Posts by Rob Costello, Dairy Technical/Business Support Manager, Milk Specialties Global

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Wednesday, March 23, 2011

Electrolytes - Alkalinizing Agents

What They Are and How They Affect Acid-Base Regulation

(this post is the third in a 4-part series on electrolytes and how they influence acid-base chemistry)

Earlier in this series, we saw that strong ions fully dissociate from other substances when they dissolve in water. This dissociation not only affects the electrolyte solution being fed to the calf, it also has profound effects within the animal itself. Each strong ion forms an oriented complex with water molecules, isolating the ion and preventing it from entering into reactions within the body. And, by attracting either OH- or H+ from surrounding water molecules, these oriented complexes have a big effect on plasma pH. The important thing to remember is that you don't have to add or remove OH- and H+ from the body to change the acid-base status of the animal. Water readily forms and dissociates into OHand H+ in response to changes within the system. If this doesn't sound familiar, you may want to review the first two posts in this series before reading on.

Acidosis, Electrolyte Formulation and Alkalinizing Agents
Electrolyte products can be formulated to capitalize on the relationships between strong ions and water to bring about a change in the acid-base status of an animal. Sodium and chloride are the primary strong ions in plasma, they play an integral role in the body's acid-base control processes and they are fundamental components of electrolyte solutions for calves. 

As described in the previous post, the kidneys use sodium and chloride as they make acid-base adjustments. Simply put, they remove chloride to raise pH or remove sodium to lower it. Since the plasma pH of a calf with acidosis is below normal, it stands to reason that by providing more sodium than chloride in our electrolyte solution, we should be able to positively affect the acid-base status of the calf and increase pH. 

The normal ratio of sodium to chloride in plasma is about 4:3 (140 mmol/L sodium:103 mmol/L chloride). Using sodium chloride as our only source of these two ions provides one chloride ion for every sodium, slightly over-representing chloride in terms of normal plasma concentrations. To achieve an appropriate ratio of sodium to chloride, especially if we want to have a chance at correcting acidosis, ingredients other than sodium chloride must also be used in the formula. Ingredients that provide sodium without an accompanying chloride ion include sodium bicarbonate, sodium acetate and sodium lactate, and can be used to replace a portion of the sodium chloride in the formula, thereby achieving an alkalinizing effect.

Research Study. Many research studies have been conducted to evaluate the alkalinizing capabilities of different compounds under a variety of circumstances. But one in particular fits well with this discussion and provides an excellent demonstration of acid-base adjustments in action. In this clinical study, Kasari and Naylor evaluated sodium bicarbonate, sodium lactate and sodium acetate for the treatment of acidosis in diarrheic calves. (The complete reference is provided at the end of this post).The criteria for calves in this study were:
  • under 30 days of age
  • clinical signs of diarrhea
  • greater than 8% dehydration
  • venous blood pH less than 7.25

Calves that satisfied these criteria received one of four electrolyte treatments intravenously. The Control group received an electrolyte solution where all sodium and chloride ions were provided by sodium chloride. This solution contained 146 mmol/L of sodium and 151 mmol/L of chloride. To make room for the test compounds in the other three treatments, one third of the sodium chloride was removed from the Control formula and was replaced by enough sodium bicarbonate, sodium lactate or sodium acetate to provide a total of 146 mmol/L of sodium, 102 mmol/L of chloride and 50 mmol/L of either bicarbonate, lactate or acetate. In other words, the sodium level was maintained throughout all four treatments, chloride was reduced in the three test formulas and another substance was substituted for the chloride that had been removed. All treatments were administered intravenously so that a total of 7.2 L of fluid was given over a four-hour test period. The four treatment formulas are shown in Table 1.


Table 1. Treatment Group Formulations

Results. There were no differences observed between treatments in their ability to rehydrate calves. They all did a good job and performed equally well. However, when it came to correcting acidosis, only the reduced chloride treatments improved plasma pH and brought about a change in the acid-base status of the animal. At the onset of each treatment, plasma pH averaged 7.05. At the end of the four-hour test period, average pH for all but the Control calves was between 7.20 and 7.28 (pH > 7.28 was considered normal). The pH of Control calves at the end of the treatment was still around 7.05.

Considering the acid-base concepts presented so far in this series on electrolytes, the results of this study provide evidence of the roles of sodium, chloride and water in acid-base regulation and of the importance of proper electrolyte formulation to correct acid-base disturbances. Ingredients that provide sodium separate from chloride are necessary components of well-balanced electrolytes, and are part of a group of compounds collectively referred to as alkalinizing compounds or alkalinizing agents.

I must point out though, that a common interpretation of this and other acid-base research is that bicarbonate, acetate and lactate are considered to be the alkalinizing agent of these alkalinizing compounds.The thought is that metabolism and other reactions involving these substances results in hydrogen ions being removed from the body, thereby bringing about alkalinization. If that seems like the most probable scenario, then I encourage you to review earlier posts. In any case you will certainly want to read the fourth and final post in this series which will explore the relationships among these variables from a cause-and-effect standpoint. Is bicarbonate, for example, an independent or a dependent variable -- is it in the driver's seat, or merely along for the ride? I encourage you to read on.


Reference:
Kasari, TR; Naylor, JM: Clinical evaluation of sodium bicarbonate, sodium L-lactate, and sodium acetate for the treatment of acidosis in diarrheic calves. JAVMA, Vol 187, No. 4, August 15, 1985


Curious minds want to know...

So which is it, "alkalinizing" or "alkalizing"? A search of Wiki-Docs found the following:
  • alkalinizing: used 1376 times in 733 documents
  • alkalizing: used 16 times in 15 documents


Other posts in this series:

Jan 18, 2011, Electrolytes - Product Comparisons
Feb 15, 2011, Electrolytes - Dissociation of Strong Ions
May 4, 2011, Electrolytes - Dependent & Independent Variables


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