Study question: To determine whether a positive
end-expiratory pressure (PEEP) level equivalent to the lower inflection
point (LIP) could be identified by evaluation of the airway pressure,
flow (V̇), and volume vs time waveforms during partial liquid
Design: Prospective application of
PEEP during PLV in a healthy animal model.
University hospital animal laboratory.
Five healthy sheep weighing 30 kg each.
The sequential application of 0 to 20 cm H2O PEEP in 2.5-cm
H2O steps during PLV with both pressure and volume
Measurements: Analysis of the pressure,
volume, and V̇ waveforms as PEEP is sequentially increased.
Results: At 0 cm H2O PEEP, Vt was
markedly reduced compared with PEEP Vt at ≥ 7.5 cm
H2O (p < 0.05) in pressure control ventilation (PCV),
and peak inspiratory pressure minus PEEP was markedly increased
compared with PEEP at ≥ 5.0 cm H2O (p < 0.05) in
volume control ventilation. At 10 cm H2O PEEP, all
waveforms began to stabilize, and no significant differences in any
variable assessed were measured at > 12.5 cm H2O
Conclusions: The application of PEEP during PLV
markedly alters airway waveforms. Low PEEP decreases Vt in
PCV and increases airway pressure in VCV. The PEEP level equal to the
LIP during PLV can be grossly estimated from airway waveforms. PEEP at≥
10 cm H2O is needed to normalize gas delivery to
functional residual capacity in the uninjured lung that is partially
filled with perfluorocarbon.