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Scientific Principles > Week 9 - Hemodynamic Monitoring > Flashcards

Week 9 - Hemodynamic Monitoring Flashcards

1
Q

What are the goals of the cardiovascular system?

A

Transport and delivery of oxygen and nutrients for metabolic use

Removal of waste products

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2
Q

What are the two major components in oxygen delivery to the body?

A

Oxygen Content of Blood – (Hbg x O2 Saturation x 1.34) + (PaO2 x 0.003)

Blood Delivered to Body – determined by HR and Stroke Volume (Cardiac Output)

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3
Q

What does hemodynamics mean?

A

movement of blood through the closed circulatory system

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4
Q

What is hemodynamics influenced by?

A

Blood Pressure

Blood Flow (MAP = CO (HR x SV) x SVR) – Influenced by Hagen-Poiseuille Law (π r^4 P/8 ηL)

Characteristics of Blood (ie viscosity)

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5
Q

What is the purpose of hemodynamic monitoring?

A
  • Evaluate CV system: pressure, flow, and resistance, HR
  • Establish baseline values and evaluate trends
  • Guide Interventions: pharmacologic, fluid management, positioning
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6
Q

What are the hemodynamic pressure measures?

A

Arterial Pressure: systolic, diastolic, pulse pressure, MAP – volume status

Central Venous Pressure (CVP): mean pressure

Pulmonary Artery Pressure: PA systolic, diastolic, mean – CO

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7
Q

What is the difference between systolic and diastolic pressure?

A

Systolic Pressure = max pressure
*pressure exerted when heart beats

Diastolic Pressure = minimum pressure
*pressure exerted in between heart beats

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8
Q

What does systolic and diastolic pressure each reflect?

A

Systolic pressure reflects volume and speed of ejection, compliance of the aorta

Diastolic pressure reflects vascular resistance and competence of the aortic valve (P = flow x R)

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9
Q

What is mean arterial pressure (MAP)?

A

Average driving pressure of blood during the cardiac cycle

Best indicator of tissue perfusion

Often used in titration of pressures
Induced hypotension = ~30% of MAP
Used in calculation of CPP

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10
Q

How do you calculate MAP?

A

MAP = DP + 1/3 (SP - DP)

OR

MAP = (2 x DP) + SP / 3

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11
Q

What is the pulse pressure?

A

Systolic Pressure - Diastolic Pressure = Pulse Pressure

  • reflects difference in volume ejected from LV into arterial vessels and volume that is already there
  • function of SV and SVR
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12
Q

What does a wide pulse pressure and narrow pulse pressure indicate?

A

Wide PP: increased SV and decreased SVR – ex. sepsis

Narrow PP: decreased SV and increased SVR – ex. atherosclerosis

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13
Q

What are the ways to measure arterial pressure?

A

NIBP: auscultation or automatic (oscillometric)

Arterial Line: continuous pressure transduction

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14
Q

How are you able to auscultate a blood pressure?

A

The laminar flow that normally occurs in arteries produces little vibrations of the arterial wall and therefore no sounds

However, when an artery is partially constricted (BP cuff), blood flow becomes turbulent, causing the artery to vibrate and produce sounds

*Turbulent blood flow will occur when the cuff pressure is greater than the diastolic pressure and less than the systolic

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15
Q

What are Korotkoff Sounds?

A

The “tapping” sounds associated with the turbulent flow while auscultating a BP

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16
Q

How does an automatic blood pressure monitor work (Oscillometric NIBP)?

A
  • It can pick up the vibrations of the artery due to turbulent flow even when the Korotkoff sounds are hardly audible
  • Measures the oscillations in the machine umbilical cable
  • Measures MAP (point of max oscillation amplitude) and calculates systolic and diastolic from formulas that examine the rate of change of the pressure pulsations

– All oscillations will be recorded – Highest pulse wave is determined – Envelope will be recorded – Based on highest point of envelope SYS/DIA are calculated

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17
Q

How does an automatic BP monitor calculate the systolic and diastolic?

A 
Measures MAP (point of max oscillation amplitude)
**most accurate measurement

SBP is identified as the pressure at which the pulsations are increasing and are at 25% to 50% of maximum

DBP is commonly recorded when the pulse amplitude has decreased to a small fraction of its peak value
**most unreliable measurement

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18
Q

What are the limitations of Oscillometric NIBP measurement?

A
  • Motion artifact
  • Bruising at cuff site (use soft roll)
  • Nerve damage
  • Arterial or IV occlusion during inflation
  • If proximal to pulse ox, damping of waveform and reading
  • If SBP below 80, NIBP often over estimates MAP
  • Must have correct cuff size
  • Dysrhythmias make values difficult to interpret or increase cycle time
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19
Q

How do you make sure you are using the correct cuff size for NIBP?

