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Lumb & Jones, 6th Ed. > Chp. 12: Blood Pressure Monitoring > Flashcards

Chp. 12: Blood Pressure Monitoring Flashcards

1
Q

SAP

A

Pressure exerted by blood against arterial walls during systole of the cardiac cycle

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2
Q

DAP

A

Pressure exerted by blood on arterial walls during diastole

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3
Q

MAP

A

Determines perfusion pressure in tissues and directly influenced by CO and SVR

Area under pressure/time curve divided by cardiac cycle duration

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4
Q

Is digital pulse palpation accurate for assessing BP under GA?

A

No, because most sedative and anesthetic agents affect vasomotor tone.

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5
Q

Equations for MAP

A

MAP = CO x SVR

MAP = DAP + 1/3 (SAP-DAP) [rough estimate]

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6
Q

Cardiac Output Equation

A

CO = HR x SV

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7
Q

Chronotropy

A

Physiologic timing of HR

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8
Q

Lusitropy

A

Period of cardiac relaxation that occurs during diastole when cardiac myocytes have decrease level of systolic calcium

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9
Q

Inotropy

A

Contractility due to increased calcium uptake causing contractile effects

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10
Q

Dromotropy

A

Actual conduction of impulse

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11
Q

Systemic Vascular Resistance

A

Amount of force the vasculature system exerts on circulating blood, excluding the pulmonary circulation

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12
Q

How does SVR influence BP?

A

Through vessel length, vessel diameter, and viscosity of blood

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13
Q

Hagan-Poiseuille Equation

A

DeltaP = Q8Ln/(pi)r4

(reducing vessel diameter by half decreases flow to 1/16th of original)

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14
Q

Prehypertension
Hypertension
Severe hypertension

A
  • Pre: SAP 140-150mmHg
  • Hyper (may lead to target organ damage): SAP 160-179mmHg
  • Severe: SAP >180mmHg
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15
Q

Autoregulation

A

Ability of organs to maintain a relatively constant blood flow despite changes in perfusion

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16
Q

Three main mechanisms of autoregulation

A

1) Metabolic regulation
2) Myogenic mechanisms
3) Shear stress-dependent (endothelial)

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17
Q

Metabolic autoregulation

A

Changes in metabolism results in the release of vasodilatory substances such as adenosine, CO2, and lactic acid

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18
Q

Myogenic mechanism of autoregulation (pressure-dependent)

A

Autoregulate flow via smooth muscle-lined vessels

Increase pressure leads to vasoconstriction; decreased pressure is followed by vasodilation in smaller arteries and arterioles

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19
Q

Shear-stress dependent (endothelial) autoregulation

A

Endothelial release of vasoactive factors such as NO and prostacyclin, causing vasodilation of smooth muscle-lined vessels, as well as endothelia, which modulates vasoconstriction

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20
Q

Main mechanism of autoregulation in the brain

A

Metabolic

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21
Q

Range of MAP for cerebral autoregulation (dog)

A

70-140mmHg

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22
Q

How are SAP, DAP, and MAP determined with invasive BP monitoring?

A

SAP and DAP are directly measured and MAP is calculated as the AUC over the cardiac cycle

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23
Q

Standard IBP components

A

1) Arterial catheter
2) Fluid-filled, non-compliant tubing
3) Pressure transducer
4) Signal conditioning and monitoring software

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24
Q

What is the role of saline-filled tubing in IBP measurement?

A

Produces “hydraulic coupling” between arterial circulation and transducer

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25
Q

Ohm’s Law

A

R = P/I

R is resistance, P is voltage, I is current

26
Q

Describe how a BP transducer works.

A

Four strain gauges (resistors) are bonded to a movable diaphragm and arranged in a Wheatstone bridge circuit. Mechanical pressure variations associated with arterial pulsations physically deform the diaphragm, creating tension in two of the strain gauges and simultaneous compression of the other two. These changes lead to variations in electrical resistance and the bridge becomes unbalanced. The potential difference generated is proportional to the pressure applied.

27
Q

Where is the IBP transducer leveled?

A

The level of the aortic root or base of RA.

28
Q

What happens if the art line transducer is positioned above the RA? Below the RA?

A

If positioned above, artificially low pressures result. If below, artificially high pressures result.

29
Q

For every 10cm above the RA that an arterial transducer is positioned, how many mmHg is added to displayed pressures?

A

7.4mmHg

30
Q

True or False: Zeroing of the transducer must be performed at the level of the RA.

A

False, atmospheric pressure does not vary with modest positional changes.

31
Q

Fourier analysis

A

The IBP waveform is created by Fourier analysis, which sums the various sine waves of differing amplitudes and frequencies into a single complex waveform

32
Q

Should the IBP system have low or high natural frequency?

A

Highest possible, to minimize resonance distortion (esp. in patients with faster HRs and steeper systolic upstrokes).

33
Q

What influences the natural frequency of the system?

A

Radius and length of tubing, elasticity of the system, density of the fluid.

34
Q

How do you maximize the natural frequency of the IBP system?

A

1) Shorten the length of the pressure tubing
2) Increase the diameter of the pressure tubing
3) Use non-compliant pressure tubing
4) Use a low-density fluid (ie, saline) to fill the system

35
Q

Will air bubbles increase or decrease the natural frequency of the IBP system?

