diameter. Our results have clearly shown that both methods are precise measuring modalities for this purpose. With further studies, these two objective methods of measuring the subglottic diameter could be adopted universally. The precise knowledge of this diameter could help physicians recognize and describe the severity of a narrowed lumen. Reporting results in such a standardized fashion, by either US or VB, could facilitate communication among clinicians and institutions.     

Down syndrome: analysis of airway size and a guide for appropriate intubation

OBJECTIVES/HYPOTHESIS: The purpose of this study is to prospectively evaluate the airway size of children with Down syndrome (DS). Previous studies have observed an increase in postintubation stridor in children with DS. Anesthetic literature suggests using a smaller endotracheal tube in children with DS, but more specific recommendations are not offered. With this study, recommendations are presented for the appropriate endotracheal tube size to use in children with DS undergoing intubation. STUDY DESIGN: A prospective, nonrandomized study was performed on a cohort of 42 children with DS and 32 control subjects. Sizing of the airway was assessed through measurement of an air leak around the endotracheal tube at intubation. The size of the airway was also evaluated through measurements of the tracheal diameter at the "tracheotomy point" on magnetic resonance imagine (MRI) studies of the head and neck which were performed on a group of children with DS. These were compared with normative values of the tracheal diameter in children. METHODS: The proper size of endotracheal tube in a population of children with DS and in a group of normal controls was determined. The "proper size" of an endotracheal tube was defined as that size of tube which allowed an audible air leak around the tube between 10 and 30 cm of H2O pressure. Anesthetic technique was controlled and identical for all study subjects. Participants had no previous history of airway compromise, stridor, or previous intubation. Weight and age were recorded and evaluated for their influence on the results. A retrospective evaluation was made of MRI studies of the neck that were performed on children with DS. Using measurement techniques described by Reed et al., the tracheal diameters at the "tracheostomy point" were compared with normative values for children. Measurements were both obtained by the author and confirmed by a pediatric radiologist. RESULTS: Using this prescribed method to determine the proper size of endotracheal tube, the control group used endotracheal tubes that were predicted from established anesthesia charts and formulas. However, children with DS required endotracheal tubes at least two sizes smaller. Age was found to be a more reliable factor in predicting the endotracheal tube size. A table of endotracheal tube sizes for intubation in children with DS is presented. Evaluation of the tracheal diameter at the tracheotomy point revealed that children with DS have a smaller trachea when compared with control children. It is not only the subglottis that is smaller; the tracheal diameter as well must be assumed to be of a smaller diameter in children with DS. CONCLUSIONS: Children with DS have smaller airways than other children. This is because of an overall decrease in the diameter of the tracheal lumens. Initial intubation of a child with DS should be performed with an endotracheal tube at least two sizes smaller than would be used in a child of the same age without DS, to avert potential trauma to the airway.     

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.     

Role of balloon dilation in the management of adult idiopathic subglottic stenosis

OBJECTIVES: We evaluated the efficacy of balloon dilation for adjunctive and symptomatic management of isolated idiopathic subglottic stenosis in adults. METHODS: Adults with airway obstruction symptoms classified as idiopathic subglottic stenosis based on history and findings of a single discrete stenotic area on microlaryngoscopy and bronchoscopy were included in this series. Patients who met these criteria underwent dilation with a 10- to 14-mm balloon in a single procedure or in 2 consecutive dilations within 7 days. The patients were followed for up to 30 months after dilation. RESULTS: Six patients met the criteria. One of the 6 had prior laser treatments and a cricotracheal resection. One patient had a previous scar band lysis procedure. The remaining 4 patients had no prior procedures. The airway sizes prior to dilation ranged from a 2.5 endotracheal tube to a 5.0 endotracheal tube. In all cases the airway was dilated to 2.0 to 3.5 endotracheal tube sizes larger than the initial size. To date, 4 patients have been followed for 10 to 30 months without symptoms of recurrent airway stenosis. One patient was symptom-free for 22 months, then presented with progressive airway difficulty following an upper respiratory tract infection, and has undergone a repeat dilation. No patients had adverse effects or complications from the procedure. CONCLUSIONS: Balloon dilation of idiopathic subglottic stenosis in adults is a relatively safe and effective method to manage this disease entity for cases of isolated and discrete lesions. Patients who underwent a single procedure have remained symptom-free for up to 30 months after balloon dilation.     

