Hemodynamics--Central Venous Pressure (CVP) and Pulmonary Artery Wedge Pressure (PAWP)

author: Karry | Engineer of International Sales | UTECH

2024-04-22

"Central venous pressure" (CVP) is the pressure of the superior and inferior vena cava into the right atrium and can be directly measured by placement of a central venous catheter with a normal range of 6-12cmH2O."Pulmonary artery wedge pressure" (PAWP) indicates the lateral pressure of blood flowing through the pulmonary circulation to pulmonary artery vessels. The normal range is 6~12mmHg, both of which are commonly used in clinical hemodynamic monitoring, and are of great significance for the evaluation of volume status and cardiac function.

Central venous pressure (CVP)

CVP is an indicator of patient volume assessed by an inserted venous catheter. The central venous catheter was inserted through the terminal vein or into the central vein (Figure 1). The waveform and real-time data of the CVP are connected to the monitor via a venous catheter (Figure 2).

Pulse oximeter

Figure 1

Pulse oximeter

Figure 2

Interpretation of the CVP waveform:

Number	name	position	Clinical role and significance
1	a wave	Located after the P wave of the ECG	Reflecting the right atrial systolic function, its effect is to drain blood to the right ventricle at the end of right ventricular diastole.
2	c wave	Following the QRS wave	It is the right ventricular contraction, the tricuspid valve closure and penetration into the right atrium, leading to a transient increase in the right atrial pressure.
3	x wave	After the c wave	As the right ventricle continues to contract, the right atrium begins to relax, causing a rapid decline in the right atrial pressure.
4	v wave	Located after x wave	Is the result of right atrial relaxation, rapid filling.
5	y wave	Located after v wave	Is due to the opening of the tricuspid valve and the rapid emptying of the right atrium.

The increase of CVP does not reflect the change of cardiac output, and the higher the CVP, the lower the cardiac output.Therefore, the change of CVP should be analyzed in combination with the change of cardiac output (Table 1).

Studies have shown that extreme CVP values help determine responses in the body.Avoid liquid fluids may be wise when CVP is significantly elevated.Some experts point out that to keep CVP as low as possible, because elevated CVP may lead to organ dysfunction.Therefore, CVP can be reduced during the stabilization and recovery periods with safe tissue perfusion.

Table 1 Association between central venous pressure and rehydration

No.	CVP	BP	C ause	Principle of Management
1	low	low	The blood volume was severely inadequate	Full rehydration
2	low	normal	hypovolemia	Appropriate rehydration
3	High	low	Cardiac insufficiency or a relatively excessive blood volume	Give heart tonic drugs to correct acidosis and relax blood vessels
4	High	normal	Excessive volume vasoconstriction	Diastolic blood vessels
5	normal	low	Cardiac insufficiency or hypovolemia	Rehydration test (· Rehydration test: 250ml of isotonic saline, intravenous injection within 5 to 10 minutes.If blood pressure increases and central venous pressure remains unchanged, indicating blood volume insufficiency: if blood pressure is unchanged and central venous pressure increases 3 ~ 5cmH2O indicating cardiac insufficiency)

Pulmonary artery wedge pressure (PAWP)

Since the valve is not present between the pulmonary vein and the left atrium, the left atrial pressure can be inversely transmitted to the pulmonary capillaries through the pulmonary vein.PAWP can estimate the pulmonary circulation status and left ventricular function, identify cardiac or pulmonary pulmonary edema, determine the therapeutic effect of vasoactive drugs, diagnose hypovolemia, and determine the effect of blood transfusion, infusion, etc.

During the placement of the pulmonary artery catheter (PAC), continuous pressure changes can be recorded with the position of the catheter end (Figure 3).

Pulse oximeter

The pulmonary artery catheter can be placed about 20 cm through the internal jugular vein, the tube end reaches the right atrium, and recorded in the low flat section of the right chamber pressure waveform; the balloon is inflated, the PAC flows into the right ventricle through the tricuspid valve.When the catheter tip reaches the right ventricle, the pressure rises sharply, then the descending branch quickly drops down to near zero, when the typical right ventricular waveform (RVP) will appear.

When the implantation depth reached 35 cm, the catheter entered the pulmonary artery (PAP).At this time, the systolic blood pressure changed little, but the diastolic blood pressure increased significantly, which is larger than the right ventricular diastolic pressure, manifested as the pulmonary artery pressure waveform.By advancing the catheter, the pulmonary artery branch is embedded and the PAWP waveform appears (Figure 4).

Pulse oximeter

Interpretation of the PAWP waveform:

Number	Waveform name	Position	Clinical significance and role
1	a wave	Located after the P wave of the ECG	Reflecting the right atrial systolic function, the pulmonary artery pressure increased sharply.
2	c wave	Following the QRS wave	It is the right ventricular contraction, the tricuspid valve closure and penetration into the right atrium, resulting in a transient increase in the right atrial pressure, when the pulmonary artery pressure increases slightly.
3	v wave	After the c wave	As the right ventricle continues to contract, the right atrium begins to relax, and the pulmonary artery pressure increases sharply again.

Comparison of CVP and PAWP

	CVP	PAWP
Reflect indicators	Right ventricular preload	Left ventricular preload
normal value	5-12 mmH2O	6-12 mmHg
measuring position	precava	Branch of pulmonary arterioles
The puncture of blood vessels	Internal jugular vein, external jugular vein, and Femoral vein, and subclavian vein	Internal jugular vein, femoral vein, and subclavian vein
catheter	Central venous catheter, pulmonary artery catheter (Measured simultaneously with the PCWP)	PAC (Swan-Ganz Catheter)
Outlier significance	<5 mmH 2O: Insufficient circulation capacity >12 mmH 2O: cardiac insufficiency or capacity overload	<6 mmHg: possible hypovolemia > 18 mmHg: usually reflecting left heart failure > 25 mmHg: possible acute pulmonary edema
influencing factor	Circulating blood volume, venous tension, myocardial contractility, intrathoracic pressure, pulmonary circulation resistance, pericardiac pressure, (such as pericardial disease), other factors, such as catheter blockage, etc.	Mitral valve disease, left atrial mass, pulmonary vein occlusive Disease, mechanical ventilation (PEEP), pulmonary hypertension, and hypovolemia.
clinical application	Guidance for fluid infusion and blood transfusion; To determine the therapeutic effect of vasoactive drug therapy: > 16 cmH2O, infusion should be careful or suspended infusion or the application of drugs to adjust the cardiac function	Estimate the pulmonary circulation status: Evaluation of left ventricular function to identify cardiogenic or pulmonary pulmonary edema: Determine the therapeutic effect of vasoactive drugs; Evaluation of blood volume status; Judge the effect of blood transfusion, infusion, etc. To determine the therapeutic effect of vasoactive drugs; to evaluate the blood volume status;