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Boards: Monitoring > IBP > Flashcards

IBP Flashcards

1
Q

Wheatstone Bridge

A
  • Electrical circuit with one unknown resistor, one variable resistor, two unknown resistor
  • Pulse into transducer causes mechanical deformation of strain gauge
  • Pressure then sent to unknown resistor –> pressure gauge
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2
Q

Measuring Device

A

aneroid manometer, commercial transducer/physiograph

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3
Q

Transducer Level with Newer Monitors

A

internally compensate for vertical differences btw patient, transducer with ‘offset pressure’ – once zeroed, cannot change height of transducer without rezeroing

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4
Q

Transducer Level with Older Monitors

A

Older monitors: no offset feature, transducer/zeroing stopcock must be at level of RA

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4
Q

Frequency Response of Measuring System Determined By:

A
  1. Resonant Frequency
  2. Damping Coefficient
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5
Q

Resonant Frequency

A

rate of system oscillation IRT change in pressure

duration of one complete cycle (peak to peak, trough to trough)

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6
Q

Damping Coefficient

A

rate at which oscillations rest after change in pressure

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7
Q

Basics of IBP

A

–each cardiac contraction exerts pressure = mechanical motion of flow within catheter, transmitted to transducer via rigid fluid-filled tubing

–Transducer converts motion to electrical signials

–Monitor displays beat to beat arterial waveform as well as numerical pressures

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8
Q

Challenges with IBP in Cats

A

–Arteries = small, expertise required
–Constrict with cut down manipulation
–Collateral circulation spare: femoral, MT, coccygeal placement can lead to distal ischemia

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9
Q

Pressure Wave Analysis

A

Allows for better understanding of patient’s heart function as correlates to cardiac cycle

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10
Q

Systolic Phase

A

Rapid rise in pressure to peak followed by rapid decline

Opening of poetic valve, corresponds to LV ejection

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11
Q

Dicrotic Notch

A

Closure of aortic valves

Beginning of diastole

Turns into the dicrotic wave distally DT delay

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12
Q

Diastolic Phase

A

Run off of blood into peripheral circulation

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13
Q

Distal Systolic Pulse Amplification

A

Occurs further from aorta that measurement is occurring

SAP increases, MAP/DAP decreases

Dicrotic notch displaces R DT delay - transforms into dicrotic wave

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14
Q

Small, Weak Pulses

A

Pulse wave diminished, pulse feels weak/small

Upstroke may feel slowed, peak is prolonged

Causes:
–decreased SV
–Increased PVR: exposure to cold, severe heart failure

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15
Q

Normal Pulses

A

Pulse pressure ~30-40mm Hg
Pulse contour smooth, rounded - notch not palpable

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16
Q

Large, Bounding Pulses

A

Pulse pressure increased
Rise, fall may feel rapid - peak is brief

Causes:
–Increased SV: slow HR
–Decreased peripheral resistance: can occur with increased SV in fever, anemia, hyperthyroidism, aortic regurgitation, AV fistula, PDA
–Decreased aortic wall compliance: aging or athlerosclerosis in people, primates, birds

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17
Q

Bisferiens Pulse

A

Increased arterial pulse with double systolic peak

Causes:
–Pure aortic regurgitation
–Combined aortic stenosis, regurgitation
0-HCM

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18
Q

Pulses Alternans

A

Pulse alternates in amplitude from beat to beat even though rhythm basically regular

Can be caused by left ventricular failure or decreased ventricular filling

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19
Q

Bigeminal Pulses

A

May mimic pulses alternans

Normal beat alternating with premature contraction
–SV of premature beat diminished IRT that of normal beat - pulse varies in amplitude accordingly

20
Q

Paradoxical Pulses

A

Palpate decrease in pulse’s amplitude on quiet inspiration, decrease by >10mm Hg

Pericardial tamponade, exacerbations of asthma, COPD

Similar to pulse pressure variation

21
Q

Contraindications for arterial line placement

A

Infection
–Can be catastrophic in critically ill patients/multiple comorbidities
–Location of catheter, duration of placement affect rates
–Remove as long as no longer required
Lack of collateral circulation resulting in vascular insufficiency
Hematoma formation
Venous stenosis
Blood Loss
Embolism
Excessive heparinization
Inadvertent Nerve Damage

22
Q

Column Manometer

A

Long fluid administration set suspicion from high point
MAP 140mm Hg = 186cm column of water

23
Q

Aneroid Manometer

A

–Expel all air from air/fluid tubing via air from syringe 2 out through stopcock 1
–Close stopcock 2 to syringe 2
–Inject sterile saline from syringe 1 into tubing toward manometer until pressure&raquo_space;> MAP
–Close stopcock to syringe 1
–Allow high pressured saline to flow from air/fluid mixed tubing toward patient –> equilibrated pressure = MAP

