HEMODYNAMIC-EFFECTS OF MANUAL HYPERINFLATION IN CRITICALLY ILL MECHANICALLY VENTILATED PATIENTS

Subject objective: To assess the hemodynamic effects of manual lung hy perinflation in mechanically ventilated patients and to measure the di fferent inspiratory pressures and tidal volumes generated by different operators. Design: Measurements of aortic blood now (by esophageal Do ppler ultrasonography), systemic blood pressure, tidal volumes (by res pirometry), and inspiratory pressures in the ventilator circuit were m easured on the ventilator, during six intended manual hyperinflations (tidal volume > 150% that delivered by ventilator) using a 2-L rebreat hing bag, and at 1, 5, 10, and 15 min after reconnection to the ventil ator. Setting: Intensive care unit. Patients: Eighteen mechanically ve ntilated patients with normovolemia and stable circulatory status were assessed on a total of 20 occasions. Interventions: Patients were dis connected from the ventilator to enable six manual hyperinflations to be given. Measurements were made before and at 5-min intervals until n o further hemodynamic changes were seen. Measurements and results: Hyp erinflation (50% increase in tidal volume) was achieved only in 10 of 20 studies. Large variations were seen in percentage change in peak in spiratory pressure (-30% to +250%) and tidal volume (-33% to +127%) ge nerated. Falls in cardiac output correlated to the increase in tidal v olume but not to the increase in peak inspiratory pressure and took up to 15 min to recover to baseline values, Changes in cardiac output we re independent of lung compliance and concurrent vasoactive drug suppo rt. No consistent change was noted in either blood pressure or heart r ate. Conclusions: Lung hyperinflation is frequently not achieved by th e manual technique. Significant changes in cardiac output can occur an d appear to be related to the tidal volume rather than pressure genera ted.