Practical Approach to Physical-Chemical Acid-Base Management. Stewart at the Bedside

Abstract

The late Peter Stewart developed an approach to the analysis of acid-base disturbances in biological systems based on basic physical-chemical principles. His key argument was that the traditional carbon dioxide/bicarbonate analysis with just the use of the Henderson-Hasselbalch equation does not account for the important role in the regulation of H(+) concentration played by strong ions, weak acids and water itself. Acceptance of his analysis has been limited because it requires a complicated set of calculations to account for all the variables and it does not provide simple clinical guidance. However, the analysis can be made more pragmatic by using a series of simple equations to quantify the major processes in acid-base disturbances. These include the traditional PCO2 component and the addition of four metabolic processes, which we classify as "water-effects," "chloride-effects," "albumin effects," and "others." Six values are required for the analysis: [Na(+)], [Cl(-)], pH, Pco2, albumin concentration, and base excess. The advantage of this approach is that it gives a better understanding of the mechanisms behind acid-base abnormalities and more readily leads to clinical actions that can prevent or correct the abnormalities. We have developed a simple free mobile app that can be used to input the necessary values to use this approach at the bedside (Physical/Chemical Acid Base Calculator).

Serum chloride in heart failure: a salty prognosis

“…More plausibly, low chloride levels select patients at excess risk for adverse events in HF. A deeper understanding of three of the major mechanisms driving reduced serum chloride in HF may help clarify this differential selection . First, maladaptive neurohormonal activation and non‐osmotic arginine vasopressin release contribute to hypochloraemia by decreased free water excretion and increased thirst signals.…”

Sodium Acetate Coated Tenofovir-Loaded Chitosan Nanoparticles for Improved Physico-Chemical Properties

“…Indeed, triphosphoric acid, the acid form of the polyanion TPP can undergo as many as 5 dissociations, and therefore has 5 pKa values (pKa1 = 1; pKa = 2.2; pKa3 = 2.3; pKa4 = 3.7 and pKa = 8.5) (28). That means, at pH =pKa4 +2 = 5.7, TPP is almost fully ionized based on Henderson Hasselbalch equation (29) and may crosslink with protonated amino group of chitosan polymer through electrostatic attraction. At this step of the process, the TPP aqueous solution or mixture with the drug (TFV) is also added dropwise into chitosan aqueous solution.…”

Acidosis and Anion Gap

“…In Stewart approach, a large number of variables are needed to calculate SID. Sodium, potassium, calcium and magnesium are strong positive ions, and chloride and lactate are the negative ions [25]. A − Resembles weak anions, that vary with pH.…”

“…Here narrowing of SID from an increase in [Na + ] has alkalizing effect, whereas an increase in [Cl − ] has acidifying effect. From the ionic basis metabolic acid base disturbances are about four major types [25]: (1) The water effect, and it is produced by dilutional effect on SID. Free water intake and intravenous infusion can produce it.…”