Pulmonary Artery Catheter (PAC): Clinical Uses and Monitoring

A pulmonary artery catheter (PAC), commonly called a Swan-Ganz catheter, is an invasive hemodynamic monitoring device used to assess cardiovascular function in critically ill patients.

By advancing through the right side of the heart into the pulmonary artery, the catheter allows clinicians to measure pressures, evaluate cardiac output, obtain mixed venous blood, and calculate variables related to systemic and pulmonary circulation.

Although PAC use has declined because of its invasive nature and potential complications, understanding its measurements remains important for respiratory therapists and other clinicians involved in critical care and cardiopulmonary monitoring.

What Is a Pulmonary Artery Catheter?

A pulmonary artery catheter is a long, flexible, balloon-tipped catheter that is inserted into the central venous circulation and advanced through the right atrium, right ventricle, and into the pulmonary artery. Depending on the catheter design, it can provide several important hemodynamic measurements from a single device.

These measurements may include:

• Right atrial pressure or central venous pressure
• Pulmonary artery pressure
• Pulmonary capillary wedge pressure
• Cardiac output
• Cardiac index
• Mixed venous oxygen saturation
• Pulmonary vascular resistance
• Systemic vascular resistance
• Stroke volume and related derived variables

Because the catheter is positioned within the pulmonary circulation, it can provide information about right ventricular preload, right ventricular afterload, left ventricular filling pressure, cardiac performance, vascular resistance, and the balance between systemic oxygen delivery and consumption.

The PAC may be particularly useful when a patient’s hemodynamic condition is complex and cannot be adequately evaluated using routine physical examination, blood pressure monitoring, pulse oximetry, or less invasive methods.

Structure of the Pulmonary Artery Catheter

A typical adult pulmonary artery catheter is approximately 110 cm long and contains several lumens that perform different functions. Markings along the catheter, often placed at 10-cm intervals, help clinicians determine the approximate depth of insertion.

Distal Lumen

The distal lumen terminates at the tip of the catheter in the pulmonary artery. It is used to measure pulmonary artery pressure and obtain mixed venous blood samples.

Because blood sampled from the pulmonary artery contains venous blood returning from throughout the body, it provides a true mixed venous specimen. This makes the distal lumen important for evaluating mixed venous oxygen saturation and systemic oxygen extraction.

Proximal Lumen

The proximal lumen generally opens approximately 30 cm behind the distal tip. When the catheter is properly positioned, this opening lies within the right atrium.

The proximal lumen may be used to:

• Measure right atrial pressure
• Measure central venous pressure
• Inject fluid during thermodilution cardiac output measurements
• Administer compatible intravenous fluids or medications

Balloon Lumen

A separate lumen controls inflation of a small balloon near the distal tip of the catheter. The balloon allows the catheter to float through the bloodstream during insertion and permits temporary occlusion of a small pulmonary artery branch when pulmonary capillary wedge pressure is measured.

The balloon is normally kept deflated during routine pulmonary artery pressure monitoring.

Thermistor

A temperature-sensitive thermistor is positioned near the distal catheter tip. It detects changes in blood temperature during thermodilution cardiac output measurements.

Some catheters also contain a thermal filament capable of continuously estimating cardiac output without repeated cold-fluid injections.

Fiberoptic Components

Specialized PACs may contain fiberoptic technology that continuously measures mixed venous oxygen saturation. These catheters use reflected light to estimate the percentage of hemoglobin saturated with oxygen in pulmonary arterial blood.

Indications for Pulmonary Artery Catheterization

Pulmonary artery catheterization is generally reserved for critically ill patients when detailed hemodynamic information is expected to influence diagnosis or treatment.

Potential indications include:

• Severe cardiogenic shock
• Complicated hypovolemic shock
• Septic shock requiring vasoactive therapy
• Significant left ventricular failure
• Severe right ventricular failure
• Pulmonary hypertension
• Acute myocardial infarction with hemodynamic instability
• Pulmonary edema of uncertain origin
• Severe pulmonary vascular disease
• Complicated respiratory failure
• Acute respiratory distress syndrome
• Assessment of cardiac output during selected procedures or exercise testing

The catheter may also help clinicians evaluate a patient’s response to intravenous fluids, vasopressors, vasodilators, inotropic medications, mechanical ventilation, and changes in PEEP.

Its use must be justified by the clinical information it provides because pulmonary artery catheterization is invasive and carries significant risk.

Pulmonary Artery Catheter Insertion

PAC insertion is usually performed through a large central vein. Common insertion sites include the internal jugular vein, subclavian vein, femoral vein, or, in some cases, a large upper-extremity vein such as the basilic vein.

When appropriate, the patient may be placed in the Trendelenburg position before insertion. This can increase venous filling and decrease the risk of air entering the central circulation during catheter placement.

The catheter and monitoring system are prepared using sterile technique. The pressure transducer is leveled and zeroed, the catheter lumens are flushed, and the balloon is tested before insertion.

Advancement Through the Heart

The PAC is first advanced into the right atrium. Once a right atrial pressure waveform is identified, the balloon is inflated. Blood flow then carries the balloon-tipped catheter forward through the tricuspid valve and into the right ventricle.

The catheter continues through the pulmonic valve into the pulmonary artery. Further advancement with the balloon inflated eventually causes the catheter to temporarily wedge in a smaller pulmonary arterial branch.

Pressure waveforms change as the catheter passes through each chamber or vessel. These waveform changes allow clinicians to identify the catheter’s location.

