Determination of ideal PtcO2 measurement time in evaluation of hypoxic wound patients

Evaluation of ideal time for baseline PtcO2 readings in air, elevation test, and oxygen challenge during evaluation of hypoxic wound patients.

Retrospective analysis. IRB APPROVAL: Western IRB deemed this study exempt from requiring IRB approval.

202 patients with lower extremity wounds.

Patients had PtcO2 measurements using 6 electrodes positioned in 3 paired locations along the limb (above the knee: AK; below the knee: BK; and foot). Measurements were made from each electrode at 7 different time-event occasions: position of limb (supine or elevated), type of breathing gas (sea level air or oxygen), and time of measurement. A total of 8,484 measurements were analyzed by first examining each electrode's data, and then pooling the data for each location pair.

PtcO2 readings for air (10 minutes) were less than air at 20 minutes. Maximal readings were close to the 20-minute mark for AK and BK measurements, and closer to 30 minutes for the foot. Elevation test at 3 versus 5 minutes showed a continuing decline in PtcO2 values. Oxygen challenge readings at 5 and 10 minutes were significantly different: the latter always larger than the former.

Ideal times for baseline readings, leg elevation test, and oxygen challenge test are at least 20, 5, and 10 minutes, respectively.