Cardiovascular Monitoring Flashcards
(93 cards)
1
Q
Demand-mediated subendocardial ischemia resulting in ST-segment depression is the most commonly observed form of perioperative ischemia. ST-segment depression is most commonly observed in an anterolateral precordial lead regardless of the coronary territory responsible
T or F
A
T
2
Q
Because of the absence of anatomic collateral flow at the elbow, brachial artery catheterization for perioperative blood pressure monitoring is not a safe
alternative to radial or femoral arterial catheterization
T or F
A
F
Despite the absence of anatomic collateral flow at the elbow, brachial artery catheterization for perioperative blood pressure monitoring is a safe alternative to radial or femoral arterial catheterization
3
Q
Why the arterial blood pressure recorded from peripheral sites has a wider pulse pressure than when measured more centrally?
A
▪ Because of wave reflection and other physical phenomena
4
Q
Which eletrode can be placed in any part of the body? Why this is possible?
A
Placement of the right leg lead can be anywhere on the body because it is a ground electrode, and its location will not alter the display of any of the selected standard leads
5
Q
Best leads for ischemia detection
A
mid-precordial leads (V3, V4, V5)
6
Q
In addition to the standard lead locations, lead … , positioned in the … is the best lead for identifying right ventricular (RV) ischemia
A
V4R, a mirror image of lead V4
fourth intercostal space at the midclavicular line
7
Q
A standard ECG is recorded at a gain of … and is indicated by a … mV rectangular calibration signal on a paper recording or by a … mV vertical marker at the edge of the bedside monitor ECG waveform
A
10 mm/mV
1
1
8
Q
During stress testing and with acute subendocardial ischemia, the electrical forces responsible for the ST segment are deviated toward the …, causing … .
With acute transmural epicardial ischemia, the electrical forces in the ischemic area are deviated toward the…, causing …
A
inner layer of the heart
ST-segment depression or demand-mediated ischemia
outer layer of the heart
ST-segment elevation or supply-mediated ischemia in the overlying leads
9
Q
With demand-mediated ischemia, as heart rate increases, … occurs.
As the severity of ischemia progresses, the ST segment typically becomes …, the magnitude of ST-segment depression increases, and the ST segment becomes … .
A
J-point depression and upsloping ST-segment depression
horizontal (flattens)
downsloping
10
Q
Standard criteria for stress-induced ischemia are …
A
1 mm (0.1 mV) or more of horizontal or downsloping ST-segment depression measured 60 or 80 ms after the J point
11
Q
London and colleagues studied high-risk patients undergoing noncardiac surgery and showed that the greatest sensitivity for ischemia was obtained with lead 1…, followed by lead 2… .
Combining leads 3… increased the sensitivity to 4…%, whereas with the standard lead 5… combination, the sensitivity was only 6…%.
They also suggested that if three leads (7…) could be simultaneously examined, the sensitivity would increase to 8…%.
A
1) V5 (75%)
2) V4 (61%)
3) V4 and V5
4) 90
5) II and V5
6) 80
7) II, V4, and V5
8) 98
OBS.: Landesberg and associates monitored continuous 12-lead ST-segment changes greater than 0.2 mV from baseline in a single lead or more than 0.1 mV in two contiguous leads at J+60 ms, lasting longer than 10 minutes in patients undergoing major vascular surgery. They showed that leads V3 and V4 were more sensitive
than V5 in detecting perioperative ischemia (87%, 79%, and 66%, respectively). As a result of these and other investigations, it appears most appropriate to monitor lead V3, V4, or V5 for optimal detection of perioperative ST-segment depression, choosing the specific lead location to avoid interference with the surgical prep and procedure.
12
Q
Comparisons of the upper arm, forearm, and wrist in morbidly obese patients show the best results for the … and worst for the …
In general, the ankle is always a … choice
A
wrist
upper arm
poor
13
Q
A large number of clinical studies have assessed the level of agreement between indirect and direct measurement of blood pressure. Generally, the two techniques show the highest level of agreement for … values while … are the most divergent.
As a rule, the … is underestimated while the … is overestimated with the discrepancy increasing with worsening hypotension
A
MAP
Systolic pressures
systolic
diastolic
14
Q
Below an MAP of …, NIBP does not appear useful as a guide to
therapy. Levels of agreement also decrease in the … patient
A
65 mm Hg
critically ill and the elderly
15
Q
Complications of Noninvasive Blood Pressure (NIBP) Measurement
A
▪ Pain
▪ Petechiae and ecchymoses
▪ Limb edema
▪ Venous stasis and thrombophlebitis
▪ Peripheral neuropathy
▪ Compartment syndrome
16
Q
Describe the Modified Allen test
A
1) Instruct the patient to clench his or her fist; if the patient is unable to do this, close the person’s hand tightly.
2) Using your fingers, apply occlusive pressure to both the ulnar and radial arteries, to obstruct blood flow to the hand.
3) While applying occlusive pressure to both arteries, have the patient relax his or her hand, and check whether the palm and fingers have blanched. If this is not the case, you have not completely occluded the arteries with your fingers.
