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HEART CHAMBER PRESSURES
www.propofology.com
Dr. David Lyness
@Gas_Craic
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Pulmonary Capillary Wedge Pressure is an indirect measurement of left atrial pressure.
It is measured by inserting balloon-tipped, multi-lumen catheter (Swan-Ganz catheter) into a peripheral vein (e.g., jugular or femoral vein), then advancing the catheter into the right atrium, right ventricle, pulmonary artery, and then into a branch of the pulmonary artery.
Just behind the tip of the catheter is a small balloon that can be inflated with air (~1 cc).
The catheter has a lumen (port) that opens at the tip of the catheter distal to the balloon.
This port is connected to a pressure transducer.
When properly positioned in a branch of the pulmonary artery, the distal port measures pulmonary artery pressure (~ 25/10 mmHg).
The balloon is then inflated, which occludes the branch of the pulmonary artery.
When this occurs, the pressure in the distal port rapidly falls, and after several seconds, reaches a stable lower value that is very similar to
left atrial pressure (mean pressure normally 8-10 mmHg).
The pressure flucuates during the cardiac cycle and normally shows a, c and v waves.
The balloon is then deflated. The same catheter can be used to measure cardiac output by the thermodilution technique.
The pressure recorded during balloon inflation is similar to left atrial pressure because the occluded vessel and its distal branches that eventually form the pulmonary veins act as a long catheter that measures the blood pressures within the pulmonary veins and left atrium.
Can be helpful to measure PCWP to diagnose the severity of LVF and to quantify the degree of mitral valve stenosis.
PCWP is also important to measure when evaluating pulmonary hypertension.
Aortic valve stenosis and regurgitation, and mitral regurgitation also elevate LAP.
When these pressures are above 20 mmHg, pulmonary edema is likely to occur.
Note that LAP is the outflow or venous pressure for the pulmonary circulation and therefore increases in LAP are transmitted almost fully back to the pulmonary capillaries thereby increasing their hydrostatic pressure and filtration of fluid.
PCWP is also important to measure when evaluating pulmonary hypertension.
Pulmonary hypertension = increased pulmonary vascular resistance.
To calculate this, pulmonary blood flow (thermodilution technique), pulmonary artery pressure and PCWP measurements are required. Pulmonary hypertension can also result from increases in pulmonary venous pressure and pulmonary blood volume secondary to LVF or mitral/aortic valve disease.
PCWP can be useful for fluid delivery. Historically used to maintain PCWP between 12-14 mmHg via fluid bolus - this is increasingly considered a poor strategy.
PCWP can be useful for fluid delivery. Historically used to maintain PCWP between 12-14 mmHg via fluid bolus - this is increasingly considered a poor strategy.
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