Respiratory System Compliance and Driving Pressure during spontaneous assisted breathing: association with clinical outcomes
CCCF ePoster library. Grassi A. Nov 7, 2018; 234660; 139
Dr. Alice Grassi
Dr. Alice Grassi
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Introduction: Airway Driving Pressure (DP) and Respiratory System Compliance (Crs) are known to correlate with patients’ outcome during Controlled Mechanical Ventilation (CMV)1. Moreover, Crs is related to aerated lung volume during CMV2. Monitoring patient respiratory mechanics during Assisted Mechanical Ventilation is more challenging but could help avoiding lung injury. The measurement of DP and Crs during Pressure Support Ventilation (PSV) is feasible3,4 and routinely performed in our clinical practice but correlation with lung volumes and clinical outcomes has not been investigated yet.

Objective: We aimed to understand the reliability of respiratory system mechanical properties (DP and Crs) measured during PSV and their association with aerated lung volume and with clinical outcomes.

Methods: We conducted a retrospective study on patients undergoing invasive mechanical ventilation for at least 5 days. We included subjects affected by ARDS, who spent >24 hours in CMV followed by >24 hours in PSV. We collected from the Electronic Medical record data of the first and last CMV day and averaged the first three days of PSV. If the patient underwent a CT scan during the PSV period, we analyzed the images offline to quantify the aerated lung volume. We analyzed a) the correlation between measurements taken during CMV and PSV b) the association between DP, Crs and Peak pressure (i.e. PSV level + PEEP) values measured during PSV and mortality in ICU and c) the correlation between aerated lung volume measured on CT scan images and Crs measured during PSV. Data are expressed as median[IQR]. We compared variables between survivors and non survivors by Mann-Whitney test and we compared mortality rates through quartiles of DP, Crs and Peak pressure using X2 tests.

Results: We screened 360 patients, 167 of which met the inclusion criteria. Crs measured during the last day of CMV and during the first three days of PSV were correlated  (R2=0.63). Crs and DP collected during PSV were significantly different between survivors and non survivors (Crs 51.1[42.2-61.1] vs 40.1[29.8-50] ml/cmH2O, DP 10[8.3-11.3] vs 11.4[9-14] cmH2O during PSV in survivors vs non survivors, p<0.01 for both comparisons). When DP and Crs were partitioned into quartiles, increasing DP and decreasing Crs were correlated with increasing mortality (Fig.1, p=0.012 for DP, p=0.385 for Ppeak, p=0.0033 for Crs). No correlation with mortality was found for Peak Pressure values. Aerated lung volume as measured on CT scans images correlated with Crs (R2 = 0,47, Fig. 2)

Conclusions: The measurement of DP and Crs during PSV is feasible and clinically meaningful. Both DP and Compliance of the respiratory system are strongly associated with mortality in patients undergoing spontaneous assisted breathing. Crs measured during PSV correlates with aerated lung volume.

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