High-Frequency Ventilation- Basics and Practical Applications

Appendix Case reports
0.00: Decision for HFV at peak pressures of 30 mbar and FiO 2
of 0.9..
0.15: Combining HFV and IMV, we set the MAP 5 mbar higher
than during conventional ventilation. Soon oxygen requirement
goes up. Despite 100% amplitude insufficient oscillatory
volume VTHF of about 1.2 ml/kg causes progressive
hypercapnia. Slight decrease in heart rate. Administration
of Dopamin and Dobutrex as continuous infusion.
0.30: In spite of the reduced blood pressure we turn up MAP to
19 mbar, trying to improve oxygenation. Reducing the
oscillatory frequency to 8 Hz yields higher VTHF and
DCO 2 at this elevated MAP level. Within few minutes we
observe a slight reduction in hypercapnia. Since blood
pressure has gone up a little, we continue HFV.
1.00: Further reduction of oscillatory frequency to 6 Hz again
increases VTHF and DCO 2 . As a consequence, pCO 2
values normalise.
1.30-2.00: Oxygenation is deteriorating again. Not even a longer
inspiratory time in IMV helps. We take another radiograph,
which shows an increase in local over distention. Once
more we test lung function and find that static compliance
has deteriorated, indicating increased FRC. Resistance
has further increased. Since HFV has apparently led to
a deterioration of the clinical situation, we return to conventional
ventilation.
The flow-volume curve of case 2 shows a concave deformation.
Such patients should not receive HFV because their condition is
likely to deteriorate due to airtrapping.
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