From the Guidelines
Ultrasound (US) is the preferred initial imaging modality for evaluating patients with acute kidney injury (AKI) and urinary retention, as it can detect hydronephrosis and guide intervention. The use of US in this context is supported by the American College of Radiology, which notes that US has the greatest diagnostic value in detecting hydronephrosis associated with acute urinary tract obstruction 1. The primary indications for US in AKI with urinary retention include suspected urolithiasis, hydronephrosis, or evaluation of the size and position of the kidneys.
Some key points to consider when using US in this context include:
- US is highly sensitive (>90%) for hydronephrosis and bladder distension, allowing localization of the level of obstruction and guiding intervention such as Foley catheter placement or nephrostomy/stenting 1
- The highest yield for US is in patients with risk factors for urinary obstruction, such as pelvic tumors, bladder disorders, prostate hypertrophy, stone disease, and pelvic surgery 1
- Hydronephrosis does not necessarily indicate obstruction, and other causes such as a distended bladder, reflux, pregnancy, postobstructive dilation, or diuresis may cause ureteral and collecting system dilatation 1
- Color Doppler can be used to assess global perfusion and confirm arterial and venous patency 1
In cases of urinary retention with AKI, prompt imaging with US is essential to identify reversible causes of obstruction that may require urgent intervention such as catheterization or nephrostomy tube placement to relieve pressure and prevent further kidney damage 1. The use of US in this context is also supported by the American College of Emergency Physicians, which notes that emergency ultrasound of the kidneys and urinary tract may identify both normal and pathological conditions, and can be used to evaluate obstructive uropathy and acute urinary retention 1.
From the Research
Indications for USG in AKI/Retention
- The use of ultrasound (USG) in Acute Kidney Injury (AKI) is essential for identifying reversible causes of AKI or underlying chronic kidney disease 2.
- USG assessment can help in the early detection of AKI, which is crucial for preventing long-term sequelae such as chronic kidney disease, cardiovascular events, and mortality 3, 4.
- The ultrasound SERVeillance framework, which includes assessment of renal size, echogenicity, renal hilum, and vascularity, can be used for the imaging assessment of AKI 2.
Management of AKI
- The management of AKI involves appropriate volume control, nephrotoxic drug management, and the timing and type of kidney support 3, 5.
- Fluid and electrolyte management are essential in the management of AKI, and kidney replacement therapy is frequently required in critically ill patients 3, 5.
- Early determination of etiology, management, and long-term follow-up of AKI are essential to prevent long-term consequences such as chronic kidney disease and cardiovascular morbidity 4.
Diagnosis and Definition of AKI
- AKI is defined as an increase in serum creatinine or a decrease in urine output over hours to days 4, 6.
- The Kidney Disease: Improving Global Outcomes (KDIGO) group has established consensus definitions for AKI, which include an increase in serum creatinine levels by at least 0.3 mg/dl within 48 hours or 1.5-fold the baseline, or urine volume less than 0.5 ml/kg/hour for at least 6 hours 6.