Download Monitoring of flaps

Evaluation and Monitoring of flap viability
The ideal monitoring device should have the following characteristics:
1.
reflect the condition of the entire flap
2.
be reliable, reproducible, consistent and sensitive
3.
provide continuous monitoring
4.
not be easily affected by the external environment
5.
user friendly and easily interpreted
6.
affordable
Subjective / physical criteria
Clinical observation remains the gold standard:
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bleeding from a stab wound
Useful for detecting extrinsic, not intrinsic, complications:
 no bleeding - arterial failure
 delayed bleeding of bright red blood - arterial spasm
 brisk bright red bleeding - normal or hyperaemic
 cyanotic bleeding that clears to bright red - venous congestion
temperature
surface temperature or differential thermometry (gradient exceeding 30C is
significant)
capillary refill
tissue turgor
Objective tests
I Vital dye measurements
Flourescein (also: Disulphine blue / vital green)
 given as bolus injection of 1.5ml/kg intravenously
 use Wood’s lamp to assess dye staining, after approximately 20 - 30 minutes
 Disadvantages
 the test underestimates flap survival
 the test can only be repeated every 8 hours
 anaphylaxis (rare) and nausea (more common)
Perfusion flourometry
 emmitted flourescence of the tissue is measured using a fibreoptic light guide
(dermoflourometer)
 accurate readings can be made as early as two minutes after injection
 serial injections and measurements can be made because the doses are small
(0.15ml/kg)
 fewer side effects than standard flourescein testing
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a dye flourescence index (DFI) of >/= 30% is “safe”
II Photoelectric assessment
Ultrasound doppler
 uses reflected sound to pick up pulsatile vessels
 colour flow ultrasound (CFUS)
o sensitive to venous and arterial insufficiency at flow rates as low as 3.0ml/min
o proficient at visualizing luminal dissections, intimal flaps, thromboses and
arteriolar constrictions
Laser doppler
 measures the frequency shift of light and therefore has limited penetration (1.5mm)
 laser doppler flowmeter
o gives an output voltage proportional to the total flux of RBCs in the volume of
tissue sampled (~1mm3) - includes the subdermal plexus
o gives Doppler flow measurement as well as photometry value; - allows reliable
prediction of venous congestion by an increase of haemoglobin-concentration,
and of arterial occlusion by a decrease in blood flow parameters and oxygen
saturation.
o a baseline of 30% is sufficient to predict flap survival
o sensitivity of 93%, specificity of 94%
 Advantages
o high reliability (approaching 100% in 1st 24 hours after flap transfer)
o provides method for continuous, non-invasive monitoring of skin perfusion
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Disadvantages
o not quantitative
o obtains information from a single site only
o is sensitive to the movement of the subject
o has limited accuracy below the critical threshold at which tissue necrosis is
guaranteed
Cook-Swartz venous Doppler system
 a technique for monitoring venous flow in free tissue transfer consisting of an
implantable, removable, 20 MHz ultrasonic probe around the venous pedicle and a
battery operated portable monitor.
Photoplethysmography
 measures fluid volume by detecting variations in infra-red light absorption by the skin
III Metabolic
Transcutaneous oxygen tension
 oxygen electrode is applied to the skin
 effective predictor of the effectiveness of the delay procedure
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sensitive indicator of acute impairment of the supplying vessels
Change in haematocrit
Change in pH
Magnetic resonance spectroscopy
Optode (Golde and Mahoney, 1994)
 implantable, optochemical, oxygen-sensing, electrode device
 allows rapid and continuous monitoring of tissue pO2
 independent of anastomotic proximity
Pulse oximeter
 requires further study
Near infra-red spectroscopy (NIRS)
 provides continuous monitoring of changes in the oxy-, deoxy- and total haemoglobin
concentrations of flap blood
 deeper evaluation (up to 10cm) than laser doppler
 able to delineate the difference between arterial, venous, and total vascular occlusion
IV Radioactive microspheres
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Can be used to measure blood flow in experimental situations only
Spheres are tagged with a radioisotope and injected centrally
The spheres then embolize peripherally and the amount of radioactivity in a tissue
with a known perfusion rate can be compared to the flap to determine it’s perfusion
Different size spheres determine different things:
o spheres of about 15μm will indicate nutrient blood flow
o larger spheres will indicate shunt flow or total flow
The sphere test can only be done 3 times before the haemodynamic effects of
embolization become too extreme
According to McCarthy, spheres are the optimal technique for quantitative
measurements of blood flow in the research laboratory (as of the time when McCarthy
was written)
V Other methods of flap monitoring
Magnetic resonance imaging
Measurement of the fibrillation potential in skeletal muscle
Clearance tests
Electromagnetic flowmetry
The monitoring is needed for 2 main reasons:
1. monitoring of free flaps
2. to detect early distal ischaemia
For free flap monitoring the methods of choice are:
1. if there is a skin paddle - surface temperature monitoring
2. if there is only buried tissue differential thermometry with thermocouple probes or
internal Doppler probes (although these are not widely used)
To detect distal ischaemia:
1. Fluorescein dye is the best available monitor
2. In the lab, radioactive microspheres are the gold standard