Module 7 Hemodynamics Flashcards
1
Q
Hemodynamic
A
- the physical characteristics of actively circulating blood in the vascular system.
- these facts include blood flow rate (cardiac output), blood pressures, and vascular resistance.
2
Q
What factors determine Hemodynamic Characteristics?
A
- Cardiac contractility
- Blood volume
- vascular smooth muscle tone
3
Q
Why do we take clinical hemodynamic measurements?
A
- They are valuable in the assessment of cardiovascular function and adequacy of intravascular fluid volume.
- Also valuable in the monitoring and evaluation of the effects of various therapeutic interventions such as drug therapy and intravenous fluid therapy
4
Q
Why do we use a pulmonary artery catheter, and what is another name for it?
A
- used to measure hemodynamic variables.
- often referred to as the Swan-Ganz Catheter.
5
Q
How and where is the pulmonary artery catheter inserted?
A
- It is inserted into the heart and pulmonary vessels by way of the internal jugular vein.
- This vein provides a direct path to the right atrium.
- Other insertion sites include the subclavian vein, the femoral vein, and the basilic or median cubital veins in the right arm
6
Q
Percutaneous Catheterization
A
The process of surgically puncturing the skin to gain vascular access to insert the catherter.
7
Q
When the catheter is properly placed, what do the proximal and distal port communicate with?
A
- The proximal port communicates with the right atrium through the proximal lumen
- the distal port communicates with a small branch of the pulmonary artery through the distal lumen at the catheters tip.
8
Q
Another definition of hemodynamics
A
The study of the forces (pressures) that influence the circulation of the blood.
9
Q
PCWP
What does this stand for?
What is it?
A
- Pulmonary capillary wedge pressure
- The catheter has gained vascular acces, it is introduced into the vein with the balloon deflated; at that time a syringe is used to aspirate a small amount of blood from the catheters dital lumen, which is then flushed gently back with a small amount of saline solution. This makes sure the distal lumen is open.
- when the catheter tip enters the thoracic vein, the balloon is inflated to its recommended volume. ; at this volume the balloon protrudes slightly beyond the hard catheter tip, cushioning but not covering the distal opening. This allows cushioning and protection of the endothelium and endocardium. as well as allowing the blood to float the catheter tip through the heart to its proper position in the pulmonary artery.
- when the balloon tipped catheter wedges in a small pulmonary arteriole, it blocks blood flow between the catheters distal lumen and the left atrium.
- because blood flow is stopped, the BP measured through the distal lumen is about the same as the left atrial pressure. this is called the pulmonary capillary wedge pressure
10
Q
How do we get the measurements of the pressures from the catheter?
A
- The proximal and distal catheter lumens are connected to pressure transducers, mechanical devices that convert pressure fluctuations to electrical signals.
- the electrical signals are displayed as pressure waveforms on a monitoring screen; pressure is displayed in the vertical axis and time on the horizontal axis.
11
Q
How do waveform shapes aid in catheter insetion into the heart and pulmonary artery?
A
- they give information about the catheter tips location
12
Q
CO
How is it measured?
A
- Cardiac output
- It is directly measured from pulmonary and systemic arterial catheters
- directly measured with the pulmonary artery catheter using the thermodilution technique
13
Q
CVP
A
Central Venous pressure
14
Q
PAP
A
Peripheral Arterial Pressure
15
Q
PAWP
What Does it measure?
A
- Pulmonary Artery Wedge Pressure
- It measures pressures generated by the LEFT VENTRICLE
- it is used to assess left ventricular function
16
Q
PVR
A
Pulmonary vascular resistance
17
Q
SVR
What is it?
How is it determined?
A
- Systemic Vacular resistance
- primarily determined by vessel diameter and distensibility (compliance)
- SVR= (MAP-CVP)x 80/ Cardiac output
18
Q
MAP
A
Mean Arterial Pressure
The amount of arterial pressure that is necessary to maintain adequate perfusion of vital organs, it is calculated by
Systolic BP+2(diastolic BP) divided by 3
19
Q
What are the three main routes used to collect the pressures that influence the circulation of the blood, ie. the BP, CVP, PAP, PAWP, CO, PVR, SVR…
A
- Arterial lines- for info about the systemic system and perfusion
- Central Lines - for information about fluid balance and function of the right heart
- Pulmonary artery lines - for info about the pulmonary system, fluid balance, and the function of the left heart.
