K. B. Greenland

Changes in airway configuration with different head and neck positions using magnetic resonance imaging of normal airways: a new concept with possible clinical applications

BACKGROUND The sniffing position is often considered optimal for direct laryngoscopy. Another concept of airway configuration involving a laryngeal vestibule axis and two curves has also been suggested. We investigated whether this theory can be supported mathematically and if it supports the sniffing position as being optimal for direct laryngoscopy. METHODS Magnetic resonance imaging scans were performed in 42 normal adult volunteers. The airway passage was divided into two curves-primary (oro-pharyngeal curve) and secondary (pharyngo-glotto-tracheal curve). Airway configuration was evaluated in the neutral, extension, head lift, and sniffing positions. The airway passage, point of inflection (where the two curves meet), its tangent, and the line of sight were plotted on each scan. RESULTS The point of inflection lay within the laryngeal vestibule in all positions. The head lift and sniffing positions caused the tangent to the point of inflection to approximate the horizontal plane. The sniffing, extension, and head lift positions caused a reduction in the area between the line of sight and the airway curve compared with the neutral position. CONCLUSIONS A two-curve theory is proposed as a basis for explaining airway configuration. The changes in these curves with head and neck positioning support the sniffing position as optimal for direct laryngoscopy. Application of this new concept to other forms of laryngoscopy should be investigated.

Education in airway management

In airway management, poor judgment, education and training are leading causes of patient morbidity and mortality. The traditional model of medical education, which relies on experiential learning in the clinical environment, is inconsistent and often inadequate. Curriculum change is underway in many medical organisations in an effort to correct these problems, and airway management is likely to be explicitly addressed as a clinical fundamental within any new anaesthetic curriculum. Competency‐based medical education with regular assessment of clinical ability is likely to be introduced for all anaesthetists engaged in airway management. Essential clinical competencies need to be defined and improvements in training techniques can be expected based on medical education research. Practitioners need to understand their equipment and diversify their airway skills to cope with a variety of clinical presentations. Expertise stems from deliberate practice and a desire constantly to improve performance with a career‐long commitment to education.

A proposed model for direct laryngoscopy and tracheal intubation.

Deputy Director (Research), Department of Anaesthesia and Perioperative Medicine, Royal Brisbane & Women’s Hospital, Butterfield St., Herston, Brisbane, Queensland, Australia; Senior Lecturer, Anaesthesiology and Critical Care – School of Medicine, University of Queensland; Honorary Associate Professor, Department of Anaesthesiology, University of Hong Kong, Room 424 K Block, Queen Mary Hospital, Pokfulam Road, Hong Kong SAR

Intubation via a laryngeal mask airway with an Aintree catheter – not all laryngeal masks are the same

A response to a previously published article or letter can be submitted to the Online Correspondence section at http://www.anaesthesiacorrespondence.com. A selection of this correspondence is published several times a year in Anaesthesia. All correspondence intended for publication in Anaesthesia should be addressed to Dr David Bogod, Editor-in-Chief, and submitted as an e-mail attachment to anaesthesia@nottingham.ac.uk. For multi-author letters, a covering letter signed by all authors must be submitted either by post, fax (44 (0) 115 962 7670) or by e-mail as a scanned document before correspondence can be published. Alternatively, letters may be submitted typewritten on one side of paper, double spaced with wide margins to Anaesthesia, 1st Floor, Maternity Unit, Nottingham City Hospital, Hucknall Road, Nottingham, NG5 1PB, UK. All paper submissions must include a signed covering letter, a disc or CD-ROM with a Word for Windows or .rtf version of the letter and an email address for the corresponding author. Copy should be prepared in the usual style of the Correspondence section. Authors must follow the advice about references and other matters contained in the Author Guidelines at http://www.blackwellpublishing.com/journals/ana/submiss.htm. Correspondence presented in any other style or format will be returned to the author for revision.

External auditory meatus–sternal notch relationship in adults in the sniffing position: a magnetic resonance imaging study

1 Laws HJ, Harbrecht U, Köster B. Hereditary heterozygote factor VII deficiency. Klin Padiatr 1992; 204: 453–4 2 Giansily-Blaizot M, Schved JF. Potential predictors of bleeding risk in inherited factor VII deficiency—clinical, biological and molecular criteria. Thromb Hemost 2005; 94: 899–900 3 Hedner U. Recombinant activated factor VII as a universal haemostatic agent. Blood Coagul Fibrinol 1998; 9(Suppl 1): S147–52 4 Pang G, Donaldson A. Probable right atrial thrombus immediately after recombinant activated factor VII administration. Br J Anaesth 2007; 99: 221–5 5 Ahonen J, Jokela R. Recombinant factor VIIa for life-threatening post-partum haemorrhage. Br J Anaesth 2005; 94: 592–5

Comparison of the Levitan FPS Scope™ and the single-use bougie for simulated difficult intubation in anaesthetised patients

Summary A randomised cross‐over study was performed in 34 patients with no evidence of airway difficulties, following induction of general anaesthesia, to compare the efficacy of the Levitan FPS scope™ (LFPS) and the single‐use bougie for tracheal intubation during simulated grade IIIa laryngoscopy. Success rates for intratracheal placement of the device, and the time required for insertion and tracheal intubation were recorded. Both devices were equally successful (31/34 for the LFPS vs 29/34 for the bougie) for insertion into the glottis. The mean insertion time for the LFPS was statistically longer than that for the bougie (4.4–12.5 s) but this difference was not clinically relevant. Intubation times were similar between the two devices. Major problems hindering successful intubation using the LFPS were the presence of a narrow epiglottic‐pharyngeal wall space and copious secretions. An inability to maintain the desired shape was the principal cause of failure with the bougie.

