Inspiratory efforts below a certain threshold are difficult to evaluate in a hospital setting and are likely not high enough to prevent muscle wasting. Flow index, generated from examining the inspiratory part of the flow-time waveform, is a new non-invasive metric for gauging the intensity of an individual’s efforts to breathe in. The main purpose of this research was to verify the efficacy of the flow index in identifying instances of minimal inspiratory effort from afar. From a previously published study involving 100 patients with traumatic brain injuries who were receiving pressure support breathing, researchers were able to gather data sets containing flow, airway pressure, and esophageal pressure (Pes)-time waveforms. Offline analysis of waveform data was performed. Work of breathing (WOB) 4less than 0.3 J/L, Pes-time product (PTPes)per minute less than 50 cmH2O•s/min, or inspiratory muscle pressure (Pmus) less than 5 cmH2O were all considered modest inspiratory efforts, with the qualifier “or incidence of ineffective effort more than 10%” added for each. An established method for determining the flow index was used. Effort characteristics resulting from the Pes were studied in relation to the flow index. Investigators looked at how well the flow index can diagnose low effort. (Pearson’s correlation coefficients ranged from 0.546 to 0.634, P < 0.001)., indicating a moderate relationship between the flow index and WOB, Pmus, and PTPes per breath and per minute. Using the WOB, PTPes/min, and Pmus criteria, 62%, 51%, and 55% of patients were diagnosed with modest inspiratory effort, respectively. The area under the receiver operating characteristic curve for the flow index to diagnose low effort was 0.88, 0.81, and 0.88 for the 3 respective definitions. By using the cutoff value of flow index less than 2.1, the diagnostic performance for the 3 definitions showed a sensitivity of 0.95–0.96, a specificity of 0.57–0.71, a positive predictive value of 0.70–0.84, and a negative predictive value of 0.90–0.93.

Source: annalsofintensivecare.springeropen.com/articles/10.1186/s13613-022-01063-z