Epidurals, Ethics, and Expectations: Talking Risks and Benefits in Obstetric Anesthesia

Cerebral salt wasting (CSW) is caused by increased secretion of natriuretic peptides (likely mediated by activation of the sympathetic nervous system) leading to excessive excretion of sodium in the urine. High intra-tubular sodium content secondarily provokes an osmotic gradient that drags water into the urine. Consequently, CSW is associated with intravascular volume contraction. Therefore, CSW is characterized by hyponatremia (Na+ < 135 mEq/L) and hypo-osmolality. With the loss of water in the urine, total body water is reduced in CSW. This distinguishes it from syndrome of inappropriate ADH (SIADH), which is a euvolemic, hypo-osmolar hyponatremia secondary to the elevated levels of antidiuretic hormone (ADH). The causes of a hypo-osmolar hypervolemic hyponatremia are congestive heart failure, cirrhosis and nephrotic syndrome. The cause of an iso-osmolar euvolemic hyponatremia is hyperglycemia, hyperlipidemia and hyperproteinemia. In the latter conditions the sodium is falsely lowered.