INTRODUCTION. Analysis of the shape of the airway pressure/time curve (Paw-t) during constant flow mechanical ventilation (Stress Index = SI) has been used to predict mechanical stress. The mathematical coefficient describing the shape of the Paw-t curve may therefore identify and quantify mechanical stress during ventilation. In experimental studies, the threshold values for SI that best discriminated lungs with and without morphological, histological signs and biological markers of Ventilator Induced Lung Injury ranged between 0.9 and 1.1. The implementation of a SI monitoring software on ventilator would allow an easier use and bedside access. OBJECTIVES. We compared Stress Index values collected on the ventilator using a dedicated software with the values obtained using experimental device. METHODS. The experimental device (KleisTEK Engineering, Bari, Italy) measures the flow with a pneumotacograph connected to a differential pressure transducer inserted between theY piece of the ventilator circuit and the Endotracheal Tube (ET). The Paw is measured proximal to ET. All variables are collected and the mean portion of Paw-t curve was analyzed trough the algorithm of Levemberg-Marquardt. SI is represented by the b factor of the equation: Pao=a 9 t^(b) + c. Servo-i (Maquet) have been implemented by a real time SI analysis software using measurements of flow and Paw as performed by the ventilator. Multiples measurements on different ventilation settings have been performed at the same time with the two devices (Servo-i and KleisTEK) on 10 ARDS patients. Data have been compared with the statistical analysis proposed by Bland&Altman in order to assess agreement between two SI measurement techniques. RESULTS. The strength of the relation between two variables is r = 0.92 (CI 0.9–0.93; p\0.0001). CONCLUSIONS. Statistical analysis show a good correlation and agreement in the measurements taken by the ventilator’s software than those of the reference device.
AGREEMENT OF TWO METHODS FOR ASSESSING PRESSURE/TIME CURVE PROFILE (STRESS INDEX) IN ARDS
TERRAGNI, Pierpaolo;FAGGIANO, Chiara;
2011-01-01
Abstract
INTRODUCTION. Analysis of the shape of the airway pressure/time curve (Paw-t) during constant flow mechanical ventilation (Stress Index = SI) has been used to predict mechanical stress. The mathematical coefficient describing the shape of the Paw-t curve may therefore identify and quantify mechanical stress during ventilation. In experimental studies, the threshold values for SI that best discriminated lungs with and without morphological, histological signs and biological markers of Ventilator Induced Lung Injury ranged between 0.9 and 1.1. The implementation of a SI monitoring software on ventilator would allow an easier use and bedside access. OBJECTIVES. We compared Stress Index values collected on the ventilator using a dedicated software with the values obtained using experimental device. METHODS. The experimental device (KleisTEK Engineering, Bari, Italy) measures the flow with a pneumotacograph connected to a differential pressure transducer inserted between theY piece of the ventilator circuit and the Endotracheal Tube (ET). The Paw is measured proximal to ET. All variables are collected and the mean portion of Paw-t curve was analyzed trough the algorithm of Levemberg-Marquardt. SI is represented by the b factor of the equation: Pao=a 9 t^(b) + c. Servo-i (Maquet) have been implemented by a real time SI analysis software using measurements of flow and Paw as performed by the ventilator. Multiples measurements on different ventilation settings have been performed at the same time with the two devices (Servo-i and KleisTEK) on 10 ARDS patients. Data have been compared with the statistical analysis proposed by Bland&Altman in order to assess agreement between two SI measurement techniques. RESULTS. The strength of the relation between two variables is r = 0.92 (CI 0.9–0.93; p\0.0001). CONCLUSIONS. Statistical analysis show a good correlation and agreement in the measurements taken by the ventilator’s software than those of the reference device.
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