Long-term effects of spontaneous breathing during ventilatory support in patients with acute lung injury

Improved gas exchange has been observed during spontaneous breathing with a irway pressure release ventilation (APRV) as compared with controlled mecha nical ventilation. This study was designed to determine whether use of APRV with spontaneous breathing as a primary ventilatory support modality bette r prevents deterioration of cardiopulmonary function than does initial cont rolled mechanical ventilation in patients at risk for acute respiratory dis tress syndrome (ARDS). Thirty patients with multiple trauma were randomly a ssigned to either breathe spontaneously with APRV (APRV Group) (n = 15) or to receive pressure-controlled, time-cycled mechanical ventilation (PCV) fo r 72 h followed by weaning with APRV (PCV Group) (n = 15). Patients maintai ned spontaneous breathing during APRV with continuous infusion of sufentani l and midazolam (Ramsay sedation score [RSS] of 3). Absence of spontaneous breathing (PCV Group) was induced with sufentanil and midazolam (RSS of 5) and neuromuscular blockade. Primary use of APRV was associated with increas es (p < 0.85) in respiratory system compliance (C-RS), arterial oxygen tens ion (Pa-O2), cardiac index (CI), and oxygen delivery (Do(2)), and with redu ctions (p < 0.05) in venous admixture ((Q) over dot VA/(Q) over dot T), and oxygen extraction. In contrast, patients who received 72 h of PCV had lowe r C-RS, Pa-O2 CI, Do(2), and (Q) over dot A/(Q) over dot T values (p < 0.05 ) and required higher doses of sufentanil (p < 0.05), midazolam (p < 0.05), noradrenalin (p = 0.05), and dobutamine (p < 0.05). C-RS, Pa-O2, CI and Do (2) were lowest (p < 0.05) and (Q) over dot VA/(Q) over dot T was highest ( p < 0.05) during PCV. Primary use of APRV was consistently associated with a shorter duration of ventilatory support (APRV Group: 15 +/- 2 d [mean +/- SEM]; PCV Group: 21 +/- 2 d) (p < 0.05) and length of intensive care unit (ICU) stay (APRV Group: 23 +/- 2 d; PCV Group: 30 +/- 2 d) (p < 0.05). Thes e findings indicate that maintaining spontaneous breathing during APRV requ ires less sedation and improves cardiopulmonary function, presumably by rec ruiting nonventilated lung units, requiring a shorter duration of ventilato ry support and ICU stay.