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Background:

Maxillofacial fractures present unique airway problems to the anaesthesiologist. Nasotracheal intubation is contraindicated due to associated Lefort I, II or III fractures. The requirement for intraoperative maxillomandibular fixation (MMF) to re-establish dental occlusion in such cases precludes orotracheal intubation. Tracheostomy has a high complication rate and in many patients, an alternative to the oral airway is not required beyond the perioperative period. Hernandez1 in 1986 first described “The submental route for endotracheal intubation”. Later some workers faced difficult tube passage, bleeding, and sublingual gland involvement with this approach. They modified this to strict midline submental intubation and there were no operative or postoperative complications in their cases.67&8. Therefore we used mid line approach for submental orotracheal intubation in this study to demonstrate its feasibility and reliability and that it can be used as an excellent substitute to short term tracheostomy.

Patients & Methods:

We used midline submental intubation in 25 cases selected out of 310 consecutively treated patients with maxillofacial trauma over a 3 year period. After induction orotracheal intubation was done with spiral re-inforced tube. A 1.5-2.0 cm skin incision was made in the submental region in the midline 2.0 cm behind the symphysis and endotracheal tube was taken out through this incision in all the cases. At the end of the surgery the procedure was reversed, the submental wound was stitched; all the patients could be extubated & none of them required post-operative mechanical ventilation.

Conclusion:

There were no significant operative or postoperative complications. Postoperative submental scarring was acceptable[6]. We conclude that midline submental intubation is a simple and useful technique with low morbidity. It can be chosen in selected cases of maxillofacial trauma and is an excellent substitute to tracheostomy where postoperative mechanical ventilation is not required.

Introduction

Management of airway is a significant issue especially in cases of complex maxillofacial trauma like panfacial fractures or concomitant nasoethmoidal injuries, where the nasotracheal intubation is contraindicated or possess a significant problem. In these cases the only other alternative is tracheostomy. Submental intubation is an alternative to tracheostomy and it can be easily performed with little or lesser post-operative complications. This method involves lesser expenses as it does away with longer post-operative stay in the hospital as required by tracheostomy patients.

Technique

The patient is orally intubated with a reinforced armoured tube with a detachable plastic gas connector. An incision is made in the submental area of the patient and a tunnel is prepared from this region to the floor of the mouth through which the proximal end of the tube is diverted. Thus the occlusion of the patient can be checked intraoperatively. After completion of the surgery the proximal end in reintroduced onto the oral cavity and the patient is extubated orally.

Discussion

Originally proposed by Altemir in 1986, this method cannot be used in all cases as it is not without limitations. In spite of these, submental intubation can be a useful alternative to tracheostomy, especially in regions where cost cutting is a major factor in health infrastructure.

Conclusion

Maxillofacial surgeons addressing major facial trauma surgery may have this procedure in mind before opting for tracheostomy. It avoids a lot of complications associated with tracheostomy.

Introduction

Airway management for patients who suffered midfacial fractures is complicated. In maxillofacial injuries, a choice has often to be made between different ways of intubation when surgical access to both the nasal and oral cavities is necessary. Submental intubation technique is an alternative to nasoendotracheal intubation and tracheostomy in the management of patients with severe midfacial fractures. This procedure is simple to do and has a low morbidity.

Material

Submental intubation-paramedian technique has been used in 15 cases from May 2005–April 2007 in Hosmat Hospital, Bangalore. All patients had fractures disturbing the dental occlusion plus either an associated fracture of the skull base or a displaced nasal fracture.

Results

Average duration of procedure was 7 minutes. Average duration of tube in vitro after surgery was 20 hours. There were 2 postoperative complications of tube obstruction which were successfully managed.

Conclusion

Submental intubation demands certain technical skills but it is simple, rapid and may avoid tracheostomy in selected patients.

