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Feasibility of early spontaneous breathing in acute respiratory distress syndrome

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Airway pressure release ventilation (APRV) is as a pressure preset mode that allows unrestricted spontaneous breathing throughout the entire ventilator cycle. In ARDS, this mode may decrease the need for sedation, increase alveolar recruitment and improve hemodynamic tolerance. The aim of this study is to assess the feasibility of a protocol combining APRV settings and sedation adaptation in order to obtain levels of spontaneous breathing between 10 and 50% of total minute ventilation.


We designed a monocentric study including 10 patients with early ARDS. We used a Dräger Evita XL ventilator. We initially used the volume-assist control (VAC) mode to set the PEEP, tidal volume and respiratory rate according to the increased recruitment strategy of the ExPress trial [1]. These settings were used to adjust the ventilator's parameters in APRV mode: low pressure at the same level as the PEEP applied in VAC, high pressure (<32 cmH2O) set to reach a tidal volume of 6 ml/kg of predicted body weight (PBW), T high between 0.8 and 1 second, T low set to reach the same respiratory rate as in VAC. Patients were initially paralyzed. Then sedation was adapted to keep RASS ≥-4 and a level of spontaneous breathing between 10 and 50% of total minute ventilation. A computer was continuously connected to the ventilator for 5 days in order to record respiratory variables.


At inclusion, baseline characteristics of the patients were the following: five men and five women, 59 years old on average (25 to 85), SAPS II score of 42 (20 to 71), PO2/FiO2 ratio of 107 (74 to 175) and respiratory system compliance (Cst,rs) of 25 ml/cmH2O (18 to 36). We did not observe any pneumothorax. Eight of patients had RASS ≥-4 during the 5 days of enrollment. From day 2, the level of spontaneous breathing ranged between 10 and 50% of total minute ventilation in eight patients. The tidal volume (spontaneous and mechanical) measured for 5 days for each patient was mainly distributed around 6 ml/kg PBW (Figure 1). The mean PO2/FiO2 ratio increased from 107 ± 29 at enrollment to 173 ± 91 at day 5 (P < 0.05).

Figure 1

Tidal volume distribution (ml/kg PBW) for 5 days for each patient.


APRV settings and the protocol for sedation used in this trial allowed to reach sufficient spontaneous breathing for the majority of the patients without any major complication and with a tidal volume below 8 ml/kg PBW. For a few patients, spontaneous breathing seems to be hard to obtain, especially within the first 2 days.


  1. 1.

    Mercat A, Richard JC, Vielle B, Expiratory Pressure (Express) Study Group, et al.: Positive end-expiratory pressure setting in adults with acute lung injury and acute respiratory distress syndrome: a randomized controlled trial. JAMA 2008, 299: 646-655. 10.1001/jama.299.6.646

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Correspondence to S Mortaza.

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Mortaza, S., Mercat, A. Feasibility of early spontaneous breathing in acute respiratory distress syndrome. Crit Care 16, P106 (2012).

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  • Tidal Volume
  • Acute Respiratory Distress Syndrome
  • Spontaneous Breathing
  • Alveolar Recruitment
  • Predicted Body Weight