Understanding Preload Responsiveness 

Preload responsiveness refers to whether a patient increases their stroke volume (volume of blood ejected per heart beat) when given IV fluids or a passive leg raise. Preload responsiveness can be detected by changes in the flow time of the carotid artery (ccFT), and is important to diagnose for patients with shock, sepsis, bleeding, or surgery, as it allows for precision fluid management. Despite increasing evidence supporting the accuracy of ccFTto detect preload responsiveness, three main issues have contributed to inconsistent results in the literature: measurement error by humans, timing mismatches in measurements, and a variable number of heartbeats sampled to estimate ccFT.

A New Study with Refined Techniques

A recent study by Kenny et al. sought to optimize the accuracy of ccFT for detecting preload responsiveness, with the gold standard of transesophageal echocardiography (TEE). This was achieved by synchronizing the timing of measurements from the carotid artery and TEE. The objective of the study was to improve accuracy of ccFT through synchronization of timing with the TEE, automating measurements, and increasing the number of beats averaged to obtain the ccFT.

The Methodology

This ethics board approved study assessed 23 patients undergoing cardiac surgery. A wearable carotid Doppler ultrasound device, FloPatch, was used to measure ccFT. Simultaneously, TEE provided detailed images of the heart and was used to calculate stroke volume.

Key Findings

From the 2310 cardiac cycles analyzed, there were several key findings:

  1. FloPatch accurately detected changes in stroke volume with high sensitivity (91%) and specificity (84%). 
  2. The more cardiac cycles analyzed, the more accurate the results (up to a maximum of 24 consecutive heart beats

Implications for Practice

This study adds to the growing body of evidence demonstrating that carotid Doppler and FloPatch is a non-invasive, rapid, and accurate method to detect preload responsiveness. In addition, carotid Doppler is considerably less invasive than TEE, and does not require advanced training to operate. FloPatch provides a portable solution to tailor precision fluid management in the emergency department, intensive care unit, and operating room.

Kenny JS, et al. Carotid artery corrected flow time detects stroke volume change measured by transesophageal echocardiography.
Intensive Care Medicine Experimental, 11(Suppl 1):000424; 2023.