Ch. 13 Part 2 Flashcards
1
Q
follows a spectrum of very invasive, moderately invasive, minimally invasive, and noninvasive methods
In general, cardiovascular surgical units use more invasive hemodynamic monitoring, whereas nonsurgical critical care areas begin with less-invasive monitoring, adding invasive technologies based on the patient’s physiologic requirements.
Hemodynamic Monitoring Equipment
Intraarterial Blood Pressure Monitoring
Central Venous Pressure Monitoring
Pulmonary Artery Pressure Monitoring
Continuous Monitoring of Mixed Venous and Central Venous Oxygen Saturation
A
Hemodynamic Monitoring
2
Q
four component parts:
Heparin
Calibration of Hemodynamic Monitoring Equipment
Zeroing the Transducer
Midaxillary Line (Phlebostatic Axis)
Leveling the Transducer
Head of Bed Backrest Position
Lateral Position
A
Hemodynamic Monitoring Equipment
3
Q
- An invasive catheter and high-pressure tubing connect the patient to the transducer.
- The transducer receives the physiologic signal from the catheter and tubing and converts it into electrical energy.
- The flush system maintains patency of the fluid-filled system and catheter.
- The bedside monitor contains the amplifier with recorder, which increases the volume of the electrical signal and displays it on an oscilloscope and on a digital scale in millimeters of mercury (mm Hg).
A
four component parts:
4
Q
Use of the anticoagulant heparin added to the normal saline flush setup to maintain catheter patency is controversial.
Although many units do add heparin to flush solutions, other critical care units avoid heparin because of concern about development of heparin-induced antibodies that can trigger an autoimmune condition known as heparin-induced thrombocytopenia (HIT).
Dextrose solutions are not recommended as flush solutions in monitoring catheters.
A
Heparin
5
Q
Two baseline measurements are necessary:
1. Calibration of the system to atmospheric pressure, also known as zeroing the transducer
2. Determination of the midaxillary axis for transducer height placement, necessary to accurately level the transducer
A
Calibration of Hemodynamic Monitoring Equipment
6
Q
calibrate the equipment to atmospheric pressure, referred to as zeroing the transducer, the three-way stopcock nearest to the transducer is turned simultaneously to open the transducer to air (atmospheric pressure) and to close it to the patient and the flush system.
Using zero to represent current atmospheric pressure provides a convenient baseline for hemodynamic measurement purposes.
Some monitors also require calibration of the upper scale limit while the system remains open to air.
Disposable transducers are very accurate, and after they are calibrated to atmospheric pressure, drift from the zero baseline is minimal.
A
Zeroing the Transducer
7
Q
physical reference point on the side of the chest that is used as a baseline for consistent transducer height placement.
a theoretical line is drawn from the fourth sternal intercostal space, where it joins the sternum, to a theoretical line on the side of the chest that is one half of the depth of the lateral chest wall.
The level of the transducer “air reference stopcock” approximates the position of the tip of an invasive hemodynamic monitoring catheter within the chest.
A
Midaxillary Line (Phlebostatic Axis)
8
Q
This process aligns the transducer with the level of the left atrium. The purpose is to line up the air fluid interface with the left atrium to correct for changes in hydrostatic pressure in blood vessels above and below the level of the heart.
If the transducer is placed above this atrial level, gravity and lack of fluid pressure give an erroneously low reading.
Every inch the transducer is positioned above the catheter tip, the measurement is 1.87 mm Hg less than the true value.
When there is a change in the patient’s position, the transducer must be leveled again to ensure that accurate hemodynamic pressure measurements are recorded.
Patient Position During Hemodynamic Monitoring.
emphasis on raising the head of the bed above 30 degrees to prevent aspiration, and position changes to prevent sacral skin pressure injury, require a reevaluation of transducer level with each position change.
A
Leveling the Transducer
9
Q
Nurse researchers have determined that the central venous pressure (CVP), pulmonary artery pressure (PAP), and pulmonary artery occlusion pressure (PAOP), also known as pulmonary artery wedge pressure, can be reliably measured at head of bed backrest positions from 0 (flat) to 60 degrees if the patient is lying on his or her back (supine).
Most patients do not need the head of the bed to be lowered to 0 degrees to obtain accurate CVP, PAP, or PAOP readings, as long as the midaxillary line is used as the reference point.
A
Head of Bed Backrest Position
10
Q
30-degree angle position, the landmark to use for leveling the transducer is one-half of the distance from the surface of the bed to the left sternal border.6 In the 90-degree right-lateral position, the transducer fluid air interface was positioned at the fourth intercostal space at the midsternum. In the 90-degree left-lateral position, the transducer was positioned at the left parasternal border (beside the sternum). It is important to know that measurements can be recorded in nonsupine positions, because critically ill patients must be turned to prevent development of pressure injury and other complications of immobility.
A
Lateral Position
11
Q
Indications
Catheters
Insertion and Allen Test
Nursing Management
Infection
Perfusion Pressure
Noninvasive Cuff Blood Pressure
Arterial Pressure Waveform Interpretation
Hemodynamic Monitoring Alarms
Invasive Hemodynamic Monitoring
A
Intraarterial Blood Pressure Monitoring
12
Q
Arterial blood pressure monitoring is indicated for any major medical or surgical condition that has the potential to alter blood pressure or cardiac output (CO), tissue perfusion, or fluid volume status.
The system is designed for continuous measurement of three blood pressure parameters: systole, diastole, and mean arterial pressure (MAP).