20
Q
What is Pascal’s principle and how does it apply to hemodynamics?
A
- A change in pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and to the walls of the containing vessel.
- Application: When monitoring arterial blood pressure with a transducer connected to an arterial catheter via fluid filled pressure tubing… any changes in the arterial blood pressure are transmitted throughout the fluid filled line and are recorded by the transducer.
21
Q
Ohm’s Law
Electrical:
Fluids:
A
- Electrical: Voltage=current x resistance
- Fluids: Pressure=flow x resistance
- Change in Pressure=Flow x Resistance
- Change in pressure is the driving pressure
- therefore,
- Resistance = change in pressure/Flow
22
Q
What is an arterial line?
Where does it go?
What does it do?
A
- A thin catheter inserted into an artery.** **
- Most commonly the RADIAL ARTERY. But it can also be inserted into the BRACHIAL artery, or the FEMORAL artery. It should be placed where there is collateral circulation to the area.
- It monitors blood pressure real time. Rather than intermittent.
23
Q
What are the three main routes used to collect data on BP, CVP, PAP, PAWP…CO, PVR, SVR…
A
- Arterial Lines
- Central Lines
- Pulmonary Artery Lines
24
Q
What Information do we get from an Arterial Line?
A
Info about the systemic system and perfusion.
25
Perfusion
The process of the delivery of blood to a capillary bed in the biological tissue
26
What is a Central Venous Line?
Where does it go?
What does it measure?
1. A catheter placed into the external Jugular vein in the neck.
2. It goes into the right atrium
3. It gives us information about the fluid balance and function of the right heart.
4. Measures RIGHT ATRIAL pressure.
5. Measures RIGHT VENTRICULAR pressure if the valves are open.
6. Measures Diastolic Pressure
27
What is a Pulmonary Artery Line?
What Does it measure?
Where does it go?
1. It goes to the PULMONARY ARTERY
2. Measures, **PULMONARY ARTERY WEDGE PRESSURE, PULMONARY CAPILLARY WEDGE PRESSURE, Cardiac output (using the thermodilution technique)**
3. Also referred to as the Swan-Ganz Catheter.
4. It's a catheter that is inserted through the heart and into the Pulmonary Artery.
28
When would the Pulmonary artery End-diastolic pressure (PAEDP) almost equalize with the Pulmonary Capillary Wedge Pressure (PCWP)? And If?
At the very end of diastole if pulmonary Vascular Resistance is normal.
This is why PAEDP is sometimes used instead of PCWP in estimation of Left Ventricular Filling Pressure.
29
What is Pascals Principle?
And give a clinical application.
Pascals Principle states that a change in pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and to the walls of the containing vessel.
Application:
* When monitoring arterial blood pressure with a transducer connected to an arterial catheter via fluid filled pressure tubing... any changes in the arterial blood pressure are transmitted throughout the fluid filled line and are recorded by the transducer.
30
What is Ohm's Law
Electrical?
Fluids?
1. Electrical - Voltage = current x resitstance
2. Fluids - Pressure = Flow x resistance
change in Pressure = flow x resistance
Change in Pessure is the DRIVING PRESSURE
Resistance= change in pressure/flow
31
What is the calculation for MAP (mean Arterial Pressure)
MAP = (SP+2xDP)/3
SP= SYSTOLIC PRESSURE
DP= DIASTOLIC PRESSURE
32
WHAT IS THE CALCULATION FOR
SVR
SVR = [(MAP - CVP) / CO] x 80
33
WHAT IS THE CALCULATION FOR
PVR (PULMONARY VASCULAR RESISTANCE)
PVR =(MPAP-PAWP/CO) x 80
34
how do we calculate CO, cardiac output?
CO = SV x HR
Stroke Volume x heart rate
Stroke volume is affected by
1. preload
2. afterload (higher afterload, you get less out of heart)
3. contractile force or contractility
35
preload
the volume of blood that is in a chamber of the heart.
36
What happens if we increase preload?
increased preload (to a point) results in increased pressure and stronger pumping.
preload is the greatest determinant of stroke volume.
37
What does central venous pressure measure?
