Exploring the limits of prolonged apnoea with high-flow nasal oxygen: an observational study.

High-flow nasal oxygen is increasingly used for oxygenation during apnoea. Extending apnoea duration using this technique has mainly been investigated during minor laryngeal surgery, but it is unclear how long it can be administered for before it should be discontinued due to acidosis. We aimed to describe the dynamics of arterial blood gases during apnoeic oxygenation with high-flow nasal oxygen with jaw thrust only, to explore the limits of this technique. We included adult orthopaedic patients scheduled for general anaesthesia. After pre-oxygenation, anaesthesia with neuromuscular blockade was induced and high-flow nasal oxygen (70 l.min-1 ) was continued with jaw thrust as the only means of airway management, with monitoring of vital signs and arterial blood gas sampling every 5 minutes. Apnoeic oxygenation with high-flow nasal oxygen was discontinued when arterial carbon dioxide tension (PaCO2 ) exceeded 12 kPa or pH fell to 7.15. This technique was used in 35 patients and median (IQR [range]) apnoea time was 25 (20-30 [20-45]) min and was discontinued in all patients when pH fell to 7.15. The mean (SD) PaCO2 increase was 0.25 (0.06) kPa.min-1 but it varied substantially (range 0.13-0.35 kPa.min-1 ). Mean (SD) arterial oxygen tension was 48.6 (11.8) kPa when high-flow nasal oxygen was stopped. Patients with apnoea time > 25 minutes were significantly older (p = 0.025). We conclude that apnoeic oxygenation with high-flow nasal oxygen resulted in a significant respiratory acidosis that varies substantially on the individual level, but oxygenation was maintained.

Infrared Red Intubation System (IRRIS) guided flexile videoscope assisted difficult airway management.

BACKGROUND: Tracheal intubation with a flexible scope is a cornerstone technique in patients with severely difficult airways, but may fail. We report on a technique, Infrared Red Intubation System (IRRIS), that seems to facilitate the identification of the glottis. METHODS: The IRRIS is placed over the patient's cricothyroid membrane and emits blinking infrared light through the patient's skin into the subglottic space. When a flexible videoscope (one that does not filter infrared light) is introduced into the airway, it will display this as a blinking white light emerging from the glottis, retrograde transillumination, showing the pathway to the trachea. We have introduced this as an adjunct when managing our patients with difficult airways. We describe the technique and retrospectively report on the first ten patients where it was used. RESULTS: All ten patients had significant pathology in the airway, radiation therapy, predictors for difficult intubation and/or morbid obesity. In all cases the blinking light was visible during the flexible endoscopy and provided unambiguous identification of the glottis, from a distance. The blinking nature of the light from the IRRIS helped to distinguish it from the reflections in the mucosa that inevitably arise when the mucosa is hit by the light from the flexible scope itself. CONCLUSION: The addition of the IRRIS technique to intubation with flexible videoscopes may be a tool that will make intubation of the most difficult airways easier and may be of special help to the clinician who only rarely uses flexible videoscopes for tracheal intubation.

A new retrograde transillumination technique for videolaryngoscopic tracheal intubation.

This single-centre, prospective trial was designed to assess the efficacy of a new retrograde transillumination device called the 'Infrared Red Intubation System' (IRRIS) to aid videolaryngoscopic tracheal intubation. We included 40 adult patients, who were undergoing elective urological surgery under general anaesthesia. We assessed the ability to differentiate the transilluminated glottis from other structures and found a median (IQR [range]) larynx recognition time of 8 (5-14 [3-28]) s. The difference in laryngeal visibility on the screen between the deactivated vs. activated device expressed on a visual analogue scale was significant (6 (4-7 [2-10]) vs. 10 (8-10 [4-10]); p < 0.001). The number of laryngoscope insertions was 1 (1-2 [1-3]) and the device showed high values on a visual analogue scale ranging from 0 (lowest score) to 10 (highest score) for helpfulness (6 (5-7 [2-10])), credibility (10 (8-10 [5-10])) and ease of use (10 (9-10 [8-10])). Tracheal intubation with the system lasted 26 (16-32 [6-89]) s. No alternative technique of securing the airway was necessary. The lowest SpO2 during intubation was 98 (97-99 [91-100])%. We conclude that this method of retrograde transillumination can assist videolaryngoscopy.

Optimization and characterization of highly nonlinear fiber for broadband optical time lens applications.