A
Indications
13
Q
Seldinger technique is typically used, which involves the following steps:
1. Entry into the artery using a needle
2. Passage of a supple guidewire through the needle into the artery
3. Removal of the needle
4. Passage of the catheter over the guidewire
5. Removal of the guidewire, leaving the catheter in the artery
A
Catheters
14
Q
Several major peripheral arteries are suitable for receiving a catheter and for long-term hemodynamic monitoring. The most frequently used site is the radial artery. The femoral artery is a larger vessel that is also frequently cannulated. Other smaller arteries such as the dorsalis pedis, axillary, or brachial arteries are used only when other arterial access is unavailable.2
The major advantage of the radial artery is the supply of collateral circulation to the hand provided by the ulnar artery through the palmar arch in most people.
collateral circulation must be assessed by using Doppler flow or by the modified Allen test according to institutional protocol.
A
Insertion and Allen Test
15
Q
Intraarterial blood pressure monitoring is designed for continuous assessment of arterial perfusion to the major organ systems of the body. MAP is the clinical parameter most often used to assess perfusion, because MAP represents perfusion pressure throughout the cardiac cycle.
A
Nursing Management
16
Q
associated with the same risk of blood-stream infections as central venous catheters. Therefore infection prevention measures must be just as meticulous for arterial catheters as for central catheters
A
Infection
17
Q
A MAP greater than 60 mm Hg is necessary to perfuse the cor-
onary arteries. A higher MAP may be required to perfuse the brain and the kidneys. A MAP between 70 and 90 mm Hg is preferable for a patient with heart disease to decrease left ventricular (LV) workload. After carotid endarterectomy or neurosurgery, a higher MAP of 90 to 110 mm Hg may be more appropriate to increase cerebral perfusion pressure.
If CO decreases, the body compensates by constricting peripheral vessels to maintain the blood pressure.
Nursing assessment of a patient with an arterial line includes comparison of clinical findings with arterial line readings including perfusion pressure and MAP.
A
Perfusion Pressure
18
Q
In most nonemergency situations, following the trend of the arterial pressure is more valuable than an isolated measurement
A
Pulse Pressure
19
Q
If the arterial line becomes unreliable or dislodged, a cuff pressure can be used as a reserve system. However, research studies indicate that a noninvasive cuff blood pressure does not produce the same values as an intraarterial catheter.
The concern is that the cuff pressure may be unreliable because of peripheral vasoconstriction. It is usual practice to compare a cuff pressure after the arterial line is inserted to identify and document any difference in pressure readings.
A
Noninvasive Cuff Blood Pressure
20
Q
As the aortic valve opens, blood is ejected from the left ventricle and is recorded as an increase of pressure in the arterial system.
The highest point recorded is called systole. After peak ejection (systole), the force decreases, and the pressure falls. A notch (dicrotic notch) may be visible on the downstroke of this arterial waveform, representing closure of the aortic valve. The dicrotic notch signifies the start of blood flow into the arterial vasculature. The lowest point recorded is called diastole.
Decreased arterial perfusion.
Pulse deficit.
Pulsus paradoxus.
Pulsus alternans.
Damped waveform.
Underdamped waveform.
Fast-flush square waveform test.
A
Arterial Pressure Waveform Interpretation
21
Q
Specific problems with heart rhythm can translate into poor arterial perfusion if CO decreases. Poor perfusion may be seen as a single, nonperfused beat after a premature ventricular contraction (PVC) or as multiple, nonperfused beats
A
Decreased arterial perfusion.
22
Q
A pulse deficit occurs when the apical HR and the peripheral pulse are not equal. In the critical care unit, this can be seen on the bedside monitor. Normally, there is one arterial upstroke for each QRS complex, and if there are more QRS complexes than arterial upstrokes, a pulse deficit is present
To determine whether a pulse deficit is significant, it is necessary to evaluate the clinical effect on the patient and whether any change in MAP or pulse pressure has occurred.
A
Pulse deficit.
23
Q
a decrease of more than 10 mm Hg in the arterial waveform that occurs during inhalation (inspiration). It is caused by a fall in CO as a result of increased negative intrathoracic pressure during inhalation.
In certain clinical conditions, the pulsus paradoxus is obvious and can be clearly seen on an arterial waveform. It can be used as a clinical diagnostic test for a patient with cardiac tamponade, pericardial effusion, or constrictive pericarditis.
Pulsus paradoxus may also be observed in hypovolemic surgical patients who are mechanically ventilated with large tidal volumes
A
Pulsus paradoxus.
24
Q
every other arterial pulsation is weak. This sometimes occurs in individuals with advanced LV heart failure.
A
Pulsus alternans.
25
If the arterial monitor shows a low blood pressure, it is important to determine whether the problem is related to the patient or to the monitoring equipment,
In this case the arterial waveform is more rounded, without a dicrotic notch, compared with a normal waveform, and the digital readout correlated with the patient’s cuff pressure, adding confirmation that the patient was hypotensive.
A damped (flattened) arterial waveform: in this case the patient’s cuff pressure was significantly higher than the digital readout, representing a problem with equipment.
Damped waveform occurs when communication from the artery to the transducer is interrupted and produces falsely lower values on the monitor and oscilloscope.
Troubleshooting techniques are used to find the origin of the problem and to remove the cause of damping
Damped waveform.
26
Another cause of arterial waveform distortion is underdamping, also called overshoot or fling. Underdamping is recognized by a narrow upward systolic peak that produces a falsely high systolic reading compared with the patient’s cuff blood pressure,
over-shoot is caused by an increase in dynamic response or increased oscillations within the system
Underdamped waveform.
27
dynamic response of the monitoring system can be verified for accuracy at the bedside by the fast-flush square waveform test, also called the dynamic frequency response test
nurse performs this test to ensure that the patient pressures and waveform shown on the bedside monitor are accurate
makes use of the manual flush system on the transducer.
If air bubbles, clots, or kinks are in the system, the waveform becomes damped, or flattened, and this is reflected in the square waveform result.
should be incorporated into nursing care procedures at the bedside when the hemodynamic system is first set up, at least once per shift, after opening the system for any reason, and when there is concern about the accuracy of the waveform.
must be able to assess whether a low MAP or narrowed perfusion pressure represents decreased arterial perfusion or equipment malfunction.