Right Atrium pressure
38
how do you measure the L ventricle pressure?
to measure L ventricle pressure, you need to know L atrium pressure, which you can measure using the PAWP
39
What does L ventricular preload do to pulmonary capillary pressure?
increases pulmonary capillary pressure = higher atrial pressure
40
Driving pressure ( important)
the difference between high and low pressure that causes the blood to move
41
know how to calculate systemic vascular resistance from this slide
physiology: Pulmonary vs. systemic system
42
What hemdynamic value is used to represent preload of the Right Ventricle?
CVP
Central Venous Pressure
43
What hemodynamic value is used to represent preload of the Left ventricle
PAWP
pulmonary arterial wedge pressure
44
List three indications for monitoring arterial pressure in a patient
1. Severe hypotensin or hypertension
2. in patients who may need frequent arterial blood gas assessment
3. patients in shock or respiratory failure are candidates for placement of an arterial line.
45
When placing an arterial line in the femoral artery, what are some points to consider?
1. there is less vasoconstriction
2. no collateral circulation\
3. it is harder to monitor for bleeding
46
look at the Arterial pressure waveform slide
what does the dicrotic notch on the right represent?
the dicrotic notch represents aortic valve closure
47
what is the normal value for arterial pressure?
120/80 mm Hg
48
What would be considered hypertension in arterial blood pressure
values \>or = 160/90 mm Hg
49
What would the value for arterial pressure that would be considered hypotension?
\< or = 90/60 mm Hg
50
What is arterial pressure a sign of
arterial pressure is only a general sign of circulatory status
51
What can hypotension be a sign of?
hypotension is often a sign of low cardiac output
52
list three things that can cause hypotension
1. low blood volume
2. poor cardiac function
3. low vascular resistance
53
what can a low diastolic pressure result in?
compromised coronary artery perfusion
54
list three complications of continuous arterial pressure monitoring
1. **Ischemia** - occurs with embolism, thrombus, or arterial spasm. *Can result in tissue necrosis if not recognized rapidly*
2. **Hemorrhage** - occurs if line becomes disconnected
3. **infection**
55
List 4 indications for monitoring CVP (central venous Pressure)
1. to assess circulating blood volume and filling pressures of the heart
2. to assess right ventricular function
3. is needed in patients who have had major surgery or trauma
4. patients with pulmonary edema often benefit from CVP monitoring
56
what is the most popular catheter used for monitoring CVP
7 french with a triple lumen
the triple lumen allows infusion of medications and a port from which to obtain blood samples
57
name a popular site for the insertion of the catheter
jugular vein
58
know the CVP waveforms diagram
59
What does the ECG consist of?
Waves and complexes plotted as voltage on the verticle axis and time on the horizontal axis
60
What produces the p wave
atrial depolarization
61
depolarization
a change in the cells membrane potential making it more positive or less negative.
62
What causes the QRS complex of the ECG?
it is produced by ventricular depolarization
* first small downward (-ve) deflection is the Q wave
* The next tall upward (+ve) deflection is the R wave
* the following small negative deflection is the S wave
The QRS complex is associated with ventricular contraction
* the T wave is produced by ventricular repolarization
* the atria also has a repolarization wave, but it is obliterated by the QRS complex
63
What does the height or amplitude on the ECG represent?
What is the amplitude of waves and complexes related to?
1. it represents voltage
2. the amplitude of waves and complexes is related to muscle mass
3. because the ventricles have a much greater muscle mass than the atrium, they generate a much greater voltage when they depolarize.
64
What is a normal PR interval, and where is it measured from?
1. A normal PR interval is between 0.12 and 0.20 second
2. a PR level greater than .20 second indicates abnormally slowed impulse conduction
3. it is shorter in fast heart rates than in slow heart rates.
65
What is the normal length of time for the QRS complex?
what does QRS width represent?
What is the J point?
1. The QRS complex normally lasts 0.08-0.10 second.
2. The QRS width represents ventricular conduction time and is measured from the point at which the tracing leaves the baseline, to the point at which it returns.
3. The point at which it returns is called the J point
66
Where is the ST segment and what does it represent?
1. it extends from the J point to the beginning of the T wave and it represents the early phase of ventricular repolarization
2. at its end the ST segment curves slightly into the beginning of the T wave
3. fast heart rates have shorter ST waves than slow heart rates
67
What is a normal ST segment?
a normal ST segment is flat, lying on the baseline.