24
Q

Wheatstone bridge Circuit

A

–4 resistances: 2 known, 1 unknown
–Silicone diaphragm of transducer moves small plate connected to 4 strain gauges

With any one movement, two gauges stretched, two compressed
–Mechanical stretch causes change in resistance
–Potential difference generated proportional to pressure applied

25
Q

Law Associated with Wheatstone Bridge

A

Ohm’s Law: V = IR
(potential difference [voltage] = current * resistance)

26
Q

Atmospheric Pressure and Wheatstone bridge

A

Atmospheric pressure must be discounted from pressure measurement: transducer exposed to atmospheric pressure, calibrated to 0

Level of RA, midaxillary line

Once zeroed, relative height of transducer cannot be changed without re-zeroing

27
Q

Pressure in System and Transducer Height

A

Weight of column of fluid within tubing exerts hydrostatic pressure on transducer: proper leveling minimizes effect

For every 2.5cm above/below catheter (transducer?) level, pressure in system changes 1.87mm Hg

28
Q

If the system is too low…

A

Transducer exerts greater pressure and produces abnormally high values

7.5mm Hg subtracted for every 10cm above heart

29
Q

If the system is too high…

A

Abnormally low readings
7.5mm Hg added for every 10cm above heart

30
Q

Fidelity of Reproduction of PP Waveform

A

Result of interactions btw frequency response of catheter and measuring system; patient factors

Frequency response = 2 parameters
1. Resonant frequency
2. Damping Coefficient

31
Q

Natural Frequency

A

Frequency at which system tends to oscillate in absence of any driving or damping forces

Every system has own natural oscillatory frequency (resonant frequency)

Arterial pressure waveform: many different sine waves (Fournier analysis) with each sine wave having own frequency

32
Q

Problem with Natural Frequencies of Arterial Waveform vs Transduction System

A

If resonant frequency to transduction system coincides with one of frequencies making up arterial waveform, resonance and distortion of signal will occur

33
Q

Resonant Frequency of ABP

A

Fn waveforms = 30 Fn - goal is 6-10x HR
LJ: typically 10-25Hz

Optimal frequency depends on HR, systolic vigor

34
Q

Resonant Frequency

A

rate of system oscillation IRT change in pressure

35
Q

Resonant Frequency of Catheters, Infusion Tubing

A

Fn >40 Hz

36
Q

Resonant frequency of Transducers

A

50-100Hz - 1.5-5x HIGHER than frequency of waveforms monitor

Optimally damped transducer system with resonant frequency >36Hz accurately reproduce shape of arterial waveform up to HR of 180bpm

37
Q

Damping

A

Anything that reduces energy in oscillating system, reduces amplitude of oscillations

Some degree of damping required in all systems
–If excessive (overdamping) or insufficient (underdamping), output effected

38
Q

Where does most damping come from?

A

Friction of fluid pathway

39
Q

Damping Coefficient

A

rate at which oscillations rest after change in pressure

Following system flush, amplitude ratio of two consecutive resonant waves calculated by dividing smaller ratio by larger

40
Q

Dynamic Pressure Response Test

A

Sudden release of pressure on measurement system, ie flushing

Determines resonant frequency, amplitude reduction ratio

Observe oscillation pattern as pressure returns to baseline

Registered pressure >300mm Hg, returns to baseline with 1-2 pos/neg oscillations if dampened appropriately

41
Q

Amplitude Reduction Ratio

A

height of any half complete cycle (peak to trough or trough to peak) divided by height of previous half cycle

o Typical: 0.2-0.6

42
Q

Amplitude Reduction Ratio

A

height of any half complete cycle (peak to trough or trough to peak) divided by height of previous half cycle

o Typical: 0.2-0.6

43
Q

Overdamped Signals

A

Coefficient >1

System will not oscillate freely, details lost (eg dicrotic notch)

Underestimate SAP, overestimate DAP

44
Q

Causes of Overdamped Signals

A
  • Small gauge catheter, often limited by patient size
  • Blood clots, air bubbles
  • Longer, more compliant tubing
45
Q

Underdamped Signals

A

Coefficient <0.7

Tendency to overshoot, oscillate around resting point - exaggerated, spikey appearance

Overestimate SAP, underestimate DAP

46
Q

How respond to underdamped signals

A
  • Change something in measurement system: remove kinks/clots, remove or add air bubble, change to different length or different compliant tubing
47
Q

Wilson et al 2018 (VAA)

A

comparison of IBP in three pairs of peripheral arteries – facial vs transverse facial, metatarsal vs facial, metatarsal vs transverse facial
o Poor agreement btw sites: largest = SAP btw F/TF, smallest MAP btw TF/MT
o BP measured in peripheral arteries cannot be used interchangeably

Boards: Monitoring (19 decks)

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