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