Hemodynamics Flashcards
Law of laplace in cardiomyopathy
LV wall stress increases as LV wall thickness decreases
LV wall stress increases as LV radius increases
radius is directly related to stress
Thickness is inversely related to stress
Ohms law in hemodynamics
I=V/R
Flow= blood pressure/resistance
What is blood pressure
Force of circulating blood exerted on the blood vessel walls
Terms for manual blood pressure
Sphygmomanometer
Riva-Rocco
Too loose of a NIBP will cause what?
Overestimation of BP
Describe changes to BP in arms when patient is in lateral decubitus position
Lower arm-overestimates
Upper arm- underestimates
Define SBP in terms of oscillometry
Max pressure at which slope of oscillation amplitude increases
DBP in oscillometry
Minimum pressure at which slope of oscillation amplitude decreases
Actual measured values in automatic vs manual cuff pressures
Automatic: MAP
Manual: SBP and DBP
Below a MAP of 65 what BP technique is not useful in guiding hemodynamic therapy?
Oscillometry
Factors that impair oscillometry
Hemodynamic instability
Irregular heart rhythms
Cuff issues
Basis for and drawbacks of continuous NIBP
Photoplethysmography
-require calibration
-impacted by tone/perfusion
-sensitive to finger motion
-limited use in critically ill patients
Indications for arterial cannulation
If you’re thinking about it- DO IT
Barry
What to know about the Allen’s test
Patency of collateral circulation in hand from ulnar artery
Tests are only abnormal or normal….
Use a pulse ox on the thumb
Timeframe color should return to hand 5-15 seconds
Sensitivity/specificity of Allen’s test
80%
When to use US for art line placement
Lack of pulsatile flow
What are alternate sites to the radial artery?
Ulnar, brachial and axillary
Why do we not use lower extremity NIBP
They have not been validated!!!
Advantages to femoral line
Reflect central arterial pressure
Norepi infusion rates are reduced up to 30%
Risks of femoral cannulation
Cerebral embolization
Retroperitoneal hemorrhage (preform below inguinal ligament)
What to know about forearm pressures
Overestimate SBP and underestimate DBP
Electrical/mechanical time delay in
Ascending aorta and
Radial arterial catheter
AoV- 180msec
Radial-220 msec
2 limbs of arterial waveform
Anacrotic
Dicrotic
MAP calculation
1/3 SBP + 2/3 DBP
Which phase of the cardiac cycle decreases the most in tachycardia?
Diastole
Early indicator of hemodynamic instability
SBP instability
May also be greater indicator of organ blood flow
Physiologic contributions to peak systolic pressure
LV contraction
Central arterial compliance
Reflected pressure wave from vascular tree
What changes do we see in distal monitoring sites?
Increased peak pressure due to pulse amplification do to reflected pressure waves from distal noncompliant vascular tree
7 things you see in distal sites
High peak pressure
Widened pulse pressure
Delayed upstroke
Delayed incisura
Steeper diastolic runoff
Prominent diastolic wave
Decreased end diastolic pressure
What is systolic decline and when is it most rapid
Time when efflux from arterial compartment is > influx from LV
-rapid in LV outflow obstruction
Why is diastolic pressure not 0?
Elastic recoil of the vessels- contributes to 40% of delivered stroke volume
What is end diastolic pressure
Pressure exerted on AoV by vascular tree
Pressure seen by L coronary arteries
What lowers DBP?
Loss of elastic recoil
Aortic insufficiency- regurg
Distal monitoring
Causes of widened pulse pressure
Atherosclerosis
Sepsis
AI
Underdampening
systolic pressure overshoot due to resonance
(Widened pulse pressure)
Over dampening
Slurred upstroke and loss of fine detail including dicrotic notch
(Diminished pulse pressure)
Impact of under or over dampening on an arterial waveform MAP
Unchanged
Aortic stenosis artline
Narrow pulse pressure
Delayed upstroke
Parvus et tardus
(AI)Aortic regurgitation on artline
Double peak
Wide pulse pressure
Pulsus bisferiens
HOCM
Artline
Spike and dome (mid systolic dysfunction)
Severe systolic LV dysfunction -artline
Alternating pulse pressure amplitude
Pulsus alternans
Very similar to paradoxus…
Tamponade on Art line
Pulsus paradoxus (>10mmhg in SBP with inspiration
What determines pulse pressure?
