Chapter 16 Assessment of Hemodynamic Pressures

Learning Objectives After reading this chapter you will be able to: Describe the following regarding arterial cannulation: Indications for placing an A line Catheter; common insertion sites Procedure for placement of the catheter Interpretation of arterial pressure waveforms Pressures measured and their interpretation Potential complications

Learning Objectives Describe the following regarding central venous pressure (CVP) monitoring: Indications for placing a CVP catheter Catheter; insertion sites Procedure for placement of the catheter Interpretation of the CVP waveform Interpretation of pressures measured Relationship of CVP to left and right ventricular function Potential complications

Learning Objectives Describe the following regarding pulmonary artery (PA) pressure monitoring: Indications for placing a PA catheter Catheter; insertion sites Procedure for placement of the catheter Interpretation of PA waveforms Interpretation of pressures measured

Learning Objectives (cont’d) Relationship between PA diastolic pressure and pulmonary capillary wedge pressure (PCWP) How to obtain an accurate PCWP reading Relationship between transmural pressure and PCWP Effect of positive end-expiratory pressure on PCWP measurements Complications of using the PA catheter

Introduction Hemodynamic monitoring is performed to: Evaluate intravascular fluid volume Evaluate cardiac function Evaluate vascular function Identify sudden changes in the patient’s hemodynamic status Invasive monitoring is needed to obtain an accurate evaluation of hemodynamics

Arterial Pressure Monitoring Indications In patients with severe hypotension or hypertension In patients who may need frequent arterial blood gas assessment Patients in shock or respiratory failure are candidates for placement of an arterial line

Placement of the Arterial Line Most often placed in the radial artery This site is readily accessible and has collateral circulation This site is easy to monitor for bleeding or other complications The femoral artery is less affected by vasoconstriction but more difficult to monitor for bleeding

Arterial Pressure Waveforms The arterial pressure wave should have a clear upstroke on the left A dicrotic notch on the downstroke on the right The dicrotic notch represents aortic valve closure

Arterial Pressure Waveforms (cont’d)

Arterial Pressure Waveforms (cont’d)

Interpretation of Arterial Pressures Normal = 120/80 mm Hg Hypertension = >160/90 mm Hg Hypotension = <90/60 mm Hg Arterial pressure is only a general sign of circulatory status Hypotension is often a late sign of low cardiac output

Interpretation of Arterial Pressures (cont’d) Hypotension is caused by: Low blood volume Poor cardiac function Low vascular resistance A low diastolic pressure can compromise coronary artery perfusion

Interpretation of Arterial Pressures (cont’d) Hypertension is caused by: Excessive contraction of the left ventricle Vasoconstriction Administration of vasopressors Sympathetic stimulation (as occurs with fear and stress)

Interpretation of Arterial Pressures (cont’d) Pulse pressure: difference between systolic and diastolic pressures Normal is 30 to 40 mm Hg A low pulse pressure is common when stroke volume is low Mean arterial pressure (MAP) is normally 80 to 100 mm Hg MAP <60 mm Hg compromises function of vital organs

Complications of Continuous Arterial Pressure Monitoring Ischemia Occurs with embolism, thrombus, or arterial spasm Can result in tissue necrosis if not recognized rapidly Hemorrhage Occurs if line becomes disconnected Infection

Monitoring CVP Indications To assess circulating blood volume and filling pressures of the heart To assess right ventricular function Patients who have had major surgery or trauma need a CVP catheter Patients with pulmonary edema often benefit from CVP monitoring

CVP Catheters and Insertion Sites Most popular catheter is 7 French with a triple lumen The triple lumen allows infusion of medications and a port from which to obtain blood samples The internal jugular is a popular site for insertion of the catheter

CVP Waveforms Reflects the pressures in the right atrium Normal waveforms have three waves: “a”, “c”, and “v” “a” wave occurs with atrial contraction “c” wave occurs with movement of AV valve back toward the atrium during systole “v” occurs with atrial filling during systole

CVP Waveforms (cont’d)

Respiratory Influence on CVP Waveforms Spontaneous inspiratory efforts cause CVP to decrease and are seen on the waveform Positive pressure breaths cause the CVP to increase CVP monitoring during mechanical ventilation requires brief disconnection of the ventilator unless PEEP is being applied

Methods of Measuring CVP Transducer system CVP reported in mm Hg More accurate and provides a waveform Water monometer Reported in cm H2O Inexpensive Easy to use

Interpretation of CVP Causes of increased CVP Fluid overload Right/left heart failure Pulmonary hypertension Tricuspid valve stenosis Pulmonary embolism Increased venous return

Interpretation of CVP (cont’d) Causes of decreased CVP Reduced circulating blood volume Vasodilation (reduced venous return) Leaks in the pressure system Spontaneous inspiration

Complications of CVP Monitoring During placement Bleeding Pneumothorax Over time Infection (main potential problem) Embolus Air embolus

Pulmonary Artery Pressure Monitoring Developed to allow better evaluation of left ventricular function Allows assessment of: Left ventricular filling pressure Pulmonary vascular resistance Arteriovenous oxygen difference Mixed venous oxygen levels

Indications for PA Pressure Monitoring Indications not well defined Research shows many complications and may be of limited benefit Today PA catheter is placed on a case-by-case basis taking into consideration patient’s condition and staff qualifications

Indications for PA Pressure Monitoring (cont’d) Conditions for using the catheter Severe cardiogenic pulmonary edema Patients with ARDS who are hemodynamically unstable In patients who have had major thoracic surgery Patients with septic or severe cardiogenic shock

Catheters and Insertion Sites

Catheters and Insertion Sites (cont’d) The PA catheter has multiple lumens and is balloon tipped The balloon is used to float the catheter in place and to measure left ventricular filling pressures Most common sites for insertion include the subclavian and internal jugular veins

Insertion of the Catheter Catheter is floated through the right side of the heart and into the pulmonary artery Once it wedges into place, balloon is deflated Distinctive waveforms seen as catheter passes through the right atrium, right ventricle, pulmonary artery, and into the wedge position

PA Pressure Waveforms

Interpretation PA systolic pressure (20-30 mm Hg) Increases with high pulmonary vascular resistance Decreases with poor right heart function and pulmonary vasodilation PA diastolic pressure (8-15 mm Hg) Normally reflects left heart filling pressures Does not reflect left heart filling pressures when pulmonary vascular resistance elevated

Interpretation (cont’d) Wedge pressure Normally 4 to 12 mm Hg Must be interpreted in light of the patient’s medical history (history of MI will cause a stiff left ventricle and lead to higher pressures) Elevates with left heart failure or mitral stenosis Decreases with hypovolemia

Obtaining an Accurate Wedge Pressure Requires careful calibration of equipment Measure at end exhalation Catheter tip must be in West zone III where blood flow is continuous Low blood volume and high alveolar pressures can cause wedge pressure readings to be inaccurate

Complications of PA Monitoring During cannulation hemothorax, pneumothorax, and damage to blood vessels are possible Dysrhythmias can occur as catheter passes through the heart and during monitoring Catheter source of infection, thrombus, embolism, bleeding, and hematoma Pulmonary infarction possible

Summary Hemodynamic monitoring common in the ICU to identify cardiovascular problems and to measure the effects of therapies Continuous monitoring of arterial pressure, CVP, and PA pressures available Placement of catheter and its continuous use have potentially serious complications A risk/reward assessment must be done