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Ann Thorac Surg 2005;80:1887-1892
© 2005 The Society of Thoracic Surgeons

New technology

LIFEBRIDGE: A Portable, Modular, Rapidly Available "Plug-and-Play" Mechanical Circulatory Support System

Uwe Mehlhorn, MD a , * , Michael Brieske, Dipl-Inf b , Uwe M. Fischer, MD a , Markus Ferrari, MD c , Patrick Brass, MD d , Juergen H. Fischer, MD e , Hans-R. Zerkowski, MD f

a Department of Cardiothoracic Surgery, University of Cologne, Cologne, Germany
b Lifebridge, Medizintechnik Gmbh, Ampfing, Germany
c Department of Cardiology, University of Jena, Jena, Germany
d Department of Anesthesiology, University of Cologne, Cologne, Germany
e Institute for Experimental Medicine, University of Cologne, Cologne, Germany
f Division of Cardiothoracic Surgery, Unispital Basel, Basel, Switzerland

Accepted for publication March 4, 2005.

* Address correspondence to Dr Mehlhorn, Department of Cardiothoracic Surgery, University of Cologne, Joseph-Stelzmann-Str 9, Cologne, 50924 Germany (Email: uwe.mehlhorn{at}uk-koeln.de).


   Abstract
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PURPOSE: We describe the LIFEBRIDGE, a portable, modular, rapidly available "plug-and-play" mechanical circulatory support system, and report its experimental safety evaluation.

DESCRIPTION: The modular construction consists of a disposable patient module with cardiopulmonary bypass circuit, control module, and base module with power supply, emdedded PC, and user interface. The system weighs about 20 kg, has a modular design, and has semi-automatic priming that allows action within 5 minutes, and a 7-step air elimination program that prevents air embolization.

EVALUATION: In eight pigs (85 ± 10 kg) we investigated this system using central (right atrium and ascending aorta) cannulation (n = 4) or peripheral (iliac) cannulation (n = 4). Pump flows were 5.7 ± 0.2 L/min with central and 4.1 ± 0.2 L/min with peripheral cannulation, yielding sufficient animal perfusion and gas exchange. Using an intraaortic 8-MHz Doppler device, we demonstrated that venous air boluses of up to 100 mL were effectively removed, thus avoiding air embolization. Changing heights between animals and LIFEBRIDGE did not affect its proper action.

CONCLUSIONS: This initial evaluation demonstrates that the LIFEBRIDGE is rapidly available, provides adequate perfusion and gas exchange, and operates safely even under simulated transport conditions.


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Drs Mehlhorn, Brieske, Ferrari, and Zerkowski disclose a financial relationship with Lifebridge Medizintechnik GmbH, Ampfing, Germany.

 

Mechanical circulatory support (MCS) is an integral component of interdisciplinary heart failure programs. Different MCS systems are used for various indications including destination therapy, bridge-to-bridge, bridge-to-transplant, or bridge-to-recovery, respectively, and postcardiotomy cardiogenic shock, high-risk cardiology interventions, pulmonary embolism, myocarditis, and accidental hypothermia. In addition, closed chest temporary MCS using peripheral cardiopulmonary bypass has been successfully applied as a salvage approach in patients with cardiogenic shock or cardiopulmonary arrest [1–8]. Although interest in this approach has grown over the last decade and has been associated with increased survival in these patients, only few programs provide mobile services for emergency circulatory resuscitation [1–8]. One reason for the absence of more widespread use of the mobile MCS is probably the lack of a commercially available device that combines portability, rapid and easy deployment, and safe operation, with adaptability to various applications and patient requirements, along with low cost.

Lifebridge Medizintechnik GmbH (Ampfing, Germany) has developed the LIFEBRIDGE, a portable, modular, rapidly available "plug-and-play" MCS system intended to be used for short-term peripheral cardiopulmonary bypass in emergency circulatory resuscitations, or for MCS in high-risk cardiology interventions, or as an alternative to the heart-lung machine in heart surgery procedures.

