Mark Wefers Bettink

Chapter 8 150 Oxygen measurements were performed by means of the COMET ® monitor (Photonics Healthcare, Utrecht, the Netherlands). A self-adhesive patch containing 8mg ALA (Alacare, photonamic GmbH und Co. KG, Pinneberg, Germany) was applied on the sternal skin, for induction of PpIX. The Alacare patch is still under investigation for FDA approval for the intended use of the COMET ® measurement. To enhance ALA penetration adequate skin preparation proved essential. Hair was shaved (if present) and the skin was rubbed with a fine abrasive pad of a standard ECG sticker to remove the top parts of the stratum corneum. During ALA application, the skin was protected from light by the patch for minimal 5 hours. During these 5 hours a suitable concentration of PpIX was synthesized to enable measurements of mitoPO 2. After induction of anesthesia, the ALA patch was removed and the measuring probe applied to the ALA-treated skin. The mitoPO 2 was automatically measured every 5 minutes during the operation. In addition to mitoPO 2 , tissue oxygenation saturation and perfusion parameters were measured intraoperatively (O2C, oxygen to see version 2424, Lea Medizintechnik GmbH, Giessen, Germany). The O2C measures three parameters: The local capillary venous saturation (StO 2 ), the local velocity of blood given in velocity units (VU) and the local micro vascular blood flow given in flow units (AU). Both the COMET ® Skin Sensor and the O2C probe (LFX-43) were positioned on the sternum next to each other. All measurements were performed from the start of surgery until the end of surgery, in order to exclude the effects of induction of anesthesia and the accompanying influences of medication and preoxygenation on mitochondrial and microvascular parameters. To observe the applicability and stability of the mitoPO 2 measurements the primary outcome measures included mitoPO 2 (mmHg), flow (AU), probe temperature (degrees Celsius) and MAP (mmHg) over time. Statistical analysis A sample size calculation was performed using G*Power software and was based on previous research in healthy volunteers 7,12 . Because of technical improvements less device-induced variation was expected and therefore a lower standard deviation was assumed. MitoPO 2 was suspected to be slightly higher due to the continuous oxygen supplementation during surgery. A sample size of 20 patients was calculated with an assumed mean difference of 12 mmHg and standard deviation of 18 mmHg, a type I error probability of 0.05 and a power of 80%.