How should the Plasmalyte (crystalloid fluid) rate be adjusted in patients with lactic acidosis and acute kidney injury (AKI)?

Adjusting Plasmalyte Rate in Patients with Lactic Acidosis and AKI

Direct Recommendation

In patients with lactic acidosis and AKI, use buffered crystalloid solutions like Plasmalyte at an initial rate of 75-100 mL/h (approximately 1-1.5 mL/kg/h), guided by repeated hemodynamic assessment, with the goal of achieving euvolemia while avoiding fluid overload. 1, 2

Rationale for Buffered Crystalloids in This Context

Why Plasmalyte Over Normal Saline

• Buffered crystalloid solutions (including Plasmalyte) are strongly recommended over 0.9% saline in AKI patients because large volumes of saline cause hyperchloremic acidosis, renal vasoconstriction, and worsen kidney injury 1
• In patients with existing lactic acidosis, adding hyperchloremic acidosis from saline creates a compounded acid-base disturbance that complicates management 1
• Multiple large trials demonstrate that buffered solutions reduce major adverse kidney events (MAKE) compared to saline, particularly when larger fluid volumes are administered 1

Critical Caveat About Lactate-Buffered Solutions

• While Plasmalyte is acceptable, avoid lactate-buffered solutions (like Lactated Ringer's) in patients with severe lactic acidosis and circulatory shock 1
• KDIGO guidelines specifically recommend bicarbonate-buffered solutions over lactate-buffered solutions for RRT in patients with AKI and lactic acidemia 1
• Plasmalyte contains acetate and gluconate (not lactate) as buffers, making it appropriate for this clinical scenario 1

Initial Fluid Rate Strategy

Starting Rate

• Begin with 75-100 mL/h (approximately 1-1.5 mL/kg/h for average adults) to maintain adequate renal perfusion 2
• This rate targets urine output >0.5 mL/kg/h while preventing tubular toxicity from dehydration 2

Hemodynamic Assessment Before Initiation

• Assess for contraindications before starting fluids: volume overload, cardiac dysfunction, pulmonary edema, or signs of fluid intolerance 1, 2
• Use dynamic indices (passive leg-raising test, pulse pressure variation, stroke volume variation) rather than static pressures (CVP) to assess fluid responsiveness 1, 3
• In hemodynamically unstable patients with lactic acidosis, earlier vasopressor use may be more appropriate than aggressive fluid loading 1

Adjusting the Rate: A Phased Approach

Phase 1: Initial Resuscitation (First 6-12 Hours)

• If hypovolemic with ongoing hypoperfusion: Increase rate to achieve hemodynamic stability, but reassess frequently 1
• If euvolemic or fluid-responsive: Continue maintenance rate of 75-100 mL/h 2
• If signs of fluid overload develop: Reduce rate or discontinue, consider earlier RRT 1, 4

Phase 2: Post-Stabilization (After 12-24 Hours)

• Switch to conservative fluid strategy once hemodynamic stabilization is achieved 1, 4, 3
• Target neutral to negative fluid balance to prevent organ dysfunction from interstitial edema 4, 3
• In AKI patients, fluid overload >10-15% body weight is associated with adverse outcomes 1

Phase 3: Ongoing Management

• Reassess fluid status every 6-12 hours using clinical examination, urine output, hemodynamic parameters, and cumulative fluid balance 2, 3
• Adjust rate based on: urine output trends, resolution of lactic acidosis, improvement in AKI stage, and absence of fluid overload signs 2, 3

Monitoring Parameters

Essential Monitoring

• Urine output: Target >0.5 mL/kg/h 2
• Lactate levels: Should stabilize or decrease within 4-24 hours if perfusion is adequate 5
• Serum creatinine and AKI stage: Track progression or regression 1
• Fluid balance: Calculate cumulative balance every 6-12 hours 2, 4
• Signs of fluid overload: Pulmonary edema, peripheral edema, worsening oxygenation 4, 3

Acid-Base Monitoring

• Serial arterial blood gases: Monitor pH, lactate, and base deficit 5
• Electrolytes: Avoid potassium-containing solutions until serum potassium is confirmed normal 2
• In severe lactic acidosis with AKI, lactate may not fully correct with fluids alone and may require RRT 5

When to Transition to Renal Replacement Therapy

Indications for RRT

• Persistent severe lactic acidosis (lactate >5 mmol/L, pH <7.35) despite fluid resuscitation 5
• Fluid overload requiring negative fluid balance that cannot be achieved with diuretics 1, 4
• Progressive AKI (Stage 2-3) with oliguria, hyperkalemia, or uremia 1

RRT Fluid Considerations

• Use bicarbonate-buffered dialysate/replacement fluid rather than lactate-buffered solutions in patients with lactic acidosis 1
• Target effluent volume of 20-25 mL/kg/h for CRRT 1
• CRRT is preferred over intermittent hemodialysis in hemodynamically unstable patients 1

Common Pitfalls to Avoid

• Continuing aggressive fluid administration after hemodynamic stabilization: This leads to fluid overload, delayed renal recovery, and increased mortality 4, 3
• Using 0.9% saline instead of buffered crystalloids: Worsens acidosis and kidney injury 1
• Relying on CVP or PAOP for fluid responsiveness: Use dynamic indices instead 1, 3
• Ignoring cumulative fluid balance: Even "maintenance" rates can lead to significant positive balance over days 4
• Delaying RRT in fluid-overloaded patients: Conservative fluid strategy may require earlier RRT initiation 4, 3