* but it may be elevated as much as 2mm above the baseline or depressed as much as 0.5 mm below the baseline and still be considered normal
68
What does an ST segment that becomes depressed more than 0.5 mm during a stress test signal?
myocardial ischemia
69
What does an elevated ST segment indicate?
myocardial tissue injury
70
Where is the QT interval measuredand what does it represent?
What is a normal value for the QT interval?
1. it is measured from the beginning of the QRS complex to the end of the T wave.
2. The QT time represents the general refractory period of the ventricles.
3. during this time the ventricles generally cannot accept another depolarizing stimulus
4. QT time is usually less than 0.04 second.
71
Vulnerable period
as repolarization progresses, *some of the ventricular muscle fibers are repolarized, whereas some are still depolarized.* this represents the **VULNERABLE PERIOD** during which part of the heart can respond to an additional stimulus and part of it cannot.
This is located at the **peak of the T wave** and is sometimes called the **relative refractory period of the heart**
a **depolarizing stimulus** during this vulnerable time can create **electrical chaos i**n the heart, rendering it **functionless.**
72
What is a prolonged QT period associated with?
a prolonged QT period is associated with life threatening heart rhythm disturbances because it is associated with a longer vulnerable period.
73
how do spontaneous inspiratory efforts affect CVP?
spontaneous inspiratory efforts cause central venous pressure to decrease and are seen on the waveform
74
how do positive pressure breaths affect CVP?
positive pressure breaths cause the CVP to increase
75
What do you need to do to monitor CVP during mechanical ventilation
you need to briefly disconnect the ventilator unless PEEP is being applied
76
What is PEEP
positive end-expiratory pressure
it's the pressure in the lungs above atmospheric pressure that exists at the end of expiration.
there are two types
1. extrinsic (applied by a ventilator)
2. intrinsic (caused by non-complete exhalation)
77
list 6 causes of increased CVP
1. fluid overload
2. right/left heart failure
3. pulmonary hypertension
4. tricuspid valve stenosis
5. pulmonary embolism
6. increased venous return
78
list 4 causes of decreased CVP
1. reuced circulating blood volume
2. vasodilation (reduced venous return)
3. leaks in the pressure system
4. spontaneous inspiration
79
Know this!
What are some complications of CVP monitoring
1. during placement
2. over time
During placement
* bleeding
* pneumorthorax
Over time
* infection
* embolus
* air embolus
80
Why was pulmonary Artery function developed?
what does it evaluate?
Where does it go?
What do we assess with it?
1. It was developed to allow better evaluation of left ventricular function
2. it allows assessment of
* Left ventricular filling pressure
* pulmonary vascular resistance
* arterio-venous oxygen difference
* mixed venous oxygen levels
81
List 4 indications for PA pressure monitoring (pulmonary artery.
1. severe cardiogenic pulmonary edema
2. patients with ADRS who are hemodynamically unstable
3. patients who have had major thoracic surgery
4. patients with septic or severe cardiogenic shock
82
Describe the PA catheter
what does it measure
what are the two most common sites for insertion?
1. The PA catheter has multiple lumens and is balloon tipped.
2. the balloon is used to float the catheter into place and to measure left ventricular filling pressures
3. most common sites for insertion are; subclavian and internal jugular veins
83
How is a PA catheter inserted? 3 points
1. the catheter is floated through the right side of the heart and into the pulmonary artery
2. once it wedges into place, the balloon is deflated
3. distinctive waveforms can be visualized on the monitor as the catheter passes through the right atrium, right ventricle, pulmonary artery, and into the wedge position. This helps guide insertion.
84
what impacts PA systolic pressure (20-30 mm Hg)?
causes it to increase or decrease?
1. it increases with high pulmonary vascular resistance
2. it decreases with poor right heart function and pulmonary vasodilation
85
What does the PA measurement of diastolic pressure (8-15 mm Hg) reflect?
1. it NORMALLY reflects left heart filling pressures
2. it does NOT reflect left heart filling pressure when PULMONARY VASCULAR RESISTANCE IS ELEVATED.
3. it is very similar to wedge pressure in a normal person.
86
What would increase a PAWP (pulmonary artery wedge pressure)?
Elevates with left heart failure or mitral stenosis
87
What would cause a PAWP to decrease?
hypovolemia (low blood volume)
88
what is a normal wedge pressure?
4 to 12 mm Hg
pulmonary must be interpreted in light of the patient's medical history (history of MI will cause a stiff left ventricle and lead to higher pressure)
89
List 4 things involved in obtaining an accurate PAWP.
