Mod1: Monitoring for Cardiac Surgery - BLOOD PRESSURE MONITORING Flashcards
BLOOD PRESSURE MONITORING
What is the Most frequently monitored hemodynamic variable?
BLOOD PRESSURE
BLOOD PRESSURE MONITORING
Which information is made available to us via the MAP?
Organ perfusion
(Especially Brain, Liver and Kidneys)
BLOOD PRESSURE MONITORING
Which information is made available to us via the diastolic blood pressure?
Coronary perfusion
(Coronaries feel during diastole)
BLOOD PRESSURE MONITORING
Which information is made available to us via the Pulse pressure?
Stroke Volume
(Volume status)
CO
SVR
BLOOD PRESSURE MONITORING
Why is Noninvasive BP not typically used as primary BP monitoring during CPB?
Inadequacy of monitoring hemodynamic parameters
Inaccurate at extreme pressures
Intermittent data, not continuous
Requires pulsatile flow (which is not available during CPB)
Often used merely as adjunct to direct arterial blood pressure monitoring
BLOOD PRESSURE MONITORING
What remains the “Gold Standard” for monitoring BP during cardiac surgery?
Direct arterial blood pressure

BLOOD PRESSURE MONITORING
What are advantages of Direct arterial blood pressure monitoring?
Displays real-time blood pressure monitoring
Allows for pharmacological or mechanical BP manipulation while maintaining awareness of beat to beat BP
Allows for analysis of waveform can give information on SVR, SV, and cardiac output
Allows for close monitoring of ABG’s, coagulation (ACT’s), and electrolytes
Allows for Direct ABP monitoring possible during non-pulsatile CPB

BLOOD PRESSURE MONITORING
Which information can be gathered via analysis of direct arterial BP waveform?
Cardiac Output
SV
SVR

INTERPRETING ARTERIAL WAVEFORM
Which wave on the QRS complex represents the begining of systole?
The R-wave

INTERPRETING ARTERIAL WAVEFORM
When does the arterial pulse wave occur in reference to the ECG tracing?
160-180 milliseconds after the R-wave

INTERPRETING ARTERIAL WAVEFORM
What happens during the Systolic phase or Systolic upstroke?
What is it associated with on the ECG tracing?

Begins with a Rapid increase of pressure to a peak
Opening of the Aortic valve
Blood ejecting into the aorta from LV
Peak systole = Systolic BP
Follows the R-wave on EKG

INTERPRETING ARTERIAL WAVEFORM
What happens during the Systolic runoff?

Represents the time when
the eflux of blood out of the ventricle is lower than
the influx of blood into the aorta

INTERPRETING ARTERIAL WAVEFORM
What does the Dicrotic notch represents?

Closure of the aortic valve

INTERPRETING ARTERIAL WAVEFORM
What happens during the “diastolic runoff”?

Drop in pressure that occurs after the aortic valve closes
Blood is now going into the peripheral circulation

INTERPRETING ARTERIAL WAVEFORM
What does End-Diastolic-Blood-Pressure (EDBP) also referred to as “Aortic Diastolic Pressure” represents?

Pressure exerted by the vasculature back onto the aortic valve

INTERPRETING ARTERIAL WAVEFORM
What reflects DBP on the arterial waveform?

Lowest reading before the next systolic upstroke

INTERPRETING ARTERIAL WAVEFORM
What reflects MAP on the arterial waveform?
Area under the curve

INTERPRETING ARTERIAL WAVEFORM
How is Pulse pressure calculated?
What is its normal value?
PP = SBP - DBP
Normal value: 40 - 60 mmHg

INTERPRETING ARTERIAL WAVEFORM
Which informations could be gathered via Pulse Pressure?
Fluid status and Vascular competence
Via SV, CO, and SVR
INTERPRETING ARTERIAL WAVEFORM
What could a Narrow PP (less than 40mmHg) indicate?
Hypovolemia
Cardiac tamponade
Anything that causes a low CO state

INTERPRETING ARTERIAL WAVEFORM
What could a Widened PP (more than 60mmHg) indicate?
Worsening aortic valve insufficiency
Usually Aortic Regurgitation
During diastole, the arterial BP will drop to backfill the LV through that regurgitant aortic valve that is supposed to be closed
May also get what’s called “Bisferiens pulse” which occurs d/t to run off of blood into the periphery and into the LV

INTERPRETING ARTERIAL WAVEFORM
What’s another name for the biphasic-pulse aortic waveform that shows two peaks per cardiac cycle, a small one followed by a strong and broad one? What does it indicate?
Bisferiens pulse
It is a sign of problems with the aortic valve, including aortic stenosis and aortic regurgitation, as well as hypertrophic cardiomyopathy causing subaortic stenosis
It is associated with a widened Pulse pressure