We demonstrate simple and intuitive methods, for dispersion optimization and characterization of highly nonlinear fiber (HNLF) for use in four-wave-mixing (FWM) based time lens applications. A composite dispersion-flattened HNLF is optimized for high bandwidth time lens processing, by segmentation to mitigate FWM impairments due to dispersion fluctuations. The fiber is used for FWM conversion of 32 WDM-channels with 50 GHz spacing in a time lens, with -4.6 dB total efficiency, and <1 dB per-channel efficiency difference. The novel characterization method is based on two tunable continuous-wave lasers. The method is experimentally verified to predict the spectral output profile of time lenses for broadband multicarrier input, with detailed numerical simulations for support.

Ventilation via the 2.4 mm internal diameter Tritube® with cuff - new possibilities in airway management.

BACKGROUND: A small tube may facilitate tracheal intubation and improve surgical access. We describe our initial experience with the Tritube® that is a novel cuffed endotracheal tube with a 2.4 mm internal diameter. METHODS: The Tritube® was used in seven adult Ear-Nose-and Throat surgical patients with airway narrowing or whose surgical access was facilitated by this small-bore endotracheal tube. Ventilation through Tritube® is performed with the manually operated Ventrain® -ventilator that allows active suctioning during expiration, therefore facilitating normoventilation through small diameter airways. RESULTS: The small diameter of Tritube® seemed to improve glottis visualisation during intubations and gave excellent working conditions for surgery. Two patients were intubated awake with a flexible scope and a guide wire or with an angulated video laryngoscope. One patient had almost complete glottic occlusion that just allowed for passage of the Tritube® . Adequate ventilation was achieved in all patients and intratracheal pressure was kept between 5 and 20 cm H2 O. The tube was well tolerated after emergence from anaesthesia and kept intratracheally in five awake patients in the post-operative recovery unit, in one case for more than 1 h. Ventilating with Ventrain® through Tritube® demands meticulous breath by breath measurement and adjustment of the intratracheal pressure. CONCLUSION: The 2.4 mm internal diameter Tritube® seems to facilitate tracheal intubation and to provide unprecedented view of the intubated airway during oral, pharyngeal, laryngeal or tracheal procedures in adults. This technique has the potential to replace temporary tracheostomy, jet-ventilation or extra-corporal membrane oxygenation in selected patients.

Ultrasonographic identification of the cricothyroid membrane: best evidence, techniques, and clinical impact.

Inability to identify the cricothyroid membrane by inspection and palpation contributes substantially to the high failure rate of cricothyrotomy. This narrative review summarizes the current evidence for application of airway ultrasonography for identification of the cricothyroid membrane compared with the clinical techniques. We identified the best-documented techniques for bedside use, their success rates, and the necessary training for airway-ultrasound-naïve clinicians. After a short but structured training, the cricothyroid membrane can be identified using ultrasound in difficult patients by previously airway-ultrasound naïve anaesthetists with double the success rate of palpation. Based on the literature, we recommend identifying the cricothyroid membrane before induction of anaesthesia in all patients. Although inspection and palpation may suffice in most patients, the remaining patients will need ultrasonographic identification; a service that we should aim at making available in all locations where anaesthesia is undertaken and where patients with difficult airways could be encountered.

A randomised cross-over comparison of the transverse and longitudinal techniques for ultrasound-guided identification of the cricothyroid membrane in morbidly obese subjects.

We compared the transverse and longitudinal approaches to ultrasound-guided identification of the cricothyroid membrane, to determine which was faster and more successful. Forty-two anaesthetists received a one-hour structured training programme consisting of e-learning, a lecture and hands-on training, and then applied both techniques in a randomised, cross-over sequence to obese females with body mass index 39.0 - 43.9 kg.m(-2) . The mean (SD) time to identify the cricothyroid membrane was 24.0 (12.4) s using the transverse technique compared with 37.6 (17.9) s for the longitudinal technique (p = 0.0003). Successful identification of the cricothyroid membrane was achieved by 38 (90%) anaesthetists using either technique. All anaesthetists were successful in identifying the cricothyroid membrane with at least one of the techniques. We advocate the learning and application of these two techniques for identification of the cricothyroid membrane before starting anaesthesia in difficult patients, especially when anatomical landmarks are impalpable. Further use in emergency situations is feasible, if clinicians have experience and the ultrasound machine is readily available.

Tracheal intubation in patients with anticipated difficult airway using Boedeker intubation forceps and McGrath videolaryngoscope.