1. careful calibration of equipment
2. measure at the end of exhalation
3. catheter tip must be in the West zone lll where blood flow is continuous
4. Low blood volume and high alveolar pressures can cause wedge pressure readings to be inaccurate.
90
List 4 complications of PA monitoring
1. during cannulation, hemothorax, pneumothorax, and damage to blood vessels are possible.
2. Dysrhythmias can occur as catheter passes through the heart and during monitoring
3. catheter source of infection, thrombus, embolism, bleeding, and hematoma
4. pulmonary infraction possible
91
Directly measured hemodynamic variables
normal ranges for the following:
Pulmonary artery catheter
1. Right atrial (central venous)pressure (RAP,CVP)
2. pulmonary artery pressure (PAP)
3. mean pulmonary artery pressure (MPAP)
4. pulmonary capillary wedge pressure (PCWP)
5. cardiac output (CO)
6. heart rate (HR)
Systemic arterial catheter:
1. arterial pressure (BP)
2. Mean Arterial pressure (MAP)
Pulmonary artery catheter
1. RAP, CVP - less than 6 mm Hg
2. PAP 20-30/6-15 mm Hg
3. MPAP 10-20 mm Hg
4. PCWP 4-12 mm Hg
5. CO 4-8 L/min
6. HR 60-80 beats/min
Systemic arterial catheter
1. BP 120/80
2. MAP 80-100 mm Hg
92
What is the normal range for Cardiac index?
How do you calculate it?
1. 2.5-4.0L/min/m2
2. CO/BSA (body surface area) in square meters
93
What is the normal range for Stroke Volume?
How do you calculate it?
1. 60-130 mL/beat
2. CO/HR
94
What is the normal range for Stroke volume index (SVI) or Stroke index (SI)?
How is it calculated?
1. 30-50 mL/m2
2. SV/BSA (body surface area)
95
What is the normal range for Systemic vascular resistance? (SVR)
How is it calculated?
1. 900-1400 dynes.sec.cm-5
2. ([MAP-RAP]/CO)x 80
96
What is the normal range for systemic vascular resistance index? (SVRI)
how do you calculate it?
1. 1700-2600dynes.sec.cm-5/m2
2. ([MAP-RAP]/CI)x80
97
What is the normal range for pulmonary vascular restistance?
How do you calculate it?(PVR)
1. 100-250 dynes.sec.cm-5
2. ([MPAP-PCWP]/CO)X80
98
What is tne normal range for Pulmonary Vascular Resistance index? (PVRI)?
How do you calculate it?
1. 200-450dynes.sec.cm-5/m2
2. ([MPAP-PCWP]/CI)x80
99
What is the normal range for Left Ventricular stroke work index (LVSWI)?
How do you calculate it?
1. 40-75 g-m/m2/beat
2. SI x (MAP-PCWP) x 0.0136
100
What is the normal range for right ventricular stroke work index? (RVSWI)
How do you calculate it?
1. 4-8 g-m/m2/beat
2. SI x (MPAP- CVP) x 0.0136
101
What is the CO, Cardiac output?
The amount of blood pumped out in 1 minute
102
How do you calculate CO?
CO= SVxHR
103
What is stroke volume?
the amount of blood ejected from the left ventricle with each contraction
104
What is normal stroke volume? \*\*\* KNOW
from 60-130 ml
105
What is normal cardiac output?\*\*\*KNOW
4-8L/min at rest
106
Venous return
The amount of blood returning to the right atria each minute
107
normally venous return is the same as \_\_\_\_\_\_\_\_\_\_\_\_\_\_?
Cardiac output
108
How does vasodilation effect venous return?
Vasodilation causes it to increase,
Vasoconstriction causes it to decrease
109
What happens to CO in a healthy heart when venous return increases?
It increases
110
How is CI, cardiac index calculated?
dividing the CO/BSA (body surface area)
111
what is cardiac work?
a measurement of the energy spent ejecting blood from the ventricles against aortic and pulmonary artery pressures
it correlates well with the amount of oxygen needed by the heart
normally cardiac work is much higher for the left ventricle
112
What does measuring cardiac index do for us?
Provides a standardized interpretation of the cardiac function
113
What is Ejection Fraction? \*\*\* KNOW this card well
What percent is it at rest?
What percent with strenuous exercise?
