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Ultrasound - Renal

Indications

To assess and exclude the presence of:

Obstructive uropathy

Acute urinary retention

Consider in the following presentations:

Abdominal or loin pain

Haematuria

Undifferentiated fever or shock

Contraindications (absolute in bold)

Airway management or resuscitation required

Alternatives

Formal ultrasound scan

CT KUB

CT abdomen with contrast

Informed consent

Medical emergency

Consent is not required if the patient lacks capacity or is unable to consent

Brief verbal discussion is recommended if the situation allows

or

Verbal consent

Less complex non-emergency procedure with low risk of complications

Potential complications

Failure to visualise structures (excess tissue, pain)

Failure of image interpretation (false negative or positive)

Procedural hygiene

Standard precautions

PPE: non-sterile gloves

Area

Any bed

Staff

Procedural clinician

Equipment

Towel

Ultrasound machine and gel

Curvilinear ultrasound probe (abdominal pre-set or adjust depth to centre important structures)

Positioning

Patient supine on a bed

Right kidney: probe at most inferior rib space in the mid-axillary line (marker towards head)

Left kidney: probe at the second most inferior rib space in the posterior maxillary line (marker towards head)

Bladder: probe superior to pubic symphysis with beam inferior (marker to the right)

Medication

500ml oral or IV fluid bolus 20 minutes prior to imaging (dehydration may mask renal obstruction)

Sequence (scanning)

Visualise the right kidney using the liver as an acoustic window, applying anticlockwise rotation to align with ribs

Rock the probe from superior to inferior pole of the kidney (visualising the entire kidney)

Rotate the probe 90 degrees (marker anterior) and fan from superior to inferior (view in a second plane)

Visualise the left kidney using the spleen as an acoustic window, applying clockwise rotation to align with ribs

Rock the probe from superior to inferior pole of the kidney (visualising the entire kidney)

Rotate the probe 90 degrees (marker anterior) and fan from superior to inferior (view in a second plane)

Visualise the bladder in the transverse plane rocking probe to visualising the entire bladder (marker right)

Rotate the probe 90 degrees (marker towards head) and fan from superior to inferior (longitudinal view)

Consider ultrasound of the aorta to exclude abdominal aortic aneurysm

Sequence (assessing obstructive uropathy)

Compare both kidneys to identify the presence of either unilateral or bilateral pathology

Normal: renal sinus is a homogeneously hyperechoic (renal collecting system contains no urine)

Mild hydronephrosis: enlarged anechoic calices (dilated with urine) with preservation of renal papillae

Moderate hydronephrosis: calices are confluent resulting obliterated papillae in a ‘bear’s paw’ appearance

Severe hydronephrosis: caliceal ballooning with effacement of the renal parenchyma and cortical thinning

Sequence (assessing urinary retention)

Scan bladder in the transverse plane and measure bladder width at widest point (marker to the right)

Rotate probe 90 degrees (marker towards head) and measure the bladder length and anterior-posterior depth

Bladder volume = 0.75 x width x length x depth (>600ml often indicates retention)

Post-procedure care

Clean ultrasound gel from patient

Initiate further management if required

Document (indication, structures identified, interpretation)

Tips

Taking and holding a deep breath can improve the renal views

A full bladder with distension may be a cause of artefactual hydronephrosis

Most ultrasound machines will calculate bladder volume for you once measurements are inputted

Always consider symptomatic abdominal aortic aneurysm as a cause of abdominal pain

Discussion

The main indications for emergency department ultrasound are to exclude urinary retention at the bedside and to exclude obstructive uropathy as a potential source of infection in the critically unwell patient.

Renal ultrasound can also be used in suspected renal colic when clinical suspicion of a kidney stone is high and concern for alternative causes is low (this patient group can also be managed without any imaging in the emergency department). Patients suitable for renal ultrasound are generally younger patients with typical renal colic pain that remits spontaneously, or with analgesia, and have no features on history, examination or laboratory investigations that suggest complicated renal stones or a serious alternate diagnosis (fever, UTI, lack of haematuria, high analgesia requirements, palpable mass). Other groups will require a reduced-radiation dose CT (CT KUB).

Ultrasound sensitivity and specificity for identifying stones in renal colic is low, but ultrasound is accurate at identifying hydronephrosis, the present of which is specific for larger kidney stones >5mm. Many stones will not be visualised and do not cause hydronephrosis, however in these cases a normal renal sonogram identifies renal colic patients at low risk for urologic intervention who may be suitable for observation without CT.

An emergency department point-of-care ultrasound may therefore be useful in renal colic to screen for hydronephrosis. The presence of which likely indicates a larger stone which warrants investigation with a CT KUB. A normal POCUS scan can be treated as likely renal colic with a smaller stone likely to pass spontaneously.

Peer review

This guideline has been reviewed and approved by the following expert groups:

Emergency Care Institute

Please direct feedback for this procedure to ACI-ECIs@health.nsw.gov.au.

References

Roberts JR, Custalow CB, Thomsen TW. Roberts and Hedges’ clinical procedures in emergency medicine and acute care. 7th ed. Philadelphia, PA: Elsevier; 2019.

Dunn RJ, Borland M, O’Brien D (eds.). The emergency medicine manual. Online ed. Tennyson, SA: Venom Publishing; 2019.

Huggins JT, Mayo P. Indication for bedside ultrasonography in the critically-ill adult patient. UpToDate, 2020 Jan 17. Available from: https://www.uptodate.com/contents/indications-for-bedside-ultrasonography-in-the-critically-ill-adult-patient

Emergency ultrasound imaging criteria compendium. Ann Emerg Med. 2016;68(1):e11-e48. doi:10.1016/j.annemergmed.2016.04.028

Dawson M, Mallin M. Introduction to bedside ultrasound: volume 1. New York NY: Apple Books; 2013.

Dawson M, Mallin M. Introduction to bedside ultrasound: volume 2. New York NY: Apple Books; 2013.

Choosing Wisely Australia. Recommendations: . 2015. Available from: https://www.choosingwisely.org.au/recommendations/acem

Skolarikos A, Straub M, Knoll T, et al. Metabolic evaluation and recurrence prevention for urinary stone patients: EAU guidelines. Eur Urol. 2015;67(4):750-763. doi:10.1016/j.eururo.2014.10.029

Moore CL, Carpenter CR, Heilbrun ML, et al. Imaging in suspected renal colic: systematic review of the literature and multispecialty consensus. J Urol. 2019;202(3):475-483. doi:10.1097/JU.0000000000000342

Wong C, Teitge B, Ross M, Young P, Robertson HL, Lang E. The accuracy and prognostic value of point-of-care ultrasound for nephrolithiasis in the emergency department: a systematic review and meta-analysis. Acad Emerg Med. 2018;25(6):684-698. doi:10.1111/acem.13388

Yan JW, McLeod SL, Edmonds ML, Sedran RJ, Theakston KD. Normal renal sonogram identifies renal colic patients at low risk for urologic intervention: a prospective cohort study. CJEM. 2015;17(1):38-45. doi:10.2310/8000.2013.131333

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