INTERPRETING ARTERIAL WAVEFORM
Explain the mechanics of Systolic Pressure Variation (SPV), volume status, and how it affects SBP?
PPV causes and increase in intrathoracic pressure which impedes VR, compresses the lungs, and causes blood in the pulmonary vasculature to be pushed to the left side of the heart, and ejected with each beat
This result in increase in BP during inspiration
During expiration, there is no augmentation to the amount of blood pumped out, resulting in a decrease in SBP

INTERPRETING ARTERIAL WAVEFORM
What’s the normal value of Systolic Pressure Variation (SPV)
10 mmHg

INTERPRETING ARTERIAL WAVEFORM
What do large variations in Systolic Pressure Variation (>15 mmHg) indicate? How do this affect ABP?
Hypovolemia = ↓ ABP with PPV
Patients are said to be hypovolemic when the respiratory variations are more than 15mmHg.
It’s the same exact concept as SVV (stroke volume variation)
SVV is measured as percent

INTERPRETING ARTERIAL WAVEFORM
What does the ARTERIAL WAVEFORM reflects?
Changes in pressures over time
Qualitative estimates of hemodynamic indices of Contractility, SV, SVR

INTERPRETING ARTERIAL WAVEFORM
On the following chart, what does “a” represents?

Contractility
Grossly judged by rate of pressure rise/slope of upstroke during systole
The steeper the slope, the quicker the rise, the greater the contractile forces
Converly, the shallower the slope, the slower the rise and the weaker the contractile forces
This is a controversial way to the determine the pt’s volume status

INTERPRETING ARTERIAL WAVEFORM
On the following chart, what does “b” represents?

Stroke Volume
Area under the aortic pressure waveform
Onset of systole to dicrotic notch

INTERPRETING ARTERIAL WAVEFORM
What determines the location of the Dicrotic notch?
Timing of the Aortic closure in the cardiac cycle

INTERPRETING ARTERIAL WAVEFORM
What charaterizes Aortic closure and dicrotic notch location in pts that are hypovolemic?
Aortic closure occurs slower
Consequently the Dicrotic notch occurs farther down the dicrotic limb

INTERPRETING ARTERIAL WAVEFORM
Why is using arterial waveform interpretation alone to determine volume status controversial?
The location of the arterial line itself affects where the Dicrotic nocth occurs on the dicrotic limb
Pts with radial arterial line or arterial lines that are more peripheral will have their Dicrotic nocth occur lower on the dicrotic limb vs pts with arterial lines placed more proximal (axillary or sunclavian arteries or aortic root)
This is why you cannot necessarily use the location of the Dicrotic notch to determine volume status

INTERPRETING ARTERIAL WAVEFORM
What on the arterial waveform represents Systemic Vascular resistance?
Position of Dicrotic notch

- High on downslope = ↑ SVR*
- Low on downslope = ↓ SVR*
INTERPRETING ARTERIAL WAVEFORM
What value of SVR correspond to a Dicrotic notch High on downslope?
↑ SVR

INTERPRETING ARTERIAL WAVEFORM
What value of SVR correspond to a Dicrotic notch Low on downslope?
↓ SVR

INTERPRETING ARTERIAL WAVEFORM
What does the “c” on the chart represents?

Systolic time

INTERPRETING ARTERIAL WAVEFORM
What does the “d” on the chart represents?

Diastolic time

ARTERIAL BP - SITES OF CANNULATION
Why is the Radial artery the most common cannulation site?
Ease of placement
Accurate estimation of true aortic pressure

ARTERIAL BP - SITES OF CANNULATION
What are contraindications for radial arterial line placement?
Positive Allen’s test
Radial artery harvest
ARTERIAL BP - SITES OF CANNULATION
Why is the Allen’s test performed before radial artery line placement?
Too determine whether ulnar artery collateral circulation to the hand is present in the case of arterial thrombosis
The test screens for pts with inadequate palmar collateralisation from the ulnar artery
ARTERIAL BP - SITES OF CANNULATION
How is the Allen’s test performed?
Apply firm pressure over both the radial and ulnar arteries simultaneously while having the pt squeeze their hand to promote exanguination
Release pressure over the ulnar artery, keeping the radial artery compressed
Measure time for capillary refill of the nail bed

