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Online ISSN 1827-1596
Tartari S., Poole D., Bocchi A., Sgarbi A., Alvisi R.
Università degli Studi - Ferrara Dipartimento di Scienze Biomediche e Terapie Avanzate Sezione di Anestesia e Rianimazione (Direttore: Prof. R. Alvisi)
Aim. The aim of this study was to evaluate and compare the parameters for mechanical respiration in pediatric patients undergoing controlled ventilation with a laryngeal mask (LM) and an uncuffed orotracheal tube.
Methods. The study examined 100 ASA 1 patients undergoing general anesthesia with myoresolution and mechanical ventilation using a Servo Ventilator 900 (constant flow, 25% insufflation, 10% teleinspiratory pause, tidal volume 10 ml/kg). All patients were divided into 2 groups matched for age and weight. An uncuffed orotracheal tube was used in one group (Group T) and a laryngeal mask (LM) in the other (Group M). The following parameters were measured: peak and pause pressure in the respiratory passage (Paw), total inspiratory resistance (R tot), compliance (C) and air loss expressed as a fraction of inspired volume (Vi-Ve/Vi). The statistical analysis of results was performed using Student’s “t”-test and the level of significance was p<0.05.
Results. Peak pressures were comparable in the two groups and were lower than the pressure needed to open the lower esophageal sphincter. These values could be further reduced by the extension of insufflation time achieved by abolishing the teleinspiratory pause included in the study to measure air resistances and compliance. Air losses were also similar in both groups, being respectively 13 and 11%. This means that environmental pollution using LM was not greater than with the uncuffed tube and confirms that, even with the latter, the protection of the airways cannot be regarded as absolute. Total inspiratory resistances were respectively 16.1 cm H20/l/sec in group T and 15.1 cm H20/l/sec in group M. This occurred in spite of the fact that the latter showed an in vitro capacity to oppose lower resistances compared to the corresponding tubes given that it was shorter with a larger diameter. Studies using the mechanical model did not include the laryngeal mask-larynx connection which may cause increased resistance owing to the variable position of the epiglottis, although this cannot be identified clinically.
Conclusions. The laryngeal mask allows mechanical ventilation with low pressure in the respiratory passage and reduced air losses compared to the uncuffed tracheal tube. The risk of gastroesophageal insufflation is therefore minimal and artificial ventilation is reliable, if correctly performed. Lower levels of inspiratory resistance might be an advantage in spontaneous breathing owing to the consequent reduction of respiratory effort, but they do not appear to be significantly lower than with the tracheal tube.