The normal sequence is:

1. Right atrium
2. Right ventricle
3. Pulmonary artery
4. Pulmonary artery wedge position

Note: Once the wedge waveform has been identified, the balloon is deflated. The pulmonary artery waveform should immediately return.

Right Atrial and Central Venous Pressure

The proximal lumen of the PAC can be used to measure right atrial pressure, which closely corresponds to central venous pressure.

A typical normal right atrial or central venous pressure is approximately 2 to 6 mm Hg, although some references use an upper value of approximately 7 mm Hg.

Right atrial pressure provides information about right ventricular preload and is affected by:

• Circulating blood volume
• Venous return
• Venous vascular tone
• Right ventricular function
• Intrathoracic pressure
• Mechanical ventilation

Low CVP or Right Atrial Pressure

A low pressure may be associated with decreased circulating volume or excessive vascular dilation.

Possible causes include:

• Hemorrhage
• Dehydration
• Hypovolemia
• Shock
• Peripheral vasodilation
• Cardiovascular collapse

Note: A low CVP does not automatically confirm hypovolemia. The value must be considered along with blood pressure, urine output, heart rate, physical findings, cardiac function, and other hemodynamic measurements.

Elevated CVP or Right Atrial Pressure

An elevated pressure may occur when blood volume increases, venous return is impaired, or the right ventricle is unable to effectively pump blood forward.

Possible causes include:

• Fluid overload
• Right ventricular failure
• Pulmonary hypertension
• Pulmonary embolism
• Tricuspid valve disease
• Cardiac tamponade
• Tension pneumothorax
• Left-sided heart failure
• Positive-pressure ventilation
• High levels of PEEP

Note: Because intrathoracic pressure influences measured CVP, mechanical ventilator settings must always be considered during interpretation.

Pulmonary Artery Pressure

Pulmonary artery pressure is measured through the distal lumen while the balloon is deflated. The pressure represents the force generated within the pulmonary artery during right ventricular systole and diastole.

Typical pulmonary artery pressure is approximately 25/10 mm Hg.

Common normal ranges include:

• Systolic PAP: approximately 15 to 30 mm Hg
• Diastolic PAP: approximately 5 to 15 mm Hg
• Mean PAP: approximately 10 to 20 mm Hg

Note: Slight differences in reference ranges occur among sources and patient populations.

Pulmonary Artery Waveform

The pulmonary artery waveform contains a systolic peak, diastolic phase, and a dicrotic notch. The dicrotic notch is caused by closure of the pulmonic valve at the end of ventricular systole. Pulmonary artery systolic pressure is generally similar to right ventricular systolic pressure.

However, pulmonary artery diastolic pressure remains elevated compared with right ventricular diastolic pressure because resistance exists within the pulmonary vascular system.

Elevated Pulmonary Artery Pressure

Pulmonary artery pressure may increase when pulmonary vascular resistance rises, pulmonary blood flow increases, or pressure backs up from the left side of the heart.

Possible causes include:

• Pulmonary hypertension
• Left ventricular failure
• Fluid overload
• Mitral valve disease
• Pulmonary embolism
• Emphysema
• Pulmonary fibrosis
• Hypoxemia
• Increased pulmonary blood flow
• Congenital left-to-right shunts

Note: Positive-pressure ventilation can also raise pulmonary vascular pressures, particularly when excessive PEEP causes alveolar overdistention and compression of pulmonary capillaries.

Decreased Pulmonary Artery Pressure

Reduced PAP may occur when circulating blood volume or pulmonary blood flow decreases.

Possible causes include:

• Hypovolemia
• Hemorrhage
• Severe vasodilation
• Anaphylaxis
• Cardiovascular collapse

Note: Trends are often more clinically useful than isolated measurements.

Pulmonary Capillary Wedge Pressure

Pulmonary capillary wedge pressure, also called pulmonary artery wedge pressure, is one of the most important measurements obtained from a PAC.

PCWP provides an indirect estimate of left atrial pressure and, under appropriate conditions, left ventricular end-diastolic pressure. It is therefore used as an indicator of left ventricular filling pressure or preload.

Normal PCWP is generally approximately 5 to 12 mm Hg, although values up to around 15 mm Hg may be considered normal depending on the reference.

How PCWP Is Measured

To measure PCWP, the balloon at the distal end of the PAC is temporarily inflated. The inflated balloon travels forward until it occludes a small branch of the pulmonary artery.

Once flow is temporarily stopped, the distal catheter lumen measures pressure transmitted backward from the pulmonary venous circulation and left atrium.

Only the amount of air recommended for the catheter should be used. A typical adult balloon may require approximately 1 to 1.5 mL of air, while smaller catheters require less. The balloon should remain inflated only long enough to obtain the measurement. It must then be completely deflated.

Importance of End-Expiratory Measurement

PCWP is generally measured at end-expiration because intrathoracic pressure has the least influence on cardiovascular measurements at this point in the respiratory cycle. This is important in both spontaneously breathing and mechanically ventilated patients.

Positive-pressure ventilation and PEEP may artificially increase measured intrathoracic and vascular pressures. Therefore, wedge pressure must always be interpreted in the context of ventilator settings and respiratory mechanics.

Elevated PCWP

An elevated wedge pressure generally indicates increased left-sided filling pressure or excessive intravascular volume.

Potential causes include:

• Left ventricular failure
• Congestive heart failure
• Fluid overload
• Mitral valve disease
• Cardiac tamponade
• Constrictive pericarditis

A PCWP greater than approximately 18 mm Hg is often associated with left ventricular dysfunction or excessive fluid volume. As wedge pressure continues to rise, hydrostatic pressure within the pulmonary circulation increases and fluid may begin moving into the lung tissue.

