Purpose:  The purpose of the study was to evaluate the detection of vascular complications earlier than clinical evidence using a noninvasive near-infrared tissue oximeter monitor.

Clinical signs of vascular obstruction in microsurgical free tissue transfer are often recognized late. Early detection of circulatory compromise allows for earlier re-exploration and better outcomes.

208 flaps in 145 patients undergoing autologous tissue perforator free flap breast reconstruction were enrolled in a flap monitoring study from January  2005 to January 2008. The monitoring study was in addition to the clinical monitoring protocol already in place.

Methods & Materials:  The monitoring method studied was the ViOptix ODISsey™ Tissue Oximeter. The device uses an optical tissue characterization based on measuring scattering and absorption of near infrared light which is related to the oxygen content of the hemoglobin in that particular tissue. The tissue oximeter documents changing flap physiology in real time, captures and displays the data graphically.

Tissue oxygen saturation and its derivates were evaluated as candidates for a more sensitive algorithm to predict vascular flap complications. Criteria studied in various combinations were the absolute value of tissue oxygen saturation (StO2), the amount of its change (DStO2) and the rate of its change (ΔStO₂/Δt).

Experience:  208 monitored breast flaps [197  DIEP, 10  s-GAP, 1  SIEA] in 145 patients (62 bilateral and 84 unilateral). Patients were monitored intra-operatively and post-operatively for 36 hours

Results:  No flap being monitored was lost. Among the 208 flaps monitored, five patients exhibited complications that were predicted by the tissue oximeter before clinical signs were evident. If blood flow was completely occluded by either venous or arterial thrombosis, the tissue oximeter provided information that enabled diagnosis to be made in less than one hour.

Eight additional surgeries were performed for vascular problems: 2 Hematoma: 1 without compromise, 1 with compromise; 4 Venous: 1 intraop, 1 extra superficial vein thrombosis, 2 deep vein thromboses; 2 Arterial.

StO2 and its drop rate are two hypoxia indicators used simultaneously in flap monitoring. The drop rate indicator DStO2/Dt, when it is equal to or greater than 20% per hour sustained more than 30 minutes predicted vascular complications.

 

Â	StO2 and its drop rate can be combined to indicate possible hypoxia in a flap. All flaps with StO2 ≤30% and ΔStO2/Δt ≥ 20% per hour were flaps with complications

Diagnostic Accuracy Criterion StO2£30% & ΔStO2/Δt ³20%/h True positive (a) 4+3* False positive (b) 0 False negative (c) 0 True negative (d) 201 Sensitivity (a/(a+c)) 100% Specificity (d/(b+d)) 100% PPV**  (a/(a+b)) 100% NPV*** (d/(c+d)) 100%

* These 3 cases are represented by green plus signs in Figure 1 For these cases, the criteria were not fully satisfied at the time of intervention. Therefore these 3 cases are considered true positives. **Positive Predictive Value ***Negative Predictive Value

Correlation between tissue oxygen saturation (StO₂) and hemoglobin (HbT):  In venous hypertension there was a rise in hemoglobin and a drop in the tissue oxygen saturation.

Conclusions: Use of the new diagnostic algorithm with the tissue oximeter monitor post-operatively was successful in predicting complication within one hour of the onset of the occlusive event with high diagnostic accuracy in 208 flap procedures.

The oximeter provided accurate quantitative information that enabled the detection of vascular complications often before they were noticeable through clinical observation.