A comparison of the effects of manual and ventilator hyperinflation on static lung compliance and sputum production in intubated and ventilated intensive care patients.
Respiratory distress syndrome (RDS) was modelled in rabbits using pulmonary lavage to remove surfactant. The stability of the resulting pressure-volume hysteresis of the lungs in vivo was studied with the aid of whole-body plethysmography during apnoeic oxygenation made possible by total extracorporeal carbon dioxide removal. Systemic oxygen delivery was measured as a function of the constant airway pressure during apnoea. In 6 subjects a single brief inflation of the lungs to 3.5kPa resulted in a doubling of both expired lung volume (volume above functional residual capacity) and arterial oxygen partial pressure at an airway pressurre of 0.65kPa. These rises were well maintained for 40min following the inflation. In a further 6 subjects with RDS single inflations permitted optimum systemic oxygen transport to occur at the low airway pressure of 0.3kPa, similar to the optimum airway pressure in 6 healthy control subjects. Where pressure-volume hysteresis is present in RDS it can be exploited during apnoeic oxygenation, and probably during high frequency ventilation, to improve oxygenation by the use of infrequent single inflations of the lungs.