Acid-base balance Flashcards
What is being regulated in acid-base balance?
The hydrogen ion concentration [H+]
How does the body get rid of H+?
Most, or all, of the H+ is excreted in urine
What do hydrogen ions react with to form carbonic acid?
Bicarbonate
H+ + HCO3- –> H2CO3
What is carbonic acid removed as?
Carbon dioxide and water
What are the 2 acid-base problems that can arise in the body?
- Too much H+
2. Too much CO2
Explain compensation
The body will try and restore the concentrations back to normal by compensation. If there is too much H+ the body will blow off CO2. If there is too much CO2 the kidney will excrete more H+.
Define acidaemia
Increased [H+]
pH < 7.35
Define alkalaemia
Decreased [H+]
pH > 7.45
Define acidosis
The process tending to cause increased [H+]
Define alkalosis
The process tending to cause decreased [H+]
What is the primary change if it is respiratory?
The primary change is in the pCO2
What is the primary change if it is metabolic?
The primary change is in the HCO3-
Define respiratory acidosis
Increased [H+] due to an increased pCO2
Define respiratory alkalosis
Decreased [H+] due to a decreased pCO2
Define metabolic acidosis
Increased [H+] due to decreased HCO3-
Define metabolic alkalosis
Decreased [H+] due to increased HCO3-
What is the primary problem in metabolic acidosis and how is it compensated for?
Too much H+
Respiratory compensation - CO2 is blown off (reduces the pCO2)
What is the primary problem in respiratory acidosis and how is it compensated for?
Too much CO2
Metabolic compensation - excrete more H+
What are the 4 arterial blood gases?
H+, pCO2, HCO3-, pO2
Give 3 causes of respiratory acidosis
Choking
Bronchopneumonia
COPD
Give 3 causes of respiratory alkalosis
Hysterical over breathing
Mechanical over-ventilation
Raised intracranial pressure – potentially impact on the respiratory centre in the brain
Give 3 causes of metabolic acidosis
Impaired H+ excretion
Increased H+ production or ingestion
Loss of HCO3-
Give 3 causes of metabolic alkalosis
Loss of H+ in vomit
Alkali ingestion
Potassium deficiency
What is the equation for oxygen delivery?
DO2 = CO x [(1.3 x Hb x SaO2) + 0.003 x PaO2]
cardiac output x arterial oxygen concentration
What are 4 causes of tissues hypoxia?
Anaemic hypoxia
Perfusional hypoxia
Toxic hypoxia
Hypoxaemic hypoxia
What is FiO2?
FiO2 is the fraction of inspired oxygen. In other words, what percentage of the air being inspired is oxygen.
What range of saturation should you keep a patient with a chronic condition?
SaO2 88-92%
What range of saturation should most patients be kept in?
SaO2 94-98%
Give 4 buffers for H+ in the body
Haemoglobin
Bicarbonate
Potassium
Ammonium
What is the clinical term for uncompensated respiratory acidosis?
Acute Type II respiratory failure
What is the clinical term for compensated respiratory acidosis?
Chronic Type II respiratory failure
What is the clinical term for decompensated respiratory acidosis?
Acute on chronic respiratory acidosis
What is the anion gap?
The difference between the positively charged (cations) and the negatively charged (anions) in serum, plasma or urine. Values show the number of extra positive things.
How is the anion gap calculated?
Calculated by subtracting the serum concentration of chloride and bicarbonate (anions) from the concentration of sodium and potassium (cations)
-Na+ + K+ = Cl- + HCO3-
What does a higher than normal anion gap show?
Metabolic acidosis
What are the causes of a high anion gap?
AMUDPILES
Alcohol, methanol, uraemia, DKA, paraquat, infection, lactic acid, ethylene glycol and salicylates
What is base excess?
The amount of strong acid required to bring the pH back to 7.4, when CO2 is corrected to 5.3 (normal BE is between 2 and -2)
What is base excess used to diagnose?
Metabolic acidosis and alkalosis
BE > +2 = metabolic alkalosis
BE < -2 = metabolic acidosis
