1. What is a Swan-Ganz catheter?
A Swan-Ganz catheter is a relatively soft, flexible catheter with an inflatable balloon at its tip that is used in right-sided heart catheterization. The balloon tip allows the catheter to float with the flow of blood from the great veins through the right-sided heart chambers and into the pulmonary artery, before wedging in a distal branch of the pulmonary artery.
2. How is a Swan-Ganz catheter constructed?
The basic Swan-Ganz catheter in current clinical use has four lumens. One is connected to the distal port of the catheter, allowing for measurement of pulmonary artery pressure when the balloon is deflated and pulmonary artery wedge pressure (PAWP) when the balloon is inflated. The second lumen is attached to a temperature-sensing thermocouple 5 cm proximal to the catheter tip and is used for measurement of cardiac output (CO) by thermodilution. The third lumen is connected to a port 15 cm proximal to the catheter tip, allowing for measurement of pressure in the right atrium and for infusion of drugs or fluids into the central circulation. The fourth lumen is used to inflate the balloon with air when initially floating the catheter into position and later to reinflate the balloon for intermittent measurement of PAWP. Many catheters contain an additional proximal port for infusion of fluids and drugs. Some catheters have an additional lumen through which a temporary pacing electrode can be passed into the apex of the right ventricle for internal cardiac pacing.
3. What information can be gained from a Swan-Ganz catheter?
Direct measurements obtained from the catheter include vascular pressures and oxygen saturations within the cardiac chambers, cardiac output, and systemic venous oxygen saturation (SvO2). These hemodynamic measurements can be used to calculate other hemodynamic parameters, such as systemic vascular resistance and pulmonary vascular resistance.
4. How is a Swan-Ganz catheter inserted?
At the bedside, venous access is usually obtained by introducing an 8.5 French sheath into the internal jugular or subclavian vein using the Seldinger technique. The right internal jugular or left subclavian veins are preferred sites because the natural curve of the catheter will allow easier flotation into the pulmonary artery. Less commonly, the antecubital or femoral veins are used.
Next, a 7.5 French Swan-Ganz catheter is passed through the introducer sheath and advanced approximately 15 cm to exit the sheath into the central vein. The balloon is then inflated with 1.5 cc air, and the catheter is advanced slowly, allowing the balloon to float through the right atrium, right ventricle, and pulmonary artery, and finally achieving a wedge position in a distal branch of the pulmonary artery that is smaller in diameter than the balloon itself. The wedge position is usually achieved when the catheter has advanced a total of 35 to 55 cm, depending on which central vein is cannulated.
5. Describe the normal pressure waveforms along the path of an advancing Swan-Ganz catheter.
The a wave is produced by atrial contraction and follows the electrical P wave on electrocardiogram (ECG). The x descent reflects atrial relaxation. The c wave is produced at the beginning of ventricular systole as the closed tricuspid valve bulges into the right atrium. The x’ descent is
thought to be the result of the descent of the atrioventricular ring during ventricular contraction and continued atrial relaxation. The v wave is caused by venous filling of the atrium during ventricular systole, when the tricuspid valve is closed. This should correspond with the electrical T wave. However, at the bedside, because of a lag in pressure transmission, the a wave will align with the QRS complex and the v wave will follow the T wave. Finally, the y descent is produced by rapid atrial emptying, when the tricuspid valve opens at the onset of diastole.
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Figure 11-1. Atrial pressure tracing.
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Figure 11-2. Pressure tracings as the catheter is advanced through the right-sided chambers. As the catheter moves from the right atrium to the right ventricle, a ventricular wave form is seen representing isovolumic contraction, ejection, and diastole. When the catheter passes into the pulmonary artery, the diastolic pressure rises. The dicrotic notch (dn) is produced by the closure of the pulmonic valve. If the catheter is advanced farther, it attains the wedge position.