Fast-flush square waveform test.
28
All critically ill patients must have the hemodynamic monitoring alarms on and adjusted to sound an audible alarm if the patient should experience a change in blood pressure, HR, respiratory rate, or other significant monitored variable.
Alarm limits must be customized to the patient’s physiologic baseline to reduce false-positive alarms.
Hemodynamic Monitoring Alarms
29
Invasive hemodynamic monitoring refers to monitoring situations where catheters are placed into central veins or pass through the right heart chambers predominantly describing central venous catheters, pulmonary artery catheters, thermodilution CO, and continuous mixed-venous oxygen saturation monitoring. Some of the newer monitoring methods that combine arterial and central venous monitoring systems also are considered invasive
Invasive Hemodynamic Monitoring
30
Indications
Central Venous Catheters
Insertion
Central Venous Catheter Complications
Nursing Management
Specialized Central Venous Catheters
Central Venous Pressure Monitoring
31
whenever a patient has a significant alteration in fluid volume used as a guide for fluid volume replacement in hypovolemia. In addition to clinical signs and symptoms, CVP is also monitored in hypervolemia to assess the effect of diuresis after diuretic administration
Indications
32
Antimicrobial-impregnated or heparin-coated catheters have a lower rate of bloodstream infections.
Central Venous Catheters
33
large veins of the upper thorax, the subclavian (SC) and internal jugular (IJ), are most commonly used for percutaneous CVC line insertion. The femoral vein in the groin is used when the thoracic veins are not accessible.
Internal jugular vein.
Subclavian vein.
Femoral vein.
Insertion
34
most frequently used easiest to canalize.
blood flow is significantly higher in the IJ vein
Another advantage of the IJ vein is that the risk of creating an iatrogenic pneumothorax is small.
Disadvantages to the IJ vein are patient discomfort from the indwelling catheter when moving the head or neck and contamination of the IJ vein site from oral or tracheal secretions, especially if the patient is intubated or has a tracheostomy.
infections are higher in the IJ than the SC position for indwelling catheters left in place for more than 4 days.
Internal jugular vein.
35
anticipated CVC dwelling time is prolonged (more than 5 days), the SC site is preferred.
has the lowest infection rate and produces the least patient discomfort from the catheter.
disadvantages are that the SC vein is more difficult to access and carries a higher risk of iatrogenic pneumothorax or hemothorax, although the risk varies greatly depending on the experience and skill of the physician inserting the catheter.
Subclavian vein.
36
considered the easiest cannulation site, because there are no curves in the insertion route.
The large diameter of the femoral vein carries a high blood flow that is advantageous for specialized procedures such as continuous renal replacement therapy or plasmapheresis. Because there is a higher rate of nosocomial infection with femoral catheters, this site is not recommended.
The tip of the catheter is designed to remain in the vena cava and should not migrate into the right atrium. Because many patients are awake and alert when a CVC is inserted, a brief explanation about the procedure can minimize patient anxiety and result in cooperation during the insertion.
The electrocardiogram (ECG) should be monitored during CVC insertion because of the associated risk of dysrhythmias.
A chest radiograph is obtained after upper thoracic CVC placement to verify placement and the absence of an iatrogenic hemothorax or pneumothorax, especially if the SC vein was accessed.
Femoral vein.
37
Air embolus
Thrombus formation.
Infection.
Central Venous Catheter Complications
38
Air can enter during insertion through a disconnected or broken catheter by means of an open stopcock, or air can enter along the path of a removed CVC. This is more likely if the patient is in an upright position,
Treatment involves immediately occluding the external site where air is entering, administering 100% oxygen, and placing the patient on the left side with the head downward (left lateral Trendelenburg position). This position displaces the air from the right ventricular outflow tract to the apex of the heart, where the air may be aspirated by catheter intervention or gradually absorbed by the bloodstream as the patient remains in the left lateral Trendelenburg position. Precautions to prevent an air embolism in a central line include using only screw (Luer-Lock) connections and using only closed-top screw caps on all three-way stopcocks.
Air embolus
39
it may involve development of a fibrin sleeve around the catheter, or the thrombus may be attached directly to the vessel wall
Other factors that promote clot formation include rupture of vascular endothelium, interruption of laminar blood flow, and physical presence of the catheter, all of which activate the coagulation cascade.
Because of concerns over the development of HIT, many hospitals use a saline-only flush to maintain CVC patency.
Thrombus formation.
40
infection incidence strongly correlates with the length of time the CVC has been inserted, with longer insertion
times associated with higher infection rates.
identified at the catheter insertion site or as a blood-stream infection (septicemia). Systemic manifestations of infection can be present without inflammation at the catheter site.
Most infections are transmitted from the skin, and infection prevention begins before insertion of the CVC.
To decrease the infection risk, most hospitals routinely audit use of CVCs to reduce the CVC duration to the absolute minimum, as fewer insertion days means fewer CLABSIs.
Infection.
41
The CVC is used to monitor the CVP and waveform. The CVP catheter is used to measure the filling pressures of the right side of the heart.
Normal CVP is 2 to 5 mm Hg (3 to 8 cm H2O).
Central venous pressure volume assessment.
Passive leg raise.
Removal.
Patient position.
Central venous pressure waveform interpretation.
Nursing Management
42
Use of the CVP value to assess volume status is considered inaccurate.
Use of the CVP value to assess volume status is considered inaccurate.
Central venous pressure volume assessment.
43
Another method to assess fluid responsiveness is to passively raise and support the patient’s legs to allow the venous blood from the lower extremities to flow rapidly into the vena cava and return to the right heart.
This method has the advantage of not infusing any IV fluid.
However, a change in the CVP value is not considered as reliable as using real-time monitoring of CO using a pulse wave analysis method
Passive leg raise.
