Effects of Extracorporeal Membrane Oxygenation on the Coagulation System

Summary

We present a protocol for establishing a long-term awake extracorporeal membrane oxygenation (ECMO) model in sheep. Special attention is given to the management and evaluation of the coagulation system during the ECMO model.

Abstract

This study aimed to investigate the effects of long-term awake extracorporeal membrane oxygenation (ECMO) on the coagulation system in a sheep model. A total of ten healthy sheep were included in the study, with 5 sheep in each group. In the veno-arterial ECMO (V-A ECMO) group, cannulation was performed in the right carotid artery and the right external jugular vein. In the veno-venous ECMO (V-V ECMO) group, a dual-lumen catheter was utilized to insert into the right external jugular vein. After initiating ECMO, the sheep were recovered from anesthesia and remained awake for 7 days. The target activated clotting time (ACT) goal was set at 220-250 s. In both groups, the actual ACT fluctuated around 250 s with the dose of heparin gradually increasing, reaching almost 60 IU/kg/min at the end of the experiments. Moreover, the activated partial thromboplastin time (APTT) and thrombin time (TT) values were significantly higher in the V-A ECMO group compared to the V-V ECMO group, despite receiving the same doses of heparin. Although laboratory test results fluctuated within a normal and reasonable range, infarct foci in the kidneys were observed in both groups at the end of the study.

Introduction

Extracorporeal membrane oxygenation (ECMO) serves as a life-saving intervention, providing cardiopulmonary support for severely ill patients. It is classified into two primary forms: veno-arterial ECMO (V-A ECMO) and veno-venous ECMO (V-V ECMO)^1,2. V-A ECMO is employed for patients experiencing circulatory failure, whereas V-V ECMO is preferred for those with respiratory failure but without severe cardiovascular dysfunction^3,4.

Thrombosis and bleeding are prevalent complications in ECMO patients⁵. The ECMO circuit exposes blood to artificial surfaces, initiating complex coagulation responses⁶. These processes can lead to endothelial damage and microcirculation disorders, resulting in subsequent dysfunction in vital organs^7,8. Consequently, effective systemic anticoagulation management is considered crucial for ECMO patients. Despite this, there remains a lack of evidence to guide anticoagulation strategies in various ECMO-related clinical settings.

The establishment of a stable ECMO animal model can provide insights into the impact of ECMO on the body, contributing significantly to the optimization of ECMO management strategies, reduction of ECMO-related complications, and improvement of patient outcomes in clinical practice. Large animals, such as sheep and pigs, are the primary choices for establishing ECMO models due to their physiological parameters closely resembling those of humans^9,10. However, previous large animal ECMO models had a maintenance time of less than 24 h, making it challenging to comprehensively evaluate the impact of ECMO on the coagulation system¹¹. Therefore, there is a need to establish long-term ECMO large animal models to thoroughly explore the pathophysiological mechanisms of ECMO. Utilizing long-term large animal models to investigate the effects of ECMO on the coagulation system can provide more robust evidence for clinical practice.

This study aims to establish a long-term (7 days) awake V-A and V-V ECMO model in healthy sheep. The central focus of the entire model establishment and evaluation is the management of anticoagulation.

Protocol

This experimental protocol received approval from the Institutional Animal Care and Use Committee of Fuwai Hospital (no. 0101-2-20-HX(X)). All procedures adhered to the guidelines outlined in the National Institutes of Health's Guide for the Use and Care of Laboratory Animals. The experiment took place at the Beijing Key Laboratory of Pre-clinical Research and Evaluation for Cardiovascular Implant Materials, Animal Experimental Center of Fuwai Hospital (registration no. CNAS LA0009). Healthy sheep that met the requir…

Representative Results

A total of ten sheep were evaluated during the entire experiment, with five sheep in each group (Table 1). Following the initiation of ECMO, all sheep recovered from anesthesia and remained awake for 7 days. In both groups, ECMO flow exceeded 1.8 L/min. In the V-V ECMO group, the flow fluctuated around 1.8 L/min, while in the V-A ECMO group, it ranged from 2.3 L/min to 1.8 L/min (Figure 1A). The vital signs of each sheep remained stable. The blood lactic acid level was below…

Discussion

This study outlines the procedure for establishing robust, long-term survival models for V-V and V-A ECMO in sheep. All surviving animals exhibited stable vital signs, and no severe bleeding or coagulation events occurred. ECMO flow and oxygenation performance remained stable, with no major pathological injuries observed. The study provides detailed information on anticoagulation management.

Anticoagulation management plays a crucial role in ECMO perioperative care. Initially, based on previou…

Materials

ACT analyzer	Hemochron, USA	Jr Signature
Anaesthesia machine	Drager, Germany	Primus
Arterial catheter	Edwards Lifescience, USA	18-Fr	Provide return access into an artery for VA-EMCO
Blood chemistry analyzer	IDEXX Laboratories, USA	Catalyst One
Blood gas analyzer	Abbott, USA	Abbott i-STAT1
Centrifugal pump	Jiangsu STMed Technologies, China	STM CP-24 I
Centrifugal pump drive and console	Jiangsu STMed Technologies, China	OASSIST STM001
Coagulation test analyzer	Beijing Succeeder Technology, China	SF-8050
Complete blood count analyzer	Siemens Healthcare, Germany	ADVIA 2120i
Dual-channel micro-injection pump	Zhejiang Smith Medical Instrument, China	WZS-50F6
Dual-lumen catheter	MAQUET Avalon Elite, Germany	23-Fr	Provide return and drainage accesses into the right external jugular vein for VV-ECMO
Flurbiprofen	Beijing Tide Pharmaceutical Co., Ltd., China	5ml: 50mg
GraphPad software	GraphPad Software, USA	GraphPad Prism v9.0	Statistical analysis
Heparin	Shanghai Shangyao No.1 Biochemical Pharmaceutical Co., Ltd., China	2ml: 12500IU
High-frequency electrosurgical	COVIDIEN, USA	Force F
Multi-parameter medical monitor	Philips, Netherlands	MP60
Oxygenator kit	Medos, Germany	Hilite 7000LT
Oxygenator kit	Maquet, Germany	BE-PLS 2050
Propofol	Xi’an Libang Pharmaceutical Co. Ltd, China	20ml: 0.2g
Single-lumen central venous catheter	TuoRen, China	18Fr	Insert in left carotid artery  for hemodynamic monitoring and blood sampling.
Small Tail Han sheep	Jinyutongfeng Commercial and Trade Co. Ltd, China	weight: 50-65 kg, age: 12-24 months
Triple-lumen central venous catheter	TuoRen, China	7Fr	Insert in left jugular vein for intravenous fluid administration, drug injection, and blood sampling.
Ultrasound machine	GE, USA	E9
Venous catheter	Edwards Lifescience, USA	24-Fr	Provide the drainage access into a vein for VA-ECMO
Ventilator	Drager, Germany	Savina