4) Release the occlusive pressure on the ulnar artery only to determine whether the modified Allen test is positive or negative.
- Positive modified Allen test: If the hand flushes within 5-15 seconds it indicates that the ulnar artery has good blood flow; this normal flushing of the hand is considered to be a positive test.
- Negative modified Allen test: If the hand does not flush within 5-15 seconds, it indicates that ulnar circulation is inadequate or nonexistent; in this situation, the radial artery supplying arterial blood to that hand should not be punctured.
17
Q
Complications of Direct Arterial Pressure Monitoring
A
▪ Distal ischemia, pseudoaneurysm, arteriovenous fistula
▪ Hemorrhage
▪ Arterial embolization
▪ Infection
▪ Peripheral neuropathy
▪ Misinterpretation of data
▪ Misuse of equipment
18
Q
Factors associated with increased risk of complications during invasive arterial pressure monitoring
A
- vasospastic arterial disease
- previous arterial injury
- thrombocytosis
- protracted shock
- high-dose vasopressor administration
- prolonged cannulation
- infection
19
Q
The displayed pressure waveform during invasive arterial pressure monitoring is a summation of … .
Other factors that affect the displayed waveform are …
A
both antegrade and retrograde (reflected) sine waves, each with its own frequency, amplitude, and phase shift
the stroke volume (left ventricular [LV] ejection), both static and dynamic arterial compliance, and the speed of the pressure wave
20
Q
An underdamped system may combine elements of the measurement system itself with the measured sine waves and display systolic pressure overshoot. In contrast, an overdamped
waveform exhibits a slurred upstroke, absent dicrotic notch, and loss
of fine detail. In such cases, the pulse pressure will be falsely narrow
but MAP remains reasonably accurate
T or F
A
T
21
Q
The most common reasons for underdamping are …
Overdamping results from …
A
excessively stiff tubing and a defective transducer.
decreases in pressure within the system (i.e. inadequate pressure in the pressure bag), loose connections, kinks in the tubing or catheter, or air bubbles
22
Q
Describe the components of a normal arterial blood pressure waveform
A
(1) Systolic upstroke,
(2) systolic peak pressure,
(3) systolic decline,
(4) dicrotic notch,
(5) diastolic runoff,
(6) enddiastolic pressure
23
Q
Explain the distal pulse amplification phenomenon
A
Pressure waveforms recorded simultaneously from different sites have different morphologies due to the physical characteristics of the vascular tree.
As the pressure wave travels toward the periphery, the arterial upstroke becomes steeper, the systolic peak rises, the dicrotic notch appears later, the diastolic wave becomes more prominent, and end-diastolic pressure falls. As a result, peripheral arterial waveforms have higher systolic, lower diastolic, and wider pulse pressures compared with central aortic waveforms. Interestingly, the displayed MAP is only slightly increased.
24
Q
Characteristics of the arterial blood pressure waveform in Aortic stenosis
A
Pulsus parvus (narrow pulse pressure)
Pulsus tardus (delayed upstroke)
25
Characteristics of the arterial blood pressure waveform in Aortic regurgitation
Bisferiens pulse (double peak)
Wide pulse pressure
26
Characteristics of the arterial blood pressure waveform in Hypertrophic
cardiomyopathy
Spike and dome (mid-systolic obstruction)
27
Characteristics of the arterial blood pressure waveform in Systolic left ventricular failure
Pulsus alternans (alternating pulse pressure amplitude)
28
Characteristics of the arterial blood pressure waveform in Cardiac tamponade
Pulsus paradoxus (exaggerated decrease in systolic blood pressure during
spontaneous inspiration)
29
The arterial pressure pulse in a patient with aortic regurgitation may have two systolic peaks (bisferiens pulse), with the first peak resulting from ... and the second from ...
antegrade ejection
a wave reflected from the periphery
30
In hypertrophic cardiomyopathy, the waveform assumes a peculiar bifid shape termed a “spike-anddome” configuration. Explain
After an initial sharp blood pressure increase resulting from rapid, early systolic ejection, arterial pressure abruptly falls as mid-systolic left ventricular outflow obstruction interrupts stroke volume ejection. This is finally followed by a second, late-systolic increase associated with arrival of reflected waves from the periphery
31
Pulsus alternans is a pattern of alternating larger and smaller pressure waves that vary with the respiratory cycle and are generally associated with ...
severe left ventricular systolic dysfunction or aortic stenosis
32
Describe the Pulsus paradoxus
is an exaggerated variation in arterial pressure (>10–12 mm Hg) during quiet
breathing. is not truly paradoxical, but rather an exaggeration of a normal variation in
blood pressure that accompanies spontaneous ventilation. It is an important sign in cardiac tamponade but may also be seen with pericardial constriction, severe airway obstruction, bronchospasm, dyspnea, or any condition that involves large swings in intrathoracic pressure. Importantly, though, in cases of cardiac tamponade, the
pulse pressure and left ventricular stroke volume decrease during inspiration, in contrast to the pattern associated with large variations in intrathoracic pressure in which pulse pressure remains constant
33
Explain the physiologic aspect of Arterial Pressure Monitoring and Waveform Analysis for Prediction of Volume Responsiveness
During the inspiratory phase of a positive pressure breath, increased intrathoracic pressure simultaneously decreases left ventricular (LV) afterload while at the same time increasing total lung volume, displacing blood from the pulmonary venous reservoir into the left side of the heart, increasing LV preload and augmenting
LV stroke volume (higher pulse pressure during inspiration). In the absence of changes in system resistance, an increase in systemic arterial pressure results. At the same time, rising intrathoracic pressure impairs systemic venous return, lowers right ventricular (RV) preload, and potentially increases RV afterload by slightly increasing pulmonary vascular resistance. These effects combine to reduce RV ejection during the early phase of inspiration.
