The dye fluorescent index (DFI) can be used to determine if a proposed amputation site is sufficiently perfused to heal adequately.
Fluorescent detection instrument (dermofluorometer)
(1) dual channel fiberoptic light guide
(2) one channel transmits a blue light capable of exciting a fluorescein dye
(3) the second channels transmits the fluorescent light generated back to a photomultiplier tube for detection
Technique:
(1) background readings are taken at the proposed amputation site and at a reference site on the arm or upper torso before a fluorescent dye is injected
(2) readings are taken at the same sites again after dye is injected
(3) multiple readings are taken and an average reading used
Dose of fluorescein dye to inject:
(1) If the patient is Caucasian, then the dose is 4 mg/kg.
(2) If the patient is of darker complexion, then the dose is 6-8 mg/kg.
(3) The dose is diluted in 20 mL of normal saline and injected intravenously slowly.
fluorescent reading =
= (fluorescent reading after dye) - (background reading before dye)
dye fluorescent index =
= (average fluorescent reading for proposed amputation site) / (average fluorescent reading at reference area) * 100
Interpretation:
• Areas with better perfusion will have higher fluorescence than those that are poorly perfused, with readings 10-20 times greater than background
• DFI > 42: high rate of amputation site healing
• DFI 38 - 42: borderline rate of healing
• DFI < 38: show poor healing
Limitations:
• Cellulitis or other skin disorders can interfere with the fluorescent readings