6. How is the location of the catheter determined?
At the bedside, continuous monitoring of pressure tracings from the distal port and simultaneous ECG tracings allow the operator to determine the catheter’s position and to detect any arrhythmias caused by the catheter as it passes through the right ventricle. Fluoroscopy can be used in the cardiac catheterization laboratory to guide placement. The use of fluoroscopy should especially be considered if a Swan-Ganz catheter is placed via the femoral or brachial veins or in patients with dilated right ventricles.
7. How do we know that the catheter is in the true wedge position?
There are three ways to confirm that the catheter is in the wedge position. At the bedside, an atrial tracing (reflecting left atrial pressure) will be seen when the catheter is in the wedge position. Secondly, if the catheter is withdrawn from the wedge position, the mean arterial pressure should be observed to rise from the wedge pressure (reflecting a physiologic gradient between the mean pulmonary artery and mean wedge pressure). Gentle aspiration of blood from the distal port should reveal highly oxygenated blood if the catheter is truly wedged. Additionally, in the catheterization laboratory, fluoroscopy can be used to determine that the catheter is in a distal pulmonary arteriole, immobile in the wedge position.
8. What does the PAWP signify?
When the catheter is in the wedge position (Fig. 11-3, B), proximal blood flow is occluded and a static column of blood is created between the catheter tip and the distal cardiac chambers. With the balloon shielding the catheter tip from the pressure in the pulmonary artery proximally, the pressure transducer measures pressure distally in the pulmonary arterioles. This pressure closely approximates left atrial pressure. When the mitral valve is open at end diastole, left ventricular end-diastolic pressure is measured (Fig. 11-3, C), assuming that there is no obstruction between the catheter tip and the left ventricle (i.e., mitral stenosis). The PAWP can be used to approximate left ventricular preload.
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Figure 11-3. A, With the balloon tip deflated, the pressure transducer at the catheter tip sees blood flow from the proximal pulmonary artery. B, With the balloon tip inflated, proximal blood flow is occluded and a static column of blood is created between the catheter tip and the distal cardiac chamber. With the mitral valve closed, left atrial pressure is approximated. C, With the mitral valve open at end diastole, left ventricular end-diastolic pressure can be measured, assuming there is no significant mitral stenosis.
9. How is cardiac output determined?
Cardiac output can be determined either by the measured thermodilution method or the calculated Fick method.
With thermodilution, 5to 10 ml of normal salineis injected rapidly via the proximal port into the right atrium. The injectate mixes completely with blood and causes a drop in temperature that is measured continuously by a thermocouple near the catheter tip. The area under the curve is calculated and is inversely related to cardiac output (Figure 11-4). This method of measurement is not reliable in patients with low cardiac output or significant tricuspid regurgitation. In a
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Figure 11-4. Area under the curve is inversely proportional to cardiac output. A, Illustration depicts larger area under the curve (AUC) in patient with low cardiac output. B, Temperature equilibrates faster in a patient with a higher cardiac output, resulting in a smaller AUC.
low-cardiac-output state, blood is rewarmed by the walls of the cardiac chambers and surrounding tissue, resulting in an overestimation of cardiac output. Alternatively, the Fick method can be used to calculate cardiac output.
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This method is based on the principle that the consumption of a substance (oxygen) by any organ is determined by the arterial-venous (A-V) difference of the substance and the blood flow (CO) to that organ. The consumption of oxygen by a patient can be measured using a covered hood in the cardiac catheterization laboratory, and the A-V difference can be measured by obtaining blood samples from the right atrium and pulmonary artery. This method is more accurate in patients with atrial fibrillation, tricuspid regurgitation, and low cardiac output than the thermodilution method. Common sources of error include improper collection of blood samples.
At the bedside, use of a covered hood can be cumbersome and impractical. For this reason, some laboratories assume that resting oxygen consumption is 125 ml/meter2 and calculate cardiac output based on an assumed Fick equation. However, studies have shown that there is wide variability in resting oxygen consumption among patients, particularly in those patients who are critically ill. As expected, use of an assumed Fick calculation can introduce significant error into the estimation of cardiac output.
10. What are normal values for intravascular pressures and hemodynamic parameters?
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11. Why are cardiac output and left ventricular (LV) preload important?
