Recommended Ultrasound Protocol for Kidney and Liver Assessment
For kidney and liver ultrasound assessment, use a curved array 2-5 MHz probe to image both kidneys in longitudinal and transverse planes via intercostal/flank approaches, assess the bladder for volume and obstruction, and evaluate the liver from subcostal windows—this constitutes the basic protocol endorsed by emergency and intensive care guidelines 1, 2.
Kidney Imaging Technique
Patient Positioning and Probe Selection
- Use a curved array abdominal probe (2-5 MHz frequency range) 1
- Position patient in lateral decubitus with bolster under lower side and upper arm fully abducted to spread intercostal spaces 1
- A small footprint or phased array probe facilitates scanning between ribs 1
Right Kidney Approach
- Anterior subcostal approach: Use liver as acoustic window with patient in left lateral decubitus or prone position 1
- Have patient take and hold deep breath to extend liver window 1
- Intercostal approach: Scan between anterior axillary line and midline posteriorly if bowel gas obscures subcostal view 1
- Obtain longitudinal views with probe indicator toward head, parallel to intercostal spaces 1
- Rotate probe 90° counter-clockwise for transverse views 1
Left Kidney Approach
- Requires intercostal approach (no hepatic window available) 1
- Use same technique as right flank intercostal scanning 1
Bladder Assessment
- Image bladder in all suspected renal pathology cases 1
- Scan from top to bottom and side to side in transverse and sagittal planes 1
- Assess for hydronephrosis, bladder overdistention, and volume status—this is a strong recommendation and basic skill 2
Liver Imaging Technique
Standard Approach
- Scan from epigastrium to mesogastrium at umbilicus level 2
- Use transverse and longitudinal planes 2
- Obtain images via right subcostal area, mid-axillary line with orientation marker pointing cranially 2
What to Assess
- Liver morphology and size using B-mode imaging 3, 4
- Hepatorenal recess for free fluid 2
- Portal vein hemodynamics if advanced assessment needed 3
Critical Common Pitfalls
Rib shadowing obscures kidney visualization in transverse views—use small footprint probe or scan in intercostal spaces with longitudinal orientation first 1.
Bowel gas blocks anterior subcostal views of right kidney—switch immediately to intercostal flank approach rather than persisting with inadequate windows 1.
Incomplete examination missing one kidney—always image both kidneys for comparison and to exclude congenital absence 1.
Overlooking bladder assessment—hydronephrosis and urinary retention are frequently unsuspected causes of pathology and must be evaluated systematically 1, 2.
Essential Views to Document
For Kidneys (Basic Skill Level)
- Both kidneys in longitudinal axis 1
- Both kidneys in transverse axis 1
- Bladder in transverse and sagittal planes 1
- Specific assessment for presence/absence of hydronephrosis 2
- Qualitative bladder volume assessment 2
For Liver (Basic Skill Level)
- Transverse and longitudinal views from subcostal approach 2
- Hepatorenal recess evaluation for free fluid 2
Advanced Considerations
The guidelines distinguish basic from advanced skills. Renal Doppler resistive index assessment is NOT recommended as basic skill due to insufficient validation in less experienced operators 2. Similarly, multiparametric liver ultrasound (elastography, fat quantification, contrast-enhanced ultrasound) represents advanced techniques beyond basic assessment 3.
For cirrhotic patients with acute kidney injury, consider expanded POCUS protocol including IVC assessment and lung ultrasound, though this exceeds basic kidney-liver protocol 5, 6.