Acid Base Disorders Flashcards
What is the relationship between h+ ions and ph
-inverse relationship
-low ph me and high concentration of h+
What is the body’s ph
7.4 +/- 0.05
Why does the body need to maintain ph
-alter structure and function of proteins(eg it can change the charges on the r groups on the amino acids)
-it can affect biological activity of ions such as cations
-affect movement of molecules within cells
Sources of H+ ions in the body
1)Metabolic acids
-anaerobic glucose/fatty acid metabolism
-oxidation of sulphur containing amino acids and cationic amino acids and cationic amino acids
2)Respiratory acids
-co2
What are the body’s mechanisms to control concentration of H+
1)Buffering systems such as carbonic acid-bicarbonate,protein,phosphate which has an immediate response
2)Respiratory system which is activated almost immediately
3)Renal system slowest mechanism to respond
Renal regulation
-excretion of H+
-bicarbonate recovery
-bicarbonate regeneration
Respiratory regulation
-expiration of CO2 Trough the lungs
Renal regulation-Bicarbonate recovery
-in the glomerular filtrate bicarbonate ions join H+ in order to form carbonic acid which is then transformed by carbonic anhydrase to water and carbon dioxide as its an unstable molecule due to it being a weak acid.
-water then leaves the kidney through urine and carbon dioxide diffuses through the highly selective membrane into the proximal tubule cell
-carbon dioxide then joins water and forms carbonic acid(reaction due to the action of anhydrase)
-carbonic anhydrase then splits into bicarbonate ions and hydrogen ions.Bicarbonate can then diffuse into the blood stream and be recovered
Renal regulation-Bicarbonate recovery
-in the glomerular filtrate bicarbonate ions join H+ in order to form carbonic acid which is then transformed by carbonic anhydrase to water and carbon dioxide as its an unstable molecule due to it being a weak acid.
-water then leaves the kidney through urine and carbon dioxide diffuses through the highly selective membrane into the proximal tubule cell
-carbon dioxide then joins water and forms carbonic acid(reaction due to the action of anhydrase)
-carbonic anhydrase then splits into bicarbonate ions and hydrogen ions.Bicarbonate can then diffuse into the blood stream and be recovered
Bicarbonate regeneration
-Just as in recovery hydrogen ions leave the proximal tubule cell, then they join phosphate or ammonia to form either do hydrogen phosphate or ammonium which can be excreted in the urine
-there is a net loss of H+ from the body during bicarbonate recovery due to the urinary buffers
Describe the partial pressures of gasses in peripheral tissues
-high partial pressure of of carbon dioxide
-low partial pressure of oxygen
Describe the partial pressures of gasses in peripheral tissues
-high partial pressure of of carbon dioxide
-low partial pressure of oxygen
Describe the partial pressures of gasses in the lungs
-Low partial pressure of carbon dioxide
-High partial pressure of oxygen
Describes what happens to carbon dioxide in peripheral tissues
-co2 produced in the tissues is transported to the lungs as bicarbonate in blood plasma
-this is done when some of the carbon dioxide in the erythrocyte either 1)forms carbamine compounds with proteins such as heamologlobin forming carbaminoheamoglobim 2)dissolves im water 3)reacts with carbonic anhydrase to form carbonic acid which then dissociates into h+ which binds to Haemoglobin(h+hb) and bicarbonate which leaves into the plasma
Describe the chloride shift that happens in erythrocytes
-chloride irons move into erythrocytes while bicarbonate moves out to the venous blood
-this is done by co2 diffusing into erythrocytes and being converted to bicarbonate by carbonic anhydrase
-the chloride shift mitigates the changes in ph
Describe what happens to oxygen in the erythrocytes in the lungs
-oxygen enters erythrocytes and joins hydroxy Haemoglobin which dissociates into h+ which reacts with the bicarbonate ions from the plasma to form carbonic acid and hbo2
-carbonic anhydrase then splits carbonic acid into water and co2 which leaves the erythrocyte in order to be exhaled
Blood gas analysis