The purpose of this article is to describe the LIFEBRIDGE system and report its experimental safety evaluation in a large animal model.


   Material and Methods
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Technical Description
The LIFEBRIDGE consists of three modules. * The disposable patient module contains a standardized extracorporeal circuit consisting of a venous reservoir, a rotary blood pump head, an oxygenator, an arterial filter, silicon tubing, as well as pressure, bubble, and level sensors (Fig 1). Components are fixed in moulded parts of expanded polypropylene that provide excellent protection against external influences. The patient module is primed with regular Ringer's lactate prior to use.



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  		Fig 1. Circuit of the LIFEBRIDGE system (Medizintechnik GmbH, Ampfing, Germany).

 
The control module contains all parts required for driving and controlling the extracorporeal circulation, including a blood pump motor, a roller pump for active air elimination, automatic clamps for blood flow regulation, and an integrated back-up battery that allows stand-alone operation of the control and patient module for up to 20 minutes.

The base module has a tubular frame that provides tilt-resistant standing of the system. It contains a main power plug (110/220 V), Li-Po-batteries (Bullith Batteries, Ismaning, Germany) for stand-alone operation up to 2 hours, and an embedded PC with a connected touch-sensitive flat panel and a rotary switch, as the user interface. The PC records and stores data relevant to the perfusion protocols. In addition, the base module implements the pivot mounting used to rotate the control and patient module by 90° during the semi-automatic priming procedure. {dagger} The base module is stored at the hospital; the empty, non-primed patient module is tested, calibrated, and sterilized at the company, then preassembled with the control module and transported and stored (for up to 1 year) in a sealed, reusable container. If an operating patient module needs to be changed, running patient-control modules are disconnected from the base module and continue operation powered by the control module back-up battery. A new, preassembled patient-control module is connected to the base module, primed, and the patient lines are clamped, disconnected from the faulty system, connected to the fresh system, and perfusion is continued. For the setting of electrical, battery, or pump failure, a separate charged battery set is provided in a backpack together with a drive unit that can replace the pump motor within less than 1 minute.

Modular configuration and semi-automatic priming allows for "plug-and-play" within 5 minutes. Due to its dimensions and weight, the system is suitable for portable use. Tables 1 and 2 Go provide the components and technical specifications of the LIFEBRIDGE system.


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  		Table 1. Components of the LIFEBRIDGE
 

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  		Table 2. Technical Specifications of the LIFEBRIDGE
 
Prevention of Air Embolization
One important LIFEBRIDGE safety feature is prevention of air embolization into the patient. This prevention program consists of seven stages as well as an implemented automatic "air management procedure" triggered through air detection by a bubble detector placed behind the arterial filter. If bubbles are detected, the arterial line is rapidly closed by means of the arterial clamp (Fig 1) within less than 300 msec. By simultaneous opening, the arteriovenous shunt, bubble-contaminated blood is diverted to the venous reservoir without jeopardizing the patient. After bubble removal, the shunt is closed and the arterial line is reopened to reestablish patient perfusion. The seven-stage air embolization prevention system consists of:
1 Air entering into the venous line or re-circulating through the purge lines and collects at the reservoir top by means of the buoy effect. An integrated roller pump (Fig 1) actively removes the air from the reservoir.
2 A 120 µm screen separates the reservoir into the entry and exit chamber, thus preventing transition of micro bubbles from the reservoir inlet to the outlet.
3 A venous reservoir low-blood level detected by the bottom level sensor results in a blood pump stop.
4 Centrifugal pumps do not transport massive air. This safety aspect is enforced by mounting the pump head with its tangential outlet down.
5 The oxygenator itself is an air barrier. Air will be eliminated through the venous reservoir through its re-circulation line.
6 The arterial filter centers air by means of forced circular flow. By its purge line, air is eliminated through the venous reservoir.
7 Whenever bubbles are detected behind the arterial filter, the "air management procedure" will eliminate them as previously described.

