Gas monitoring and uptake.

The breath-by-breath monitoring of anesthetic gases can provide information, beyond the usual safety control. The study of the decay and concentration effects along the circuit can be useful to evaluate their kinetics. The presence of unexpected gases coming from the patient's tissues is another important topic. By means of gas monitoring devices we can study the physiologic changes consequent to the modifications to the patient position, or the respiratory variations due to V/Q mismatching. The end-expired fraction of the anesthetic (FE') is not so close to MAC as first proposed in the 1960s, but it remains the most precise index of the depth of anesthesia. The traditional concept of quantitative anesthesia is still sufficiently actual to be considered in the design of new anesthesia machines.