Acid-Base and Electrolyte Handbook for Veterinary Technicians

Angela Randels-Thorp, David Liss, Angela Randels-Thorp, David Liss

• Publisher: Wiley-Blackwell
• Year: 2016
• Print ISBN: 9781118646540
• eBook ISBN: 9781118922873
• Edition: 1
• Topic: Medicine
• Subtopic: Veterinary Medicine

Acid-Base and Electrolyte Handbook for Veterinary Technicians provides an easy to understand yet comprehensive approach to acid-base and electrolyte balance.

• Coversthe physiology of fluids and their effect on acid-base and electrolyte balance
• Offers detailed information on managing acid-base and electrolyte derangements in disease
• Includes access to a companion website with case studies and multiple choice questions

CHAPTER 1
Introduction to Acid‐Base and Electrolytes

Angela Randels‐Thorp, CVT, VTS (ECC, SAIM) and David Liss, RVT, VTS (ECC, SAIM)

Understanding of acid‐base and electrolyte chemistry and physiology is both an important and valuable knowledge base for all veterinary technicians, and especially those in emergency and critical care or specialty practice. These very topics, however, are frequently thought of as boring at best or utterly confusing at worst. In actuality neither is true. These topics are often approached in a piecemeal or qualitative way, which lends itself to confusion. It is the goal of this text to provide a useful, easy‐to‐learn, and practical approach to the concepts regarding acid‐base and electrolytes.

Introduction to acid‐base

Assessment of acid‐base status provides insight into three physiologic processes: alveolar ventilation, acid‐base status, and oxygenation. Evaluating acid‐base status has become an integral part of the emergent/critical care patient workup and should be performed as a baseline on all emergent patients. Deviation from normal acid‐base balances is indicative of clinical disease processes and can aid the clinician in identifying underlying causes of illness in the patient. Venous samples can provide most of the information needed regarding acid‐base status and even alveolar ventilation. Arterial samples are required, however, in order to provide oxygenation status (Sorrell‐Raschi 2009). It is ever more important for the emergency and critical care (ECC) technician to be familiar in his/her understanding of acid‐base values and what they mean.

What is acidity?

In the simplest of terms, the acidity or alkalinity of a solution is based on how many hydrogen (H⁺) ions, or molecules of carbon dioxide (CO₂), are present. Hydrogen ions are produced daily as a normal part of metabolism of protein and phospholipids, and are considered a fixed, non‐volatile acid. Carbon dioxide is a byproduct of the metabolism of fat and carbohydrates in the body, and is considered a volatile acid (volatile = readily vaporized). Gaseous CO₂ is soluble in water. CO₂ is considered an acid because it readily combines with H₂O in the presence of carbonic anhydrase (enzyme/catalyst) to form carbonic acid (H₂CO₃). Without the catalyst, this change occurs very slowly. CO₂ is continually removed by ventilation and thereby kept at a stable partial pressure (pCO₂) in the body. The change in dissolved CO₂ in body fluids is proportional to pCO₂ in the gas phase. Elimination of these acids is dependent on the function of the lung, kidney, and liver.

Bronsted and Lowry state an acid is a proton donor (H⁺) and a base is a proton acceptor (A^–) (DiBartola 2006: 229). The H⁺ concentration ([H⁺]) of body fluids must be kept at a constant level to prevent detrimental changes in enzyme function and cellular structure. Levels compatible with life are between 16 and 160 nEq/L. Excessive hydrogen ions in the blood result in acidemia. Decreased hydrogen ions in the blood result in alkalemia (Kovacic 2009). Hydrogen ions are not typically measured or tested in clinical practice. Therefore, Sorenson developed pH notation in order to provide simpler notation of the wide range of [H⁺] (DiBartola 2006: 229). There is an inverse relationship between pH and [H⁺] (Ex: ↑[H⁺] → ↓pH). Normal pH ranges between 7.35 and 7.45, approximately. The processes which lead to changes in production, retention, or excretion of acids or bases, which may or may not result in a change in pH, are called acidosis or alkalosis.

Buffering systems

The body contains several mechanisms in order to maintain the desired “normal” pH level, which is called buffering. A buffer is a compound that can accept or donate protons (H⁺) and minimize a change in pH. Buffers consist of a weak acid and its conjugate salt (Sorrell‐Raschi 2009). If a strong acid is added to a buffer, the protons from the acid dissociate to the salt of the buffer and the change of pH is therefore minimized. With these buffers the body is continually converting CO₂, H₂O, H⁺, and

to maintain pH within normal ranges. The following equation represents this constant interaction:

There are several compounds that serve as buffers in the body. The primary buffer of extracellular fluid (ECF) is bicarbonate (

). Non‐bicarbonate buffers consist of proteins and inorganic and organic phosphates, which are primarily intracellular fluid (ICF) buffers. Bone is a prominent source of buffer (calcium carbonate and calcium phosphate). Up to 40% of buffering can be done from resources found in bone. Upon treatment/administration of sodium bicarbonate (

), carbonate that has been released to buffer can then be deposited back into the bone. In the blood, proteins, including hemoglobin and plasma, serve as buffers. Hemoglobin constitutes 80% of the buffering capacity of blood, whereas plasma proteins only account for 20% of buffering in the blood.

The body’s buffering system is considered an open buffering system, with both bicarbonate and carbonic acid systems. In a closed system the exchanges would have to occur in a reciprocal manner. Since the body eliminates the majority of CO₂ through ventilation, keeping ...

Table of contents

• Cover
• Title Page
• Table of Contents
• List of Contributors
• Foreword
• About the Companion Website
• CHAPTER 1: Introduction to Acid‐Base and Electrolytes
• CHAPTER 2: Disorders of Sodium
• CHAPTER 3: Disorders of Chloride
• CHAPTER 4: Disorders of Potassium
• CHAPTER 5: Disorders of Magnesium
• CHAPTER 6: Disorders of Phosphorus
• CHAPTER 7: Disorders of Calcium
• CHAPTER 8: Traditional Acid‐Base Physiology and Approach to Blood Gas
• CHAPTER 9: Metabolic Blood Gas Disorders
• CHAPTER 10: Respiratory Acid‐Base Disorders
• CHAPTER 11: Mixed Acid‐Base Disorders
• CHAPTER 12: Strong Ion Approach to Acid‐Base
• CHAPTER 13: Companion Exotic Animal Electrolyte and Acid‐Base
• Index
• End User License Agreement