Unit 6 - Hemodynamic Monitors & Equipment Flashcards
what do Korotkoff sounds represent
turbulent flow in an artery that was previously occluded by the BP cuff
BP auscultation
- relies on korotkoff sounds
- SBP is measured at the first sound
- DBP is measured when the last sound disappears
what is cuff pressure when korotkoff sounds are produced
between SBP and DBP
how do NIBP machines measure BP
Oscillatory Method
Inflatable cuff occludes arterial blood flow, and as the cuff pressure is released, the monitor measures the pressure fluctuations that occur in response to arterial pulsations
when is SBP measured with oscilattory method
when oscillations 1st appear (the reappearance of flow after cuff occlusion)
when is DBP measured with oscillatory method
measured at the minimum pressure where oscillations can still be generated
BP measurement reading that’s the most susceptible to error with oscillatory method
DBP
why won’t NIBP work in a pt on CPD or with LVAD
requires pulsatile flow
ideal bladder length for BP cuff
80% of extremity circumference
ideal bladder width of NIBP cuff
40% of extremity circumference
NIBP reading with a cuff that’s too small
overestimates SBP
cuff pressure required to occlude artery is higher
NIBP reading when cuff is too large
underestimates SBP
cuff pressure required to occlude artery is lower
what happens to SBP, DBP, and pulse pressure measurements as pulse moves from aortic root toward periphery
SBP increase
DBP decrease
PP widens
SBP, DBP, and PP at aortic root
SBP lowest, DBP highest, PP narrowest
SBP, DBP, and pulse pressure at radial artery compared to aortic root
SBP higher
DBP lower
PP wider
BP reading if BP cuff above heart
BP reading falsely decreased (less hydrostatic pressure)
BP reading if cuff below heart
BP reading falsely increased (more hydrostatic pressure)
every 10 cm change in BP cuff above/below heart = BP changes by _____
7.4 mmHg
Complications of NIBP Measurement
- pain
- neuropathy (radial, ulnar, median)
- measurement errors
- limb ischemia
- compartment syndrome
- bruising
- petechiae
- interference with IV medications
what is measured at the peak of art line waveform
SBP
what is measured at the trough of art line waveform
DBP
what does the upstroke of art line waveform represent
contractility
what part of arterial line waveform represents stroke volume
area under curve
where does art line monitor BP
at level of transducer (not at site of catheter insertion)
art line transducer location that won’t be affected by changes in body or extremity position
level of RA
causes of falsely increased NIBP
- BP cuff too small
- BP cuff too loose
- Bp measured on extremity below level of heart
causes of falsely decreased NIBP
- BP cuff too large
- cuff deflated too rapidly
- measured on extremity above level of heart
measurement that remains constant throughout arterial tree
MAP
where does art line pressure have the greatest pulse pressure
dorsalis pedis
SBP increases along arterial tree as a function of pressure waves reflec
where is arterial DBP measurement lowest
dorsalis pedis
what does optimal waveform morphology balance
amount of damping with amount of distortion from transducer system
High-pressure flush test (square test):
shows how fast the system vibrates in response to a pressure signal
what informs about damping characteristics in art line system
number of oscillations after flush test
when is an art line considered optimally damped
baseline is re-established after 1 oscillation
when is art line waveform considered under damped
baseline re-established after several oscillations
BP measurements with under damped art line
SBP overestimated, DBP underestimated, MAP accurate
causes of underdamped art line
- stiff (non-compliant) tubing
- catheter whip (artifact)
when is an art line system considered over damped
baseline re-established with no oscillations
BP measurements in overdamped art line system
SBP underestimated, DBP overestimated, MAP accurate
causes of overdamped art line system
- air bubble in pressure tubing
- clot in catheter
- low flush bag pressure
- kinks
- loose connection
how does dicrotic notch change with art line monitoring location
moves further away from systolic peak the further the monitoring site is from the heart
where should CVL tip rest
just above the junction of vena cava & right atrium
risks assoc. with CVL catheter in heart chambers
↑ risk dysrhythmias, thrombus formation, cardiac perforation
where should pulmonary artery catheter tip be
- in the pulmonary artery, distal to pulmonic valve
- 25-35 cm from VC junction
3 steps to calculate distance of CVL insertion
- Know the distance from site of entry to VC junction
- Know distance from VC junction to where catheter tip should be (only applies if placing PAC)
- Add these 2 numbers together to determine distance from site of insertion to catheter tip
distance from subclavian vein to junction of vena cava and RA
10 cm
distance from right IJ to junction of vena cava and RA
15 cm
distance from left IJ to junction of vena cava and RA
20 cm
distance from femoral vein to junction of vena cava and RA
40 cm (either side)
distance from median basilic vein to junction of vena cava and RA
right = 40 cm
left = 50 cm
distance from vana cava/RA junction to RA
0-10 cm
distance from vena cava/RA junction to RV
10-15 cm
distance from vena cava/RA junction to PA
15-30 cm
distance from vana cava/RA junction to where PAOP is measured
25-35 cm
what should you assume if PAC advanced 10 cm past calculated distance and expected waveform still isn’t seen
what should you do?
