Changes in breathing pattern and respiratory muscle performance parameters during difficult weaning


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Abstract

ObjectiveThis study examined, using nonlnvaslve means, the changes in breathing pattern and inspiratory muscle pressure-time indices during difficult progressive withdrawal of pressure-support ventilation.DesignA prospective analysis of the temporal evolution of several respiratory variables in difficult-to-wean patients.SettingA university hospital intensive care unit.PatientsA heterogeneous group of 17 patients receiving prolonged mechanical ventilation.InterventionsDaily measurements of breathing pattern and respiratory muscle performance parameters in difficult-to-wean patients.Measurements and Main ResultsWe examined breathing pattern variables, rapid shallow breathing (respiratory rate/tidal volume), tracheal occlusion pressure, maximal Inspiratory pressure (PI max), and the tension-time index of the inspiratory muscles (TTmus = PI/PI max x Ti/Ttot) (where Ti/Ttot is inspiratory fraction of the cycle). All measurements were repeated at 24-hr intervals throughout the difficult weaning period. The patients were extubated on satisfying ten of 12 classical weaning criteria.Eleven patients were successfully weaned from mechanical ventilation while six patients were not.Weaning failure was associated with the following: a) longer periods of mechanical ventilation before weaning; b) high values of tracheal occlusion pressure, respiratory rate, minute ventilation, and effective impedance maintained throughout the difficult weaning period; and c) persistent high PaCO2 and intrinsic positive end-expiratory pressure values. As the weaning failure patients' inspiratory muscles confronted an increasing inspiratory load, values of the tension-time index of the inspiratory muscles entered or remained in the fatigue zone. In contrast, weaning success patients normalized their breathing pattern and decreased their tracheal occlusion pressure, effective impedance, and tension-time index values.ConclusionsBreathing pattern alterations and respiratory muscle performance impairments lead to ventilator dependency after prolonged mechanical ventilation. The measurement of variables such as the noninvasive tracheal occlusion pressure, inspiratory power of breathing, and tension-time index of the inspiratory muscles facilitate the management of difficult-to-wean patients. (Crit Care Med 1998; 26:79-87)

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