Indications and complications for arterial and pulmonary artery catheters are listed in Table 29-1 and normal hemodynamic values are listed in Table 29-2.
Table 29-1Indications and Contraindications for Arterial and Venous Cannulation ||Download (.pdf) Table 29-1 Indications and Contraindications for Arterial and Venous Cannulation
• Indications: continuous blood pressure monitoring, frequent blood gases
• Complications: hemorrhage, infection, ischemia (embolus, thrombus, spasm)
Central venous catheter
• Indications: fluid administration, nutritional support, CVP measurements, central venous blood gases
• Complications: pneumothorax, embolus and thrombus formation, infection
Pulmonary artery cannulation
• Indications: PCWP measurements, cardiac output measurements, mixed venous blood gases
• Complications: pneumothorax, arrhythmias, embolus and thrombus formation, infection, cardiovascular injury
Table 29-2Normal Values for Direct Measured and Derived Hemodynamic Values ||Download (.pdf) Table 29-2 Normal Values for Direct Measured and Derived Hemodynamic Values
|Direct measurements |
|Central venous pressure ||< 6 mm Hg |
|Pulmonary capillary wedge pressure ||4-12 mm Hg |
|Pulmonary artery pressure || |
| systolic ||20-30 mm Hg |
| diastolic ||6-15 mm Hg |
| mean ||10-20 mm Hg |
|Systemic arterial blood pressure || |
| systolic/diastolic ||120/80 mm Hg |
| mean ||80-100 mm Hg |
|Cardiac output ||4-8 L/min |
|Heart rate ||60-100 beats/min |
|Derived measurements |
|Cardiac index ||2.5-4 L/min/m2 |
|Stroke volume ||60-130 mL |
|Pulmonary vascular resistance ||110-250 dynes × s·cm–5 |
|Systemic vascular resistance ||900-1400 dynes × s·cm–5 |
|Right ventricular stroke work index ||8-10 g·m/m2/beat |
|Left ventricular stroke work index ||50-60 g·m/m2/beat |
Common sites for indwelling arterial catheters are the radial, brachial, axillary, and femoral arteries. Because of the presence of collateral circulation, the radial artery usually is the vessel of choice. Direct measurement of arterial blood pressure allows continuous display of systolic pressure, diastolic pressure, and mean arterial pressure.
Central venous pressure (CVP) is measured from a catheter located in the superior vena cava or right atrium. CVP reflects right atrial pressure, which reflects right ventricular end-diastolic pressure and the performance of the right ventricle. In patients with normal cardiac reserve and PVR, CVP reflects preload.
A pulmonary artery catheter is used to evaluate intravascular pressure and cardiac output. However, the use of the pulmonary artery catheter has decreased significantly in recent years after publication of studies that questioned whether its use resulted in improved patient outcomes. The pulmonary artery catheter is a special balloon tipped flow-directed catheter used for pulmonary artery pressure (PAP) and pulmonary capillary wedge pressure (PCWP) monitoring. The standard catheter consists of a proximal port (at the level of the right atrium to infuse fluids, measure CVP, and inject cold solution for cardiac output), distal port (in the pulmonary artery), a balloon (which is inflated for PCWP measurements), and a thermistor (to measure temperature and calculate cardiac output). Pulmonary artery catheters can also be used to monitor mixed venous oxygen saturation, right ventricular ejection fraction, and to provide temporary cardiac pacing. An elevated PAP may indicate left-to-right shunt, left ventricular failure, mitral stenosis, or pulmonary hypertension. When the balloon is inflated, the catheter floats forward to a small branch of the pulmonary artery. Blood flow past the balloon is thus obstructed, and PCWP is measured (Figure 29-1). PCWP (also called pulmonary artery wedge pressure or pulmonary artery occlusion pressure) is a reflection of left atrial pressure. An elevated PCWP may indicate left ventricular failure, mitral stenosis, or cardiac insufficiency.
Pressure waveforms recorded by the pulmonary artery catheter. As the catheter is advanced from the venous cannulation site, the first waveform recorded will be the central venous pressure trace. Passage of the catheter from the right atrium (RA) into the right ventricle (RV) is accompanied by a marked increase in systolic pressure. As the catheter tip enters the pulmonary artery (PA), a dicrotic notch may appear in the systolic wave and the diastolic pressure will increase in magnitude and will be downsloping in contrast to the upsloping diastolic pressure in the right ventricle (RV). With further advancement of the catheter, the balloon will occlude blood flow and the tip will record the pulmonary artery occlusion pressure, characterized by disappearance of the systolic pressure wave and reappearance of venous a, c, and v waves. Numbers show the approximate depth when inserting the PAC from the right internal jugular vein. (Modified with permission from Mark JB. Atlas of Cardiovascular Monitoring. New York, NY: Churchill Livingstone; 1998: Fig. 3.1.)
Thermodilution cardiac output is measured by injecting a cold solution into the central circulation (right atrium). The downstream temperature change in the pulmonary artery allows cardiac output to be calculated. A thermistor located near the tip of the pulmonary artery catheter measures the blood temperature in the pulmonary artery. The temperature of the patient, the temperature of the injection solution, and the change in blood temperature are the variables used to compute cardiac output. A continuous thermodilution cardiac output technique emits a safe amount of heat into the blood without using a fluid injectate, and cardiac output is computed by analysis of temperature changes in the pulmonary artery using signal processing techniques. Pulse contour waveform analysis techniques allow minimally invasive continuous cardiac output monitoring without the need for a pulmonary artery catheter.
Cardiac output is often normalized to patient size by dividing cardiac output (Q̇c) by body surface area (BSA):
where CI is cardiac index. The volume of blood ejected from the ventricle with each contraction, stroke volume (SV), can be calculated by dividing cardiac output by heart rate (fc):
SV can also be normalized to patient size:
where SVI is stroke volume indexed.
Hemodynamic monitoring allows preload, afterload, and contractility to be assessed. This provides the clinician with the information necessary to assess cardiac output (Figure 29-2). Preload is determined by myocardial stretch at end diastole (end-diastolic tension). An increase in blood volume and an increase in venous tone will increase preload. A decrease in blood volume (eg, diuretic administration) will decrease preload. The CVP is an indicator of right ventricular preload, and PCWP is an indicator of left ventricular preload. Excessive preload is associated with cardiac failure and insufficient preload is associated with hypovolemia or sepsis.
The relationship between measured and derived hemodynamic parameters and cardiac output.
Afterload is the resistance that the ventricle must overcome to eject blood. The afterload of the right ventricle is pulmonary vascular resistance (PVR):
where MPAP is the mean PAP. PVR can be indexed to patient size:
where PVRI is the PVR index. The afterload of the left ventricle is systemic vascular resistance (SVR):
where MAP is mean systemic arterial pressure. SVR can also be indexed to patient size:
where SVRI is the SVR index. Afterload is determined primarily by vascular tone; an increase in vascular tone increases afterload and a decrease in vascular tone decreases afterload. Thus, vasodilating agents decrease afterload, whereas vascoconstricting agents increase afterload.
Contractility is the intrinsic ability of the myocardium to contract, independent of preload and afterload. The contractility of the right ventricle is determined by the right ventricular stroke work index (RVSWI):
The contractility of the left ventricle is determined by the left ventricular stroke work index (LVSWI):
Contractility is manipulated by use of inotropic and beta-blocking agents. Inotropic agents increase contractility, and β-blocking agents decrease contractility.