Exam 6 - Arterial Blood Pressure Monitoring Flashcards
Arterial Blood Pressure
- Measure of force of blood on arterial walls
- Result of pressure generated by beating heart and resistance
- Flow and pressure is pulsatile (systolic and diastolic)
- Not the same in all points of arterial tree
Effect of gravity on MAP
- If standing: lower above heart….higher below heart
- Heart level is standard reference - Laying down is same throughout
- Same at all vertical points
MAP
- Avg pressure in system during systole AND diastole
- Reflects: Driving pressure
Peak pressure
Compliance of large arteries
- Reflects: Driving pressure
Estimation of MAP
- (1/3)(SBP) + (2/3)(DBP)
- MAP assumes 60 bpm (in reality HR is not fixed)
- Diastolic fluctuates all the time
- May not be true reflection of MAP under certain conditions
Actual MAP
- (CO)(SVR) + CVP
- determined by area under curve per given cardiac cycle
- obtained via invasive monitoring
- display is averaged over several cardiac cycles
Why MAP is good assessment tool
- MAP is same in all parts of arterial tree
- Not significantly affected by overshoot, artifact, dampening
- PVR and SVR can be calculated using MAP
- Gives approx pressure within systemic and cerebral cap beds
Pressure waves
- precedes actual flow of blood (ECG-Pulse delay)
- Pressure wave: 10 m/s
- Blood flow: 0.5 m/s
- Can affect pressure wave form shape due to reflection
5 components of pressure wave form
1 - Anacrotic limb (ascending limb) (systolic upstroke)
2 - Systolic peak
3 - Dicrotic limb (descending limb) (diastolic decline)
4 - Dicrotic notch (Aortic valve closes)
5 - End Diastole
Physiology of true pressure wave
Phase 1 - Inotropic component
- Aortic valve opens, steep upstroke, early systole
Phase 2 - Volume displacement curve
- blood into aorta, fills out and maintains pressure
- Round due to continued ejection, blood displacement, distention of arterial walls
- May see anacrotic notch (change from inotropic to displacement)
- Low SV (curve narrow w/ low amplitude)
Phase 3 - Late systole and Diastole
- sloping decline (runoff > input) , dicrotic notch (start of diastole)
dP/dT
- Slope of lines on pressure wave from curves
- change in pressure over change in time
High amplitude inotropic spike
- increased pressure generation
- increased acceleration of blood flow
- HYPERDYNAMIC (anemia, AI)
- increased reflection of pressure waves (vasoconstriction)
- may want to remove volume
- slope is quick to rise
Decreased amplitude of inotropic spike
- Myocardial depression (ischemia, CM)
- hypovolemia
- decreased reflections (vasodilation)
- may want to add volume
- hypotensive
Effects of pressure waves
1 - Gravitational effects (standing, laying down)
2 - Reflected waves
- preceded blood flow, bounce off arterioles and back, additive
- pulse pressure greater as you move down arterial tree
- usually results in overestimating actual wave
3 - Physiological effects
- Age, hyper/hypotension, hypovolemia, arrhythmia,
- Vessels get stiffer over time
- Kids have bigger dicrotic notch
Pulse pressure
- difference between systolic and diastolic pressure
- High PP can be predictor of heart problems
- >60 is abnormal - Low PP can mean poor heart function (more common)
- <40 is abnormal
High PP causes
- Calcification of Aorta
- Atheroslerosis
- Aortic Dissection
- Endocarditis
- AI
- Anemia
- Pregnancy
- Anxiety
- Heart block
- Hypertension
Low PP causes
- Hypovolemia
- CM
- CHF
- Shock
- Arrhythmia
- Trauma
Indirect blood pressure measurement
- non-invasive
- detects blood flow under cuff
- flow detected by return to pulse or korotokoff sounds
Direct blood pressure measurement
- cannulated artery (may not correlate with blood flow)
- changes in pressure waveform reflect changes in CV function
Indirect BP techniques w/ operator
- Ausculation (stethoscope) (may underestimate)
- Palpation (does systolic only)
- Ausculation with Doppler assist (systolic only) (good for shock)
- Manometer oscillation observation (systolic and MAP)
- Photoelectric devices (pulseOx) (systolic only)
Blood pressure cuff measuring
- Inflate to 30 mmHg above point when sound ceases
- deflate at 3 mmHg/sec until no sounds
Indirect BP techniques without operator (automated)
- Oscillometry
- Infrared
- Ultrasonic determination
- Arterial tonometry
- All need pulsatile flow / good for stable patients
Indirect vs Direct in measured pressure
- Indirect usually underestimates more than over
- can have technical problems (cuff, deflation, severe physiology differences in patients)
- can have patient problems (regional and generalized pressure gradients at different points in tree)
Direct continuous Intra-arterial pressure monitoring
- most reliable for real time systolic, diastolic, and MAP
- simple, pain free, low risk access for blood sampling
- good for continuous monitoring / serial blood gases
- bad for peripheral vascular disease / hemorrhagic disorders / patient on anticoagulants or thrombotic agents
- avoid placement:
- area of infection / previous surgery site / grafts
Direct arterial cannulation
- Radial artery
- Femoral artery
- Brachial artery
- Axillary artery
- Dorsalis Pedis artery
Direct arterial complications
- Embolisms
- Distal ischemia
- infection
- hemorrhage
- vasculitis
- arterial dissection
Effect of A-fib
- erratic blood flow
Effect of hypertension
- high amplitude peak
- steep upstroke curve
Effect of Hypotension
- Inotropic peak and dicrotic notch disappears
- waveform looks smooth and damped
Effect of vasoconstriction
- increased pressure wave reflection
- very high frequency waveforms (looks like tachycardia)
Effect of hypovolemia
- low amplitude waves
- smaller upstroke peak
