Osmolality and volume regulation Introduction Osmolality in plasma is related to the number of solutes (soluble particles) dissolved in a kg of plasma water, with a normal osmolality between 280 and 295 mOsm Measurement of serum osmolality is used to evaluate the body's regulation of water and sodium balance, while urine osmolality evaluates the kidney's ability to concentrate urine. In a steady state, our total body…

Introduction Symptoms of phosphate depletion have been described through the years, from the times of the ancient Romans to observations by veterinarians on livestock. Phosphate compounds are in all cells and participate in numerous biochemical processes. Phosphate is a component of DNA and RNA, phospholipids, high-energy compounds such as ATP and creatine phosphate, and many coenzymes. When both phosphate depletion and hypophosphatemia are present, serious biochemical…

Introduction In 1695, from well water in Epsom, England, Dr. Nehemiah Grew prepared Epsom salts, a name still given to magnesium sulfate. The biological significance of magnesium as a constituent of plants has been known since the 18th century, with magnesium ion an essential component of chlorophyll. Hypomagnesemia is observed in about 10% of hospitalized patients and especially critically ill patients who often have other coexisting…

Introduction and history In 1883, Sydney Ringer showed that calcium was essential for myocardial contraction ( ) . In 1934, Franklin McLean and Baird Hastings published a report in the Journal of Biological Chemistry showing that the ionized calcium concentration was proportional to the amplitude of frog heart contraction, whereas protein-bound and citrate-bound calcium had no effect ( ) . After many attempts to develop improved…

Introduction Hypoxemia, a decreased partial pressure of oxygen in the blood, is a commonly encountered clinical problem among patients with acute or chronic cardiopulmonary disorders. Accurately characterizing the cause and severity of hypoxemia in a timely manner can have significant implications for clinical management and patient prognosis. The blood gas measurements play an integral part in the evaluation of the hypoxemic patient, as does the understanding…

Physiologic differences between arterial and venous blood for blood gas and acid–base measurements More than any other analytes, p O 2 , p CO 2 , and pH change markedly from arterial to venous blood. While the pH apparently changes only slightly (i.e., 7.40 to 7.37 = 0.4% difference), the actual H ion concentration has a much greater relative change, going from 3.98 × 10 −8…

Metabolic acidosis Metabolic acidosis is defined as a clinical process that leads to a decreased blood pH (acidemia) and a decreased HCO 3 level. It is caused by a gain of acidic compounds and/or loss of a base, usually bicarbonate. Electrolyte movements can also play a role in acid–base balance that are sometimes manifested as an increased anion gap. Physiologic mechanisms of metabolic acidosis ( )…

Introduction and history of blood gases The term “blood gas” refers to the parameters pH, p CO 2 , and p O 2 measured in blood. Note that the little “p” in pH stands for negative log, while the italicized p in p CO 2 and p O 2 stands for the partial pressure of each of these gases. In addition to pH, p CO 2…