Focused Real-Time Ultrasonography for Nephrologists

Abstract

We propose that renal consults are enhanced by incorporating a nephrology-focused ultrasound protocol including ultrasound evaluation of cardiac contractility, the presence or absence of pericardial effusion, inferior vena cava size and collapsibility to guide volume management, bladder volume to assess for obstruction or retention, and kidney size and structure to potentially gauge chronicity of renal disease or identify other structural abnormalities. The benefits of immediate and ongoing assessment of cardiac function and intravascular volume status (prerenal), possible urinary obstruction or retention (postrenal), and potential etiologies of acute kidney injury or chronic kidney disease far outweigh the limitations of bedside ultrasonography performed by nephrologists. The alternative is reliance on formal ultrasonography, which creates a disconnect between those who order, perform, and interpret studies, creates delays between when clinical questions are asked and answered, and may increase expense. Ultrasound-enhanced physical examination provides immediate information about our patients, which frequently alters our assessments and management plans.

Figure 1

Prerenal assessment: cardiac contractility and intravascular volume. A1 = subcostal cardiac view (curvilinear or phased-array probe), A2 = parasternal long- and short-axis views (phased-array), B1 = IVC long-axis view (curvilinear or phased-array), B2 = IVC long-axis from midaxillary line view (curvilinear or phased-array), and C = subclavian vein view (high-frequency linear probe) [25]. Adapted from Perera et al. with the authors' permission [4].

Figure 2

Subcostal cardiac landmarks. Subcostal view is a good window for locating the right atrium prior to the IVC, is useful for qualitative assessment of cardiac contractility, and is sensitive for detecting pericardial effusion or tamponade (frequently unsuspected). As in all transthoracic cardiac views, the right ventricle is closest to the ultrasound probe (see Figure 1, probe position A1). Reproduced from http://www.sonoguide.com/FAST.html 10/08/2016.

Figure 3

Subcostal inferior vena cava landmarks. (a) Position of ultrasound probe for visualization of the inferior vena cava (IVC) (see Figure 1, probe position B1). The IVC is located to the right of midline and aorta (AO). (b) Corresponding ultrasound image of the IVC. The IVC is typically measured 2 cm from the right atrium (RA) or just distal to the hepatic vein. The hepatic vein junction to IVC and the IVC junction to right atrium are confirmatory landmarks. Reproduced with permission from Killu et al. [26].

Figure 4

Postrenal/renal assessment: bladder and kidneys. Either a curvilinear or phased-array probe can be used to assess the bladder and kidneys. A = suprapubic view for bladder volume and Foley bulb position, B = RUQ hepatorenal view, and C = LUQ splenorenal view. Adapted from Perera et al. with the authors' permission [4].

Figure 5

Postrenal assessment: bladder. (a) To calculate bladder volume, the maximum anterior-posterior bladder diameter is measured on an axis perpendicular to that of the longitudinal measurements. Volume (mL) = length (cm) × width (cm) × height (cm) × (0.52 to 0.57) for an ellipsoid (see Figure 4, probe position A). (b) shows a Foley bulb deployed in the pelvis of a patient with anuric renal failure. (c) shows a Foley bulb inflated in the prostate. (d) shows a Foley catheter positioned in a bladder filled with coagulated blood of an anuric patient. (e) Bladder is distended around the Foley bulb due to catheter obstruction. (f) Patient with ascites. Suprapubic view is sensitive for detecting pelvic fluid. It may be difficult to differentiate bladder fluid from ascites with ultrasound.

Figure 6

Renal assessment: ultrasound landmarks for kidneys. (a) RUQ hepatorenal view: landmarks for locating the kidney in the lateral right upper quadrant using a phased-array probe. The echogenic line separating the lung from the liver is the diaphragm (see Figure 4, probe position B). Adapted from Perera et al. with the authors' permission [27]. (b) LUQ splenorenal view: landmarks for locating the kidney in the lateral left upper quadrant using a curvilinear probe. The echogenic line separating the lung from the spleen is the diaphragm (see Figure 4, probe position C). Adapted from Montoya et al. with the authors' permission [1].