Comparison of the Williams Airway Intubator and Ovassapian Fibreoptic Intubating Airway for fibreoptic orotracheal intubation.

A randomised study was carried out in 60 anaesthetised patients with no evidence of airway difficulties, to compare the Williams Airway Intubator and the Ovassapian Fibreoptic Intubating Airway for bronchoscopic view and ease of railroading a tracheal tube during fibreoptic orotracheal intubation. The Williams Airway Intubator provided a better view of the glottis (41 (68.3%) unobstructed views) than the Ovassapian Fibreoptic Intubating Airway (15 (25%) unobstructed views; p < 0.0001) and a shorter time was needed to complete bronchoscopy (median (95% CI) difference 4 s (1–7); p = 0.01). Four (6.7%) bronchoscopies failed using the Williams Airway Intubator compared with 26 (43.3%) using the Ovassapian Fibreoptic Intubating Airway (p < 0.0001). Both airways provided similar intubating conditions when the glottis was visible.

The sniffing and extension-extension position: the need to develop the clinical relevance

equipment, should be tempered with a degree of caution. Any single-use item of equipment that is selected should certainly be properly evaluated before use [9] and be ‘fit for purpose’. Cook’s hospital policy is, however at variance with the Association of Anaesthetists of Great Britain and Ireland advice. He has recently noted when discussing introducers that ‘the only one used in our hospital (until a replacement is proven to be of similar efficacy and safety) is the original gum elastic bougie’ [10]. The Frova introducer was brought into clinical practice in 1998 without any published evaluation of its clinical effectiveness or safety. It seems surprising that Drs Sorbello and Frova are reluctant to accept the evidence and modify the design of the device. We thank them again for their interest in our study, but they should accept that error in this case lies in the device, not in the artist.

Differences in two new rigid indirect laryngoscopes

The Airtraq (Prodol Meditec S.A., Vizcaya, Spain) and the Airway Scope (AWS-S100, Pentax, Tokyo, Japan) are two new rigid indirect laryngoscopes [1]. These devices have been developed to provide a view of the glottis without the need to align the oral, pharyngeal, and laryngeal axes. Both have a blade curvature of approximately 90 which aims to replicate the anatomical curve of the oropharynx. Despite their similar appearance, the two devices function quite differently at the tip. When a curved tracheal tube is advanced from the Airtraq, the tube passes below the tip of the device initially and then with further advancement it moves upward, towards the glottis (Fig. 8). As a result, inserting the Airtraq too close to the glottis will only allow the initial posterior movement of the tube and result in a failure to intubate. We did not appreciate this point when we started using this device and initially experienced a failed intubation rate of 50%. The inventor, Dr Pedro Acha emphasises the ‘back and up manoeuvre’ which involves withdrawing the device away from the glottis and lifting the device up before attempting to intubate (P. Acha personal communication). In contrast, the path of the tracheal tube leaving the Airway Scope is more direct. This appears to be due to the narrower tracheal tube conduit in the Airway Scope compared to the Airtraq. Unlike the Airtraq, the tube travels for a short distance almost in line with the blade tip before angling upwards (Fig. 9). The Airway Scope therefore requires proximity to the larynx for successful intubation and is intended to be placed under the epiglottis. Failures have been reported when the distance from the mouth to the larynx is longer than the set length of the Airway Scope blade [2]. We have also had two such failures. In these circumstances the blade has not been long enough to lift up the epiglottis and the advancing tracheal tube has moved upwards and caught on the epiglottis. Although these devices have proved useful even for the occasional or novice laryngoscopist [3–5], our experience suggests knowledge of these subtle points of technique is important to ensure successful intubation. Figure 8 Tracheal tube advancing from Airtraq (a) early and (b) late.

Comparison of the Berman Intubating Airway and the Williams Airway Intubator for fibreoptic orotracheal intubation in anaesthetised patients

Sixty patients with no clinical indicators of a difficult airway were selected to undergo a fibreoptic assessment after induction of general anaesthesia using both the Berman Intubating Airway and the Williams Airway Intubator. The bronchoscopic view and ease of railroading a tracheal tube during fibreoptic orotracheal intubation were studied. The bronchoscopic views obtained by the Berman Airway and the Williams Airway were significantly different (p < 0.008, test of symmetry). The estimated odds ratio of obtaining an obstructed path was 3.06 times higher for the Berman than the Williams Airway. However, if the glottis could be reached with the bronchoscope, there was no significant difference in the degree of ease of intubation between the two airways.