Airway management in patients with faciomaxillary injuries is challenging due to disruption of components of upper airway. The anesthesiologist has to share the airway with the surgeons. Oral and nasal routes for intubation are often not feasible. Most patients have associated nasal fractures, which precludes use of nasal route of intubation. Intermittent intraoperative dental occlusion is needed to check alignment of the fracture fragments, which contraindicates the use of orotracheal intubation. Tracheostomy in such situations is conventional and time-tested; however, it has life-threatening complications, it needs special postoperative care, lengthens hospital stay, and adds to expenses. Retromolar intubation may be an option, But the retromolar space may not be adequate in all adult patients. Submental intubation provides intraoperative airway control, avoids use of oral and nasal route, with minimal complications. Submental intubation allows intraoperative dental occlusion and is an acceptable option, especially when long-term postoperative ventilation is not planned. This technique has minimal complications and has better patients’ and surgeons’ acceptability. There have been several modifications of this technique with an expectation of an improved outcome. The limitations are longer time for preparation, inability to maintain long-term postoperative ventilation and unfamiliarity of the technique itself. The technique is an acceptable alternative to tracheostomy for the good per-operative airway access.

Submental endotracheal intubation is a simple and secure alternative to either nasoendotracheal intubation or a tracheostomy in the airway management of maxillofacial trauma. However, a submental endotracheal intubation is quite difficult to manage if adverse events such as a tube obstruction, accidental extubation, or a leaking cuff with the endotracheal tube in the submental route occur, which could endanger the patient. This paper describes the use of a LMA-Fastrach™ETT in the submental endotracheal intubation of patients suffering from maxillofacial trauma. One of the patients was a 16-year-old male, and the other was a 19-year-old male. They were scheduled for an open reduction and internal fixation of the maxillofacial fracture including naso-orbital-ethmoidal (NOE) complex, and a zygomaticomaxillary complex fracture. A submental intubation with a LMA-Fastrach™ETT was performed in both cases, and the operation proceeded without any difficulties. These cases show that the use of the LMA-Fastrach™ETT can improve the safety and efficacy of submental endotracheal intubation. This is because the LMA-Fastrach™ETT has a freely detachable connector, and is flexible enough to keep the patency despite the acute angle of airway.

Background:

Oromaxillofacial surgical procedures present a unique set of problems both for the surgeon and for the anesthesist. Achieving dental occlusion is one of the fundamental aims of most oromaxillofacial procedures. Oral intubation precludes this surgical prerequisite of checking dental occlusion. Having the tube in the field of surgery is often disturbing for the surgeon too, especially in the patient for whom skull base surgery is planned. Nasotracheal intubation is usually contraindicated in the presence of nasal bone fractures seen either in isolation or as a component of Le Fort fractures. We utilized submental endotracheal intubation in such situations and the experience has been very satisfying.

Materials and Methods:

The technique has been used in 20 patients with maxillofacial injuries and those requiring Le Fort I approach with or without maxillary swing for skull base tumors. Initial oral intubation is done with a flexo-metallic tube. A small 1.5 cm incision is given in the submental region and a blunt tunnel is created in the floor of the mouth staying close to the lingual surface of mandible and a small opening is made in the mucosa. The tracheal end of tube is stabilized with Magil′s forceps, and the proximal end is brought out through submental incision by using a blunt hemostat taking care not to injure the pilot balloon. At the end of procedure extubation is done through submental location only.

Results:

The technique of submental intubation was used in a series of twenty patients from January 2005 to date. There were fifteen male patients and five female patients with a mean age of twenty seven years (range 10 to 52). Seven patients had Le Fort I osteotomy as part of the approach for skull base surgery. Twelve patients had midfacial fractures at the Le Fort II level, of which 8 patients in addition had naso-ethomoidal fractures and 10 patients an associated fracture mandible. Twelve patients were extubated in the theatre. Eight patients had delayed extubation in the post-operative ward between 1 and 3 days postoperatively.

Conclusion:

In conclusion, the submental intubation technique has proved to be a simple solution for many a difficult problem one would encounter during oromaxillofacial surgical procedures. It provides a safe and reliable route for the endotracheal tube during intubation while staying clear of the surgical field and permitting the checking of the dental occlusion, all without causing any significant morbidity for the patient. Its usefulness both in the emergency setting and for elective procedures has been proved. The simplicity of the technique with no specialized equipment or technical expertise required makes it especially advantageous. This technique therefore, when used in appropriate cases, allows both the surgeon and the anesthetist deliver a better quality of patient care.

Introduction:

In maxillofacial injuries, a choice has often to be made between different ways of intubation when surgical access to fractured nasal bone and simultaneous establishment of occlusion are required. We report our experience with submental intubation in the airway management of complex maxillofacial trauma patients.

