Hyperchloremic Metabolic Acidosis During Cardiac Ablation

Mechanism of Development

The administration of normal saline or unbalanced colloid solutions as priming volume or infusion fluids during cardiopulmonary bypass (CPB) is the primary cause of hyperchloremic metabolic acidosis, according to the British Journal of Anaesthesia 1, 2
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 2, 3
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, 2

Hyperchloremic acidosis increases the risk of tissue injury and organ dysfunction during CPB 2, 3
Fluid overload with chloride-rich solutions can lead to edema that impairs pulmonary gas exchange and tissue oxygenation 4
Excessive chloride load from normal saline infusions causes decreased renal blood flow and glomerular filtration rate, exacerbation of sodium retention, reduced gastric blood flow, decreased gastric intramucosal pH, and impaired gastric motility 4

The British Journal of Anaesthesia recommends using balanced crystalloid solutions instead of normal saline for priming and maintenance fluids during CPB 1, 2, 5
Maintaining near-zero fluid and electrolyte balance during the procedure reduces complications by 59% compared to states of fluid imbalance 4
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 4

Discontinuing normal saline infusions and switching to balanced crystalloid solutions can help resolve hyperchloremic acidosis 4, 5
Maintaining adequate urine output is associated with faster resolution of hyperchloremic acidosis, and fluid restriction can be as detrimental as fluid excess, causing decreased venous return, cardiac output, tissue perfusion, and oxygen delivery 4

The British Journal of Anaesthesia recommends buffered crystalloid solutions like Plasma-Lyte R over 0.9% normal saline for managing hyperchloremic metabolic acidosis during prolonged surgery due to their more physiologic electrolyte composition and reduced risk of worsening acidosis 6
Administration of large volumes of 0.9% saline causes hyperchloremic acidosis, which occurs through dilution of bicarbonate and direct chloride load, leading to decreased strong ion difference 6
Hyperchloremic acidosis from 0.9% saline is associated with increased 30-day mortality in surgical patients 6

The British Journal of Anaesthesia states that 0.9% saline administration is associated with renal vasoconstriction and increased risk of acute kidney injury 6
0.9% saline administration is also associated with increased need for vasopressor therapy 6
The British Journal of Anaesthesia recommends buffered crystalloid solutions over 0.9% saline for kidney transplantation, as they reduce the risk of delayed graft function 6
For neurosurgical procedures, balanced isotonic solutions like Plasma-Lyte are preferred as they avoid hyperchloremic metabolic acidosis 7

The volume of fluid administered may have a dose-response relationship with adverse outcomes, regardless of fluid type 6
Some recent large RCTs found no difference in complications between 0.9% saline and buffered solutions, but these studies used relatively small fluid volumes 6