Resp Care
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Comparative Study Clinical Trial Controlled Clinical Trial
The effects of pressure control versus volume control assisted ventilation on patient work of breathing in acute lung injury and acute respiratory distress syndrome.
Patient work of breathing (WOB) during assisted ventilation is reduced when inspiratory flow (V(I)) from the ventilator exceeds patient flow demand. Patients in acute respiratory failure often have unstable breathing patterns and their requirements for V(I) may change from breath to breath. Volume control ventilation (VCV) traditionally incorporates a pre-set ventilator V(I) that remains constant even under conditions of changing patient flow demand. In contrast, pressure control ventilation (PCV) incorporates a variable decelerating flow wave form with a high ventilator V(I) as inspiration commences. We compared the effects of flow patterns on assisted WOB during VCV and PCV. ⋯ In the setting of ALI and ARDS, PCV significantly reduced patient WOB relative to VCV. The decrease in patient WOB was attributed to the higher ventilator peak V(I) of PCV.
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Positive end-expiratory pressure (PEEP) may interfere with accurate assessment of cardiac function. PEEP may decrease left ventricular volume by lowering the transmural gradient between ventricular and pleural surface pressure (P(PL)) around the heart while raising the absolute pulmonary arterial occlusion pressure (PAOP). Clinical formulas used to predict the transmural PAOP (PAOP(TM)) require subtracting 25-50% of the PEEP level from the PAOP. However, both PAOP and P(PL) are influenced by transmitted PEEP and transmitted intra-abdominal pressure (IAP). We compared PAOP(TM) calculated by measuring intra-esophageal pressure (P(ES)) with PAOP(TM) estimated by clinical formulas. ⋯ PAOP(TM) calculated by P(ES) may reflect transmitted IAP to the pleural surface. Using P(ES) to calculate PAOP(TM) may provide a more accurate assessment of hemodynamic status than predicting PAOP(TM) using clinical formulas based solely on estimated PEEP transmission.
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Blood gas analysis is extremely important in perioperative management of neonates with congenital heart disease, where ventilator manipulation of the pulmonary vascular resistance is crucial. Delays in blood gas analysis resulting from transport of samples to a central laboratory may compromise management of these patients. Furthermore, neonates with congenital heart defects may have lower arterial oxygen (PaO2) levels due to intracardiac right-to-left shunting. We evaluated the Sensicath System in neonatal patients following cardiac surgery by simultaneously measuring specimens on the central laboratory blood gas analyzer. ⋯ When compared to a Corning 855 blood gas analyzer, the Sensicath System was found to provide acceptable blood gas values, with no iatrogenic blood loss. This system may be especially helpful in infants with congenital heart defects, since rapid results are necessary for optimal patient care.