Aims:

To evaluate the outcome of airway management in patients with complex maxillofacial fracture by submental intubation, time required for intubation, accidental extubation, postoperative complications, and to discuss indications, contraindications, advantages and disadvantages of submental intubation.

Settings and Design:

A retrospective study is designed.

Materials and Methods:

The medical records of seven patients who underwent submental intubation from December 2008 to June 2010 were reviewed and no statistical analysis was used.

Results:

At the end of the procedure all seven patients were extubated without any complications. Postoperatively only one patient presented with superficial infection of the submental wound.

Conclusions:

Submental endotracheal intubation is a simple technique with very low morbidity and can be used as an alternative to tracheostomy in selected cases of maxillofacial trauma.

ABSTRACT

This retrospective study evaluated the safety and efficacy of submental intubation not only for trauma treatment but also for oncological cranial base surgery. The medical records of 24 patients who underwent submental intubation from 1996 to 2002 were reviewed. There were 6 procedures for craniofacial trauma, 12 transmaxillary approaches to the clivus for clivus chordomas, and 6 transmaxillary approaches to the cranial base for chondrosarcomas. Time required for intubation, accidental extubation, postoperative complications, and the healing of intraoral and submental scars were evaluated. The submental orotracheal intubation was completed successfully in all patients. No accidental extubations or tube injuries occurred. The mean time required for intubation was 5 minutes. The only complication was one case of superficial infection of the submental wound. The intraoral and submental accesses healed with minimal scarring in all patients. Submental orotracheal intubation is a useful and safe technique for airway management of craniomaxillofacial traumas and during transfacial approaches to the cranial base. It avoids the complications associated with tracheostomy. It also permits considerable downward retraction of the maxilla after a Le Fort I osteotomy and is associated with good clival exposure. Furthermore, it does not interfere with maxillomandibular fixation at the end of the surgery.

Submental intubation (SI) has been proposed as an alternative to nasoendotracheal intubation when oral endotracheal intubation is contraindicated. In patients who require intubation for maxillofacial reconstruction, this is an alternative to a traditional tracheostomy. The present case report presents an 18-year-old woman who suffered a comminuted mandibular fracture. Two days after her accident, she was taken to the operating room for open reduction with internal fixation of her mandible; however, the anesthesia staff was unable to nasally intubate the patient. A SI was performed. The procedure was completed without complications and the surgery accomplished with the SI. The patient was able to avoid a tracheostomy for an isolated operation. SI avoids the dangers of nasoendotracheal intubation in patients with midfacial fractures and avoids complications related to tracheostomy. Thus, SI may serve as an alternative to tracheostomy in patients without other medical conditions and indications for long-term intubation.

Hernandez first described the submental route for endotracheal intubation in 1986 as an alternative airway maneuver for maxillofacial procedures. Since that time, several case studies have been performed demonstrating the efficacy of the submental approach. This method was recently implemented in the case of a patient with altered nasal anatomy who sustained a mandibular fracture necessitating maxillomandibular fixation. Unlike most of the cases described in the literature, this patient's operative course was confounded by the need to extubate through the submental tunnel. The patient tolerated the procedure well and was able to avoid other forms of surgical airway.

Summary

Intubating a patient with panfacial fractures is always a challenge to the anaesthesiologist. In a 40-yr-old male patient with left Le Fort's III fracture with nasal bone and symphysis menti fracture, we successfully carried out oral endotracheal intubation which was then modified to submandibular approach to provide adequate surgical field. Initially oral endotracheal intubation was performed, then an incision was made in the submandibular region through which the endotracheal tube was brought out and maintained as submandibular approach throughout the surgery.

Complex maxillofacial trauma requires a modification of intubation as it precludes both oral and nasal intubation. Tracheostomy is not preferred due to its associated complications. Submental intubation comes as a rescue in such situations as it provides an uninterrupted access to the operative field with due control over airway and minimal side effects.

No report to date describes the added risk traumatic, degloving injuries of the oral cavity may pose when treating fractures of the mandible. The authors describe the oral degloving injury, characterized by separation of periosteum and soft tissue of the anterior floor of the mouth from the inner cortex of the anterior segment. Vascular anatomy of the floor of the mouth is reviewed as a prelude to a description of pathomechanics of the injury and a case report. The higher incidence of oral degloving in youth and in young adulthood and parallels in elective, orthognathic surgery are identified. When this unusual clinical presentation occurs, and when open reduction of fractures of the anterior segment is chosen, a vestibular incision is best avoided. Instead, a submental or upper neck incision is chosen for sufficient exposure to allow reduction and the application of appliances. Meticulous closure of the intraoral void is achieved using one of two techniques, depending on the level of degloving.

