The physiological basis of respiratory support.

The complex interplay between the characteristics of the respiratory system, its changes as a result of respiratory disease and the effects of mechanical ventilation makes it important to analyse the physiology of the respiratory system in any given clinical situation. Key variables to be considered are the elastic recoil, resistance and time constant of the respiratory system, as well as the characteristics of the respiratory pump. The effects of respiratory support on the intrathoracic organs and lung perfusion must be taken into account. Respiratory support modes can then be tailored to provide maximum benefit and a minimum of negative effects. When the relatively few basic principles that underlie the mechanical behaviour of the respiratory system in most circumstances are kept in mind, the challenge of optimal support seems solvable for most children with respiratory insufficiency.