ECLS for Patient Ventilator Synchrony?

Extracorporeal Cardiopulmonary Life Support. Image from MAQUET 

Introduction

Promoting patient  safety and comfort are two main goals when utilizing mechanical ventilation. In patients with severe lung failure maintaining both lung protective goals and patient comfort is a difficult task. One can provide safety by minimizing the set tidal volume to 4-6 ml/kg/IDBW however this leads to flow asynchronies in the patient who has a high inspiratory drive. One can utilize pressure control ventilation to prevent these flow asynchronies conversely this most likely results in tidal volumes greater than lung protective goals. In these patients it is very difficult to balance these two goals of mechanical ventilation and patient comfort is usually sacrificed, or is  accomplished with high levels of sedation and sometimes neuromuscluar blocking agents. 

Increasing sedation and administering neuromuscular blocking agents increases the risk for ventilator induced diaphragmatic dysfunction (VIDD), increased length of stay, and mortality. So it would be ideal to allow for both lung protection and patient comfort (ventilator synchrony) with minimal sedation use.

In the below summarized abstract [1] researchers couple Extracorporeal Cardiopulmonary Life Support (ECLS) with Neurally Adjusted Ventilatory (NAVA) Assist to balance lung protection and patient comfort with little sedation use. 

Overview

This study aimed to measure the physiologic ventilatory response in patients with severe lung failure treated with ECMO and NAVA. The hypothesis was that the combination of both methods could automatically provide protective ventilation with optimized blood gases. A case series of six patients treated with ECMO for severe lung failure was reported. In the recovery phase of the disease, patients were ventilated with NAVA and ventilatory response and gas exchange parameters were measured under different sweep gas flows and temporarily inactivated ECMO.

Results

Tidal volumes on ECMO ranged between 2ml/kg and 5ml/kg of expected body weight and increased up to 8ml/kg with inactivated ECMO. Peak inspiratory pressure reached 19–29 cmH₂O with active, and 21–45 cmH₂O with inactivated ECMO. Ventilatory response to decreased sweep gas flow was rapid, and patients immediately regulated PaCO₂ closely towards a physiological pH value. An increase in minute ventilation was a result of intensified breathing frequency and tidal volumes.  Additionally, protective ventilation was only stopped if pH control was not achieved.

Conclusion

Response to decreased ECMO sweep gas flow was rapid with NAVA. Additionally, patients immediately regulated PaCO₂ closely towards a physiological pH value. Therefore, the combination of NAVA and ECMO may permit closed-loop ventilation with automated protective ventilation.

After Thought

Combining these two technologies provided a lung protective therapy which provided both patient safety and promoted patient comfort. This technique also allowed for the patient to spontaneous breathe decreasing the risk for VIDD. 
 The therapy describe above has been termed "pump assisted lung protection" (PALP) or low flow CO2 removal. 

[1]. Karagiannidis, C., Lubnow, M., Philipp, A., Riegger, G. A. J., Schmid, C., Pfeifer, M., & Mueller, T., (2010). Autoregulation of ventilation with neutrally adjusted ventilatory assist on extracorporeal lung support. Intensive Care Medicine, 36(12), 2038-2044.