Subglottic stenosis and Down syndrome

The possibility of subglottic stenosis in children with Down syndrome is well recognized. Nevertheless, this anomaly and its effect on laryngeal and respiratory function are frequently overlooked. When subglottic stenosis is present in a child with Down syndrome, the standard intubation technique may require modification. In these children, an endotracheal tube of a size appropriate to the patient's age may be too tight in the subglottic area. By aggravating a previously asymptomatic subglottic stenosis, long-term endotracheal intubation in this type of patient may be more likely to lead to a clinically significant subglottic stenosis. In our experience, subglottic stenosis in children with Down syndrome is more difficult to repair and is associated with a lower success rate of decannulation. Additionally, it is important in the management of these children not to create an even more severe subglottic stenosis.     

Canine model of subglottic stenosis secondary to prolonged endotracheal intubation

Acquired subglottic stenosis is usually a consequence of prolonged endotracheal intubation. The present study describes a canine model of subglottic stenosis which is congruent with the known and suspected pathogenesis of the disease in man. Eighteen young pups (Canis familiaris) were used. A modified cuffed endotracheal tube was placed within the subglottis and secured by inflating the cuff. The capillary tube supplying the cuff was sealed and cut so as to lie below the epiglottis. Three animals died of tracheal rupture or collapse prior to or on the thirteenth day following intubation. In the remaining animals, the cuffed tube was removed and the subglottis was examined. All exhibited ulcerations and exuberant polyploid granulations at the level of the subglottis and trachea. A 4 mm uncuffed endotracheal tube was introduced and secured within the subglottis and trachea of a number of the pups to provide an airway. After a 3-week period, the tube was removed and the dogs were sacrificed. Examination of the specimens showed various degrees of “hard” cicatricial stenosis of the subglottis and trachea. Histologic studies showed destruction of the cartilage with replacement by scar tissue and partial epithelialization. This model may be useful to investigations of the prevention and treatment of the disease.     

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.     

Paediatric subglottic stenosis

Most reports on paediatric subglottic stenosis have arisen from tertiary referral centres. At the Sheffield Children's Hospital, referrals come from the surrounding region such that almost all paediatric airway problems from this area are seen. This allows an opportunity to look at the overall picture of this condition. A retrospective study was performed to identify all children with subglottic stenosis requiring a tracheostomy since 1979 and to examine the management and eventual outcome in relation to the severity of their stenosis. Forty-two children were identified. There have been four mortalities, two of which have been tube related. Twenty-two laryngotracheoplasty procedures have been performed in 17 patients. Successful decannulation has been achieved in 82%. In the majority of children with more minor stenoses conservative management has lead to successful decannulation. However, with increasingly severe stenosis the necessity of undergoing a laryngotracheoplasty procedure to provide an adequate airway becomes more likely.     

Independent effects of denervating the cricothyroid muscle and stenting on the anterior cricoid split: canine model

The anterior cricoid split (ACS) has gained in popularity since its introduction in 1980, for the treatment of the difficult to extubate child. The procedure allows a successful extubation and avoids a tracheotomy about 75% of the time. How the ACS allows extubation remains poorly understood. Animal research has shown that in the canine model the ACS results in a gap in the cricoid cartilage with a subjective increase in the subglottic space (Senders and Eisele, 1978). This gap in the cricoid cartilage develops whether or not an endotracheal tube stent is used. This experiment was designed to quantitatively evaluate the effect of the ACS on the subglottic space with or without the use of the stent, and to evaluate the effect of the cricothyroid muscle on the ACS procedure. The results show that the ACS does result in an increase in the subcricoid space, and that the use of an endotracheal tube stent does result in a larger increase. The cricothyroid muscle has a strong immediate effect on the gap in the cricoid cartilage, which is eliminated by sectioning the external laryngeal nerve. The long-term effects of sectioning the external laryngeal nerve on the gap in the cricoid cartilage were not conclusive.     

