Pseudohyponatremia remains a problem for clinical laboratories. In this study, we analyzed the mechanisms, diagnosis, clinical consequences, and conditions associated with pseudohyponatremia, and future developments for its elimination. The two methods involved assess the serum sodium concentration ([Na]_S) using sodium ion-specific electrodes: (a) a direct ion-specific electrode (ISE), and (b) an indirect ISE. A direct ISE does not require dilution of a sample prior to its measurement, whereas an indirect ISE needs pre-measurement sample dilution. [Na]_S measurements using an indirect ISE are influenced by abnormal concentrations of serum proteins or lipids. Pseudohyponatremia occurs when the [Na]_S is measured with an indirect ISE and the serum solid content concentrations are elevated, resulting in reciprocal depressions in serum water and [Na]_S values. Pseudonormonatremia or pseudohypernatremia are encountered in hypoproteinemic patients who have a decreased plasma solids content. Three mechanisms are responsible for pseudohyponatremia: (a) a reduction in the [Na]_S due to lower serum water and sodium concentrations, the electrolyte exclusion effect; (b) an increase in the measured sample’s water concentration post-dilution to a greater extent when compared to normal serum, lowering the [Na] in this sample; (c) when serum hyperviscosity reduces serum delivery to the device that apportions serum and diluent. Patients with pseudohyponatremia and a normal [Na]_S do not develop water movement across cell membranes and clinical manifestations of hypotonic hyponatremia. Pseudohyponatremia does not require treatment to address the [Na]_S, making any inadvertent correction treatment potentially detrimental.

Chronic metabolic acidosis is common in dialysis patients. Bicarbonate administration via the dialysate helps maintain the acid–base balance in these patients. Serum bicarbonate level in dialysis patients is determined by several factors that include dietary protein intake, nutritional status and dialysis prescription, etc. Additionally, a meaningful interpretation of serum bicarbonate in dialysis patients requires an understanding of complexities involving its measurement. Both very low as well very high levels of serum bicarbonate have been associated with adverse outcomes in observational studies. However, recent observational data, when adjusted for the confounding effects of nutritional status, do not associate higher predialysis serum bicarbonate with adverse consequences. At this time, there are no prospective studies available that have examined the association of serum bicarbonate with hard outcomes in dialysis patients. The ideal level of serum bicarbonate in dialysis patients is therefore unknown. This article examines the available data with regard to the benefits of higher predialysis serum bicarbonate.

Two and a half centuries have passed since the therapeutic use of peritoneal cavity for the treatment of ascites by peritoneal lavage was reported. George Ganter was the first to describe the use of peritoneal dialysis (PD) in humans. This chapter will describe the various milestones in the field of PD achieved over the years. These include the understanding of solute and water transport across the peritoneal membrane, developments in PD technique and technology, progress in the prevention and treatment of infections, and other important milestones.