Clinical Acid-Base Flashcards
How would pH, HCO3- and pCO2 be affected in a metabolic acidosis?
pH: decreased
HCO3: decreased
pCO2: decreased
How would pH, HCO3- and pCO2 be affected in a metabolic alkalosis?
pH: increased
HCO3: increased
pCO2: increased
How would pH, HCO3- and pCO2 be affected in an acute respiratory acidosis?
pH: decreased
HCO3: increased
pCO2: increased
How would pH, HCO3- and pCO2 be affected in a chronic respiratory acidosis?
pH: decreased
HCO3: very increased
pCO2: increased
How would pH, HCO3- and pCO2 be affected in an acute respiratory alkalosis?
pH: increased
HCO3: decreased
pCO2: decreased
How would pH, HCO3- and pCO2 be affected in chronic respiratory alkalosis?
pH: increased
HCO3: very decreased
pCO2: decreased
Write the bicarbonate buffering equation
H+ + HCO3- H2CO3 H2O + CO2
What are the causes of respiratory alkalosis?
Hyperventilation which may be caused by stress, exercise, septic shock, altitude, pregnancy and drugs such as salicylate and doxapram
What are the compensatory mechanisms for respiratory alkalosis?
- H+ levels are increased due to decreased distal renal acid secretion
- HCO3- levels fall due to increased proximal renal excretion of bicarbonate
What are the causes of respiratory acidosis?
Hypoventilation which may be caused by:
- Loss of hypoxic drive (CNS dysfunction)
- Restrictive chest wall abnormalities e.g. kyphoscoliosis, pneumothorax, obesity
- Type 2 respiratory failure (hypoxia with hypercapnia) e.g. COPD or status asthmaticus
- Myaesthesia gravis (neurological impairment of chest wall movement)
What are the compensatory mechanisms for respiratory acidosis?
Increased bicarbonate levels in order to buffer the excess H+ (produced due to equilibrium shift as a result of excess CO2 retention)
What are the causes of metabolic alkalosis?
Decreased H+ and/or increased HCO3- levels
What may cause the reduction in H+ levels that leads to the development of metabolic alkalosis?
- Vomiting (loss of stomach acid/HCl)
- Hypokalaemia; extracellular K+ falls and therefore potassium moves out of cells and into the blood, so to retain electroneutrality H+ moves out of the blood and into the cells –> plasma H+ fall
What may cause the increase of HCO3- levels that leads to the development of metabolic alkalosis?
Iatrogenic causes (drug-induced) such as antacids (contain bicarbonate)
What are the compensatory mechanisms for metabolic alkalosis?
Hypoventilation (to retain carbon dioxide)
What are the causes of metabolic acidosis?
Gain of H+ and/or decrease in HCO3-
What may cause the increased H+ level that leads to the development of metabolic acidosis?
- Increased organic acid production e.g. lactate or ketones (elevated anion gap)
- Reduced H+ secretion in the distal tubules due to renal failure
What may cause the decreased bicarbonate level that leads to the development of metabolic acidosis?
- Diarrhoea
- Renal failure causing an inability to reabsorb bicarbonate in the proximal tubules
- Carbonic anhydrase inhibitors (prevent the conversion of H2CO3 into the ionic form and therefore bicarbonate cannot be reabsorbed)
What is the cause of a normal gap metabolic acidosis?
Increased loss of bicarbonate leading to compensation via hyperchloraemia
What are the causes of an elevated gap metabolic acidosis? (KUSMALE)
Ketoacidosis Uraemia Salicyclate poisoning Methanol Aldehyde Lactate Ethylene glycol intoxication
What is the main difference in terms of compensation between normal and elevated gap metabolic acidosis?
In normal gap there is chloride compensation (hyperchloraemia) to retain electro-neutrality due to bicarbonate loss
What is the physiologic pH value range?
7.35-7.45
What is the normal pCO2 range?
35-45mmHg
What is the normal pO2 range?
72-104mmHg
