Dear Editor, Invasive arterial blood pressure (IBP) monitoring is routinely employed in anaesthesia and critical care practice, particularly in neurosurgical and high-risk surgical procedures. Accurate interpretation of invasive pressure waveforms is essential as artefacts and technical factors may generate a “ghost” of arterial pulsation—an apparent rhythmic trace without true vascular origin—potentially leading to diagnostic confusion and inappropriate clinical decisions. We report an unusual observation during preparation for IBP monitoring: An oscillatory waveform was displayed on the monitor before arterial cannulation. During the routine setting up, the pressure transducer system was flushed and primed with normal saline, zeroed to atmospheric pressure, and connected to a pressurised flush bag maintained at approximately 300 mmHg. Before the distal end of the pressure tubing was connected to any arterial cannula or vascular access, a regular sinusoidal oscillatory waveform appeared on the monitor. Notably, the distal end of the tubing remained completely unconnected to the patient. The waveform lacked classical arterial morphological features such as a steep systolic upstroke (anacrotic limb) and a dicrotic notch. Despite this, the monitor interpreted the signal as an invasive arterial trace and generated numerical blood pressure values of 23/10 mmHg Figure 1. On deflating the pressure bag, the waveform disappeared immediately, confirming its non-physiological origin.Figure 1: Monitor screenshot showing a sinusoidal oscillatory waveform interpreted as invasive arterial pressure displayed on the invasive blood pressure channelThe pressure monitoring system (TruWave™ PX260, manufactured by Edwards Lifesciences) consisted of a pressure monitoring set with 3 cc volume, 60 inch diameter, and a length of 150 cm. The system was connected to a pressurised flush bag maintained at approximately 300 mmHg. Monitoring was performed using a BeneView T9 patient monitor (Mindray Bio-Medical Electronics Co., Ltd., Shenzhen, China), running System Software Version V5.0 (Internal Version 05.45.00.01, July 2019). Fluid-filled arterial pressure monitoring systems function as second-order dynamic systems, and accurate waveform production requires a sufficiently high natural frequency and optimal dynamic response.1,2 Even small volumes of trapped air have been shown to significantly alter system compliance and impair dynamic response, leading to distortion of the transmitted pressure waveform.2,3 The pressurised flush system creates a closed hydraulic column that is capable of transmitting even minimal mechanical perturbations. Minor oscillations generated within the flush device or transducer diaphragm may propagate through the saline-filled tubing. When the catheter–tubing–transducer assembly behaves as an underdamped system, these perturbations may undergo resonance amplification, producing a continuous sinusoidal waveform. The pressure transducer converts mechanical oscillations into proportional electrical signals. Modern invasive monitors apply signal conditioning and periodicity detection algorithms including frequency-domain analysis to identify pulse-like waveforms within a physiological frequency range. A continuous sinusoidal oscillation contains a dominant fundamental frequency and may therefore be recognised as a pulse-like signal. Once a regular oscillatory pattern is confirmed, systolic and diastolic values are derived from peak and trough amplitudes of each detected cycle. Consequently, a purely mechanical sinusoidal oscillation of sufficient amplitude may be algorithmically interpreted as an arterial waveform, generating discrete blood pressure values even in the absence of vascular coupling. However, the proposed mechanism remains theoretical as no reproducibility testing, natural frequency measurements, or formal analysis of the damping coefficient was performed. Alternative mechanical explanations cannot be excluded, including a continuous micro-leak in the pressurised flush device or undetected micro-bubbles within the tubing, either of which could alter the system’s damping characteristics and promote spontaneous oscillation. Therefore, the physical explanation should be interpreted as speculative. The artefact was recognised during routine setup prior to arterial cannulation. No patient connection had occurred, and no diagnostic delay or near-miss intervention resulted from this event. The waveform resolved immediately when the pressure bag was deflated. Awareness of this benign but potentially misleading artefact is important to avoid misinterpretation during arterial line setup, particularly in time-pressured clinical environments. This observation reinforces the need to confirm the actual vascular connection and to correlate invasive pressure readings with clinical context before accepting the displayed waveforms as physiological. Disclosure of use of artificial intelligence (AI)-assistive or generative tools No artificial intelligence (AI)-assisted technologies were used in the preparation of this manuscript. Author contributions SY Concepts, definition of intellectual content, literature search, conduct of cases, data, manuscript preparation, review and approval All the authors have participated in the review, drafting and final approval of the manuscript. DG Design, manuscript preparation. RV Conduct of cases, data, manuscript preparation. SS Conduct of cases, manuscript preparation review and approval. All the authors have participated in the review, drafting and final approval of the manuscript. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
Yadav et al. (Sun,) studied this question.