A

Decrease

36
Q

Damping

A

The frictional forces that oppose the oscillations and result in decrease wave amplitude

37
Q

What is the optimal damping coefficient?

A

0.7

38
Q

Dynamic Pressure Response Test (a.k.a. “Fast Flush Test)

A

High pressure is rapidly introduced to the catheter for 1-2 seconds and then abruptly stopped. A square waveform is produced. The waveform should return to baseline within one to two oscillations, neither greater than 1/3 the height of the previous. Absence indicates overdamping; many oscillations indicate underdamping.

39
Q

Is a smaller gauge catheter more likely to be over or underdamped?

A

Overdamped

40
Q

What factors cause overdamping of the IBP system?

A

Air bubbles, catheter obstruction, overly compliant tubing, long tubing, too many stopcocks

41
Q

What is the effect of overdamping on SAP, DAP, and MAP? Of underdamping?

A

Overdamping underestimates SAP and DAP is overestimated or accurate. Underdamping overestimates SAP and underestimates DAP. MAP is least affected.

42
Q

How does Doppler BP measurement work?

A

Movement of RBCs results in a change in pitch of reflected sound waves (generated from contact of piezoelectric crystals with pulsatile RBCs). The cuff is inflated until audible signal is lost and then 20-30 additional mmHg. Pressure is released slowly and the sphygmomanometer pressure correlating to return of the first Korotkoff sound is SAP.

43
Q

Does Doppler BP over or underestimate BP in cats?

A

Underestimate

44
Q

How does oscillometric BP measurement work?

A

It is a counter pressure measurement technique whereby the arterial pulse produces changes in the volume of a limb, which can be transmitted to and detected as changes in pressure within a cuff encircling the limb. The cuff is inflated to 20-30mmHg past obstruction of blood flow and then slowly deflated via linear or step-deflation methods. Arterial flow gradually returns and corresponding changes in cuff pressure amplitudes persist until inflation pressure is released and flow returns to normal.

45
Q

What is the most accurate oscillometric NIBP value?

A

MAP

46
Q

When is the Oscillometric BP method inaccurate?

A

Reduced blood flow, poor cuff sizing, patient movement/shivering, extremes of patient size, severe hypo/hypertension, cardiac arrhythmias

47
Q

Central Venous Pressure

A

Measures the hydrostatic pressure of the intrathoracic vena can, as a close reflection of RA pressure (an intravascular rather than transmural pressure)

48
Q

Why has CVP fallen out of favor?

A

Relationship between CVP, CO, and vascular system is complex and complicates interpretation. The non-linear nature of the Frank-Starling curve and factors causing changes in cardiac and pulmonary compliance results in circumstances where pressure does not correlate well with volume status.

49
Q

Reference range for CVP

A

0-10 cmH20, more commonly 0-5 cmH2O

50
Q

Hypovolemic, euvolemic, and hypervolemic CVP ranges

A

Hypovolemia: Negative values
Euvolemia: 0-5 cmH2O
Hypervolemia: 7-10 cmH2O

51
Q

Kussmaul’s Sign

A

Decrease in CVP observed during inspiration in fluid responsive patients

52
Q

Risks of jugular catheter placement

A

Cardiac arrhythmias (APCs or VPCs), hemorrhage, hematoma, air embolus, thrombus, pneumomediastinum, pneumothorax, hemothorax, tracheal trauma, carotid artery puncture

53
Q

Long-term jugular catheter complications

A

Infection, recurrent laryngeal nerve damage, jugular vein stenosis or occlusion

54
Q

Contraindications to jugular catheter placement

A

Increased ICP, coagulopathies, those at increased risk of thromboembolic events

55
Q

Pulse Pressure Variation

A

Measure of difference between systolic and diastolic pressures during IPPV.

IPPV increases pleural pressure > compresses vena cava > increases RAP > decreases venous return > decreases RA preload > decreases RV output and PA blood flow > decreases LV filling and output

During inspiration, RV preload is decreased and RV afterload is increased while LV preload is increased and LV afterload is decreased

56
Q

What are the four main reasons for hypovolemic patients demonstrating greater respiratory variations in SV and arterial pressure?

A

1) Vena cava is more collapsible
2) Underfilled RA is more sensitive to transmission of pleural pressure during inspiration
3) Effect of inspiration on RV afterload is more significant where West’s zone I and II conditions are met
4) Left and right ventricles are functioning on the steep portion of the Frank-Starling curve where there is greater sensitivity to preload changes

57
Q

What PPV values predict fluid responsiveness?

A

PPV values > 7-16%

58
Q

What factors influence PPV?

A

Volume status, fluid type and volume, ventilator settings, chest wall compliance, intra-abdominal pressure, venous vasomotor tone, presence of cardiac abnormalities

59
Q

Plethysmography Variability Index

A

Built into specific pulse oximeters.

During IPPV, RV SV is minimal at end-inspiration due to reduction in venous return and LV preload and SV decrease and are minimal at end-expiration, causing changes in pulse wave amplitude. Magnitude of variation is proportional to likelihood that SV will increase with augmented preload.

60
Q

What PVI values predict fluid responsiveness?

A

Greater than or equal to 13%

Lumb & Jones, 6th Ed. (17 decks)

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