Continuous external negative pressure improves oxygenation and respiratory mechanics in Experimental Lung Injury in Pigs - A pilot proof-of-concept trial

Abstract

Background: Continuous external negative pressure (CENP) during positive pressure ventilation can recruit dependent lung regions. We hypothesised that CENP applied regionally to the thorax or the abdomen only, increases the caudal end-expiratory transpulmonary pressure depending on positive end-expiratory pressure (PEEP) in lung-injured pigs. Eight pigs were anesthetised and mechanically ventilated in the supine position. Pressure sensors were placed in the left pleural space, and a lung injury was induced by saline lung lavages. A CENP shell was placed at the abdomen and thorax (randomised order), and animals were ventilated with PEEP 15, 7 and zero cmH2O (15 min each). On each PEEP level, CENP of - 40, - 30, - 20, - 10 and 0 cmH2O was applied (3 min each). Respiratory and haemodynamic variables were recorded. Electrical impedance tomography allowed assessment of centre of ventilation.

Results: Compared to positive pressure ventilation alone, the caudal transpulmonary pressure was significantly increased by CENP of ≤ 20 cmH2O at all PEEP levels. CENP of - 20 cmH2O reduced the mean airway pressure at zero PEEP (P = 0.025). The driving pressure decreased at CENP of ≤ 10 at PEEP of 0 and 7 cmH2O (P < 0.001 each) but increased at CENP of - 30 cmH2O during the highest PEEP (P = 0.001). CENP of - 30 cmH2O reduced the mechanical power during zero PEEP (P < 0.001). Both elastance (P < 0.001) and resistance (P < 0.001) were decreased at CENP ≤ 30 at PEEP of 0 and 7 cmH2O. Oxygenation increased at CENP of ≤ 20 at PEEP of 0 and 7 cmH2O (P < 0.001 each). Applying external negative pressure significantly shifted the centre of aeration towards dorsal lung regions irrespectively of the PEEP level. Cardiac output decreased significantly at CENP -20 cmH2O at all PEEP levels (P < 0.001). Effects on caudal transpulmonary pressure, elastance and cardiac output were more pronounced when CENP was applied to the abdomen compared with the thorax.

Conclusions: In this lung injury model in pigs, CENP increased the end-expiratory caudal transpulmonary pressure. This lead to a shift of lung aeration towards dependent zones as well as improved respiratory mechanics and oxygenation, especially when CENP was applied to the abdomen as compared to the thorax. CENP values ≤ 20 cmH2O impaired the haemodynamics.

Keywords: ARDS; Acute respiratory distress syndrome; CENP; Continuous external negative pressure; Electrical impedance tomography; Lung mechanics; Mechanical ventilation; Negative pressure ventilation; Pleural pressure; Transpulmonary pressure.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1

Time course of the experiment (a) and positioning of the shell on the pig thorax (b). Legend: VATS, video-assisted thoracoscopy; PEEP, positive end-expiratory pressure; CENP, continuous external negative pressure

Fig. 2

End-expiratory caudal transpulmonary pressure (left) and respiratory system elastance (right). Legend: CENP, continuous external negative pressure; PEEP, positive end-expiratory pressure. Triangles indicate different shell positions (abdomen and thorax), colours represent different PEEP levels, super-posed numbers indicate significance (P < 0.05) of the respective CENP level compared with the CENP level of the number and stars indicate difference between both positions

Fig. 3

Arterial oxygenation (PaO2, left) and cardiac output (CO, right). Legend: CENP, continuous external negative pressure; PEEP, positive end-expiratory pressure. Triangles indicate different shell positions (abdomen and thorax), colours represent different PEEP levels, super-posed numbers indicate significance (P < 0.05) of the respective CENP level compared with the CENP level of the number and stars indicate difference between both positions

Fig. 4

Centre of aeration (left) and centre of ventilation (right) as a percentage from dorsal. Legend: CENP, continuous external negative pressure; PEEP, positive end-expiratory pressure. Triangles indicate different shell positions (abdomen and thorax), colours represent different PEEP levels, super-posed numbers indicate significance (P < 0.05) of the respective CENP level compared with the CENP level of the number and stars indicate the difference between both positions