intrinsic/auto PEEP due to dynamic airway collapse (“air trapping”). The FRC is increased by recruiting more alveoli and by increasing alveolar size. Intrinsic (auto) PEEP occurs when the inspiratory/expiratory time ratio approaches 1:1. Hyperinflation of the thoracic cavity results in increased intra-thoracic pressure and subsequently a decrease in cardiac output. Ideally, the I/E ventilator ratio should be maintained at 1:3 or 1:4 for obstructive pulmonary patients.