Hemodynamic Monitoring Flashcards
What is the formula for blood pressure?
Pressure = Flow x Resistance
Anytime there is a change in blood pressure, its due to ____…?
- Either a change in flow or a change in resistance
What is flow?
- Cardiac output (HR x Stroke Volume)
What affects stroke volume?
- Preload
- Afterload
- Contractility
What are the goals of the Cardiovascular System?
- Transport and delivery of oxygen and nutrients for metabolic use
- Removal of waste products
Define Hemodynamics.
- Movement of blood through the closed circulatory system
What influences hemodynamics?
- Blood pressure
- Blood flow
- Characteristics of blood (viscosity)
MAP = ?
MAP = CO (HR x SV) x SVR
What is systolic pressure?
- Max pressure
- Pressure exerted when heart beats
- Reflects volume and speed of ejection, compliance of the aorta
What is diastolic pressure?
- Minimum pressure
- Pressure exerted between heart beats
- Reflects vascular resistance and competence of the aortic valve
What is the best indicator of tissue perfusion?
Mean Arterial Pressure (MAP)
What is MAP?
- Average driving pressure of blood during the cardiac cycle
- MAP often used in titration of pressures
- Induced hypotension
- Calculation of CPP
How is CPP calculated?
CPP = MAP - ICP
*If your CVP is higher than your ICP, your supposed to use CVP.
What is Pulse Pressure?
- Systolic Pressure - Diastolic Pressure
- Reflects difference in volume ejected from LV into arterial vessels and volume that is already there.
How is auscultation of NIBP obtained?
- When an artery is partially constricted, blood flow becomes turbulent, causing the artery to vibrate and produce sounds
- Turbulent flow will occur when the cuff pressure is greater than the diastolic pressure and less than the systolic pressure
What are Korotkoff sounds?
- The “tapping” sounds associated with the turbulent flow
Oscillometric method and Korotkoff sounds.
- Even when the Korotkoff sounds are hardly audible, the oscillometric method can pick up the vibrations of the artery due to turbulent flow
How does the Automatic Blood Pressure Monitor work?
- Measures the oscillations in the machine umbilical cable
- Measures MAP (point of maximum oscillation amplitude), then calculates systolic and diastolic from formulas that examine the rate of change of the pressure pulsations
With the automatic blood pressure monitor, what is the most unreliable measurement?
- Diastolic pressure
How is the Oscillomteric systolic blood pressure recorded?
- It is recorded at the point where cuff pressure oscillations begin to increase
Mean pressure corresponds to?
- the point of maximal oscillations
The oscillomteric diastolic pressure is measured…?
- at the point where the oscillations become attenuated
What are the limitations of Oscillometric Measurement?
- Motion Artifact
- Bruising at cuff site
- Nerve damage
- Arterial or intravenous occlusion during inflation
- If proximal to pulse oximeter, damping of pulse ox waveform and reading
- If SBP below 80, NIBP often over estimated MAP
- Must have correct cuff size
- Dysrhythmias make values difficult to interpret or increase cycle time
How do you determine correct blood pressure cuff size?
- If the bladder is at least 80% the circumference of the arm the reading should be accurate
What are some trouble shooting techniques for NIBP?
- Most common problem is air leaks at cuff, tubing or connection to unit
- Have patient keep arm still
- Disconnect unit and reconnect it to reset
Invasive arterial blood pressure monitoring is…?
- the most accurate way to monitor beat to beat blood pressure and easy access to blood gas monitoring
What are the indications for invasive arterial BP monitoring?
- Hemodynamic instability or predicted instability
- Surgical procedure with anticipated significant blood loss or fluid shifts
- Monitoring of induced hypotension
- Monitoring response to vasoactive drugs
- NIBP is not feasible (burns, obese, shock)
- Repeated blood sampling
On the arterial waveform, what does the dicrotic notch indicate?
- Aortic valve closure
On the arterial waveform, what does the anacrotic notch indicate?
- Aortic valve opens
What is the phlebostatic axis?
- Usually at mid-axillary line or level of right atrium
A 20 cm difference in height when measuring BP produces ______?
- a 15 mm Hg difference in pressure
Normally, total systolic pressure variation does not exceed ______?
