Abstract
BACKGROUND:
Studies have found that increasing the respiratory frequency during mechanical ventilation does not always improve alveolar minute ventilation and may cause air-trapping.
OBJECTIVE:
To investigate the theoretical and practical basis of higher-than-normal ventilation frequencies.
METHODS:
We used an interactive mathematical model of ventilator output during pressure-control ventilation to predict the frequency at which alveolar ventilation is maximized with the lowest tidal volume (VT) for a given pressure. We then tested our predicted optimum frequencies and VT values with various lung compliances and higher-than-normal frequencies, with a lung simulator and 5 mechanical ventilators (Dräger Evita XL, Hamilton Galileo, Puritan Bennett 840, Siemens Servo 300 and Servo-i).
RESULTS:
Compliances between 10 mL/cm H2O and 42 mL/cm H2O yielded VT between 4.1 mL/kg (optimum frequency 75 cycles/min) and 6.0 mL/kg (optimum frequency 27 cycles/min). The intrinsic positive end-expiratory pressure at the optimum frequency was always less than 2 cm H2O. All the ventilators except the Hamilton Galileo had an optimum frequency near 50 cycles/min, whereas the predicted optimum frequency was 60 cycles/min.
CONCLUSIONS:
With these ventilators and pressure-control ventilation, alveolar minute ventilation can be optimized with higher-than-normal frequency and lower VT than is commonly used in patients with acute respiratory distress syndrome. We call this strategy mid-frequency ventilation.
Keywords
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