Journal of Capital Medical University ›› 2024, Vol. 45 ›› Issue (2): 194-200.doi: 10.3969/j.issn.1006-7795.2024.02.004

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The feasibility and validity of inspiratory muscle pressure index to assess inspiratory effort

Song Dejing1,3#, Gao Ran1#, Yang Yanlin1, Zhang Linlin1, Zhou Jianxin2*   

  1. 1.Department of Intensive Care Unit, Beijing Tiantan Hospital, Capital Medical University, Beijing 100070, China;2.Department of Intensive Care Unit, Beijing Shijitan Hospital, Capital Medical University, Beijing 100038, China;3.Department of Intensive Care Unit, China-Japan Friendship Hospital, Beijing 100029, China
  • Received:2023-12-19 Online:2024-04-21 Published:2024-04-25
  • Supported by:
    This study was supported by Capital's Funds for Health Improvement and Research Medical Development Fund (2024-1-2081), Major Epidemic Prevention and Control  of Key Clinical Specialty Projects of Beijing (2022) (2022-ZX-007) .

Abstract: Objective  To explore the correlation of simple measurement of inspiratory muscle pressure index from the ventilator (PMIvent) and reference measurement of inspiratory muscle pressure index on experimental condition (PMIref), the relationship between PMIvent and inspiratory effort, and further to determine the clinical feasibility and validity of PMI for assessing inspiratory effort during pressure support ventilation (PSV).  Methods  Adult acute respiratory failure patients undergoing mechanical ventilation were screened daily and enrolled 24 h after switching to PSV mode. Baseline ventilators were set according to the principle of keeping tidal volume/ predicted body weight(VT/PBW) at 6-8 mL/kg and respiratory rate (RR) at 20-30 breaths/min and the decision of the responsible ICU physician. A downward support pressure ( PS )titration was conducted from 20 cmH2O to 2 cmH2O. Three end-inspiratory holdings (EIO) and three end-expiratory holdings (EEO) were performed. PMIvent was calculated as the difference between plateau pressure (Pplat) within 2 s after EIO and the airway peak pressure (Ppeak) at EIO. PMIref was calculated as the difference between Pplat at one cardiac cycle after EIO and Ppeak at EIO. Flow, airway pressure (Paw), and esophageal pressure (Pes) signals were displayed continuously and saved. PMIref, PMIvent and esophageal pressure time product per breath (PTPes) were measured. PTPes per minute was calculated as the product of PTPes and RR. The “normal” range of PTPes per minute was defined as 50 to 200 cmH2O·s·min-1. The accuracy of PMIvent compared to PMIref was assessed with a Bland-Altman plot. The correlation between PMI and inspiratory effort was evaluated as the coefficient of determination (R2). The ability of PMI to detect high/low effort was assessed using the area under the receiver operating characteristics curve (ROC AUC). The optimal cut-off values were selected based on the Youden index. Results  The accuracy and precision of PMIvent compared to PMIref showed a low bias (0.18) with smaller 95% limits of agreements (-0.44,0.80). PMIref was significantly related to the PTPes per minute (between-patients R2=0.61, within-patients R2=0.80, respectively). PMIvent was also related to the PTPes per minute (between-patients R2=0.62, within-patients R2=0.81). For a cut-off PTPes<50 cmH2O·s·min-1, PMIvent showed an ROC AUC of 0.93 [0.89,0.96], and the best threshold was -0.77 cmH2O. Conclusion  PMIvent can effectively replace PMIref. Like PMIref, PMIvent was significantly related to inspiratory effort and had the potential value to predict low inspiratory effort. 

Key words: mechanical ventilation, inspiratory effort, pressure muscle index, esophageal pressure time product

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