Directly proportional to change in circulatory volume (stroke volume) and inversely to arterial compliance (C)
Pp= (SV)/C
Hint: think of diastolic pressure and how it changes with compliance and then how a change in diastolic will change the PP
What is a wide or narrow pulse pressure?
Narrow: < 25% of SBP
Wide: >50% of sBP
What’s the new vital sign you will always calculate?
Pulse pressure
What are the determinants of SV
This is very important
Preload
Contractility
Afterload
If arterial compliance is unchanged, what does a change in pulse pressure reflect?
A change in stroke volume
What is preload?
RVEDV
Or
LVEDV
VOLUME (wall tension)
What are surrogate measures of preload?
LVEDP, CVP and PAWP
When does CVP correlate with RVEDP?
In the absence of tricuspid valve disease
What conditions make digital readouts inaccurate?
High respiratory pressures
Tricuspid regurgitation (common in ventilated patients)
Zeroing a CVP
STOPCOCK (not transducer) 5cm below the sternal angle
Utility of CVC according to Barry
Vasoactive medications
No fall in CVP during inspiration of mechanically ventilated patient
What does this mean and what do we call the relationship?
Suggests CO will not increase with fluid
Negative predictive value
CVP waveform components
A- end diastole
C- early systole
X-mid systole
V- late systole
H-mid to late diastole
Describe PAC floating waveforms
RA-CVP waveform
RV-systolic increase, diastolic unchanged
PA- diastolic STEP UP
Wedge-similar to CVP
West zones
Zone 1, where alveolar pressure is higher than arterial or venous pressure;
Zone 2, where the arterial pressure is higher than alveolar and venous, a relationship which changes during the respiratory cycle.
Zone 3, where both arterial and venous pressure is higher than alveolar.
What pulmonary term will we NOT use and what will we use instead
FUCK PCWP (capillary)
Use PAWP (wedge pressure)
Problems with PAC monitoring
Pressure gradients
Changes in ventricular compliance
What indicates correct placement of a PA cath?
Minimal effect of airway pressure (peep) on PAWP measurement
PAWP is not indicative of LVEDP in cases of high PEEP
PAC flotation tips
Patient head down will facilitate passing tricuspid
patient RSD and head up may help pass RVOT
Deep inspiration may augment venous return and facilitate catheter out of RVOT
Why are PAC readings extremely sensitive to artifact?
Long, more prone to clots/air/motion
Mechanical tendency to overwedge
Mitral valve disease distorts waveform
What is catheter fling?
Artifactual peaks and troughs that distort digital readings
What is overwedging and how do you correct?
Gradual rise in non-pulsatile waveform
Tip against vessel wall
Withdrawal of catheter
What does Pa waveform look like in MR?
Tall V wave overestimated on digital readouts
When do you get correct values for LVEDP?…
End diastole (R wave)
What may indicate Myocardial ischemia on a PAC waveform?
Rise in LVEDP
-increased a height
Determinants of SVR
Vascular tone
Hematocrit
Plasma protein concentration
Temperature
Define impedance
Resistance to changing flow
Not- resistance to flow (SVR)
Surrogate measures for filling pressures related to preload
PAP and CVP
What is a poor positive predictor of fluid responsiveness because it has a complicated relationship?
CVP
Most sensitive detection of myocardial ischemia
Echo
SWMA
Calculated values form PAC
SVR and PVR
Relative contraindication to PAC placement .
LBBB
Windkessel effect
The mechanical energy stored in the stretched elastin serves to maintain the blood pressure during diastole
When is end diastole measured in PAWP wave?
A wave
Two things seen in MI on a PAC tracing
Increased a wave (impaired diastole)
Decreased LVEF (impaired systole) and or rise in LVEDP
MAP calculation- not BP based
CO*SVR
