College of Medicine: Acid-Base Imbalance in Anesthesia - Gondar

This report provides a detailed overview of acid-base imbalances, particularly in the context of anesthesia. It begins with an introduction to acid-base physiology, defining pH and highlighting the body's mechanisms for maintaining a narrow pH range through chemical buffers, respiratory control of CO2 elimination, and renal control of HCO3- elimination. The report discusses different types of acid-base disorders, including respiratory and metabolic acidosis and alkalosis, and their respective compensatory mechanisms. It also covers the interpretation of arterial blood gas (ABG) analysis, the adverse effects of severe acidosis and alkalemia, and rules of thumb for recognizing and evaluating simple acid-base disorders. Specific examples and equations are provided to aid in the diagnosis and management of these imbalances, making it a valuable resource for understanding acid-base disturbances in clinical settings. Desklib provides access to this and other solved assignments for students.

University of Gondar
College of medicine and health science
department of anesthesia
Misganaw M
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Acid- Base Imbalance

INTRODUCTION
 Disorders in acid-base balance are commonly
found in critically ill patients.
 Clinicians responsible for these patients need a clear
understanding of acid-base pathophysiology in order to
provide effective treatment for these disorders
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INTRODUCTION
Definition:
 pH is defined as potential of H+ Ion concentration in
body fluid and acid- base balance is:
 Balance of H conc. In extracellular fluid (ECF) .
 To Achieve Homeostasis .
 Balance Between:
 H+ is produced as a by-product of metabolism
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INTRODUCTION
The body maintains a narrow pH range by 3 mechanisms:
1. Chemical buffers (extracellular and intracellular)
react instantly to compensate for the addition or
subtraction of H+ ions.
2. CO2 elimination is controlled by the lungs
(respiratory system). Decreases (increases) in pH result
in decreases (increases) in PCO2 within minutes.
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3. HCO3- elimination is controlled by the kidneys. Decreases (increases) in pH result in increases
(decreases) in HCO3-. It takes hours to days for the renal system to compensate
for changes in pH
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INTRODUCTION The three different buffering systems are:
1) Respiratory buffering system
• Uses bicarbonate
2) Blood buffering system
• Uses bicarbonate, phosphate, and protein
3) Renal buffering system
• Uses bicarbonate, phosphate, and ammonia
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INTRODUCTION A normal [H+] of 40 nEq/L corresponds to a pH of
7.40. Because the pH is a negative logarithm of the [H+],
changes in pH are inversely related to changes in [H+]
(e.g., a decrease in pH is associated with an increase
in [H+])
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ACID-BASE DISORDERS
 Types of Acid-Base Disorders
 . A respiratory acid-base disorder is a change in [H+] that is a
direct result of a change in PCO2, an increase in PCO2 will
increase the [H+] and produce a respiratory acidosis, while a
decrease in PCO2 will decrease the [H+] and produce a
respiratory alkalosis.
 . A metabolic acid-base disorder is a change in [H+] that is a
direct result of a change in HCO3.
 an increase in HCO3 will decrease the [H+] and produce a
metabolic alkalosis, while a decrease in HCO3 will
increase the [H+] and produce a metabolic acidosis.
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 Metabolic acid-base disorders elicit prompt ventilatory
responses that are mediated by peripheral
chemoreceptors located in the carotid body at the carotid
bifurcation in the neck. A metabolic acidosis stimulates these chemoreceptors
and initiates an increase in ventilation and subsequent
decrease in arterial PCO2(PaCO2).
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NORMAL BLOOD GAS ANALAYIS
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Variables Arterial Blood Mixed Venous Blood
pH 7.35–7.45 7.31–7.41
Pco2 35–45 41–51
Po2 80–100 35–40
HCO3 22–26 22–26
Base
excess -2 to +2 -2 to +2
O2
saturation > 95% 70%–75%

INTERPRETING ABGS a. Acidemia (pH less than 7.35) versus alkalemia (pH
greater than 7.45) b. Acidemia and alkalemia refer to an abnormal pH being
either low or high, respectively. Acidosis and alkalosis refer to the metabolic or
respiratory processes that led to the abnormal pH.
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ADVERSE EFFECTS OF SEVERE
ACIDOSIS (PH OF 7.25 OR LESS
Impaired cardiac output Increased metabolic demands
Peripheral ischemia
(centralization of blood) Insulin resistance
Increased pulmonary vascular
resistance Decreased ATP synthesis
Hypotension Increased protein breakdown
Increased risk of arrhythmias Hyperkalemia
Decreased catecholamine
responsiveness Diaphragmatic fatigue/dyspnea
Obtundation/coma Hyperventilation
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Adverse Effects of Severe Acidemia (pH 7.25 or less)