- Poster presentation
- Open Access
Relationship of the stress index, lung recruitment and gas exchange in patients with acute respiratory distress syndrome
© BioMed Central Ltd 2008
- Published: 13 March 2008
- Acute Respiratory Distress Syndrome
- Stress Index
- Inspiratory Flow
- Acute Respiratory Distress Syndrome Patient
- Plateau Pressure
The study objective was to investigate the relationship of stress index and positive end-expiratory pressure (PEEP) in patients with acute respiratory distress syndrome (ARDS). To determine the relationship of the stress index, lung recruitment, oxygenation and respiration mechanics.
Fourteen patients with ARDS were enrolled in the study. During volume control ventilation with constant inspiratory flow, the pressure–time (P–t) curve was fitted to a power equation: P = a × time b + c, where coefficient b (stress index) describes the shape of the curve: b = 1, straight curve; b < 1, progressive increase in slope; and b > 1, progressive decrease in slope. PEEP was set to obtain a b value between 0.9 and 1.1 after application of a recruiting maneuver (RM). PEEP was changed to obtain 0.6 <b < 0.8 and 1.1 <b < 1.3. The experimental conditions sequence was random. The recruited volume (RV) was measured by the static pressure–volume curve method. The hemodynamics, pulmonary mechanics and gas exchange were observed at the same time.
The PEEPs at b < 1, b = 1 and b > 1 were 8.3 ± 1.5 cmH2O, 15.0 ± 1.9 cmH2O and 18.4 ± 1.9 cmH2O, respectively, which were significantly different (P < 0.001). At b = 1 and b > 1, the partial arterial oxygen tension (PaO2/FiO2) (350.1 ± 113.0 mmHg, 338.3 ± 123.8 mmHg) was higher than that (165.1 ± 59.9 mmHg) of pre-RM (P < 0.05). The plateau pressures (P plat) at b = 1 (29.0 ± 3.5 cmH2O) and b > 1 (32.9 ± 7.3 cmH2O) post-RM were significantly higher than that at b < 1 (21.9 ± 4.3 cmH2O) (P < 0.05). The P plat at b > 1 was higher than that (25.3 ± 15.9 cmH2O) pre-RM (P < 0.05). Compared with the static pulmonary compliance (C st) at b = 1 (38.6 ± 10.9 ml/cmH2O), the C st at b > 1 (26.4 ± 6.5 ml/cmH2O) decreased significantly (P < 0.05). The RV at b = 1 and b > 1 (401.6 ± 204.0 ml, 588.3 ± 269.1 ml) were significant higher than that at pre-RM and b < 1 (135.9 ± 111.1 ml, 175.2 ± 122.4 ml) (P < 0.05). At pre-RM, b < 1, b = 1 and b > 1, the HR, mean arterial pressure and lactate were not significantly different (P > 0.05).
The stress index at post-RM could be a good method of PEEP titration for ARDS patients.
This article is published under license to BioMed Central Ltd.