A pressure around 20 to 25 mm Hg may be associated with interstitial pulmonary edema. Values around 25 to 30 mm Hg may produce increasing alveolar filling and clinically significant pulmonary edema.

Low PCWP

A PCWP below approximately 4 to 5 mm Hg may indicate reduced left ventricular preload.

Potential causes include:

• Hypovolemia
• Hemorrhage
• Dehydration
• Vasodilation
• Shock

Note: Other signs of reduced circulating volume may include tachycardia, hypotension, reduced urine output, poor skin turgor, and flattened neck veins.

Differentiating Cardiogenic and Noncardiogenic Pulmonary Edema

PCWP can help differentiate pulmonary edema caused by left ventricular failure from pulmonary edema caused by increased pulmonary capillary permeability.

Cardiogenic pulmonary edema is usually associated with an elevated PCWP because pressure is transmitted backward from the left ventricle and left atrium into the pulmonary circulation.

In contrast, patients with acute respiratory distress syndrome may have severe pulmonary edema despite a relatively normal PCWP. In ARDS, the primary problem is increased permeability of the alveolar-capillary membrane rather than excessive hydrostatic pressure caused by left ventricular failure.

PCWP should not be interpreted alone, but it can provide useful information when combined with chest imaging, oxygenation, physical examination, cardiac function, and other hemodynamic findings.

PAd-PCWP Gradient

The relationship between pulmonary artery diastolic pressure and PCWP may help evaluate pulmonary vascular resistance.

The calculation is:

PAd-PCWP Gradient = Pulmonary Artery Diastolic Pressure – PCWP

Normally, the gradient is approximately 5 mm Hg or less.

For example, if the pulmonary artery pressure is 35/25 mm Hg and the PCWP is 22 mm Hg:

25 – 22 = 3 mm Hg

A gradient of 3 mm Hg is within the expected range.

If the PAP is 35/25 mm Hg and the PCWP is 8 mm Hg:

25 – 8 = 17 mm Hg

This increased gradient suggests increased pulmonary vascular resistance and pulmonary hypertension.

In left ventricular failure, both pulmonary artery diastolic pressure and PCWP may rise together, leaving the gradient relatively normal. In pulmonary embolism or COPD-related pulmonary hypertension, PAP may rise while PCWP remains relatively normal, producing a larger gradient.

Cardiac Output

Cardiac output is the volume of blood pumped by the heart each minute.

The relationship can be expressed as:

Cardiac Output = Heart Rate × Stroke Volume

A normal resting adult cardiac output is approximately 4 to 8 L/min, with approximately 5 L/min commonly used as an average value.

Cardiac output may increase dramatically during exercise. In healthy adults, values of approximately 25 to 35 L/min can be reached during intense activity.

Thermodilution Cardiac Output

A thermodilution PAC measures cardiac output by observing temperature changes within the bloodstream.

A known volume of fluid, traditionally room-temperature or cooled saline, is rapidly injected through the proximal catheter port in the right atrium. The fluid mixes with blood as it passes through the right ventricle and pulmonary artery.

The thermistor near the catheter tip detects the change in blood temperature. A computer then evaluates the temperature-versus-time curve and calculates cardiac output.

Accurate measurement requires correct entry of variables such as:

• Catheter size
• Injectate volume
• Injectate temperature
• Calibration factors required by the monitoring system

Note: Multiple measurements are commonly obtained and averaged because individual thermodilution readings can vary.

Factors Affecting Cardiac Output

Reduced cardiac output can occur with:

• Hypovolemia
• Myocardial infarction
• Left ventricular failure
• Right ventricular failure
• Cardiomyopathy
• Severe arrhythmias
• Increased systemic vascular resistance
• Increased pulmonary vascular resistance

Note: Mechanical ventilation can also reduce cardiac output. High airway pressures and excessive PEEP may increase intrathoracic pressure, reduce venous return, lower right ventricular preload, and subsequently decrease left ventricular filling.

Cardiac Index

Cardiac output is influenced by body size. A cardiac output of 4 L/min may be adequate for a small patient but inadequate for a much larger patient.

Cardiac index corrects cardiac output for body surface area:

Cardiac Index = Cardiac Output ÷ Body Surface Area

A typical normal adult cardiac index is approximately 2.5 to 4 L/min/m².

A reduced cardiac index suggests that cardiac blood flow may be inadequate relative to the patient’s body size and metabolic requirements.

Pulmonary Vascular Resistance

Pulmonary vascular resistance represents the resistance the right ventricle must overcome to move blood through the pulmonary circulation. It is therefore an important component of right ventricular afterload.

Normal PVR varies somewhat by reference, but values commonly fall within approximately 50 to 250 dynes·s/cm⁵.

PVR may increase with:

• Pulmonary embolism
• Pulmonary hypertension
• Hypoxemia
• Acidosis
• Emphysema
• Interstitial pulmonary fibrosis
• Pneumothorax
• Excessive alveolar pressure
• Vasopressor therapy

Note: Pulmonary vasodilators, supplemental oxygen, inhaled nitric oxide, and treatment of the underlying cause may decrease pulmonary vascular resistance. A substantial increase in PVR increases right ventricular workload and may eventually contribute to right ventricular failure.

