Not all pulse contour algorithms are created equal

We read with interest the article by Lamarche-Fontaneto et al. [1] on cardiac output (CO) monitors in septic shock. We fully agree that pulmonary artery catheterization and transpulmonary thermodilution have value in this context, not only for measuring CO but also for gaining additional insights, such as pulmonary artery pressures or extravascular lung water. However, we felt that pulse contour techniques were dismissed too quickly, without considering the differences between the underlying algorithms.

Pulse contour techniques are generally classified as either calibrated or non-calibrated, with the common belief that calibrated ones are more accurate and precise. It is important to note that the algorithms may be identical. For example, the PiCCO and the ProAQT systems (Getinge, Sweden) use the same pulse contour algorithm. Similarly, the LiDCOplus and LiDCOrapid systems rely on the same PulseCO algorithm (Masimo, USA). The former are simply calibrated or reset periodically using dilution methods, while the latter are not. Consequently, calibrated methods are seen as more accurate, not because they have superior algorithms, but primarily because they are regularly reset to reference values.

Regarding uncalibrated pulse contour analysis, it is unclear why Lamarche-Fontaneto et al. [1] mentioned that “PRAM is not plug-and-play and waveform quality must be continuously verified and optimized.” Unlike the FloTrac and ProAQT algorithms, which require specific pressure transducers, the PRAM algorithm can analyze arterial pressure waveforms recorded with any standard pressure transducer. Therefore, it is easier to set up. This feature, shared with other algorithms (e.g., the MBA algorithm from Retia, USA), also offers the advantage of improving the sustainability and reducing the cost of CO monitoring [2]. Additionally, all algorithms that analyze waveform characteristics are affected by artifacts and damping phenomena, and we are not aware of any studies comparing how abnormal waveforms impact the performance of existing pulse contour algorithms. Notably, the PRAM algorithm now incorporates an electronic filter specifically designed to detect and correct underdamping phenomena [3], which may offer an advantage over other pulse contour methods. Regardless of the algorithm used, clinicians need to inspect the arterial pressure waveform for abnormalities and address them promptly. Failure to do so can lead to inaccurate blood pressure and CO measurements.

Clinical studies have reported significant variability in the performance of uncalibrated pulse contour algorithms. This variability likely stems from differences in clinical settings (operating room vs. ICU) and patient conditions (hemodynamic stability vs. instability). The heterogeneity of validation studies complicates any direct comparison between algorithms. However, a few studies [4,5,6,7,8] have directly compared several pulse contour algorithms against a reference CO measurement technique; these are summarized in Table 1. In addition, some algorithms have been shown to underestimate CO in the context of vasodilation and vasopressor administration [9], while others appear unaffected [10]. These findings emphasize that pulse contour algorithms do not perform uniformly and should not be thrown away in the same bucket.

Table 1 Studies comparing simultaneously several pulse contour algorithms to a reference cardiac output measurement technique

Full size table

In conclusion, we argue that not all uncalibrated pulse contour algorithms are created equal. The most robust among them may warrant further evaluation in complex ICU patients, including those with septic shock.

No datasets were generated or analysed during the current study.

CO:

cardiac output

ICU:

Intensive Care Unit

MBA:

MultiBeat Analysis

PRAM:

Pressure Recording Analytical Method

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Authors and Affiliations

1. MiCo, Vallamand, Switzerland

   Frederic Michard

2. Department of Health Science, Section of Anaesthesia and Intensive Care, Department of Anesthesia and Intensive Care, University of Florence, Azienda Ospedaliero-Universitaria Careggi, Florence, Italy

   Stefano Romagnoli

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1. Frederic MichardView author publications

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2. Stefano RomagnoliView author publications

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FM drafted the manuscript, and both authors revised the manuscript and approved the final version.

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Correspondence to Frederic Michard.

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Competing interests

FM is the founder and managing director of MiCo, a Swiss consulting and research firm. MiCo does not sell any medical devices. SR received fees for congress presentations, travel, and accommodation from Masimo (Irvine, CA, USA) and Vygon (Ecouen, France).

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Michard, F., Romagnoli, S. Not all pulse contour algorithms are created equal. Crit Care 29, 336 (2025). https://doi.org/10.1186/s13054-025-05589-z

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• Received: 18 July 2025

• Accepted: 26 July 2025

• Published: 30 July 2025

• DOI: https://doi.org/10.1186/s13054-025-05589-z

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Keywords

• Hemodynamic monitoring
• Cardiac output
• Pulse contour analysis
• Pulse contour algorithm
• Pulse wave analysis