During the expiratory phase, however, the situation is reversed. The smaller RV stroke volume seen during inspiration traverses thepulmonary vascular bed and enters the left heart, resulting in reduced LV filling, reduced LV stroke volume, and a fall in systemic arterial blood pressure.
This waxing and waning cycle in stroke volume and systemic arterial blood pressure is known as the systolic pressure variation (SPV).
34
Systolic Pressure Variation is often subdivided into inspiratory and expiratory
components by measuring the increase (Δ Up) and decrease (Δ Down) in systolic pressure relative to the ...
In a mechanically ventilated patient, normal SPV is ..., with Δ Up being ... and Δ Down being ...
Values greater than this are felt to indicate ...
Patients with increased SPV during positive pressure ventilation may be described clinically as ...
end-expiratory, apneic baseline pressure
7–10 mm Hg
2–4 mm Hg
5–6 mm Hg
hypovolemia
having residual preload reserve or being “volume responsive.”
35
Pulse pressure variation (PPV) is calculated as ...
the difference between maximal (PPMax) and minimal (PPMin) pulse pressure values during a single mechanical respiratory cycle, divided by the average of these two values.
Pulse pressure (PP) = Psyst - Pdiast
PPV = (PPmax - PPmin) / [(PPmax - PPmin)/2]
36
Volume expansion does not result in a dichotomous outcome and the asymmetric nature of the Frank–Starling curve dictates that the cost–benefit ratio of acting in one direction will be different from acting in the other. For any given change in preload, the change in stroke volume depends on the direction of the preload change, with
that direction being dependent on how close to the peak of the curve the patient is at the time of measurement. Consequently, the concept of a “gray zone” has been proposed that defines a range of values between which evidence-based decision-making is not possible. For PPV, this zone appears to be ... such that those above ... should receive volume expansion while those below ... should not.
Between those two values, the measurement is not able to provide meaningful guidance and the decision should be based on other criteria
9%–13%
13%
9%
37
More sophisticated methods of pulse contour analysis allow real-time measurement of stroke volume variation (SVV), as well as calculation of a stroke volume variation index (SVVI). When these measures exceed ..., the patient is likely to have a positive response to volume expansion.
10%–13%
38
Describe factors that afect the accuracy of the pulse pressure variation
- Increased abdominal pressure
- Use of vasopressors
- Patient position, including steep Trendelenburg, prone, or lateral
decubitus
- Irregular heart rhythms
- Severely impaired ventricular function
- Pulmonary hypertension or reduced RV ejection fraction (may not have consistent responses to changes in intrathoracic pressure)
- Minimally invasive or open thoracic surgery (due to the loss of the chest as a closed space)
- Tachypnea (especially in the setting of respiratory failure), or significant bradycardia (may disrupt the relationship between respiratory cycle–induced changes in
intrathoracic pressure and cardiac chamber volumes)
39
Conditions necessary for adequate PPV/SVV
- Mechanical ventilation with 8–10 mL/kg tidal volume
- Positive endexpiratory pressure ≥5 mm Hg
- Regular cardiac rhythm
- Normal intra-abdominal pressure
- Closed chest
40
Measuring PPV or SVV during or immediately following a recruitment maneuver may decrease its sensitivity and specificity in predicting fluid responsiveness
T or F
Measuring PPV or SVV during or immediately following a recruitment maneuver increased its sensitivity and specificity in predicting fluid responsiveness although a broader gray zone of up to 26% should be considered
41
Indications for Central Venous Cannulation
▪ Central venous pressure monitoring
▪ Pulmonary artery catheterization and monitoring
▪ Transvenous cardiac pacing
▪ Temporary hemodialysis
▪ Drug administration
▪ Concentrated vasoactive drugs
▪ Hyperalimentation
▪ Chemotherapy
▪ Agents irritating to peripheral veins
▪ Prolonged antibiotic therapy (e.g., endocarditis)
▪ Rapid infusion of fluids (via large cannulas)
- Trauma
- Major surgery
▪ Aspiration of air emboli
▪ Inadequate peripheral intravenous access
▪ Sampling site for repeated blood testing
42
Complications of Central Venous Pressure Monitoring
▪ Mechanical
- Vascular injury (Arterial; Venous; Cardiac tamponade)
- Respiratory compromise (Airway compression from hematoma; ▪ Pneumothorax)
- Nerve injury
- Arrhythmias
▪ Thromboembolic
- Venous thrombosis
- Pulmonary embolism
- Arterial thrombosis and embolism
- Catheter or guidewire embolism
▪ Infectious
- Insertion site infection
- Catheter infection
- Bloodstream infection
- Endocarditis
▪ Misinterpretation of data
▪ Misuse of equipment
43
Nerve injury is another potential complication of central venous cannulation. Damage may occur to the ...
