Exam 2 Flashcards
Pulse Pressure
determined by the interaction of the stroke volume of the heart, compliance of the aorta, and the resistance to flow in the arterial tree
Mean Arterial Pressure
Actual mean is determined by the area under the arterial pressure curve divided by the beat period
Calculus: integration of the area under the curve
Why is MAP a good assessment tool?
- mean pressure the same in all parts of the arterial tree
- mean pressure not significantly affected by overshoot, artifact and the frequency response characteristics of the system
- pulmonary and SVR values are calculated using the mean pressure
- mean pressure represents the inlet pressure to the systemic and cerebral capillary networks
Causes of False-High Reading
Cuff too small cuff not centered over the brachial artery cuff not applied snugly arm below heart level Very obese arm cone-shaped arm
Causes of False-Low Reading
Cuff too large
arm located above heart level
Failure to correctly determine the onset of the first Korotkoff sound
Auscultation
May be up to 20 mmHg lower than direct
Proper cuff size: obese or patients with cone-shaped arms
Deflate cuff at at approx. 3mmHg/sec
Diastolic reading muffled (hyperdynamic)
Problems with damping of sounds in pt w. reduced stroke volume and severe vasoconstriction
concerns with frequency of pressure determination
Complications of deflating cuff too fast or slow?
Too fast- underestimate values
Too slow creates venous congestions which distorts Korotkoff sounds
Indirect BP Manual Techniques
Auscultation Palpation- determine systolic only Auscultation assisted by Doppler- determine systolic only; easier to determine pressure in "shocky" patients Manometer oscillation observation Photoelectric devices
Photoelectric Devices
Indirect manual technique pulse ox is an example determines sytolic only patient motion is a problem problems when arterioles of extremities are constricted
Manometer oscillation observation
Indirect Manual Techniques
Determine systolic and mean/first oscillation
systolic/maximal oscillation
mean/minimal oscillation in hypotensive patients
Indirect Automated Technique Examples
oscillometery- detection of pulsatile arterial wall vibrations/most commonly used
Infrasound- detect pulsatile vibrations via microphone
Ultrasonic determination of axial flow- use doppler to detect sound of flowing blood (TEE)
Arterial tonometry-pressure sensor over radial artery detects pusatile forces
Indirect Automated Technique Characteristics
Depend on adequate pulsatile blood flow to extremities
Many determine mean pressure
Good for following trends in stable patients
Poor results in hypotension or pts receiving potent vasoactive drug titration
Indirect vs. Direct: Patient Factors
Regional arterial pressure gradients due to: atherosclerosis, peripheral vascular disease, aortic dissection, arterial embolism, surgical retraction, patient position
Generalized arterial pressure gradients due to: severe vasoconstriction and shock, peripheral vasodilation with rewarming during and after CPB, normal widening of the peripheral pressure pulse
Indirect vs. Direct: Technical Factors
Cuff problems: too small, arm shape, extrinsic cuff compression, limb position relative to heart Rapid deflation (underestimation) Physiologic problems and method limitations- rapid P changes, dysrhythmias, severe vasoconstriction and shock, shiver and pt movement, BTBV
Vasoconstricted patients with low stroke volume
Obtained pressures with indirect method underestimate true systolic pressure
oscillometry, palpation, and auscultation: indirectly measure blood pressures tend to underestimate systolic BP and overestimate diastolic pressure (dampened)
Adequacy of tissue perfusion in direct method
difficult to determine by direct method based on pressure readings
Direct Continuous Intra-Arterial Pressure Monitoring
Most reliable method of determining real-time systemic arterial systolic, diastolic and mean pressures
Relatively pain-free
Simple
Relatively low-risk access for arterial blood sampling
Indications for Arterial Cannulation
Need continuous arterial pressure monitoring
Patient has a need for serial blood gases
Who needs continuous arterial pressure monitoring?
critically ill, injured, undergoing major surgery
Provides ability to detect sudden changes, evaluate changes in the trend, immediately assess effects of therapy
Who needs serial blood gases?