Systemic Vascular Resistance

Systemic vascular resistance reflects the resistance against which the left ventricle pumps. It is an important indicator of systemic afterload. A typical normal SVR is approximately 900 to 1400 dynes·s/cm⁵.

SVR may increase with:

• Systemic vasoconstriction
• Hypovolemia
• Catecholamine release
• Vasopressor therapy
• Later stages of some forms of shock

SVR may decrease with:

• Vasodilator medications
• Sepsis
• Anaphylaxis
• Other conditions producing systemic vasodilation

Note: Cardiac output, blood pressure, and vascular resistance must be interpreted together because blood pressure alone does not fully describe circulatory performance.

Mixed Venous Oxygen Saturation

Mixed venous oxygen saturation, or SvO₂, is measured from blood obtained from the pulmonary artery. A normal SvO₂ is approximately 75%, with a typical range of roughly 60% to 80%. Some references place the expected range closer to 68% to 77%.

Mixed venous oxygen tension is normally approximately 40 mm Hg. SvO₂ reflects the relationship between oxygen delivery to the tissues and tissue oxygen consumption.

Decreased SvO₂

When oxygen delivery decreases or oxygen consumption increases, the tissues extract a larger proportion of oxygen from circulating blood. The oxygen saturation of returning venous blood therefore falls.

Causes of reduced SvO₂ may include:

• Low cardiac output
• Heart failure
• Cardiogenic shock
• Hypoxemia
• Anemia
• Myocardial infarction
• Increased work of breathing
• Fever
• Seizures
• Physical activity
• Pain
• Stress

Note: As SvO₂ falls progressively, the risk of inadequate tissue oxygenation increases. Values below approximately 60% may indicate limited oxygen delivery relative to metabolic demand. Very low values can be associated with anaerobic metabolism and lactic acidosis.

Increased SvO₂

An elevated SvO₂ does not necessarily indicate improved cardiovascular function. Higher values may occur when oxygen consumption decreases because of:

• Sedation
• Analgesia
• Hypothermia
• Reduced metabolic activity
• Complete mechanical ventilatory support

Note: An abnormally high SvO₂ may also occur when tissues cannot effectively extract or use delivered oxygen, as may occur in some patients with severe sepsis. Improper catheter positioning can also produce a falsely elevated value.

Direct Fick Cardiac Output

A PAC can also provide the mixed venous blood sample required for calculation of cardiac output using the direct Fick method.

The Fick relationship is based on oxygen consumption and the difference between arterial and mixed venous oxygen content.

In simplified form:

Cardiac Output = Oxygen Consumption ÷ Arteriovenous Oxygen Content Difference

This method requires simultaneous or nearly simultaneous measurement of arterial oxygen content, mixed venous oxygen content, and whole-body oxygen consumption.

Correct catheter position is essential. The sample must represent true mixed venous blood and should not be contaminated with flush solution or arterialized blood from a wedged catheter.

Pulmonary Artery Catheters During Exercise Testing

Pulmonary artery catheterization may occasionally be used during cardiopulmonary exercise testing when more detailed assessment of cardiac or pulmonary vascular function is required.

In a healthy individual, cardiac output rises as workload increases. Early in exercise, both heart rate and stroke volume contribute to this increase. At higher exercise intensities, further increases in cardiac output occur primarily through increasing heart rate.

Failure of cardiac output to increase appropriately may suggest disorders such as:

• Cardiomyopathy
• Ventricular dysfunction
• Valvular disease
• Cardiac outflow obstruction
• Significant arrhythmias
• Pulmonary hypertension
• Elevated systemic vascular resistance

Note: PAC measurements during exercise can therefore help determine whether exercise limitation is primarily cardiac, pulmonary vascular, or related to another physiological system.

Technical Accuracy and Transducer Position

Reliable PAC measurements depend heavily on correct monitoring technique. The pressure transducer must be properly leveled, zeroed, and calibrated.

If the transducer is positioned below the patient’s midheart level, measured pressures will be falsely elevated. If the transducer is positioned too high, pressures will be falsely low.

The fluid-filled tubing system must remain patent and free of significant air bubbles or obstruction. Thrombus formation, loose connections, or excessive tubing can dampen the waveform and produce inaccurate values. Pressure waveforms should always be evaluated along with the numerical measurement.

Effects of Mechanical Ventilation

Mechanical ventilation affects hemodynamic measurements because positive airway pressure changes intrathoracic pressure and cardiopulmonary interactions.

Positive-pressure ventilation may reduce venous return by increasing pressure around the right atrium and vena cava. This can decrease right ventricular preload and cardiac output, particularly in patients who are hypovolemic.

PEEP can also increase pulmonary vascular resistance when alveolar overdistention compresses pulmonary capillaries.

As a result, high airway pressures may:

• Increase measured intrathoracic vascular pressures
• Decrease venous return
• Reduce cardiac output
• Increase pulmonary vascular resistance
• Increase right ventricular workload

Note: PAC data must therefore be interpreted in relation to ventilator settings, lung compliance, PEEP, airway pressure, and the phase of the respiratory cycle.

Complications of Pulmonary Artery Catheterization

PAC placement and continued use carry several potentially serious complications.

Dysrhythmias

Premature ventricular contractions and ventricular tachycardia may occur as the catheter passes through or irritates the right ventricle. New ventricular ectopy after catheter placement may indicate catheter migration back into the right ventricle.

Pneumothorax and Hemothorax

Central venous access, particularly through the subclavian or internal jugular region, can result in pneumothorax or hemothorax. A chest radiograph may be obtained after catheter placement to evaluate catheter position and identify procedure-related complications.