• Arterial blood collected into syringe containing anticoagulant (eg heparin) and transported on ice(prevents glycolysis)
• Any air from syringe expelled before/after blood collection
• [H+] and pCO2 measured directly in arterial blood
• Blood gas analysers measure [H+] and pCO2 and are programmed to calculate bicarbonate
What readings does the blood gas analysis provide
Conc of h+
Partial pressure of carbon dioxide
Conc of bicarbonate
Relationship between the 3 values provided by blood gas analysis
-if the change is due to the partial pressure of carbon dioxide it is a respiratory disorder
-if the change is due to the concentration of bicarbonate ions it is a metabolic acid
Relationship between ph and concentration of bicarbonate
Directly proportional (if one goes up so does the other)
Relationship between ph and partial pressure of carbon dioxide
Inversely related (if one goes up the other one goes down)
Explain compensation
Is ph decreases so does the concentration of bicarbonate ions this means its a metabolic disorder so there will be respiratory compensation
If ph decreases co2 concentration increases meaning a respiratory disorder so metabolic compensation
Causes of metabolic acidosis
1)Increased H+ formation
• Ketoacidosis (type 1 diabetes)
• Lactic acidosis
• Poisoning (e.g. salicylate, ethylene glycol)
• Inherited organic acidosis
2)decreased H+ excretion
• Renal tubular acidosis
• Acute renal failure
• Chronic renal failure
• Mineralocorticoid deficiency
3)Acid ingestion
4)loss of bicarbonate caused by eg diarrhea,pancreatic fistula
Clinical presenation(symptoms) of metabolic acidosis
Hyperventilation (Kussmaul respiration)
Neuromuscular irritability: arrhythmias, cardiac arrest
CNS depression can go on and cause coma, lead to death
Management of metabolic acidosis
-Treat underlying cause
-Administration of bicarbonate to correct severe acidosis (drip), careful only done in cases of severe acidosis. If you don’t get it right it can cause alkalosis
Causes of metabolic alkalosis
1)Gastrointestinal loss of H+
Vomiting
Gastric aspiration
2)Renal loss of H+
• Conns syndrome (aldosterone)
• Cushing’s syndrome (cortisol, similar effect
to aldosterone)
3)Drugs eg carbenoxolone (to treat ulcers), similar action to aldosterone
• Thiazide diuretics (blood pressure)
4)Potassium depletion
5)Administration of alkali
• alkali ingestion
• Inappropriate treatment of acidosis
Clinical presentation(symptoms) of metabolic alkalosis
Hypoventilation
Paraesthesia: pins and needles effect in hands and feet
Tetany: spasms of the muscles of face and hand due to changes in calcium
Muscle cramps
Management of metabolic alkalosis
-Treat underlying cause
-Correct hypovolaemia (blood volume declined) if present
Causes of respiratory acidosis
1)Airways obstruction
Chronic obstructive airway disease (bronchitis, emphysema) Bronchospasm (e.g. asthma)
2)Inhibition of respiratory centre
Some drugs will affect it anaesthetics, sedatives, cerebral trauma, tumours in brain
3)Neuromuscular disease: poliomyelitis, tetanus, neurotoxins, Guillain–
Barré syndrome
4)Pulmonary disease: pulmonary fibrosis, severe pneumonia, respiratory distress syndrome.
5)Acute: choking, bronchopneumonia, acute exacerbation of asthma
6)Chronic: chronic bronchitis, emphysema
Clinical presentation(symptoms) of respiratory acidosis
Peripheral vasodilation
Headaches
CNS depression
Management of respiratory acidosis
-Aim to improve alveolar ventilation and lower PCO2
-Maximise alveolar ventilation in chronic respiratory acidosis using physiotherapy
bronchodilators
Causes of respiratory alkalosis
1)Hypoxia: high altitude, sever anaemia, pulmonary disease
2)Increased respiration: respiratory stimulants eg salicylates, primary hyperventilation syndrome, artificial hyperventilation
3)Pulmonary disease: pulmonary oedema, pulmonary embolism
Clinical presentation of respiratory alkalosis
Confusion/ coma
Headaches/ dizziness
Management of respiratory alkalosis
Treat underlying cause of hyperventilation
Acute: rebreathing
3 rules when interpreting acid base disorders
- Check [H+] (or pH)
- Check PCO2 and [HCO3-] which is consistent with [H+]:
metabolic or respiratory - Check the third component - any compensation (full or partial)
