Resistance and additional inspiratory work imposed by the laryngeal mask airway

Abstract

Laryngeal mask airways and tracheal tubes were studied to determine both their resistance to constant gas flows and additional inspiratory work during simulated inspiration. Laryngeal mask airways imposed less resistance and required lower additional inspiratory work compared with the corresponding sized tracheal tubes. If inspiratory loading during anaesthesia is an important consideration, then the laryngeal mask airway may be preferable to a tracheal tube.

The effect of introducing fibreoptic bronchoscopes on gas flow in laryngeal masks and tracheal tubes

“…Dunbav-Reid design to prevent occlusion of the lumen by the downfolded epiglottis [20]. Bhatt et (11. suggested that the mask aperture bars may impede gas flow and lead to increased resistance to breathing [8]. Our data confirm this suggestion, but we consider an increase in flow resistance of 3.6% to be clinically irrelevant.…”

“…These differences probably reflect the increased turbulence during the ventilatory cycle and differences in the measuring technique. Both Al-Hasani [lo] and Bhatt et ul., [8] used pressure transducers placed at the proximal end of the airway device and at mid-point of an artificial tracheal to calculate flow. In the current study only circuit pressures were measured.…”

“…In addition, it has been suggested that the mask aperture bars, designed to prevent the epiglottis from obstructing the lumen, may lead to increased work of breathing [8], but this has not been quantified.…”

“…In this context it has been utilised for management of the difficult airway [l], vocal cord biopsy [2], percutaneous tracheostomy [3], thyroid surgery [4] and diagnostic laryngo-bronchoscopy [5-71. Compared with equivalent sized tracheal tubes, the LMA has a relatively large internal diameter (ID) and imposes lower resistance to constant gas flow and reduced inspiratory work [8]. The LMA will also accommodate larger airway instruments and in small infants may be the only airway device large enough through which to perform laryngo-bronchoscopy [6], although very small fibreoptic scopes have been recently developed [9].…”

Comparative effects of laryngeal mask and tracheal tube on total respiratory resistance in anaesthetised patients

“…Size 3 and 4 laryngeal masks are shorter and wider than size 8 and 8.5 tracheal tubes. Bhatt and colleagues [12] reported that the resistance of size 3 and 4 laryngeal masks was non-linear and lower than that of a size 8 tracheal tube (0.053 and 0.15 kPa.l-'.s, respectively for a flow of 1 Is-'). These results are in agreement with the values of K, presented in Table 1.…”