Acid-base: Khundmiri Flashcards
What is alkalosis and acidosis?
Alkalosis – removal of excess Hydrogen ions from body
Acidosis – addition of Hydrogen ions
What are weak acids and bases?
A weak acid or a base is a molecule that are less likely to dissociate or accept Hydrogen ions or HCO3-.
Most physiological acids and bases are weak acids and weak bases
The most important is the H2CO3 and HCO3-
Why is venous pH lower?
due to higher concentration of CO2
Precise Hydrogen ions regulation is essential because the activities of almost all enzyme systems in the body are influenced by Hydrogen ions concentration. Therefore, changes in Hydrogen ions concentration alter virtually all cell and body functions.
How does body defend against changes in pH?
- buffer system
- lungs (if buffer cannot do it)
- kidney (respond very slow several hours to days—most POWERFUL control of acid-base balance
What are the buffers in extracellular fluid?
- bicarbonates
- proteins: when it comes to RBC and hemoglobin that control hydrogen ion concentration
Which system is the most POWERFUL controller of acid-base balance?
kidney
What is a buffer?
buffer is any substance that can reversibly react with hydrogen ions
Why is bicarbonate the most important buffer system of the body compared to phosphate or sulfate?
your bicarbonate buffer system can be dissociated to CO2 and H2O and backa nad forth by bicarbonate and hydrogen ions that can be taken care by the lungs
the pH is not closer (which is what I was thinking)
Henderson-Hasselbalch
pKa of bicarbonate is 6.1 vs. 7.4
How do you Increase hydrogen ion concentration?
80 mEq of Hydrogen is ingested or produced each day by metabolism (all adding up to about 200 mEq of hydrogen ions)
What is the pKA?
the pH at which the acids and bases are at equal concentration
If you add acid pH will go _______and if you add base pH will go______.
down
up
What are very important factors as to why bicarbonate forms the most effective buffer system?
- it can be easily converted to CO2 and H2O
- because of the absolute concentration to the buffer system
Absolute concentration of the buffers is also important – low concentration of buffers require less amount of acid or base to diminish the buffering capacity
intracellular fluid pH is regulated by phosphates and proteins BUT extracellular fluid is regulated by bicarbonate
What is the Henderson-Hasselbalch equation?
provides the basis for acid base regulation in the body
- kidneys regulate bicarbonate concentration
- lungs regulate CO2 concentration
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What is the difference between metabolic and respiratory acidosis?
Impaired regulation by kidneys result in metabolic acidosis (decreased [HCO3-]) and alkalosis (increased [HCO3-])
Impaired regulation by lungs result in respiratory acidosis (increased PCO2) and alkalosis (decreased PCO2)
Describe the Phosphate buffer system.
pKa is 6.8 which is close to 7.4
very low concentration in ECF; it is 8% of the bicarbonate buffer system in the extracellular fluid
Because of its very low concentration in the ECF, the total buffering capacity of phosphate buffer system is much less compared to bicarbonate buffer system
However, this buffer system is extremely important in maintenance of tubular fluid pH (important in kidneys proximal tubules) because of its higher concentration increasing its buffering capacity. Another reason is the pH in tubular fluid is lower than ECF and is close the pK of Pi buffer.
Phosphate as a Tubular Fluid Buffer
-Phosphate buffering capacity does not change much with acid-base disturbances (phosphate is not the major tubular buffer in chronic acidosis)
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Describe proteins as buffer.
- very high concentration INSIDE the cells
- regulate binding of hydrogen ions to lysine residues
- 60-70% chemical buffering in cells occur through proteins
- The pK of proteins is closer to the intracellular pH making them ideal for intracellular buffering
What is Isohydric Principle?
In physiological conditions all buffer systems work together in tandem to maintain the [hydrogen ion] concentrations as they use the same hydrogen ions for maintaining the body pH. Therefore changes in [hydrogen ions] in ECF will change all the buffer systems.
all acids will combine in acid and base pairs; it is the sum of all acid and base pairs
anything that cause a change in one buffer system will change the balance of all other buffers due to shifting of hydrogen ions between the buffer systems causing acid base imbalance
What is the first line of control of acid base balance?
acid-base: it’s done in minutes
What is the second line of control of acid base balance?
- respiratory regulation of acid base balance
- controls extracellular fluid pH by controlling concentration of CO2
- increase in ventilation will increase removal of CO2 and thus hydrogen ion concentration
CO2 is formed metabolically in the body – diffuses into the interstitial fluids, transported to lungs and removed by pulmonary ventilation primarily in what form?
primarily in the form of bicarbonate
What does exercise do to CO2 levels?
it increases metabolic formation of CO2 thus increasing the rate of glycolysis which will add up to CO2
What happens to pH if ventilation changes?
if CO2 remains constant remain at 7.4
higher the rate of ventilation lower is the pCO2
Ventilation Inversely Regulate ECF [Hydrogen ion]
How does change in alveolar ventilation affect pH?
