Development and validation of a measurement system for continuously monitoring postoperative reservoir levels

  • S. EichhornEmail author
  • T. Reisinger
  • J. Böhm
  • S. Voss
  • S. Doppler
  • R. Lange
  • M. Krane
Scientific Note


Following cardiac surgical procedures, multiple drainage systems remain in place inside the patient’s chest to prevent the development of pericardial effusion or pneumothorax. Therefore, postoperative bleeding must be diligently observed. Currently, observation of the exudate rate is performed through periodical visual inspection of the reservoir. To improve postoperative monitoring, a measurement system based on load cells was developed to automatically detect bleeding rates. A reservoir retaining bracket was instrumented with a load cell. The signal was digitized by a microcontroller and then processed and displayed on customized software written in LabView. In cases where bleeding rates reach critical levels, the device will automatically sound an alarm. Additionally, the bleeding rate is displayed on the screen with the status of the alarm, as well as the fluid level of the reservoir. These data are all logged to a file. The measurement system has been validated for gain stability and drift, as well as for sensor accuracy, with different in vitro examinations. Additionally, performance of the measurement device was tested in a clinical pilot study on patients recovering from cardiac surgical procedures. The in vitro investigation showed that the monitoring device had excellent gain and drift stability, as well as sensor accuracy, with a resolution of 2.6 mL/h for the bleeding rate. During the clinical examination, bleeding rates of all patients were correctly measured. Continuously recording drainage volume using the developed system was comparable to manual measurements performed every 30 min by a nurse. Implementation of continuous digital measurements could improve patient safety and reduce the workload of medical professionals working in intensive care units.


Postoperative monitoring Surgical reservoir Measurement system 



This study was funded by budget funds from the German Heart Center Munich (Munich, Germany).

Compliance with ethical standards

Conflict of interest

All authors declare no conflict of interest.

Ethical approval

All procedures involving human participants were performed in accordance with the ethical standards of the institutional and/or national research committee (the Committee for Medical Ethics of the medical faculty at the Technische Universität München / No. 517/16K) and with the Declaration of Helsinki and its later amendments or comparable ethical standards.

Informed consent

Informed consent was obtained from all individuals participating in this study.


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Copyright information

© Australasian College of Physical Scientists and Engineers in Medicine 2019

Authors and Affiliations

  • S. Eichhorn
    • 1
    • 2
    Email author
  • T. Reisinger
    • 1
    • 2
  • J. Böhm
    • 1
    • 2
  • S. Voss
    • 1
    • 2
  • S. Doppler
    • 1
    • 2
  • R. Lange
    • 1
    • 2
    • 3
  • M. Krane
    • 1
    • 2
    • 3
  1. 1.Department of Cardiovascular SurgeryGerman Heart Center Munich at the Technische Universität MünchenMunichGermany
  2. 2.Department of Cardiovascular SurgeryINSURE (Institute for Translational Cardiac Surgery), Technische Universität MünchenMunichGermany
  3. 3.DZHK (German Center for Cardiovascular Research), Partner Site Munich Heart AllianceMunichGermany

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