44
Removal of the CVC usually is a nursing responsibility. Complications are uncommon, and the ones to anticipate are bleeding and air embolus
Recommended techniques to avoid air embolus during CVC removal include removing the catheter when the patient is supine in bed (not in a chair) and placing the patient flat or in reverse Trendelenburg position if the patient’s clinical condition permits this maneuver.
If the patient is alert and able to cooperate, he or she is asked to take a deep breath to raise intrathoracic pressure during removal.
After removal, to decrease the risk of air entering by a “track,” an occlusive dressing is applied to the site. If bleeding at the site occurs after removal, firm pressure is applied.
Removal.
45
To achieve accurate CVP measurements, the midaxillary line (phlebostatic axis) is used as a reference
point on the body, and the transducer or water manometer zero must be level with this point. midaxillary line is used and the transducer is correctly aligned, any head of bed position of up to 60 degrees may be used for accurate CVP readings for most patients. Elevating the head of the bed is especially helpful for a patient with cardiopulmonary problems who cannot tolerate a flat position.
Patient position.
46
The normal right atrial (CVP) waveform has three positive deflections—a, c, and v waves—that correspond to specific atrial events in the cardiac cycle
The a wave reflects atrial contraction and follows the P wave seen on the ECG.
x descent and represents atrial relaxation.c wave reflects the bulging of the closed tricuspid valve into the right atrium during ventricular contraction; v wave represents atrial filling and increased pressure against the closed tricuspid valve
y descent and represents the fall in pressure as the tricuspid valve opens and blood flows from the right atrium to the right ventricle.
Cannon waves.
Central venous pressure waveform interpretation.
47
Dysrhythmias can change the pattern of the CVP waveform.
These cannon waves are observed as large pulses in the jugular veins. Other pathologic conditions, such as advanced right ventricular failure or tricuspid valve insufficiency, allow regurgitant backflow of blood from the right ventricle to the right atrium during ventricular contraction, producing large v waves on the right atrial waveform. In atrial fibrillation, the CVP waveform has no recognizable pattern because of the disorganization of the atria.
Cannon waves.
48
CVC that incorporates a fiberoptic sensor to continuously measure central venous oxygen saturation (ScvO2) can be used as a traditional CVC and additionally used to follow the trend of venous oxygen saturation
Specialized Central Venous Catheters
49
The PA catheter is the most invasive of the critical care monitoring catheters
It is also known as a right heart catheter or Swan-Ganz catheter
PA catheters are less common, except during open-heart surgery, in management of acute heart failure, and in management of acute pulmonary hypertension.
Invasive.
Consequently, routine use of the PA catheter has decreased dramatically.
One of the criticisms of the PA catheter is that the data it provides may result in overtreatment.
Indications
Cardiac Output Determinants
Oxygen supply and demand
Pulmonary Artery Catheters
Insertion
Pulmonary Artery Waveform Interpretation
Medical Management
Nursing Management
Cardiac Output Measurement with a Pulmonary Artery Catheter
Pulmonary Artery Pressure Monitoring
50
thermodilution PA catheter is reserved for the most hemodynamically unstable patients for the diagnosis and evaluation of cardiogenic shock, pulmonary hypertension, and management during and after heart surgery
can provide information about PA pressures (systolic, diastolic, mean), PAOP (wedge pressure), and CO.
location of the tip of the PA catheter in the pulmonary artery can provide access for measurement of mixed venous oxygen saturation.
Indications
51
CO is the product of HR multiplied by SV. SV is the volume of blood ejected by the heart during each beat (reported in milliliters).
Clinical factors that contribute to the heart’s SV are preload, afterload, and contractility and may be monitored using the PA catheter contributor to CO is HR, which is usually recorded from the ECG leads.
Cardiac Output Determinants
52
peripheral tissues need more oxygen (e.g., during exercise or sepsis), the normal, healthy heart can augment HR and SV and greatly increase CO.
tissues require more oxygen, these normal mechanisms are often nonfunctional, and the critical care nurse assesses the need for and then optimizes hemodynamic function.
Preload.
Afterload.
Contractility.
Oxygen supply and demand
53
describe the hemodynamic numbers related to preload as filling pressures. These values refer to the pressures resulting from the volumes in the atria and ventricles.
Preload is the volume in the ventricle at end-diastole.
LV volume can be measured directly during cardiac catheterization, but it is not generally measured in the critical care unit.
principle is that the presence of blood within the ventricle creates pressures that can be measured by the PA catheter and transducer and can be displayed on the bedside monitor.
Estimation of preload.
Frank-Starling law of the heart.
Ejection fraction.
Cardiac dysfunction.
Pulmonary artery diastolic pressure and pulmonary artery occlusion pressure relationship.
Pulmonary hypertension.
Heart failure.
Mitral stenosis
Mitral regurgitation.
Preload.
54
When the PA catheter is correctly positioned with the tip in one of the large branches of the PA, the only valve between the PA catheter tip and the left ventricle is the mitral valve.
During diastole, when the mitral valve is open, no vascular obstruction exists between the tip of the PA catheter and the left ventricle
LV preload volume creates left ventricular end-diastolic pressure
a PA catheter, preload is estimated by measuring the PAOP or wedge pressure. Normal left atrial pressure or PAOP is 5 to 12 mm Hg.
Estimation of preload.
55
Change in preload relies on the Frank-Starling law of the heart. This law states that the force of ventricular ejection is directly related to the following two elements:
1. Volume in the ventricle at end-diastole (preload)
2. Amount of myocardial stretch placed on the ventricle as a result
Frank-Starling law of the heart.
56
The relationship of preload to the CO is complex, because not all of the preload volume is ejected with every heartbeat. The percentage of preload volume ejected from the left ventricle per beat is measured during cardiac catheterization and is described as the ejection fraction (EF).
normal EF in a healthy heart is 70%.
Ejection fraction.
57
A significant relationship exists between LVEDP and cardiac muscle dysfunction. As a general rule, the higher the pressure inside the left ventricle, the greater the degree of cardiac dysfunction.