BACKGROUND: Videolaryngoscopes with sharp angulated blades improve the view of the vocal cords but this does not necessarily result in higher success rates of intubation The aim of this study was to evaluate the efficacy of using Boedeker intubation forceps in conjunction with McGrath Series 5 Videolaryngoscope (MVL) in patients with predictors for difficult intubation. METHODS: The study was conducted at the Department of Anaesthesia, Copenhagen University Hospital from September to December 2013. Patients with one or more predictors of difficult intubation scheduled for general anaesthesia were assessed for eligibility. Patients were intubated using Boedeker intubation forceps and MVL. The primary endpoint was time to intubation. The secondary endpoints were intubation success rate, number of intubation attempts, intubation conditions and post-operative hoarseness. RESULTS: Thirty-three patients were assessed for eligibility, and 25 patients were included in the study with a median SARI score of 3 (IQR 3-4). Twenty-two (88%, 95% confidence interval [74-100%]) of the patients were successfully intubated by the method with a median time to intubation of 115 s (IQR 78-247). Steering and advancement of the tube were reported as acceptable in 21 (84%) and 22 cases (88%), respectively, and excellent in 10 cases (45%) for both measures. Ten cases (40%) were intubated on the first attempt. There were three cases (12%) of failed intubation; in these cases, successful intubation was obtained by using a styletted tube. CONCLUSION(S): Most patients with anticipated difficult intubation can be successfully intubated with Boedeker intubation forceps and MVL. However, endotracheal tube placement failed in 3/25 patients despite a good laryngeal view.

The disposable Ambu aScope vs. a conventional flexible videoscope for awake intubation -- a randomised study.

BACKGROUND: A new disposable flexible videoscope, the Ambu® aScope, has several potential advantages compared with reusable devices, but it is a prerequisite for its widespread use that it functions sufficiently well in the management of patients in whom difficulty with airway management is anticipated and awake intubation is indicated. METHODS: In a pilot study, 20 patients with normal airways were intubated with the aScope. Subsequently, 40 patients with predicted difficult tracheal intubation were randomly assigned to be intubated awake with either the aScope or the reusable Olympus BF videobronchoscope. RESULTS: All patients were successfully intubated awake. The median total intubation time, including the administration of local anaesthesia, was 278 vs. 234 s in the aScope and Olympus groups, respectively (P = 0.03). In two cases in the aScope group, the image became blurred immediately after the first injection of lidocaine via the injection channel, and the time that it took to replace the scopes was included in the intubation times. CONCLUSION: Both the disposable aScope and the reusable Olympus videoscope allowed safe awake intubation in our elective patients with severely difficult, but uncompromised, airways. The occasional need to employ a spare scope because of malfunctioning would make the disposable aScope less suitable in patients with acutely compromised airways.

Laryngeal morbidity after tracheal intubation: the Endoflex(®) tube compared to conventional endotracheal intubation with stylet.

BACKGROUND: Tracheal intubation may cause vocal fold damage. The trial was designed to assess laryngeal morbidity comparing the Endoflex(®) tube with a conventional endotracheal tube with stylet. We hypothesised that laryngeal morbidity within the first 24 h after extubation would be lower with the Endoflex tube than with the conventional endotracheal tube with stylet because of less rigidity. METHODS: This randomised trial included 130 elective surgical patients scheduled for general anaesthesia with endotracheal intubation. Pre- and post-operative assessment of hoarseness, vocal fold pathology, and voice analysis using the Multidimensional Voice Program was performed. Induction of anaesthesia was standardised. After complete neuromuscular paralysis, intubation was done with an Endoflex tube or a conventional endotracheal tube with stylet. RESULTS: Post-operative hoarseness was found in 45% with the Endoflex tube and 55% with the endotracheal tube with stylet at 24 h after extubation (P = 0.44). Post-operative vocal fold injury was present in 23% in the Endoflex tube group and in 36% in the endotracheal tube with stylet group (P = 0.13). The increase in shimmer, the voice analysis variable reflecting vocal fold oedema, was 0.5% in the Endoflex tube group and 2.5% in the endotracheal tube with stylet group (P = 0.02). CONCLUSION: No significant difference was found in the incidence of hoarseness or vocal fold injury using the Endoflex tube. However, the statistically significant lower increase in the shimmer values in that group implies that the Endoflex may be associated with less laryngeal morbidity.

