Invasive BP Flashcards
What is the average blood flow velocity?
80-300 ml/sec
What is the accepted form of blood pressure ?
Distending wall pressure
As vessels get more narrow, what happens to distending wall pressure?
More energy is displaced upon the wall which increases the pressure. This is why the farther down the leg you go, the larger the systolic pressure gets and lower the diastolic pressure gets
What is the dicrotic notch?
Is the point at which pressure is decreasing from maximum, and the sudden small increase spike is when aortic valve closes and pressure begins to decrease once again
A normal waveform for invasive blood pressure should have how many dicrotic notches?
1
What is the term for when the waveform has more than 1 dicrotic notch?
Ringing
Ludwig in 1846 was the first to have an invasive monitor that produced a waveform, what kind of machine did it use?
Kymograph (kymo = smoke) so used a smoked drum
What are the 4 systems of the clinical pressure measurement device (think A line setup)?
Mechanical coupling
Transducer
Display
Electronic components
How many mL is automatically/continuously flushed into artery to prevent clotting?
3 mL / hour
What are the 2 static sources of error for IBP?
1) Incorrect zero —–making voltage on wheatstone bridge, telling system what is zero pressure mark and which is atmospheric mark
2) Incorrect gain —–the system can no longer adjust gain (in reality is testing/changing the display)
What are sources of dynamic error for IBP?
Waveform is altered due to monitor
Waveform alteration due to pressure propagation through the vasculature
What is difference between zero and reference points for IBP?
Zero point is atmospheric pressure that can be zeroed at any point
Reference point is point where transducer is placed and will read and display at. (normally want to be at heart level)
What do you want to keep your CPP above at which to satisfactorily perfuse the brain?
at least 60 mmHg
When doing upright crani’s, where do you want to put the transducer?
Level of the brain because that is the most important part to be infused
What pressure do you want to pressurize the pressurized bag during A-line setup?
300 mmHg
What is point of greatest uptake of energy in the vessel?
Point of resonance
When something is said to resonate, what does that mean?
That the input and output have frequencies that are nearly identical
What is an integral multiple of the base frequency?
Harmonics
Arterial blood pressure waveforms are produced by summation of sine waves from the fundamental wave and 63% of the second harmonic wave. T or F?
TRUE
Dampening device takes away energy that sometimes can worsen the system. T or F?
TRUE
Dynamic errors arise when significant frequency components of the pressure waveform interact with the Resonant Frequency of the measurement system
This was outlined by biggs, so there ya go
What is the ideal dampening coefficient?
0.7
What is the most common way of adding dampening to the system?
Addition of air
What is the frequency component of IBP waveform determined by?
Where waveform orginates from HR
Contractility
Durometer measures what?
Stiffness of the tubing
What are the variables we can adjust?
Tubing compliance
Tubing length (remember a short stiffy is better than a long floppy)
If you dampen a system too much, what will be the only pressure that will be given?
Mean
So if you have any of increased HR, then you have a increased frequency, which will cause an increase in harmonics, this will cause what?
Increased ringing in the waveform
When a A line has narrowing pulse pressures, what is the term called?
Overdamped
What is a normal dampening coefficient?
0.2 - 0.3
Know the natural frequency formula used to describe when a tubing system tends to ring.
fn = (1/2π) square root [(πD^2 / 4pL) x (ÀP / ÀV)]
What are all factors that could increase likelihood of ringing?
decreased diameter of tubing
decreased change P / change volume
increased length
Increased density
Increased compliance
Why do we use small diameter catheters?
To avoid blocking artery flow
Why do we use an inflexible tube?
To decrease compliance which in turn decreases likelihood of ringing
Why do we use a long tubing system?
For convenience
What would be a less dense fluid to use besides saline?
:Air - but is compressible
:Oils - but could possibly enter artery = BAD
What do all modern pressure transducers require to operate?
Source of electricity
What are most modern transducers powered by?
