Abstract
BACKGROUND:
Elevated dead space fraction (the ratio of dead space to tidal volume [VD/VT]) is a feature of ARDS. PEEP can partially reverse atelectasis, prevent alveoli recollapse, and improve lung compliance and gas exchange in patients with ARDS. However, whether VD/VT variables have a close relationship with PEEP and collapse alveolar recruitment remains under recognized. Meanwhile, few clinicians titrate PEEP in consideration of changes in VD/VT. Therefore, we performed the study to evaluate VD/VT, arterial oxygenation, and compliance changes during PEEP titration following lung recruitment in ARDS patients.
METHODS:
Twenty-three ARDS patients ventilated in volume-controlled mode were enrolled in the study. Sustained inflation (40 cm H2O, 30 s) was used as a recruitment maneuver, followed by decremental PEEP changes from 20 to 6 cm H2O, in steps of 2 cm H2O, and then to 0 cm H2O. VD/VT, pulmonary mechanics parameters, gas exchange parameters, and hemodynamic parameters were recorded after 20 min at each PEEP step.
RESULTS:
Compared with VD/VT at the PEEP levels of 20 cm H2O and 0 cm H2O, VD/VT was significantly lower at 12 cm H2O (P = .02), and compliance of the static respiratory system (CRS) was significantly higher at pressure step 12/10 cm H2O (P < .001). Compared with PaCO2 at the PEEP level of 20 cm H2O, PaCO2 was significantly lower at 12 cm H2O (P < .001). Arterial oxygenation values and functional residual capacity were reduced gradually during PEEP, decreasing from 20 cm H2O to 0 cm H2O.
CONCLUSIONS:
A significant change of VD/VT, compliance and arterial oxygenation could be induced by PEEP titration in subjects with ARDS. Optimal PEEP in these subjects was 12 cm H2O, because at this pressure level the highest compliance in conjunction with the lowest VD/VT indicated a maximum amount of effectively expanded alveoli. Monitoring of VD/VT was useful for detecting lung collapse and for establishing open-lung PEEP after a recruitment maneuver.
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