Dangerous Doughty--a quantitative study of disproportion between the size of endotracheal tubes and splits in tonsillectomy gag blades

The Doughty split tongue blade is used routinely with the Boyle Davis mouth gag during tonsillectomy. If the width of the slot in the blade is excessive, then the endotracheal tube may herniate through the slot in the blade and become fixed and inseparable from the blade. We report two cases of paediatric tonsillectomy where this potentially serious complication occurred. The slot widths of disposable and reusable Doughty blades were measured and specifications were obtained from several manufacturers. All disposable paediatric Doughty blades and some of the reusable blades were found to have excessively and potentially dangerously wide slots. Compression testing of endotracheal tubes by the manufacturer demonstrated marked increases in deformability on warming to body temperature. Ensuring that the slot width of the Doughty blade is not excessive for the endotracheal tube used is essential and we give recommendations.     

Neonatal subglottic stenosis--incidence and trends

OBJECTIVE/HYPOTHESIS: Neonatal subglottic stenosis is a known entity arising from endotracheal tube intubation. In the 1970s and 1980s, estimates of the incidence of subglottic stenosis were in the range of 0.9% to 8.3% of intubated neonates. Because of improved techniques of handling neonates who require ventilatory support, we thought the actual incidence of neonatal subglottic stenosis in the late 1990s was much lower. STUDY DESIGN: We retrospectively reviewed all neonatal intensive-care unit (NICU) admissions from 1997 at our institution, which serves as a level 3 NICU. We also performed a MEDLINE search of the reported incidence of neonatal subglottic stenosis between 1960 and 1999. METHODS: Analysis was performed to identify all children who developed subglottic stenosis at our institution. Data were also collected and analyzed with regard to average gestational age, average birth weight, average duration of intubation, and the number of children requiring tracheostomy. The reports identified in the literature were reviewed as to the incidence of subglottic stenosis. RESULTS: A total of 544 neonates were admitted to the unit. Of these, 281 were intubated for an average of 11 days. No patients developed subglottic stenosis. Three patients required tracheostomies for other reasons. All studies published after 1983 reported an incidence of neonatal subglottic stenosis as less than 4.0%, and all studies published after 1990 reported an incidence of neonatal subglottic stenosis as less than 0.63%. CONCLUSIONS: Although our report applies to only a single institution in a single year, after reviewing the literature we think a downward trend exists in the incidence of neonatal subglottic stenosis in the late 1990s. The current incidence of neonatal subglottic stenosis is likely between 0.0% and 2.0%.     

The Hunsaker Mon-Jet ventilation tube for microlaryngeal surgery: optimal laryngeal exposure

Methods of delivering and monitoring anesthesia during microlaryngeal surgery are constantly evolving. In 1994, Hunsaker and colleagues introduced a laser-safe subglottic Mon-Jet ventilation tube, which has the ability to periodically measure end-tidal carbon dioxide levels. We conducted a retrospective review of 84 consecutive patients who had undergone microlaryngeal procedures with the aid of the Hunsaker Mon-Jet tube. Study parameters included the length of anesthetic induction and recovery times, the duration of surgery, the degree of surgical access to the larynx, and the incidence of anesthetic and surgical complications. We found that anesthetic induction and recovery times with the use of the Mon-Jet tube were comparable to those seen with standard endotracheal intubation. We also observed an apparent reduction in surgical time and a consistent subjective improvement in surgical visualization and access. The complication rate was acceptable, airway control was adequate, and use of the Mon-Jet tube was safe in all patients. We conclude that the Mon-Jet tube is a safe and effective subglottic jet ventilation system and that it has distinct advantages over other methods for both the surgeon and the anesthesiologist.     

Airway complications in patients with closed-head injuries

The neurologic deficits in the closed-head injury population present special problems when managing the airway. Many of these closed-head injury patients require long-term intubation with endotracheal tube or tracheostomy to treat their central respiratory problems and control oral and pulmonary secretions. Four hundred sixty-seven closed-head injury patients were seen over a five-year period. Seventy-two of these patients required long-term endotracheal intubation, tracheostomy, or both. A prospective study by direct endoscopic examination prior to decannulation showed 23 of these 72 patients (32%) had important laryngeal or tracheal findings. The principal abnormalities observed were vocal cord paralysis, tracheal stenosis, subglottic stenosis, glottic stenosis, and tracheomalacia. This study suggests also that severely mentally impaired patients (cognitive function II and III) should retain their tracheostomy because of the high morbidity and mortality among these patients (31%) when they are decannulated. This mortality was directly related to poor pulmonary toilet, with pneumonia and sepsis being the major causes of death. This study did not show that the use of steroids or ventilators in the initial management adversely effected airway complications.     