This study evaluated a retrograde orotracheal intubation technique and compared it to the traditional normograde intubation technique used in llamas. Oral anatomical features, which can impair visualization of the epiglottis and laryngeal structures, and the production of excessive salivary secretions make it difficult to establish an airway under emergency conditions. Normograde intubation involves placing a stylet through the mouth into the trachea and advancing the endotracheal tube over the stylet into the trachea. For retrograde intubation, a nested trochar with cannula is placed into the cervical trachea and a stylet is advanced through the cannula and out the mouth. The endotracheal tube is advanced over the stylet back into the trachea. Our evaluation of both techniques found no statistical difference in time to place the stylet or endotracheal tube; however, fewer attempts were needed to place the tube using the retrograde technique. We found the retrograde technique to be a viable option for intubating llamas.

Abstract

The placement of endotracheal tubes in the airway, particularly through the nose, can cause trauma. Their design might be an important etiologic factor, but they have changed little since their introduction. Recently Parker Medical (Bridgewater, Conn ) introduced the Parker Flex-Tip (PFT) tube, suggesting that it causes less trauma. This study aimed to compare the PFT endotracheal tube to a side-beveled, standard-tip endotracheal tube (ETT) for nasotracheal intubation (Figures 1 and 2). Forty consecutive oral surgery patients requiring nasotracheal intubation were randomized to receive either a standard ETT or the PFT tube. Intubations were recorded using a fiber-optic camera positioned proximal to the Murphy eye of the tube. This allowed visualization of the path and action of the tube tip as it traversed the nasal, pharyngeal, laryngeal, and tracheal airway regions. Video recordings made during intubation and extubation were evaluated for bleeding, trauma, and intubation time. Both bleeding and trauma were recorded using a visual analogue scale (VAS) and by 3 different evaluators. The PFT received significantly better VAS values than the standard tubes from all 3 raters (P < 0.05) in both the extent of trauma and bleeding. Since the intubations were purposefully conducted slowly for photographic reasons, neither tube displayed a time advantage. This study suggests that the PFT tube design may be safer by causing less trauma and bleeding than standard tube designs for nasotracheal intubation.

We present the case of a dermoid cyst with an oral and a submental component in a 21-year-old Japanese woman who presented with complaints of a mass in the oral cavity and difficulty in chewing and swallowing solid foods for about 2 years. MRI shows a 55 × 65 mm well-circumscribed cystic mass extending from the sublingual area to the mylohyoid muscle. Under general anesthesia and with nasotracheal intubation, the patient underwent surgical removal of the mass. Although the cyst was large and extending mylohyoid muscle, intraoral midline incision was performed through the mucosa overlying the swelling and the cyst was separated from the surrounding tissues with appropriate traction and countertraction and successfully removed without extraoral incision. Oral approach in surgical enucleation is useful procedure to avoid cosmetic problems in large and extending mylohyoid muscle cyst.

Background

Difficult airway especially failed intubation has been associated with a high incidence of mortality and morbidity. Most of mortalities occur when an anaesthesiologist encounters an unanticipated difficult airway.

Findings

In 1999, a 23 yr. old, 65 kg weight and 170 cm height female patient had been scheduled for arthroscopy. Despite totally normal airway assessment (thyromental distance, mouth opening, jaw and neck movement ...) I was astonished by encountering a grade IV Cormack - Lehane laryngoscopic view. Tracheal intubation was impossible and ventilation was very difficult.

On attempt to attain a better laryngoscopic view, while manipulating submandibular region I encountered a bulky noncompliant submental space (Submental Sign). This event made me more alert regarding this finding. Thereafter I noted for this sign throughout the past years and I found it very helpful.

These findings encouraged me to write this report, and suggest a routine examination of submental space in order to keep the safety of the patient at the heart of the care we provide.

Conclusion

Evaluation of the submental space is suggested as an alternative predictor of difficult airway and routine examination of the submental space is of value in airway assessment.

