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Concerning the cuff-free subglottic part of the tracheal tube
- Keith B. Greenland, David Chong and Mike Irwin (20 December 2004)
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Keith B. Greenland University of Hong Kong, David Chong and Mike Irwin
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Dear Sir, We would like to compliment Weiss and colleagues (1) on their recent publication concerning the evaluation of the appropriateness of the intubation depth mark on the new “Microcuff” paediatric tracheal tube. We are presently completing a study examining the appropriateness of depth makers on commonly used adult-sized tracheal tubes in Chinese patients by using the “draw back” technique similar to that used in this study. Amongst various dimensions of adult tracheal tubes, we reviewed the distance from the depth mark and the proximal edge of the cuff and found for example that this was approximately 30-35mm in adult Portex tubes (Portex Ltd, Hythe, Kent, UK) and 27-31mm in Rusch Ruschelit® Super Safety Clear (Teleflex Inc., Limerick, PA). While Mallinckrodt Hi-Lo™ tubes (Mallinckrodt Ltd., Tucson, AZ, USA) do not have depth marks. We propose that the tracheal cuff in both paediatric and adult patients should be below both the vocal cords and the cricoid cartilage and the tip should be above the carina. It seems prudent to avoid the cricoid ring, as this part of the airway is a complete ring as opposed to the trachea, which has a membranous posterior wall that may act to dissipate the pressure of an inflated tracheal tube cuff. Unfortunately the medical literature has few articles that assess the length from the vocal cords to the inferior edge of the cricoid cartilage. One such study in adults by Bennett and co workers (2) showed that the caudo-cephalic distance for the cricothyroid membrane was 13.69 +/- SD 0.96 mm and that the distance from the upper limit of the cricothyroid membrane to the vocal cords was 9.78 +/- SD 0.52 mm. In the present study, Weiss and co workers state “the short cuff allows a cuff-free subglottic tube shaft (distance between intubation depth mark and upper border of the cuff) of 9 mm in a 3.0-mm ID tracheal tube and of 22 mm for a 7.0-mm ID tracheal tube” with two studies as references (3, 4). These studies examined the dimensions of the laryngeal cartilages and the length of the vocal cords but did not measure the position of the vocal cords in relation to any of the cartilages in the paediatric age groups they selected. We would be interested if the authors would expand upon which of the measurements in these studies influenced the above statement and if they were aware why the manufacturer chose this particular range (9-22 mm) for this part of the tube construction. Dr. K.B. Greenland M.B., B.S., F.A.N.Z.C.A., F.H.K.A.M. Department of Anaesthesia and Perioperative Medicine, Royal Brisbane and Women’s Hospital, Brisbane, Queensland, Australia. (Formerly Honorary Assistant Professor, Department of Anaesthesiology, University of Hong Kong) Dr. D. Chong MB, BS Medical Officer, Department of Anaesthesiology, Queen Elizabeth Hospital, Kowloon, Hong Kong Dr. Michael G. Irwin M.B., Ch.B., M.D., F.R.C.A., F.H.K.A.M. Associate Professor and Head, Department of Anaesthesiology, University of Hong Kong References: 1. Weiss M, Gerber A, Dullenkopf A. Appropriate placement of intubation depth marks in a new cuffed paediatric tracheal tube. British Journal of Anaesthesia 2005;94(1):80-7. 2. Bennett J, Guha S, Sankar A. Cricothyrotomy: the anatomical basis. J R Coll Surg Edinb 1996;41(1):57-60. 3. Schild J. Relationship of laryngeal dimensions to body size and gestational age in premature neonates and small infants. Laryngoscope 1984;94:1284-92. 4. Kahance J. Growth of the human prepubertal and pubertal larynx. J Speech Hear Res 1982;25:446-55. Conflict of Interest:None declared |
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