Download Chapter 16

Chapter 16
Assessment of Hemodynamic
Pressures
Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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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
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Learning Objectives

Describe the following regarding central
venous pressure (CVP) monitoring:
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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
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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
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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
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Introduction
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Hemodynamic monitoring is performed to:
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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
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Arterial Pressure Monitoring

Indications
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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
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Placement of the Arterial Line
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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
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Arterial Pressure Waveforms
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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
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Arterial Pressure Waveforms
(cont’d)
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10
Arterial Pressure Waveforms
(cont’d)
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Interpretation of Arterial Pressures
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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
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Interpretation of Arterial Pressures
(cont’d)
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Hypotension is caused by:
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Low blood volume
Poor cardiac function
Low vascular resistance
A low diastolic pressure can compromise
coronary artery perfusion
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Interpretation of Arterial Pressures
(cont’d)
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Hypertension is caused by:
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Excessive contraction of the left ventricle
Vasoconstriction
Administration of vasopressors
Sympathetic stimulation (as occurs with fear
and stress)
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Interpretation of Arterial Pressures
(cont’d)
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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
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Complications of Continuous
Arterial Pressure Monitoring
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Ischemia
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Hemorrhage
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Occurs with embolism, thrombus, or arterial
spasm
Can result in tissue necrosis if not recognized
rapidly
Occurs if line becomes disconnected
Infection
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Monitoring CVP

Indications
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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
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CVP Catheters and Insertion Sites
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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
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CVP Waveforms
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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
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CVP Waveforms (cont’d)
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Respiratory Influence on
CVP Waveforms
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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
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Methods of Measuring CVP
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Transducer system
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CVP reported in mm Hg
More accurate and provides a waveform
Water monometer
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Reported in cm H2O
Inexpensive
Easy to use
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Interpretation of CVP
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Causes of increased CVP
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Fluid overload
Right/left heart failure
Pulmonary hypertension
Tricuspid valve stenosis
Pulmonary embolism
Increased venous return
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Interpretation of CVP (cont’d)
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Causes of decreased CVP
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Reduced circulating blood volume
Vasodilation (reduced venous return)
Leaks in the pressure system
Spontaneous inspiration
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Complications of CVP Monitoring
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During placement
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Bleeding
Pneumothorax
Over time
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Infection (main potential problem)
Embolus
Air embolus
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Pulmonary Artery Pressure
Monitoring
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Developed to allow better evaluation of left
ventricular function
Allows assessment of:
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Left ventricular filling pressure
Pulmonary vascular resistance
Arteriovenous oxygen difference
Mixed venous oxygen levels
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Indications for PA Pressure
Monitoring
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Indications not well defined
Research shows many complications and
may be of limited benefit
Today PA catheter is placed on a case-bycase basis taking into consideration
patient’s condition and staff qualifications
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Indications for PA Pressure
Monitoring (cont’d)

Conditions for using the catheter

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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
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Catheters and Insertion Sites
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Catheters and Insertion Sites
(cont’d)
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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
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Insertion of the Catheter
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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
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PA Pressure Waveforms
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Interpretation

PA systolic pressure (20-30 mm Hg)
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Increases with high pulmonary vascular
resistance
Decreases with poor right heart function and
pulmonary vasodilation
PA diastolic pressure (8-15 mm Hg)
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Normally reflects left heart filling pressures
Does not reflect left heart filling pressures
when pulmonary vascular resistance elevated
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Interpretation (cont’d)
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Wedge pressure
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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
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Obtaining an Accurate Wedge
Pressure
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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
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Complications of PA Monitoring
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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
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Summary
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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
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