Laryngeal mask versus endotracheal tube in a ferret model

Acquired subglottic stenosis in infants is a difficult iatrogenic problem with notable morbidity, primarily caused by prolonged endotracheal intubation. The laryngeal mask airway (LMA) is a recently developed, alternative airway device that does not contact the subglottis. To explore the possibility of preventing subglottic stenosis, we compared the endotracheal tube (ETT) and the LMA in terms of the incidence and severity of glottic and subglottic injury resulting from prolonged intubation in the adult ferret model of the infant airway. Ten adult ferrets were randomly intubated under inhalational anesthesia with either a 4.0 cuffless ETT or a size 1 LMA for a 24- to 48-hour period. Rigid laryngeal endoscopy was used to detect pharyngeal or glottic injury during the period of intubation and on a routine basis for 3 months after extubation. All 5 ferrets in the ETT group developed endoscopically evident glottic and subglottic injury; 2 of the 5 developed a symptomatic, mature subglottic stenosis. The 5 ferrets in the LMA group had endoscopically normal larynges. However, all ferrets in the LMA group developed significant tongue edema and cyanosis during the first 24 hours of intubation, and 3 of the 5 died of respiratory failure due to airway obstruction. In the 2 LMA survivors, evidence of oropharyngeal injury persisted until 6 weeks after extubation. We conclude that the LMA does not cause subglottic injury in this model. However, its prolonged use results in significant pharyngeal morbidity that raises serious doubt as to its potential routine use in infants requiring prolonged ventilatory support.     

Physiologic effects of open and closed tracheostomy tubes on the pharyngeal swallow

Studies linking aspiration and dysphagia to an open tracheostomy tube exemplify the possibility that the larynx may have an influence on oropharyngeal swallow function. Experiments addressing the effects of tracheostomy tube occlusion during the swallow have looked at the presence and severity of aspiration, but few have included measurements that capture the changes in swallowing physiology. Also, hypotheses for the importance of near-normal subglottic air pressure during the swallow have not been offered to date. As such, the aim of this study was to compare the depth of laryngeal penetration, bolus speed, and duration of pharyngeal muscle contraction during the swallow in individuals with tracheostomy tubes while their tubes were open and closed. The results of this series of experiments indicate that within the same tracheostomized patient, pharyngeal swallowing physiology is measurably different in the absence of subglottic air pressure (open tube) as compared to the closed tube condition.     

Evaluation of neonatal subglottic stenosis: a 3-year prospective study

Subglottic stenosis is the most common cause of chronic airway obstruction. It results in prolonged tracheal cannulation of infants and children. Following the widespread adoption over the past 20 years of prolonged intubation for respiratory support in neonates, the incidence of acquired subglottic stenosis increased dramatically. On January 1, 1987, we began a 3-year prospective study to delineate potential etiologic factors involved in the development of subglottic stenosis in neonates. The present study analyzes data from 289 infants. Relationships between birth weight, gestational age, endotracheal tube size, duration of intubation and ventilation, number and difficulty of intubations, and the subsequent need for medical and surgical therapy are discussed. Whole organ larynges from autopsy specimens provide histological correlation.     

Primary cricotracheal resection in children: indications, technique and outcome

OBJECTIVE: Treatment of subglottic stenosis has benefited greatly from development of grafting techniques such as larygontracheoplasty. Meanwhile, cricotracheal resection of the stenotic area and a major part of the cricoid cartilage have been shown to give excellent results in adults. PATIENTS AND METHODS: From June 1993 to June 2000, we performed cricotracheal resection, as the primary surgical procedure, for acquired (n=13), congenital (n=2) or mixed (n=l) subglottic stenosis in 16 pediatric patients comprising seven boys and nine girls. At the time of surgery, the mean weight was 16 kg and the mean age was 5 years. Degree of stenosis was classified as grade II in one case, grade III in 12, and grade IV in three. Eight patients underwent two-stage procedures with postoperative tracheostomy. A rolled reinforced silastic stent was placed for a mean period of 20 days and the tracheostomy tube was removed within a mean period of 44 days after stent removal. Eight patients underwent single-stage procedures. The Portex endotracheal tube was used for a mean period of 4 days. RESULTS: All patients underwent regular clinical and endoscopic postoperative examination. Mean follow-up was 38 months. No interference with laryngotracheal growth has been noted in any case, including the five with follow-ups longer than 5 years. CONCLUSIONS: The indications for laryngotracheoplasty and cricotracheal resection in children with subglottic stenosis are still unclear. Decisions must be made on a case-by-case basis. In this article the authors discuss decisional factors in terms of clinical findings, surgical techniques, potential complications, and outcome.     

