Flow Index accurately identifies breaths with low or high inspiratory effort during pressure support ventilation

Gianni Ciabatti,Francesco Murgolo,Alessia Giovannini,Federica Fusina,Rossella Di Mussi,Maria Elena Franceschetti,Valeria Lippolis,Luigi Pisani,Salvatore Grasso,Antonio Rosano,Filippo Albani,Giuseppe Natalini

doi:10.1186/s13054-021-03855-4

Abstract

BackgroundFlow Index, a numerical expression of the shape of the inspiratory flow-time waveform recorded during pressure support ventilation, is associated with patient inspiratory effort. The aim of this study was to assess the accuracy of Flow Index in detecting high or low inspiratory effort during pressure support ventilation and to establish cutoff values for the Flow index to identify these conditions. The secondary aim was to compare the performance of Flow index,of breathing pattern parameters and of airway occlusion pressure (P0.1) in detecting high or low inspiratory effort during pressure support ventilation.MethodsData from 24 subjects was included in the analysis, accounting for a total of 702 breaths. Breaths with high inspiratory effort were defined by a pressure developed by inspiratory muscles (Pmusc) greater than 10 cmH2O while breaths with low inspiratory effort were defined by a Pmusc lower than 5 cmH2O. The areas under the receiver operating characteristic curves of Flow Index and respiratory rate, tidal volume,respiratory rate over tidal volume and P0.1 were analyzed and compared to identify breaths with low or high inspiratory effort.ResultsPmusc, P0.1, Pressure Time Product and Flow Index differed between breaths with high, low and intermediate inspiratory effort, while RR, RR/VT and VT/kg of IBW did not differ in a statistically significant way. A Flow index higher than 4.5 identified breaths with high inspiratory effort [AUC 0.89 (CI 95% 0.85–0.93)], a Flow Index lower than 2.6 identified breaths with low inspiratory effort [AUC 0.80 (CI 95% 0.76–0.83)].ConclusionsFlow Index is accurate in detecting high and low spontaneous inspiratory effort during pressure support ventilation.

Highlights

Flow Index, a numerical expression of the shape of the inspiratory flow-time waveform recorded during pressure support ventilation, is associated with patient inspiratory effort
Data was collected in patients admitted to the Intensive Care Unit (ICU) of Fondazione Poliambulanza, Brescia, Italy, who met all of the following criteria: age > 18 years, dependence on invasive mechanical ventilation, being in pressure support ventilation (PSV), having an esophageal balloon catheter already in place
Protocol In order to explore the whole spectrum of patient effort, three pressure support (PS) levels were applied to each patient: (1) the PS level at enrollment was defined as basal, (2) the lowest tolerated PS level without dyspnea while keeping the ratio between respiratory rate and tidal volume (RR/Tidal volume (VT)) < 100 min−1 L−1 was defined as low, and (3) the maximal tolerated PS level to achieve near relaxation was defined as high

Summary

Introduction

Flow Index, a numerical expression of the shape of the inspiratory flow-time waveform recorded during pressure support ventilation, is associated with patient inspiratory effort. Monitoring the esophageal pressure (Pes), which is the gold standard to evaluate the pressure developed by the respiratory muscles (Pmusc), is relatively invasive and requires considerable technical expertise in order to correctly interpret the Pes waveforms [5, 6]. Breathing pattern parameters, such as tidal volume and respiratory rate, or the rapid shallow breathing index (RR/VT) [7] are used as surrogates to infer patient effort, but they may be inaccurate and misleading [8]. Concerning ΔPocc, it is useful only in evaluating high patient effort, it requires active intervention from the attending physician, it is not continuous and not all ventilators allow to perform occlusions during PSV [12, 13]

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