In addition, chronic pain syndromes have been attributed to this procedure
brachial plexus, stellate ganglion, phrenic nerve, or vocal cords.
44
Describe the normal cardiovascular pressures for RA, RV, PA, PAWP, LA, LV, central aorta)
Pressures...................................Average (mmHg)........Range (mmHg).
RIGHT ATRIUM
- a wave..............................................6................................2-7
- v wave..............................................5................................2-7
- Mean................................................3................................1-5
RIGHT VENTRICLE
- Peak systolic...................................25...............................15-30
- End-diastolic...................................6.................................1-7
PULMONARY ARTERY
- Peak systolic...................................25..............................15-30
- End-diastolic...................................9................................4-12
- Mean...............................................15...............................9-19
PULMONARY ARTERY WEDGE
- Mean................................................9................................4-12
LEFT ATRIUM
- a wave..............................................10..............................4-16
- v wave...............................................12.............................6-21
- Mean.................................................8...............................2-12
LEFT VENTRICLE
- Peak systolic.....................................130...........................90-140
- End-diastolic......................................8...............................5-12
CENTRAL AORTA
- Peak systolic......................................130...........................90-140
- End-diastolic......................................70..............................60-90
- Mean..................................................90...............................70-105
45
Venous return is mostly determined by the gradient between the ... and CVP.
... results from the ... and is the force that drives blood back to the right atrium.
This pressure has been estimated to be between ... in healthy individuals at rest, but it cannot be measured in the clinical setting
mean circulatory filling pressure (MCFP) '
MCFP
elastic recoil pressure from distended small veins and venules
8 and 10 mm Hg
46
How does the Intrathoracic Pressure affect the CVP?
During spontaneous breathing, inspiration decreases pleural and pericardial pressures, which are transmitted, in part, to the right atrium, and result in a lower measured CVP. Although measured CVP decreases during the inspiratory phase of spontaneous ventilation, transmural CVP, the difference between right atrial pressure and juxtacardiac pressure, increases slightly as more blood is drawn into the right atrium. The opposite pattern is observed during positive pressure ventilation, in which inspiration increases intrathoracic pressure and the measured CVP, but decreases transmural CVP, because the elevated intrathoracic pressure reduces venous return.
47
Which ventilation moment is best to measure CVP? Why?
End-expiratory
At the end of expiration, intrathoracic and juxtacardiac pressures approach atmospheric pressure regardless of ventilatory status and will have the least influence on measured CVP
48
For accurate measurement of CVP, the zero reference point (the affixed stopcock rather than the transducer) should be aligned at ...
approximately 5 cm below the sternal angle to identify the uppermost fluid level in the right atrium or one-third of the thoracic anteroposterior dimension to identify the mid-right atrial level
49
Describe the Central Venous Pressure Waveform Components
- a wave: End-diastole; Atrial contraction
- c wave: Early systole Isovolumic ventricular contraction; tricuspid motion toward right atrium
- x descent: Mid-systole; Atrial relaxation, descent of the base, systolic collapse
- v wave: Late systole; Systolic filling of atrium
- y descent: Early diastole Early; ventricular filling, diastolic collapse
*** h wave: Mid to late diastole (between v and a); Diastolic plateau; The h wave is not normally seen unless the heart rate is slow and venous pressure is elevated
*** The c wave observed in a jugular venous pressure trace might have a slightly more complex origin. This wave has been attributed to early systolic pressure transmission from the adjacent carotid artery and may be termed a carotid impact wave. Because the jugular venous pressure also reflects right atrial pressure, however, this c wave likely represents both arterial [carotid impact] and venous [tricuspid motion] origins.
50
The x component of the central venous pressure waveform can be divided into two portions. Describe then
The x descent can be divided into two portions, x and x′, corresponding to the segments before and after the c wave.
51
The v wave usually peaks just after the ECG ... wave
T
52
The arterial pressure upstroke occurs nearly ... after the ECG R wave
This normal physiologic delay reflects the times required for ...
200 ms
the spread of the electrical depolarization through the ventricle (≈60 ms), isovolumic left ventricular contraction (≈60 ms), transmission of aortic pressure rise to the radial artery (≈50 ms), and transmission of the radial artery pressure rise through fluid-filled tubing to the transducer (≈10 ms).
53
What is the a–c wave?
