S4 L1 Respiratory System: Carbon dioxide Transport; CO Role in pH balance and intro to ABG Analysis Flashcards
Carbon dioxide is in the blood in three forms
- State them and order ‘largest to smallest transporter’
- Is CO2 only a waste product?
Acid-base balance (control of pH):
- Normal range of arterial pH?
- What happens is pH drops below 7.35, what happens if it rises above 7.45?
- What is a buffer?
Three forms:
1 (60% of all transported CO2). CO2 reacts chemically with water to form bicarbonate – HCO3-
(chemists refer to bicarbonate as hydrogen carbonate; medical literature uses
bicarbonate)
2 (30% of all transported CO2) CO2 also reacts with Hb (but at different site from O2) – carbamino-haemoglobin compound (carbamino)
Binds to amino group on the globin chains, to form carb amino-haemoglonin compound
This is in the blood component (attached to ‘cells’), not included in plasma component
3 (10% of all transported CO2) CO2 is more soluble than oxygen (dissolves) – dissolved
No, CO2 is very important in the bodies pH buffering system
Normal range: pH 7.35-7.45
pH above 7.45: Ionised calcium falls (affects nerves, muscles e.g. heart, respiratory muscles)
pH below 7.35: Denature proteins
Buffer is:
Buffers are compounds which are able to bind or release
hydrogen ions such that they dampen swings in the pH.
Drop
Major pH buffer system of the body
- What is the ‘name’ of this buffer system?
- State it?
- Reversible?
- Enzyme?
- Where is enzyme present? Yes in one place, not in another
- What happens to this system with hypoventilation?
Carbon dioxide in arterial blood - dissolved
- How to work out how much CO2 has dissolved
- The buffer equation: What is the net movement?
- Reversible?
- Intermediatary?
[CO2]dissolved = solubility constant/factor x pCO2
• Solubility factor for CO2 at 37 degrees Celsius = 0.23 mmol/L/kPa (vs oxygen
- 0.01 mmol/L/kPa)
• pCO2 of CO2 arterial blood =5.3 kPa
5.3 kPa X 0.23mmol/L/kPA= 1.2 mmol/L dissolved CO2
– more dissolved CO2 even though lower pCO2 c/w pO2 –
because of markedly increased solubility c/w oxygen
What is the Henderson Hasselbalch Equation?
What are the ‘values’ that go into each bit?
Learn what part of the HH equation? (plus a value…)
Referring to Henderson Hasselbach Equation:
- What happens if CO2 increases?
- What happens if HCO3- increases?
- Ratio of HCO3- to CO2?
- What does the amount of CO2 dissolved depend on?
- pCO2 of alveoli determines what pCO2 of____?
- What happens to this equation in hyperventilation?
The amount of CO2 dissolved depends directly on the partial pressure of CO2
■ If pCO2 rises (and there is no change in bicarbonate) plasma pH will fall (becomes more acidic)
■ If pCO2 falls (and there is no change in bicarbonate) plasma pH will rise (becomes more alkaline)
■ The pCO2 of alveoli is the determining factor – determines arterial pCO2
■ Alveolar, and hence arterial pCO2 controlled by altering the rate of breathing
Bicarbonate in plasma:
- Plasma contain 25mmol/L HCO3-, where does it come from?
- Where is bicarbonate produced? Reaction reminder, enzyme, explain what happens to H+
- Concentration is of bicarbonate is controlled by….
This high [HCO3]:
- cannot come from CO2 alone in plasma – not enough dissolved - CO2 in plasma to create this much HCO3
- Bicarbonate production in the RBC (see pic)
Control:
although RBC makes the HCO3, it does not CONTROL HCO3 concentration, HCO3 concentration controlled by KIDNEY
Role of Kidney and lungs in CO2: Bicarbonate levels
- Ratio reminder
- pH is determined by…
- Which organs controls what?
- Terms of pH disorders?
- Compensation meaning?
How does Bicarbonate buffer extra acid?
- When exercise, what is produced?
- Pathological acid examples and conditions caused by
- How does this effect the HH equation?
- How is extra CO2 removed?
- What happens when ___ stores (__ reacts with the acid), runs out?
Properties of haemoglobin are important for H+ buffering:
- How does the ‘type’ of haemoglobin affect H+ buffering
Haemoglobin at the tissue:
- State of the hb
- H+ bound? (remember H+ is the ‘buffer’), it is produced and then binds
- How does this affect the HH equation?
- How does this affect amount of CO2 in the blood?
Haemoglobin at the tissue:
- State of the hb
- H+ bound? (remember H+ is the ‘buffer’), it is produced and then binds
- How does this affect the HH equation?
- How does this affect amount of CO2 in the blood?
State of Hb
How this affects the H+ bound
How this affects the HH equation
Summary: RBC cells, CO2 and Bicarbonate
Formation of carbamino compounds
- Site CO2 binds?
- Deoxygenated vs oxygenated hb better at forming carbamino compounds?
- Binds directly to what…?
- What is the Haldane Effect: Describe it? What does it mean?
Haldane effect -
In the lungs deoxygenated Hb bound to CO2 become saturated with oxygen
Become oxygenated Hb: T state to R state
Gives up the extra H+ it took on at the tissue
H+ ions increase in conc, this react with HCO3- to form CO2
Reaction is pushed to the left
CO2 diffuses down its partial pressure gradient
CO2 is breathed out
How to interpret an ABG: Steps…
- What is the normal range of pH in arterial blood?
- What is the acidotic and alkalotic part of the normal range?
- Will someone ever overcompensate?
- How to tell if someone has fully or partially compensated?
1) Look at pH - remember body never overcompensates
a) If pH < 7.35: acidaemia/acidosis
b) If pH > 7.45: alkaemia/alkalosis
2) Look at pCO2
3) Look at HCO3-
4) Look at HCO3- again (checking for compensation)
5) Look at pCO2 again (checking for compensation)
- 35-7.40 acidotic part of normal range
- 40-7.45 alkalotic part of normal range
Body can compensate if a problem, however body wilI never overcompensate only ‘just’ compensates i.e. if patient has primary respiratory acidosis, buffer system will not overcompensate leading to them become alkalosis
Partially compensated: Change in blood pH, and abnormal pCO2 and pHCO3 values
Fully compensated: No change in blood pH, and abnormal pCO2 and pHCO3 values
ABG and acidosis (What would ABG look like? Explain pH equation thing)
- Respiroty acidosis
- Metabolic acidosis
ABG and Alkalosis (What would ABG look like? Explain pH equation thing)
- Respirtory alkalosis
- Metabolic alkalosis
Summary of what ABG to expect on all the types of acidosis and alkalosis?
How to know if they are compensated?
Example of a condition leading to each?
Look at PP for example questions
Respiratory acidosis - COPD, asthma
Metabolic acidosis - Diabetic ketoacidosis, sepsis
Respiratory alkalosis - panic attack, leading to hyperventilation
Metabolic alkalosis - volume depletion (particularly when there is a loss of gastric acid and Cl-, e.g. due to recurrent vomiting)
