Do Pre-Operative Transcutaneous Oxygen Perfusion Measurements Predict Atraumatic Major Lower Extremity Amputation Wound Healing?

CATEGORY: Other INTRODUCTION/PURPOSE: Determining appropriate amputation level is a challenging task requiring clinical, laboratory, and imaging data. However, there is no validated consensus on the method with the most prognostic accuracy. Transcutaneous oxygen perfusion measurement (TcPO2) is a noninvasive means of measuring tissue oxygenation. A TcPO2 > 30-40mm Hg is widely cited as a positive predictor of post-operative wound healing, but its validity has not been well defined. We hypothesized that TcPO2 levels positively correlate with the success of amputation wound healing. Additionally, we secondarily investigated the correlation between other preoperative demographics and clinical variables and their impact on post-operative amputation wound healing. METHODS: A retrospective chart review was performed on patients who underwent lower extremity above, through, or below knee amputations at a single institution with documented preoperative TcPO2 values between January 1, 2012 and December 1, 2018 and a minimum 30 days post-operative clinical follow up. Amputations performed for oncologic pathology, infected arthroplasty, osteomyelitis and traumatic amputations were excluded in order to isolate TcPO2 as a decision-making test for amputation level. This yielded one hundred and forty-one total amputations. Of these ninety-three were below knee amputations (BKA), six through knee amputations, and forty-two above knee amputations (AKA). Chi-square and t-tests were used to compare successful and failed amputations where appropriate. RESULTS: Eighty-six of the amputations were successful and fifty-five failed, as defined by post-operative wound dehiscence or infection. Of these, thirty-seven were BKAs, four were through knee amputations and fourteen were AKAs. There was a significant difference in preoperative TcPO2 levels between the successful and failure groups at 46.2 and 38.3 respectively (p = 0.02). A TcPO2 of 30-40mm Hg had a success rate of 68.8%, and a TcPO2 < 20mm Hg a success rate of 18.2%. A receiver operating characteristic curve for TcPO2 levels predicting amputation success elucidated that with an area under the curve of 0.53 for the AKA cohort and 0.61 for the BKA cohort, the diagnostic ability is far from prognostic. CONCLUSION: Our results provide new insight into the predictive accuracy of preoperative TcPO2 levels. There is not a linear association between TcPO2 and success rate. A TcPO2 < 20mm Hg has a high positive predictive value for failure, but higher TcPO2 levels are not 100% predictive of amputation wound healing as reported by prior studies. Multiple factors should be considered when selecting amputation level.