Subglottic stenosis following percutaneous tracheostomy: a single centre report as a descriptive study

Tracheal stenosis is a potential complication of tracheostomy. The present study aimed to describe the epidemiologic profile of subglottic stenosis in a referral medical centre. During a 4-year period, all patients who had been admitted in an Intensive Care Unit of Imam Khomeini Hospital (affiliated to Tehran University of Medical Sciences) and had undergone percutaneous tracheostomy during 7-10 days after endotracheal intubation were enrolled in the study. After removing the tracheostomy tube, patients were evaluated regarding development of tracheal stenosis using fiberoptic bronchoscopy and multi-slice computed tomography scan. During the study period, percutaneous tracheostomy was performed in 140 patients with a mean age of 38 years. Overall 54 patients died due to the severity of the disorder during hospitalization. In the remaining 86 patients, 54 cases needed permanent or long-term mechanical ventilation and were excluded from the study. Twelve patients died during the first 3 months and 20 patients were left for final assessment. Multi-slice computed tomography scan imaging showed subglottic stenosis in 17 cases (85%). Of these, 9 patients (52%) had tracheal stenosis of < 50%. Tracheal stenosis of 25- 40% was found in 5 cases (25%). Patients in whom the tracheostomy tube had been removed in the first 3 weeks after tracheostomy did not present tracheal stenosis (n = 3, 15%). The present study revealed that subglottic stenosis is frequent in patients who have undergone percutaneous tracheostomy in the Intensive Care unit setting. However, the stenosis is generally mild and is not associated with serious and/ or life-threatening clinical manifestations.     

Subglottic stenosis: another challenge for intubation and potential mechanism of airway obstruction in Pierre Robin Sequence

Objective

To determine the endotracheal tube (ETT) size and presence of subglottic narrowing in children less than 1 year old with Pierre Robin Sequence (PRS).

Materials and methods

We performed a retrospective review from 2005 to 2009 of infants with PRS who underwent diagnostic laryngoscopy (DL) and intubation.

Results

Fifteen children with a median age of 25 days were reviewed. All patients, except one, were born full term. Subglottic narrowing was visualized in 5 patients (33%). 73% of all patients required an ETT size smaller than what is recommended by intubation guidelines in the literature in regards to normative data based on age and weight.

Conclusion

Infants with PRS may have a higher incidence of subglottic stenosis and require a smaller ETT compared to the normal population. This pilot study warrants a larger prospective investigation to validate these findings.     

A method for ventilating patients during laryngoscopy

A method of ventilating patients during laryngoscopy was described in 40 patients. The technique used a combination of a small endotracheal tube and a high pressure oxygen jet with general anesthesia. A plastic chest tube 3.5 mm internal diameter (I.D.) was used as an endotracheal tube. The patients were ventilated with intermittent high pressure oxygen jet (50 p.s.i.) using a 1.5 mm I.D. intravenous plastic catheter introduced into the end of the endotracheal tube. Three holes were made in the proximal end of the endotracheal tube to permit air entrainment which was measured. Anesthesia was obtained with sodium thiamylal and In-novar®. Muscular relaxation was maintained with succinylcholine. Arterial blood gases were monitored and showed adequate ventilation in the majority of the patients. In 18 patients the endotracheal pressure was measured. In two instances the pressure was elevated (35 cm H₂O). No postoperative complications occurred. This technique was useful, safe, and well accepted by the surgeons. The authors consider that this technique avoids the disadvantages of conventional endotracheal anesthesia as well as those of the ventilating laryngoscope. It is contraindicated in patients with poor lung and chest wall compliance, particularly the obese. Subsequent to this study, 85 additional patients were similarly anesthetized without complications.