DC (direct current) because can be used on a transport monitor and be power by a battery and can also be plugged into a wall and convert AC to DC power kinda like best of both worlds
On the pressure transducers themselves, what color coordinates with arterial readings?
Red
On the pressure transducers themselves, what color coordinates with CVP readings?
Blue
On the pressure transducers themselves, what color coordinates with PA or ICP readings?
Yellow
The leak valve on pressure transducers allows how many mL / hour to flow through it?
3 mL/hour
What does the actual transducer look like on the contraption?
Is the black dot in middle
Are current transducers temperature dependent?
NO
We all know how to place an A line now thanks to lab 5, if you need review, please go back and do so.
I still hate you all
What are top 3 locations for placement of A lines?
1) Radial
2) Axillary
3) Femoral
Why is axillary preferred over brachial artery?
Because axillary is larger in diameter than the brachial so once catheter in place more blood can flow through and not be occluded
What are some complications that can distort A line readings?
Distal ischemia
Pseudo-aneurysms
Hemorrhage
Local infection/sepsis
Misuse of equipment
Misinterpretation of data
What are some complications of A line monitoring?
Vascular compromise (ischemia / sclerosis)
Disconnect Hemorrhage
Accidental injection
Infection
Nerve damage
The Milar technique is what?
A very expensive and rarely used technique in which the catheter tip has a pressure transducer located on it
How does the peripheral arterial pressure waveform relate to the central arterial pressure?
Not very well under some clinical conditions
T or F: Dicrotic notch always occurs after the T-wave.
TRUE
so to confirm actual dicrotic notch, compare to an ECG waveform
An anacrotic notch is what?
A notch of upslope of pressure waveform almost equivalent in amplitude as dicrotic notch
When central circulation goes to peripheral circulation, what generally occurs with blood pressure?
Systolic pressure increases
Diastolic pressure decreases
Mean pressure decreases
dP / dt increases
Waveform appears peaked and narrower
What is water hammer?
When you completely occlude the artery and the blood is forced to stop abruptly and greatly increases pressure and pressure reading of A line
When else does water hammer occur naturally in the body?
Tiny water hammers occur everywhere when branching of arteries occurs and also occurs when a valve is closed suddenly and pressure wave spikes because of blood flowing against it
Central vasculature is generally considered to be from where to where?
Aorta to Brachiocephalic trunk to subclavian artery to axillary artery
How are muscle fibers aligned in central vasculature?
Muscle fibers arranged longitudinally
Do vasoactive drugs have greater effect on central or peripheral vasculature?
Peripheral Have little to no effect on vessel properties of central vasculature
Peripheral vasculature starts and ends where?
Axillary artery to brachial artery to radial artery to ulnar and median arteries
How are muscle fibers aligned in peripheral vasculature?
Multiple layers of spirally arranged smooth muscle fibers
T or F: There is a progressive increase in stiffness as distance from heart increases
TRUE (stiffness also called Young’s modulus)
What happens to the aorta with increasing age?
Increases in diameter
Wall thickens and becomes more stiff
Branches off the aorta have what effect with increasing age?
Do not change in diameter, but wall thickens and becomes stiffer
T or F: In general, big vessels dilate and walls thicken, while small vessels show only wall thickening with increasing age
TRUE
Dopamine works on what and has what effect on vasculature?
Is a mixed alpha and beta agonist
Causes vasculature to become more compliant
Methoxamine works on what and what has it been replaced with in today’s medicine?
Strong alpha agonist
Phenylephrine
At what Hz in humans will produce very little magnitude in the vasculature?
6-8 Hz
What reduces viscosity in patients?
Large string sugars
Let patient bleed
Keep from clotting and cut down on red cells
What is the resistance equation?
R = Viscosity x length / Diameter ^4
In the clotting cascade, what ion is very important for clotting and loss of free ions of this results in prevention of clotting?
Calcium
What is very similar to plasmylyte?
Normosol (Calcium is not in either)
When trying to determine brain perfusion pressure, what anatomical location should you place transducer?
Ear canal