- 10 mm Hg
What is pulse pressure variation?
- the difference between the maximal and minimal pulse pressure values during one mechanical respiratory cycle
- Normal PPV should not exceed 13%
What does central venous pressure indicate?
- RVEDV or Preload of RV (fluid status)
What is a normal CVP?
- Normal 6-10 mmHg
Low CVP, tachycardia, and low BP usually indicates?
hypovolemia
Persistent hypotension following fluid bolus and higher than normal CVP usually indicates ______?
Myocardial congestion - MI, tamponade, tension pnuemo
On the central venous waveform, what does the “a” represent?
- Atrial contraction
- absent in atrial fibrillation
- larger in tricuspid stenosis and pulmonary HTN
On the central venous waveform, what does the “c” represent?
- bulging of the tricuspid valve into the RA
On the central venous waveform, what does the “x” represent?
- Atrial relaxation
On the central venous waveform, what does the “v” represent?
- Rise in arterial pressure before tricuspid valve opens
On the central venous waveform, what does the “y” represent?
- Atrial emptying as blood enters ventricle
What is a better indicator of left heart pressure then CVP especially when there is impaired LV function, significant valvular disease, and pulmonary HTN?
- Pulmonary Artery Pressure Monitoring
What does SVO2 (mixed venous oxygen saturation) evaluate?
- Evaluate oxygen consumption and delivery
What is the Seldinger Technique?
- Introducer then guide wire then catheter over wire
The PA catheter tip is inserted to a depth of _______?
- 20 cm
What are the normal continuous PA pressure values?
- Systolic: 15-30 mm Hg
- Diastolic: 5-15 mm Hg
What is the normal PACWP?
- 4-14 mm Hg
What is the Thermodilution Cardiac Output?
- Cold water is injected through PA catheter and the change in temperature from the proximal to distal end of the catheter is measured and analyzed against time.
What is LiDCO?
- Lithium Dilution Cardiac Output
- Minimally invasive way of CONTINUOUS cardiac output monitoring
- Uses the pulse pressure analysis algorithm for continuous measurement of changes in CO
- Provides info on SV variation and pulse pressure variation
What does the EKG monitor?
- Electrical impulses through the heart
- A very small electrical signal is amplified and then broadcasted over a 0.01 to 250 Hz bandwidth
- Prone to electrical interference - clean dry skin
What leads are typically used in the OR?
- Lead II: Rhythm detection, P waves, inferior portion of the heart supplied by the RCA
- Lead V5: Bulk of the left ventricle supplied by LAD
- Lead I: Circumflex artery
What is the lead placement for V5?
- 5th intercostal space, anterior axillary line
What is respiratory impedance?
- Impedance pnuemography
- Measures movement of the chest electrodes
- Anesthesia monitors do not default to show this, but helpful during sedation cases
What is pulse oximetry?
- Measurement of arterial hemoglobin oxygenation
- Oxygenated and deoxygenated blood absorb light differently
- Absorbance of light indicated state of hemoglobin
Pulse oximetry uses which law?
- Beer-Lambert Law
In regards to pulse oximetry, what are the two light emitting diodes (LEDs)?
- Infrared (940 nm wave length) - oxyhemoglobin
- Red (660 nm wave length) - REDuced hemoglobin
In terms of light absorbance, oxyhemoglobin absorbs more _____…?
- Infrared light (940 nm) than red light
In terms of light absorbance, deoxyhemoglobin (REDuced) absorbs more ______…?
- red light (660 nm) than infrared light
Carboxyhemoglobin (CO poison)
- Appears like oxyhemoglobin at 660 nm
- Raises the appearance of oxygenated hemoglobin
- Falsely high readings
Methemoglobin (benzocaine, methylene blue)
- Gives a saturation of 85% no matter what the true oxygenation is
The accuracy of SPO2 should be questioned if…?
- there is not a clear waveform
If you can feel the pulse at the carotid, systolic BP is greater than ____?
60 mm Hg
If you can palpate the femoral pulse, the systolic BP is greater than ____?
70 mm Hg
If you can palpate the radial pulse, the systolic BP is greater than ____?
80 mm Hg
