Comparison of maximal inspiratory pressure to resistive breathing for weaning prediction

Abstract

Introduction: The effect of MIP on extravascular lung water generation (EVLW) is not known. Our aim was to compare a resistive breathing trial (RBT) to MIP in terms of EVLW generation and in predicting the weaning outcome.

Methods: In patients undergoing a spontaneous breathing trial (SBT) for the first time we compared the EVLW generated, using lung ultrasound (B-lines), during MIP to SBT and RBT; MIP, airway pressure swings during RBT (ΔPaw_RBT) and its ratio to rapid shallow breathing index during RBT (ΔPaw/RSBI)_RBT were assessed as indices of weaning prediction. Additionally, we assessed the relationship of MIP, ΔPaw_RBT and (ΔPaw/RSBI)_RBT to esophageal (Pes) and transdiaphragmatic pressure (Pdi) and the pressure-time product of the Pes (PTPes). Weaning failure was defined as SBT failure or need for reintubation at 48 h.

Measurement and main results: Thirty-three patients were enrolled. B-lines, heart rate and blood pressure were higher during MIP compared to RBT (p < 0.001). ΔPaw_RBT, (ΔPaw/RSBI)_RBT and MIP were higher in patients succeeding weaning compared to those who failed [19.53 cmH₂O (±11.91) vs 10.77 cmH₂O (±8.94), p = 0.027], [0.16 cmH₂O·L·min⁻¹ (0.16) vs 0.05 cmH₂O·L·min⁻¹ (0.03), p < 0.001)], [41.39 cmH₂O (14.59) vs 16.34 cmH₂O (20.3), p = 0.002]. ROC analysis showed no difference between MIP and ΔPaw_RBT or (ΔPaw/RSBI)_RBT in predicting weaning outcome; ΔPaw_RBT and (ΔPaw/RSBI)_RBT correlated with Pes, Pdi and PTPes (p < 0.05).

Conclusions: (ΔPaw/RSBI)_RBT predicted weaning outcome with similar accuracy to MIP and was associated with less B-lines, HR and BP alterations; RBT-derived airway pressures are a promising novel method for weaning outcome prediction and respiratory muscle strength assessment.

Keywords: Esophageal pressure; MIP; Resistive breathing; Ultrasound; Weaning.