Respiratory failure
Management of ventilator support
Treatment of severe acid-base disturbances
Need more than three or four arterial blood samples on a daily basis
Contraindications for Arterial Cannulation
Peripheral Vascular Disease
Hemorrhagic disorders
On anticoagulants or receiving thrombotic agents
Where should you not insert a catheter?
area of infection
site previous vascular surgery (cutdown)
through synthetic vascular graft material
Pressure Wave Generation
Ventricular ejection creates blood flow and a pressure wave
Pressure wave precedes the actual blood flow of blood
Creation of pressure wave-form is affected by this relationship
Speeds of Pressure Wave & Blood flow
pressure wave: 10 m/s
blood flow: 0.5 m/s
Almost sound like a phase shift-out of sync
True Pressure Wave Phases
Phase 1: Inotropic component
Phase 2: Volume Displacement Curve
Phase 3: Late Systole and Diastole
Phase 1: Inotropic Component
Aortic Valve Opens
Energy created by contracting LV transferred to the aorta
Pressure wave created- starts moving down arterial tree
Simultaneously- first part of stroke volume pumped into aortic root
Anacrotic rise (dP/dT)- steepness, rate of rise & heigh of rise related to rate of acceleration of blood (indication LV contractility)
What dose Anacrotic rise indicate?
LV contractility
Phase 2: Volume Displacement
Movement of blood into aorta fills out and sustains the pressure pulse
Rounded appearance results from: continued ejection of the SV, displacement of blood, distention of arterial walls
Anacrotic notch: may be present, mark change from inotropic component to displacement
Low stroke volume (curve narrow with low amplitude)
What marks change from inotropic component to displacement?
Anacrotic notch
Phase 3: Late Systole & Diastole
Sloping decline- rate of peripheral runoff exceeds vol input
Closure of aortic valve: start of diastole, dicrotic notch
Continuous decline as blood moves from aortic root to the peripheral vessels
Undulations may result from reflected pressure waves
High amplitude of inotropic spike
Increase rate of LV pressure generation & increased acceleration of aortic blood flow
Increased reflection of pressure waves from the periphery: vasoconstriction
Overshoot artifact
Decreased amplitude of inotropic spike
myocardial depression
hypovolemia
decreased reflection of pressure wave from the periphery (vasodilation)
High Pressure, Low Flow
Low flow: might be perfusing core but periphery gets acidotic
Low Pressure, High Flow
Perfusing all tissues; not much downside
Maintain flow using drugs
never change flow and give systemic vasoconstrictor making extremities hypoxic
Overshoot
Overshoot of systolic pressure most common artifact seen in clinical practice
May come and go (changing HR, development of hyperdynamic conditions)
Due to underdamping or inadequate frequency response
Effects on Pressure Waves
Gravitational Effects
Reflected Waves Effects
Physiological Effects
Gravitational Effects
Vertical patient vs. supine
Vertical: pressure decreases moving upward from heart
Pressure increases moving downward from heart
pressure the same at all points at same vertical level
Supine: no differences due to gravity
“Orthostatic Hypotension”
Standard Reference Level for blood pressure
Heart!
Reflected Pressure Waves
Pressure waveform precedes the actual flow of blood: ventricles generate tension then contract
Pressure waves reflected back toward aortic root by smaller distal vessels: added to pressure waveform as tit travels down the arterial tree (fourier analysis)
Pulse pressure increases as wave travels down the arterial tree (sys higher, diastolic lower)
Since pulse pressure increases as it goes down the arterial tree: underdamping or overdamping?
Underdamping
Systolic higher, diastolic lower
Normal Pulse Pressure
Greater than 40 mmHg is abnormal
High Pulse Pressure
Heart Problems (older adults) Stiffness of aorta (calcification) Athersclerosis Aortic dissection Endocarditis Chronic aortic regurgitation (AI) Fever Anemia Pregnancy Anxiety Heart Block Raised ICP
Low (Narrow) Pulse Pressure
Poor Heart function (see this a lot)
Most common cause: drop in LV stroke volume
In trauma: significant blood loss (insufficent preload leading to reduced CO)
If extremely low: 25mmHg or less the cause may be low SV as in CHF or shock
Physiological Factors affecting Waveforms
Arrythmias Hypertension Hypotension Age Vasoconstriction Hypovolemia Respiration Variation
Effect of Hypotension on Arterial Waveform
Peak of inotropic component and dicrotic notch disappear
Waveform looks to be damped
Aging
Difference between central aortic and distal systolic pressures decreases
-minimal change in the pressure pulse
-loss of arterial compliance
Inotropic component tends to be dominant
Direct Arterial Cannulation Locations
See pg 151-152 chart in book
Radial artery Brachial artery Axillary artery Femoral artery Dorsalis Pedis Artery
Direct Arterial Complications
Embolism Vascular insufficiency (distal ischemia) Iscemic necrosis of overlying skin Infection Hemorrhage Accidental intra-arterial drug injection Vasculitis Arterial dissection