ARTERIAL BP - SITES OF CANNULATION
What is a positive Allen’s test?
What does a positive Allen’s test indicate?
Capillary refill of nail bed >10 seconds
Indicates inadequate collateral circulation from the ulnar artery
ARTERIAL BP - SITES OF CANNULATION
Why should the radial artery line be placed in opposite side if the IMA is to be harvested for graft?
Due to the dampen or obliterate tracing resulting from compression of chest wall & subclavian artery
This slide states that if the IMA is to be harvested for grafting, the radial artery catheter should be placed on the opposite side. This is not practice that you will see.
The main reason that the surgeon request that the radial artery catheter be placed on one side over the other is if he plans to harvest the radial artery for one of the bypass grafts. OR if there is some type of blockage in the subclavian that would preclude you from placing a catheter in it and reducing blood flow even more. And the reason is because of <strong>compression of the chest wall with the sternal retractor</strong>.
However, this is not actual practice that you will see, although it theoretically could happen because the internal mammary arteries branch off the subclavian artery proximal to where the subclavian becomes the axillary artery.
Here you can see the right subclavian artery and how the internal thoracic or internal mammary artery branches off the subclavian artery.
This picture shows it branching off the axillary because the subclavian actually turns into the axillary artery as it passes underneath the clavicle.
So theoretically, <strong>you could have an obliteration of the pulse with the sternal retractor</strong> that’s used to take down the mammary.

ARTERIAL BP - SITES OF CANNULATION
Where should the arterial line be placed if both IMA’s are to be harvested?
Femoral artery
ARTERIAL BP - SITES OF CANNULATION
Why is the use of the Brachial artery relatively contraindicated as a cannulation site?
Brachial artery has no benefit of collateral flow as does the ulnar
<em>Brachial artery (medial to the antecubital fossa)</em>

ARTERIAL BP - SITES OF CANNULATION
In which instances is Brachial artery cannulated?
Invasive BP monitoring is required, but
Radial arteries cannot be cannulated for some reason
ARTERIAL BP - SITES OF CANNULATION
True or False: Brachial arterial line are usually only used for short periods of time
True
ARTERIAL BP - SITES OF CANNULATION
Why does Brachial arterial line more accurately reflects central aortic pressure than the radial artery?
Closer to the heart

ARTERIAL BP - SITES OF CANNULATION
Why should shortest, smallest gauge (18 or less) cath be used for Brachial artery line cannulation?
To decrease the incidence of thromboembolism

ARTERIAL BP - SITES OF CANNULATION
What’s the largest vesselcommonly use to monitor arterial BP with comparable results to all other sites?
Femoral artery
Large & superficial making for easy access
ARTERIAL BP - SITES OF CANNULATION
Why is the Femoral artery an excellent access to the central arterial tree?
Its waveform more closely resemble aortic pressure waveform than do waveforms from more peripheral sites
ARTERIAL BP - SITES OF CANNULATION
Why is there a Low risk of distal ischemic sequela with femoral artery cannulation?
Because of its large Diameter
ARTERIAL BP - SITES OF CANNULATION
When is the risk for plaque immobilization and pseudoaneurysm significant with femoral artery line placement?
When initially placing the line
ARTERIAL BP - SITES OF CANNULATION
Why should the femoral artery be placed below the inguinal line?
To reduce the risk of damaging the inguinal liguament

ARTERIAL BP - SITES OF CANNULATION
True or False: during femoral cannulation, you must be cautious of hitting a hematoma or creating uncontrolled hematomas into the pelvis or retroperitoneal space
True

ARTERIAL BP - SITES OF CANNULATION
Why femoral artery cannulation suggested in pts with expected difficulty weaning from CPB d/t known ↓ EF or severe wall motion abnormalities?
They may require IABP
Access may be used should IABP placement become necessary

ARTERIAL BP - SITES OF CANNULATION
What are contraindications to femoral artery cannulation?
Prior vascular surgery
Skin infection

ARTERIAL BP - SITES OF CANNULATION
What are advantages of Axillary artery cannulation?
More comfortable for the patient
Large and superficial
Easy access to central arterial tree
Provides a central arterial pressure waveform that more closely resemble the aortic root pressure

ARTERIAL BP - SITES OF CANNULATION
Why is there increased risk of cerebral embolus of air or debris with axillary artery cannulation?
Because cannulation site more centrally located
Air or debris can easily enter the circulation during flushing of the catheter
ARTERIAL BP - SITES OF CANNULATION
Why is left axillary cannulation preferred?
Reduce risk of cerebral embolus of air or debris
ARTERIAL BP - SITES OF CANNULATION
What could cause nerve damage with axillary catheter placement?
Hematoma formation
Traumatic cannulation
ARTERIAL BP - SITES OF CANNULATION
True or False: Infection at site is a contraindication for axillary artery cannulation
True
ARTERIAL BP - SITES OF CANNULATION
When is Aortic root cannulation indicated for arterial BP monitoring? Who places it?
When difficulties are encountered in obtaining reliable BP
Placed by surgeon

