Feasibility of Measuring Driving Pressure and Patient Effort in Assisted Modes of Ventilation: An Observational Study

Abstract Rationale Driving pressure (DP) has established prognostic significance in patients receiving controlled modes of ventilation (CMV). During assisted ventilation, DP is influenced by negative pressure generated through patient effort and can be measured using an end-inspiratory hold maneuver. However, the feasibility of obtaining acceptable measurements in lightly sedated or awake patients is uncertain. We aimed to determine if measuring driving pressure and estimating patient effort was feasible in patients receiving pressure support ventilation (PSV). Methods We conducted a prospective observational cohort study in three adult intensive care units at McMaster University (Hamilton, Canada). We included adult patients who were mechanically ventilated on CMV and switched to PSV within 48 hours. End-inspiratory holds were conducted to obtain DP (plateau pressure – positive end-expiratory pressure) and pressure muscle index (PMI, peak airway pressure – plateau pressure) which is a marker of patient effort. The primary outcome was feasibility rate, determined by the percentage of acceptable inspiratory holds (duration of occlusion over 2 seconds, airflow equal to 0 ml/sec during the hold, absence of visible patient effort). Sedation was assessed using the Richmond Agitation Sedation Scale (RASS). We compared driving pressure, PMI and P0.1 between survivors and non-survivors using t-tests (p-value of 0.05 for statistical significance). Results In total, we enrolled 100 patients and performed 302 end-inspiratory holds. Of these, 29 were deemed unacceptable, resulting in a 90% feasibility rate. The most common reasons for an unacceptable measurement were tachypnea (respiratory rate >30) (11, 38%) or agitation (RASS ≥3+)(18, 62%). When comparing 30-day survivors (n=71) and non-survivors (n=26), there were no important differences in DP and PMI (Table). Average daily RASS was -1 [-2,0]. Conclusions Measuring driving pressure and patient effort using PMI in those receiving assisted ventilation is feasible and may provide insight into respiratory system compliance (as determined by driving pressure) and patient effort. Measurements are straightforward, easy to learn, take seconds and can be conducted at the bedside without complication, even in awake patients who are not agitated or tachypneic (respiratory rate >30). Further studies are needed to determine if this information can be used to guide clinical decision-making and weaning efforts. Funding source: Physician Services Incorporated (PSI)

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