The pressure rises at end-diastole (end of filling) because the compromised ventricle cannot eject all of the preload blood volume.
A plan of care for this patient includes decreasing LV preload through (1) restriction of IV and oral fluids, (2) venodilation, and (3) diuresis.
Cardiac dysfunction.
58
The most accurate is the PAOP method. The second method involves measuring PADP during diastole when the normal PADP is equal to or 1 to 3 mm Hg higher than the mean PAOP and LVEDP. It is physiologically impossible for the PAOP to be higher than the PADP. The clinician must recalibrate and troubleshoot the monitoring system if this appears to occur
Pulmonary artery diastolic pressure and pulmonary artery occlusion pressure relationship.
59
Specific clinical conditions can alter the normal PADP/PAOP relationship. In pulmonary hypertension, the pulmonary arterial systolic and diastolic pressures are independently raised above the LV pressures.
The numeric difference between the PADP and the PAOP value is called a gradient. If a large gradient exists between the PAOP (wedge pressure) and PADP (pulmonary artery diastolic pressure), this is evidence of pulmonary hypertension
Pulmonary hypertension.
60
In failure of the left side of the heart, the PAOP and PADP are elevated and approximately equal. Left-sided heart failure may also cause pulmonary hypertension over time. Eventually, damage to the lung vasculature occurs because of exposure to high LV pressure.
Heart failure.
61
alters the accuracy of PAOP and PADP as parameters of LV function. In mitral valve stenosis, left atrial pressure and PAOP are increased and cause pulmonary congestion; however, these elevated values do not reflect the LVEDP because a stenotic mitral valve obstructs the normal path of blood flow from the left atrium to the left ventricle; this decreases LV preload and consequently lowers LVEDP.
non-stenotic mitral valve is essential for accurate readings, because a narrowed mitral valve increases left atrial filling pressures in the presence of a normal LVEDP
Mitral stenosis
62
the mean PAOP (wedge pressure) reading is artificially elevated because of abnormal backflow of blood from the left ventricle to the left atrium during systole
Mitral regurgitation.
63
defined as the pressure the ventricle generates to overcome the resistance to ejection created by the arteries and arterioles. It is a calculated measurement derived from information obtained from the PA catheter. increased afterload, ventricular wall tension rises. decrease in afterload, wall tension is lowered.
Systemic vascular resistance.
Systemic vascular resistance and afterload reduction.
Pulmonary vascular resistance.
Afterload.
64
Resistance to ejection from the left side of the heart is estimated by calculating the SVR. The calculation represents the pressure difference between the average arterial pressure (MAP) and venous pressure (CVP) divided by flow (CO).
To index this value to the patient’s body surface area, the cardiac index (CI) is placed in the formula in the same position as the CO.
the lower the SVR value (arteries more dilated), the higher the CO.
Systemic vascular resistance.
65
When the SVR is elevated, continuous infusions of vasodilators such as sodium nitroprusside or high-dose nitroglycerin may be used to reduce SVR.
If the SVR is extremely low (e.g., less than 500 dyn *sec * cm25), as may occur in sepsis, the CO will be elevated, and MAP will be low. In this situation, volume and vasopressors are infused to increase MAP and SVR.
For a person with a normal heart without cardiac dysfunction, an elevated SVR may have minimal effect on CO. The importance of SVR on CO is related to the functional quality of the myocardium.
Systemic vascular resistance and afterload reduction.
66
Resistance to ejection from the right side of the heart is estimated by calculating the pulmonary vascular resistance (PVR).
Acute pulmonary hypertension, greater than 25 mm Hg, can occur as a sequela of severe acute respiratory distress syndrome (ARDS).
Traditionally, a PA catheter was used to monitor vasodilator therapy and fluid management.
Pulmonary vascular resistance.
67
Many factors have an effect on contractility, including preload volume as measured by PAOP, SVR, myocardial oxygenation, electrolyte balance, positive and negative inotropic medications, and amount of functional myocardium available to contribute to contraction. These factors can have a positive inotropic effect, enhancing contractility, or a negative inotropic effect, decreasing contractility.
Significant factors related to contractility that can be measured by the PA catheter include preload filling pressures, SVR, and CO.
Preload has an effect on contractility by means of Starling’s
mechanism.
As volume in the ventricle rises, contractility increases. If the ventricle is overdistended with volume, contractility falls
Hypoxemia acts as a negative inotrope, because the myocardium must have oxygen available to the cells to contract efficiently.
Optimizing contractility. Contractility.
Contractility.
68
IV medications such as dopamine, dobutamine, and milrinone are prescribed for their positive inotropic effect.
if LV contractility is increased in response to treatment, this effect is frequently reflected by changes in PAOP (wedge pressure) and by an increase in CO
Optimizing contractility.
69
traditional PA catheter, invented by Swan and Ganz, has four lumens for measurement of right atrial pressure (similar to CVP), PA pressures, PAOP, and CO
Multifunction catheters may have additional lumens, which can be used for IV infusion and to measure continuous SvO2, right ventricular volume, and continuous CO
PA flow-directed catheter is 110 cm long. The most commonly used size is 7.5 or 8.0 Fr, although 5.0 and 7.0 Fr sizes are available.
Each of the four lumens exits into the heart or pulmonary artery at a different point, graduated along the catheter length
Right atrial lumen.
Pulmonary artery lumen.
Balloon lumen.
Thermistor lumen.
Additional features.
Pulmonary Artery Catheters
70
proximal lumen is situated in the right atrium and is used for IV infusion, CVP measurement, withdrawal of venous blood samples, and injection of fluid for CO determinations.
Right atrial lumen.
71
The distal PA lumen is located at the tip of the PA catheter and is situated in the pulmonary artery. It is used to record pressures within the artery and can be used for withdrawal of blood samples to measure mixed venous blood gases, also known as SvO2.
