Chapter 24: Photo-plethysmography venous Flashcards
PPG of the venous system is used to
document venous insufficiency
venous reflux
PPG is used for patients with
chronic swelling
ulcers
varicose veins
limitations of venous PPG
cannot do if pt has DVT
skin thickening prevents adequate reading
intact skin required for sensor placement
pt positioning for venous PPG
seated with legs dangling
PPG can determine
changes in blood content of skin which reflects intravenous volume
PPG consists of
photocell which consist of light emitting diode and photo sensor
PPG diode
transmits infrared light into subcutaneous tissues
this light is reflected back to photo sensor
what determines the reflection
cutaneous blood flow
increased blood flow results in
increased attenuation which decreases reflection
displayed as a positive upstroke
electrical coupling is a
method to increase gain and display signal
two types of electrical coupling
DC and AC
DC coupling
direct current
voltage either positive of negative
current flows in only one direction
DC coupling detects
slower changes in blood content
DC coupling is used for
venous studies
AC coupling
alternating current
voltage reverses polarity 60 times a second
current flows in both directions
AC coupling detects
fast changes in blood flow
AC coupling is used for
arterial studies
calibration of PPG for venous studies
not calibrated volumetrically
maintain same size or gain throughout study
difference in tracing should mean difference in blood volume
PPG display
arterial pulsations evident and super imposed on tracing of venous flow
PPG test set up
sensor applied to LE 5-10cm above medial malleolus
must not be over varicosity
patient completes a series of exaggerated dorsiflexions to empty calf veins
manual compression of calf can be performed (bilaterally to ensure consistency)
the strip chart recorder for venous PPG
running slow 5mm/sec
stylus records heat on paper
after dorsiflexion of food or manual compression
tracing continues to be obtained
record venous refill time/venous reactive time (VRT)
if the VRT is <20 seconds
study must be repeated with tourniquet applied to eliminate influence of superficial system
Normal venous refill time
> or = to 20 seconds without tourniquet
