Choice of Isotonic Perioperative Fluid in Children

To the Editor We whole heartedly agree with Bailey et al.1 and Moritz and Ayus,2 who support the practice of perioperative isotonic fluid administration in the postoperative surgical patient. The 3 most recent studies referenced in the editorial3–5 add further support in favor of isotonic fluids preventing or minimizing hyponatremia while not exposing patients to the potential risks of hypernatremia. In recommending 0.9% saline as the isotonic fluid of choice, the authors have based their selection on comparison with lactated Ringer's solution, a “balanced salt” solution. Although considered isotonic with plasma, concerns are raised regarding the relative hypotonic nature of the fluid with a sodium concentration of 130 mEq/L. The concern we have with the use of normal saline as a perioperative fluid is the associated hyperchloremic metabolic acidosis, which is a regular feature if large volumes of normal saline are infused intraoperatively.6,7 It is our understanding that the acidosis is due to associated increase in chloride ion concentration and alteration in the strong ion difference. Although outcome studies are lacking, we have concerns that the large chloride load and associated acidosis may be deleterious for both cardiac and renal function in the perioperative phase, especially in children undergoing cardiac surgery or in those with renal disease. It can also make differentiating the cause of an increasing base deficit difficult in procedures associated with significant blood loss and fluid replacement when periods of hypotension and/or hypoperfusion may occur. An alternative isotonic, isosmotic “balanced salt ”solution is commercially available and has been widely used as our intraoperative replacement fluid of choice for more than 15 years. This fluid is Plasma-Lyte 148 (Baxter, Deerfield, IL). The osmolality of the solution is 294 mOsm and therefore more closely approximates plasma osmolality than lactated Ringer's solution. It has a slightly reduced sodium concentration compared with normal saline with a sodium ion concentration of 140 mmol/L (but significantly higher than lactated Ringer's solution) and a significantly lower chloride concentration of 98 mmol/L (Table 1). It also has potassium, magnesium, and gluconate/acetate as a bicarbonate ion producing buffer. It does not contain calcium and thus there is no concern with its interface with blood and blood products. Comparison with 0.9% saline as an intraoperative fluid in adults many years ago demonstrated a similar benefit to that shown by lactated Ringer's solution in producing less hyperchloremic acidosis.8Table 1: Comparative Chemistry of Crystalloid SolutionsWe therefore suggest the use of Plasma-Lyte 148 solution as an alternative to normal saline as a perioperative isotonic solution in children. However, we accept that the clinical comparison with normal saline has not been undertaken in children and that this would be useful in elucidating which isotonic fluid is best in the perioperative period. James Houghton, FANZCA Niall Wilton, MRCP, FRCA Specialist Anaesthetists Starship Children's Hospital Auckland, New Zealand [email protected]