Arterial measurements Flashcards
Causes of an increased Phase I Inotropic component of an arterial waveform? (3)
- Increased LV pressure generation
- Increased reflection of pressure waves from the periphery
- overshoot artifact
Causes of an decreased Phase I Inotropic component of an arterial waveform may be caused by?
- myocardial depression
- hypovolemia
- decreased SVR (vasodilation) - reduces reflected waves from periphery
What does the dicrotic notch signify?
Closure of the aortic valve and the start of disatole
What physiologic action starts a Phase I Inotropic wave form?
Opening of the aortic valve and expulsion of blood from the LV into the peripheral circulation
How fast should a manual BP cuff be delated?
no faster than 3mmHg/sec.
Causes of a more vertical Phase I wave form?
Anything that increases the force of blood ejected from the LV and causes a hyperdynamic circulation such as,
- anemia,
- thyroid toxicosis
- compensated aortic regurgitation
Causes of a more sloped Phase I waveform?
Any condition that has a decreased volume or force of blood expelled from the LV, such as
- ischemic disease
- cardiomyopathy
- hypovolemia
- PVCs
- A-fib
- aortic stenosis
Disadvantages of a radial artery site?
- overshoot artifact is increased
- unable to measure central circulatory pressure
- thrombus formation due to small catheter size
- as in all sites, compromised blood flow, phlebitis, damage to vessel or adjacent structures.
What test must be performed prior to radial artery cannulation?
Allen’s test to assess for adequate collateral circulation to the hand.
Should you ever flush an arterial line manually with a syringe?
NO, may cause “retrograde flow” which can cause tissue ischemia or even embolism. p.203 Darovic
What medications can be used to reduce the likelihood of arterial spasm with catheter insertion and removal?
Lidocaine or phentolamine
Bleeding from a femoral artery can lead to…
retroperitoneal sequestration of up to 1,000 - 1,500 ml of blood. p.205 Darovic
What may skin blanching over an arterial site during a fast flush indicate?
Arterial insufficiency and ischemia
How and why should a blood specimen be drawn from an art line?
Slow and gently as to not damage the arterial segment p. 206 then a SYSTEM flush of 1-3 seconds to clear the line.
What is the technique for removing a radial artery catheter?
- compression is applied proximally AND distally to the arterial puncture site and the catheter is slowly withdrawn while aspirating to remove any emboli. p. 207 Darovic
- followed by firm manual pressure for 10 minutes
- monitor for bleeding, hematoma, circulation and sensation
Can art line pressure be used to evaluate tissue perfusion?
NO, p. 208 Darovic
What does the PCWP/PAOP correlate well with?
LA and LVEDPs when the mitral valve is open
Which anatomical location has the greatest success of the catheter being advanced into the SVC or RA?
Right internal jugular vein
Why is the right IJ preferred over left for art line insertion?
- straighter shot to the SVC/RA
- larger than left
- further from the common carotid artery than the left
If an air embolism is suspected during SCV line insertion, what interventions are warranted?
- place patient LEFT side down
2. attempt to aspirate air out of the circulation from the venous catheter p. 229 Darovic
What measurements does a CVP correlate well with?
RAP (directly) and RVEDPs (indirectly when the tricuspid valve is open)
What is the normal RA mean pressure?
0-8 mmHg
How does CVP or RA pressure correlate with RVEDPs?
When the tricuspid valve is open between the RA and RV the pressure gradient equalizes and reflects the pressure of the RV at end-diastole. p. 232 D
What can an elevated RA pressure indicate?
RV failure or fluid overload
How would you differentiate between FVO and RV failure in the presence of an elevated RA or CVP reading?
Heart Failure 1. RV gallop (S3) 2. weak, rapid pulses 3. dependent edema 4. low CO (restless, oliguric) FVO 1. bounding pulses 2. no gallop rhythm 3. increased UO and low urine SG r/t dilution
How might PPV and/or PEEP affect CVP readings?
An increased intrathoracic pressure may artificially increase the CVP reading and PEEP over 10mmHg may introduce artifact to the waveform p. 235 D
Describe damping of a wave frorm?
Damping is the influence within a system that is a dissipation of energy during an oscillation. In other words, think of damping like a shock absorber. This artificially decreases the signal (amplitude).
Causes of over damping?
Potential causes Air/Air bubbles in tubing Kinks in tubing Clots in tubing arterial spasms
How does overdamping affect the waveform morphology?
Waveform loses its characteristic landmarks and appears unnaturally smooth with a diminished or absent dicrotic notch
How does overdamping affect the BP readings?
SBP, DBP, MAP, PP
- Underestimation of the systolic blood pressure
- Overestimation of the diastolic blood pressure
- Narrowed pulse pressure
- MAP not impacted
HINT: “OD=O,D”, OVERdamping leads to OVERestimation of the Diastolic BP
Whereas underdamping does the opposite (leads to OVER estimation of the SBP and UNDER estimation of the DBP).
What affect does underdamping have on the waveform morphology?
Systolic pressure overshoot with a narrow peak and non-physiological oscillations during the diastolic phase
What is underdamping?
when the oscillations are too pronounced and can lead to a false high systolic or a false low diastolic pressure
Potential causes of underdamping?
Artifact from catheter (catheter whip)
Tachydysrhythmia
stiff or non-compliant tubing
Underdamping affect of BP readings?
SBP, DBP, MAP, PP
Overestimation of the systolic blood pressure
Underestimation of diastolic blood pressure
Wider pulse pressure
MAP not impacted
What is an overshoot artifact and what causes it?
In an underdamped system, the wave form is artificially elevated in amplitude and has numerous non-physiologic oscillations of the downstroke/ diastolic runoff.
Describe the results of a square wave test?
> 2 oscillations before returning to baseline = underdamped
1 to 2 oscillations before returning to baseline = just right
0 to 1 oscillation before returning to baseline = overdamped
After a square wave test is performed, you observe 1-2 oscillations before an arterial waveform returns to baseline. How would you interpret this?
A properly calibrated set up
After a square wave test is performed, you observe 1->2 oscillations before an arterial waveform returns to baseline. How would you interpret this?
The setup is underdamped
After a square wave test is performed, you observe 1-0-1 oscillations before an arterial waveform returns to baseline. How would you interpret this?
The setup is overdamped
How do arterial waveform readings change related to the distance from the heart the measurement is taken?
“Systolic values increase while diastolic values decrease as the pulse moves away from the heart” p. 95 D MAP tends to stay nearly constant.
What physiologic action creates the dicrotic notch?
Rapid closing of the semilunar valves (aortic and pulmonic)
Describe changes in arterial waveform morphology as the point of measurement gets further away from the heart?
- Systolic pressure are higher
- waveforms and narrower and steeper
- the dicrotic notch is delayed and lower p.95 D
What can cause overshoot artifact on arterial waveforms?
“Overshoot is produced by reflected waves within the catheter–manometer system. The magnitude of overshoot can be reduced by mechanical or electrical damping. Overdamping eliminates overshoot, but it reduces frequency response. Optimal damping reduces overshoot without producing a major drop in frequency response”
