Simple Acid/Base Disorders Flashcards
Simple Acid/base disorder occur if
Renal or respiratory functions abnormal
Acid or base load overwhelm the body
What do respiratory disorder affect
The Partial pressure of CO2
What do renal disorder affect
Bicarbonate concentration
What is important to consider in acid/base disorders
dont just occur in isolation and in otherwise healthy individuals need a combination of factors
What occurs in respiratory acidosis
an acidosis resulting from reduced ventilation, casusing a retention of CO2
this increases CO2, causing the pH to decrease
What is the causes of respiratory acidosis
Acute
- drugs which depress the medullary respiratory centres such as barbiturates and opiates
- Obstruction of major airway
Chronic
- Lung disease
{Bronchitis, emphysema, asthma}
What is the response to respiratory acidosis to protect the pH
Need to Increases HCO3 concentration:
How does HCO3 concentration increase ins response to respiratory acidosis
-Increased partial pressure of CO2 (due to retention of CO2) will increase H+ secretion and increase ability to reabsorbs HCO3
- Acid conditions will stimulate renal glutaminase Increasing NH3+ production so increase the generation of new HCO3 increase reabsorption of
new HCO3
How do you treat respiratory acidosis
Need to correct original disturbance, so only restoration of ventilation can remove primary disturbance
Why in bronchitis which is a case of chronic respiratory acidosis the blood gas values are never normalised but the pH is normal
as the underlying disease process prevents the correction of ventilation but because the kidney maintains high (HCO3) the pH is protected
When does problems arise for patients with lung disease
so problems arise when patients with lung disease develop renal dysfunction
as lung disease patients have chronic respiratory acidosis, but as long as kidney function is not impaired pH can be maintained at a level compatible with life
Why is there a smaller decrease in pH in chronic respiratory acidosis than in acute respiratory acidosis
This is due to the mechanism to raise (HCO3) and balance out the pH,
as renal compensations takes time due to renal glutaminase taking 4-5 days to reach maximum,
So acutely there is a big drop in pH as renal compensation hasn’t kicked in, but chronic there isn’t a great change in pH as is controlled by renal compensation
What is occurs in respiratory alkalosis
alkalosis of respiratory origin so must be due to fall in PCO2 and this can only occur through increased ventilation and CO2 blow off
What is the causes of respiratory alkalosis
Acute
- Voluntary hyperventilation
- Aspirin
- First ascent to altitude
Chronic
- Long tem residue at altitude
How does altitude increased affect your PCO2
decrease Partial pressure of oxygen to <60mmHg(kPa) stimuates peripheral chemoreceptors to increase ventilation, increased ventilation causes fall in PCO2
What is the response to respiratory alkalosis to protect the pH
(HCO3) should decreases
How does HCO3 concentration decrease ins response to respiratory alkalosis
if decreased PCO2, less H+ is available for secretion
therefore less filtered load of HCO3- is reanbsorbed so HCO3 is lost in the urine
How do you treat respiratory alkalosis
Normalise ventilation to correct initial disturbance
What occurs in metabolic acidosis
An acidosis of metabolic origin due to a decrease in HCO3 concentration
decrease in (HCO3) either due to increased buffering of H+ or direct loss of HCO3
What is the causes of metabolic acidosis
Increased H+ production
- ketoacidosis in a diabetic
- Lactic acidosis
renal failure -Failure to excrete the normal dietary load of H+
Loss of HCO3-
- due to diarrhoea
What is the response to metabolic acidosis to protect the pH
PCO2 must be decreased
How does PCO2 decrease ins response to metabolic acidosis
Respiratory regulation, as the acids stimulates the ventilation so the PCO2 falls
How is ventilation increased in respiratory compensation
Increase ventilation in depth rather than rate
What is this type of hyperventilation in respiratory compensation called, what is it a sign of
kussmaul breathing
is an established clinical sign of renal failure of diabetic ketoacidosis
What problems occur in renal compensation for metabolic acidosis
Respiratory compensation delays renal correction
