Acid-Base Balance Exemplars

pH Definition

Represents the acidity or alkalinity of a solution

Acid Definition

Released Hydrogen (H+) substance that dissociates into H+ ion and conjugate base

The greater the H+…

The more acidic and the lower the pH

Base

Substance that takes up H+ ions

The lower the H+, the more…

Alkaline or basic and the higher the pH

Most Important Base

HCO3 (Bicarbonate)

What are body acids formed as?

End products of protein, carbohydrate, fat metabolism

Ratio of Base Bicarbonate to Carbonic Acid

20 Bicarbonate: 1 Carbonic Acid

What are the major organs involved in regulating the acid-base balance?

Lungs, Kidneys, Bone

Volatile

Weak Acid → Eliminated as CO2 gas (ex: carbonic acid)

Nonvolatile

Strong Acid → Eliminated by kidney (ex: sulfuric and phosphoric acid)

Cellular Metabolism

Carbonic Acid and converts back to this in lungs, CO2 is exhaled, formed during aerobic metabolism

What is Carbonic Acid derived from?

CO2 and H2O

Metabolic Acid

General term that includes all acids except carbonic acid, move from cells to body fluids, then buffered and excreted by kidneys

Buffer

Pair of chemicals (weak acid and base)

What is the most important buffer?

Bicarbonate

What does Bicarbonate buffer?

Metabolic acid produced by cells of ingested (can release H+ if too little acid present, reverse if there is too much)

Where is carbonic acid excreted?

Respiratory System (gas forms)

Where is metabolic acid excreted?

Kidneys

When optimal acid-base balance occurs, buffers are…

Not overwhelmed by amount of acid that is generated

Normal pH Range

7.35-7.45

Hyperventilation

Excretes more carbonic acid

Hypoventilation

Holds onto more carbonic acid

What do chemoreceptors focus on?

CO2 and H+ levels and adjust rate and depth accordingly

Where does Bicarbonate from blood enter?

Renal Tubules

What does the secretion of H+ result in?

Combination with other molecules including ammonia (NH3) becomes NH4+ and excreted in urine

Buffer System for Respiratory System

Phosphate System

Buffer System for Renal System

Plasma Protein System

Phosphate System

Maintains intracellular pH, extracellular fluid, functions similar to bicarbonate system

Plasma Protein System

Maintains intracellular pH, hemoglobin and other plasma proteins can buffer H+

What can Acid-Base Balance affect?

Tissue Perfusion

What do changes in H+ concentration impact?

Potassium and calcium l/t impacting contraction of smooth muscle in vessels

Acidosis

Decreases cardiac contractility (decreased perfusion)

Alkalosis

Vasoconstriction (in cerebral blood flow): cardiac contractility, increases with pH 7.7, dysrhythmias d/t hypokalemia

Acidosis Pathophysiology

H+ enters cells and K+ moves out (when an organic acid) l/t hyperkalemia

Alkalosis Pathophysiology

H+ out of cells with K+ moving in l/t hypokalemia

Shift to Right

Acidosis → Decreased affinity to hold on oxygen

Shift to Left

Alkalosis → Increased affinity to hold onto oxygen

Neuromuscular Function of Acidosis

As more H+ binds to protein, there are fewer sites open for calcium to bind… blocks sodium channels l/t muscle weakness (hypercalcemia)

Neuromuscular Function of Alkalosis

Increased neuromuscular activity d/t less competition with H+ for receptor sites… associated with positive symptoms (chvostek, trousseau sign, DTRs) (hypocalcemia)

Chvostek Sign

Tapping face in front of ear l/t contraction of lips nose and face (seen in alkalosis/hypocalcemia)

Trousseau Sign

When blood pressure cuff inflates l/t involuntary spasm of the hand (seen in alkalosis/hypocalcemia)

CNS Changes in Acidosis

Cerebral vasodilation → increased blood flow → increased ICP

CNS Changes in Alkalosis

Cerebral vasoconstriction → decreased blood flow → decreased O2 delivery to brain

Respiratory response to too much carbonic acid (respiratory acidosis)

Cause of Problem: Hypoventilation
Correction: Hyperventilation

Renal response to too much carbonic acid (respiratory acidosis)

Compensation: Increased secretion of H+ and increased NH3 production

Respiratory response to too little carbonic acid (respiratory alkalosis)

Cause of Problem: Hyperventilation
Correction: Hypoventilation

Renal response to too little carbonic acid (respiratory alkalosis)

Compensation: Decreased secretion of H+ and decreased NH3 production

Respiratory response to too much metabolic acid (metabolic acidosis)

Compensation: Hyperventilation

Renal response to too much metabolic acid (metabolic acidosis)

Correction: Increased secretion of H+ and NH3 production

Respiratory response to too little metabolic acid (metabolic alkalosis)

Compensation: Hypoventilation

Renal response to too little metabolic acid (metabolic alkalosis)

Correction: Decreased secretion H+ and less NH3 production

pH of Acidosis

pH is too low (d/t too much acid or not enough base)

Key S/S of Metabolic Acidosis

Kussmaul Breathing (Hyperventilation) seen in DKA patients

Why is reduced excretion of metabolic acid a cause of metabolic acidosis?

Reduced excretion of metabolic acids (non volatile) d/t renal disease and oliguria

Why is excessive production/intake of metabolic acids a cause of metabolic acidosis?

Seen in DKA → Ketoacids build up faster than the kidneys can excrete them l/t lowered blood pH

Why is excessive excretion of bicarbonate a cause of metabolic acidosis?

Seen in prolonged diarrhea → l/t reduction of bicarbonate

Acute Hypoventilation

Pneumonia and Asthma

Chronic Hypoventilation

COPD (their chemoreceptors focus on O2)

What should we look at to determine if it is chronic or acute hypoventilation?

ABGs

What is the result of the accumulation of too much carbonic acid?

Hypoventilation

Other causes of hypoventilation

Ineffective chest movements for respiration and suppression of respirations in brain (d/t opioids or injury)

Alkalosis pH

pH too high (d/t not enough acid or too much base)

What are the causes of too much base in metabolic alkalosis?

Massive blood transfusions, diuretic therapy, too much IV sodium bicarbonate

What are the causes of too little metabolic acid in metabolic alkalosis?

Prolonged N/V, nasogastric suctioning, mineralocorticoid excess

What is the result of too little carbonic acid?

Hyperventilation

What does Hyperventilation occur in?

Acute hypoxia/pain, acute anxiety/emotional distress, brain stimulation of respiratory center d/t inflammation or injury

What does Hyperventilation lead to?

Hypocapnia (Low CO2)

Hypocapnia Level

CO2 < 35

Common Clinical Findings in Respiratory Acidosis

Hypoventilation (cause of the problem), cardiac dysrhythmias

Common Clinical Findings in Metabolic Acidosis

Hyperventilation (compensatory mechanism), abdominal pain, N/V, cardiac dysrhythmias

Common Clinical Findings of Respiratory Alkalosis

Perioral and digital paresthesia, carpopedal spasm, tetany, hyperventilation (cause of the problem)

Common Clinical Findings of Metabolic Alkalosis

Perioral and digital paresthesias, carpopedal spasm, hypoventilation (compensatory mechanism)