Determination of the best volume of perfluorocarbone to ensure partial liquid ventilation in the pig with ARDS

Introduction

Partial liquid ventilation consists of filling the residual functional capacity with perfluorocarbon (PFC), while providing tidal volume by conventional ventilation. Several studies have shown that smaller volumes of PFC allow significant improvement in ventilation parameters during experimental ARDS. To date no study has compared several small volumes of PFC. The purpose of this study was to make a comparison with the minimum doses of PFC in a pig model presenting ARDS.

Method

16 pigs, average weight 24 ± 5 kg, under general anesthesia and myorelaxation were prepared with installation of a central venous catheter and an arterial catheter with continuous oxygen monitoring The animals were then ventilated (Evita 4, Dräger) with intermittent positive pressure ventilation (FiO₂:1) in order to obtain PaCO₂ at 35 ± 1 mmHg. At this point ARDS was induced by intravenous injection over half an hour of 0.3 ml/kg oleic acid. ARDS was confirmed by a PaO₂/FiO₂ <150 taken over two successive arterial samples. A pressure-volume curve was established and used to identify the lower inflection point (LIP) and the level of the `best PEEP'. The animals were then split into four groups of four, with a control group being given continuous positive pressure ventilation (CPPV) without PFC. The second group was administered 5 ml/kg intra tracheal perfluorocarbon (Rimar 101, Mitsubishi Milano) then given CPPV ventilation. The third group was administered 10 ml/kg PFC and the last group 15 ml/kg. In all four groups CPPV ventilation was maintained with the `best PEEP'. Arterial pressure, central venous pressure, heart rate, SaO₂ and PETCO₂ were recorded continuously. Blood gases and ventilation parameters: peak inspiratory pressure, tidal volume and pulmonary compliance were recorded every 15 min. The three groups were compared using an ANOVA, a Friedman test and a Mann and Whitney U-test (P < 0.05 significant).

Results

In the control group lung compliance and PaO₂ continued to drop for all the animals; in PLV groups, lung compliance decrease after administration of PFC. After a few minutes, the compliance increase significantly. In the 5 ml/kg group lung compliance and PaO₂ rose to an average of 354 ± 197 mmHg and 15.4. In the 10 and 15 ml/kg group PaO₂ was restored to its initial level of 448 ± 74 and 445 ± 86 mmHg. Lung compliance increase to satifactory values (21.4 ± 3.1; 21.48 ± 2.4). All the animals in the control group died in a mean time of 109 ± 25 min, the animals in the 5 ml/kg group survived on average 158 ± 17 min, the animals in the 10 ml/kg and 15 ml/kg groups survived for the whole 3 h the experiment lasted (P < 0.05).

Discussion

It would thus appear that in pigs a dose of 5 ml/kg PFC enables satisfactory ventilation parameters to be restored, but the level remains lower than that obtained with 10 ml/kg. The fact that a low dose does not have long-lasting effects might be due to faster evaporation of the product and a drop in its efficiency. There is no beneficial effect with larger dose than 10 ml/kg.

Figure 1

Evolution of the PaO₂ in the four groups. x: times when the pigs died.

Figure 2

Evolution of lung compliance.