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Gas exchange assessment in the critically ill 

Gas exchange assessment in the critically ill
Gas exchange assessment in the critically ill

Peter D. Wagner

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date: 27 February 2020

Chapter 75 laid out the basic principles that govern pulmonary gas exchange, a step necessary for the appropriate application and interpretation of common clinical tests of gas exchange. The present chapter discusses the several common tests and indices used to analyse and quantify gas exchange abnormalities in critically-ill patients. There is special emphasis on inherent limitations of each technique, as well as on ways to minimize technical and experimental errors when the necessary measurements are made. Limitations and errors are considered to be of major clinical importance because, while the measurements and indices themselves are easy to obtain, and have been in routine use for many years, serious errors of interpretation can occur if the limitations and common errors are not appreciated and allowed for. In particular, it is pointed out that factors external to the lungs can dramatically change arterial oxygenation in the critically-ill patient. This means that not all changes in gas exchange reflect changes in lung pathology. It is not uncommon for arterial PO2 to change without change in lung disease severity when external factors such as metabolic rate, cardiac output, and blood temperature change.

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