Pulmonary Artery Rupture

Pulmonary artery rupture is one of the most serious complications of PAC use. It may result from excessive catheter advancement, balloon overinflation, distal catheter migration, or vascular injury. Pulmonary hemorrhage can be rapidly fatal and requires immediate recognition and treatment.

Pulmonary Infarction

Leaving the balloon inflated for too long can obstruct blood flow through a pulmonary artery branch. Prolonged wedging can cause thrombosis and pulmonary infarction. The balloon should therefore be inflated only long enough to obtain a wedge measurement.

Balloon-Related Problems

The balloon must not be overinflated. Excessive balloon volume may rupture the balloon, injure the vessel, obstruct the pulmonic valve, or contribute to pulmonary artery damage.

If the catheter wedges with significantly less air than normally required, the catheter may have migrated too far distally. The catheter should never be flushed while the balloon is inflated in the wedge position.

Infection

PAC placement introduces a foreign device into the central circulation. Infection risk increases with prolonged catheter use.

Potential complications include:

• Local insertion-site infection
• Central line-associated bloodstream infection
• Sepsis
• Endocarditis

Note: Sterile insertion technique, proper dressing care, line maintenance, and removal of unnecessary catheters reduce infection risk.

Thrombosis

Blood can clot around the catheter or within the catheter lumen. Thrombus formation may impair waveform transmission, obstruct blood flow, or increase the risk of embolic complications.

Troubleshooting Abnormal Waveforms

Changes in PAC waveforms may indicate catheter migration, obstruction, air in the tubing, blood clot formation, incorrect leveling, or equipment malfunction. A catheter that migrates from the pulmonary artery into the right ventricle may produce a ventricular waveform and provoke ventricular dysrhythmias.

A catheter that advances too far may spontaneously wedge even with the balloon deflated. This is dangerous because continuous obstruction of pulmonary arterial blood flow can cause ischemia and infarction.

If abnormal waveforms occur, catheter position and the monitoring system should be evaluated before relying on the displayed pressure values.

Interpreting PAC Measurements Together

The greatest value of pulmonary artery catheterization comes from interpreting measurements collectively rather than individually.

For example, a patient with hypotension and low cardiac output may have very different underlying problems depending on the accompanying measurements.

Low PCWP with low cardiac output may suggest inadequate preload from hypovolemia. High PCWP with low cardiac output may suggest left ventricular failure. Elevated PAP with a normal PCWP may suggest increased pulmonary vascular resistance.

Elevated PAP together with elevated PCWP may indicate transmission of increased left-sided pressure backward into the pulmonary circulation.

A reduced SvO₂ may indicate that systemic oxygen delivery is inadequate, particularly when accompanied by reduced cardiac output. Clinical findings, ventilator settings, laboratory data, blood pressure, urine output, oxygenation, and imaging must all be considered alongside PAC measurements.

Declining Use of Pulmonary Artery Catheters

Pulmonary artery catheter use has declined substantially compared with previous decades.

Several factors have contributed to this trend, including:

• Invasive placement
• Risk of serious complications
• Difficulty interpreting some measurements
• Variability among clinicians
• Availability of less invasive technologies
• Questions about whether routine PAC use improves outcomes in all patient groups

Modern hemodynamic monitoring options may include echocardiography, Doppler-based cardiac output measurements, arterial waveform analysis, pulse contour methods, and other minimally invasive or noninvasive technologies.

However, the PAC remains capable of providing a unique combination of pressure, flow, and oxygen-transport information in selected critically ill patients.

Clinical Importance for Respiratory Therapists

Respiratory therapists frequently care for mechanically ventilated patients whose cardiovascular function is closely linked to respiratory treatment.

Understanding PAC measurements can help respiratory therapists recognize how ventilator adjustments affect cardiac performance.

Increasing PEEP, for example, may improve oxygenation but simultaneously increase intrathoracic pressure, reduce venous return, decrease cardiac output, and increase pulmonary vascular resistance.

Likewise, correcting severe hypoxemia or acidosis may decrease pulmonary vascular resistance and reduce right ventricular workload.

Familiarity with PAP, PCWP, cardiac output, cardiac index, PVR, SVR, and SvO₂ helps respiratory therapists interpret cardiopulmonary interactions and communicate effectively with the critical care team.

Pulmonary Artery Catheter Practice Questions

1. What is a pulmonary artery catheter?
A pulmonary artery catheter (PAC) is an invasive hemodynamic monitoring device used to measure pressures, blood flow, and oxygen-related variables within the cardiovascular system.

2. What is another common name for a pulmonary artery catheter?
A pulmonary artery catheter is commonly called a Swan-Ganz catheter.

3. Where is the distal tip of a pulmonary artery catheter positioned?
The distal tip is positioned within the pulmonary artery.

4. Through which heart chambers does a pulmonary artery catheter pass during insertion?
The catheter passes through the right atrium and right ventricle before entering the pulmonary artery.

5. What are common insertion sites for a pulmonary artery catheter?
Common insertion sites include the internal jugular vein, subclavian vein, femoral vein, and basilic vein.

6. What major measurements can be obtained with a pulmonary artery catheter?
A PAC can measure right atrial pressure, pulmonary artery pressure, pulmonary capillary wedge pressure, cardiac output, cardiac index, and mixed venous oxygen saturation.

7. What is the purpose of the distal lumen of a pulmonary artery catheter?
The distal lumen is used to measure pulmonary artery pressure and obtain mixed venous blood samples.