All prevention measures are inherent to the system except for numbers 3 and 7 as previously described, which are implemented in the control software.

Animal Investigations
All animal procedures were approved by the Animal Welfare Representative of the University of Cologne and were consistent with the 1996 NRC "Guide for the Care and Use of Laboratory Animals" (National Academy Press, Washington, DC). Eight pigs (85 ± 10 kg [standard deviation]) of either sex were pre-medicated with 20 mg/kg Ketamin (Ketavet [Pharmacia & Upjohn, Erlangen, Germany]) and 2 mg/kg Azaperon (Stresnil [Janssen Cilag, Neuss, Germany]), intubated and ventilated (FiO2 0.5) using a volume-cycled respirator (Engström Medical AB, Solna, Sweden). Anesthesia was induced with 0.5 mg/kg Propofol (Disoprivan 2%, Astra Zeneca) and 10 mg/kg Ketamin, and was maintained by intravenous infusion of 1 mg/kg/min Ketamin. Fluid-filled catheters were placed into the right carotid artery and right jugular vein and were connected to pressure transducers for arterial and central venous pressure monitoring, arterial and venous blood sampling, and fluid administration, respectively. The left iliac artery and vein were dissected and followed by a median sternotomy and pericardiotomy, and administration of 300 IU heparin/kg. In four pigs the ascending aorta was cannulated with a standard 8-mm aortic cannula (A232-80 [Stoeckert, Munich, Germany]), the right atrium was cannulated with a two-stage venous cannula (36/48 French cannula, TS3648B-86 [Maquet Cardiopulmonary, Hirrlingen, Germany]), and in the remaining four pigs, iliac vessels were cannulated with a 17-French arterial cannula (DLP57417 [Medtronic Inc, Minneapolis, MN]) and a 19-French venous cannula (FV319-550 mm [Stoeckert]); and the tip of this last cannula was advanced into the right atrium.

Intraaortic Emboli Detection
For intraaortic emboli detection, we introduced an 8-MHz Doppler probe (MTB Basler [Regensdorf, Switzerland]) into the descending aorta with its tip about 20 cm distally to the ascending aortic cannula in the four pigs with central cannulation, and about 20 cm proximally to the iliac arterial cannula in the four pigs with peripheral cannulation, respectively. The probe was connected to a Multi-Dop-T-Doppler device (DWL [Singen, Germany]). This system has been demonstrated to reliably detect air bubbles as small as 0.5 µL [9].

Experimental Protocol
After animal preparation, the LIFEBRIDGE was semi-automatically primed * by rotating the control and patient module on the base module by 90° to bring the pump head inflow into an upright position (Fig 2), and then the venous reservoir was passively filled with Ringer's lactate by gravity. The pump was started at 500 rpm with the arteriovenous shunt and patient lines (Figs 1, 2) open, and the system was actively filled until no recirculating air was detected by the bubble sensor. To completely remove the air from the entire circuit, the pump speed was increased to 1,200 rpm, and the control and patient module were rotated back by 90° into the operating position (Fig 2). After automatic removal of recirculating air, the shunt line was occluded, the patient line was cut between the clamps and was connected to the arterial and venous cannula, respectively. Extracorporeal circulation was established by successively increasing the pump speed up to 3,000 to 3,300 rpm, mechanical ventilation was ceased in animals with central cannulation and halved in those with peripheral cannulation, and the arterial blood gases of the animals were maintained within physiologic range by adjusting gas flow through the oxygenator of the LIFEBRIDGE. To test the intraaortic bubble detection device, 100 µL air were test injected into the arterial cannula, and both were optically and acustically detected in all cases. All animals were then subjected to a venous air injection protocol, consisting of consecutive injections of 5, 10, 20, 50, and 100 mL air boluses into the venous line. To simulate transport conditions, this protocol was repeated at different heights of 60, 40, 20, and 0 cm between the animal's right atrium and the LIFEBRIDGE's pump head. Between air injections, the intraaortic Doppler signal was continuously recorded for more than 3 min, and 100 µL arterial test air was given after each height change to confirm functionality of the bubble detection system.



