Acid-Base Balance Objectives

Define Acid-Base Balance

equilibrium between acid and base

Differentiate between a volatile acid and a fixed acid

Volatile Acid: tissue metabolism produces massive amounts of CO₂ which is hydrolyzed into volatile acid H₂CO₃

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Fixed Acid: acids that are unable to change to a gaseous state and so must be eliminated by the kidneys

State and describe the CO₂ hydration equation

(H_2 CO_3 ): CO_2 (g)+ H_2 O(l)⇄ H2CO3(aq)

In respiratory, this equation helps to explain the transporting of CO₂ in the blood, with equilibrium shifting to the right to produce more bicarbonate when carbon dioxide levels rise, and to the left to release carbon dioxide in the lungs for exhalation.

List the three body systems that regulate pH

1. chemical buffering system

2. renal / urinary system

3. respiratory system 

List and describe the three chemical buffer systems of the body

1. Bicarbonate buffer system

   1. Most important system

   2. Works primarily in the blood

   3. Involves reactions between carbonic acid and bicarbonate; released acids are consumed by hydrogen ions to form water and carbon dioxide, where excess CO₂ is removed by the body in order to maintain normal pH. When bases are released, the body can produce more carbonic acid to neutralize

2. Phosphate buffer system

   1. Most effective in ICF and urine

   2. Buffers phosphate, which is important for maintaining pH within the cells and urine in the kidneys as it removes excess hydrogen ions

3. Protein buffer system

   1. Most abundant

   2. Found in ICF and ECF

   3. Regulates pH within the cells and the bloodstream

   4. Proteins can donate or accept hydrogen ions due to having both acidic and basic functional groups, which allows them to buffer a wide range of pH changes inside and outside of cells

Describe how the respiratory system contributes to acid-base balance

The respiratory system is able to contribute to acid-base balance because it is able to control the level of carbon dioxide in the blood, which also directly affects pH. An increase of metabolic activity increases acid levels, increasing rate of breathing to exhale excess CO₂, reducing concentration of carbonic acid, and raising blood pH. When blood becomes to alkaline (or basic), slow rate of breathing retains carbon dioxide, which lowers pH.

Define the terms hyperventilation and hypoventilation

Hyperventilation: breathing faster and deeper than the body's metabolic needs; leads to excessive loss of CO₂

Hypoventilation: shallow or slow breathing that leads to a buildup of CO₂ and shortage of O₂ (oxygen)

Describe how the renal system contributes to acid-base balance (Rule of Thumb page 292)

The renal system contributes to acid-base balance by filtering out and excreting / removing excess acids as hydrogen ions while also reabsorbing and generating new bicarbonate in order to neutralize acidity in the body.

 

“The kidneys control the metabolic component of acid–base balance by excreting hydrogen ions and conserving or generating bicarbonate as needed.”

State the values of pH, PCO₂, and HCO₃ of normal acid base balance

pH: 7.35-7.45 (less than normal = acidic; more than normal = alkalotic)

PaO₂: 80-100mmHg

PaCO₂: 35-45mmHg (less than normal = alkalotic; more than normal = acidosis)

HCO₃: 21-28meq/L (less than normal = acidic; more than normal = alkalotic)

Define respiratory acidosis and respiratory alkalosis

Respiratory Acidosis: a condition where the body accumulates too much carbon dioxide in the blood, leading to a decrease in pH (acidity)

Respiratory Alkalosis: a condition where the body's pH level becomes too high due to excess loss of carbon dioxide through the lungs

List the causes of respiratory acidosis and respiratory alkalosis

Respiratory Acidosis:

• Hypoventilation

• Renal retention HCO₃^- lowers pH towards normal

• High CO2

 

Respiratory Alkalosis:

• Hyperventilation

• Renal elimination HCO₃^- lowers pH toward normal

• Low CO₂

Describe the renal compensation that takes place with Respiratory Acidosis and Respiratory Alkalosis

Respiratory Acidosis: the kidney compensates by retaining bicarbonate and excreting hydrogen ions to neutralize excess acid in the blood

Respiratory Alkalosis: the kidney compensates by excreting or removing bicarbonate and decreasing hydrogen ion secretion to lower blood pH to the normal range

Describe how the respiratory system would correct  for a Respiratory Acidosis and Respiratory Alkalosis

Respiratory Acidosis: increase rate of breathing, causing hyperventilation, to exhale carbon dioxide

Respiratory Alkalosis: slowing down breathing, causing hypoventilation, in order to retain carbon dioxide

Define Meabolic Acidosis and Metabolic Alkalosis

Metabolic Acidosis: a condition where too much acid is present in the fluids in the body due to low blood pH (acidic)

Metabolic Alkalosis: a condition where blood pH is too high (alkaline) due to excess loss of acid / excess bicarbonate

Describe the respiratory compensation that takes place with Metabolic Acidosis and Metabolic Alkalosis

Metabolic Acidosis: increases rate of breathing to remove carbon dioxide

Metabolic Alkalosis: decreases rate of breathing to retain carbon dioxide

State the purpose of the anion gap calculation and state the normal value (Egan page 301)

The purpose of the anion gap calculation is to help determine and diagnose acid-base disorders (i.e. metabolic acidosis), specifically whether or not it is due to the accumulation of unmeasured acids (such as lactic acid, ketoacids, or toxins) or a loss of bicarbonate. Normal value is between 9-14mEq/L (8-16mEq/L based on Egans)

 

Anion Gap=[Na+]−([Cl−]+[HCO3−​])

List the common causes of anion gap and non-anion gap metabolic acidosis (Egan box 14.5)

Anion Gap Metabolic Acidosis (accumulation of fixed acids):

• Lactic acidosis

• Ketoacidosis (diabetic, alcoholic, or starvation)

• Renal failure (uremic acidosis)

• Ingestion of toxins:

  • Salicylates (aspirin)

  • Methanol

  • Ethylene glycol

  • Paraldehyde

 

Non-anion Gap Metabolic Acidosis (bicarbonate loss or chloride gain):

• Diarrhea

• Pancreatic or small bowel fistulas

• Renal tubular acidosis

• Ureteral diversion

• Administration of acids (e.g., ammonium chloride, hydrochloric acid)

• Excessive chloride administration (hyperchloremic acidosis)

Describe the use of Base excess/Deficit (Egan page 306)

Base excess (BE) or base deficit (BD) is used to assess the metabolic component of an acid–base imbalance. It quantifies the amount of strong acid or base that must be added to a blood sample to return the pH to 7.40 at a PaCO₂ of 40 mm Hg and a temperature of 37 °C.

Given an arterial blood gas, correctly classify the acid-base status

An ABG is respiratory or metabolic if the PaCO₂ or HCO₃^- matches the pH. It is acidic or alkalotic based on what the pH is. Compensation is determined if either the PaCO₂ or HCO₃^- within the normal range.