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Questions and Answers
What is the correct formula to calculate the pH of arterial blood?
What is the correct formula to calculate the pH of arterial blood?
What is the primary cause of respiratory acidosis?
What is the primary cause of respiratory acidosis?
What is the role of the bicarbonate buffer system in respiratory acidosis?
What is the role of the bicarbonate buffer system in respiratory acidosis?
What is the effect of chronic CO2 retention on the bicarbonate buffer system?
What is the effect of chronic CO2 retention on the bicarbonate buffer system?
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What is the primary cause of respiratory alkalosis?
What is the primary cause of respiratory alkalosis?
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What is the role of the kidneys in respiratory acidosis?
What is the role of the kidneys in respiratory acidosis?
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What is the effect of acute CO2 retention on the bicarbonate buffer system?
What is the effect of acute CO2 retention on the bicarbonate buffer system?
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What is the role of the bicarbonate buffer system in respiratory alkalosis?
What is the role of the bicarbonate buffer system in respiratory alkalosis?
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What is the effect of chronic respiratory acidosis on the kidneys?
What is the effect of chronic respiratory acidosis on the kidneys?
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What is the primary mechanism of respiratory regulation of pH?
What is the primary mechanism of respiratory regulation of pH?
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Study Notes
Electrolyte Balance and Acid-Base Disorders
- Hypercalcaemia is related to alkalosis and hypokalaemia
- Acidosis is associated with decreased cardiac contractility, while alkalosis is associated with decreased oxygen delivery due to increased Hb affinity to oxygen
Sources of Hydrogen Ions (H+)
- Metabolic processes: aerobic metabolism, triglyceride breakdown, ketoacids, and metabolism of phosphoric, sulphuric, and amino acids
- Anaerobic metabolism: lactic acid
- Phosphoric, sulphuric, and hydrochloric acids
Maintaining [H+]
- Buffers: bicarbonate, phosphate, haemoglobin, and protein buffers
- Respiratory system: seconds to minutes
- Kidneys: hours to days
Buffers
- Definition: a mixture of a weak acid and its conjugate base that lessens a change in [H+] when a strong acid/base is added
- Types: bicarbonate, phosphate, haemoglobin, and protein buffers
Bicarbonate Buffer
- Equation: H2CO3 ⇌ H+ + HCO3-
- pKa = 6.1
- pH = 7.4
- Role: volatile acid, reclaimed/regenerated, and excreted as H+
Henderson-Hasselbalch Equation
- Equation: pH = 6.1 + log ([HCO3-]/(0.03 x PaCO2))
- Used to calculate pH
Phosphate Buffer
- Equation: H2PO4- ⇌ H+ + HPO42-
- pKa = 6.8
- Role: intracellular and in urine
Other Buffers
- Haemoglobin buffer: in red blood cells, plasma, and tissues
- Protein buffers: in intracellular fluid and other proteins
- Bone buffer: in bone water, exchange of protons on bone surface, and release of carbonate and phosphate proton buffers
Respiratory Regulation
- Role: regulates pH of cerebrospinal fluid (CSF)
- Equation: CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-
- Crosses blood-brain barrier (BBB)
- Central chemoreceptors: increase ventilation in response to decreased pH and decreased PCO2
- Peripheral chemoreceptors: increase ventilation in response to increased PCO2 and decreased PO2
Renal Regulation
- Metabolic component: HCO3- and H+
- HCO3- reabsorption and regeneration: 80% in proximal tubules, 10% in distal tubules, and 4% in collecting ducts
- H+ excretion: 4% in proximal tubules, 10% in distal tubules, and 80% in collecting ducts
Bicarbonate Reabsorption
- Process: HCO3- reabsorption, regeneration, and conservation
- Steps:
- Filtered HCO3- and Na+ in proximal tubules
- H+ and HCO3- in tubular lumen
- H+ excretion in urine
- Net HCO3- reabsorption in blood
Bicarbonate Regeneration
- Process: linked to H+ excretion and titratable acidity
- Steps:
- Filtered HPO42- and H+ in proximal tubules
- H+ excretion in urine
- New HCO3- absorbed in blood
Approach to Acid-Base Disorders
- Traditional approach: Henderson-Hasselbalch equation
- Stewart's approach: physiochemical approach, independent variables: ATOT, SID, and PaCO2
Interpreting pH, HCO3, PCO2
- Primary disorder: respiratory or metabolic
- Compensation: response by non-primary system to bring pH back within range
- Correction: response by the body to bring all parameters within range
Laboratory Parameters
- Blood gas: pH, PCO2, and HCO3-
- U&E: electrolyte levels, including potassium, sodium, and chloride
Terminology
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Acid: substance that donates H+ ions
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Base: substance that accepts H+ ions
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Acidosis: excess acid
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Alkalosis: excess base
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Acidaemia: pH < 7.35
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Alkalaemia: pH > 7.45### Arterial/Capillary Blood
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Electrodes are used for blood gas analysis
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Anticoagulated, sealed syringe, and on ice are necessary for blood sample collection
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Minimal delays are essential to ensure accurate results
Blood Parameters
- Actual bicarbonate can be calculated using the H-H equation, which requires pH and PaCO2 values
- Standard bicarbonate is a better indicator, as it is corrected for abnormal PaCO2
- Standard base excess is corrected for CO2, temperature, and the effect of Hb as a buffer
Laboratory Parameters
- U&E (Urea and Electrolytes) require a serum sample with minimal delays
- Measured TCO2 (Total CO2) is calculated using 4 parameters: Na+, K+, CL-, and HCO3-
Arterial Blood Gas
- Measured pH is calculated using the equation: pH = 6.1 + log [0.03 x PaCO2]
- Calculated base excess and standard bicarbonate are also derived from arterial blood gas analysis
- Measured HCO3- (bicarbonate) is an important parameter in acid-base disorders
Acid Base Disorders
- pH < 7.35 indicates acidosis, while pH > 7.45 indicates alkalosis
- Respiratory acid-base disorders can be classified into respiratory acidosis and respiratory alkalosis
Respiratory Acid Base Disorders
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Respiratory acidosis is caused by inadequate mechanical ventilation, CNS depression, hypoventilation, airway obstruction, lung defects, and increased CO2 intake
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Primary disorder: hypoventilation, which leads to increased CO2 and decreased pH
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Compensation: metabolic compensation, which increases HCO3- to buffer excess H+
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Compensation in acute CO2: ventilation, buffering of H+ by Hb and proteins, and small HCO3- increase
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Compensation in chronic CO2: greater HCO3- increase, H+ excretion, and HCO3- reabsorption/regeneration
Respiratory Alkalosis
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Causes: excessive mechanical ventilation, CNS stimulation, hyperventilation, and lung defects
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Primary disorder: hyperventilation, which leads to decreased CO2 and increased pH
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Compensation: metabolic compensation, which decreases HCO3- to buffer excess H+
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Compensation in acute CO2: equilibrium shifts, intracellular buffering, small HCO3- decrease, and chronic CO2: greater HCO3- decrease, H+ excretion, and HCO3- reabsorption/regeneration
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Description
This quiz tests your understanding of electrolyte balance, acid-base regulation, and their effects on cardiac contractility and oxygen delivery. It covers topics such as hypercalcaemia, alkalosis, and metabolic processes.
