The Science Journal of the American Association for Respiratory Care

1998 OPEN FORUM Abstracts

THE RELATIONSHIP BETWEEN VENTILATORY MECHANICS AND THE LOWER INFLECTION POINT OF THE P-V CURVE DURING PARTIAL LIQUID VENTILATION.

Gabriela Ferreyra PT, Sven Goddon MD, Yuji Fujino MD, Robert M. Kacmarek PhD RRT. Anaesthesia & Respiratory Care, Massachusetts General Hospital and Harvard Medical School, Boston, MA.

Introduction: Partial Liquid Ventilation (PLV) with Perflubron (PFB) has previously been shown to be an effective way of improving gas exchange in models of lung injury and in infants with IRDS. However little is known about how to approach optimal ventilator settings during PLV. We have previously shown that PEEP set above the lower inflection point (LIP) markedly improves gas exchange during PLV (1). The goal of this study was to investigate whether a change in ventilatory mechanics (VM) could be used to determine the LIP during PLV.

Methods: Determination of static P-V curves using a super-syringe were performed before and after filling the lungs with 30 ml/kg PFB in 5 healthy, anaesthetized sheep (27.5±3 kg). Measurements were made in increments of 100 ml, inflating the lungs to a maximal airway pressure of 50 cm H_{2}O. A blinded investigator identified LIP. Each sheep was ventilated with both Pressure Control Ventilation (PCV) and Volume Control Ventilation (VCV) with increasing levels of PEEP in increments of 2.5 cm H_{2}O at an I:E ratio of 1:1. In PCV driving pressure was set to achieve a V_{t} of 10 ml/kg at PEEP 10, in VCV V_{t} was set at 10 ml/kg. Airway pressure and flow waveforms at the opening of the ETT were recorded and compared.

Results: Before filling no LIP could be identified. After filling LIP was 13 ± 1.2 cm H2O. During PCV time to peak flow (t to PF) was used as a reflection of resistance and V_{t} as a reflection of compliance. During VCV inspiratory resistance was calculated and the difference between P_{PLAT} and PEEP was used as a reflection of compliance. (Mean±SD, p < =0.05 = * vs. PEEP 0, # vs. PEEP 10)

PCV

PEEP (cmH2O) 0 5 7.5 10

t to PF (s) 0.65+0.23 0.37+0.24 0.24+0.12* 0.15+0.01*

Vt (ml) 0.13+0.05 0.21+0.07 0.25+0.07* 0.30+0.07*

PEEP (cmH2O) 12.5 15

t to PF (s) 0.15+0.02* 0.15+0.02*

Vt (ml) 0.34+0.07* 0.37+0.06*#

VCV

PEEP (cmH2O) 0 5 7.5 10

Ri (cmH2O/l/s) 26.8+10.7 10.3+6.6* 7.8+1.6* 7.2+1.3*

Pplat-PEEP (cmH2O) 20.6+6.6 18.1+5.7 16.4+5.2 14.9+5.1

PEEP (cmH2O) 12.5 15

Ri (cmH2O/l/s) 6.7+1.1* 6.3+1.0*

Pplat-PEEP (cmH2O) 13.9+4.8* 12.8+4.4*#

Conclusion: During PCV VM were optimized at PEEP>=10 cm H_{2}O and in VCV at PEEP>=7.5 cm H_{2}O. VM as determined underestimated the PEEP level equal to LIP. (1) Fujino Y et al.: AJRCCM 155:A745 (1997).

This abstract is funded in part by Alliance Pharmaceutical Corp. (San Diego, CA) and Hoechst Marion Roussel Inc (Frankfurt, Germany).

The 44th International Respiratory Congress Abstracts-On-Disk®, November 7 - 10, 1998, Atlanta, Georgia.

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