invasive and non-invasive BP monitoring Flashcards
why is BP monitoring significant?
- key indicator of perfusion
- most important dereminant of LV afterload
- reflects the workload of the heart
describe manual indirect BP measurement
rapid systolic estimation (return of flow technique)
-palpation: during deflation, palpable pulse retruns
-visual: during deflation, finger pulse oximetry or arterial catheter waveforms reappear
systolic and diastolic measurement
-auscultatory: (Korotkoff) turbulent flow sounds
-systolic: point at which the first turbulent arterial flow sound returns
-diastolic: point at which the sound becomes muffled/diminished or no longer heard
-no mean BP estimation available
what are errors with cuff measurement?
- shock or pressors obliterate sound generation causing false low reading
- low compliance (distendability) of tissues causing false high reading (shivering, non-compressible arteries d/t arteriosclerosis)
- cuff size: width should be 20% greater than arm diameter; cuff too large causes false low reading, too small false high
- too rapid a cuff deflation rate causes false low (3mmHg a second or 2 mmHg per heart beat)
describe automated non-invasive BP (NIBP)
- also known as the dynamap or oscillator
- data interpretation algorithms are utilized to determine BP
- measures systolic, diastolic, and mean BP
- electronic storage of data occurs
- automated which allows the clinician to devote their time to other patient care needs
- based on oscillometry (measuring vibrations): arterial pulsations cause varying amplitudes which are measured along with the rate of change of amplitudes
how do NIBP monitors determine BP?
- systolic pressure: amplitude of pulsations are increasing and are at 25-50% of maximum
- mean arterial pressure (MAP): peak amplitude of pulsations
- diastolic pressure: amplitude of pulsations has declined from the peak value approx. 80%
- diastolic reading is considered the most inaccurate
what are clinical indications for invasive BP monitoring?
need for real-time continuous pressure monitoring
-hemodynamic instability
-vasoactive agent use
-deliberate hyper or hypotensive state required
-precision BP control needed
cuff measurement is unreliable
-poor circulation/perfusion- low BP
-erratic pulse (a fib, PVCs, tachycardia)
-burns, AV shunts
waveform diagnostics desired
repeated blood sampling needed
what are sites for art lines?
- radial artery (most utilized)
- ulnar (rarely used d/t principle source of blood flow to hand)
- brachial (no collateral circulation, near median nerve)
- axillary (left more than right)
- femoral (resembles aortic pressure; accessible in a low perfusion state
- dorsalis pedis/posterior tibial: requires long tubing, increased reflectance d/t peripheral vascular tree
what are complications associated with invasive BP monitoring?
- ischemia distal to site
- hematoma-compartmental syndrome
- arterial trauma
- infection
- thrombus formation
- vasospasm
- bleeding
- fistula
- air embolus
- heparin overdose
what is dynamic response of invasive BP monitoring?
- physical behavior of the system
- based on three physical properties: elasticity, mass, friction
- characterized and assessed by: natural frequency and damping coefficient
define Hertz (Hz)
-unit for measuring frequency, number of cycles per second; 1 cycle per second = 1 Hz
define oscillation
- 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 occurrence
define harmonics
- 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 occurrence
define resonance
- exaggerated wave amplitudes occurring when the monitored frequency matches the systems natural frequency resulting in overshoot or overestimated wave reading
- when harmonics occur the system is resonate
- resonance is useful for the ear b/c the amplification can help distinguish sounds but resonance is not good for direct arterial BP measurement
describe electrical transducers
-a fluid filled catheter and tubing sends a pressure wave to fluid filled transducer where diaphragm displacement/movement creates an electrical signal
what happens when the system is undamped?
diaphragm moves too easily it may oscillate too long and if subsequent wave arrives while it’s still oscillating, stacking occurs
what happens when the system is overdamped?
the diaphragm is too stiff and fails to oscillate in response to a pressure wave
describe natural frequency
- how easily or rapidly the sytem oscillates
- all objects have a natural frequency at which they optimally vibrate when disturbed or struck (based on object’s properties; slower through denser objects)
- measured in Hz unit (cycles per second)
- higher the natural frequency, the more precise and accurate the signal quality with less distortion
what should natural frequency be?
at least 5 times the frequency of the waveforms to be monitored
*if HR 180 (3Hz or 180/60) then 5 x 3 = 15Hz NF required
