Critical Care Nephrology and Kidney Support — Advanced

A child with a congenital solitary kidney requires long-term surveillance for hyperfiltration injury. Annual blood pressure measurement and urine protein assessment, together with avoidance of nephrotoxins and escalation if hypertension, proteinuria, or reduced kidney function develops, is appropriate. Routine permanent restriction of physical activity, prophylactic ACE inhibition without hypertension or proteinuria, or transplant listing with normal kidney function is not indicated.

In patients receiving diuretics, urine sodium and FENa are unreliable because diuretics increase natriuresis and raise urine sodium irrespective of intravascular volume status. FEUrea is less affected by diuretics and a low FEUrea (classically <35%) suggests a pre-renal (functional) aetiology. Renal ultrasound is useful to exclude obstruction but does not reliably distinguish pre-renal from intrinsic renal causes. Serum BNP provides information about cardiac strain but is not specific enough to determine the mechanism of AKI in this setting.

Persistent hyperkalaemia with ECG changes despite temporising measures is an indication for urgent removal of potassium by renal replacement therapy (usually haemodialysis if available rapidly). Repeating temporising therapies may delay definitive treatment when ECG abnormalities persist. Oral/resin binders act slowly and are unsuitable as sole therapy in this emergency. Sodium bicarbonate may help if there is severe acidosis, but if ECG changes persist it is insufficient alone. An insulin infusion strategy is not a standard immediate substitute for dialysis when temporising measures have failed.

In haemodynamically unstable critically ill patients requiring ongoing vasopressor support, continuous renal replacement therapy (CRRT) is generally preferred because it provides slower, continuous solute and fluid removal with better haemodynamic tolerance. Intermittent haemodialysis may precipitate hypotension in unstable patients. Short daily IHD is used chronically but is not appropriate acutely in severe shock. Peritoneal dialysis is rarely used in high-acuity septic shock in modern ICUs and provides limited ultrafiltration in the presence of intra-abdominal processes. SLED can be considered where CRRT is unavailable, but CRRT remains the standard for persistent severe haemodynamic instability.

Regional citrate anticoagulation is generally preferred for CRRT in patients without contraindications, especially when bleeding risk is high, because it limits systemic anticoagulation. However, severe liver failure (or severe shock with impaired citrate metabolism) is a relative contraindication to citrate due to risk of citrate accumulation and metabolic complications. In this context, avoiding citrate and running CRRT without anticoagulation (with higher blood flow rates, regular saline flushes and maximised circuit care) is appropriate. Systemic unfractionated heparin increases bleeding risk and is undesirable in severe hepatic failure with coagulopathy. LMWH is contraindicated if bleeding risk is high and is poorly controllable. Warfarin is inappropriate for extracorporeal circuit protection.

KDIGO guidelines recommend prescribing an effluent volume that achieves an average delivered dose of approximately 20–25 mL/kg/h for CRRT. Higher doses (e.g., 35–50 mL/kg/h) have not shown outcome benefit in randomised trials and increase costs/complications. Lower doses (<20 mL/kg/h) risk inadequate solute control. The figure refers to delivered (not simply prescribed) dose; attention should be paid to interruptions and clotting which reduce delivered therapy.

Severe metabolic acidosis that is refractory to appropriate medical therapy and associated with clinical consequences (hemodynamic instability, progressive encephalopathy) is an accepted indication for initiating renal replacement therapy. There is no fixed rule requiring pH <6.9 before dialysis; waiting that low would be unsafe. The presence of hyperkalaemia is not required to start dialysis for acidosis. Choice of modality (CRRT versus intermittent haemodialysis) depends on haemodynamic stability; switching to intermittent haemodialysis just to correct acidosis is not appropriate if the patient is unstable.

In confirmed HIT, all heparin products should be stopped. When citrate is contraindicated and systemic monitoring is available, a direct thrombin inhibitor such as argatroban is an appropriate preferred systemic anticoagulant for the extracorporeal circuit. Regional citrate is an alternative only when not contraindicated; LMWH and unfractionated heparin should not be used.

Recent evidence and guideline interpretations favour the use of balanced crystalloids over 0.9% saline in patients with sepsis to reduce the risk of kidney injury and need for RRT. Balanced solutions have lower chloride content and more physiologic strong ion difference, which may reduce hyperchloraemic metabolic acidosis and adverse renal effects. 0.9% saline is still used but is not preferred in this context. Dextrose-containing fluids and hypotonic or hypertonic saline are not appropriate for routine large-volume resuscitation in sepsis.

S. aureus bacteraemia in a patient with a vascular access device is a high-risk situation associated with metastatic infection; guidance supports prompt removal of the implicated catheter and systemic antibiotic therapy. Exchanging the catheter over a guidewire risks ongoing seeding. Short IV antibiotics alone without catheter removal are insufficient. Antibiotic lock therapy is adjunctive and never a sole therapy for S. aureus bacteraemia.