A

Bladder length should be at least 80% of the circumference of the arm

Bladder width should be 40% of the circumference of the arm

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20
Q

How do you trouble shoot auto NIBP?

A
  • 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
  • most machines auto default to every 5 minutes, be sure to increase rate on induction
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21
Q

What is the function of invasive arterial blood pressure monitoring?

A

Most accurate way to monitor beat to beat blood pressure and easy access to blood gas monitoring

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22
Q

When is invasive arterial blood pressure monitoring typically used?

A
  • 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 (burn, obese, shock)
  • Repeated blood sampling
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23
Q

What is the shape of invasive arterial line waveform dependent on?

A
  • Depends on force generated by ventricle
  • Speed of ejection
  • Compliance of the arterial vessels
  • Rate of forward blood run-off (dependent on resistance to forward flow or SVR)
24
Q

What does the dicrotic notch indicate?

A

Arterial Line Waveform: closure of the aortic valve

PA Line Waveform: closure of pulmonic valve

25
Q

Describe the shape of the arterial live waveform

A
  1. Bottom Point: Aortic valve opens (Anacrotic Notch)
  2. Up Slope: Pressure increases as blood flows into the aorta
  3. Top Point: Max Pressure (SBP)
  4. Down Slope: Pressure falls as blood flows out of the aorta – Dicrotic Notch (Aortic valve closes)
  5. Bottom of Down Slope: Minimum pressure (DBP)
26
Q

How do you trouble shoot pressure monitoring systems?

A
  • Keep it Simple: minimize number of stopcocks and long lengths of tubing
  • Remove all air bubbles
  • Zero Line: accurate reference point from which all subsequent measures are made (usually at mid axillary line or level of right atrium)
  • Flash Flush
27
Q

What are limitations of pressure transducers?

A

Can get resonance from moving the line

Can have damping usually from air bubbles

28
Q

What are the complications from an arterial line?

A
  • Distal ischemia, pseudoaneurysm
  • Hemorrhage, hematoma
  • Arterial embolization
  • Local infection, sepsis
  • Peripheral neuropathy
  • Misinterpretation of data
29
Q

What determines the differences in NIBP with positioning?

A

Differences in NIBP are determined by the positions of the arms above and below the level of the heart and are equal to the hydrostatic pressure differences between the level of the heart and the respective arm

*A 20 cm difference in height produces a 15 mmHg difference in MAP

30
Q

What is systolic pressure variation and what can it indicate?

A 
The SBP (max height) recorded with each heart beat in an arterial line waveform
*Normally, total systolic pressure variation doesn't exceed 10 mmHg

Large variation down indicates hypovolemia

31
Q

What is pulse pressure variation?

A

Difference between the maximal (PPMax) and minimal (PPMin) pulse pressure values during one mechanical respiratory cycle, divided by the average of these two values

PPV = (PPmax - PPmin) / ([PPmax + PPmin] /2)

*Normal PPV should not exceed 13%

32
Q

What is central venous pressure monitoring used for?

A

Indication of right ventricle end diastolic volume or Preload of RV (fluid status)

Collect venous blood oxygen samples

33
Q

What is a normal CVP?

A

Normal = 6-10 mmHg

  • low CVP, tachycardia and low BP usually correspond to hypovolemia
  • Persistent hypotension following fluid bolus and higher than normal CVP usually indicates myocardial congestion (MI, tamponade, tension pneumo)
34
Q

What are the CVP catheter types?

A

Single Lumen: rapid, high volume resuscitation and pressure monitoring

Multi-Lumen: drug therapy, nutritional support, pressure monitoring

35
Q

What are the parts of a central venous waveform?

A

a: atrial contraction (absent in a-fib, larger in tricuspid stenosis, pulm stenosis, and pulm HTN)
c: due to bulging of tricuspid valve into RA
x: atrial relaxation
v: rise in arterial pressure before tricuspid valve opens (venous return filling atrium)
y: atrial emptying as blood enters ventricle

Positive Deflection = a, c, and v
Negative Deflection = x, and y

36
Q

What sections of the CVP waveform are during diastole and which are during ventricular systole?

A

Top of v-wave, y-wave, a-wave = during diastole

C-wave, x-wave, and to the top of v-wave = during ventricular systole

37
Q

What is pulmonary artery pressure monitoring a good indicator of?

