Multisensor transcutaneous oximetric mapping to predict below-knee amputation wound healing: use of a critical Po2.

Preoperative transcutaneous oxygen tension (tcPo2) measurements of calf and brachial skin were performed on 40 patients before they underwent below-knee amputation (BKA); dual calf measurements on the anterior and posterior skin were obtained. Both anterior and posterior calf tcPo2 values were significantly lower in patients with unsuccessful wound healing after BKA compared to those with successful healing (p less than 0.01). Successful wound healing occurred in 50% (6/12) of patients with calf tcPo2 values less than 20 torr and in 96% (27/28) of patients with calf tcPo2 values greater than 20 torr. Calculation of a critical Po2 index (defined as the lesser of the anterior and posterior calf/brachial tcPo2 ratios) resulted in improved predictive accuracy; 100% (6/6) of patients with a critical Po2 index of 0.20 or less had unsuccessful wound healing after BKA, whereas 97% (33/34) of patients with a critical Po2 index greater than 0.20 had successful healing. The use of a critical Po2 index greater than 0.20 as predictive of successful healing after BKA was associated with a sensitivity, specificity, and overall accuracy of 100%, 86%, and 98%, respectively, compared to 82%, 86%, and 83%, respectively, by use of absolute calf tcPo2 values. In conclusion, multisensor transcutaneous oximetric mapping is an accurate method for predicting wound healing success after BKA. Measurement of both anterior and posterior calf tcPo2 should be performed; calf tcPo2 values less than 20 torr may indicate local ischemia, but ischemia should be confirmed by comparison of calf tcPo2 with brachial tcPo2 before the patient is denied BKA.(ABSTRACT TRUNCATED AT 250 WORDS)