catheter is coiled
- Deflate balloon, withdraw catheter to junction of VC and RA, try again
- If resistance encountered when pulling back catheter is possibly knotted or entangled with chordae tendineae obtain CXR to r/o
possible complications while obtaining CVL access
- arterial puncture
- PTX
- air embolism
- neuropathy
- catheter knot
- dysrhythmias (most common)
The best way to treat PACs/PVCs with CVL insertion
withdraw catheter and start over
complications assoc with floating PAC
PA rupture, RBBB, dysrhythmias
risks of left IJ CVL
risk of puncturing thoracic duct
can cause chylothorax (lymph in chest)
when does risk of CVL infection increase
3 days after placement
classic presentation of PA rupture
hemoptysis
factors that increase risk of PA rupture with PAC placement
- anticoagulation
- hypothermia
- advanced age
- inserting catheter too far
- prolonged balloon inflation
- chronic irritation of vessel wall
- unrecognized wedging
- filling balloon with liquid instead of air
what does the CVP waveform represent
pressure inside RA
components of CVP waveform
- 3 peaks (a, c, v)
- 3 troughs (x,y)
mechanical and electrical events associated with A wave of CVP waveform
- mechanical: RA contraction
- electrical: just after P wave (atrial depolarization)
mechanical and electrical events associated with C wave of CVP waveform
- mechanical: RV contraction (bulging of tricuspid into RA)
- electrical: just after QRS (ventricular depolarization)
mechanical and electrical events associated with x descent of CVP waveform
- mechanical: RA relaxation
- electrical: ST segment
mechanical and electrical events associated with V wave of CVP waveform
- mechanical: passive RA filling
- electrical: just after T wave begins (ventricular repolarization)
mechanical and electrical events associated with Y descent of CVP waveform
- mechanical: RA empties through open tricuspid valve
- electrical: after T wave ends
where should CVP be zeroed
at phlebostatic axis
CVP reading if transducer is above or below phlebostatic axis
4th intercostal space mid anteroposterior level
- Transducer above = underestimates CVP
- Transducer below = overestimates CVP
during which part of respiratory cycle should CVP be measured & why
end-expiration
* During this phase of ventilatory cycle, extravascular pressure = atmospheric pressure
* Allows CVP measurement relative to atmospheric pressure
intersection between vascular function curve and CO curve
CVP
normal CVP value
1-10 mmHg
3 things CVP is a function of
- intravascular volume
- venous tone
- RV compliance
causes of an increased CVP reading
- transducer below phlebostatic axis
- hypervolemia
- RV failure
- tricuspid stenosis/regurg
- pulmonic stenosis
- PEEP
- VSD
- constrictive pericarditis
- cardiac tamponade
causes of decreased CVP reading
transducer above phlebostatic axis, hypovolemia
what causes loss of a wave in CVP waveform
- occurs when priming function of the RA is lost
- A fib, V-pacing if underlying rhythm is asystole
causes of large a wave in CVP waveform
atrium contracts & empties against high resistance (either valve or non-compliant vent.)
* Tricuspid stenosis
* diastolic dysfunction
* myocardial ischemia
* chronic lung disease - RVH
* AV dissociation
* junctional rhythm
* V pacing (asynchronous)
* PVCs
causes of large v wave in CVP waveform
- tricuspid regurg - allows a portion of RV volume to pass through closed but incompetent tricuspid valve during RV systole
- acute increase in intravascular volume
- RV papillary muscle ischemia
CVP waveform with tricuspid regurg
- large v wave
- c and v waves may blend into each other
normal RA pressure
1-10 mmHg
same as CVP
normal RA pressure
1-10 mmHg
same as CVP
normal RV pressure
15-30 / 0-8
normal PA pressure
15-30 / 5-15
normal PAOP
5-15 mmHg
when is the dictrotic notch formed in PAP waveform
during pulmonic valve closure during diastole
where should tip of PAC be
in lung zone 3
where is this waveform measured
right atrium
where is this waveform measured
right ventricle
where is this waveform measured
pulmonary artery
what does this waveform represent
PAOP
why should PAC tip be in West lung zone 3
Continuous column of blood between tip of PAC and LV in this region
where is west zone 3 located when:
* sitting
* supine
* prone
* lateral
- Sitting = lung base
- Supine = towards back
- Prone = towards chest
- Lateral = dependent lung
when does PAC placement give the most accurate estimation of LVEDP
when tip placed in West zone 3
relationship between Pa, PA, and Pv in West zone 3
Pa > Pv > PA
things that suggest the PAC tip is NOT in zone 3
- PAOP > PA end-diastolic pressure
- Nonphaseic PAOP tracing
- Inability to aspirate blood from distal port when balloon in wedged position