A

Better indicator of left heart pressure than CVP, especially when:

  • LV function is impaired
  • Significant valvular disease
  • Pulmonary HTN

PCWP = best estimation of LVEDV (LV preload)
CO is measured via thermodilution
SVO2 (mixed venous O2 saturation) - evaluate oxygen consumption and delivery

38
Q

What does inflation of the balloon on PA catheters ensure?

A

that blood flow will move the catheter forward in the direction of blood flow

39
Q

How are PA catheters inserted?

A

Right heart catheterization with large bore introducer sheath
-Typically via subclavian or IJ veins – Seldinger technique (introducer then guide wire then catheter over wire)

Inserted to a depth of 20cm

CVP waveform must be identified to confirm that the PA catheter is in the R vena cave or atrium

Balloon then fully inflated, blood will carry or float the catheter through the RA, RV, and into the pulmonary artery

40
Q

What do you need to do prior to insertion of a PA catheter?

A
  • Flush all lumens with solution
  • Check integrity of balloon (always deflate passively)
  • Prepare transducer system that has been leveled and zeroed
  • Connect lines to appropriate lumens (PA pressure monitor is distal – CVP monitor is proximal)
41
Q

What are the normal measures obtained from a PA catheter?

A

Continuous pulmonary artery pressures:

  • Systolic = 15-30 mmHg
  • Diastolic = 5-15 mmHg

PACWP (wedge) = 4-14 mmHg

42
Q

How does a PA catheter measure cardiac output?

A

Via thermodilution

“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

43
Q

What are complications of CVP and PA lines?

A
  • Infection
  • Pneumothorax
  • Vessel erosion or perforation
  • Venous air embolism
  • Hemorrhage (rupture of PA)
  • Cardiac dysrhythmias
44
Q

What is LiDCO?

A

Lithium Dilution Cardiac Output

  • minimally invasive way of continuous CO monitoring
  • uses the pulse pressure analysis algorithm for continuous measurement of changes in CO (derive SV from arterial pressure waveform, calculate HR, CO = SVxHR, calibration)
  • provides info on SV variation and pulse pressure variation
45
Q

What is a Flotrac?

A

The Flotrac sensor attaches to any existing arterial line and monitors:

  • Stroke volume (calculated using arterial pulsilitiy, then CO is calculated)
  • Stroke volume variation
  • MAP
  • Cardiac output
  • Systemic vascular resistance (SVR)
46
Q

What does an EKG monitor?

A

Electrical impulses through the heart:

  • HR
  • Arrhythmias
  • MI
  • Pacemaker function
  • Electrolyte abnormalities

*Does NOT monitor contractility or output (PEA)

47
Q

How does EKG monitoring work?

A
  • Silver chloride electrode with a conductive gel which decreases the electrical resistance of the skin
  • 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)
48
Q

What are the important EKG leads to monitor during anesthetic cases?

A

Lead II: rhythm detection, p-wave
*Shows inferior portion of the heart supplied by the RCA

Lead V5: shows bulk of the LV supplied by LAD

*lead I = circumflex artery

49
Q

Where do you place the chest lead to monitor V5?

A

5th intercostal space, anterior axillary line

50
Q

What is impedance pnuemography?

A

measures movement of the chest electrodes to determine respiratory rate

*anesthesia monitors don’t default to show this, but helpful with sedation cases

51
Q

What does the pulse oximetry measure?

A

measurement of arterial hemoglobin oxygenation

  • oxygenated and deoxygenated blood absorb light differently
  • Beer-Lambert Law

Without a clear waveform accuracy of SPO2 should be questioned

52
Q

How is an oxygen saturation determined with pulse oximetry?

A

Measure “pulsatile signals across perfused tissue at two discrete wavelengths”

Absorbance of light indicated state of hemoglobin

Two Light Emitting Diodes (LEDs):

  • Infrared (940 nm wave length) = Oxyhemoglobin
  • Red (660 nm wave length) = Reduced Hemoglobin

Light Detector

*as the amount of oxy hbg and deoxy hbg changes, the light ratio changes – pulse ox uses the ratio to work out the oxygen saturation

53
Q

What is the different light absorbance in pulse oximetry?

A

Oxy Hbg absorbs more infrared light (940 nm) than red light

Deoxy Hbg (reduced) absorbs more red light (660 nm) than infrared light

54
Q

What hemoglobinopathies can affect pulse ox reading?

A

Carboxyhemoglobin (CO poison): appears like oxyhemoglobin at 660 nm thus 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

55
Q

What is the SPB if you can palpate a carotid pulse? Femoral? Radial?

A

Palpable Carotid = SBP above 60

Palpable Femoral = SBP above 70

Palpable Radial = SBP above 80

Scientific Principles (16 decks)

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