M3 Acid-Base Imbalance

What is the normal pH of blood

7.35 - 7.45

• death is likely if the pH is >7.8 or <6.8

Which two organs control the acid-base balance

kidneys and lungs

• the kidneys can modify the excretion rate of body acids and the production and absorption of bicarbonate ions

• the lungs alter the CO2 levels in the carbonic acid by changing respiratory rate

Chemical buffers

First line defense against a change in pH because they are always present in body fluids

• 3 major systems:

  • bicarbonate buffers - most important, control small fluctuations in pH, and respond immediately

  • transcellular hydrogen/potassium exchange - alterations in potassium levels affect acid-base balance and vice versa

  • proteins - work rapidly

The respiratory system

2nd line of defense

• The lungs change respiratory rate and depth to alter carbon dioxide levels (carbonic acid)

• under control of the nervous system through special receptors in the brain that are sensitive to changes in carbon dioxide

• This is a more rapid but short-lived response

• 50-75% effective

The renal system

third line of defense

• Most effective but take longer time to begin (function for days)

• regulate bicarbonate excretion and production

Acidosis

occurs when serum pH is less than 7.35 and more hydrogen ions (H⁺) are present

• the body’s metabolic processes mostly produce acids, and the kidneys and lungs work together to reduce this

• respiratory - increase in CO2 levels caused by hypoventilation

• metabolic - decreased serum bicarbonate ion usually caused by shock, DKA, renal failure, or diarrhea

Alkalosis

occurs when serum pH is greater than 7.45. Serum becomes more basic with fewer hydrogen ions (H⁺)

• less common

• respiratory - decreased CO2 levels caused by hyperventilation

• metabolic - increased serum bicarbonate ions or decreased serum hydrogen ions caused by severe vomiting or excessive antacid intake

Metabolic Acidosis

ph <7.35 and HCO3 <22 mEq/L

• pH is decreased, HCO3 is decreased, and PCO2 is decreased

• causes are related to excess acid or a deficit of base (HCO3)

  • overproduction of hydrogen ions (taking too much acetylsalicylic acid aka aspirin)

  • lack of elimination of hydrogen ions (renal failure)

  • underproduction of bicarbonate ions (renal failure)

  • elimination of bicarbonate ions (diarrhea)

    • metabolic acidosis = comes out of your ass

  • DKA

• respiratory system increases respirations to blow off extra CO2 and eliminate the excess acid

How do you treat metabolic acidosis

• provide hydration to restore water, nutrients, and electrolytes

• administration of alkalotic IV solution (sodium bicarbonate or sodium lactate)

  • for severe acidosis and make sure to monitor for symptoms of alkalosis

• mechanical ventilation

Signs and Symptoms of metabolic acidosis

• headache

• decreased BP

• hyperkalemia

• muscle twitching

• warm, flushed skin (vasodilation)

• diarrhea

• ↑ confusion or drowsiness

• kussmaul respirations

Metabolic Alkalosis

pH >7.45 and HCO3 >28 mEq/L

• pH is increased and HCO3 is increased

• occurs when there is a loss of H+ ion or an increase in the HCO3 levels

  • excessive loss of gastric acid (vomiting)

    • when you throw up, you make the sound “Alk”

  • ingestion or administration of alkalizing salts

• respiratory system decreases breathing to keep more CO2 and decreased pH

Treatment for metabolic alkalosis

• potassium chloride or potassium supplement

• if severe:

  • hydrochloric acid

  • ammonium chloride

• restore normal fluid balance

  • NS based IV fluid replacement

Signs and Symptoms of metabolic alkalosis

• restlessness followed by lethargy

• dysrhythmias (tachycardia)

• compensatory hypoventilation

• confusion, dizziness, irritability

• vomiting

• tremors, muscle cramps, tingling of fingers and toes

• hypokalemia

Respiratory Acidosis

caused by an increase in carbonic acid (H₂CO₃) from a buildup of carbon dioxide

• most common cause is hypoventilation, which results in excess CO₂ in arterial blood leading to a rise in carbonic acid

  • can also be caused by pneumonia or COPD

• The kidneys support respiratory compensation by excreting acid and reabsorbing bicarbonate ions to offset the hydrogen

Respiratory Alkalosis

a deficit in H₂CO₃ due to blowing off CO₂ (hyperventilation)

• an immediate intervention is to rebreathe the exhaled air containing blown-off CO₂ from a paper bag placed over the face

• Kidneys conserve H⁺ ions and excrete HCO₃ in alkaline urine

• can be caused by anxiety

• kidneys compensate by increasing the urinary excretion of bicarbonate while limiting bicarbonate reabsorption to lower pH

ROME mnemonic

Respiratory Opposite (pH ↑ PCO2 ↓ & pH ↓ PCO2 ↑)

Metabolic Equal (pH ↑ PHCO3 ↑ & pH ↓ PHCO3 ↓)

Normal bicarbonate levels

22-28 mEq/L

Normal carbon dioxide levels

35-45 mmHg

Fluid balance

total body water composed of:

• intracellular fluid

• extracellular fluid

  • interstitial fluid

  • intravascular fluid

60% of adult human body weight is water

What is the number 1 indicator for fluid volume

weight