Central venous pressures and pulmonary arterial pressures are measured when it is necessary to know

a) whether enough blood is available to the right heart,

b) if enough blood is available to the left heart,

c) if the heart is capable of pumping the blood through the $ pulmonary and peripheral vascular bed

d) how much left ventricular myo-cardial wall stress will be required to pump the blood.

Central venous pressure (CVP) is usually measured in the right atrium. The catheter tip may lie in the right atrium close to the

tricuspid valve, somewhere else in the right atrium, or in the superior vena cava. Although there are no valves between the tricuspid valve and the vena cava, one must realize that, during diastole, the mean pressure is a little higher in the vena cava than in the right atrium close to the tricuspid valve; otherwise blood would not flow. When the catheter enters the atrium, one y even find a negative pressure. If the patient is not supine and horizontal, the hydrostatic pressure between the catheter tip and the right atrium influences the pressure. The patient's position, therefore in this case as well, has to be taken into account.

In order to find the proper location of the catheter, look at the aP-wave. If the catheter is to be placed in the right atrium, place it where the P-wave amplitude peaks.

Other cardiac pressures may be measured by means of a flow directed balloon Swan-Ganz catheter.

The Swan-Ganz catheter is inserted in one of the veins mentioned below:

the internal jugular vein

the subclavian vein

the femoral vein

the radial vein

Each of these veins have direct access to the vena cava, leading to the heart chambers on the right side of the heart.

When the catheter is inserted, the inflated ballon located at the catheter tip causes the catheter to follow the blood flow through the right heart chambers to the pulmonary artery and capillaries.

The catheter is advanced through the vena cava to the right atrium. The pressure (RAP right atrial pressure) is low because the pressure produced during the ventricular systole is blocked by the closed tricuspid valve. It is in magnitude similar to the ventricular diastolic .pressures.

When the catheter is further advanced through the tricuspid valve to the right ventricle, the range of the pressure (RVP = right ventricular pressure) excursion on the pressure monitor will greatly increase in response to high systolic and low diastolic pressure.

NB! The right ventricle is the chamber of the right heart where catheter tip location is easiest to recognize due to the relatively large pressure variations, variations between systolic and diastolic pressures.

As the catheter tip advances into the pulmonary artery, the pulmonary valve closes during diastole and prevents the pressure in the pulmonary artery (PAP) from dropping to as low a level as* it does in the right ventricle. During systole the pulmonary valve is open and distal catheter lumen is presented with the same high pressure in the PA (pulmonary artery) as in the RV (right ventricle).

PI With the balloon still inflated, the catheter is further advanced until a pulmonary capillary wedge (PCWP) pressure is recorded. The pressure in the central pulmonary artery is blocked off and

A the mean pulmonary capillary wedge pressure generally drops to a level slightly less than the PA (pulmonary arterial) diastolic pressure. The pulmonary capillary wedge pressure permits, within

Ml limits, measurement of the left ventricular end diastolic pressure. The reason why this is possible is that the Swan Ganz catheter is a flow-directed catheter equipped with balloons which

• can be either inflated or deflated. When the inflated balloon lodges in a smaller branch of the pulmonary artery it occludes

• that branch. As the pressure is measured distal to the occlusion,

• the registered pressure reflects the pressure in the left atrium.

The importance of the PCWP (pulmonary capillary wedge pressure is that since it normally closely approximates the pressure in _ the left ventricle during end diastole, it provides one means of measuring how well the left ventricle is functioning.

I As soon as the PCWP has be recorded, the balloon is deflated and continuous monitoring can be carried out. It is of course very important to make sure that the catheter has been secured in B place at the entry site. It is furthermore recommended to follow the ECG while the insertion takes place. This is due to the fact that the catheter may become an active electrode while in the heart; in which case, very little current produces depolarization,

an extra systole or even ventricular fibrillation. Location of the catheter tip by means of an X-ray is sound practice whenever assurance is needed that the catheter tip is , properly placed. Naturally the characteristic pressure waveforms seen on the pres-jSure monitor confirm the location of the catheter as well.

The reason for monitoring various pressures is to secure an adequate blood supply, thereby also an adequate cardiac output. As is the case with arterial blood pressure, various factors affect blood supply to the heart and relevant vessels.


Keywords:Central venous pressures , pulmonary arterial pressures ,right heart,left heart,pumping the blood ,right atrium,tricuspid valve,superior vena cava, diastole,P-wave amplitude peak, cardiac pressures ,internal jugular vein, subclavian vein ,femoral vein,radial vein,right ventricle, pulmonary artery ,pulmonary capillary wedge ,left atrium,blood supply,heart, relevant vessels.