Size matters: choosing the right tracheal tube.

Abstract

A common question asked in the anaesthetic room is ‘‘what size of tube?’’. Ultimately, the intended purpose and duration of intubation should govern the choice of size. In 1928, Magill suggested ‘‘the largest endotracheal tube which the larynx will comfortably accommodate’’ [1]. Even 30 years ago, it was common practice to place 9.0or even 10.0mm tubes for males and 8.0-mm tubes for females. Over recent years it has become common for anaesthetists to place tubes 1–2 mm smaller. This evolution in practice was initially driven by the observation that there was little impact on ventilator pressures during anaesthesia, and is maintained by a perceived reduction in sore throat and hoarseness, increased ease of insertion and less tracheal damage. The incidence of postoperative sore throat after tracheal intubation varies from 14% to 50%, as does hoarseness, although the latter is rarely sustained [2–7]. Contributory factors include the size of the tube, cuff design and pressure, variation in skills and techniques between anaesthetists and the subjectivity of the symptom of sore throat in individual patients [5, 8–14]. It has been clearly shown that smaller tubes cause less sore throat, with the incidence halved when tubes were reduced from 9.0 mm to 7.0 mm for men and from 8.5 mm to 6.5 mm for women, although these are shortterm effects and the incidence of occasional prolonged symptoms seems independent of tube size [5– 7]. Be that as it may, sore throat is not limited to patients subjected to tracheal intubation but is also seen with supraglottic airways; even with the laryngeal mask airway (LMA) variable numbers of patients (14–42%) may complain of sore throat postoperatively, a figure not dissimilar from – but usually lower than – that following tracheal intubation [4, 15, 16]. Larger LMAs are associated with a higher incidence of sore throat and hoarseness [17]. Cuff design is important as with the old red rubber tubes, the cuff pressure could readily contribute to mucosal ischaemia or inflammation [18]. Even now, failure to monitor cuff pressure can result in high pressures [19]. Thin-walled, lowpressure, high-volume cuffs should preclude this problem although it is suggested that the high-volume cuffs are associated with a higher incidence of sore throat due to the greater surface area of cuff-tracheal contact. This is despite the fact that the actual mucosal damage is less than with low-volume cuffs [10, 20– 24]. Paradoxically, Loeser et al. showed that uncuffed tubes were also associated with sore throat, so the cuff is not the entire problem [25]. There can be little argument with Stenqvist et al.’s demonstration of minimal changes in ventilator pressures during routine anaesthesia using tubes as small as 6.0 mm [8]. Spontaneous breathing through a tracheal tube during anaesthesia is a largely redundant technique with the advent of the LMA and most healthy patients can cope with a few minutes’ breathing through a small tube at the end of anaesthesia. Smaller tubes may be easier to insert, including using fibreoptic endoscopy, as the view of the larynx during passage of the tube is subjectively better [26]. Insertion is likely to be less traumatic and there is an association between larger tubes and glottic and tracheal damage, particularly in women [27, 28]. Computed tomographic imaging six months after intubation has demonstrated some degree of laryngeal abnormality including tears, scars and laryngocoeles in 86 of 100 patients, although the clinical implications of these findings are unclear [12]. For anaesthesia, these arguments all favour the use of a smaller tube, hence the logical move in this direction. In the intensive care unit (ICU) population, however, the purpose and duration of intubation is often very different compared with that during anaesthesia. In the ICU, patients may require tracheal intubation for a longer Anaesthesia 2012, 67, 815–822

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