things that cause PAOP to overestimate LVEDP
for given PAOP, true volume in LV is less than predicted by PAOP
- Impaired LV compliance (ischemia)
- Mitral valve disease (stenosis or regurg)
- L - R cardiac shunt
- Tachycardia
- PPV, PEEP
- COPD
- Pulmonary HTN
- Misplaced
what does it mean for a PAOP to overestimate LVEDP
for given PAOP, true volume in LV is less than predicted by PAOP
how does aortic valve insufficiency affect PAOP measurement
will underestimate LVEDV
when does thermodilution underestimate CO
injectate too much or too cold
when does thermodilution overestimate CO
injectate volume too low or hot, partially wedged PAC, thrombus on PAC top
method to improve accuracy of thermodilution CO measurement
Common practice to average 3 separate injections to arrive at final CO (improves accuracy)
how is CO measured via thermodilution
- 5% dextrose or 0.9% NaCl of known quantity and temp bloused through proximal port of PAC
- Each injection should be in same phase of respiratory cycle and completed in < 4 seconds
used to calculate and plot temp change vs. time to determine CO
Modified Stewart-Hamilton equation
significant drawback of continuous CO monitoring (COO)
30-second delay between time measured and time seen on monitor
CCO value averages data over what time frame
3-6 minutes
SVO2 calculation and normal values
SvO2 is a function of what 4 variables
- Q = Cardiac output (L/min)
- VO2 = Oxygen consumption (mL O2/min)
- Hgb = Amount of hemoglobin (g/dL)
- SaO2 = Loading of hemoglobin in arterial blood (%)
when does SvO2 become an indirect monitor of CO
Hgb, SaO2 and VO2 held constant
conditions associated with decreased SvO2
O2 consumption increases or O2 delivery decreases
* ↑ O2 consumption: stress, pain, thyroid storm, shivering, fever, light anesthesia
* ↓ O2 delivery: ↓ PaO2, ↓ Hgb (anemia), ↓ CO
conditions that increase SvO2
O2 consumption decreases or O2 delivery increases
* ↓ O2 consumption: hypothermia, cyanide toxicity
* ↑ O2 delivery: ↑ PaO2, ↑ Hgb, ↑ CO
how does sepsis affect SvO2
- increases
- creates high CO state with arterial admixture
- O2 bypasses tissues
classic example of increased SvO2 d/t impaired O2 uptake by tissues
cyanide poisoning from Nipride
how does a L-R shunt affect SvO2
increases
oxygenated blood travels from L to R heart, added to pulmonary venous blood
where can a true mixed venous sample be collected
pulmonary artery
must contain blood from SVC, IVC, and coronary sinus
CO is a function of what 3 factors
- preload
- contractility
- afterload
how does pulse contour analysis allow for accurate fluid balance assessment
by providing more precise measures of fluid responsiveness, O2 delivery, and microcirculatory flow
what is pulse pressure variation calculated from
arterial waveform measures max and min pulse pressure values throughout respiratory cycle
percentage change is called pulse pressure variation
Pulse contour analysis provides a measure of:
preload responsiveness as a function of how stroke volume changes during respiratory cycle (assumes PPV)
as a general rule, when is preload responsiveness assumed
when 200-250 mL fluid bolus improves SV > 10%
dynamic measures of pulse contour
PVI, SVV, SPV, PPV
when do dynamic measures of pulse contour tend to predict volume responsiveness
when calculated measurement is > 13-15%
why will a hypovolemic patient have a greater degree of SV variation throughout respiratory cycle
as a function of intrathoracic pressure’s effect on RV filling and function
things that can cause errors in contour analysis
- SV
- small Vt
- PEEP
- open chest
- RV dysfunction
- dysrhythmias
gold standard for assessing myocardial function
TEE
where should tip of esophageal doppler probe be
~35 cm from incisors (T5-T6 or at 3rd sternocostal junction)
how does esophageal doppler give information about fluid status
Emits ultrasound beam towards descending aorta & reflects off the blood traveling through it
* By measuring aortic diameter and blood’s velocity through descending aorta, can derive several useful variables to guide fluid management
limitations to esophageal doppler use
aortic stenosis, aortic insufficiency, disease of thoracic aorta, aortic cross-clamping, after CPB, pregnancy
esophageal doppler contraindication
Esophageal disease is a relative contraindication
what does a wave represent in PAOP waveform
LA systole
what does c wave represent in PAOP waveform
mitral valve elevation into LA during LV systole/RV contraction (isovolumetric contraction)
what does v wave represent in PAOP waveform
passive LA filling
PAOP is an estimate of:
LVEDP
events associated with a wave of CVP waveform
- atrial systole
- ventricular diastole
Best TEE view for LV ischemia
midpapillary muscle level in shot axis
