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Reply: Usable versus Overall Tracheal Tube Length: The Difference May Be Critical

Asai, Takashi MD

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In Reply:‐Firstly, I point out that, before publication of the three articles to which Harvey et al. refer, I had already detected possible damage to the vocal cords associated with tracheal intubation through the laryngeal mask and provided several solutions (including the use of a 5.0‐mm microlaryngeal tube). [1,2]
Figure 1
Figure 1
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I have noticed recently that there are two types of 6.0‐mm Mallinckrodt reinforced tracheal tubes‐with and without a Murphy eye. The tube to which I referred in the previous letter [3] does not have a Murphy eye and is manufactured in Ireland. I have used it in about 100 patients in the UK, [4,5] and the lengths of these tubes were always between 31 and 33 cm (excluding the connector part) (Figure 1). [3,6] Another group in the UK also has found this advantage. [6] In contrast, as Harvey et al. claim, the length of the tube without a Murphy eye (manufactured in United States) seems to be similar to that of a “standard” tube (about 28.5 cm).
I also contacted the manufacturer, which stated that the specified lengths should be similar between these two tubes (29.8 and 30.0 cm). However, the manufacturer admitted that, at the moment, the tube could be 2 cm shorter than these specifications (to be discussed). That means that the length of these reinforced tubes may not always be longer than usual. I found such a variability in another type of Mallinckrodt tube, the Endotrol tube. [2] Therefore, the 6.0‐mm Mallinckrodt reinforced tube, in particular the tube that has a Murphy eye (manufactured in United States), may not be suitable for tracheal intubation through the laryngeal mask.
The following is a comment I received from the Manufacturer (Ms. J.D. Balchin, Business director, Mallinckrodt Medical (UK) Ltd., Northampton, UK): “Previously, the reinforced tube with a Murphy eye had been manufactured in the USA and the non‐Murphy eye tube in Ireland. All reinforced products are now manufactured in the Athlone facility in Ireland and the dimensions are the same.”
"The manufacturing blue prints for both of these tubes now state that the length of 6.0‐mm tube (without the connector) is 300 mm, with a plus of 30 mm or a minus of 22 mm tolerance, which allows for the extremes of product. The length variation is due to the nature of the extrusion and the processing operations of reinforced tracheal tubes. These specifications comply to lengths stated in the European standards for tracheal tubes and connectors (pr EN1782).
Takashi Asai, M.D.
Department of Anesthesiology; Kansai Medical University; Moriguchi, Osaka, Japan
(Accepted for publication March 27, 1997.)
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References

1. Asai T: Use of the laryngeal mask for tracheal intubation in patients at increased risk of aspiration of gastric contents. Anesthesiology 1992; 77:1029-30.

2. Asai T, Latto IP, Vaughan RS: The distance between the grille of the laryngeal mask airway and the vocal cords: Is conventional intubation through the laryngeal mask safe? Anaesthesia 1993; 48:667-9.

3. Asai T: Tracheal intubation through the laryngeal mask airway. Anesthesiology 1996; 85:439.

4. Koga K, Asai T, Latto IP, Vaughan RS: Effect of size of a tracheal tube and the efficacy of the use of the laryngeal mask for fibrescope-aided tracheal intubation. Anaesthesia 1997; 52:131-5.

5. Asai T, Oldham T, Latto IP: Unexpected difficulty in the lighted stylet-aided tracheal intubation through the laryngeal mask. Br J Anaesth 1997; 78:111-2.

6. Silk JM, Hill HM, Calder I, Asai T, Latto IP, Vaughan RS: The distance between the grille of the larygeal mask airway and the vocal cords. Anaesthesia 1994; 49:170-1.

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