Relation between peak and integral of the diaphragm electromyographic activity at different levels of support during weaning from mechanical ventilation : a physiologic study

Purpose: To investigate the relationship between peak (EAdipeak) and area under the curve (EAdiAUC) of diaphragm electrical activity, and to evaluate the validity of their ratio (P/I index) as a measure of the imbalance between drive and sustainability of effort demand at different support levels. Materials: Prospective physiological study on 18 ready-to-wean patients ventilated with neurally adjusted ventilatory assist (NAVA) undergoing 2 levels of NAVA (NAVA100%and NAVA50%) followed by a weaning trial with continuous positive airway pressure, according to which patients were classified as success or failure. Tidal volume (VT), respiratory rate, EAdipeak, EAdiAUC, rapid shallow breathing index (respiratory rate/VT), neuroventilatory index (VT/EAdipeak), and P/I index were obtained at the end of each step. Results: The slopes of regression line between EAdipeakand EAdiAUC(a mathematical equivalent of P/I index) and P/I index were significantly higher in failures. At variance with other variables, P/I index did not vary with level of support. P/I index was inversely correlated with inspiratory time at all support levels. Conclusions: The relationship between EAdipeakand EAdiAUCand the P/I index may give important information on the balance between respiratory drive and inspiratory demand sustainability.