Inferior Vena Cava (IVC) Size in Acute Renal Failure

Consecutive patients presenting to the intensive care unit with a diagnosis of acute renal failure (defined as a 1.5 fold increase in plasma Creatinine level compared to baseline ).

Baseline characteristics will be recorded and followed for each patient, these include:

• Demographics
• Medical history
• Hemodynamic parameter such as Central Venous Pressure (CVP), Mean Arterial Pressure (MAP) , and measurement of superior vena cava (SVC) size by ultrasound.
• Laboratory parameter such as chemistry, fractional excretion of sodium , fractional excretion of urea , beta natriuretic peptide , albumin
• Radiographic parameters
• Echocardiographic parameters including Left Ventricular Ejection Fraction (LVEF), Right Ventricular (RV) function and IVC size and variations
• Mechanical ventilation
• Daily fluid balance

Focused bedside ultrasound will be performed for each patient as part of their routine care and initial assessment. The IVC size will be measured at the subcostal window, during inspiration and expiration, using the (Sonosite) Cardiac probe P-21 (5-1 MHZ). The measurement is obtained by applying the M-mode, perpendicular to the IVC axis and 2 cm caudal from its junction with the right atrium.

In spontaneously breathing, non-ventilated patients, we will calculate the IVC collapsibility index (IVC-CI) = [IVC max-IVC min]/IVC max.

Whereas in patients who are mechanically ventilated we will calculate their IVC variation index (ΔIVC) = IVC max-IVC min/ IVC mean diameter.

IVC-CI, ΔIVC, IVC size will be used to classify patient as volume responders or non-responder. Prior studies have suggested Intravascular volume depletion is likely present when the, IVC<1 cm , IVC-CI is > 50% in spontaneously breathing patients and volume responsiveness when the ΔIVC is ≥ 12% in mechanically ventilated patient .

The Fractional excretion of sodium as well as the fractional excretion of urea (when diuretics are used) will be calculated to classify the etiology of the renal failure as pre-renal or intrinsic renal failure.

Fluid balance as well as the change in plasma Creatinine level at 48 hours post admission will be recorded.

Two groups of patients will be identified:

• Group 1 includes the patients who were managed in concordance with their IVC measurements (Volume responders who had a positive fluid balance at 48 h post admission and volume non responders who had an even or negative fluid balance at 48 hours post admission).
• Group 2 includes the patients in whom the fluid management was discordant with the IVC measurement.

Analyses will be done at 24 as well as 48 hours post admission.

Inclusion criteria

• patients presenting to the intensive care unit with a diagnosis of acute renal failure (defined as a 1.5 fold increase in plasma Creatinine level compared to baseline)

Exclusion criteria

• Age<18 years
• Hemodialysis or continuous renal replacement therapy(CRRT)
• Untreated obstructive uropathy
• Pulmonary emboli