1 - Acid / Base Balance

Question 1

Normal Values for:

pH

[HCO₃^-]

P_CO2

Answer 1

Acidosis < 7.4 < Alkalosis

[HCO₃^-] = 24 mEg/L

P_CO2 = 40 mmHg

Question 2

Metabolic vs Respiratory Disorder

Answer 2

• Metabolic: Primary change in [HCO3-]
• Respiratory: Primary change in P_CO2

Question 3

Objectives: Explain the three general mechanisms the body employs to changes in pH

Answer 3

1. Extracellular / Intracellular Buffering
2. Adjustments to PCO2 by ventilatory rate
3. Adjustments in renal acid excretion

Question 4

Explain extracellular and intracellular buffering

Answer 4

• Extracellular - Fast (instantaneous)
  
  • ​Most Important: CO2/HCO3 System
• Intracellular - Minutes
• Metabolic Disorders - Addition or Acidic/Basic to bodily fluids: Primary Extracellular buffering
  
  • ​Metabolic Acidosis: Low pH and [HCO3-]
  • Metabolic Alkalosis: High pH and [HCO3-]

Question 5

How can the Henderson Equation be used to represent extracellular buffering?

What are two other extracellular buffers?

Answer 5

[H+] = 24 x (P_CO2 / [HCO₃^-] )

Phosphate: H + HPO₄ ↔ H₂PO₄

Protein: H + Protein ↔ H-protein

Question 6

Explain hwo intracellular buffering works

Answer 6

Move H+ into or out of cells in response to acid/bases

• If acidic outside cell, will move H+ inside cell
• If basic outside cell, will move H+ outside cell

Inside cell, H+ is titrated by Phosphate and Protein buffers

Question 7

How does respiratory compensation occur in acidosis and alkalosis?

Answer 7

• Metabolic Acidosis: Increase ventilatory rate, excrete CO₂
• Metabolic Alkalosis: Decrease ventilatory rate, retain CO₂

Question 8

Explain the renal defense mechanisms in response to pH changes

Answer 8

• Acidosis:
  
  • Increase secretion of H+
  • Reasorb bicarbonate
  • Catabolism of Glutamine to Release Bicarb into blood, and excrete ammonium into urine
• Alkalosis:
  
  • Decrease secretion of H+
  • Decrease bicarb reabsorption

Question 9

How can metabolic acidosis develop?

Answer 9

• Metabolic Acidosis: Low plasma bicarb, low pH (high H+)
• Develop:
  
  • Addition of Nonvolatile Acid (diabetic ketoacidosis)
  • Loss of nonvolatile alkali (diarrhea - shitting bicarb)
  • Failure of kidneys to excrete sufficient acid (kidney failure)

Question 10

Explain how to use the anion gap to aid in the differential diagnosis of metabolic acidosis

Answer 10

[(Na + K) - (Cl + HCO3)] = (unmeasured anions) - (unmeasured cations)

• Normal: 16 mEq/L
• High: Unmeasured Anions
  
  • Diabetic ketoacidosis
  • Salicylate poisoning
  • Lactic acidosis
• Normal: Hyperchloremic
  
  • Diarrhea
  • Drainage of pancreatic juice

Question 11

What are the compensation mechanisms for metabolic acidosis?

Answer 11

• Buffering: Both extra/intracellular
• Respiratory: Hyperventilation
• Renal: Increase acid excretion

Question 12

How can metabolic alkalosis develop?

Answer 12

• Metabolic Alkalosis: Increased plasma bicarb, pH
• Develop:
  
  • Addition of Nonvolatile alkali
    
    • Antacid
  • Loss of Nonvolatile acid
    
    • Vomiting (stomach acid - HCl)
• Buffering: Extra/Intracellular Buffering
• Respiratory: Hypoventilation
• Renal: Excretion of bicarbonate increased (retain H+)

Question 13

Respiratory Acidosis

Answer 13

• Respiratory Acidosis: Elevated P_CO2 and reduced pH
• Develop:
  
  • Inadequate Ventilation
    
    • Drug induced suppression
  • Impaired Gas Diffusion
    
    • Pulmonary edema
• Buffering: Intracellular Compartment
• Renal: Increased bicarb reabsorption and ammonium excretion

Question 14

Respiratory Alkalosis

Answer 14

• Respiratory Alkalosis: Reduced PCO2, high pH
• Develop:
  
  • Hyperventilation
    
    • Drugs, anxiety, fear
• Buffering: Intracellular
• Renal:
  
  • Inhibition of bicarbonate reabsorption (bicarb excretion), reduced ammonium excretion

Question 15

Combined Acid-Base Disorders

Combined Simple

Answer 15

Combined Complex

• Respiratory System compensates for a metabolic problem
• Renal System compensates for a respiratory problem

Combined Simple

• Second acid-base distrbance compounds first
  
  • Acidosis / Alkalosis will get worse
  • Respiratory Failure, then Renal Fairure
  • Infant with IRDS
  • Hyperventilation then vomiting