Purpose: During neurally adjusted ventilatory assist (NAVA) the ventilator is driven by the patients electrical activation of the diaphragm (EAdi), detected by a special esophageal catheter. A reliable positioning of the EAdi-catheter is mandatory to trace a representative EAdi signal. We aimed to determine whether a formula that is based on the measurement from nose to ear lobe to xiphoid process of the sternum (NEX distance) modified for EAdi-catheter placement (NEX(mod)) is sufficient for predicting the accurate catheter position.
Methods: Twenty-six patients were enrolled in this study. The optimal EAdi-catheter position (OPT) was defined by: (1) stable EAdi signal, (2) electrical activity highlighted in central leads of the catheter positioning tool, and (3) absence of p-wave in distal lead. Afterwards NEX(mod) was calculated and compared to the OPT finding.
Results: At NEX(mod) the EAdi signal was suitable for running NAVA in 18 out of 25 patients (72%). NEX(mod) was identical with OPT in four patients (16%). NAVA was possible in all patients at OPT. Median OPT position was 2 cm caudal of the NEX(mod) ranging from 3 cm too cranial to a position 12 cm too caudal (P < 0.01). In one patient excluded from further analysis EAdi-catheter placement led to the diagnosis of bilateral injury of the phrenic nerves.
Conclusions: EAdi-catheter placement based on the NEX(mod) formula allows running NAVA in about two-thirds of all patients. The additional tools provided are efficient and facilitate the correct positioning of the EAdi-catheter for neurally adjusted ventilatory assist.