Correlation of Common Carotid Artery Blood Flow Parameters With Transthoracic Echocardiographic Cardiac Output for Assessing Fluid Responsiveness After Passive Leg Raising (PLR) Test in Critically Ill Patients

Abstract

Introduction The passive leg raising (PLR) test is a simple, non-invasive method of knowing fluid responsiveness by acting as an internal-fluid challenge. The PLR test coupled with a non-invasive assessment of stroke volume would be the ideal method to assess fluid responsiveness. This study aimed to determine the correlation between transthoracic echocardiographic cardiac output (TTE-CO) and common carotid artery blood flow (CCABF) parameters in determining fluid responsiveness with the PLR test. Methods We performed a prospective observational study on 40 critically ill patients. Patients were evaluated with a 7-13 MHz linear transducer probe for CCABF parameters calculated using time-averaged mean velocity (TAmean) and with a 1-5 MHz cardiac probe equipped with tissue doppler imaging (TDI) for TTE-CO calculated using left ventricular outflow tract velocity time integral (LVOT VTI) with an apical five-chamber view. Two separate PLR tests (five minutes apart) were done within 48 hours of ICU admission. The first PLR test was to assess the effects on TTE-CO. The second PLR test was performed to assess the effects on CCABF parameters. Patients were designated as fluid responders (FR) if changes in TTE-CO (Δ TTE-CO) ≥ 10 %. Results A positive PLR test was observed in 33% of patients. A strong correlation was present between absolute values of TTE-CO calculated using LVOT VTI and the absolute values of CCABF calculated using TAmean (r=0.60, p<0.05). However, a weak correlation was found between Δ TTE-CO and changes in CCABF (Δ CCABF) during the PLR test (r=0.05, p<0.74). A positive PLR test response could not be detected by Δ CCABF (area under the curve (AUC): 0.59 ± 0.09). Conclusions We found a moderate correlation between TTE-CO and CCABF at baseline. However, Δ TTE-CO had a very poor correlation with Δ CCABF, during the PLR test. Considering this, CCABF parameters may not be recommended as a means to detect fluid responsiveness with PLR tests in critically ill patients.

Keywords: carotid doppler; fluid responsiveness; lvot vti; passive leg raising test; transthoracic echocardiography.

Figure 1. Flow diagram of patients

Figure 2. Position of the patient during the two PLR maneuvers

PLR, passive leg raising

Figure 3. Probe position for carotid Doppler measurements (anterior view)

Figure 4. Probe position for carotid Doppler measurements (lateral view)

Figure 5. Schematic presentation of Doppler findings of common carotid artery.

PS, peak systolic velocity (white arrow); ED, end-diastolic velocity (yellow arrow); TAmean, time-averaged mean velocity; TAmax, time-averaged peak velocity; PI, pulsatility index; RI, resistivity index; HR, heart rate

Figure 6. Probe position for apical five-chamber view (anterior view)

Figure 7. Probe position for apical five-chamber view (lateral view)

Figure 8. Schematic presentation of LVOT VTI measurement in apical five-chamber view (area under yellow tracing)

LVOT VTI, left ventricular outflow tract velocity time integral

Figure 9. ROC curve for predicting fluid responsiveness with change in CCA blood flow

CCA, common carotid artery; ROC, receiver operating characteristic