Inspiratory work imposed by continuous positive airway pressure (CPAP) machines: the effect of CPAP level and endotracheal tube size

Abstract

Inspiratory work imposed by Continuous Positive Airway Pressure (CPAP) machines has been a matter of concern. The imposed inspiratory work of CPAP machine circuits (Wcir) and the effect of the total breathing apparatus with endotracheal tube (ETT) and connector included in the circuit (Wapp), were measured in three continuous flow (CF) and various configurations of three demand flow (DF) CPAP machines. The performance was assessed at 0, 5, 10 and 15 cmH2O CPAP using a Michigan Instruments Test Lung Model 1600, internal compliance set at 50 ml/cmH2O, driven at square wave inspiratory flows (VI) of 20, 40 and 60 l/min at a tidal volume of 500 ml. Work, expressed in mJ/l, was calculated from the area of pressure-volume loops. Inspiratory work, Wcir and Wapp, was dependent upon the particular CPAP machine, VI and ETT size, but not upon CPAP level, being maximum at VI 601/min and with ETT 7.0 mm i.d. Work values (Wcir) varied from 50 to 325 mJ/l with both CF and DF machines and up to 1100 mJ/l with ETT and connector (Wapp). No consistent advantage of CF over DF machines was demonstrated. There was little advantage of high gas flows (greater than 5 l/min) in various DF circuits. Within an individual machine maximum negative pressures generated during inspiration correlated with both Wcir and Wapp.

Bench testing of pressure support ventilation with three different generations of ventilators

“…Most experimental and clinical studies designed to test trigger sensitivity have focused on comparisons among the different available systems for a given ventilator. Continuous positive airway pressure systems have been compared on different ventilators [16,17,18,19,20], whereas only a few studies evaluating trigger performance of ICU ventilators are currently available [10]. Recently, Williams et al reported a bench test study in which the performance of seven ventilators, set in PSV mode, were tested under different conditions [10].…”

Ventilación con liberación de presión en las vías respiratorias (APRV): un enfoque para su uso correcto

“…Sin embargo, en la lesión pulmonar aguda/síndrome de dificultad respiratoria aguda, el área de superficie disponible para el intercambio de gases se reduce significativamente, aquí, la presión positiva de la vía aérea sola puede ser inadecuada para lograr la eliminación necesaria de CO2 sin producir un trabajo respiratorio excesivo. A diferencia de la presión positiva continua de la vía aérea (CPAP), el APRV interrumpe brevemente la presión de la vía aérea para complementar la ventilación espontánea por minuto y evitar la acumulación de CO2 [11], con esto se disminuye el poder mecánico pulmonar. El PM se relaciona directamente con el daño a nivel alveolar secundario al uso de ventilación mecánica invasiva; Gattinoni et al, describe que el PM aumenta de manera exponencial con volúmenes tidales elevados, aumentos en la frecuencia respiratoria y en la presión de conducción de la vía aérea; el uso del APRV busca disminuir estas variables al mantener los alveolos abiertos y con mínimo movimiento [12].…”

Optimizing Patient-Ventilator Synchrony

“…Several triggering strategies may be employed to improve patient-ventilator synchrony. A number of studies have compared pressure triggering (PT) and flow triggering (FT) during CPAP, [70][71][72][73][74][75] whereas a smaller number have examined these sensing mechanisms during SIMV, 22,76 assist control ventilation, 39 and pressure support ventilation. 39,40,77,78 The majority of these studies found a reduction in the work of breathing with FT when compared to PT, though this may not be the case when PT sensitivity is set at 0.5 or 1.0 cmH 2 O during PSV.…”