If CO2 remains constant, the ECF PCO2 is effected by ventilation – higher the rate of ventilation lower is the pCO2
Ventilation Inversely Regulate ECF [hydrogen ion]
Why is it that your increased pH is NOT effective in terms of ventilation?
Reduction in pH produces a marked increase in ventilation
increased pH is NOT effective in terms of ventilation because CO2 is acidic ????
Describe the feedback Control of [hydrogen ions] by the Respiratory System.
- increase in [hydrogen ions] stimulates alveolar ventilation thus decreasing ECF PCO2 reducing [hydrogen ion] to normal
- decrease in [hydrogen ions] decreases ventilation thus increasing ECF HCO3- with [hydrogen ions] returning to normal
Respiratory Control of [hydrogen ion] is not Efficient: it is rapid but is not complete ????
What happens in Emphysema?
How do you control under these conditions?
Build up of CO2 (no proper ventilation – result in respiratory acidosis which will be controlled through your kidneys
Ability to respond to metabolic acidosis – decreased due to blunted ventilation
Kidneys are sole remaining mechanism to regulate acid-base balance
How does kidney control acid base?
HA=acid
body will metabolize fat and carbohydrates which is going to be converted to H2O and CO2 which will be taken care of by the lungs
O2 and proteins will all form acids which will go through fecal loss and form bicarbonate
acids which will be changed to nonvolatile acids (NaA)
- volatile acid is bicarbonate
- nonvolatile acids are phosphates, proteins, and sulfate
nonvolatile acids will be converted to sodium bicarbonate which will then be converted to sodium salt acid of hydrogen and CO2 which ill go back to the lungs to be removed and acid will go back to kidneys to make new bicarbone
How does kidney control acid base? What is total renal acid excretion (RNAE)?
HA=acid
acids will go through and change into nonvolatile acids (NaA)
volatile acid is bicarbonate
nonvolatile acids are phosphate proteins and sulfate and will be removed from the kidneys allowing for new bicarbonate to be made
Describe Renal Regulation of Acid-Base Balance
In total your kidney are filtering 4.3 mol of bicarbonate everyday.
Out of which, almost everything will be reabsorbed in the kidneys
What is the function of the kidneys?
conserve bicarbonate and excrete acidic or basic urine depending on body needs
Where is most of your bicarbonate reabsorbed? Where does your fine tuning occur?
- 85% will be reabsorbed in the proximal tubule
- fine tuning occurs in the cortical collecting duct ; the amount of acid released os only about 5%
NaH exchanger
vs.
HATPase
NaH exchanger: antiporter; depends on the concentration of Na ions
H ATPase; uses ATP and removes one hydrogen ion
anionic exchanger and bicarbonate will receive bicarnobate
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For every net loss of hydrogen ion you reabsorb bicarbonate ion
The net action of this is
the removal of acid
minimal pH is 6.7 that occurs in proximal tubes
pH 4.5 in the collecting duct
What is the difference between principal and intercalated cells of the collecting duct?
principle responsible for control Na concentration in the body
intercalated responsible for acid base control
What is the difference between intercalated A and B cells?
A for acid: secrete hydrogen ions
B for base: secrete bicarbonate ion
What is Pendrin?
takes in a chloride and removes a bicarbonate
people with mutation in pendrin are deaf
What happens in acidosis?
increased hydrogen concentration responds by producing NEW bicarbonate
bicarbonate is produced when hydrogen ions are buffered by nonvolatile acids
ONE METHOD
Buffering of secreted H+ by filtered phosphate (NaHPO4-) and generation of “new” HCO3-
ANOTHER METHOD (ammonia to ammonium buffer) to generate NEW bicarbonate is when glutamate is converted to alpha ketoglutarate and ammonia (IS NOT IN THE SLIDES); alpha ketoglutarate will be reabsorbed in the interstitial fluid; ammonia goes out as ammonium
In patients with chronic acidosis, how do they buffer excess hydrogen ions?
ammonia to ammonium buffer is the choice
phosphate is not the major tubular buffer in chronic acidosis
How do you classify the following respiratory diseases? How do you compensate for them?
Metabolic acidosis
respiratory acidosis
metabolic alkalosis
respiratory alkalosis
KNOW THIS CHART FOR EXAM
these are the questions!!!
Metabolic acidosis: pH and PCO2 are decreased; compensate by increasing ventilation and renal HCO3- production
respiratory acidosis: pH is decreased but PCO2 is increased; compensate by increasing renal HCO3 production
metabolic alkalosis: pH and PCO2 are increased; compensate by decreasing ventilation and renal HCO3- production AKA increasing HCO3 excretion
respiratory alkalosis:
pH is increased but PCO2 is decreased; compensate by decreasing renal HCO3 production AKA increasing renal excretion
Acid-Base Disturbances: Metabolic acidosis
- aspirin poisoning (increased Hplus intake)
- diabetes mellitus (increased Hplus production due to ketoacid and lactic acid production)
- diarrhea (HCO3- loss)
- renal tubular acidosis (decreased Hplus secretion, decreased HCO3- reabs.)