In certain clinical situations, the knowledge of cardiac output and PAWP (surrogate of LV preload; see Question 8) can help to make diagnoses and/or guide management (see Question 12). PAWP can be applied to the Starling curve and help to predict whether cardiac output may improve if filling pressures are altered.
12. When is placing a Swan-Ganz catheter clinically indicated, and do all patients derive clinical benefit?
Other situations in which a Swan-Ganz catheter can considered include the following:
Heart Failure/Shock
Differentiation between cardiogenic and noncardiogenic pulmonary edema when a trial of diuretic and/or vasodilator therapy has failed
It is not indicated for the routine management of pulmonary edema.
Differentiation of causes of shock and guide management when a trial of intravascular volume expansion has failed (see Question 15)
Determination of whether pericardial tamponade is present when clinical assessment is inconclusive and echocardiography is unavailable
Assessment of valvular heart diseas
Determination of reversibility of pulmonary vasoconstriction in patients being considered for heart transplantation & Management of congestive heart failure refractory to standard medical therapy, especially in the setting of acute myocardial infarction
Of note, a major, randomized trial, Evaluation Study of Congestive Heart Failure and Pulmonary
Artery Catheterization Effectiveness (ESCAPE), showed no significant difference in endpoints of mortality and days out of hospital at 6 months in this category of patients.
Acute Myocardial Infarction
American College of Cardiology/American Heart Association (ACC/AHA) guidelines state that Swan-Ganz catheters should be used in those patients who have progressive hypotension unresponsive to fluids and in patients with suspected mechanical complications of ST-elevation myocardial infarction (MI) if an echocardiogram has not been performed (class I). However, mortality benefit has not been demonstrated in a randomized trial. The use of Swan-Ganz catheters can also be considered in the following situations:
Diagnosis of mechanical complications of myocardial infarction (i.e., mitral regurgitation, ventricular septal defect)
Diagnosis of intracardiac shunts and to establish their severity before surgical correction (see Question 16)
Guidance of management of cardiogenic shock with pharmacologic or mechanical support
Guidance of management of right ventricular infarction with hypotension or signs of low cardiac output not responding to intravascular volume expansion or low doses of inotropic drugs
Short-term guidance of pharmacologic or mechanical management of acute mitral regurgitation before surgical correction
Perioperative Use
A 2003 randomized trial in high-risk surgical patients showed no significant difference in mortality with the use of Swan-Ganz catheters. Although the routine use of Swan-Ganz catheters perioperatively remains of unclear benefit, it should be considered in the following situations:
In patients undergoing cardiac surgery, to differentiate between causes of low cardiac output or to differentiate between right and left ventricular dysfunction, when clinical assessment and echocardiography is inadequate
Guidance of perioperative management in selected patients with decompensated heart failure undergoing intermediate or high-risk noncardiac surgery
Pulmonary Hypertension
Exclusion of postcapillary causes of pulmonary hypertension (i.e., elevated PAWP)
To establish diagnosis and assess severity of primary pulmonary hypertension (normal PAWP)
Selection and establishment of safety and efficacy of long-term vasodilator therapy basedon acute hemodynamic response
Use in Intensive Care Units
Many studies have shown that clinical data predict PAWP and CO poorly and that insertion of the catheter often changes patient management. However, despite widespread use of these devices in intensive care units, only a few observational studies have shown their use to decrease mortality. A 2005 meta-analysis of several randomized trials showed that the use of Swan-Ganz catheters was associated with neither benefit nor or increased mortality. Current thinking is reflected in a 1997 pulmonary artery consensus statement recommending that the decision to insert a Swan-Ganz catheter be made on an individual basis, such that the potential risks and benefits are considered in each case.