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  		Fig 2. Semi-automatic priming procedure (operating position on the left-hand side and priming position on the right-hand side).

 

   Results
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In all eight experiments the priming procedure was completed within 4 minutes. At 3,000 to 3,300 rpm the flows of the LIFEBRIDGE system were 5.7 ± 0.2 (range, 5.5 to 6.0 L/min) resulting in complete cardiac unloading in animals with central cannulation, and 4.1 ± 0.2 (range, 3.8 to 4.2 L/min) with peripheral cannulation associated with partial cardiac unloading. Throughout the experiments, the animals' blood gases were within physiologic range with a venous SO2 > 75% and no need for buffering, which indicated sufficient perfusion and gas exchange. Perfusion flows remained stable under all height changes between the animals and the LIFEBRIDGE system (Table 3), and we did not detect any air embolization into the animals' aortas after venous air injection. Even 100 mL venous air injection did not decrease perfusion flow, as air collected in the venous reservoir and was automatically removed. Even "worst-case-conditions" did not result in arterial air embolization; in one pig we intentionally deactivated venous reservoir level sensors and automatic air elimination, and disconnected the venous line until the reservoir and pump head were completely aired and perfusion was stopped. We re-filled the reservoir and pump head with Ringer's lactate, removed the air from the system, and commenced perfusion within 2 minutes with no intraaortic bubble detection.


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  		Table 3. Hemodynamics and Perfusion Data
 

   Comment
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This initial experimental evaluation demonstrates that the LIFEBRIDGE system provides adequate perfusion and gas exchange. Depending on the cannulation site and the dimension of the cannulas, complete cardiac unloading was accomplished that suggests that the LIFEBRIDGE system may be used as an alternative to the heart-lung machine for heart surgery procedures similar to other miniaturized systems [10]. However, the main advantages of this system are true portability due to its dimensions and weight, rapid availability due to its "plug-and-play" design, and simple and safe applicability even for non-perfusionists due to its unique incorporated security features. In addition, the animal data suggest safe operation even under transport conditions as injected air was effectively removed, thus avoiding air embolization, and height changes between animals and the LIFEBRIDGE system did not affect its operation. Therefore we believe that these experimental data appear to justify future clinical evaluation under controlled conditions. Initially we plan to investigate the LIFEBRIDGE system in the setting of elective coronary artery surgery with the back-up of the heart-lung machine as well as in the setting of elective high-risk percutaneous coronary interventions prior to its intended use as an emergency circulatory support system in acute cardiac failure. In the latter setting, two potential problems associated with peripheral cannulation are left ventricular distension and limb ischemia. Left ventricular distension may be minimized by catheter-based transaortic left ventricular venting [11], and peripheral leg ischemia can be prevented by placing a distal perfusion catheter [12].


   Disclosures and Freedom of Investigation
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Uwe Mehlhorn is a consultant and scientific advisory board member. Ekkehard Gutsch, Joachim Wehrle, Kai-U. Kretz, Alois Philipp, and Markus Ferrari are consultants. Hans R. Zerkowski is a member of the board of directors and the scientific advisory board of Lifebridge Medizintechnik GmbH (Ampfing, Germany). Lifebridge Medizintechnik GmbH funded all costs of the present study and donated the tested technology. All authors had full control of the design of the study, methods used, outcomes parameters, analysis of data, and production of the written report.


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The Society of Thoracic Surgeons, the Southern Thoracic Surgical Association, and The Annals of Thoracic Surgery neither endorse nor discourage use of the new technology described in this article.


