Analysis of respiratory mechanics during artificial ventilation

Mechanical or artificial ventilation is the most important life-saving therapeutic instrument in modern intensive care medicine. The ventilator takes on the convective transport of the respiratory gas, i.e. delivery of oxygen and removal of carbon dioxide. The technical gas delivery system (ventilator, respiratory tubing system, gas humidifier) and the respiratory system (lungs and thorax) of the patients form a connected pneumatic system of high complexity. The respiratory system produces a mechanical impedance to ventilator output. Impedance is composed of an elastic, a non-elastic, i.e. resistive, and an inertive part. The corresponding indices describing respiratory mechanics are compliance, flow resistance and inertance. Based on the equation of motion of the respiratory system, several methods of analysing respiratory mechanics during mechanical ventilation are described. Quantitative analysis of respiratory system mechanics (a) is a prerequisite for the understanding of the complex patient-ventilator interaction, (b) provides important clinical information on pulmonary function and the course of disease, and (c) allows the physician at the bedside to adjust the ventilatory settings to the needs of the individual patient.