13. What are absolute and relative contraindications to placement of a Swan-Ganz catheter?
Absolute Contraindications
Right-sided endocarditis
Mechanical tricuspid or pulmonic valve prosthesis
Presence of thrombus or tumor in a right-sided heart chamber
Relative Contraindications
Coagulopathy
Recent implantation of a permanent pacemaker or cardioverter defibrillator
Left bundle branch block
Bioprosthetic tricuspid or pulmonic valve
14. What diagnoses can the catheter help make?
The characteristic waveform of the Swan-Ganz catheter is altered in several disease states. & In pericardial tamponade, equalization of diastolic pressures across all chambers is seen (Fig. 11-5).
In atrial fibrillation, the a wave disappears from the right atrial pressure tracing, whereas in atrial flutter, mechanical flutter waves occur at a rate of 300/min.
Cannon a waves occur when the atria contract against closed valves due to atrioventricular dissociation. Irregular cannon a waves during a wide-complex tachycardia strongly suggest ventricular tachycardia.
Complications of myocardial infarction can be detected on the PAWP tracing, such as giant v waves seen with acute mitral insufficiency, and the dip and plateau pattern of the right ventricular (RV) pressure tracing seen with RV infarction.
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15. How can causes of shock be differentiated by Swan-Ganz catheterization?
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16. How can left-to-right intracardiac shunts be diagnosed by Swan-Ganz catheterization?
An intracardiac shunt results in flow of blood from left-sided to right-sided cardiac chambers or vice versa. Left-to-right shunts results in flow from the left-sided chambers to right-sided chambers. With ventricular septal defects, flow is often left-to-right as a result of higher left-sided pressures. Atrial septal defects can result in a shunt in either direction. Because of the flow of oxygenated blood into right-sided chambers, a sudden increase in oxygen saturation in right-sided chambers is observed. A step-up in mean oxygen saturation of 7% between the caval chambers and the right atrium is diagnostic of an atrial septal defect. A step-up of 5% between the right atrium and right ventricle is diagnostic for a ventricular septal defect.
17. What complications are associated with use of a Swan-Ganz catheter?
All complications of central venous cannulation, including bleeding and infection
Local infection rates range from 18% to 63% in patients with catheter in place for an average of 3 days.
Bloodstream infection has been reported in up to 5% of patients. & Transient right bundle branch block
Complete heart block (especially in patients with preexisting left bundle branch block)
Ventricular tachyarrhythmias
Clinically insignificant ventricular arrhythmias can occur in up to 30% to 60% of patients.
Sustained arrhythmias usually occur in patients with myocardial ischemia or infarction.
Pulmonary infarction (incidence 0% to 1.3%)
Pulmonary artery rupture
Risk factors include pulmonary hypertension and recent cardiopulmonary bypass. & Thrombophlebitis
Venous or intracardiac thrombus formation & Endocarditis
Catheter knotting
18. How can complications be minimized?
The use of fluoroscopy should be considered for placement of the catheter, particularly if access is obtained from a nontraditional site or if the patient has a dilated right ventricle.
Consideration should be given to removing the catheter after the first set of data is obtained.
The duration the catheter is kept in place should be minimized because infectious and thrombotic complications increase significantly after 3 to 4 days.
Use of the introducer side arm for infusion of medications should be minimized.
Manipulation of the catheter should only be performed by trained personnel.
19. The wedge tracing is abnormal. What do I do?
Check a chest radiograph for proper catheter position. The tip should lie in lung zone 3, below the level of the left atrium.
Aspirate and flush the catheter to remove clots and bubbles.
Check all connecting lines and stopcocks.
Confirm that the pressure transducers are zeroed to the level of the right atrium.
Check that the balloon is not overinflated; try letting out the air and refilling it slowly.
Consider the possibility that the tracing really is a wedge tracing with a giant v wave, as is seen in acute mitral insufficiency and several other conditions.
20. The cardiac output doesn’t make sense. What is wrong?
Check that at least three values were averaged and that the range of these values is no greater than 20% of the mean.
Check the chest radiograph: Is the distal tip of the catheter in the pulmonary artery and the proximal port in the right atrium?
Check to see if the computer is calibrated to the proper temperatures.
If the computer can display the time versus temperature curve, check that the curve is shaped properly.
