Transcutaneous PCO(2) Measurement at Low Temperature for Reliable and Continuous Free Flap Monitoring: Experimental and Clinical Study

BACKGROUND: Measurement of transcutaneous oxygen pressure (TcPO(2)) and transcutaneous carbon dioxide pressure (TcPCO(2)) has been used for free flap monitoring. Because these values are obtained with sensor probes heated to 44°C, there is potential for low-temperature burns on skin flaps. We measured TcPO(2) and TcPCO(2) at 37°C in both animals and humans to determine the feasibility and safety of the procedure as a postoperative flap monitoring method. METHODS: Twelve epigastric island flaps were elevated in rabbits, and TcPO(2) and TcPCO(2) were measured at 37°C before and after ligation of the pedicles. In addition, TcPO(2) and TcPCO(2) at 37°C were measured in healthy men. Subsequently, the method was applied to postoperative monitoring of free flaps in 49 clinical cases. RESULTS: TcPO(2) and TcPCO(2) values were significantly affected by the experimental flap elevation. A rapid increase in TcPCO(2) was observed with both arterial and venous occlusion. In the healthy men, TcPO(2) and TcPCO(2) were measurable at all skin surface sites. In the clinical cases of free flap transfer, TcPO(2) values remained very low for at least 72 hours. TcPCO(2) values ranged from 40 to 70 mm Hg for 72 hours in more than 80% of cases. In 2 cases, TcPCO(2) values increased to more than 90 mm Hg, and exploration surgery was performed. These compromised flaps were saved by reanastomosis of the veins. CONCLUSIONS: Continuous monitoring of TcPCO(2) at 37°C can provide objective information and alert doctors and nurses to the need for checking the free flap.