Passive leg raise (PLR) is commonly used to evaluate preload fluid responsiveness and may be considered more reproducible than the fluid bolus technique1. The PLR test has the same effect as mobilization of 300 cc of blood from the lower body into the cardiac chambers. The peripheral venous catheter is the most commonly used method of vascular access, and the peripheral venous pressure (PVP) reflects ‘downstream’ pressure to the right atrium. In this experiment, we utilized PVP waveform analysis to assess blood volume status and fluid responsiveness during mild blood volume changes, autotransfusion of 300 cc of blood (PLR test) and the loss of 600 cc of blood at -30 mmHg of Lower Body Negative Pressure (LBNP).
With IRB approval, 38 healthy subjects underwent a PLR test for 2 minutes followed by LBNP induced mild hypovolemia of -30 mmHg. Each subject was connected to EKG, BP monitor, and NICOM (Cheetah Medical, MA, USA) to measure Thoracic Fluid Content (TFC). The Intravenous catheter was transduced and PVP waveforms were recorded at 100 Hz with a data acquisition system (Collect 5/S, GE). PVP waveform was analyzed using time domain analysis (mean PVP value) and frequency analysis (spectrum,2K, Hamming, Amplitude Density(AD), 93.75% overlap) with LabChart 7.3.7 (ADInstruments). The frequency domain analysis of the PVP waveform included measuring the amplitude density of PVP DC (at respiratory frequency) and cardiac frequency and calculating the PVP DC% (the ratio of AD at respiratory to cardiac) at baseline, PLR and -30 mmHg.
According to the PVP waveforms analysis, from the baseline to the PLR test, the mean PVP and TFC significantly increased by 48% and 1% respectively, while the DC% PVP decreased significantly by 2%. However, from the PLR test to -30 mmHg, the mean PVP and TFC significantly decreased by 50% and 6% respectively, while the DC% PVP significantly increased by 109%.
Transient PLR testing resulted in increased preload, which led to an increase in total fluid content and was reflected as an increase in Mean PVP at the peripheral and a reduction in the PVP DC%.
During mild hypovolemia, then PVP DC% increased, while mean PVP and TFC decreased. These results have demonstrated the potential of using the PVP waveform as a clinical tool for monitoring changes in blood volume.
El Sobky, Abubakr T., "New Method of Analysis of PVP Waveform to Detect Changes in Blood Volume" (2020). Internship Reflection Papers. 2074.
The views expressed in this paper are solely those of the author.