The a wave generally begins and peaks in end-diastole, but the peak may appear delayed to coincide with the ECG R wave, especially in a patient with a short PR interval. In this instance, a and c waves merge, and this composite wave is termed an a–c wave
54
Tachycardia reduces the length of diastole and the duration of the ... descent,
causing ... waves to merge
y
v and a
55
Describe the Central Venous Pressure Waveform Abnormalities of AF, AV dissociation, Tricuspid regurgitation, Tricuspid stenosis, RV ischemia, Pericardial constriction and Cardiac tamponade
1) Atrial fibrillation:
- Loss of a wave
- Prominent c wave
2) Atrioventricular dissociation:
- Cannon a wave
3) Tricuspid regurgitation:
- Tall systolic c–v wave
- Loss of x descent
4) Tricuspid stenosis:
- Tall a wave
- Attenuation of y descent
5) Right ventricular ischemia
- Tall a and v waves
- Steep x and y descents
- M or W configuration
6) Pericardial constriction
- Tall a and v waves
- Steep x and y descents
- M or W configuration
7) Cardiac tamponade:
- increased mean pressure
- Dominant x descent
- Attenuated y descent
56
In atrial fibrillation, the a wave disappears and the c wave becomes more prominent because ...
atrial volume is greater at end-diastole and onset of systole, owing to the absence of effective atrial contraction
57
Tricuspid regurgitation produces abnormal systolic filling of the right atrium through the incompetent valve. A broad, tall systolic ... wave results, beginning in early
systole and obliterating the ... in atrial pressure. The CVP trace is said to be ..., resembling ... pressure
c–v
systolic x descent
ventricularized
right ventricular
58
Tricuspid stenosis produces a diastolic defect in atrial emptying and ventricular filling. Mean CVP is elevated, and a pressure gradient exists throughout diastole between right atrium and ventricle. The a wave is unusually ... and the y descent is ..., owing to the ...
Other conditions that reduce right ventricular compliance, such as ..., may produce a ... in the CVP trace but do not ...
prominent
attenuated
impaired diastolic egress of blood from the atrium
right ventricular ischemia, pulmonary hypertension, or pulmonic valve stenosis
prominent end-diastolic a wave
attenuate the early diastolic y descent
59
Describe the components of the Pulmonary Artery Catheter
The standard pulmonary artery catheter (PAC) has a 7.0 to 9.0 Fr circumference, is 110 cm in length marked at 10-cm intervals, and contains four internal lumens.
1) The distal port at the catheter tip is used for PAP monitoring;
2) while the second is 30 cm more proximal and is used for CVP monitoring.
3)The third lumen leads to a balloon near the tip which is used to float the catheter through the cardiac chambers, and
4) the fourth houses wires for a temperature thermistor, the end of which lies just proximal to the balloon.
Contemporary PACs also have an additional lumen that allows continuous measurement of mixed venous oximetry at the catheter tip as well as a heating coil between the proximal and distal lumens that is used for continuous CO measurement
60
Describe the Characteristic waveforms recorded during passage of the pulmonary artery catheter
- The right atrial pressure resembles a central venous pressure waveform and displays a, c, and v waves.
- Right ventricular pressure is characterized by a rapid systolic upstroke, a wide pulse pressure, and low diastolic pressure
- Entry of the PAC into the pulmonary artery is heralded by a step-up in diastolic pressure and a change in waveform morphology
* On occasion, it may be difficult to distinguish right ventricularpressure from PAP, particularly if only the numeric values for these pressures are examined. However, careful observation of the pressure waveforms, focusing on the diastolic pressure contours, allows differentiation. During diastole, the PAP will fall owing to continuous runoff flow to the lung, while the pressure in the right ventricle will increase due to filling from the right atrium
- Pulmonary artery wedge pressure has a similar morphology to right
atrial pressure, although the a–c and v waves appear later in the cardiac cycle relative to the electrocardiogram.
61
The tip of the PAC should be within ... of the cardiac silhouette on a standard
anteroposterior chest film
2 cm
62
If a right ventricular waveform is not observed after inserting the catheter ..., coiling in the right atrium is likely. Similarly, if a pulmonary artery waveform is not observed after inserting the catheter to ... , coiling in the right ventricle has probably
occurred. The balloon should be deflated, the catheter withdrawn to
..., and the PAC floating sequence repeated
40 cm
50 cm
20 cm
63
Describe maneuvers that may facilitate the passage of the PAC
The air-filled balloon tends to float to nondependent regions as it passes through the heart into the pulmonary vasculature. Consequently, positioning a patient head down will aid flotation across the tricuspid valve, and tilting the patient onto the right side and placing the head up will encourage flotation out of the right ventricle, as well as
reduce the incidence of arrhythmias during insertion.
Deep inspiration during spontaneous ventilation will increase venous return and right ventricular output transiently, and may facilitate catheter flotation in a patient with low CO.
On occasion, a catheter may be floated to proper position when stiffened by injecting 10 to 20 mL of ice-cold solution through the distal lumen.
In addition, counterclockwise rotation with the balloon inflated during insertion
may help catheter flotation into the right atrium and through the tricuspid valve.
