Purpose: Neurally adjusted ventilatory assist (NAVA) relies on the patient's electrical activity of the diaphragm (EAdi) for actuating the ventilator. Thus a reliable positioning of the oesophageal EAdi catheter is mandatory. We aimed to evaluate the effects of body position (BP), positive end-expiratory pressure (PEEP) and intra-abdominal pressure (IAP) on catheter positioning.
Methods: Twenty-one patients were enrolled in this study. In six different situations [supine or 45° head of bed elevation (HBE) at PEEP 5 and 15 cmH(2)O; left lateral anti-decubitus at PEEP 5 cmH(2)O; supine at PEEP 5 cmH(2)O with abdominal surgical belt (ASB)] the catheter position was evaluated for the stability of the EAdi signal and information provided by a catheter positioning tool (highlighted electrical activity in central leads, absence of p waves in the distal lead).
Results: With an optimal catheter position EAdi signals were stable for all tested situations. During "45° PEEP 15" and "supine PEEP 15" absence of p waves in the distal lead revealed a difference compared with "supine PEEP 5" (p = 0.03), suggesting a caudal shift of the diaphragm relative to the oesophagus. The analysis of the highlighted electrical activity in the central leads supports this finding, revealing an influence of PEEP, BP and IAP on EAdi catheter position (p < 0.01).
Conclusion: PEEP, BP and IAP may affect the EAdi catheter position, although not compromising a stable signal. Additional information as provided by the catheter positioning tool is needed to ensure an optimal EAdi catheter position.