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Effects of different spontaneous breathing modes on respiratory mechanics and gas exchange

Objective

In patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS) the use of spontaneous breathing modes in mechanical ventilation can be beneficial. Nevertheless the opportunity to combine different forms of assisted ventilation is not sufficiently investigated. We evaluated the effects of the combination of different modes of spontaneous ventilation on respiratory mechanics and gas exchange in patients with ALI or ARDS.

Design

A prospective, interventional study.

Setting

ICU of a university hospital.

Patients

Seven patients who were ventilated mechanically for at least 24 hours due to acute respiratory insufficiency.

Methods

Each patient was ventilated using one of four ventilation modes for a time period of 45 min, followed by a 15 min equilibration period. All four respiratory settings were applied in randomly assigned order in every patient. A: biphasic positive airway pressure (BIPAP); B: BIPAP in combination with pressure support (BIPAP + PSV); C: BIPAP in combination with automatic tube compensation (BIPAP + ATC); D: pressure support ventilation in combination with ATC (PSV + ATC). In every ventilator setting all patients had spontaneous breathing efforts in at least 30% based upon minute ventilation (VE). The settings were adjusted to achieve a tidal volume (VT) of 6–8 ml/kg body weight. Hemodynamic data were obtained every 15 min and at the end of each period blood gas analyses were obtained. The primary endpoints were the patient's work of breathing obtained by the Bicore CP-100 pulmonary monitor (Bicore, Irvine, CA, USA).

Results

The mean tidal volume was 6.51 ± 0.36 ml/kg body weight. In combination with automatic tube compensation, inspiratory pressure support obtained the highest work of breathing in all tested modes (A: 0.80 ± 0.15 J/l vs B: 0.86 ± 0.17 J/l vs C: 0.96 ± 0.19 J/l vs D: 1.47 ± 0.22 J/l). Hemodynamic parameters and indices of pulmonary gas exchange did not differ between the tested modes.

Conclusions

Our results show that PSV in combination with ATC obtained the highest work of breathing. A possible reason is that PSV assists every single breath and acts more like controlled ventilation than an assisting mode. The combination of different modes of spontaneous breathing has no benefit on the work of breathing the patient had to obtain when BIPAP is used as the primary ventilator mode.

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Reindl, M., Schaffrath, E., Max, M. et al. Effects of different spontaneous breathing modes on respiratory mechanics and gas exchange. Crit Care 10, P34 (2006). https://doi.org/10.1186/cc4381

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Keywords

  • Tidal Volume
  • Acute Lung Injury
  • Acute Respiratory Distress Syndrome
  • Pressure Support
  • Spontaneous Breathing