64
For the most part, problems encountered during catheter placement are the
same for both PAC and CVP monitoring. However, catheterization of the right ventricle and pulmonary artery causes complications uniquely associated with PACs. Describe them
▪ Catheterization
- Arrhythmias, ventricular fibrillation
- Right bundle branch block, complete heart block (if preexisting left bundle branch block)
- Right atrial rupture
- Tricuspid or pulmonic valve injury
▪ Catheter residence
- Mechanical: catheter knots, entangling with or dislodgement of pacing wires
- Thromboembolism
- Pulmonary infarction
- Infection, endocarditis
- Endocardial damage, cardiac valve injury
- Pulmonary artery rupture
- Pulmonary artery pseudoaneurysm
- Right ventricular perforation
65
The terms pulmonary artery wedge pressure and capillary wedge pressureare used interchangeably and refer to the same measurement obtained from the tip of a PAC following balloon inflation and flotation to the wedged position
T or F
F
The terms pulmonary artery wedge pressure and pulmonary artery occlusion pressure are used interchangeably and refer to the same measurement obtained from the tip of a PAC following balloon inflation and flotation to the wedged position.
However, pulmonary capillary pressure MUST NOT be confused with wedge pressure or LAP, nor should the term pulmonary capillary wedge pressure be used at all. The hydrostatic pressure in the pulmonary capillaries that causes edema formation according to the Starling equation is different from LAP. This is the pressure that must exceed LAP in order to maintain antegrade blood flow through the lungs. Although the magnitude of the difference between pulmonary capillary pressure and wedge pressure is generally small, it can increase markedly when resistance to flow in the pulmonary veins is elevated
66
In most situations, the major component of pulmonary vascular resistance occurs at the 1...
However, rare conditions like 2... may cause a marked increase in 3... resistance to flow.
Similar situations arise in conditions that disproportionately increase pulmonary 4... resistance, such as 5...
Under these conditions, measurement of wedge pressure will 6... pulmonary capillary pressure substantially and thereby 7... the risk of hydrostatic pulmonary edema
1) precapillary, pulmonary arteriolar level
2) pulmonary veno-occlusive disease
3) postcapillary
4) venous
5) central nervous system injury, acute lung injury, hypovolemic shock, endotoxemia, and norepinephrine infusion
6) underestimate
7) underestimate
67
What is the most common PAC trace artifact? What measure can be taken to resolve this artifact?
At the onset of systole, tricuspid valve closure accompanied by right ventricular contraction and ejection result in excessive catheter motion causing the most common PAC trace artifact,
This pressure artifact may produce an artificially low pressure, erroneously designated as the pulmonary artery diastolic pressure
Repositioning the PAC often solves the problem.
68
What is the over-wedging phenomenon that can be seen in a PAC?
A common artifact in PAC pressure measurement occurs when the balloon is overinflated and occludes the distal lumen orifice. This phenomenon is termed over-wedging and usually is caused by distal catheter migration and eccentric balloon inflation that forces the catheter tip against the vessel wall. The catheter now
records a gradually rising, nonpulsatile pressure as the continuous flush system builds up pressure against the obstructed distal opening. When observed, this should be corrected immediately by gentle catheter withdrawal to a more proximal location in the pulmonary artery
69
How does mitral regurgitation change the pulmonary artery and wedge pressure waveforms?
It cause a tall v wave.
Unlike a normal wedge pressure v wave produced by late systolic pulmonary
venous inflow, the prominent v wave of mitral regurgitation begins in early systole. Mitral regurgitation causes fusion of c and v waves and obliteration of the systolic x descent, as the isovolumic phase of LV systole is eliminated owing to the retrograde ejection of blood into the left atrium.
Because the prominent v wave of mitral regurgitation is generated during ventricular systole, the mean wedge pressure overestimates LV end-diastolic filling pressure,
which is better estimated by the pressure value prior to onset of the regurgitant v wave. However, it remains a good approximation for mean LAP and the subsequent risk of hydrostatic pulmonary edema.
70
The height of the wedge pressure v wave is a sensitive and
specific indicator of mitral regurgitation severity
T or F
F
Although the height of the v wave in the wedge pressure trace will be affected by the volume of regurgitant blood entering the left atrium, it also depends on the left atrial
volume and compliance. This may explain why patients with acute mitral regurgitation tend to have tall wedge pressure v waves: they have smaller, stiffer left atria with poorer compliance compared to patients with long-standing disease. Therefore, the
height of the wedge pressure v wave is neither a sensitive nor a specific indicator of mitral regurgitation severity
71
How does mitral stenosis (also left atrial myxoma or whenever there is obstruction to mitral flow) change the pulmonary artery and wedge pressure waveforms?
In this condition, the holo-diastolic pressure gradient across the mitral valve results in an increased mean wedge pressure, a slurred early diastolic y descent, and a tall end-diastolic a wave
72
How do diseases that increase LV stiffness (e.g., LV infarction, pericardial constriction, aortic stenosis, and systemic hypertension) change the pulmonary artery and wedge pressure waveforms?
Diseases that increase LV stiffness (e.g., LV infarction, pericardial constriction, aortic stenosis, and systemic hypertension) produce changes in the wedge pressure that resemble in part those seen in mitral stenosis. In these conditions, mean wedge pressure is increased, and the trace displays a prominent a wave, but the y descent remains steep, because there is no obstruction to flow across the mitral valve during diastole
73
How does Myocardial ischemia may change the pulmonary artery and wedge pressure waveforms?
