Which crystalloid choice minimizes hyperchloremic metabolic acidosis and when should I use balanced solutions?

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Balanced isotonic crystalloids are the fluid of choice for perioperative and general IV fluid administration in dogs and cats, and their use directly minimizes the risk of hyperchloremic metabolic acidosis compared with 0.9% sodium chloride (NaCl).810 The core mechanism is the strong ion difference (SID). Balanced solutions produce an in vivo SID of 24–29 mEq/L after metabolism of their organic anions, which maintains or normalizes plasma pH.8 By contrast, 0.9% NaCl carries a high chloride load that reduces plasma SID below bicarbonate concentration, driving a hyperchloremic metabolic acidosis.113 Hyperchloremic metabolic acidosis results specifically from chloride retention or excessive gain of chloride relative to sodium.13 In dogs undergoing elective orthopedic surgery at 10 mL/kg/hour for 2 hours, Hartmann's solution and a polyionic maintenance solution both produced significant increases in bicarbonate and base excess, while 0.9% saline produced a significant rise in chloride concentration (116 to 117 mmol/L) with no alkalinizing effect.3 Hyperchloremic metabolic acidosis did not develop in any group at that volume and duration, but the directional acid-base differences between saline and balanced solutions were statistically significant.3 Balanced solutions are indicated across the broadest range of clinical scenarios. Appropriate indications include shock resuscitation, dehydration, ongoing fluid losses, and maintenance fluid requirements.10 In cats, both acetate-containing and lactate-containing balanced solutions are used as alternatives to isotonic saline, with the distinction that acetate is metabolized primarily in skeletal muscle independent of oxygen and liver function, while lactate metabolism is oxygen-dependent and occurs predominantly in the liver — making acetate-containing solutions preferable in patients with hepatic dysfunction or anaerobic states.2 0.9% NaCl retains specific indications where its high chloride content is therapeutically useful