The fraction of end-diastolic volume ejected with each systole; normally 60% at rest; drops with cardiac failure.
goes up to 90% in strenuous exercise
114
List 4 factors that impact cardiac output
1. Heart rate
2. Preload
3. afterload
4. contractility
115
When does heart rate impact cardiac output? 4 points
* it is normally not a major factor
* extreme abnormalities can alter CO
* a low HR is normally compensated for by an increase in stroke volume SV
* a significantly elevated HR often causes SV to drop in people with heart disease when it reduces filling time (\>160 bpm)
116
how does preload impact cardiac output?
* Preload is created by end diastolic volume
* the greater the stretch on the myocardium prior to contraction, the greater the subsequent contraction will be.
* **when preload is too low, SV and CO will drop**
* this occurs with hypovolemia
* too much stretch can also reduce SV
117
List 3 factors that affect venous return, preload, and CO
1. Circulating blood volume
2. distribution of the blood volume
3. atrial contraction (adds 30% to subsequent ventricular SV) Atrial kick
118
What is the effect of mechanical ventilation on cardiac output?
1. Spontaneous inspiration lowers intrapleural pressures, improving venous return and CO
2. Positive pressure breaths increase intrapleural pressures and reduce venous return and CO
119
What are two components of Afterload?
1. peripheral vascular resistance
2. tension in the ventricular wall
120
What causes afterload to increase? and what happens to the O2 demand of the heart as it increases?
1. afterload increases with ventricular wall distention and peripheral vasoconstriction
2. as afterload increases, so does the Oxygen demand of the heart. \*\*\* know
121
What would we use to decrease the afterload?
What will this improve, what would be a caution to consider?
1. vasodilators
2. this can help to improve stroke volume
3. BUT if a person has low blood voume it can cause the BP to drop
122
SVR what is it a measure of?
when does it increase?
what would cause it to increase?
1. SVR is a measure of resistance to bloodflow through the systemic circulation.
2. it increases with peripheral vasoconstriction
3. hypertension and the use of vasoconstrictors cause it to increase
123
What is PVR a measure of?
when does it increase?
1. PVR is a measure of pulmonary vascular resistance.
2. it increases with pulmonary vasoconstriction as seen in hypoxemia and acidosis.
124
What is contractility a measure of?
myocardial contraction strength
125
What is contractility determined by?
the amount of stretch on a ventricle prior to contraction.
inotropic state of the heart
Contractility is reduced by hypoxia, acidosis, electrolyte abnormalities, and myocardial ischemia
126
What is thermodilution?
Thermodilution is the most common technique for measuring CO
127
how is thermodilution done?
1. it requires placement of a pulmonary artery catheter, and the use of a computer.
2. a cold bolus of saline is injected into the proximal port; temperature change over time is measured by a thermometer at the tip of the PAC
3. the degree of change between the proximal port and the distal tip is a function of CO
128
What is the Fick method? for measuring CO
1. the fick method is based on the fact that **CO can be calculated if the oxygen consumption, the arterial oxygen content, and the mixed venous oxygen content are simultaneously measured.**
2. it requires gathering of exhaled gases to determine O2 consumption.
3. **CO= [VO2/(CaO2-CvO2)]x10**
129
What are two reasons that fluid challenges might be done?
1. to assess kidney function
2. to assess LV function
130
when would you do a fluid challenge to assess kidney function?
when UO is \<30cc/hr
131
what is a fluid challenge test for kidneys?
when would we suspect kidney damage?
* a high volume of fluid (200-300ml) is given in a short period of time (5-10 min)
* if CVP is not affected then additional fluid may be given
* if the UO does not decrease then kidney damage is suspected.
132
What is the fluid challenge for assessing L ventricular functrion?
* PAWP is compared to CO after fluid administration
* remember preload is the largest single contributer to cardiac output
133
What is the goal of a fluid challenge for L ventricular function?
* to find the **optimal preload**
* this will vary from patient to patient and with changes to the patients condition
* changes in ventricular compliance will also affect this optimal wedge pressure
134
how is a fluid challenge to assess left ventricular function done?
* PAWP and CO are measured
* a fluid challenge is performed\*
* PAWP and CO are measured again
* this is continued until a ventricular function curve (starlings curve) is constructed
\* why are we concerned? by keeping fluid levels optimal, we optimize the function of the heart and thus the CO