Myocardial ischemia can also produce LV systolic dysfunction, typically as a result of supply ischemia, caused by a sudden reduction or cessation of coronary blood flow to a region of the myocardium. As ejection fraction falls significantly, LV enddiastolic
volume and pressure rise, and elevated pulmonary diastolic and wedge pressures develop.
Distortion of LV geometry or ischemia of the myocardium underlying the papillary muscles, can lead to acute mitral regurgitation with its characteristic pulmonary
artery pressure trace changes.
74
How does pericardia lconstriction change the CVP, the pulmonary artery and wedge pressure waveforms?
- Tall a and v wave
- Steep x and y descent
- M or W configuration
Despite reduced cardiac volumes, cardiac filling pressures are markedly elevated and equal in all four chambers of the heart at enddiastole. Although PAC monitoring reveals this pressure equalization, the characteristic M or W configuration is
more apparent in the CVP trace, most likely because of the damping
effect of the pulmonary vasculature on the left-sided filling.
Another hallmark of pericardial constriction is observed in the LV and RV pressure traces. These demonstrate rapid but short-lived early diastolic ventricular filling, which produces a diastolic “dip-and-plateau” pattern or “square root sign.
In some cases, particularly when heart rate is slow, a similar waveform pattern may
be noted in the CVP trace: a steep y descent (the diastolic dip) produced by rapid early diastolic flow from atrium to ventricle, followed by a mid-diastolic h wave (the plateau) from the interruption in flow imposed by the restrictive pericardial shell
75
How does mechanical ventilation affect the PAP and PAWP? Hor to minimize this effect?
During positive pressure ventilation, inspiration increases pulmonary artery and wedge pressures. By measuring these pressures at end-expiration, the confounding effect of this inspiratory increase in intrathoracic pressure is minimized
76
For the column of blood connecting the tip of the wedged catheter and the draining
pulmonary vein to be continuous, however, external compression by surrounding alveoli should be negligible (i.e., the catheter needs to reside in the so-called ...)
West zone 3 of the lung
77
Can Pulmonary artery diastolic pressure (PADP) be used to estimate LAP?
Yes.
This
is acceptable under normal circumstances because when pulmonary venous resistance is low, the pressure in the pulmonary artery at end of diastole will equilibrate with downstream pressure in the pulmonary veins and left atrium. From a monitoring standpoint, PADP has the added advantage of being available for
continuous monitoring whereas PAWP is only measured intermittently.
78
In many situations, left ventricular end-diastolic pressure can either be underestimated or overestimated by the PAWP and/or PADP. Describe situations that underestimate the LVEDP and the respective mechanism
1) Diastolic dysfunction
- Mean LAP < LVEDP
- Increased end-diastolic a wave
2) Aortic regurgitation
- LAP a wave < LVEDP
- Mitral valve closure before end-diastole
3) Pulmonic regurgitation
- PADP < LVEDP
- Bidirectional runoff for pulmonary artery flow
4) Right bundle branch block
- PADP < LVEDP
- Delayed pulmonic valve opening
5) Postpneumonectomy
- PAWP < LAP or LVEDP
- Obstruction of pulmonary blood flow
79
In many situations, left ventricular end-diastolic pressure can either be underestimated or overestimated by the PAWP and/or PADP. Describe situations that overestimate the LVEDP and the respective mechanism
1) Positive end-expiratory pressure
- Mean PAWP >Mean LAP
- Creation of lung zone 1 or 2, or pericardial pressure changes
2) Pulmonary arterial hypertension
- PADP > Mean PAWP
- Increased pulmonary vascular resistance
3) Pulmonary venoocclusive disease
- Mean PAWP >Mean LAP
- Obstruction to flow in large pulmonary veins
4) Mitral stenosis
- Mean LAP > LVEDP
- Obstruction to flow across mitral valve
5) Mitral regurgitation
- Mean LAP > LVEDP
- Retrograde systolic v wave raises mean atrial pressure
6) Ventricular septal defect
- Mean LAP > LVEDP
Antegrade systolic v wave raises mean atrial pressure
7) Tachycardia
- PADP >Mean LAP > LVEDP
- Short diastole creates pulmonary vascular and mitral valve gradients
80
The cardiovascular system is often modeled as an electrical circuit, with the relationship between cardiac output, blood pressure, and resistance to flow related in a manner similar to Ohm’s law. Describe the equation
PVR= [(MPAP - PAWP) / CO] x 80
SVR= [(MAP– CVP) / CO] x 80
SVR = systemic vascular resistance (dyne*s/cm5)
PVR= pulmonary vascular resistance (dyne*s/cm5)
MAP = mean arterial pressure (mm Hg)
CVP = central venous pressure (mm Hg)
MPAP = mean pulmonary artery pressure (mm Hg)
PAWP = pulmonary artery wedge pressure (mm Hg)
CO = cardiac output (L/min)
81
Describe the Normal Hemodynamic Values for:
.............................................................Average..............Range
- Cardiac output (L/min)................5,0....................4,0–6,5
- Stroke volume (mL)......................75....................60–90
- Systemic vascular resistance.......1200...............800–1600
(Dynes.sec.cm−5)
- Pulmonary vascular resistance......80..................40–180
(Dynes.sec.cm−5)
- Arterial oxygen content (mL/dL).....18...................6–20