Pulmonary artery lumen.
72
third lumen opens into a balloon at the end of the catheter that can be inflated with 0.8 mL (7 Fr) to 1.5 mL (7.5 Fr) of air
balloon is inflated during catheter insertion after the catheter reaches the right atrium to assist in forward flow of the catheter and to minimize right ventricular ectopy from the catheter tip
balloon is also inflated to obtain the PAOP measurements when the PA catheter is correctly positioned in the pulmonary artery
Balloon lumen.
73
fourth lumen is a thermistor (temperature sensor) used to measure changes in blood temperature
It is located 4 cm from the catheter tip and is used to measure thermodilution CO.
Thermistor lumen.
74
If continuous SvO2 is measured, the catheter has an additional fiberoptic lumen that exits at the tip of the catheter
If cardiac pacing is used, two PA catheter methods are available. One type of catheter has three atrial (A) and two ventricular (V) pacing electrodes attached to the catheter so that when it is properly positioned
The other catheter method uses a specific transvenous pacing wire that is passed through an additional catheter lumen and exits into the right ventricle if ventricular pacing is required.
Additional features.
75
If a PA catheter is to be inserted into a patient who is awake, some brief explanations about the procedure are helpful to ensure that the patient understands what is going to happen.
In most insertions, the PA catheter floats into the right pulmonary artery.
Before inserting the catheter into the vein, the physician—using sterile technique—tests the balloon for inflation and flushes the catheter with physiologic saline to remove any air.
This introducer sheath remains in place, and the supple PA catheter is threaded through it into the vena cava and into the right side of the heart.
Insertion
76
Each chamber of the heart has a distinctive waveform with recognizable characteristics.
Right atrial waveform.
Right ventricular waveform.
Pulmonary artery waveform.
Pulmonary artery occlusion waveform (wedge).
Pulmonary Artery Waveform Interpretation
77
As the PA catheter is advanced into the right atrium during insertion, a right atrial waveform must be visible on the monitor, with recognizable a, c, and v waves
Normal mean pressure in the right atrium is 2 to 5 mm Hg.
Right atrial waveform.
78
The right ventricular waveform is distinctly pulsatile, with distinct systolic and diastolic pressures. Normal right ventricular pressures are 20 to 30 mm Hg systolic and 0 to 5 mm Hg diastolic.
Right ventricular waveform.
79
As the catheter enters the pulmonary artery, the waveform again changes. The diastolic pressure rises. Normal pressures in the pulmonary artery range from 20 to 30 mm Hg systolic over 10 mm Hg diastolic. A dicrotic notch, visible on the downslope of the waveform, represents closure of the pulmonic valve.
Pulmonary artery waveform.
80
While the balloon remains inflated, the catheter is advanced into the wedge position. This maneuver produces the PAOP.
The waveform decreases in size and is nonpulsatile, reflecting a normal left atrial tracing with a and v wave deflections.
known as a wedge tracing because the balloon is “wedged” into a small pulmonary vessel, but it is technically described as the PAOP
When the balloon is reinflated, the catheter should move forward into a small artery and the wedge tracing should be visible on the monitor.
Normal PAOP ranges from 5 to 12 mm Hg.
After insertion, the introducer is sutured to the skin, and the catheter, which lies within the introducer, is secured with a catheter securement device.
chest radiograph is taken to verify placement
This practice prevents possible trauma from frequent balloon inflation; in such a situation, the PA catheter is consciously pulled back into a safe position within the pulmonary artery so that wedging cannot occur.
After insertion of the catheter, the chest radiograph or fluoroscopy is used to verify the PA catheter position to ensure that it is not looped or knotted in the right ventricle and to rule out pneumothorax or hemorrhagic complications.
Use of this external sleeve on PA catheters has been associated with lower rates of bloodstream infection.
Pulmonary artery occlusion waveform (wedge).
81
Medical goals of hemodynamic monitoring include assessment of adequacy of perfusion in stable patients, early detection of decreased perfusion, titration of therapy to meet specific therapeutic outcomes, and differentiation of different organ system dysfunctions.
Medical Management
82
Factors that affect PA measurement are the head-of-bed backrest position and lateral body position relative to transducer height placement, respiratory variation, and use of positive end-expiratory pressure (PEEP).
Patient position.
Respiratory variation.
Positive end-expiratory pressure.
Avoiding complications.
Pulmonary artery catheter removal.
Nursing Management
83
The patient does not need to be flat for accurate pressure readings to be obtained. In the supine position, when the transducer is placed at the level of the midaxillary line (phlebostatic axis), a head-of-bed position from flat up to 60 degrees is appropriate for most patients
After a patient changes position, a stabilization period of 5 to 15 minutes is recommended before taking pressure readings.
Patient position.
84
All PADP and PAOP (wedge) tracings are subject to respiratory interference, especially when the patient is on a positive-pressure, volume-cycled ventilator.
In some clinical settings, ECG signals or airway pressure and flow are recorded simultaneously with the PADP/PAOP tracing to identify end-expiration, which is the most stable point in the respiratory cycle when intrapleural pressures are close to zero.
Respiratory variation.
85
If a PEEP of greater than 10 cm H2O is used, PAOP (wedge) and PAPs will be artificially elevated, and CO may be negatively affected.
However, it is important not to disconnect a patient from the ventilator just to record PAP measurements, because this will close alveoli, will decrease the patient’s oxygenation level, and may result in persistent hypoxemia.
Trend of PA readings is more important than one individual measurement.
used as a basis for clinical interventions to support and improve cardiopulmonary function in the critically ill patient
Positive end-expiratory pressure.
86
Potential cardiac complications include ventricular dysrhythmias, endocarditis, valvular damage, cardiac rupture, and cardiac tamponade. Potential pulmonary complications include rupture of a PA, PA thrombosis, embolism or hemorrhage, and infarction of a segment of lung.