8. What is the purpose of the proximal lumen of a pulmonary artery catheter?
The proximal lumen is typically positioned in the right atrium and can be used to measure right atrial pressure, inject fluid for thermodilution, and administer compatible fluids.

9. What is the purpose of the balloon near the tip of a pulmonary artery catheter?
The balloon helps the catheter float through the right heart during insertion and is temporarily inflated to obtain pulmonary capillary wedge pressure.

10. How much air is typically used to inflate the balloon of an adult pulmonary artery catheter?
An adult pulmonary artery catheter balloon generally requires no more than approximately 1 to 1.5 mL of air.

11. What is the normal range for right atrial pressure?
Normal right atrial pressure is approximately 2–6 mm Hg.

12. What does right atrial pressure reflect?
Right atrial pressure provides information about right ventricular preload, circulating blood volume, venous return, and right ventricular function.

13. What can cause a decreased right atrial pressure?
A decreased right atrial pressure may occur with hypovolemia, hemorrhage, dehydration, shock, or peripheral vasodilation.

14. What can cause an elevated right atrial pressure?
An elevated right atrial pressure may occur with fluid overload, right ventricular failure, pulmonary hypertension, cardiac tamponade, pulmonary embolism, or positive-pressure ventilation.

15. What is a typical normal pulmonary artery pressure?
A typical normal pulmonary artery pressure is approximately 25/10 mm Hg.

16. What is the normal range for pulmonary artery systolic pressure?
Normal pulmonary artery systolic pressure is approximately 15–30 mm Hg.

17. What is the normal range for pulmonary artery diastolic pressure?
Normal pulmonary artery diastolic pressure is approximately 5–15 mm Hg.

18. What is the normal range for mean pulmonary artery pressure?
Normal mean pulmonary artery pressure is approximately 10–20 mm Hg.

19. What does the dicrotic notch on a pulmonary artery pressure waveform represent?
The dicrotic notch represents closure of the pulmonic valve at the end of right ventricular systole.

20. What conditions can cause an elevated pulmonary artery pressure?
Elevated pulmonary artery pressure may occur with pulmonary hypertension, left ventricular failure, fluid overload, pulmonary embolism, emphysema, pulmonary fibrosis, or increased pulmonary vascular resistance.

21. What conditions can cause a decreased pulmonary artery pressure?
Decreased pulmonary artery pressure may occur with hypovolemia, hemorrhage, severe vasodilation, anaphylaxis, or cardiovascular collapse.

22. What is pulmonary capillary wedge pressure?
Pulmonary capillary wedge pressure (PCWP) is an indirect measurement of left atrial pressure and left ventricular filling pressure obtained by temporarily inflating the PAC balloon.

23. What is the normal range for pulmonary capillary wedge pressure?
Normal pulmonary capillary wedge pressure is approximately 5–12 mm Hg, although some references use an upper limit of approximately 15 mm Hg.

24. What does an elevated pulmonary capillary wedge pressure suggest?
An elevated PCWP may suggest left ventricular failure, fluid overload, mitral valve disease, cardiac tamponade, or increased left-sided filling pressure.

25. What does a decreased pulmonary capillary wedge pressure suggest?
A decreased PCWP may suggest hypovolemia, hemorrhage, dehydration, vasodilation, or shock.

26. How is pulmonary capillary wedge pressure obtained?
PCWP is obtained by temporarily inflating the balloon at the distal end of the pulmonary artery catheter until a wedge waveform appears.

27. Why should the PAC balloon remain deflated during routine monitoring?
The balloon should remain deflated to allow normal pulmonary artery blood flow and continuous pulmonary artery pressure monitoring.

28. Why should the PAC balloon be inflated only briefly?
Prolonged balloon inflation can obstruct pulmonary blood flow and increase the risk of thrombosis, pulmonary infarction, or vascular injury.

29. At what point in the respiratory cycle should PCWP generally be measured?
PCWP should generally be measured at end-expiration to minimize the effect of changing intrathoracic pressure.

30. How can positive-pressure ventilation affect PCWP?
Positive-pressure ventilation can increase intrathoracic pressure and may cause the measured PCWP to appear higher than the patient’s true filling pressure.

31. How can PEEP affect hemodynamic measurements obtained from a PAC?
PEEP can increase intrathoracic pressure, reduce venous return, alter measured filling pressures, and increase pulmonary vascular resistance.

32. What PCWP level is commonly associated with left ventricular dysfunction or fluid overload?
A PCWP greater than approximately 18 mm Hg may be associated with left ventricular dysfunction or fluid overload.

33. At what PCWP range may interstitial pulmonary edema begin to occur?
Interstitial pulmonary edema may begin to occur when PCWP rises to approximately 20–25 mm Hg.

34. At what PCWP range may frank pulmonary edema occur?
Frank pulmonary edema may occur when PCWP reaches approximately 25–30 mm Hg or higher.

35. How can PCWP help differentiate cardiogenic pulmonary edema from ARDS?
Cardiogenic pulmonary edema is usually associated with an elevated PCWP, whereas ARDS may produce pulmonary edema despite a relatively normal PCWP.

36. What is the PAd–PCWP gradient?
The PAd–PCWP gradient is the difference between pulmonary artery diastolic pressure and pulmonary capillary wedge pressure.

37. What is considered a normal PAd–PCWP gradient?
A normal PAd–PCWP gradient is generally 5 mm Hg or less.

38. What does an elevated PAd–PCWP gradient suggest?
An elevated gradient suggests increased pulmonary vascular resistance or pulmonary hypertension.

