Balanced Versus Unbalanced Salt Solutions in the Perioperative Period

Abstract

Unlike organic electrolytes, elements in the blood, such as sodium (Na⁺) and chloride (Cl⁻), cannot be metabolized and their concentrations thus are dependent upon absorption and excretion. The concentration of Cl⁻ is on average 40 meq/L less than the concentration of Na⁺ and this is an important determinant of hydrogen ion (H⁺) concentration in blood (i.e., pH). Increasing Cl⁻ concentration produces acidemia and potentially affects renal, gastrointestinal, immune, and coagulation functions. There, thus, has been increasing interest in the use of intravenous solutions that have lower Cl⁻ concentrations. These solutions require anions besides Cl⁻ to “balance” the charge from Na⁺. The major anions are bicarbonate, lactate, acetate, and gluconate. The physiological actions of these electrolytes have been well described but the evidence of a clinical benefit is very limited. Three large observational studies demonstrated potential benefits of low Cl⁻ solutions on renal function. There also has been suggestions of benefits for hospital survival and reduction of infections. This was not supported by the recent only reasonable-sized randomized clinical trial to test causality. However, the amount of fluid given was not large and the population was generally at low risk, thus limiting the power of the study to detect harm. Thus, the question remains unanswered in patients who are at higher risk. It is unlikely that a pragmatic trial will be helpful and future studies will need to target subjects who are expected to receive large volumes of resuscitations fluid and who have risk factors that may make them less able to handle large Cl⁻ loads, such as diabetics, subjects with large extracellular volume, recent intravenous contrast, periods of hypotension, and use of catecholamines. More specific endpoints besides renal function also need to be considered such as gastrointestinal function, rate of infections, red cell survival, and coagulation. Based on current evidence, survival studies would likely require very large sample sizes with subjects at increased risk.