test 8 Flashcards
WHAT CAUSES CHANGES IN CARDIAC OUTPUT
• Decreased contractility
– Myocardial damage
– Drug effects
– Acidosis
– Hypoxia
• Decreased preload
• Changes in SVR
– Increased SVR: arteriosclerosis, hypertension
– Decreased SVR: septic shock
• Decreased ventricular flow (valve disease)VARIABLES AFFECTING
CARDIAC OUTPUT
- Metabolic rate and oxygen demand
- Gender
- Body size
- Age
- Posture
Factors increasing metabolism
– Sepsis – Strong emotion – Major trauma – Surgery – Exercise – Fever
CI does not account for
– personal build (fat vs muscle)
– diseases that alter metabolism, such as thyroid disorders
– fluid that may alter body weight without increasing
metabolism
• Edema
• Ascites
• Diuresis
WHAT IS AN ANATOMIC
SHUNT?
Volume and circulatory flow changes that create
differences in saturation, pressure and flow in the
chambers
LEFT→RIGHT SHUNTING
- Overloads the right ventricle
- Pulmonary blood flow > Systemic blood flow
- Seen in atrial septal defects (ASD), ventricular septal defects (VSD), patent foramen ovale (PFO) and acyanotic congenital anomalies
RIGHT→LEFT SHUNTING
- Pulmonary blood flow < Systemic blood flow
* Seen in Tetralogy of Fallot (TOF) and cyanotic congenital defects
WHAT IS THE MOST IMPORTANT HEMODYNAMIC MEASUREMENT TO ASSESS A PATIENT’S PERFUSION STATUS
Cardiac output
INVASIVE WAYS TO MEASURE CARDIAC
OUTPUT
• Fick oxygen consumption method • Dye-dilution method • Thermodilution method • FloTrac System
NONINVASIVE WAYS TO MEASURE CARDIAC
OUTPUT
- Doppler Ultrasonography & Echocardiographic Imaging (ECHO)
- Thoracic electrical bioimpedance
- Electromagnetic flow probes
FICK OXYGEN CONSUMPTION METHOD
-Simultaneous measurement of:
• Arterial oxygen content (CaO2)
• Mixed venous oxygen content (CvO2)
• Oxygen uptake by lungs
FICK METHOD - ADVANTAGES
• Most accurate when cardiac output is low
FICK METHOD-DISADVANTAGES
• Patient must maintain steady hemodynamic and
metabolic state for the length of the test (3 minutes)
• Requires multiple people
• Time consuming
• Requires meticulous technique
• Not easily repeatable / not continuous
• Results not readily available for immediate clinical intervention
• Not valid in presence of intra-cardiac and intrapulmonary
shunts
• Least accurate with high cardiac output
DYE-DILUTION METHOD
• 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
-open system- no recirculation
-closed system- recirculation
Indicator characteristics for dye-dilutional method
– mixes well with blood – easy to determine concentration – stable – not retained by the body – not toxic
Indicator used for dye-dilutional method
– O2
– indocyanine dye (cardiogreen)
– radio-iodated serum albumin
– temperature
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 approximately 40 seconds
• Time consuming
• Least accurate if the output is low
THERMODILUTION
- deposit cold temp into RA by PA cath and it mixes with the blood and the PA where the tip of the catheter measures temp
- repeat 3 times with 90 sec in between
THERMODILUTION READING
- area under the curve
- the larger the area the smaller the CO
PATIENT-GENERATED ERRORS FOR THERMODILUTION
- Alterations in ventricular performance (arrhythmias)
- Low cardiac output
- Intracardiac flow abnormalities
TECHNIQUE-GENERATED ERRORS FOR THERMODILUTION
• Wrong injectate • Wrong injectate temperature • Wrong injectate volume • Injection speed too slow • Thrombus formation on the catheter tip – delays heating/cooling of the thermister • Plasma protein deposition on catheter • Thermister defect • Incorrect computation factor entered • Rapid IV infusions during measurement • CPB rewarming
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
- Results may vary based on location in respiratory cycle
FLOTRAC SYSTEM
• 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 and multiplies it by the pulse rate
• Allows accurate insight to patient’s volume status
FLOTRAC SYSTEM MEASURES
- CO
- CI
- SV
- SVI
- SVV (stroke volume variation)
- SVR
3 methods to measure preload responsiveness
– 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 in SV
FLOTRAC - ADVANTAGES
- Connects to any arterial catheter
- Clinically validated
- Automatic
- No experienced technician required
FLOTRAC - DISADVANTAGES
- Arterial tracing must be accurate
- Not validated in VADs or TAHs
- Possible inaccurate measurements with IABP
- Arrhythmias cause inaccuracies
- Not used in pediatrics
DOPPLER ULTRASONOGRAPHY
AND ECHOCARDIOGRAPHY
(ECHO)
(noninvasive)
• Indirect assessment of cardiac output 1. DOPPLER: assesses blood flow velocity 2. ECHO: assesses aortic diameter
DOPPLER PRINCIPLE
• Transducer transmits ultrasonic waves of known
frequency from moving cells
DOPPLER AND ECHO DISADVANTAGES Technique Factors
– Time consuming
– Bulky equipment
– Experienced operator
necessary
DOPPLER AND ECHO DISADVANTAGES patient factors
– Anemia – Tachycardia – Thick chest walls – Large sternal incisions – Tracheostomy – Emphysema
THORACIC ELECTRICAL
BIOIMPEDENCE
- high Impedence = poor conductors = air and bone
- low Impedence = good conductors = blood
- patches on body that measure the systole and diastole blood volume in the thoracic cavity based on impedence
TEB - ADVANTAGES
- Non-invasive continuous real-time data
- Cost effective
- Quick
- Can be used in a variety of clinical settings
- Wide clinical application
TEB - DISADVANTAGES
• 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
• Measures the mean velocity of flow (i.e. cm/sec)
• Calculates flow
• Ultrasonic flow meter: measures the velocity
of a fluid with ultrasound to calculate volume
flow
Gold standard
- none
- each have advantages and disadvantages
