Paediatrics: Renal insufficiency

Renal insufficiency

Acute renal failure is the sudden reduction or cessation of renal function to the point where body fluid homeostasis is compromised, leading to ac-cumulation of nitrogenous waste products, with or without reduced urine output. Children in this state need immediate attention and transfer to a specialized renal unit. More commonly, we see patients with a degree of renal insufficiency that is complicating an acute medical illness—it may be present at the time of presentation or it may evolve during hospital admis-sion.

Clinical assessment

Take a thorough history and do a full examination. Assess whether there is hypertension or hypotension. Check the urine output (oliguria <0.5mL/ kg/hr) and if anuric suspect obstruction. The particular points you should consider are the following:

·  Whether there has been any preceding throat infection (streptococcus), gastroenteritis (haemolytic-uraemic syndrome (HUS)), or exposure to drugs or toxins.

·  Is there any evidence of general illness with pallor, anorexia, oedema, weakness, and fatigue?

·  Is there a rash, and is it petechial or purpuric?

·  Is there hypertension or signs of heart failure?

·  Is there tachynoea, cough, or haemoptysis?

·  Is there any nausea, vomiting, bleeding, flank mass, or ascites?

·  Is there any evidence of altered consciousness?

Investigations

The following tests are required in acute care:

·  Blood: FBC with differential.

·  Serum biochemistry: electrolytes with urea and creatinine, and arterial or capillary blood gas.

·  Urine: check for any protein, blood, or active sediment (red cell casts, tubular cells, white cell casts, or other evidence of urinary tract infection (UTI)).

·  Imaging: organize a CXR, AXR, and abdominal and renal ultrasound (US) examination with Doppler studies of renal vessel blood flow.

·  Other tests: consider taking blood samples for complement levels (C3, C4), serum titres (e.g. anti-streptolysib O (ASO) titres).

Monitoring

The form and type of monitoring will be dictated by the patient’s condi-tion. Start with:

·  Continuous pulse oximetry.

·  ECG monitoring.

·  Intermittent BP monitoring.

·  Insert a urinary catheter and follow hourly output.

Acute therapy

In the acute setting first assess the ABCs. Then, to assess intravascular volume, come to a decision about whether the patient is hypovolaemic or hypervolaemic.

Hypovolaemia

·Administer 20mL/kg 0.9% normal saline as an IV bolus, and repeat if necessary.

·If the cause of anuria is fluid depletion, fluid resuscitation should restore urine flow within 6hr.

·Give blood if necessary and continue to monitor.

·Acute tubular necrosis is likely if there is no response to the above. Repeat the fluid bolus with furosemide (1–5mg/kg IV), but do not use if obstructive uropathy is suspected—refer to a urologist.

·If the patient produces urine, expect large amounts (which will need to be replaced) as polyuric renal failure may be present.

Hypervolaemia

·  Consider a single dose of furosemide (1–5mg/kg IV).

·If the urine output is minimal then treat as acute renal failure.

Acute renal failure and kidney injury

A child in acute renal failure will need to be transferred to a renal unit. Hypertension, hyperkalaemia, hyponatraemia, and seizures will need to be treated. You should continue to monitor volume state, BP, ECG, and electrolytes. Standard treatment includes the following.

BP

·Hypertension is present if BP >95th centile.

·Restrict salt intake.

·Consider antihypertensive drugs.

Fluids

·Continue to correct and replace volume loss with normal saline.

·Thereafter, restrict fluids to urine replacement and insensible losses (300–400mL/m²/day).

Electrolytes

·Correct hyponatraemia if causing seizures.

·Correct hypocalcaemia if symptomatic—do this before correcting any acidosis.

·Discontinue any potassium administration. (Remember that for every 0.1 fall in pH, potassium will rise by 0.4mmol/L, so you may need to treat acidosis if pH <7.2 and bicarbonate <10mmol/L.)

Diet

·  Limit protein to 0.5–1.0g/kg/day.