Pulse and systolic pressure variation assessment in partially assisted ventilatory support

Objective: The use of pulse pressure variation (PPV) and systolic pressure variation (SPV) is possible during controlled ventilation (MV). Even in acute respiratory failure, controlled MV tends to be replaced by assisted ventilatory support. We tested if PPV and SPV during flow triggered synchronized intermittent mechanical ventilation (SIMV) could be as accurate as in controlled MV. Methods: Prospective case-controlled study. Thirty patients who met criteria of weaning from controlled MV. Twenty minutes pressure support ventilation with 3 min- flow triggered SIMV breathes (10 ml kg-1) T1, then three consecutive breaths in controlled MV (respiratory rate 12 min-1,10 ml kg-1) T2. PPV and SPV were measured in T1 and T2. Correlation and Bland-Altman analysis were used to compare respective values of PPV and SPV in the two modes of ventilation. Results: Significant correlations were found between dynamic indices in SIMV during pressure support ventilation and those in controlled MV mode. The mean differences between two measurements were: PPV 0.6 ± 2.8% (limit of agreement: -5.0 and 6.2), SPV 0.5 ± 2.3 mmHg (limit of agreement: -4.0 and 5.1). Conclusions: PPV and SPV measured during SIMV fitted with the findings in controlled MV. Dynamic indexes could be accurately monitored in patients breathing with assisted respiratory assistance adding an imposed large enough SIMV breath.