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Transcutanous Blood Gas Monitoring
1. Transcutaneous Blood Gas Monitoring Hutch, A., Acta Anaesthesiologica Scandinavica. Supplementum. 107:87-90,1995 Journal Arcticle. Review Transcutaneous Oxygen Measurements: Implications for Nursing Rich, Kathleen, Journal of Vascular Nursing. 19(2):55-9, 2001 June. Journal Article. Review AARC Clinical Practice Guideline. Transcutaneous Blood Gas Monitoring for Neonatal & Pediatric Patients. Anonymous, Respiratory Care. 39(12):1176-9, 1994 December. Journal Article. Practice Guideline Saif K. Ahmedi Claudia Amaya Resc 3621 Physiologic Monitoring Spring 2006
2. Introduction Transcutaneous blood gas measurement is a noninvasive, diagnostic technique that records the partial pressure of oxygen(Ptc0 2 ) and carbon dioxide (PtcCO 2 ) electrochemically at the skin surface. Its advantage over direct measurement of arterial blood gas is that it is noninvasive and is appropriate for continuous and prolonged monitoring. However, because it is an indirect measure of arterial values, arterial blood gas values using bench level co-oximeters still remain the gold standard. Unlike pulse oximeters, which measure hemoglobin saturation, TCMs measure partial pressure directly. A slight delay in warm-up and response time make it better suited for monitoring slow trends rather than instant changes. Due to the oxygen hemoglobin saturation/dissociation curve, observing saturation alone is unreliable when hyperoxemia must be closely monitored, as in premature infants. In these instances, use of a TCM is indicated when frequent arterial blood sampling may be harmful or unfeasible. PtcO 2 and PaO 2 have a 1:1 correlation in neonates due to their skin composition. In older children and adults, the PtcO 2 /PaO 2 ratio decreases as skin becomes more impermeable to O 2 . For this reason, RTs normally do not use TCMs to monitor adults and children.
3. History The possibility of skin surface measurement for estimating central PO 2 was suggested by Bramberger and Goodfriend in 1951. They showed that when a finger was immersed in an electrolyte solution maintianed at 45 o C, the PO 2 of the solution equilibrated with that of arterial blood. In 1972, Huch and associates developed a miniaturized, heated electrode that measured the skin surface PO 2 . This is the basis behind the transcutaneous oxygen monitors in use today.
11. Due to variations in skin characteristics, ratios between ABG and TCM values differ depending on age, sex, and skin site: Premature infants: 1.41 : 1.00 Neonates: 1.00 : 1.00 Children: 0.68 : 1.00 Adults: 0.79 : 1.00 Older Adults: 0.68 : 1.00 There is a tendency to measure infra-arterial values in male adults and supra-arterial values in premature infants. However, consistency is more important than absolute value, and consistency is only assured if TCM measurements are independent of flow…
12. Transcutaneous-Arterial Ratios Change With Flow Region 2 – partial pressure is effected by changes in flow. Region 3 – partial pressure does not change in a region of hyperemia. Blood pressure changes in this region also have no effect on partial pressures.
13. Transcutaneous-Arterail Ratios Change With Flow (continued) Since the energy required to maintain a constant electrode core temperature (for active hyperemia to occur) changes as blood flow increases, this change in power consumption (displayed on some devices) is sometimes used as a measure of perfusion status. A decrease in PtcCO 2 as opposed to PaCO 2 is also an indicator of poor tissue perfusion.
