Since gas exchange is a primordial function of the lungs and the conductive airways, respiratory assessment is of paramount importance. Capnography has been utilized in surgical patients for over three decades to confirm tracheal intubation and assess ventilation. Nitrogen washout provides an estimate of functional residual capacity, total lung volume, deadspace volume, and alveolar volume. Clinicians typically utilize exhaled CO2 concentration against time during a respiratory cycle. A number of applications are available in and out of the operating room. Capnography can be used as a continuous monitor of alveolar ventilation in patients with lung disease or hemodynamic instability. Mainstream capnometry appears to provide more accurate PETCO2 than conventional sidestream capnometry during spontaneous breathing in non-intubated patients. In the opinion of some investigators, the technology should be employed in all cases requiring sedation in or out of the operating room.

Heliox, a mixture of helium and oxygen, was used by Barach in New York for the first time in the treatment of asthma and upper airway obstruction after its introduction to deep sea diving. Since then it has been used not only as a rescue medication in emergency situations for spontaneously breathing patients with airway obstruction but also as the driving gas for mechanical ventilators. The increasing interest in heliox is indicated by the rising number of publications in recent years. This chapter outlines the theoretical considerations, the application of heliox in non-intubated (e.g. with upper and lower airway obstruction) as well as in ventilated patients followed by a brief overview of potential risks and cost considerations. Future developments focus on ways to routinely apply heliox during mechanical ventilation, for example, as a commercially available add-on feature to conventional ventilators.