Lavage-induced Surfactant Depletion in Pigs As a Model of the Acute Respiratory Distress Syndrome (ARDS)

Summary

Repeated pulmonary lavages in anesthetized pigs induce lung injury resembling major aspects of human acute respiratory distress syndrome (ARDS). For this purpose the lungs are repeatedly lavaged with 0.9% saline at 37 °C. The goal of the protocol is a reproducible mitigation of gas exchange and hemodynamics for research in ARDS.

Abstract

Various animal models of lung injury exist to study the complex pathomechanisms of human acute respiratory distress syndrome (ARDS) and evaluate future therapies. Severe lung injury with a reproducible deterioration of pulmonary gas exchange and hemodynamics can be induced in anesthetized pigs using repeated lung lavages with warmed 0.9% saline (50 ml/kg body weight). Including standard respiratory and hemodynamic monitoring with clinically applied devices in this model allows the evaluation of novel therapeutic strategies (drugs, modern ventilators, extracorporeal membrane oxygenators, ECMO), and bridges the gap between bench and bedside. Furthermore, induction of lung injury with lung lavages does not require the injection of pathogens/endotoxins that impact on measurements of pro- and anti-inflammatory cytokines. A disadvantage of the model is the high recruitability of atelectatic lung tissue. Standardization of the model helps to avoid pitfalls, to ensure comparability between experiments, and to reduce the number of animals needed.

Introduction

The mortality of human acute respiratory distress syndrome (ARDS) remains high with values between 40 and 50% ¹ despite more than 4 decades of intense research. Animal models of lung injury play a major role in investigating the complex pathomechanisms or novel therapeutical approaches to reduce mortality and limit long term disabilities.

Various models have been established to induce lung injury that simulates aspects of human ARDS in either large (e.g. pigs) or small animals (e.g. rodents). Methods differ strongly, including pulmonary arterial infusion of oleic acid, intravenous (i.v.) infusion of bacteria, an....

Protocol

The experiments were conducted at the Department of Experimental Medicine, Charité - Universitätsmedizin, Berlin, Germany (certified according to the EN DIN ISO 9001:2000), and were approved by the federal authorities for animal research in Berlin, Germany prior to the experiments. The principles of laboratory animal care, which were used in all experiments, were in accordance with the guidelines of the European and German Society of Laboratory Animal Sciences.

1. Animal Welfare and Laboratory Animals

1. All experiments were conducted in fully anesthetized male pigs (German Landrace × Large White) of 3-4 months....

Results

P_aO₂/F_IO₂-ratio decreases during lung lavages, but the exact impact of a single lavage is difficult to predict. We start to take arterial blood gas samples from the third lavage onwards to detect a decrease in P_aO₂/F_IO₂-ratio below 100 mmHg. Once a decrease in P_aO₂/F_IO₂-ratio below 100 mmHg is achieved, we require this ratio to remain below 100 mmHg for one h.......

Discussion

This article describes a step by step instruction to induce severe lung injury in pigs due to surfactant washout by repeated lung lavages. This specific method enables a reproducible and comparable deterioration in lung function and pulmonary vascular resistance. It is imperative to lavage the pigs until the P_aO₂/F_IO₂ ratio decreased below 100 mmHg and stays below 100 mmHg for one hr. Once, this is achieved the animals usually do not recover from the lung injury for at least 4 .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Evita Infinity V500	Dräger		intensive care ventilator
Vigilance I	Edwards		monitor
Vasofix Braunüle 20G	B Braun	4268113B	peripheral vein catheter
Mallinckrodt Tracheal Tube Cuffed	Covidien	107-80	8.0 mm ID
MultiCath3	Vygon	157,300	3 lumen central venous catheter, 20 cm length
Leader Cath Set	Vygon	115,805	arterial catheter
Percutaneus Sheath Introducer Set	Arrow	SI-09600	introducer sheath for pulmonary artery catheter of 4-6 Fr., 10 cm length
Swan-Ganz True Size Thermodilution Catheter	Edwards	132F5	pulmonary artery catheter, 75 cm length
Flow through chamber thermistor	Baxter	93-505	for measuring cardiac output
urinary catheter			no specific model requiered