Inferior vena cava collapsibility to guide fluid removal in slow continuous ultrafiltration: a pilot study

To investigate whether ultrasound determination of the inferior vena cava diameter (IVCD) and its collapsibility index (IVCCI) could be used to optimize the fluid removal rate while avoiding hypotension during slow continuous ultrafiltration (SCUF).

Twenty-four consecutive patients [13 men and 11 women, mean age 72 +/- 5 years; New York Heart Association (NYHA) functional classes III-IV] with acute decompensated heart failure (ADHF) and diuretic resistance were admitted to our 16-bed medical ICU. Blood pressure (BP), heart rate (HR), respiratory rate (RR), blood samples for hematocrit, creatinine, sodium, potassium, and arterial BGA plus lactate were obtained at baseline and than every 2 h from the beginning of SCUF. IVCD, assessed by M-mode subcostal echocardiography during spontaneous breathing, was evaluated before SCUF, at 12 h, and just after the cessation of the procedure. The IVCCI was calculated as follows: [(IVCD(max) - IVCD(min))/IVCD(max)] x 100.

Mean UF time was 20.3 +/- 4.6 h with a mean volume of 287.6 +/- 96.2 ml h(-1) and a total ultrafiltrate production of 5,780.8 +/- 1,994.6 ml. No significant difference in MAP, HR, RR, and IVCD before and after UF was found. IVCCI increased significantly after UF (P < 0.001). Hypotension was observed only in those patients (2/24) who reached an IVCCI >30%. In all the other patients, a significant increase in IVCCI was obtained without any hemodynamic instability.

IVC ultrasound is a rapid, simple, and non-invasive means for bedside monitoring of intravascular volume during SCUF and may guide fluid removal velocity.