Bronchoalveolar Lavage and Oleic Acid-Injection in Pigs as a Double-Hit Model for Acute Respiratory Distress Syndrome (ARDS)

Summary

Different, complex animal models exist to study the pathophysiology of acute respiratory distress syndrome (ARDS). Bronchoalveolar lavage and oleic acid injection induced lung injury is suitable as a new double-hit animal model for studying the acute respiratory distress syndrome.

Abstract

The treatment of ARDS continues to pose major challenges for intensive care physicians in the 21st century with mortality rates still reaching up to 50% in severe cases. Further research efforts are needed to better understand the complex pathophysiology of this disease. There are different well-established animal models to induce acute lung injury but none has been able to adequately mimic the complex pathomechanisms of ARDS. The most crucial factor for the development of this condition is the damage to the alveolar capillary unit. The combination of two well-established lung injury models allow us to mimic in more detail the underlying pathomechanism. Bronchoalveolar lavage (BAL) leads to surfactant depletion as well as alveolar collapse. The repeated instillation of fluid volumes causes subsequent hypoxemia. Surfactant depletion is a key factor of ARDS in humans. BAL is often combined with other lung injury approaches, but not with a second hit followed by oleic acid injection (OAI) yet. Oleic acid injection leads to severely impaired gas exchange, a deterioration of lung mechanics and disruption of the alveolo-capillary barrier. The OAI mimics most of the expected effects of ARDS consisting of extended inflammation of lung tissue with an increase of alveolar leakage and gas exchange impairment. A disadvantage of the combination of different models is the difficulty to determine the influence to the lung injury caused by BAL alone, OAI alone or both together. The model presented in this report represents the combination of BAL and OAI as a new double-hit lung injury model. This new model is easy to implement and an alternative to study different therapeutic approaches in ARDS in the future.

Introduction

Acute respiratory distress syndrome (ARDS) is a disease consisting of impaired gas exchange and lung infiltration, which often needs intensive care therapy. The mortality of severe ARDS remains high (up to 50%) worldwide despite almost 50 years of extensive research¹. The ARDS is defined by the Berlin Definition, including diagnostic criteria as timing, chest imaging, origin of edema and hypoxemia². To better categorize patients with different levels of ARDS severity, three different degrees of hypoxemia are defined: mild (200 mmHg < PaO₂/FIO₂ ≤ 300 mmHg), moderate (100 mmHg < PaO_....

Protocol

All animal experiments described here have been approved by the institutional and state animal care committee (Landesuntersuchungsamt Rheinland-Pfalz, Koblenz, Germany; approval number G18-1-044) and were conducted in accordance with the guidelines of the European and German Society of Laboratory Animal Sciences.

1. Anesthesia, intubation and mechanical ventilation

1. Withhold food for 6 hours before anesthesia to reduce the risk of aspiration, but allow free access to water to reduce stress.
2. Inject a combination of ketamine (4 mg∙kg^-1) and azaperone (8 mg∙kg^-1) intramuscularly for sedati....

Results

The PaO₂/FiO₂-ratio decreases after bronchoalveolar lavage and fractionated application of oleic acid (Figure 1). Because it is unclear to predict the impact of bronchoalveolar lavage (e.g., the impact of fractionated oleic acid dose) on PaO₂/FiO₂-ratio, it is recommended to monitor PaO₂/FiO₂-ratio while inducing the lung injury. Ultrafast pO₂-measurement allows to monitor PaO₂ in real-time and is well es.......

Discussion

The described double-hit method to cause a severe lung injury in pigs is suitable to study different treatment options in ARDS. The double-hit model mimics two central elements of the pathomechanism of ARDS: loss of the alveolar-capillary unit and disruption of the endothelial barrier⁷. Due to the two hits, it is important to have a study protocol with predefined target values (e.g., PaO₂/FiO₂-ratio).

The main disadvantage of this double-hit method.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
1 M Kaliumchlorid-Lösung 7.46% 20 mL	Fresenius, Kabi Deutschland GmbH	potassium chloride
Absaugkatheter Ideal CH14, 52 cm, gerade	B. Braun Melsungen AG, Germany	suction catheter
Arterenol 1 mg/mL, 25 mL	Sanofi- Aventis, Seutschland GmbH	norepinephrine
Atracurium Hikma, 50 mg/5 mL	Hikma Pharma GmbH , Martinsried	atracurium
BD Discardit II Spritze 2, 5, 10, 20 mL	Becton Dickinson S.A. Carretera Mequinenza Fraga, Spain	syringe
BD Luer Connecta	Becton Dickinson Infusion Therapy AB Helsingborg, Schweden	3-way-stopcock
BD Microlance 3 20 G	Becton Dickinson S.A. Carretera Mequinenza Fraga, Spain	canula
Datex Ohmeda S5	GE Healthcare Finland Oy, Helsinki, Finland	hemodynamic monitor
Engström Carestation	GE Heathcare, Madison USA	ventilator
Fentanyl-Janssen 0.05 mg/mL	Janssen-Cilag GmbH, Neuss	fentanyl
Führungsstab, Durchmesser 4.3	Rüsch	endotracheal tube introducer
Incetomat-line 150 cm	Fresenius, Kabi Deutschland GmbH	perfusorline
Ketamin-Hameln 50 mg/mL	Hameln Pharmaceuticals GmbH	ketamine
laryngoscope	Rüsch	laryngoscope
logicath 7 Fr 3-lumen 30 cm lang	Smith- Medical Deutschland GmbH	central venous catheter
Masimo Radical 7	Masimo Corporation Irvine, Ca 92618 USA	periphereal oxygen saturation
Neofox Oxygen sensor 300 micron fiber	Ocean optics Largo, FL USA	ultrafast pO2-measurements
Ölsäure reinst Ph. Eur NF C18H34O2 M0282.47g/mol, Dichte 0.9	Applichem GmbH Darmstadt, Deutschland	oleic acid
Original Perfusor syringe 50 mL Luer Lock	B.Braun Melsungen AG, Germany	perfusorsyringe
PA-Katheter Swan Ganz 7.5 Fr, 110 cm	Edwards Lifesciences LLC, Irvine CA, USA	PAC
PE-Trichter, 60 mm	Aquintos-Wasseraufbereitung GmbH, Germany	funnel
Percutaneous sheath introducer set 8.5 und 9 Fr, 10 cm with integral haemostasis valve/sideport	Arrow international inc. Reading, PA, USA	introducer sheath
Perfusor FM Braun	B.Braun Melsungen AG, Germany	syringe pump
Propofol 2% 20 mg/mL (50 mL Flaschen)	Fresenius, Kabi Deutschland GmbH	propofol
Radifocus Introducer II, Größe 5-8 Fr	Terumo Corporation Tokio, Japan	introducer sheath
Rüschelit Super Safety Clear 6.5 /7.0	Teleflex Medical Sdn. Bhd, Malaysia	endotracheal tube
Seldinger Nadel mit Fixierflügel	Smith- Medical Deutschland GmbH	seldinger canula
Sonosite Micromaxx Ultrasoundsystem	Sonosite Bothell, WA, USA	ultrasound
Stainless Macintosh Größe 4	Welsch Allyn69604	blade for laryngoscope
Sterofundin Infusion	B. Braun Melsungen AG, Germany	bronchoalveolar lavage
Stresnil 40 mg/mL	Lilly Deutschland GmbH, Abteilung Elanco Animal Health	azaperon
Vasofix Safety 22 G	B.Braun Melsungen AG, Germany	venous catheter