   Acknowledgments
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We thank Ekkehard Gutsch, CCP, German Heart Center Berlin, Berlin, Germany; Joachim Wehrle, CCP, Division of Cardio-Thoracic Surgery, Unispital Basel, Basel, Switzerland; Kai-U. Kretz, CCP, Heartcenter Ludwigshafen, Ludwigshafen, Germany; and Alois Philipp, CCP, Department of Cardiothoracic Surgery, University Hospital, Regensburg, Germany for their intellectual input and support in developing the LIFEBRIDGE system and conducting the animal experiments, as well as Stefanie Herrmann and Hannah Reiter for their technical assistance in performing the experiments, and Gerold Widenhorn, Compumedics Germany GmbH, Singen, Germany for analyzing the recorded Doppler signals. Financial support was provided by Lifebridge Medizintechnik GmbH (Ampfing, Germany).


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* Modularization is protected by German Utility Models 200 23 276, 299 21 375, 203 07 256. US, Canadian and International patent application pending. Back

{dagger} European patent application pending. Back

* European patent application pending. Back


   References
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  1. Dembitsky WP, Moreno-Cabral RJ, Adamson RM, Daily PO. Emergency resuscitation using portable extracorporeal membrane oxygenation Ann Thorac Surg 1993;55:304-309.[Abstract/Free Full Text]
  2. Bennett JB, Hill JG, Long 3rd WB, Bruhn PS, Haun MM, Parsons JA. Interhospital transport of the patient on extracorporeal cardiopulmonary support Ann Thorac Surg 1994;57:107-111.[Abstract/Free Full Text]
  3. Hill JG, Bruhn PS, Cohen SE, et al. Emergent applications of cardiopulmonary supporta multiinstitutional experience. Ann Thorac Surg 1992;54:699-704.[Abstract/Free Full Text]
  4. Magovern GJ, Simpson KA. Extracorporeal membrane oxygenation for adult cardiac supportthe Allegheny experience. Ann Thorac Surg 1999;68:655-661.[Abstract/Free Full Text]
  5. Bowen FW, Carboni AF, O'Hara ML, et al. Application of "double bridge mechanical" resuscitation for profound cardiogenic shock leading to cardiac transplantation Ann Thorac Surg 2001;72:86-90.[Abstract/Free Full Text]
  6. Schwarz B, Mair P, Margreiter J, et al. Experience with percutaneous venoarterial cardiopulmonary bypass for emergency circulatory support Crit Care Med 2003;31:758-764.[Medline]
  7. Zerkowski HR, Doetsch N, Hellinger A, Reidemeister JC. The concept of lung and heart-lung preservation within the scope of multiple organ procurement Langenbecks Arch Chir 1991;376:102-107.[Medline]
  8. Reichman RT, Joyo CI, Dembitsky WP, et al. Improved patient survival after cardiac arrest using a cardiopulmonary support system Ann Thorac Surg 1990;49:101-104.[Abstract/Free Full Text]
  9. Volk O, Schnitker W, Brass P, et al. Detection of air embolism by a re-usable Doppler probe integrated in a central venous line-application in-vivo Anaesthesist 2002;51:716-720.[Medline]
  10. Wiesenack C, Liebold A, Philipp A, et al. Four years' experience with a miniaturized extracorporeal circulation system and its influence on clinical outcome Artif Organs 2004;28:1082-1088.[Medline]
  11. Kitamura M, Hanzawa K, Takekubo M, Aoki K, Hayashi J. Preclinical assessment of a transaortic venting catheter for percutaneous cardiopulmonary support Artif Organs 2004;28:298-302.[Medline]
  12. Huang SC, Yu HY, Ko WJ, Chen YS. Pressure criterion for placement of distal perfusion catheter to prevent limb ischemia during adult extracorporal life support J Thorac Cardiovasc Surg 2004;128:776-777.[Free Full Text]



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