Blood gas analysis is one of the most frequently requested blood tests when caring for the critically ill patient, as it provides very valuable information about the respiratory and acid base status of the patient (Shoulders-Odom, 2000). However, many healthcare professionals find it difficult to get to grips with blood gas analysis. It often seems complex and daunting, but if you work your way through this book and carry out all the exercises, you will soon become confident and competent at analysing blood gases and will understand all the information that initially seemed so complicated. Blood gas analysis is a skill, which requires continuous practice, so once you have completed this workbook keep analysing blood gases as often as you can and discuss your findings with your mentor, until it becomes easy. With practice it will.