Influência da mecânica respiratória sobre a assincronia paciente-ventilador, na ventilação com pressão de suporte, com e sem sistema de disparo e ciclagem automáticos, e na ventilação assistida proporcional

Abstract

Obtaining a good patient-ventilator synchrony is one of the biggest challenges in the management of mechanical ventilation (MV). Pressure support ventilation (PSV) is a ventilator mode widely used in the MV weaning process. Proportional assist ventilation (PAV) is a mode of ventilator support in which the ventilator generates assistance proportional and instant to the efforts of the patient. Digital Auto-TrakTM consists in a technology capable of automatically adjusting, cycle by cycle, the mechanisms of triggering and cycling in PSV mode. Objectives: To determine the influence of respiratory mechanics on patient-ventilator asynchrony during PSV mode, with and without automatic triggering and cycling system, and PAV, in a mechanic lung model and to identify patterns on ventilation curves presented on the ventilator screen, which are related to the types of asynchrony investigated. Methods: This is an experimental bench study using the mechanic lung model, ASL 5000TM. Three profiles of respiratory mechanics were studied: normal, obstructive and restrictive, with variation of neural inspiratory time of 0.5, 1.0, 1.5 and 2.0 seconds, with maximum intensity of muscle effort (Pmus) fixed in -7.5 cmH2O, during MV in PSV and PAV modes, in five ICU ventilators, with double limb, and in one single limb ventilator. Auto-TrakTM was studied when avaliable in the ventilator. Primary outcomes were: inspiratory delay time and cycling asynchrony time identifying, in the second case, two possible types, late or premature cycling. Furthermore, we proceeded to an analysis by visual inspection of the: flow, VT and Pmus curves of ASL 5000TM and the: VT, flow and pressure curves on the ventilator screen in an attempt to identify patterns associated to asynchrony that would be identified through simple observation. Results: There was a marked influence of respiratory mechanics on patient-ventilator asynchrony. The inspiratory delay time was higher and clinically significant in the obstructive profile of respiratory mechanics, and lower, many times “zero”, with the single limb ventilator. Cycling asynchrony was common in the obstructive profile, predominantly the late cycling type, while in the restrictive profile, the premature cycling type predominated. The use of Auto-TrakTM system eliminated the occurrence of auto triggering asynchrony type in the single limb ventilator. Visual analysis of the curves detected patterns of flow x time curves that are characteristic of premature and late cycling asynchrony types and which can be identified by direct visual inspection of the ventilator screen. Conclusion: Triggering and cycling asynchronies between the patient and the ventilator are the rule rather than the exception during PSV and PAV modes, which are influenced by respiratory mechanics. The use of Auto-TrakTM system showed benefit during the use of the single limb ventilator, with substantial improvement of the triggering. Visual inspection of the flow curve on the ventilator screen may favor the identification of these types of asynchrony.