lecture 10: CO monitoring
what is the thermodilution injectate made out of ? what temp? what volume?
D5W or 0.9%NS 0⁰C to 24⁰C can be used. Volumes of 2.5, 5, or 10 ml. Inject quickly and steadily! Monitor assumes injection takes less than 4 seconds Warming of solution in your hand by 1⁰C can increase error by 3%
how do you insert the PA cath?
Flush ALL ports before insertion and confirm that where you are injecting is matched up with where the fluid exits If injecting into proximal infusion port and fluid comes out at distal end ➔ throw away Test balloon Attach PA and CVP pressure cables and zero PA catheter is sterile! Only handle the ports.
does CCO have a deterioration in measurement?
No deterioration in measurement over a 76 hour period in ICU Because of averaging over 3 - 6 min, respiratory variations are accounted for automatically. No error generated as would be in a single injection measurement Trade off is response time vs. accuracy of measurement
how do we setup the transducers?
One bag of NS acts as continuous flush device for all 3 transducers. (triple spike) All must be flushed, labeled, and zeroed prior to insertion
what does the thermodilution method require and what does it measure? TDCO
PAC measures CO known fluid at a known temp injected through proximal port temp change measured at thermistor near distal port
how accurate is the CCO?
Response to acute changes in CO is slow compared to arterial BP, Capnography, etc (AS MUCH AS 5 - 15 minutes!!) Correlation to injected thermodilution is excellent Accurate from 1.6 - 10.6 L/min CO and core temperatures ranging from 33.2 to 39.8⁰C
how does CCO work?
Same principle as thermodilution just AUTOMATIC and CONTINUAL NO INJECTATE Thermal filament in the RV portion of the PA catheter heats blood intermittently; temperature subsequently measured 15 to 25cm downstream Filament cycled on and off taking a new dilution measurement every 30 - 60sec CO value displayed is the average of the measurements over the past 3 - 6 minutes widely or acutely varying it wont keep up w it its great for someone in the ICU
what inputs does the flotrac require? what does it need this for
age, sex, height, weight calculate an estimate of SVR, particularly a guess of aortic impedance -BSA can vary i.e. Muscular 100KG vs. Obese 100KG
red? yellow? blue?
art pa cath cvp
after the injectate travels past the distal thermistor what do the monitors computate for K2
different for the constant bc its compensating for: -heat change in transit to exiting port (as much as 8c) -cath dead space -injection rate
what does a continuous CO cath look like?
extra filament creating heat heats up the blood looked at distally when blood mixes w body temp blood
what is a PAC introducer?
good when going on bypass to know the temperature sterile sheet pull cath back 3-5cm and has to stay sterile so the clips and the sleeve thing help to keep sterile and let come in and out CVP:blue PAC:yellow
what does a small AUC mean
high CO earlier peak sharper drop cath senses little changes in short period of time fast blood-doesnt take long to get to the heart
what does the AUC for thermodilution represent
inverse to the rate of blood flow inc area means dec flow
thermodilution eqn: what is k1? what is k2?
k1: constant of injectate vs blood known injectate factor k2: constant applied to the monitor by the manufacturer to take into account the temperature changes that occur NOT caused by the cardiac output of the right heart -known factor of monitor
what does a large AUC mean
low CO changes in temp over long period of time takes blood alot of time to get to the heart
what do we need for a continuous CO?
modified PAC Heated element releases small amt from filament & temp changes are interpreted as CO Accurate but slow to respond to acute changes - averages data over 3-6 minutes
is the pulse contour co accurate w high dose vasodilators or vasoconstrictors? can this be used w IABP?
no Cannot be used with IABP - extra notch to decrease afterload confuses the monitor as to which notch is the end of systole -dicrotic notch
is the FloTrac accurate during IABP use?
no balloon pump the whole point of this last slide is that the floraq does not work w the balloon pump
what is a pulse contour analysis
non invasive CO Flotrac system derives cardiac output from the structure of the arterial BP waveform
what has the same k1 values
ns and d5w
what happens when we give ppv
ppV adn we see the inc and the height an how much it was and at the end of the breath we see the lowest it is delta up adn delta down shows a number % in SV variability everytime you ive a PP breath you see a big in c in the SV bc pushed uot of the lung vasc and pushed out of the heart >13% knwo that the pt is going to respond to the fluid bolus BP down→ would the pt respond to fluid some people will but if they arent dry they might have a prob w contractility of the l ventricle or something we can give drugs not volume
what does the thermodilution curve look like? what is CO inversely proportional to
quick peak and then looks exponential CO inverse to AUC -temp change over time
intra arterial balloon pump: where does it sit? when does it inflate and deflate?
sits in aorta approx. 2 cm from take off subclavian arter Counterpulsates: - inflates during diastole(when the heart is perfused) which inc coronary artery blood flow thru retrograde pressure -deflates during systole which helps reduce afterload (SVR) through a vacuum effect. goes in at the groin the femola artery and goes in a few cm past the aortic arch when it deflated it acts liek a vaccum and gets it out of th heart so the heart doesnt have to work as mucj
explain thermodilution CO
sterile cold bolus injected and its a thermal indicator in r atrium through proximal PA cath Thermistor located 4cm from the distal end of the PA cath detects the change in temp of the blood downstream → uses modified Stewart-Hamilton equation to calculate CO (we dont need to memorize this) injectate travels past the distal thermistor, the change in blood temperature over time is shown ➔ TB(t)dt we need the right temp of the pt and the bolus
what do we use to derive SVV? what level tells us we have a low volume pt?
systolic pulse variability 13%
how does the flotraq calculate the SV index?
takes the age, sex, height, and weight the shape of the pulse waveform is used to calculate STROKE VOLUME INDEX SVI*HR = Cardiac Index (CO indexed to BSA) Records 2,000 samples of the art line waveform over 20 seconds and averages them to get a mean BP
how much error does the TDCO have?
0.5 ml variation in injectate of 5ml will cause a 10% error inject at the same point in the respiratory cycle Stroke volume of RV can vary as much as 50% in one ventilation cycle Ventilation can alter PA blood temperature by 0.01⁰C to 0.02⁰C Can be exaggerated in mechanical ventilation (cold gas) Not accurate during rapid infusion into CV line Cannot account for VSD or ASD that add shunts Tricuspid or pulmonic valve regurgitation can distort data Even under ideal circumstances, TDCO measurements have 10% error rate
how do we get a TDCO
3 measurements in short time intervals Injectate should be given @ end-exhalation, quickly and steadily Results that are within 10% of each other are then averaged turn off vent so know you are giving it at the same time in cardiac cycle
what are some problems with pulse contour?
Algorithm-based estimations Not accurate with aortic regurgitation (Pulsus Bisferiens) "double peak" confuses dichrotic notch location in computer Not accurate with arrhythmias -Ventricular arrhythmias alter the pressure waveform Computer may not detect the actual end of systole (dichrotic notch) Atrial arrhythmias change HR during the measurement cycle (CO = SV * HR)
what is pulse contour cardiac output?
Computerized analysis of the arterial pressure waveform P = QR! DOES NOT REQUIRE A PAC - only an accurate arterial pressure waveform & specialized transducer Can provide an acceptable level of accuracy but still has faults