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Femoral vein Doppler before and after dialysis

Currently, there is growing interest in femoral vein Doppler, mainly due to its perceived ease of image acquisition. Elevated femoral vein pulsatility indicates venous congestion with reasonable specificity. However, this parameter’s low sensitivity may make it unreliable for ruling out congestion (the vein is far from the heart). One study showed that femoral vein Doppler has good accuracy in detecting venous congestion and demonstrates moderate agreement with VExUS grading (Kappa value of 0.62, P < 0.001). Nevertheless, the weak correlation with CVP in this study underscores the caution required due to its low sensitivity. In another study including patients with pulmonary hypertension, a femoral vein stasis index of >0.27 correlated with a right atrial pressure of greater than or equal to 10 mmHg. The stasis index provides information on how long venous flow is interrupted during a cardiac cycle, indicating the degree of congestion (more flow interruption = more congestion). It is calculated as the cardiac cycle time minus antegrade venous flow time divided by the cardiac cycle time (antegrade means flow towards the heart). For instance, if there are no interruptions and the flow is continuous, the index is zero. This index is also applicable to intrarenal venous Doppler. A study by Husain-Syed et al. demonstrated that an increased renal venous stasis index was associated with morbidity and mortality in patients with pulmonary hypertension. However, there’s no need to stress over memorizing specific numbers. If you can qualitatively assess whether the stasis index is elevated or elevated very much, that’s sufficient. Refer to the slides below for better understanding.

I had a dialysis patient with known heart failure and reduced ejection fraction (LVEF ~20%, RV dysfunction with reduced TAPSE [1.2 cm], moderate RV dilation, and mild TR) along with pulmonary hypertension. This patient was admitted for a non-nephrology issue and underwent dialysis on two consecutive days due to mild pulmonary edema. The symptoms quickly resolved. I was then requested to perform POCUS to assess the resolution of congestion. Lung examination primarily revealed A-lines (normal). But the IVC was plethoric, and there was increased portal vein pulsatility. In the hepatic vein, an S-wave almost of similar amplitude as the D-wave was observed (S<D pattern in some cycles). The femoral vein exhibited an elevated stasis index with distinct S and D-waves [See images below]. I recommended one more dialysis session, aiming to normalize the portal vein pulsatility, considering there is only mild tricuspid regurgitation (hence, good likelihood for improvement).

Following the third dialysis session (with a removal of -2.5 L), I performed a follow-up, and you can observe improvements in all the waveforms [see images below]. The hepatic vein now exhibits a normal pattern (S>D), the portal vein shows <30% pulsatility (normal), and the stasis index in the femoral vein has significantly improved (pay particular attention to the resolved gap between S and D-waves). The IVC still exhibits a maximal diameter >2.1 cm, likely chronically dilated, though it would be nice to reassess after a few days once the dry weight is titrated down in the outpatient unit (if the nephrologist is POCUS-enabled).

As a periodic reminder, use simultaneous EKG whenever possible. It aids in precisely identifying the S and D waves and the duration of cardiac cycle if you want to calculate the stasis index. Also, in above case, without EKG, one might dismiss initial portal vein pulsatility as arterial interference (due to relatively sharp spikes). However, with EKG, it becomes evident that the spiky pattern occurs in diastole (representing the venous D-wave). Essentially, EKG minimizes guesswork.