Cardiac Output II.pptx

Monitoring Cardiac Output & Blood Flow II DILUTION METHODS: GENERAL INFORMATION Indicator characteristics  mixes well with blood  easy to determine concentration  stable  not retained by the body  not toxic Indicators used  Indocyanine dye (cardiogreen)  use densitometer to measure the...

Monitoring Cardiac Output & Blood Flow II DILUTION METHODS: GENERAL INFORMATION Indicator characteristics  mixes well with blood  easy to determine concentration  stable  not retained by the body  not toxic Indicators used  Indocyanine dye (cardiogreen)  use densitometer to measure the light absorption  temperature  Cold temperature saline or 5% dextrose  uses temperature thermistor DYE-DILUTION METHOD Device records the dye concentration in the blood after a known dye sample was injected upstream Right side injection (PA) of indocyanine green dye with a continuous sample drawn simultaneously via a systemic artery at a constant rate Plot the concentrations graphically Mostly used in DYE DILUTION ADVANTAGES Most accurate in high-cardiac output states DYE DILUTION DISADVANTAGES Not valid with intra-cardiac shunts, valve regurgitation or shock Dye unstable / photosensitive – must be mixed daily *Risk of allergic reaction to dye Requires calibration using sample of patient’s blood Carefully metered blood withdrawal One shot estimate Patient must be in stable metabolic state for THERMODILUTION SWAN GANZ CATHETER- CURRENTLY MOST WIDELY USED TECHNIQUE THERMODILUTION: HOW IT WORKS Results should be based on the average of at least three measurements that are within 90 seconds 10% between each of each other. measurementdiscard abnormal curves THERMODILUT ION SETUP If using cold injectate 0-4 THERMODILUTION: EQUATION Computation constant determined by manufacturer and is different B I I B I for each model used CO = K G G V (T - T ) UB K: Constant GB: Density of blood (kg/m3) GI: Density of injectate (kg/m3) VI: Injectate volume (L) UB: Heat energy content – blood (joules) UI  TB*dt UI: Heat energy content – injectate (joules) TI: Pre injection temp of injectate (oT C) B*: Post injection temp of oC) TBblood : Pre(injection temp of blood (oC) THE IDEAL THERMODILUTION CURVE VOLUME OF CARDIAC OUTPUT IS INVERSELY PROPORTIONAL TO THE AREA U NDER THE CURVE HIGH CO=LOW AREA UNDER CURVE LOW CO= HIGH AREA UNDER CURVE (B/C OF PROLONGED WASHOUT OF THE C OLD INDICATOR SOLUTION) THERMODILUTION: CURVE SHAPES HIGH CO=LOW area under curve LOW CO= HIGH area under curve (bc of prolonged washout of the cold indicator solution) *This method is Most accurate with high cardiac outputs PATIENT-GENERATED ERRORS THERMODILUTION *Alterations in ventricular performance *(arrhythmias) Low cardiac output *Intra-cardiac flow abnormalities PATIENT-GENERATED ERRORS THERMODILUTION TECHNIQUE-GENERATED ERRORS THERMODILUTION TECHNIQUE Wrong injectate Wrong injectate temperature Wrong injectate volume Injection speed too slow Thrombus formation on the catheter tip Plasma protein deposition on THERMODILUTION ADVANTAGES No blood withdrawal Easily and quickly performed Continuous information can be available  Venous Pulmonary Artery Catheter Results readily available for immediate clinical intervention THERMODILUTION DISADVANTAGES Not accurate in presence of tricuspid regurgitation and intra-cardiac shunts Least accurate if cardiac output is low (warming of indicator by cardiac and vascular walls and surrounding tissue) Results may vary based on location in respiratory cycle: Use a fixed point for injection (end-expiration or peak inspiration) FLOTRAC SYSTEM The minimally-invasive FloTrac system is a practical, reliable solution for hemodynamic monitoring that advanced automatically calculates key flow parameters every 20 seconds. A sensor attaches to any arterial catheter and uses a clinically validated algorithm to provide CO measurements updated every 20 seconds Calculates stroke volume based on arterial pressure, age, gender and BSA multiplies it by the pulse CO and = SV × rate HR FLOTRAC SYSTEM PARAMETERS MEASURED C O CI SV SVV (stroke volume variation) SVR FLOTRAC SYSTEM Benefits of fluid optimization: • Improved patient outcomes PRELOAD RESPONSIVENESS How likely an increase in preload will improve stroke volume 3 methods to measure:  Stroke volume variation (SVV)  Highly sensitive and specific indicator for pre-load responsiveness  Ventilated patients only  Expressed as a percentage (Normal: ~10%)  Passive leg raising (PLR)  Spontaneous ventilation  Arrhythmias  SV fluid challenge  Administration of a small volume of fluid and observing corresponding change SV FLUID MANAGEMENT EXAMPLE #1 SV is low, SVV is high (normal around 10%) Predicts whether a patient will benefit from volume before the volume is given Administer volume and CO increases Dobutamine given Dobutamine directly stimulates beta-1 receptors of the heart to increase myocardial contractility and stroke volume, resulting in increased cardiac output. FLOTRAC - ADVANTAGES Connects to any arterial catheter Clinically validated Automatic No experienced technician required FLOTRAC - DISADVANTAGES Arterial tracing must be accurate  Dampened lines  Kinked catheters  Non-leveled transducers • Not validated in VADs or TAHs • Possible inaccurate measurements with IABP • Arrhythmias cause inaccuracies • Not used in pediatrics WAYS TO MEASURE CARDIAC OUTPUT INVASI VE Fick oxygen consumption method Dye-dilution method NONINVASI VE Doppler Ultrasonography & Echocardiographic Imaging (ECHO) method FloTrac Thoracic electrical bioimpedance System Electromagne Thermodilution DOPPLER ULTRASONOGRAPHY AND ECHOCARDIOGRAPHY (ECHO) Indirect assessment of cardiac output 1.DOPPLER: assesses blood flow velocity 2.ECHO: assesses aortic diameter **Results are then used to compute cardiac output** DOPPLER PRINCIPLE Transducer transmits ultrasonic waves of known frequency Energy is scattered by moving blood cells  Velocity of flow will have a predictable effect on frequency signal Second transducer measures the frequency of the sensed signal DOPPLER PRINCIPLE By calculating the frequency shift of a particular sample volume, for example flow in an artery or a jet of blood flow over a heart valve, its speed and direction can be determined and visualized This is particularly useful in the cardiovascular setting Used in valve cases to assess insufficient valves, LV function, and EF (%) DOPPLER ULTRASONOGRAPHY A Doppler ultrasound is an imaging test that uses sound waves to moving through blood vessels. Doppler ultrasound works by show blood measuring sound waves that are reflected from moving objects, such as red blood cells. This is known as the Doppler effect. DOPPLER ULTRASONOGRAPHY AND ECHO Cardiac ECHO with Doppler Doppler is frequency – gives you Doppler ECHO is sound DOPPLER AND ECHODISADVANTAGES Technique Factors  Time consuming  (30-45 min)  Bulky equipment  Experienced operator necessary Patient Factors  Anemia  Tachycardia  Thick chest walls  Large sternal incisions  Tracheostomy  Emphysema THORACIC ELECTRICAL BIOIMPEDENCE Uses computer algorithms to measure pulsatile changes (impedence) in the conductivity of the thorax Changes in impedance analyzed to determine stroke volume, cardiac output, myocardial contractility and afterload Systole: thoracic blood volume ↑, electrical impedance ↓ Diastole: thoracic blood volume ↓, electrical impedance ↑ The amount, direction and timing of the pulsatile changes on the impedence waveform THORACIC ELECTRICAL BIOIMPEDENCETEB: ROUTINELY DISPLAYED PARAMETERS Heart rate Blood pressure Mean arterial pressure Thoracic fluid content Cardiac output / index Acceleration index (how fast the ventricular volume change occurs) Velocity index (maximum speed of blood flow) Systolic time ratio Systemic vascular resistance / index Left ventricular ejection time THORACIC ELECTRICAL BIOIMPEDENCETEB ADVANTAGES Non-invasive continuous realtime data Cost effective Quick Can be used in a variety of clinical settings Wide clinical application THORACIC ELECTRICAL BIOIMPEDENCETEB DISADVANTAGE S Accuracy is variable with Sepsis Arrhythmias L to R shunts Aortic regurgitation BLOOD FLOW PROBES Electromagnetic induction – move electrical conductor through magnetic field get induced voltage proportional to velocity of motion Electrical conductor: a column of fluid (blood) Magnetic field: applied perpendicular to direction of blood flow Voltage: measured via electrodes on either side of the vessel Measures the mean velocity of flow BLOOD FLOW PROBES Ultrasonic flow meter: measures the velocity of a fluid with ultrasound to calculate volume flow SUMMARY There is no “gold standard” method of determining cardiac output. Each technique has advantages and disadvantages These are estimates with margin(s) of error As in ALL monitoring techniques, serial trending and correlation with the clinical picture is a must A perfusionist MUST look at the total picture