Acid-Base Physiology

Question 1

Henderson-Hasselbach Equation

Answer 1

[HCO3-] = 0.03PCO2 *10^(pH-6.1)

Question 2

What are metabolic lines?

Answer 2

They describe the changes in pH and bicarbonate that occur when acid or base is added at constant PCO2.

Question 3

Respiratory Acidosis

Answer 3

• Caused by hypoventilation (insufficient ventilation to eliminate CO2 as fast as its rate of production)
• CAUSES: COPD/emphysema, asthma, narcotics/anesthesia, airway obstruction, lung collapse, muscular dystrophy or paralysis, pneumonia, bronchitis, severe pulmonary edema
• on Davenport graph, is on UPPER LEFT

Question 4

Normal values for pH, HCO3-, PCO2

Answer 4

pH = 7.4
HCO3- = 24
PCO2 = 40 mmHg

Question 5

Breathing equation

Answer 5

CO2 + H2O H2CO3 H+ + HCO3=

Question 6

Renal compensation for respiratory acidosis

Answer 6

• Increase reabsorption of HCO3- and excretion of acid

- Excretion of NH4Cl

Question 7

Respiratory Alkalosis

Answer 7

• Caused by hyperventilation (CO2 is eliminated faster than its rate of production)
• CAUSES: ventilator set too high in ICU, anxiety attack, trauma to respiratory center in brain, brain tumor
• on Davenport graph, is LOWER RIGHT

Question 8

Renal compensation for respiratory alkalosis

Answer 8

• Decreased reabsorption of HCO3-, increased reabsorption of H+
• Decreased excretion of NH4Cl

Question 9

Metabolic Alkalosis

Answer 9

• Increased pH with increased HCO3-
• CAUSES: ECF Volume contraction [Cl- Responsive]: Vomiting, gastric tubes in patients, excess diuretics OR ECF Volume Expansion [Cl- Resistant]: Hypoaldosteronism
• on Davenport graph, is UPPER RIGHT

Question 10

How do diuretics cause volume contraction and metabolic alkalosis?

Answer 10

Excess diuretics –> Loss of NaCl and fluid –> Increase renin/angiotensin/aldosterone –> Renal proton secretion –> Increase plasma bicarbonate

Question 11

Metabolic Acidosis

Answer 11

• Decreased pH with decreased bicarbonate
• CAUSES: excessive overproduction or exogenous overload leading to accumulation of acids in the blood, underexcretion of acids by the kidney, excessive renal excretion of bicarb, GI loss of bicarb. Can occur in poorly controlled diabetes mellitus or people with prolonged starvation –> insulin is low and glucagon is high –> hormonal stimulation of mitochondrial fatty acid B-oxidation and synthesis of acetyl CoA. Due to low Krebs cycle activity due to low substrate levels, acetyl coA is diverted to form acetoacetic acid and B-hydroxybutyric acid –> ketoacidosis. OR can also be caused by poison-associated anion gap acidosis by overdose of methanol (formic acid), ethylene glycol (glycolic acid), or aspirin (salicylic acid).
  ^^^^ All these are inc. organic anion, dec. bicarb
  Can also by Hyperchloremic (inc Cl-, dec. bicarb), via severe diarrhea or uremias
  -On Davenport graph, is LOWER LEFT

Question 12

Anion gap equation

Answer 12

AG = Na - (Cl + HCO3) = 12 +/- 4

Question 13

Base excess

Answer 13

The amount of [HCO3-] that should be added or subtracted to bring the patient back to normal. Base excess is + in alkalosis, - in acidosis. Negative base excess is a base deficit.