- Mixed venous oxygen content........14..................13–15
(mL/dL)
- Mixed venous oxygen saturation.....75..................70–80
(%)
- Arteriovenous oxygen difference .....4.................3–5
(mL/dL)
- Oxygen consumption (mL/min)........225............200–250
82
Factors Influencing Accuracy of Thermodilution Cardiac Output Measurement
▪ Intracardiac shunts
▪ Tricuspid or pulmonic valve regurgitation
▪ Thermistor malfunction from fibrin or clot
▪ Pulmonary artery blood temperature fluctuations
▪ Rapid intravenous fluid administration
▪ Respiratory cycle influences
▪ Extremely low cardiac output (can overestimate true CO)
▪ Temperature and volume of injectate (should be consistent)
▪ Sampling rate of the thermistor
83
About the Continuous Thermodilution Cardiac Output Monitoring:
Small quantities of heat are released from a 10-cm thermal filament incorporated into the RV portion of a PAC, approximately 15 to 25 cm from the catheter tip, and the resulting thermal signal is measured by the thermistor at the tip of the catheter in the pulmonary artery. The heating filament is cycled on and off in a pseudorandom binary sequence, and the CO is derived from cross-correlation of the measured pulmonary artery
temperature with the known sequence of heating filament activation. Typically, the displayed value for CO is updated every ... and represents the average value for the CO measured over the previous ...
30 to 60 seconds
3 to 6 minutes
84
Explain the Transpulmonary Thermodilution Cardiac Output technique
This technique provides intermittent measurements of CO using a modified Stewart–Hamilton formula, similar to standard pulmonary artery thermodilution. For transpulmonary thermodilution measurement, ice-cold saline is injected into a central venous line while the change in temperature is measured in a large peripheral artery (femoral, axillary, or brachial artery) via a special arterial catheter equipped with a thermistor
85
The lithium dilution system allows intermittent measurement of CO with thw need of a radial artery catheter and central intravenous access
T or F
F
The lithium dilution system allows intermittent measurement of CO with only a radial artery catheter and peripheral intravenous access
86
This lithium dilution system technique can be used in children, but cannot be used in ...
patients who are taking lithium or who are in their first trimester of pregnancy
87
Which drug can interfear with lithium dilution system technique for CO measurment
Inaccurate measurements may occur in patients who have just received high doses of nondepolarizing neuromuscular blockers, since the latter
interfere with the lithium sensing electrode
88
Many recent developments in CO monitoring have focused on continuous CO measurement derived from analysis of the arterial pressure waveform, generally termed pulse contour analysis or pulse wave analysis. These techniques are based on the principle of ..., where the arterial pulse pressure and its contour are primarily determined by ...
ventriculo-arterial coupling
left ventricular stroke volume and arterial impedance
89
How does stroke volume is estimated using aterial pressure waveform analysis?
By analyzing the systolic portion of the arterial pressure curve (from the beginning of systole to the dicrotic notch), stroke volume can be estimated by dividing the integral of the change in pressure over time by the value of aortic impedance
90
Measurement or estimation of total arterial impedance (a dynamic physical property) is a crucial element for the calculation of stroke volume from the arterial pressure waveform. This variable is measured by pulse wave analysis systems that use ...
either external reference calibration, internal calibration based on biometric and demographic data, or analysis of wave reflections to estimate arterial impedance.
91
Systems which use external calibration of CO in combination with pulse wave analysis utilize ...
transpulmonary thermodilution or transpulmonary lithium dilution (mentioned above)
92
A nonmorphology-based method of CO estimation, called pulse power analysis, uses nomograms that consider the patient’s age, height, and weight to calculate CO. This method is based on the law of... and assumes that the net power change in the heartbeat is the balance between the ...
conservation of mass/power
input of a mass (stroke volume) of blood minus the blood mass lost to the periphery during the heartbeat
93
Another method for cardiac output monitoring that does not require a PAC is the partial CO2 rebreathing technique.
Owing to the difficulty encountered in the standard Fick method involving measuring oxygen consumption and mixed venous hemoglobin saturation, this alternative technique is based upon a restatement of the Fick Equation for carbon dioxide elimination rather than oxygen uptake. Describe this equation
Q˙ = VCO2 / (CvCO2 − CaCO2)
Where,
Q = cardiac output
VCO2 = rate of carbon dioxide elimination
CvCO2 = carbon dioxide content of mixed venous blood
CaCO2 = carbon dioxide content of arterial blood
* This method uses the change in CO2 production and end-tidal CO2 concentration in response to a brief, sudden change in minute ventilation. With a specifically designed breathing system and monitoring computer, this measurement is easily performed in any tracheally intubated patient
