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

Martin Scharffenberg; Jakob Wittenstein; Moritz Herzog; Sebastian Tauer; Luigi Vivona; Raphael Theilen; Thomas Bluth; Thomas Kiss; Thea Koch; Giuseppe Fiorentino; Marcelo Gama de Abreu; Robert Huhle

doi:10.1186/s40635-020-00315-1

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

Intensive Care Med Exp. 2020 Dec 18;8(Suppl 1):49. doi: 10.1186/s40635-020-00315-1.

Affiliations

¹ Pulmonary Engineering Group, Dept. of Anaesthesiology and Intensive Care Medicine, University Hospital Carl Gustav Carus at Technische Universität Dresden, Fetscherstrasse 74, 01307, Dresden, Germany.
² Department of Pathophysiology and Transplantation, University of Milan, Via Francesco Sforza 35, 20122, Milano, Italia.
³ Devision of Respiratory Physiopathology, Monaldi Hospital, Naples, Italy.
⁴ Pulmonary Engineering Group, Dept. of Anaesthesiology and Intensive Care Medicine, University Hospital Carl Gustav Carus at Technische Universität Dresden, Fetscherstrasse 74, 01307, Dresden, Germany. robert.huhle@tu-dresden.de.

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.