Pulmonary Capillary Wedge Pressure

Anatomy and Physiology

To measure the PCWP, a catheter is inserted through a central vein (either femoral, subclavian, or internal jugular) and advanced into the superior or inferior vena cava to reach the right atrium. The internal jugular vein is the preferred access.[4] From the right atrium, the catheter is advanced through the tricuspid valve into the right ventricle. Once in the right ventricle, the catheter is advanced to the right ventricular outflow tract, then to the pulmonary artery after crossing the pulmonic valve. The tip of the catheter lies in the main pulmonary artery, where the balloon can be inflated for measurement of the pulmonary capillary wedge pressure. In most cases, the PCWP is also an estimate of left ventricular end-diastolic pressure (LVEDP). The normal pulmonary capillary wedge pressure is between 4 to 12 mmHg. Elevated levels of PCWP might indicate severe left ventricular failure or severe mitral stenosis.

The location of the catheter can be determined by the waveform on the monitor or by measuring both the systolic and the diastolic pressure with the tip of the catheter. In the right atrium, both the diastolic and the systolic pressure are usually less than 5 mmHg (with mild variations). While in the right ventricle, the systolic pressure is about 25 mmHg, and the diastolic pressure remains similar to right atrial diastolic pressure (<5 mmHg). In contrast, the pulmonary artery systolic pressure is similar to the right ventricular systolic pressure in the absence of pulmonic stenosis, but the diastolic pressure increases to about 10 mmHg.

Indications

Measurement of the PCWP

• Differentiate between cardiogenic pulmonary edema and noncardiogenic pulmonary edema[5]
• Confirm the diagnosis of pulmonary arterial hypertension[6]
• Assess the severity of mitral stenosis[7]
• Differentiate between different forms of shock[8]
• Measure key hemodynamic parameters and assess response to therapy

Contraindications

Absolute Contraindications[9]

• Right-sided endocarditis
• Tumors or masses on the right side of the heart
• Lack of consent

 Relative Contraindications

• Tricuspid or pulmonary valve disorders
• Left bundle branch block, as there is a chance of precipitating complete heart block[10]

Equipment

The PA catheter or Swan-Ganz catheter is usually between 60 to 110 cm in length and around 4 to 8Fr in caliber. It was named after its inventors, Jeremy Swan and William Ganz.[11]

Most PA catheters have 4 separate lumens, each of which serves individualized functions.

• The proximal lumen or blue port is located in the right atrium and measures the right atrial pressure. It can also be used to administer medications. Some PA catheters might have a separate lumen designated for infusing drugs.
• The distal lumen or yellow port is located at the distal end of the catheter and resides in the pulmonary artery. It is used to monitor PA pressures and to obtain a mixed venous sample. Medications and infusions should not be inserted through this port.
• The red port is for balloon inflation and deflation. The balloon sits approximately 2 cm from the distal end of the catheter. Each PA catheter is accompanied by a 1.5 ml syringe used to inflate or deflate the balloon. The inflated balloon helps to guide the catheter from the right atrium into the PA by following intracardiac blood flow. The inflated balloon also helps to measure the PCWP.
• Temperature or thermistor is used to measure core temperature in the pulmonary artery. This helps to measure the cardiac output via the thermodilution method.

Technique or Treatment

Before performing any procedure, it is important to perform a time-out. During the time out, the healthcare team performing the procedure should 1) verify the patient details, 2) confirm the procedure and site, 3) ensure patient consent, 4) ensure normal labs, 5) review patient medications, and 6) ensure appropriate personnel and equipment are at the bedside. The most common vein accessed for the RHC is the internal jugular vein. Usually, an ultrasound is used for locating the vein and guiding the needle. The ultrasound also helps to assess the location of the nearby artery to confirm the patency of the vessel and to ensure that there is no thrombus inside the vessel lumen. Though it can be performed without an ultrasound as well, imaging guidance has shown to decrease complications.[12][13][14]

