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Automated mechanical ventilation based on the ARDS Network protocol in porcine acute lung injury

Introduction

The results of the ARDS Network trial [1] demonstrated a significant reduction of mortality by using a mechanical ventilation protocol with tidal volumes (VT) of 6 ml/kg predicated body weight. Additionally, a computer-driven weaning protocol was successfully performed and a reduction of mechanical ventilation duration could be demonstrated [2]. The implementation of the ARDS Network protocol in routine ICU practice remains modest [3]. A possible reason is the increased organisational and temporal burden. An automated execution of the protocol would help to propagate its day-to-day use. To test the ability to automate such a complex protocol, we designed a pilot study in porcine acute lung injury using an experimental medical expert system capable of continuously controlling respiratory parameters and global as well as regional ventilation with electrical impedance tomography (EIT).

Methods

After induction of saline lavage-induced lung injury in pigs (n = 3), automated mechanical ventilation was initiated. The medical expert system used a closed-loop fuzzy controller with a rule base of if/then rules based on the ARDS Network protocol reference card. The protocol's algorithmic rules and therapeutic goals (oxygenation, pH, I:E, VT) were continuously controlled and ventilatory settings electronically adjusted accordingly. The medical attendant personnel was constantly informed with status messages about the decisions made. During the trial, all measurements were made using an online blood gas monitor (TrendCare Satellite; Diametrics Medical Inc., UK), a monitor for hemodynamic parameters (Sirecust 1281; Siemens, Germany), a capnograph (CO2SMO+; Respironics, Inc., USA), and an EIT prototype system (EIT Evaluation Kit; Draeger Medical, Germany). Subjects were ventilated for between 40 and 90 minutes.

Results

The computer-driven ventilator settings could stabilise the ventilation of the lung-injured subject in the predefined thresholds. Compared with the beginning of the study, a reduction in ventilation pressure and PaCO2 could be observed. Despite the initial low PaO2/FiO2 ratio (<200 mmHg) of the subjects, FiO2 could be decreased by the system in the given time without penetrating the thresholds for oxygenation.

Conclusion

Robust execution of an automated ARDS Network protocol with an electronically controlled ventilator is possible and leads to pulmonary stabilisation. Further trials have to be undertaken before this successful approach can be realised in ARDS patients.

References

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    Young , et al.: Crit Care Med. 2004, 32: 1260-1265. 10.1097/01.CCM.0000127784.54727.56

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Meier, T., Luepschen, H., Großherr, M. et al. Automated mechanical ventilation based on the ARDS Network protocol in porcine acute lung injury. Crit Care 11, P185 (2007). https://doi.org/10.1186/cc5345

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Keywords

  • Fuzzy Controller
  • Electrical Impedance Tomography
  • Regional Ventilation
  • Algorithmic Rule
  • Mechanical Ventilation Duration