Hemodynamic and respiratory changes during lung recruitment and descending optimal positive end-expiratory pressure titration in patients with acute respiratory distress syndrome*

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Abstract

Objectives:

To investigate respiratory and hemodynamic changes during lung recruitment and descending optimal positive end-expiratory pressure (PEEP) titration.

Design:

Prospective auto-control clinical trial.

Setting:

Adult general intensive care unit in a university hospital.

Patients:

Eighteen patients with acute respiratory distress syndrome.

Interventions:

Following baseline measurements (T0), PEEP was set at 26 cm H2O and lung recruitment was performed (40/40-maneuver). Then tidal volume was set at 4 mL/kg (T26R) and PEEP was lowered by 2 cm H2O in every 4 mins. Optimal PEEP was defined at 2 cm H2O above the PEEP where Pao2 dropped by >10%. After setting the optimal PEEP, the 40/40-maneuver was repeated and tidal volume set at 6 mL/kg (Tend).

Measurements and Main Results:

Arterial blood gas analysis was done every 4 mins and hemodynamic measurements every 8 mins until Tend, then in 30 (T30) and 60 (T60) mins. The Pao2 increased from T0 to Tend (203 ± 108 vs. 322 ± 101 mm Hg, p < .001), but the extravascular lung water (EVLW) did not change significantly. Cardiac index (CI) and the intrathoracic blood volume (ITBV) decreased from T0 to T26R (CI, 3.90 ± 1.04 vs. 3.62 ± 0.91 L/min/m2, p < .05; ITBVI, 832 ± 205 vs. 795 ± 188 mL/m2, p < .05). There was a positive correlation between CI and ITBVI (r = .699, p < .01), a negative correlation between CI and central venous pressure (r = −.294, p < .01), and no correlation between CI and mean arterial pressure (MAP).

Conclusions:

Following lung recruitment and descending optimal PEEP titration, the Pao2 improves significantly, without any change in the EVLW up to 1 hr. This suggests a decrease in atelectasis as a result of recruitment rather than a reduction of EVLW. There is a significant change in CI during the maneuver, but neither central venous pressure, heart rate, nor MAP can reflect these changes.

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