The first step of the procedure is to clean the area with an antiseptic solution, and the patient is draped to make a sterile working field. Using a vascular probe, the position of the vessel is confirmed again. Following this, local anesthesia is provided at the site of insertion. The central vein is then punctured with the needle provided, and a guidewire is introduced into the vein by the Seldinger technique. The ultrasound can be used to confirm the location of the guidewire inside the vein. After the guidewire is confirmed to be in place, the needle is removed. A scalpel blade is then used to make a 3 to 4 mm incision adjacent to the guidewire to ensure easy passage of the dilator. Care should be taken not to cut the guidewire. An 8.5 Fr dilator with an introducer sheath is inserted over the wire into the vein. The wire and dilator assembly should then be removed together as a unit leaving the introducer sheath in place. Once the introducer sheath is in position, the pulmonary artery (PA) catheter is inserted through it and advanced up to 20 cm. This should place its distal tip within the right atrium, which can be confirmed on the monitor with a right atrial pressure waveform. Once the position inside the right atrium is confirmed, the balloon is then inflated with air using the 1.5 mm syringe. The catheter is then advanced into the right ventricle and then into the pulmonary artery. The advancements are confirmed by checking the appropriate waveforms and pressures on the monitor. Once the catheter is advanced into the pulmonary artery to the point where the waveform changes into a wedge form, the balloon should be deflated. The catheter will then show the PA pressures. After obtaining the appropriate PA pressures, a PCWP/pulmonary artery occlusion pressure can now be measured. This is done by inflating the balloon slowly while observing the monitor. The balloon is inflated only until the PA pressure waveform changes into a wedged waveform. When the balloon is inflated, it creates a static column of blood between the artery distal to the catheter and the pulmonary vein. This post-capillary pressure, known as the PCWP, is an indirect estimate of the pressure in the left atrium. Once the procedure is done, a chest X-ray should be ordered to confirm the position of the catheter and to check for any complications. The tip of the PA catheter should not extend beyond 2 cm of the hilum and is usually within the mediastinal shadow.[15]

The utility of RHC is dependant on the accuracy and completeness of the data obtained. Essential measurements during the procedure include: 

• Oxygen saturation (superior vena cava, inferior vena cava, pulmonary artery, sinoatrial)
• Right atrial pressure
• Right ventricular pressure
• Pulmonary artery pressure
• Left heart filling pressure (wedge pressure, left atrial pressure, or LVEDP)
• Cardiac output/cardiac index
• Pulmonary vascular resistance
• Systemic blood pressure
• Heart rate
• Response to acute vasodilators

Misinterpretation of the wedge pressure is a common pitfall in the invasive diagnosis of pulmonary hypertension. The wedge pressure should be measured at end-expiration and in several different segments of the pulmonary vasculature. LVEDP should be obtained if there is any doubt about the accuracy of the wedge pressure tracing or if the results are unexpected in a given patient. A fluid challenge may be necessary to elicit the presence of diastolic dysfunction.

Of note, operators should proceed early with trans-septal LA catheterization for patients with mitral valve disease or prior mitral valve replacement.

Complications

Pulmonary artery catheterization is an invasive procedure that carries innate risks. Several complications have been described following the procedure, with studies noting the occurrence of complications is between 5% and 10%.[16]

The most common complications that can occur as a result of this procedure include: arrhythmias, thromboembolism, pulmonary ischemia, hemoptysis, pulmonary hemorrhage, perforation of the pulmonary artery, knotting of the catheter, arterial puncture, hematoma, and local infection can occur during or after the procedure.[17][18]

Clinical Significance

As mentioned before, PCWP is a reasonable surrogate marker of left atrial pressure and LVEDP. It is helpful to measure PCWP to diagnose the severity of left ventricular failure and quantify the degree of mitral valve stenosis. By measuring PCWP, the clinician can titrate the dose of diuretic drugs and other drugs used to reduce pulmonary venous and capillary pressure, thereby reducing pulmonary edema. Therefore, it can also guide therapeutic efficacy. 

It is also used to evaluate and diagnose pulmonary arterial hypertension (PAH), as patients with group 1 PAH will have PCWP ≤ 15 mmHg.[19] Furthermore, it is used in the calculation of pulmonary blood flow along with pulmonary artery pressure. 

PCWP is also useful in differentiating cardiogenic shock (PCWP > 15 mmHg) from non-cardiogenic shock (PCWP ≤ 15 mm Hg). It is also used to evaluate blood volume status to guide fluid administration during hypotensive shock, where the PCWP goal should be maintained between 12 to 14 mmHg.

Enhancing Healthcare Team Outcomes

Pulmonary capillary wedge pressure is an integrated measurement of the compliance of the left side of the heart and the pulmonary circulation. The measurement of PCWP can be useful in several diagnostic settings. However, since it involves an invasive procedure, a thorough understanding of the equipment, its indications and contraindications, is vital for all healthcare professionals involved in this procedure. There are several guidelines published which help to identify the role of pulmonary artery catheterization in a particular setting.[20] [Level 1] A basic understanding of the technique can also help the ancillary staff provide appropriate support to the operator performing the procedure and ensure all necessary precautions are taken. Such a team approach can help minimize complications and improve patient outcomes.