Effects of conventional and closed-loop neurally adjusted ventilatory assist in intubated spinal cord injured patients

Introduction

This study aimed to evaluate the effect of high versus low tidal volumes (VT) during volume control (VC) ventilation and neurally adjusted ventilatory assist (NAVA) in spinal cord injured (SCI) patients. We hypothesized that VC with higher VT would significantly unload and deactivate the diaphragm, whereas NAVA would not.

Methods

Seven intubated C3 to C7 SCI patients (age: 28 ± 12 years) were studied. Using VC (Servo300), VT was increased progressively (not exceeding 40 cmH₂O or 2 l VT) (high volume) and then lowered until 6 ml/kg or intolerance (low volume). NAVA was then progressively adjusted targeting similar peak pressures. Finally subjects received 15 minutes each of: high VC, low VC, high NAVA, and low NAVA in randomized order.

Results

Despite comparable increases in peak airway pressure (Pmo), VT increased with VC but was unaltered with NAVA. Inspiratory and total breath durations were lower and respiratory rate higher with NAVA compared with VC during both assist levels. VC resulted in significant diaphragm unloading and deactivation whereas both were maintained during high and low NAVA. Complete diaphragm deactivation in more than 80% of breaths was observed during VC in five of the patients.

Conclusions

VC ventilation results in significant diaphragm unloading and deactivation especially at high assist levels, whereas diaphragm activation (EAdi) is maintained with NAVA.

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