What is the most appropriate treatment for a patient with acute kidney injury (AKI) and signs of volume depletion, including orthostasis and dry mucous membranes?

Management of Acute Kidney Injury with Volume Depletion

IV 0.9% sodium chloride is the most appropriate treatment for this patient's acute kidney injury, as the clinical presentation strongly indicates hypovolemic AKI requiring immediate crystalloid volume expansion.

Clinical Assessment of the Case

This patient presents with clear signs of volume depletion causing pre-renal acute kidney injury:

• Physical findings: dry mucous membranes and orthostatic hypotension
• Laboratory findings: low urine sodium (19 mEq/L) and FENa <1% (0.9%)
• No evidence of intrinsic renal disease (no casts, blood, eosinophils)
• Multiple risk factors for AKI: medications (SGLT2 inhibitor, ACE/ARB) and comorbidities

Treatment Algorithm

1. Initial Management: Volume Expansion

• Administer IV 0.9% sodium chloride as first-line therapy 1
• KDIGO guidelines specifically recommend isotonic crystalloids rather than colloids for expansion of intravascular volume in patients with AKI 1
• Target restoration of effective circulating volume to improve renal perfusion

2. Medication Adjustments

• Hold potentially nephrotoxic medications:
  • Temporarily discontinue losartan (can worsen AKI in volume depletion)
  • Temporarily discontinue canagliflozin (SGLT2 inhibitor increases risk of volume depletion)
  • Consider holding metformin until renal function improves

3. Monitoring Response

• Track urine output, vital signs (especially blood pressure and heart rate)
• Monitor serum creatinine and electrolytes every 24-48 hours
• Reassess volume status frequently during resuscitation

Evidence-Based Rationale

Why Crystalloids Are Preferred

The KDIGO guidelines explicitly recommend "using isotonic crystalloids rather than colloids (albumin or starches) as initial management for expansion of intravascular volume in patients at risk for AKI or with AKI" 1. This recommendation is supported by:

• No evidence from randomized controlled trials supporting colloids over crystalloids for resuscitation 1
• Potential harm associated with hydroxyethyl starch (hetastarch) solutions, which can impair renal function 1

Why Other Options Are Inappropriate

1. IV 6% hetastarch: Contraindicated in AKI as starch-containing fluids have been associated with harm in patients with AKI 1

2. IV low-dose dopamine: KDIGO explicitly recommends "not using low-dose dopamine to prevent or treat AKI" (Level 1A evidence against its use) 1, 2

3. Oral tamsulosin: Not indicated for AKI management; used for benign prostatic hyperplasia but has no role in treating volume-depleted AKI

Special Considerations

Volume Assessment

• The patient's presentation with orthostasis, dry mucous membranes, and pre-renal laboratory parameters (low urine sodium, low FENa) strongly indicates hypovolemia requiring volume expansion 2
• Careful fluid assessment is essential to maintain euvolemia without causing volume overload 2

Potential Pitfalls

• Avoid excessive fluid administration: Once hemodynamic stability is achieved, transition to a neutral fluid balance strategy 3, 4
• Monitor for electrolyte disturbances: Particularly hyperchloremic metabolic acidosis with large volumes of normal saline 1
• Reassess need for renal replacement therapy: If oliguria persists despite adequate volume resuscitation 2

In this case, the patient's clinical presentation clearly indicates hypovolemic AKI requiring prompt volume expansion with isotonic crystalloids as the first-line intervention, consistent with KDIGO guidelines and best practices for AKI management.