Gum elastic bougie (GEB), a useful device for difficult airway management, has seldom been used for nasotracheal intubation. Among 632 patients undergoing dental procedures or oral surgery, GEB was used successfully in 16 patients in whom conventional nasal intubation had failed because of anatomical problems or maldirection of the tip of the tracheal tube. We recommend that GEB should be applied from the first attempt for nasal intubation in patients with difficult airways.

Changes in middle cerebral arterial flow velocity (MCAV) during rapid intravenous induction and awake intubation using transcranial Doppler sonography were investigated. The study involved 20 patients without disorders of the central nervous or cardiovascular systems who were scheduled for maxillofacial surgery. In the intravenous induction group, anesthesia was induced with sodium thiopental, and orotracheal or nasotracheal intubation was facilitated with succinylcholine chloride or alcuronium chloride. In the awake intubation group, orotracheal or nasotracheal intubation was performed under intravenous sedation with diazepam and topical anesthesia with 4% lidocaine. Arterial blood pressures, heart rate, and MCAV were monitored at specific intervals. During intravenous induction, blood pressures decreased after the administration of thiopental and muscle relaxants and increased during endotracheal intubation. MCAV was remarkably slowed after the administration of thiopental and during mask ventilation. During awake intubation, blood pressures were increased by endotracheal intubation. MCAV was decreased from the administration of diazepam to the transtracheal injection of lidocaine, but returned to the control value from endotracheal spray to endotracheal intubation. These results suggest that smooth awake intubation may be the safest method of induction for patients with cerebrovascular disorders.

Summary

Direct trauma to the airway is a rare injury which can lead to disastrous consequences due to compounding effect of bleeding, aspiration of blood, airway obstruction and severe sympathetic stimulation. Here we are presenting two cases of open tracheal injury in two adult males following assault with sharp weapon. Two different techniques of securing the airways were employed depending upon the severity and urgency of the situation. In the first case, orotracheal intubation helped the surgeon to repair airway around the endotracheal tube whereas in the second patient this stenting effect was absent as he was intubated through the distal cut-end of trachea in the face of airway emergency.

Background:

Though fiberoptic intubation (FOI) is considered the gold standard for securing a difficult airway in a child, it may be technically difficult in an anesthetized child. The hypothesis for this study was that it would be easier to perform FOI via a laryngeal mask airway (LMA) than a modified oropharyngeal airway with the advantage of maintaining anesthesia and oxygenation during the process.

Materials and Methods:

30 children aged 6 months to 5 years undergoing elective surgery under general anesthesia were randomized to two groups to have fiberoptic bronchoscope (FOB) guided intubation either via a modified Guedel airway (FOB-ORAL) or a classic LMA (FOB-LMA). In the FOB-LMA group, the LMA was removed when a second smaller endotracheal tube was anchored to the proximal end of the tracheal tube in place.

Results:

Oral fiberoptic intubation was successful in all children. The first attempt success rate was 11/15 (73.33%) in the FOB-LMA group and 3/15 (20%) in the FOB-ORAL group (P = 0.012). Subsequent attempts at intubation were successful after 90° anticlockwise rotation of the endotracheal tube over the FOB. The time taken for fiberoptic bronchoscopy was significantly less in FOB-LMA group (59.20 ± 42.85 sec vs 108.66 ± 52.43 sec). The incidence of desaturation was higher in the FOB-ORAL group (6/15 vs 0/15).

Conclusion:

In children, fiberoptic bronchoscopy and intubation via an LMA has the advantage of being easier, with shorter intubation time and continuous oxygenation and ventilation throughout the procedure. Removal of the LMA following intubation requires particular care.

Background:

Inflation and assessment of the endotracheal tube cuff pressure is often not appreciated as a critical aspect of endotracheal intubation. Appropriate endotracheal tube cuff pressure, endotracheal intubation seals the airway to prevent aspiration and provides for positive-pressure ventilation without air leak.

Materials and Methods:

Correlations between manual methods of assessing the pressure by an experienced anesthesiologists and assessment with maintenance of the pressure within the normal range by the automated pressure controller device were studied in 100 patients divided into two groups. In Group M, endotracheal tube cuff was inflated manually by a trained anesthesiologist and checked for its pressure hourly by cuff pressure monitor till the end of surgery. In Group C, endotracheal tube cuff was inflated by automated cuff pressure controller and pressure was maintained at 25-cm H2O throughout the surgeries. Repeated measure ANOVA was applied.