as normally the kidney corrects the disturbance by restoring (HCO3) and getting rid of the H+ ions, but this is a problems as source of H+ ions is from the CO2
but the respiratory compensation has lowered CO2 to protect pH, so smaller fraction of H+ secreted into renal tubule
How does renal compensation occur for metabolic acidosis
There is a decrease in HCO3 reabsorption Because of the decreased (HCO3)
So only a small fraction of H+ available for HCO3 reabsorption
meaning greater proportion of H+ is available for excretion in the form of tithable acid and NH4 causing an Increase new HCO3 generated
What occurs in metabolic alkalosis
(HCO3) must have increase through metabolism
What is the causes of metabolic alkalosis
Vomiting lots of gastric secretion (increase in H+ loss)
Aldosterone excess (Increase in renal H+ loss)
Excess liquorice ingestion (similar to aldosterone - increase renal H+ loss)
Excess administration of HCO3 (in patients with impaired renal function)
Massive blood transfusion (as contains to prevent coagulation, which is covered to HCO3)
What is the response to metabolic alkalosis to protect the pH
PCO2 will increase
what occurs in compensation of metabolic alkalosis
respiratory compensation increases PCO2 which drives H+ secretion to maintain pH,
It delays the renal compensation and further exacerbates metabolic alkalosis by adding yet more HCO3 to the plasma
The greatly filtrated load of HCO3 then exceed the level of H+ secretion to reabsorb it (in the presence of CO2) and excess HCO3 is lost in urine
What does acute respiratory alkalosis result in, and how is this demonstrated
Respiratory alkalosis, decreases the (HCO3),
If (HCO3) is decreased enough can cause metabolic acidosis,
which is shown by increased depth and rate of ventilation
What are the H+, pH, PCO2 (HCO3)
levels in respiratory acidosis
Increased H+
Decreased pH
Increased PCO2 =disturbance
Increased (HCO3) =compensation
What are the H+, pH, PCO2 (HCO3)
Levels in respiratory alkalosis
Decreased H+
Increased pH
Decreased PCO2
= disturbance
Decreased (HCO3)
= compensation
What are the H+, pH, PCO2 (HCO3)
levels in metabolic acidosi
Increased H+
Decreased pH
Decreased (HCO3)
= disturbance
Decreased PCO2
= compensation
What are the H+, pH, PCO2 (HCO3)
levels in metabolic alkalosis
Decreased H+
Increased pH
Increased (HCO3)
= disturbance
Increased PCO2
= compensation
How do you determine between cause and effect acid base disorders
Check against the pH
What must you consider with regulating ECF volume ie bad case of vomiting and acid/base regulation
Loss of NaCl and H2O causes Hypovalemia, where the Loss of HCL causes metabolic alkalosis
Even though you lose acid and alkali you become alkalosis due to decreased ECF volume stimulating aldosterone
to exchange Na+ for H+ (as Cl reduced so H= only remaining ion for exchange)
Further causing metabolic alkalosis due to excretion of H+
In the case of bad vomiting
What is more important regulation of ECF volume or the pH
restoration of volume takes precedence over correction of metabolic alkalosis,
so aim to restore volume and the alkalosis will correct itself
What acid base disorder is it usually to measure the anion gap and why
Metabolic acidosis, as there is two pattens of metabolic acidosis in terms of anion gap
either no change from normal in metabolic acids ot the anion gap increases
What metabolic acidosis has no change in anion gap
If the acidosis is due to example to a loss of bicarbonate from the gut, then the reduction of bicarbonate is compensated by an increase in chloride and so there is no change in anion gap
What metabolic acidosis causes change in anion gap
In lactic or diabetic acidosis, the reduction in bicarbonate is made up by other anions such a lactate, acetoacetate, Beta-OH butyrate, and so the anion gap is increased
What are clinical affects of acid/base disorder
High acidity will cause hyperkalaemia
(as H+ ions are buffered intracellular in exchange for K+ ions)
wasting of bones - as bone carbonate provides an additional store of buffer
What is the treatment for hyperkalaemia
Calcium resonium (exchanges Ca2+ rather than K+)
CA gluconate - decreases excitability of heart, stabilises cardiac muscle cell membranes
Insulin (+ glucose if non diabetic) - stimulates uptake of K+
What do you need to be careful in hyperkalaemia treatment
needs to be careful fro hypokalaemia, so careful monitoring or K+ is essential
