blood pressure monitoring Flashcards
Key indicator of perfusion
• Most important determinant of LV afterload
• Reflects the workload of the heart
blood pressure monitoring
rapid systolic estimation, return of flow technique
manual indirect bp measurement
The point at which the first turbulent arterial
flow sound returns.
systolic bp number
The point at which the sound becomes
muffled/diminished or non longer heard.
diastolic bp number
Errors with cuff measurement (4)
1) shock or pressors obliterating sound (false low)
2) low compliance (false high)
3) cuff size (large, false low-small, false high)
4) too rapid of cuff deflation (false low)
what is worse: a cuff too wide or too narrow?
narrow
the width of the blood pressure cuff should be ___ greater than the diameter of the patient’s extremity
20-50%
dynamap/oscillator
data interpretation algorithms utilized
measure systolic, diastolic, mean
automated non invasive bp monitoring
Arterial pulsations cause varying amplitudes which are measured along with the rate of change of amplitudes
oscillometry (measuring vibrations)
what reading with nibp is most accurate
map
what reading of nibp is least accurate
diastolic reading
how is systolic pressure determined with nibp
amplitude of pulsations
are increasing and are at 25%-50% of
maximum.
how is diastolic pressure measured with nibp
amplitude of pulsations
has declined from the peak value
approximately 80%.
map is
peak amplitude of pulsations
Invasive BP Clinical Indications (4)
- need for real-time continous pressure monitoring
- cuff measurement is unreliable
- waveform diagnostics desired
- repeated blood sampling needed
sites used for invasive bp (6)
- radial (#1)
- ulnar (#0)
- brachial
- axillary
- femoral
- DP/PT
complications of invasive bp (10)
• Ischemia distal to site • Hematoma-compartmental syndrome • Arterial trauma • Infection • Thrombus formation • Vasospasm • Bleeding • Fistula • Air embolus heparin overdose
unit for measuring frequency, number of cycles per
second. 1 cycle per second
hertz
back and forth repeated motion. A quantity that
repeatedly and regularly fluctuates above and below some mean value, as the pressure of a sound wave. NORMAL
Oscillation
stretch and recoil of spring (bouncing
vibrations/oscillations). a series of oscillations in which each
oscillation has a frequency that is an integral multiple of the same
basic frequency. ABNORMAL OCCURANCE
harmonics
exaggerated wave amplitudes occurring when the
monitored frequency matches the systems natural frequency resulting in overshoot or overestimated wave reading. good for the ear, bad for direct bp measurement
resonance
what makes the electrical signal in the transduer
diaphragm displacement/movement
explain the process of undamped (overdamped) inside the transducer
diaphragm moves too easily it may oscillate too
long. If a second subsequent wave arrives while it’s
still oscillating stacking will occur.
explain the process of overdamped in transducer
diaphragm is too stiff and fails to oscillate in
response to a pressure wave
How easily or rapidly the system oscillates, measured in Hz
natural frequency
Natural frequency should be at least
5 times the frequency of the
waveforms to be monitored.
Numerical indicator of the degree of damping.
defines an objects tendency to cease
vibrating/oscillating (how rapidly an object will
return to resting baseline).
damping coefficient
Completely undamped is a coefficient of
0, meaning the object will oscillate forever
Completely damped is a coefficient of
1, meaning the object will instantly return to baseline resting state as soon as stimulus is withdrawn
when one displacement causes
one vibration, damping coeffiecient .4
critical damping
transducer diaphragm vibrates too long after
being subjected to mechanical displacement
underdamped
underdamped system is characterized by
sbp and dbp overshoot
falsely widened pulse pressure
artifact and other external interference
skinny tall waves
sharp exaggerated waveforms
underdamped
flat long short waves
smooth, no diacrotic notch
overdamped
overdamping causes (9)
Vasodilation aortic stenosis low cardiac output clots air bubbles stopcocks kinks blood in transducer empty or lack of pressure on flush bag
underdamping causes (6)
Hypertension hyperdynamic flow states catheter whip (excessive catheter movement), atherosclerosis vasoconstriction aortic regurgitation
Systolic BP will be falsely low and diastolic BP will be
falsely high.
• Mean BP mostly unaffected.
overdamped system
how do you assess dynamic performance of bp system
square wave test
optimally damped square wave test
1.5-2 oscillations before returning to baseline
underdamped square wave test
> 2 oscillations: SBP over estimated and DBP may be low or normal
overdamped square wave test
<1 oscillation: sbp falsely low and dbp may be high or normal
optimal tubing length?
4 ft
how do you optimize dynamic response of system
- NF as high as possible
- short hard tubing
- few stopcocks
- remove air bubbles
- withdraw blood to remove clots
optimal damping number
.6-.7
where should transducer be leveled
5 cm below sternal border and 4th ics
corresponds with aortic root
1 cm of transducer height =
.75 mmHg
10 cm= 7.5 mmHg
what happens to your pressures if pt above the transducer
higher pressures
what happens when pt is under transducer
lower pressure
where is neurosurgery placement
level of the external auditory meatus of tragus of ear (circle of willis estimates cpp)
what will waveform show with aortic stenosis
delayed upstroke, narrowed pulse
pressure
what will waveform show with aortic regurg
sharp rise, double peak
what will waveform show with hypertrophic cardiomyopathy
spike and dome
due to midsystolic obstruction.
