How does positive-pressure ventilation affect cardiac output Quizlet
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Airway pressure rises, the intrapleural pressure rises. Intrathorasic blood vessels become compressed, causing the central venous pressure (CVP) to increase. Increase in CVP reduces the pressure gradient between systemic veins and the right side of the heart, which reduces venous return to the right side of the heart and thus right ventricular filling (preload). Right ventricular stroke volume decreases. On expiration, the intrathoracic pressure returns towards zero so that venous return will increase. If PEEP is applied, positive intrathoracic pressure continues to inhibit venous return through expiration. Decreases in cardiac output can occur in normovolemic patients with levels of PEEP >15 cm H2O. The reduced collapsibility of the inferior vena cava often seen with ventilation and PEEP is a clear indicator of a degree of venous stasis. Fluid administration improves venous return and cardiac output but at the cost of increased central venous pressures (CVP) and hence increased end-capillary pressures in the lungs and other organs. Effects of positive pressure on the central veins and right atrium The positive pressure in the chest decreases venous return by decreasing the effective central venous pressure, and thereby decreases right ventricular preload. That may sound odd. In fact in the CVP measurement chapter the completely opposite is stated. How can both be true? The CVP measurement certainly increases with increased PEEP. However, one must remember that our transducer tip is positioned in the SVC, and thus measures both the pressure inside the vein, and the pressure from the thoracic cavity which is transmitted to the transducer. The combination of these pressures is greater than the CVP alone; hence the measured CVP will appear to be higher. •Headache (pressure in the head) •Altered mental status (hypoxia, hypercapni, acidosis) •Motor disturbances (drowsiness, forgetfulness, irritability) •Ocular abnormalities (swelling around the optic nerve at the back of the ey) Recommended textbook solutions
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How does positiveThey concluded that positive-pressure ventilation restricted the filling of the right ventricle because the elevated intrathoracic pressure (ITP) restricted venous flow into the thorax and, thereby, reduced cardiac output.
How does positivePositive pressure in the thorax during ventilation impedes venous blood return to the right side of the heart, decreasing cardiac output. Excessive ventilation rates during positive pressure ventilation result in a decrease in cardiac output and perfusion.
How does positiveA. There is no effect on cardiac output because positive-pressure ventilation is the act of normal breathing.
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