Optimal mean airway pressure during high-frequency oscillatory ventilation determined by measurement of respiratory system reactance

In high-frequency oscillatory ventilation (HFOV), an adequate mean airway pressure is crucial for successful ventilation and optimal gas exchange, but air trapping cannot be detected by the usual measurement at the y piece. Intratracheal pressures produced by the high-frequency oscillators HFV-Infantstar (IS), Babylog 8000 (BL), and the SensorMedics 3100A (SM) [the latter with either 30% (SM30) or 50% (SM50) inspiratory time] were investigated in four anesthetized tracheotomized female piglets that were 1 day old and weighed 1.6–1.9 kg (mean 1.76 kg). The endotracheal tube was repeatedly clamped while the piglets were ventilated with an oscillation frequency of 10 Hz, and the airway pressure distal of the clamp was recorded as a measure of average intrapulmonary pressure during oscillation. Clamping resulted in a significant decrease of mean airway pressure when the piglets were ventilated with SM30(−0.86 cmH2O), BL (−0.66 cmH2O), and IS (−0.71 cmH2O), but airway pressure increased by a mean of 0.76 cmH2O with SM50. Intratracheal pressure, when measured by a catheter pressure transducer at various oscillation frequencies, was lower than at the y piece by 0.4–0.9 cmH2O (SM30), 0.3–3 cmH2O (BL), and 1–4.7 cmH2O (IS) but was 0.4–0.7 cmH2O higher with SM50. We conclude that the inspiratory-to-expiratory time (Ti/Te) ratio influences the intratracheal and intrapulmonary pressures in HFOV and may sustain a mean pressure gradient between the y piece and the trachea. A Ti/Te ratio < 1:1 may be useful to avoid air trapping when HFOV is used.

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Setting Mean Airway Pressure during High-frequency Oscillatory Ventilation According to the Static Pressure–Volume Curve in Surfactant-deficient Lung Injury

Anesthesiology ◽

10.1097/00000542-200312000-00012 ◽

2003 ◽

Vol 99 (6) ◽

pp. 1313-1322 ◽

Cited By ~ 24

Author(s):

Thomas Luecke ◽

Juergen P. Meinhardt ◽

Peter Herrmann ◽

Gerald Weisser ◽

Paolo Pelosi ◽

...

Keyword(s):

Computed Tomography ◽

Lung Volume ◽

High Frequency ◽

Airway Pressure ◽

Static Pressure ◽

High Frequency Oscillatory Ventilation ◽

Mean Airway Pressure ◽

Oscillatory Ventilation ◽

Hemodynamic Variables ◽

High Frequency Oscillatory

Background Numerous studies suggest setting positive end-expiratory pressure during conventional ventilation according to the static pressure-volume (P-V) curve, whereas data on how to adjust mean airway pressure (P(aw)) during high-frequency oscillatory ventilation (HFOV) are still scarce. The aims of the current study were to (1) examine the respiratory and hemodynamic effects of setting P(aw) during HFOV according to the static P-V curve, (2) assess the effect of increasing and decreasing P(aw) on slice volumes and aeration patterns at the lung apex and base using computed tomography, and (3) study the suitability of the P-V curve to set P(aw) by comparing computed tomography findings during HFOV with those obtained during recording of the static P-V curve at comparable pressures. Methods Saline lung lavage was performed in seven adult pigs. P-V curves were obtained with computed tomography scanning at each volume step at the lung apex and base. The lower inflection point (Pflex) was determined, and HFOV was started with P(aw) set at Pflex. The pigs were provided five 1-h cycles of HFOV. P(aw), first set at Pflex, was increased to 1.5 times Pflex (termed 1.5 Pflex(inc)) and 2 Pflex and decreased thereafter to 1.5 times Pflex and Pflex (termed 1.5 Pflex(dec) and Pflex(dec)). Hourly measurements of respiratory and hemodynamic variables as well as computed tomography scans at the apex and base were made. Results High-frequency oscillatory ventilation at a P(aw) of 1.5 Pflex(inc) reestablished preinjury arterial oxygen tension values. Further increase in P(aw) did not change oxygenation, but it decreased oxygen delivery as a result of decreased cardiac output. No differences in respiratory or hemodynamic variables were observed when comparing HFOV at corresponding P(aw) during increasing and decreasing P(aw). Variation in total slice lung volume (TLVs) was far less than expected from the static P-V curve. Overdistended lung volume was constant and less than 3% of TLVs. TLVs values during HFOV at Pflex, 1.5 Pflex(inc), and 2 Pflex were significantly greater than TLVs values at corresponding tracheal pressures on the inflation limb of the static P-V curve and located near the deflation limb. In contrast, TLVs values during HFOV at decreasing P(aw) (i.e., 1.5 Pflex(dec) and Pflex(dec)) were not significantly greater than corresponding TLV on the deflation limb of the static P-V curves. The marked hysteresis observed during static P-V curve recordings was absent during HFOV. Conclusions High-frequency oscillatory ventilation using P(aw) set according to a static P-V curve results in effective lung recruitment, and slice lung volumes during HFOV are equal to those from the deflation limb of the static P-V curve at equivalent pressures.

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