Background: Noninvasive measurement of volume responsiveness may improve care of critically ill ED patients. Ultrasound (US) measurement of cardiac output by left ventricular outflow tract velocity time integral (LVOT VTI) before and after preload augmentation with passive leg raise (PLR) shows promise as a predictor of volume responsiveness but is limited by a need for echocardiography skill and variable sonographic windows. Changes in carotid blood flow (CBF) and corrected carotid flow time (FTc) with PLR may be more reliably measured and have been studied as a predictors of volume responsiveness. Data from euvolemic patients is limited. We sought to determine how carotid flow parameters change with PLR in euvolemic ED patients and if these changes predict volume responsiveness.
Methods: We prospectively enrolled a convenience sample of non-pregnant adult patients in sinus rhythm with complaints unrelated to volume status at a tertiary care academic ED. Patients with known carotid atherosclerotic disease or prior carotid surgery were excluded. Emergency physicians used point-of-care US to measure carotid FTc, CBF, and cardiac output by LVOT VTI before and after 60 seconds of PLR. Patients with increase in cardiac output of 10% after PLR were considered volume responsive. Descriptive statistics were used to analyze data.
Results: 43 patients were enrolled; 2 refused participation and 1 was excluded due to history of carotid atherosclerosis leaving 40 for analysis. Cardiac output, FTc, and CBF increased by a mean of 5.8% (95% CI 0.2% to 11.4%), 6.9% (95% CI -0.2% to 14.0%), and 5.8% (95% CI -2.2% to 15.2%), respectively. 15 (37.5%) were volume responsive. Carotid FTc increase of 10% had sensitivity of 26.7% and specificity of 84% to predict volume responsiveness, with positive predictive value (PPV) of 50% and negative predictive value (NPV) of 65.6% . CBF increase of 10% had sensitivity of 46.7% and specificity of 68% to predict volume responsiveness with PPV of 46.7% and NPV of 68%.
Conclusion: In euvolemic, ED patients there was a mean increase of 6-7% in carotid FTc, CBF, and cardiac output after PLR. In this setting, carotid FTc and CBF did not accurately predict significant increases in cardiac output after PLR.