Results:

Repeated measure ANOVA results showed that average of endotracheal tube cuff pressure of 50 patients taken at seven different points is significantly different (F-value: 171.102, P-value: 0.000). Bonferroni correction test shows that average of endotracheal tube cuff pressure in all six groups are significantly different from constant group (P = 0.000). No case of laryngomalacia, tracheomalacia, tracheal stenosis, tracheoesophageal fistula or aspiration pneumonitis was observed.

Conclusions:

Endotracheal tube cuff pressure was significantly high when endotracheal tube cuff was inflated manually. The known complications of high endotracheal tube cuff pressure can be avoided if the cuff pressure controller device is used and manual methods cannot be relied upon for keeping the pressure within the recommended levels.

Background:

Optimal depth of endotracheal tube (ET) placement has been a serious concern because of the complications associated with its malposition.

Aims:

To find the optimal depth of placement of oral ET in Indian adult patients and its possible determinants viz. height, weight, arm span and vertebral column length.

Settings and Design:

This study was conducted in 200 ASA I and II patients requiring general anaesthesia and orotracheal intubation.

Methods:

After placing the ET with the designated black mark at vocal cords, various airway distances were measured from the right angle of mouth using a fibre optic bronchoscope.

Statistical Analysis:

The power of the study is 0.9. Mean (SD) and median (range) of various parameters and Pearson correlation coefficient was calculated.

Results:

The mean (SD) lip-carina distance, i.e., total airway length was 24.32 (1.81) cm and 21.62 (1.34) cm in males and females, respectively. With black mark of ET between vocal cords, the mean (SD) ET tip-carina distance of 3.69 (1.65) cm in males and 2.28 (1.55) cm females was found to be considerably less than the recommended safe distance.

Conclusions:

Fixing the tube at recommended 23 cm in males and 21 cm in females will lead to carinal stimulation or endobronchial placement in many Indian patients. The lip to carina distance best correlates with patient's height. Positioning the ET tip 4 cm above carina as recommended will result in placement of tube cuff inside cricoid ring with currently available tubes. Optimal depth of ET placement can be estimated by the formula “(Height in cm/7)-2.5.”

Methods: All adult patients (>18 years) with severe head injury, maxillofacial injury with need of protection of airway, or polytrauma were intubated by an emergency physician in the field. Tube position was initially evaluated by auscultation. Then, capnometry and capnography was performed (infrared method). Emergency physicians evaluated capnogram and partial pressure of end tidal carbon dioxide (EtCO2) in millimetres of mercury. Determination of final tube placement was performed by a second direct visualisation with laryngoscope. Data are mean (SD) and percentages.

Results: There were 81 patients enrolled in this study (58 with severe head injury, 6 with maxillofacial trauma, and 17 politraumatised patients). At the first attempt eight patients were intubated into the oesophagus. Afterwards endotracheal intubation was undertaken in all without complications. The initial capnometry (sensitivity 100%, specificity 100%), capnometry after sixth breath (sensitivity 100%, specificity 100%), and capnography after sixth breath (sensitivity 100%, specificity 100%) were significantly better indicators for tracheal tube placement than auscultation (sensitivity 94%, specificity 66%, p<0.01).

Conclusion: Auscultation alone is not a reliable method to confirm endotracheal tube placement in severely traumatised patients in the prehospital setting. It is necessary to combine auscultation with other methods like capnometry or capnography.

Currently, the role of ultrasound (US) in anaesthesia-related airway assessment and procedural interventions is encouraging, though it is still ill defined. US can visualise anatomical structures in the supraglottic, glottic and subglottic regions. The floor of the mouth can be visualised by both transcutaneous view of the neck and also by transoral or sublinguial views. However, imaging the epiglottis can be challenging as it is suspended in air. US may detect signs suggestive of difficult intubation, but the data are limited. Other possible applications in airway management include confirmation of correct endotracheal tube placement, prediction of post-extubation stridor, evaluation of soft tissue masses in the neck prior to intubation, assessment of subglottic diameter for determination of paediatric endotracheal tube size and percutaneous dilatational tracheostomy. With development of better probes, high-resolution imaging, real-time picture and clinical experience, US has become the potential first-line noninvasive airway assessment tool in anaesthesia and intensive care practice.