If the catheter is spontaneously wedged, the catheter must be gently pulled back out of the wedge position to prevent pulmonary infarction.
Infection is always a risk with a PA catheter.
Avoiding complications.
87
PA catheters can be safely removed from the patient by critical care nurses competent in this procedure. Removal is not usually associated with major complications. Rarely, PVCs occur as the catheter is pulled through the right ventricle.
Pulmonary artery catheter removal.
88
The PA catheter measures CO using an intermittent (bolus) or a continuous CO method.
Thermodilution cardiac output bolus measurement.
Cardiac output curve.
Injectate temperature.
Patient position and cardiac output.
Clinical conditions that alter cardiac output.
Continuous invasive cardiac output measurement.
Calculated hemodynamic profiles using a pulmonary artery catheter.
Cardiac Output Measurement with a Pulmonary Artery Catheter
89
The bolus thermodilution method is performed at the bedside and results in CO calculated in liters per minute.
Three CO values that are within a 10% mean range are obtained at one time and are averaged to calculate CO.
The thermodilution CO is very accurate when several injectate values are averaged. A known amount, usually 10 mL, of room temperature physiologic saline solution is injected into the proximal lumen of the PA catheter.
Frequently, a closed in-line system attached to a 500-mL bag of 0.9% saline is used as a reservoir to deliver the individual injections.
Thermodilution cardiac output bolus measurement.
90
The thermodilution CO method uses the indicator-dilution method, in which a known temperature is the indicator.
If the curve has an uneven pattern, it may indicate faulty injection technique, and the CO measurement must be repeated. Patient movement or coughing also alters the CO measurement
Cardiac output curve.
91
If the CO is within the normal range, it is equally accurate whether iced or room temperature injectate is used.
This is particularly important if iced injectate is used. With all delivery systems, the injectate is delivered at the same point in the respiratory cycle, usually end-exhalation.
Injectate temperature.
92
In a normovolemic, stable patient, reliable CO measurements can be obtained in a supine position (patient lying on his or her back) with the head of the bed elevated up to 60 degrees.
CO measurements performed when the patient is turned to the side are not considered as accurate as measurements performed with the patient in the supine position.
Patient position and cardiac output.
93
Two clinical conditions produce errors in the thermodilution CO measurement: tricuspid valve regurgitation and ventricular septal rupture.
If the patient has tricuspid valve regurgitation, the expected flow of blood from the right atrium to the pulmonary artery is disrupted by backflow from the right ventricle to the right atrium.
If the person has an intracardiac left-to-right shunt, as occurs after ventricular septal rupture, the thermodilution CO measures the large right-to-left shunt volume and records a higher CO than the patient’s true systemic output.
Clinical conditions that alter cardiac output.
94
The bolus thermodilution method is reliable but performed intermittently.
One method uses a thermal filament on the PA catheter to emit small energy signals (the indicator) into the bloodstream. These signals are then detected by the thermistor near the tip of the PA catheter. An indicator curve is created, and a CO value is calculated from these data.
Continuous invasive cardiac output measurement.
95
For a patient with a thermodilution PA catheter in place, additional hemodynamic information can be calculated using routine vital signs, CO, and body surface area. These measurements are calculated using specific formulas that are indexed to a patient’s body size
Calculated hemodynamic profiles using a pulmonary artery catheter.
96
Indications
Catheters
Nursing Management
Continuous Monitoring of Mixed Venous and Central Venous Oxygen Saturation
97
Continuous monitoring of venous oxygen saturation is indicated for a critically ill patient who has the potential to develop an imbalance between oxygen supply and metabolic tissue demand.
The same fiberoptic technology has been used in combination with a fiberoptic triple-lumen CVC. In this situation, the venous blood is sampled from the superior vena cava, just above the right atrium, and the ScvO2 is measured.
The following four factors contribute to this balance:
1. CO
2. Hemoglobin
3. Arterial oxygen saturation (SaO2)
4. Tissue oxygen metabolism (VO2)
Three of these factors (CO, hemoglobin, and SaO2) contribute to the supply of oxygen to the tissues. Tissue metabolism (VO2) determines oxygen consumption or the quantity of oxygen extracted at tissue level that creates the demand for oxygen
Indications
98
defined by where the fiberoptic tip is located SvO2 catheter.
The pulmonary arterial SvO2 catheter has the traditional four lumens plus a lumen containing two or three optical fibers.
optical module transmits a narrow band of light down one optical fiber
This light is reflected off the hemoglobin in the blood and returns to the optical module through the receiving fiberoptic.
The SvO2 signal is recorded on a continuous display.
ScvO2 catheter.
SvO2 or ScvO2 calibration.
Catheters
99
The central venous ScvO2 technology is incorporated into a multilumen CVC. The fiberoptic catheter tip is positioned in a central vein, such as the superior vena cava
used to measure the venous saturation is identical in both types of catheters, and the same continuous display module is used for both catheters
the ScvO2 values are slightly higher.
ScvO2 catheter.
100
The catheter is calibrated before insertion into the patient through a standardized color reference system, which is part of the catheter package.
Waveform analysis or venous saturation measurement, or both, can be used for accurate placement. After the catheter is inserted, recalibration is unnecessary unless the catheter becomes disconnected from the optical module.
To recalibrate the fiberoptic module to verify accuracy when the catheter is already inserted in a patient, a mixed venous blood sample (SvO2) or central venous sample (ScvO2) must be withdrawn from the appropriate catheter tip and sent to the laboratory for oxygen saturation analysis.
SvO2 or ScvO2 calibration.
101
SvO2 monitoring provides a continuous assessment of the balance of oxygen supply and demand for an individual patient.
Nursing assessment includes evaluation of the SvO2 or ScvO2 value and evaluation of the four factors (SaO2, CO, hemoglobin, and VO2) that maintain the oxygen supply demand balance.
Normal SvO2 values.
Normal ScvO2 values.
