Oxygen transcutaneous sensors

To reduce the invasivity, numerous supplementary methods have been evaluated to determine their usefulness in replacing some invasive methods or obtaining additional data. Some of these tested methods involve transcutaneous sensors for PO2 and PCO2 partial pressures in the tissue (tcp02 and tcpC02) and transcutaneous measurements of oxygen saturation in peripheral vessels or invasive intravasal measurements of oxygen saturation. 

The electrochemical measurement of PO2 by use of a polarographic Clark cell offers the advantage of designing small and compact sensors which show a linear response to oxygen partial pressure. Figure 23-4 presents a sectional view of a combined transcutaneous sensor for tcp02 and tcpC02. 

Since the original discovery of this phenomenon over 50 years ago, there has been progressive development in instrumentation to measure oxygen saturation along three different paths bench-top oximeters for clinical laboratories, fiber optic catheters for invasive intravascular monitoring, and transcutaneous sensors, which are noninvasive devices placed against the skin. 

Mitsubayashi, K., Wakabayashi, Y., Murotomi, D., Yamada, T., Kawase, T., Iwagaki, S., Karube, I., 2003. Wearable and flexible oxygen sensor for transcutaneous oxygen monitoring. Sensors Actuators B 95, 373—377. 

Transcutaneous determination of ethanol with an oxygen electrode covered by AOD has been described by Clark (1979). Stepwise increases of the ethanol concentration in rat blood resulted in a curve reflecting the ethanol injections, returning to the initial value only after several hours. Disturbances were caused by variations in body temperature and blood pressure. In the paper cited, Clark developed the concept of a sensor for volatile enzyme substrates. 

Most innovations in oxygen measurement have been in the engineering of sensors rather than in the electrochemistry. They nearly all rely on amperometric detection following the application of a suitable reducing potential. Innovations in design include miniaturisation for insertion into blood vessels [12,13], the inclusion of heaters for the transcutaneous measurement of blood gas [14,15] and shaping for mounting on the eye for measurement via the palpebral conjunctiva [16,17]. 

In 1954 Leland Clark demonstrated that a platinum cathode would measure the oxygen concentration of blood when it and a reference electrode were covered by an oxygen permeable membrane. Later in that same year Stow and Severinghaus showed that carbon dioxide could be estimated in blood with a glass electrode fitted with a gas permeable membrane. In the seventies the Huchs demonstrated that mechanical adaptations of these devices could be utilized to provide transcutaneous (non-invasive) measurement of arterial blood gas concentration if the skin area surrounding the sensor was heated to 44 - 45°C. 

There has been much effort in recent years to provide continuous chemical monitoring of critically ill patients or patients undergoing heart surgery. It has proved very difficult to fulfill the increased demands in such applications by any sensors. Some of the problems are sensor sterilization and calibration, effect of varying temperatures, sensor deterioration or cellular encapsulation due to continuous direct contact with blood, thrombogenicity of the sensor devices, small size, and patient safety. Noninvasive systems, e.g., transcutaneous oxygen and carbon dioxide sensors, are less affected and have had considerable success, particularly in infant care. O2 and CO2 can diffuse across the mildly heated skin to the sensors and the measured values correlate well with arterial samples. 

Modifications of miniaturized polydimethylsiloxane (PDMS)-based oxygen sensors have been reported as relevant alternatives to conventional transcutaneous pOa devices [24-27]. Koley et al. [24] presented a flexible amperometric prototype... 

Kudo H, Iguchi S, Yamada T, kawase T, Saito H, Otsuka K, Mitsubayashi K (2007) A flexible transcutaneous oxygen sensor using polymer membranes. Biomed Microdevices 9 1-6... 

Iguchi S, Mitsubayashi K, Uehara T, Ogawa M (2005) A wearable oxygen sensor for transcutaneous blood gas monitoring at the cmijunctiva. Sens Acmators B 108 733-737... 

Mitsubayashi et al. (2003) developed a wearable and flexible oxygen sensor with membrane structure, constructed using microfabrication techniques, and containing a nonpermeable sheet and a gas-permeable membrane with platinum- and Ag/AgCl-electrodes. The sensor device, applied to the skin surface of healthy male volunteers with no history of skin diseases, allowed the safe monitoring, by CV, of the transcutaneous... 

The CV and chronoamperometric data recorded showed that the wearable sensor could be used as a new transcutaneous oxygen sensor, enabling evaluating the oxygen level in the conjunctiva of a rabbit without any thermoregulation. An automatic sequential injection voltammetric E-tongue was described by Gutes et al. (2(X)7) to determine oxidizable compounds of clinical and pharmaceutical interest, such as ascorbic acid, uric acid, and paracetamol. 

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