remember every secretion of hydrogen ion reabsorbs one bicarbonate
- carbonic anhydrase inhibitors (decreases Hplus secretion)
Acid-Base Disturbances: Respiratory acidosis
- brain damage
- pneumonia
- emphysema
- other lung disorders
Acid-Base Disturbances: Metabolic alkalosis
- increase in pH increase in bicarbonate
- ingestion of TOMS
- increased base intake (e.g. NaHCO3)
- vomiting gastric acid
- mineralocorticoid excess
- overuse of diuretics (except carbonic anhydrase inhibitors)
given to HTN pts to remove fluid and Na
Acid-Base Disturbances: Respiratory alkalosis
- high altitude
- psychic (fear, pain, etc)
What are Plasma or Extracellular Fluid Factors That Increase H+ Secretion and HCO3− Reabsorption by the Renal Tubules?
- increased PCO2
- increased hydrogen ions, decreased bicarbonate ions
- decreased extracellular fluid volume
- increased angiotensin II
- increased aldosterone
- hypokalemia
What are Plasma or Extracellular Fluid Factors That Decrease H+ Secretion and HCO3− Reabsorption by the Renal Tubules?
- decreased PCO2
- decreased hydrogen ions, increased bicarbonate ions
- increased extracellular fluid volume
- decreased angiotensin II
- decreased aldosterone
- hyperkalemia
What is anion gap?
total amount of cations should be equal to total amount of anions
unmeasured cations: potassium, calcium, magnesium
unmeasured anion: proteins, phosphate, sulfate, lactate
normal anion gap is 8-16 mEq/L
anion gap= Na+ – (Cl- + HCO3-)= unmeasured anions
What are the condition for increase anion gap acidosis?
body doesn’t match the chloride concentration with loss of bicarbonate
-diabetes mellitus (ketoacidosis)
-lactic acidosis aspirin (acetysalicylic acid) poisoning
- methanol poisoning
starvation
What are the condition for normal anion gap acidosis?
- diarrhea
- renal tubular acidosis
- Addision’ disease
- carbonic anhydrase inhibitors
ABG provides information regarding what THREE important conditions for your patient?
Ventilation
Oxygenation
Acid-base Status
These are exam questions!!!
- pH
- origin (respiratory or metabolic so look at CO2 if is <35 or >45
- opposite is metabolic and same is respiratory when comparing direction of pH and PCO2
Is there compensation coming from renal or respiration?
This should tell you whether it is acute or chronic.
FOR PRIMARY METABOLIC CONDITION: The last two digits of the PaCO2 should approximate the pH value (e.g. 7.25 should relate to a PCO2 of 25 mmHg).
FOR PRIMARY RESPIRATORY CONDITION: Calculate the change in pH that would occur if the change in PCO2 were acute 0.08 pH units/10 mmHg PCO2 or for chronic, 0.03/10 mmHg PCO2
If the difference is greater than 25 mmHg with the patient breathing room air, then there is a problem with what?
gas exchange and oxygenation
Normal anion gap acidosis: USEDCARP
- Ureterostomy
- Small Bowel Fistula
- Extra Chloride
- Diarrhea
- Carbonic anhydrase inhibitor (acetazolamide)
- Adrenal Insufficiency
- Renal Tubular acidosis
- Pancreatic fistula
High anion gap acidosis: MUDPILES
- Menthol
- Uremia (Chronic renal failure)
- Diabetic ketoacidosis
- Paraldehyde
- Iron, isoniazid
- Lactic Acid
- Ethanol, ethylene glycol
- Salicylates (Aspirin poisoning)
How do we treat acidosis or alkalosis?
Correct condition that cause abnormality
Difficult to do in chronic disease states where impaired lung function and/or renal failure coexists
Acidosis: agents are administered to neutralize excess acid (e.g. sodium bicarbonate via GI absorption); HCO3- will contribute to bicarbonate buffer system; Sodium lactate/gluconate after metabolism leave behind sodium bicarbonate which increases pH.
Alkalosis: administration of ammonium chloride by mouth; metabolized in the liver to form urea; reaction liberates HCl which shifts body buffers and increases H+ to reduce pH.
Chart :Clinical Measurements and Analysis of Acid-Base Disorders
everything you should know about acid base
Acid-base nomogram showing arterial blood pH, arterial plasma HCO3−, and Pco2 values.
simple respiratory or metabolic disorder that is shaded
is mixed (not shaded)
Emphysema is the best example of mixed respiratory and metabolic acidosis
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In mixed disorders there are no compensations.
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How do you determine if the condition is acute or chronic?
• For primary respiratory condition: calculate the change in pH that would occur if the change in PCO2 were:
o Acute —> 0.08 pH units/10 mmHg PCO2
o Chronic —> 0.03 pH units/10 mmHg PCO2
• For primary metabolic condition: the last two digits of the PaCO2 should approximate the pH value (e.g. 7.25
should relate to a PCO2 of 25 mmHg)