A cost analysis of reusable and disposable flexible optical scopes for intubation.

BACKGROUND: Intubation using a flexible optical scope (FOS) is a cornerstone technique for managing the predicted and unpredicted difficult airway. The term FOS covers both fibre-optic scopes and videoscopes. The total costs of using flexible scopes for intubation are unknown. The recent introduction of a disposable flexible scope for intubation merits closer scrutiny of the total costs associated with both modalities. METHODS: The costs incurred during intubations using FOSs at a large anaesthesia department were identified, and a series of intubations using a disposable scope were analyzed for comparison. Recognized health-economic methodology was applied. RESULTS: During a 1-year period, 360 FOS intubations were performed. In this clinical setting, the average cost of an intubation using a reusable FOS was €177.7. When using the disposable Ambu(®) aScope (Ambu A/S, Ballerup, Denmark), the cost was €204.4. The break-even point, i.e. the number of intubations per month where the cost of using disposable and non-disposable equipment is identical, was 22.5/month. A subgroup analysis looking solely at intubations performed with flexible videoscopes revealed that the cost per intubation was equal for disposable and reusable videoscopes. CONCLUSION: At our institution, the total cost of an intubation is greater when using disposable compared with reusable equipment (€204.4 vs. €177.7). If video equipment with an external monitor is considered mandatory, the expenses are of equal magnitude. The cost analysis is particularly sensitive to the actual number of flexible optic intubations performed; with fewer intubations, the total cost will begin to favour disposable equipment.

Ultrasonography in the management of the airway.

In this study, it is described how to use ultrasonography (US) for real-time imaging of the airway from the mouth, over pharynx, larynx, and trachea to the peripheral alveoli, and how to use this in airway management. US has several advantages for imaging of the airway - it is safe, quick, repeatable, portable, widely available, and it must be used dynamically for maximum benefit in airway management, in direct conjunction with the airway management, i.e. immediately before, during, and after airway interventions. US can be used for direct observation of whether the tube enters the trachea or the esophagus by placing the ultrasound probe transversely on the neck at the level of the suprasternal notch during intubation, thus confirming intubation without the need for ventilation or circulation. US can be applied before anesthesia induction and diagnose several conditions that affect airway management, but it remains to be determined in which kind of patients the predictive value of such an examination is high enough to recommend this as a routine approach to airway management planning. US can identify the croicothyroid membrane prior to management of a difficult airway, can confirm ventilation by observing lung sliding bilaterally and should be the first diagnostic approach when a pneumothorax is suspected intraoperatively or during initial trauma-evaluation. US can improve percutaneous dilatational tracheostomy by identifying the correct tracheal-ring interspace, avoiding blood vessels and determining the depth from the skin to the tracheal wall.

Evidence for benefit vs novelty in new intubation equipment.

A myriad of new intubation equipment has been introduced commercially since the appearance of Macintosh/Miller blades in the 1940s. We review the role of devices that are relevant to current clinical practice based on their presence in the scientific literature. The comparative performance of new vs traditional direct laryngoscopes, their complications, their use in awake intubation techniques and the prediction of unsuccessful intubation with new devices are reviewed. Manikin studies are of limited value in this area. We conclude that in both predicted and unpredicted difficult or failed intubation, carefully selected new intubation equipment has a high success rate for tracheal intubation. Ideally, such devices should be available in all settings where tracheal intubation is performed. Most importantly, experience and competence with any of the new devices are critical for their successful use in any clinical setting.

Infrared flashing light through the cricothyroid membrane to guide flexible bronchoscopic tracheal intubation.

Flexible bronchoscopic tracheal intubation is a fundamental technique in the management of the difficult airway but requires specific skills which may be both difficult to achieve and maintain. Therefore, techniques to improve its success should be developed. We present two cases, one where the ear, nose and throat surgeon could not view the glottis due to laryngeal pathology, and one where pathology in the oropharynx obscured access to the trachea during attempts at flexible bronchoscopic and videolaryngoscopic tracheal intubation. In both cases, tracheal intubation was subsequently successful due to the use of the Infrared Red Intubation System. This is an infrared light source that is secured to the anterior neck. It emits a flashing infrared light that is captured by the flexible bronchoscope, thus guiding the way to the trachea. These are the first reports of this technology being used for flexible bronchoscopic tracheal intubation in patients with severe airway pathology where conventional approaches had failed. Both cases emphasise that this technique can be of benefit in avoiding a surgical airway.