39. How is cardiac output defined?
Cardiac output is the volume of blood pumped by the heart each minute.

40. What is the normal resting adult cardiac output range?
Normal resting adult cardiac output is approximately 4–8 L/min.

41. What is the relationship between cardiac output, heart rate, and stroke volume?
Cardiac output equals heart rate multiplied by stroke volume.

42. How does a pulmonary artery catheter measure cardiac output by thermodilution?
A known volume of fluid is injected through the proximal port, and a thermistor detects the resulting temperature change as the fluid passes through the pulmonary circulation.

43. Where is the proximal injection port located during thermodilution cardiac output measurement?
The proximal injection port is positioned in the right atrium.

44. What is the role of the thermistor in a pulmonary artery catheter?
The thermistor detects changes in blood temperature used to calculate cardiac output by thermodilution.

45. Why are multiple thermodilution cardiac output measurements often obtained?
Multiple measurements are obtained and averaged to improve reliability because individual readings can vary.

46. What is cardiac index?
Cardiac index is cardiac output adjusted for the patient’s body surface area.

47. What is the normal adult cardiac index range?
Normal adult cardiac index is approximately 2.5–4 L/min/m².

48. What does a decreased cardiac index suggest?
A decreased cardiac index suggests that cardiac output may be inadequate relative to the patient’s body size and metabolic needs.

49. How can excessive PEEP decrease cardiac output?
Excessive PEEP can increase intrathoracic pressure, reduce venous return, decrease right ventricular preload, and ultimately lower cardiac output.

50. Why is cardiac index often more useful than cardiac output alone?
Cardiac index accounts for differences in body size, allowing cardiac performance to be compared more appropriately among patients.

51. What does pulmonary vascular resistance represent?
Pulmonary vascular resistance (PVR) describes the resistance the right ventricle must overcome as it pumps blood through the pulmonary circulation.

52. What is the normal range for pulmonary vascular resistance?
Normal PVR is approximately 50–250 dynes·s/cm⁵, depending on the reference used.

53. Which conditions can increase pulmonary vascular resistance?
PVR may rise with pulmonary embolism, pulmonary hypertension, hypoxemia, acidosis, emphysema, pulmonary fibrosis, pneumothorax, or excessive alveolar pressure.

54. What effect does hypoxemia have on pulmonary vascular resistance?
Hypoxemia can trigger pulmonary vasoconstriction, which increases pulmonary vascular resistance.

55. How does inhaled nitric oxide affect pulmonary vascular resistance?
Inhaled nitric oxide can lower pulmonary vascular resistance by causing pulmonary vasodilation.

56. What does systemic vascular resistance represent?
Systemic vascular resistance (SVR) is the resistance the left ventricle must overcome to pump blood through the systemic circulation.

57. What is the normal range for systemic vascular resistance?
Normal SVR is approximately 900–1400 dynes·s/cm⁵.

58. Which factors can increase systemic vascular resistance?
SVR may increase with systemic vasoconstriction, hypovolemia, catecholamine release, vasopressor therapy, or later stages of shock.

59. Which conditions can decrease systemic vascular resistance?
SVR may decrease with vasodilator therapy, sepsis, anaphylaxis, or other causes of widespread systemic vasodilation.

60. What is mixed venous oxygen saturation?
Mixed venous oxygen saturation, or SvO₂, is the oxygen saturation of pulmonary artery blood after venous blood returning from throughout the body has mixed.

61. What is a normal mixed venous oxygen saturation?
Normal SvO₂ is approximately 75%, with a typical range of about 60% to 80%.

62. What is a normal mixed venous oxygen tension?
Normal mixed venous oxygen tension, or PvO₂, is approximately 40 mm Hg.

63. What does SvO₂ indicate?
SvO₂ reflects the relationship between systemic oxygen delivery and tissue oxygen consumption.

64. What does a low SvO₂ generally suggest?
A decreased SvO₂ generally suggests reduced oxygen delivery, increased oxygen consumption, or greater tissue oxygen extraction.

65. What can cause SvO₂ to decrease?
A decreased SvO₂ may occur with low cardiac output, heart failure, hypoxemia, anemia, fever, seizures, increased work of breathing, pain, or stress.

66. What can cause SvO₂ to increase?
An elevated SvO₂ may occur with sedation, hypothermia, reduced metabolic activity, full ventilatory support, sepsis, or impaired tissue oxygen utilization.

67. Why is pulmonary artery blood used for true mixed venous oxygen assessment?
Blood from the pulmonary artery represents venous blood that has mixed after returning from the systemic circulation, making it the standard sample for true mixed venous oxygen assessment.

68. Why should mixed venous blood be drawn slowly from a pulmonary artery catheter?
Slow withdrawal helps reduce the chance of obtaining an inaccurate sample or disturbing the blood mixture around the catheter tip.

69. How can catheter wedging alter a mixed venous blood sample?
A wedged catheter may yield arterialized pulmonary capillary blood rather than a true mixed venous specimen.

70. What does the direct Fick method calculate?
The direct Fick method calculates cardiac output using oxygen consumption and the arterial-mixed venous oxygen content difference.

71. What information is needed to calculate cardiac output with the direct Fick method?
The direct Fick method requires oxygen consumption, arterial oxygen content, and mixed venous oxygen content.

72. Why should arterial and mixed venous samples be collected at nearly the same time for Fick measurements?
Collecting the samples simultaneously or nearly simultaneously improves accuracy because oxygen consumption and oxygen content can change quickly, especially during exercise.

