Journal of Clinical Monitoring and Computing

, Volume 29, Issue 6, pp 807–813 | Cite as

Continuous noninvasive arterial pressure measurement using the volume clamp method: an evaluation of the CNAP device in intensive care unit patients

  • Julia Y. Wagner
  • Ileana Negulescu
  • Miriam Schöfthaler
  • Alexander Hapfelmeier
  • Agnes S. Meidert
  • Wolfgang Huber
  • Roland M. Schmid
  • Bernd Saugel
Original Research


The CNAP system allows continuous noninvasive arterial pressure measurement based on the volume clamp method using a finger cuff. We aimed to evaluate the agreement between arterial pressure measurements noninvasively obtained using the CNAP device and arterial catheter-derived arterial pressure measurements in intensive care unit patients. In 55 intensive care unit patients, we simultaneously recorded arterial pressure values obtained by an arterial catheter placed in the abdominal aorta through the femoral artery (criterion standard) and arterial pressure values determined noninvasively using CNAP. We performed Bland–Altman analysis and calculated the percentage error. The mean difference (±standard deviation, 95 % limits of agreement, percentage error) between noninvasive (CNAP) and invasively assessed arterial pressure was for mean arterial pressure +1 mmHg (±9 mmHg, −16 to +19 mmHg, 22 %), for systolic arterial pressure −10 mmHg (±16 mmHg, −42 to +21 mmHg, 27 %), and for diastolic arterial pressure +7 mmHg (±9 mmHg, −10 to +24 mmHg, 28 %). Our results indicate a reasonable accuracy and precision for the determination of mean and diastolic arterial pressure by noninvasive continuous arterial pressure measurements using the volume clamp method compared with the criterion standard (invasive arterial catheter). Systolic arterial pressure is determined less accurately and precisely.


Blood pressure Critical care Hemodynamic monitoring Vascular unloading technology Photoplethysmography 



The authors thank CNSystems Medizintechnik AG (Graz, Austria) for providing the technical equipment needed for the study and Johannes N. Müller for his assistance with the study.

Conflict of interest

W.H. and B.S. collaborate with Pulsion Medical Systems SE (Feldkirchen, Germany) as members of the Medical Advisory Board. J.Y.W., A.S.M., and B.S. received refunds of travel expenses from CNSystems Medizintechnik AG (Graz, Austria). CNSystems Medizintechnik AG (Graz, Austria) provided the technical equipment for recording and extraction of arterial pressure measurements. For all other authors there is no conflict of interest to disclose.


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Copyright information

© Springer Science+Business Media New York 2015

Authors and Affiliations

  • Julia Y. Wagner
    • 1
    • 4
  • Ileana Negulescu
    • 2
  • Miriam Schöfthaler
    • 2
  • Alexander Hapfelmeier
    • 3
  • Agnes S. Meidert
    • 2
  • Wolfgang Huber
    • 2
  • Roland M. Schmid
    • 2
  • Bernd Saugel
    • 2
    • 4
  1. 1.III. Medizinische KlinikKlinikum rechts der Isar der Technischen Universität MünchenMunichGermany
  2. 2.II. Medizinische Klinik und PoliklinikKlinikum rechts der Isar der Technischen Universität MünchenMunichGermany
  3. 3.Institut für Medizinische Statistik und EpidemiologieKlinikum rechts der Isar der Technischen Universität MünchenMunichGermany
  4. 4.Department of Anesthesiology, Center of Anesthesiology and Intensive Care MedicineUniversity Medical Center Hamburg-EppendorfHamburgGermany

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