What is the importance of a buffer in Hartman (lactated Ringer's solution) and Sterofundin (balanced electrolyte solution) solutions?

The Importance of Buffers in Hartmann's and Sterofundin Solutions

Primary Function: Prevention of Hyperchloremic Metabolic Acidosis

Buffers in Hartmann's solution (lactated Ringer's) and Sterofundin are essential because they prevent hyperchloremic metabolic acidosis that occurs with large-volume 0.9% saline administration, thereby reducing major adverse kidney events (MAKE), mortality, and the need for renal replacement therapy. 1

The buffer systems work by providing an alternative anion (lactate in Hartmann's, acetate/malate in Sterofundin) instead of excessive chloride, maintaining physiologic acid-base balance during fluid resuscitation. 1

Mechanism of Buffer Action

Lactate Buffer (Hartmann's Solution)

• Lactate is metabolized primarily in the liver to bicarbonate, providing alkalinizing capacity without directly administering bicarbonate 2
• Each liter of Hartmann's contains 28 mEq of lactate, which generates bicarbonate through hepatic metabolism 2
• The solution provides 9 calories per liter from lactate metabolism 2
• Lactate does not worsen lactic acidosis despite containing lactate, as demonstrated in clinical practice 3

Multi-Buffer System (Sterofundin)

• Sterofundin uses acetate and malate as buffers instead of lactate alone 4, 5
• These buffers are metabolized to bicarbonate through different pathways, providing more stable acid-base control 5, 6
• Studies show Sterofundin produces "nonremarkable changes in acid-base physiology" compared to significant acidosis with unbuffered solutions 4

Clinical Evidence for Buffered Solutions

Superiority Over 0.9% Saline

• Large-volume 0.9% saline administration causes hyperchloremic acidosis, renal vasoconstriction, and acute kidney injury 1
• A propensity-matched study of 22,851 surgical patients showed hyperchloremia in ~20% of patients receiving saline, associated with increased 30-day mortality 1
• The SALT trial demonstrated patients receiving large volumes of saline had higher rates of MAKE (death, need for dialysis, persistent renal dysfunction) compared to buffered fluids 1
• A trial of 15,802 critically ill patients confirmed buffered crystalloids were associated with lower risk of MAKE than 0.9% saline 1

Specific Surgical Outcomes

• Registry data from >30,000 patients undergoing major abdominal surgery showed fewer complications with buffered crystalloids versus saline 1
• One trial in major abdominal surgery was terminated early due to increased vasopressor requirements in the saline group 1
• In neurosurgery, Sterofundin provided "significantly better control over acid-base balance, sodium and chloride levels" compared to normal saline 5

Guideline Recommendations

Strong Recommendations for Buffered Solutions

• The British Journal of Anaesthesia 2024 guidelines strongly recommend buffered crystalloid solutions over 0.9% saline in the perioperative period (Strong recommendation, high-quality evidence) 1
• In critical illness, buffered crystalloid solutions are strongly recommended in the absence of hypochloremia (Strong recommendation, high-quality evidence) 1
• For kidney transplantation, buffered solutions are strongly recommended over saline to reduce delayed graft function (Strong recommendation, high-quality evidence) 1

Exception: Traumatic Brain Injury

• The only major exception is traumatic brain injury, where 0.9% saline is preferred 1, 3
• The benefit may be related to tonicity or salt load rather than buffer content, but this remains under investigation 1

Specific Clinical Scenarios

When Hartmann's Should Be Avoided

• Crush injury/rhabdomyolysis: Hartmann's must be avoided due to potassium content (4 mEq/L), which can worsen hyperkalemia from muscle breakdown 1, 2
• Severe liver dysfunction: Impaired lactate metabolism may limit buffer effectiveness 1, 3
• Traumatic brain injury: Use 0.9% saline instead 1, 3

Optimal Use of Buffered Solutions

• Sepsis resuscitation: Buffered crystalloids reduce kidney injury risk 3
• Hemorrhagic shock without TBI: Hartmann's is preferred 3
• Major surgery: Buffered solutions reduce complications when large volumes are needed 1
• Burn resuscitation: Hartmann's is traditionally preferred for initial fluid therapy 3

Comparative Performance: Hartmann's vs. Sterofundin

Acid-Base Control

• Both solutions effectively prevent metabolic acidosis compared to saline 4, 5
• Sterofundin showed "no significant changes in pH" during scoliosis surgery, while Hartmann's produced statistically higher lactate levels 4
• In neurosurgery, 27.7% of saline patients developed pH <7.35 versus none with Sterofundin 5

Electrolyte Management

• Sterofundin demonstrated superior correction of hypernatremia and metabolic alkalosis compared to both saline and Hartmann's in patients with sellar tumors 6
• Both buffered solutions maintain physiologic strong ion difference better than saline 4

Clinical Equivalence in Many Settings

• In dehydrated cats, acetate-buffered (Sterofundin-type) and lactate-buffered (Hartmann's) solutions showed no significant differences in acid-base status, electrolytes, or lactate concentrations 7
• For CRRT, either lactate or bicarbonate buffers are acceptable in most patients (Grade C recommendation), with bicarbonate preferred in lactic acidosis or liver failure 1

Practical Algorithm for Buffer Selection

1. Identify patient condition:

   • TBI/severe brain injury → Use 0.9% saline 1, 3
   • Crush injury/severe hyperkalemia → Avoid Hartmann's, use saline 1
   • Severe liver failure with lactic acidosis → Consider Sterofundin or bicarbonate-buffered solution over Hartmann's 1, 3

2. For all other scenarios requiring crystalloid resuscitation:

   • Default to buffered crystalloids (Hartmann's or Sterofundin) 1
   • Either solution is acceptable for most perioperative and critical care applications 1, 7

3. Volume considerations:

   • Small volumes (<1-1.5L): Differences between saline and buffered solutions are minimal 1
   • Large volumes (>1.5L): Buffered solutions are essential to prevent dose-dependent complications 1

Key Clinical Pitfalls

• Do not assume small differences in chloride content are clinically insignificant - the dose-response relationship between saline volume and adverse outcomes is well-established 1
• Do not use Hartmann's in crush syndrome despite its balanced electrolyte profile - the potassium content (4 mEq/L) is contraindicated 1, 2
• Do not avoid lactate-buffered solutions in patients with elevated lactate - they do not worsen lactic acidosis 3
• Monitor for metabolic alkalosis with bicarbonate-containing solutions in CRRT, as citrate anticoagulation can cause alkalosis 1