Acid-Base Balance Flashcards
What are the major products of metabolism
Acids - Carbon dioxide and organic acids
What is the normal pH range and which two systems maintain it
- 35 - 7.45
1) initially by a buffer system in the blood
2) excess acid excreted by lungs and kidneys
What is the definition of acidosis and alkalosis
Acidosis - abnormal decrease in arterial pH (<7.35)
Alkalosis - abnormal increase in arterial pH (>7.45)
What are all buffering systems composed of
A weak acid and it’s conjugate base
HB (weak acid) <=======> [H+] + [B-] (conjugate base)
How does a buffering system resist pH changes
Addition of acid reacts with the free base ions, moving the equation to the left in order to provide replacement base ions for the ones used to neutralise the acid
Addition of alkali reacts with the free hydrogen ions, moving the reaction to the right to provide replacement hydrogen ions for the ones used to neutralise the base
Which buffer systems are most common in the body (intracellular and extracellular)
Intracellular - proteins and phosphate act as buffers
Extracellular - bicarbonate acts as a buffer
Describe the buffer system of carbon dioxide and bicarbonate in the blood.
[CO2) + [H20] <===> [H2CO3] <===> [H+] + [HCO3-]
What are the main methods of acid/alkali excretion in the body
Excretion via the lungs - rapid response
Excretion via the kidneys - delayed response
Describe how the lungs affect pH balance in the blood
The brainstem respiratory centre detects hydrogen ion levels in the blood
- high levels of H+ ions cause an increase in respiratory rate, so that carbon dioxide (acid) is removed from the body
Dysfunction can cause respiratory acidosis (CO2 retention) or respiratory alkalosis (over-excretion)
Describe how the kidneys affect pH balance in the blood
Acid is normally excreted in the urine (urinary pH is normally 6.0)
- hydrogen ions are secreted into the urine by the distal nephron
Bicarbonate ions are generated by the renal tubules and secreted into the blood
What is respiratory acidosis
Primary disturbance of increased pCO2, leading to decreased pH and compensatory rise in bicarbonate
Causes of respiratory acidosis
Depression of respiratory centres - CVA - cerebral tumour - drugs (opiates/sedatives) - encephalitis Decreased chest wall movement - trauma/surgery - neuromuscular disorder (e.g. myasthenia gravis) - ankylosing spondylitis Pulmonary disease (causing type 2 respiratory failure) - COPD - pneumonia
What is respiratory alkalosis
Primary disturbance of decreased pCO2, leading to increase in pH and compensatory decrease in bicarbonate
Causes of respiratory alkalosis
Stimulation of respiratory centre - CNS disease (e.g. CVA or encephalitis) - hypermetabolic state (e.g. sepsis, fever and hyperthyroidism) - exercise - hypoxia (e.g. pneumonia) Excess ventilation - anxiety - medications (e.g. aspirin)
What is metabolic acidosis
Primary disturbance of decreased bicarbonate or increased hydrogen ions, leading to decreased pH and compensatory decrease in pCO2
Causes of metabolic acidosis
Increased anion gap (another source of acid production)
- renal glomerular failure
- overdose (e.g. salicylate)
- causes of respiratory alkalosis
- lactic acidosis (inadequate tissue perfusion e.g. hypovolaemia, ischaemic gut)
- ketoacidosis - diabetes or alcohol
- renal tubular acidosis
Normal anion gap
- excess acid intake e.g. parenteral nutrition
What is metabolic alkalosis
Primary disturbance of increased bicarbonate or decreased hydrogen ions, leading to increased pH and compensatory rise in pCO2
Causes of metabolic alkalosis
Excess alkali intake - e.g. alkali abuse or overtreatment of acidosis Excessive loss of acid - e.g. vomiting Increased urinary acidification - diuretics - excess aldosterone production - hypokalaemia
What is the anion gap
The difference between the cations (sodium and potassium) and anions (chloride and bicarbonate) in the blood
Normally 10-16mmol/l
How to calculate the anion gap
Total sum of cations - total sum of anions
Why does the anion gap exist when total number of cations and anions should be equal
The difference equates to the anions that aren’t measured - proteins, phosphate, sulphates and organic acids