73. What cardiac rhythm complication may occur as a PAC passes through the right ventricle?
Premature ventricular contractions or ventricular tachycardia may occur because the catheter can irritate the ventricular endocardium.

74. What does the appearance of a right ventricular waveform after PAC placement indicate?
A sudden right ventricular waveform may indicate that the catheter has migrated backward from the pulmonary artery into the right ventricle.

75. Why should a pulmonary artery catheter not be flushed while in the wedge position?
Flushing a wedged catheter can force fluid into an occluded pulmonary arterial branch and increase the risk of vascular injury or pulmonary artery rupture.

76. What is one of the most serious complications of pulmonary artery catheter use?
Pulmonary artery rupture is one of the most serious complications because it can cause severe pulmonary hemorrhage.

77. What can contribute to pulmonary artery rupture?
Pulmonary artery rupture may result from excessive catheter advancement, balloon overinflation, distal catheter migration, or vascular injury.

78. What complication can occur if the PAC balloon remains inflated for too long?
Prolonged balloon inflation can obstruct pulmonary blood flow and cause pulmonary infarction.

79. What does spontaneous wedging with the balloon deflated suggest?
Spontaneous wedging may indicate that the catheter has migrated too far distally into a small pulmonary artery branch.

80. What should be done if a PAC wedges with less balloon volume than expected?
The catheter position should be evaluated because distal migration may have occurred, and the catheter may need to be withdrawn slightly.

81. Why is continuous waveform monitoring important with a pulmonary artery catheter?
Continuous waveform monitoring helps identify catheter migration, unintended wedging, damping, and other positioning problems.

82. What can cause a dampened pulmonary artery pressure waveform?
A dampened waveform may result from thrombus formation, air bubbles, tubing problems, catheter obstruction, or improper positioning.

83. How does transducer height affect invasive pressure measurements?
A transducer positioned too low produces falsely high readings, while a transducer positioned too high produces falsely low readings.

84. Where should the pressure transducer be leveled for accurate PAC measurements?
The transducer should be leveled at the approximate level of the patient’s midheart.

85. Why must the pressure monitoring system be zeroed before measurements are interpreted?
Zeroing establishes atmospheric pressure as the reference point so the displayed pressures accurately reflect intravascular pressure.

86. What infectious complications can occur with prolonged PAC use?
Prolonged PAC use can increase the risk of insertion-site infection, bloodstream infection, sepsis, and endocarditis.

87. What should be considered if catheter-related infection is suspected?
The catheter may need to be removed and cultured if infection or sepsis is suspected.

88. What thrombotic complication can occur with a pulmonary artery catheter?
Thrombus formation can develop around or within the catheter and may interfere with blood flow or pressure transmission.

89. What mechanical complication can occur during central venous insertion of a PAC?
Pneumothorax can occur during central venous access, especially with subclavian or internal jugular insertion.

90. What other thoracic complication can occur during PAC insertion?
Hemothorax may occur if a blood vessel is injured during central venous catheter placement.

91. Why may a chest radiograph be obtained after PAC insertion?
A chest radiograph may be used to confirm catheter position and identify complications such as pneumothorax.

92. How can a pulmonary artery catheter injure the heart during insertion?
The catheter can irritate or perforate the right atrium or right ventricle and may also damage the tricuspid or pulmonic valve.

93. Why has routine PAC use declined over time?
PAC use has declined because of its invasive nature, risk of complications, interpretation challenges, and availability of less invasive hemodynamic monitoring methods.

94. What less invasive methods may be used instead of a PAC in some patients?
Alternatives may include echocardiography, Doppler methods, arterial waveform analysis, pulse contour monitoring, and other noninvasive or minimally invasive techniques.

95. Why should PAC measurements not be interpreted individually?
PAC measurements are most useful when interpreted together because preload, afterload, cardiac output, vascular resistance, and oxygen delivery are closely related.

96. What combination of findings may suggest hypovolemia?
Low filling pressures such as a low PCWP combined with reduced cardiac output may suggest inadequate preload from hypovolemia.

97. What combination of findings may suggest left ventricular failure?
A low cardiac output combined with an elevated PCWP may suggest left ventricular failure.

98. What combination of findings may suggest increased pulmonary vascular resistance?
An elevated pulmonary artery pressure with a relatively normal PCWP may suggest increased pulmonary vascular resistance.

99. Why are PAC measurements important when adjusting mechanical ventilation?
Ventilator changes can alter intrathoracic pressure, venous return, pulmonary vascular resistance, cardiac output, and measured filling pressures.

100. Why is clinical context essential when interpreting pulmonary artery catheter data?
PAC values should be interpreted with the patient’s blood pressure, oxygenation, ventilator settings, urine output, laboratory data, physical findings, and overall clinical condition.

Final Thoughts

A pulmonary artery catheter provides detailed information about cardiovascular function by measuring right-sided pressures, pulmonary artery pressure, pulmonary capillary wedge pressure, cardiac output, cardiac index, vascular resistance, and mixed venous oxygenation. These measurements can help clinicians evaluate preload, afterload, ventricular performance, pulmonary circulation, fluid status, and systemic oxygen delivery.

Accurate interpretation depends on proper catheter positioning, waveform analysis, transducer setup, sampling technique, and consideration of mechanical ventilation.

Because PAC placement carries risks such as dysrhythmias, infection, thrombosis, pulmonary infarction, and pulmonary artery rupture, its use is generally reserved for patients in whom advanced hemodynamic information may significantly guide clinical management.