SvO2 or ScvO2 and arterial oxygen saturation.
SvO2 or ScvO2 and cardiac output.
SvO2 or ScvO2 and hemoglobin.
SvO2 or ScvO2 and oxygen consumption.
Normal SvO2 or ScvO2.
Low SvO2 or ScvO2..
High SvO2.
Nursing Management
102
Normal SvO2 is approximately 75% in a healthy individual (range, 60% to 80%). In critically ill patients, an SvO2 value between 60% and 80% is evidence of adequate balance between oxygen supply and demand.
Normal SvO2 values.
103
Catheter are slightly higher, because the reading is taken before the blood enters the right heart chambers, where the cardiac sinus (vein) delivers venous blood drained from the myocardium into the right atrium. The heavily desaturated myocardial blood decreases the oxygen saturation slightly.
If the SvO2 or ScvO2 value changes by more than 10% and this change is maintained for more than 10 minutes, the clinician must determine which of the four factors is affecting SvO2.
Normal ScvO2 values.
104
A change in SvO2 or ScvO2 may be caused by a change in SaO2. If the SaO2 is increased because supplemental oxygen is being administered, the SvO2 also will increase.
If the oxygen supply is disrupted and SaO2 is decreased, SvO2 will decrease.
SvO2 can be decreased by any action or disease that reduces oxygen supply, including ARDS, endotracheal suctioning, removing a patient from the ventilator, or removing supplementary oxygen.
SvO2 or ScvO2 and arterial oxygen saturation.
105
A change in SvO2 or ScvO2 may be caused by an alteration in CO. Changes in one or more of the following four individual hemodynamic factors affect CO: preload, SVR, contractility, and HR
Any major loss of HR causes a decrease in CO.
Because CO is an important component of the continuous SvO2 value, researchers investigated whether SvO2 could be substituted for thermodilution CO as a monitoring tool.
Monitoring SvO2 is an additional level of hemodynamic monitoring but does not replace thermodilution CO.
SvO2 or ScvO2 and cardiac output.
106
Hemoglobin is the transport mechanism for oxygen in the blood.
If the hemoglobin level falls as a result of bleeding or red blood cell (RBC) destruction, the body maintains oxygen transport by increasing CO and using oxygen reserves in the venous blood return.
SvO2 or ScvO2 and hemoglobin.
107
VO2 describes the amount of oxygen the body tissues consume for normal function in 1 minute.
body’s metabolic demands increase because of exercise or increased metabolic rate, the body increases CO to augment oxygen supply and uses reserve oxygen in the venous system
Normal oxygen delivery to the tissues is 1000 mL (1 L) of oxygen per minute.
In a critically ill patient, nursing procedures can increase VO2 by 10% to 36%
Many clinical conditions that dramatically increase VO2 consumption are common in critical care units. Conditions such as sepsis, multiple-organ dysfunction syndrome, burns, head injury, and shivering can more than double the normal oxygen tissue requirements
SvO2 or ScvO2 and oxygen consumption.
108
If SvO2 or ScvO2 is within the normal range of 60% to 80% and the patient is not clinically compromised, the nurse can assume that oxygen supply and demand are balanced for the patient.
Normal SvO2 or ScvO2.
109
If SvO2 or ScvO2 falls below 60% and is sustained, the clinician must assume that oxygen supply is not equal to demand is helpful to assess the cause of decreased SvO2 or ScvO2 in a logical sequence that reflects knowledge of the meaning of the venous saturation value. The following is one such assessment sequence:
1. Clinically assess the patient.
2. Assess whether the decreased SvO2 or ScvO2 is caused by low oxygen supply. Verify the effectiveness of the ventilator or oxygen mask, or check SaO2 from arterial blood gas values.
3. Assess cardiac function by performing a CO measurement.
4. Assess hemoglobin value by checking recent laboratory results or by withdrawing a blood sample for laboratory analysis.
5. Assess whether the decreased SvO2 or ScvO2 is the result of a recent patient movement or nursing action that may have temporarily increased VO2.
Target values for venous oximetry are SvO2 of 70% or greater and ScvO2 of 65% or greater.
Patients with values below these targets are at greater risk for organ hypoperfusion and increased mortality.
If SvO2 or ScvO2 falls below 40% and is maintained at this low value, the imbalance of oxygen supply and demand will be inadequate to meet tissue needs at the cellular level.
Low SvO2 or ScvO2..
110
In certain clinical conditions, SvO2 or ScvO2 may increase to an above-normal level (greater than 80%).
occurs during times of low oxygen demand (decreased VO2), such as during anesthesia or hypothermia.
Some cases of septic shock, the tissue cells cannot use the oxygen supplied to them, and the oxygen is not extracted from the blood at the tissue level.
If the SvO2 PA catheter drifts into a wedged position, the SvO2 increases, because the fiberoptic tip of the catheter comes into contact with newly oxygenated blood.
High SvO2.
111
Usually 110 cm in length
Balloon on tip
Catheter at 10 cm increments from tip to indicate insertion
Typ 4 ports
Proximal infusion port - lumen terminates 30cm from tip catheter - in RA when tip in PA - monitor RA pressures, central venous pressures
Distal pulmonary artery port - lumen ends at distal tip of the catheter; measure PA pressure and mixed venous saturation
Balloon inflation port
Thermistor - 4cm proximal to tip; measure CO using thermodilution technique
Flushed with saline before use
At 20 cm - balloon inflated with 1.5mL of air - aids in correct placement - follows blood movement
RA - pressure <5mm - fluctuates between few mmHg
RV - increases 25mmHg; diastolic - 0 mmHg
PA - increases 25mmHg; diastolic - 10 mmHg - closure of pulmonary valve during diastole
Balloon wedges and measures indirectly LA pressure - 10mmHg - waveform sim to RA; want a PA trace
Chest XR to check position
Connected to arterial cannulation - do not admin IV meds
PA Catheter
