PURPOSE: The use of low tidal volume ventilation (LTVV) is associated with lower mortality in patients with Acute Lung Injury (ALI) and ARDS, yet adherence to such strategies is suboptimal. We conducted a retrospective analysis to identify associations between clinical and ventilatory parameters and adherence to LTVV.
METHODS: We studied patients who met consensus criteria for ALI/ARDS between 3/2007 and 3/2008. We selected all periods for which tidal volume (Vt) delivered using a mandatory mode (assist control (AC), SIMV, or BiLevel/APRV) was documented. Daily clinical and ventilation data were collected and correlated with Vt adjusted for predicted body weight (PBW) and adherence to low (< 6.5 ml/kg) and moderate (< 8.5 ml/kg) Vt, using T-tests and ANOVA.
RESULTS: Thirty subjects (18M/12F, averaging 54.2 years old, APACHE II 25, and PaO2:FiO2 147 mmHg on entry) met inclusion criteria and had 432 discrete assessments. Average Vt was 8.2 ml/kg and Vt was < 6.5 ml/kg and < 8.5 ml/kg on 23% and 57% of assessments. Vt was lower with AC (7.2 ml/kg) than with SIMV (8.8 ml/kg) or BiLevel/APRV (9.1 ml/kg) modes (p<0.0001). Pressure-targeted ventilation using AC or SIMV had lower Vt than volume-targeted ventilation (p =0.0036); both lower than BiLevel/APRV (p <0.001). Non-adherence to LTVV was significantly more common with BiLevel/APRV (p <0.0001). Vt was higher during night shifts (p =0.03) and was lowest from 8am-noon. Lower compliance with low and/or moderate Vt was observed for women, obese patients, and patients with ALI.
CONCLUSIONS: Use of BiLevel/APRV was associated with worse adherence to LTVV than other modes. Interestingly, pressure-targeted AC or SIMV was associated with lower tidal volumes than volume-targeted ventilation or BiLevel/APRV. Tidal volumes were higher at night, particularly compared to morning rounds, and for women and obese patients.
CLINICAL IMPLICATIONS: Use of structured protocols that emphasize calculation of PBW and frequent scrutiny of tidal volume could improve adherence to LTVV. Our data suggests this may be particularly important when using BiLevel/APRV, at night, and in women and obese patients.
DISCLOSURE: The following authors have nothing to disclose: Jared Shipley, Cecilia Bergh, Travis Greer, Curtis Sessler
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