How does a patient develop hyperchloremic metabolic acidosis during Transesophageal Echocardiogram (TEE) ablation?

Hyperchloremic Metabolic Acidosis During TEE Ablation: Causes and Mechanisms

The primary cause of hyperchloremic metabolic acidosis during TEE-guided cardiac ablation procedures is the administration of normal saline or unbalanced colloid solutions as priming volume or infusion fluids during cardiopulmonary bypass (CPB). 1

Mechanism of Development

• Normal saline (0.9% NaCl) and unbalanced colloid solutions contain supra-physiological concentrations of chloride (>154 mmol/L), which directly leads to hyperchloremic acidosis when used during CPB procedures 1

• In a study of 81 patients receiving either unbalanced or balanced hydroxyethyl starch solutions during cardiac procedures, those receiving unbalanced solutions demonstrated higher plasma chloride levels, lower pH levels, and more significant decreases in base excess 1

• The excessive chloride load from normal saline infusions causes:

  • Decreased renal blood flow and glomerular filtration rate 1
  • Exacerbation of sodium retention 1
  • Reduced gastric blood flow 1
  • Decreased gastric intramucosal pH 1
  • Impaired gastric motility 1

Clinical Implications

• Hyperchloremic acidosis increases the risk of tissue injury and organ dysfunction during CPB 1

• Fluid overload with chloride-rich solutions can lead to:

  • Edema that impairs pulmonary gas exchange and tissue oxygenation 1
  • Increased tissue pressure in encapsulated organs like the kidney 1
  • Compromised microvascular perfusion 1
  • Increased arterio-venous shunting 1
  • Reduced lymphatic drainage 1

• In cardiac procedures, this acidosis may persist even after the anion gap normalizes, potentially delaying recovery 2

Prevention Strategies

• Use balanced crystalloid solutions instead of normal saline for priming and maintenance fluids during CPB 1

• Maintain near-zero fluid and electrolyte balance during the procedure, as this approach has been shown to reduce complications by 59% compared to states of fluid imbalance 1

• If intravenous fluids are required postoperatively, they should be given at a rate of 25-30 ml/kg/day with no more than 70-100 mmol sodium/day 1

• Monitor chloride levels and acid-base status regularly during the procedure 1

Management Considerations

• There is general agreement that normal physiological circumstances should be maintained during CPB, including optimal pH and avoidance of hyperchloremic acidosis 1

• For patients who develop hyperchloremic acidosis:

  • Discontinue normal saline infusions 1
  • Switch to balanced crystalloid solutions 1
  • Consider diuretics like furosemide if the patient has adequate urine output, as this may help resolve hyperchloremic acidosis faster 3

• Maintain adequate urine output, as this is associated with faster resolution of hyperchloremic acidosis 3

Common Pitfalls and Caveats

• Hyperchloremic acidosis may be mistaken for persistent lactic acidosis or other forms of metabolic acidosis, leading to inappropriate management 3, 2

• The anion gap often normalizes before bicarbonate levels recover in hyperchloremic acidosis, which may create confusion in monitoring recovery 2

• Fluid restriction can be as detrimental as fluid excess, causing decreased venous return, cardiac output, tissue perfusion, and oxygen delivery 1

• Patients with pre-existing renal dysfunction are at higher risk for developing more severe hyperchloremic acidosis during these procedures 4