Neurally adjusted ventilatory assist improves patient-ventilator synchrony during prophylactic helmet ventilation following aortic surgery

Abstract

IntroductionDuring postoperative non-invasive ventilation (NIV), following abdominal aortic surgery, leaks and diaphragmatic dysfunction jeopardize patient-ventilator interaction. We hypothesized that neurally adjusted ventilatory assist (NAVA) would be efficient to perform NIV with a helmet, and would reduce triggering and cycling-off delays as well as major patient-ventilator asynchronies compared to pressure support ventilation (PSV). MethodsNine postoperative patients receiving NIV with a helmet following abdominal aortic surgery were included. After optimization of ventilator settings, 15-min recording were performed with PSV (H-PSV) and NAVA mode (H-NAVA) in a non-random order. Breathing pattern descriptors, diaphragm electrical activity, leak volume, inspiratory trigger delay and cycling-off delay and the five main asynchronies were quantified. Asynchrony index (AI) and asynchrony index influenced by leaks (AILEAKS) were computed. Data is displayed as a median [25–75 interquartiles]. ResultsTrigger delays were lower with H-NAVA than with H-PSV (respectively 143 [54; 244] and 804 [406; 906] ms, P=0.02), as were the cycling-off delays (respectively −702 [−780; −534] and 437 [176; 695] ms, P=0.004). Although it had no effect on AI, H-NAVA decreased AILEAKS (5 [2; 10] vs. 16 [8; 28] %, P=0.004), mostly due to a drastic reduction of the prevalence of ineffective triggering (0.6 [0.1; 1.15] vs. 1.7 [1.1; 4.5] min−1, P=0.009). Tidal volumes and ventilatory command remained unchanged, but peak pressure level was lower with the H-NAVA than with H-PSV (16 [15–19] vs. 22 [20; 23] cmH2O, P=0.004). ConclusionNAVA mode is sensitive enough to ensure ventilation despite postoperative diaphragmatic dysfunction. In combination with a helmet, NAVA improves patient-ventilator interaction during prophylactic postoperative NIV. The impact on patient outcome remains yet to be determined.