Intraoperative partial pressure of oxygen measurement to predict flap survival

Flap monitoring using partial pressure of oxygen (pO₂) is a proven modality. Instruments needed are expensive and are not readily available to a clinician. Here, pO₂ of flap has been determined using readily available and cheap methods, and a cut-off value is calculated which helps in predicting flap outcome.

Total 235 points on 84 skin flaps were studied. Capillary blood was collected from flap and fingertip using 1-ml syringes after at least 30 min of flap inset, and pO₂ analysed using blood gas analyser. Fall/change of pO₂ (difference of mean of pO₂ [diff-pO₂]) was also calculated by subtracting the flap pO₂ from the finger pO₂. Flap was monitored clinically in post-operative period and divided into two groups depending on its survival with Group 1 - dead points and Group 2 - alive points. pO₂ and diff-pO₂ amongst both the groups were compared and found to be statistically different (P = 0.0001). Cut-off value calculated for pO₂ was found to be <86.3 mmHg with a sensitivity of 100% and specificity of 89.05%. The difference of >68.503 mmHg of flap pO₂ compared from finger pO₂ was calculated as a cut-off with sensitivity of 94.12 and specificity of 79.60%.

Flap areas having intra-operative pO₂ value <86.3 mmHG have higher chances (60.71%) of getting necrosis later. Similarly, if diff-pO₂ compared to fingertip is >68.5 mmHg, chances of those points getting necrosed in post-operative period are high.