deck_1458802 Flashcards
What is the normal range for plasma pH?
7.38 - 7.42
What pH is classed as alkalaemia?
pH > 7.42
What pH is classed as acidaemia?
pH
What are the clinical effects of acidaemia?
- Reduced enzyme function- Reduced cardiac and skeletal muscle contractility- Reduced glycolysis - Reduced hepatic function- Increased plasma potassium
What are the clinical effect of alkalaemia?
- It causes a reduction in the concentration of free calcium in the blood. - Increase the excitability of nerves- Causes paraesthesia and tetany
How is the pH of the blood plasma controlled?
By the buffering action of the carbon dioxide/hydrogen carbonate system.
Describe what happens in the carbon dioxide/hydrogen carbonate system
If there is a high [H+] then the H+ will bind to HCO3-, forming H2CO3 to lower the [H+] to try and increase the pH. In high pH, the kidneys will release HCO3- and therefore H+ in order to try and decrease the pH.
What happens following hyperventilation?
Causes hypocapnia, so there will be a decrease in pCO2 and a relative increase in HCO3-, which will cause the pH to increase.
What is respiratory alkalosis?
When the pH rises as a result of the effects of hyperventilation and hypocapnia– there is more HCO3- in the ratio than CO2 so there are more H+ ions
What is respiratory acidaemia?
When the pH drops as a result of hypoventilation, leading to hypercapnia. – there is more CO2 in the ratio than normal, so there are fewer H+ ions to buffer, causing a decrease in pH.
What are the blood gas analysis factors that indicate respiratory alkalosis?
High pHLow pCO2
What are the blood gas analysis factors that indicate respiratory acidosis?
Low pHHigh pCO2
What can be done to compensate for respiratory alkalosis and acidosis?
The kidneys control the [HCO3-] in the blood to restore the pH to normal values. Alkalosis – decrease [HCO3-] to decrease pHAcidosis – increase [HCO3-] to increase pH
What is a characteristic of a compensated blood gas analysis?
pH is normalOther values are raised and/or lowered
What indicates that there is hyperventilation on a blood gas analysis?
High pO2 Low pCO2
What indicates that there is hypoventilation a blood gas analysis?
Low pO2High pCO2
What is metabolic acidosis on a blood gas analysis?
When there is an increased concentration of H+ from metabolism which reacts with HCO3- to produce CO2. This CO2 is then breathed out, but the [HCO3-] is lowered, altering the ratio and giving a decrease in the pH as there are less H+ ions to buffer.
What is metabolic alkalosis on a blood gas analysis ?
There is a rise in the [HCO3-] in the blood (after persistent vomiting) which alter the HCO3-:CO2 ratio. There will be more H+ ions buffered, causing an increase in the pH.
How are metabolic acidosis and alkalosis compensated for?
By changing lung ventilation– increased for lowering the pCO2– decreased for increasing the pCO2
What are the blood gas analysis features for metabolic alkalosis?
High pHHigh [HCO3-]Low pO2
What are the blood gas analysis features for metabolic acidosis?
Low pHLow [HCO3-] Increased anion gap
What are the characteristic of partially compensated respiratory acidosis?
Low pHHigh pCO2High [HCO3-]Low pO2
What are the characteristics of partially compensated respiratory alkalosis?
High pHLow pCO2Low [HCO3-]High pO2
What are the characteristics of a partially compensated metabolic acidosis?
Low pHLow pCO2Low [HCO3-]High pO2
What are the characteristics of a partially compensated metabolic alkalosis?
High pHHigh pCO2High [HCO3-]Low pO2
What is the difference between correction and compensation?
Correction is changing the respiratory function to correct respiratory disturbances. Compensation is the kidneys changing [HCO3-] levels to alter pCO2 levels.
What compensates for respiratory driven changes in the pH?
The kidneys
What compensates for metabolically driven changes in the pH?
Changes in breathing
How is the pCO2 normally controlled?
By central chemoreceptors
What detects changes in the plasma pH?
Peripheral chemoreceptors which bring about change by causing changes with the pCO2
How is HCO3- reabsorbed by the kidneys?