ARTERIAL BP - SITES OF CANNULATION
Ulnar artery cannulation is rare. The Process for cannulation of the ulnar artery is similar to that of which other vessel?
The radial artery
ARTERIAL BP - SITES OF CANNULATION
True or False: Ulnar artery provides most of the blood flow to the hand in 90 percent of pt
True
ARTERIAL BP - SITES OF CANNULATION
In which instances is the ulnar artery cannulated?
When radial artery can not be used
Positive Allen’s
Harvest for graft
ARTERIAL BP - SITES OF CANNULATION
Allen’s test must be performed prior to ulnar catheter placement. How does Allen’s test for ulnar artery cannulation differ to that for radial artery cannulation?
Occlude the ulnar artery and assess for adequate radial artery collateral flow
ARTERIAL BP - SITES OF CANNULATION
What are disadvantages of using Dorsalis pedis and posterior tibial arteries as cannulation sites for BP monitoring?
Difficult management in postop period
Difficult cannulation
Increased risk for ischemic complications
Relative contraindication with PVD/DM
Distal location increases distortion of waveform
ARTERIAL BP - SITES OF CANNULATION
In which population is it appropriate to use Dorsalis pedis and posterior tibial arteries as cannulation sites?
Pediatrics
Direct Arterial Blood Pressure
As cannulation site becomes more peripheral, what happens to Arterial upstroke?
Becomes steeper

Direct Arterial Blood Pressure
As cannulation site becomes more peripheral, what happens to Systolic peak?
Becomes higher

Direct Arterial Blood Pressure
As cannulation site becomes more peripheral, when does the Dicrotic notch appears?
Later!!!

Direct Arterial Blood Pressure
As cannulation site becomes more peripheral, what happens to Diastolic wave?
Becomes more prominent

Direct Arterial Blood Pressure
As cannulation site becomes more peripheral, what happens to End diastolic pressure?
Becomes lower

Direct Arterial Blood Pressure
As cannulation site becomes more peripheral, what happens to Systolic pressure?
Systolic pressure increases
(as much as 20-50mmHg higher than central aorta)

Direct Arterial Blood Pressure
As cannulation site becomes more peripheral, what happens to Diastolic pressure?
Becomes lower

Direct Arterial Blood Pressure
As cannulation site becomes more peripheral, what happens to Pulse pressure?
Wider pulse pressure

Direct Arterial Blood Pressure
As cannulation site becomes more peripheral, what happens to MAP?
MAP remains relatively unchanged

ARTERIAL BLOOD PRESSURE MONITORING - COMPLICATIONS
What are common complications associated with arterial blood pressure monitoring?
Distal ischemia (low)
Arterial thrombosis
Infection
Bleeding
ARTERIAL BLOOD PRESSURE MONITORING - COMPLICATIONS
What’s is the most common site of arterial BP cannulation for CPB?
The radial artery
ARTERIAL BLOOD PRESSURE MONITORING - COMPLICATIONS
Sometimes, False low of radial artery pressure is seen immediately after CPB. What could be responsible of lower BP immediately after CPB?
Peripheral vasodilation secondary to rewarming
Hypovolemia
Vasoconstriction
If suspect that peripheral artery tracing is dampened (slow upstroke or loss of dicrotic notch), obtain a direct pressure measurement from central site
ARTERIAL BLOOD PRESSURE MONITORING - COMPLICATIONS
Sometimes, False low of radial artery pressure is seen immediately after CPB. What would the surgeon do if this is suspected?
The surgeon will sometimes place a catheter into the aortic root and transduce it to compare it to the radial artery pressure
And if it is in fact lower, an alternate site will be chosen to place an arterial line
RECOMMENDATIONS FOR BLOOD PRESSURE MONITORING DURING CPB
T/F: Radial artery pressure is usually accurate before and after CPB
True
RECOMMENDATIONS FOR BLOOD PRESSURE MONITORING DURING CPB
When is Addition of a femoral artery catheter recommended?
Poor LV function is evident
Second comparable (central) BP
(BP from a more peripheral site is questionable)
Ensures arterial access should IABP become necessary
RECOMMENDATIONS FOR BLOOD PRESSURE MONITORING DURING CPB
If IMA is to be harvested for grafting, why should you place radial artery catheter in opposite side
Compression of chest wall/subclavian artery
=> dampens/obliterates tracing
This is not necessarily practice
Theoretically, because the IMA branches from the SC artery, occlusion could occur to the radial artery
This is rarely seen unless the pt has some sort of blockage in the sc artery
RECOMMENDATIONS FOR BLOOD PRESSURE MONITORING DURING CPB
If both IMA’s are to be harvested, where should the arterial cannulation be placed?
Place femoral artery catheter
RECOMMENDATIONS FOR BLOOD PRESSURE MONITORING DURING CPB
If radial artery to be harvested, where should you place arterial line?
Place radial arterial line on opposite side
RECOMMENDATIONS FOR BLOOD PRESSURE MONITORING DURING CPB
When is the only time that the radial artery is cannulated on the opposite side?
Known blockage in the subclavian artery
Radial artery is to be harvested