Na-K-ATPase creastes a Na gradient by pumping Na out of the tubular cell into the ECF. This allows Na to enter in from the lumen into the cell and the energy released allows for H+ to be pumped out into the lumen. The H+ reacts with HCO3- –> H20 and CO2 which can be brought into the tubular cell. The HCO3- is released inside the cell and H+ is recycled out to pick up more HCO3-. The HCO3- inside the cell can then move out into the ECF.
Where is HCO3- reabsorbed mostly in the kidneys?
Proximal convoluted tubuleThick ascending limb of the loop of henle
What else can occur in the PCT to give more HCO3-?
HCO3- can be created
Describe the process of creating HCO3- in the PCT
GLutamine is broken down to produce:– aplha ketoglutarate (make HCO3-)– ammonium (NH4+)HCO3- leaves in the ECF and NH4+ moves into the lumen
How is H+ secreted in the distal tubule?
Proton pumps pump H+ into the lumen using ATP. They are H+-ATPase pumps
What occurs when you export H+ ions?
K+ ions are absorbed into the blood
What is blood pH linked to?
[K+} in the blood
What is the minimum pH of buffering H+ in the urine?
4.5
How is H+ buffered in the urine?
Don’t have HCO3-, so it is buffered by phosphate. Can also attach to ammonia, forming ammonium
What is a titratable acid?
It can freely gain H+ ions in an acid-base reaction
What are the responses of cell to acidosis?
- Enhances Na/H exchange- Enhanced ammonium production (helps get rid of excess H+)- Increased H+ATPase in the distal tubule (removes H+ which could be damaging)- Increases the capacity of the tubular cells to be able to export HCO3- from the tubular cells into the ECF
What is the anion gap?
Gives an indication if any HCO3- has been replaced with something other than Cl-.
How do you calculate the anion gap and what is the normal range of values?
([Na+] + [K+]) and ([Cl-] + [HCO3-])10-15 mmol/L
What happens if the anion gap has increased?Why has this occurred?
HCO3- has been removed from the blood and replaced it with another ion. Usually it is due to metabolic processes which produce acid.
What does a normal anion gap with low [HCO3-] indicate?
Kidney problems
What does an increased anion gap and low [HCO3-] indicate?
Something wrong but not in the kidneys.
What ion is linked to the acid-base balances?
Potassium
What happens with potassium in metabolic acidosis?
K+ moves out of the cells, there is more reabsorption of K+ in the distal nephron and therefore an increased [K+] in the blood
What happens with potassium in metabolic alkalosis?
K+ moves into the cells, there is less K+ reabsorption so there is a decrease [K+] in the blood
What is hyperkalaemia linked to?
Metabolic acidosisHyperkalaemia makes the intracellular pH alkaline, so HCO3- is excreted into the blood, causing acidosis.
What is hypokalaemia linked to?
Metabolic alkalosisHypokalaemia makes the intracellular pH acidic. So there is excretion of H+ and HCO3- reabsorption
Why does the [HCO3-] increase when a patient has persistent vomiting?
Don’t have stomach acid, so there is a greater proportion of HCO3- to CO2.It also causes dehydration, so there is recovery of Na and HCO3- to increase the osmolarity of the plasma. Body stops actively secreting H+ ions as it would worsen the metabolic alkalosis.
How can you treat the metabolic alkalosis causes by persistent vomiting?
Treat the dehydration. Once this is back to normal, then the HCO3- can be excreted by the kidneys very rapidly.
What are the effects of metabolic alkalosis from persistent vomiting?
Body stops secreting H+ to avoid making metabolic alkalosis worse. K+ reabsorption also stops which can lead to hypokalaemia.
What can hypokalaemia lead to?
ParaesthesiaTetanyCVS problems
When can metabolic acidosis occur?
Excess metabolic production of acidsIngestion of acidsHCO3- is lostIssues with renal excretion of acid
When does the anion gap increase?
When the HCO3- in the plasma that has been lost is replaced by another anion which is not included in the calculation.
When is the anion gap measurement useful?
It can help distinguish between what is causing the acidosis (whether the lactate has replace the HCO3- in lactic acidosis for example)
