Lecture 3 - Anesthesia & Renal Physiology: Regulation of Acid-Base Balance Flashcards
T/F: Acid-base physiology is all about the K+ ion concentrations.
FALSE (…is all about H+ ion,,,)
Normal ECF H+ concentration is ~ ____ nEq/L since these numbers are awkward to use, the __ scale is favored.
- 40
- pH
An acid is defined as a proton (H+) ______ while a base acts as a proton ________.
- donor
- acceptor
A strong acid almost completely ________into H+ and a ________ anion WHILE a strong base avidly _____ H+ ion.
- dissociates
- conjugate
- binds
T/F: A weak acid or base reversibly donates or accepts a proton.
TRUE
T/F: A weak acid of base makes for a good buffer.
TRUE
Based on the Henderson Hasselbalch equation we know that the pH of a solution is related to the ratio of the __________ anion to the _______________ acid.
- dissociated
- undissociated
T/F: Buffers are most efficient when the pH is equal to the pKa.
True
What are the human body’s buffers:
- Bicarbonate (H2CO3/HCO3)
- Hemoglobin
- Intracellular proteins
- Phosphate
- Ammonia
T/F: The bicarbonate buffer is effective against respiratory disturbances but not to metabolic acid base disturbances.
FALSE (…effective against metabolic but not respiratory acid base disturbances.)
What is the pKa of bicarbonate?
6.1
Why bicarbonate a good buffer if the pH is 6.1:
Present in high concentrations in the ECF and because PaCO2 and HCO3 are closely regulated by the lungs and kidneys.
How does renal system compensate during acidosis?
-Increased HCO3 reabsorbtion
What are the steps the renal system goes through to reabsorb bicarbinate:
Step 1: CO2 combines with water to form H2CO3 which rapidly dissociates into H+ and HCO3.
Step 2: H+ is secreted into the proximal tubule and bicarbonate is reabsorbed to blood
Step 3: H+ in the tubule combines with filtered HCO3 to form carbonic acid
Step 4: Carbonic anhydrase hydrolyzes this to water and CO2 which goes into the cell replacing the original CO2.
Over __ to __ % of filtered bicarbonate is reabsorbed in the proximal tubule.
80
90
Over __ to __ % of filtered bicarbonate is reabsorbed in the distal tubule.
10
20
T/F: In the distal tubule a H+ pump exists which can establish a steep gradient for acidifying urine.
TRUE
H+ secreted in tubule lumen can combine with HPO4^2 to form H2PO4 that is NOT _________ and becomes _______ in urine
- reabsorbable
- trapped
Phosphate is an effective buffer in the ________ fluid.
tubular
Phosphate has a pK of ___ which in acidic urine allow to be more _________ buffer.
- 6.8
- effective
Kidneys replenish extracellular ______.
HCO3
What is the ammonium synthesized from:
glutamine
Ammonium (NH4) is important tubular fluid buffer in the:
- Proximal tubular
- Thick ascending loop
- Distal tubular
What is also synthesized in the production of ammonium (NH4):
bicarbonate
Where is ammonium produced in the kidneys?
-collecting tubules
Metabolic alkalosis is mainly possible in what two situations?
- Na+ depletion where more sodium is reabsorbed in the proximal tubule, and as this occurs Cl- moves with it to preserve electoneutrality thus as Cl- in the tubule decreases HCO3- must be reabsorbed. This is a so call “contraction alkalosis” that can occur with LONG TERM DIURETIC USE.
- Increased aldosterone (mineralocorticoid) activity increases Na+ reabsorbtion and H+ secretion in the distal tubule
A base excess that is positive would indicate ______ ________.
-metabolic alkalosis
A base excess that is negative would indicate _______ _________.
-metabolic acidosis
Potassium increases ___ mEq/L for each ___ unit decrease in pH (Physiologic effects of acidosis).
- 0.6
- 0.1
Physiologic effects of acidosis are:
- Rightward shift is seen in the oxyhemoglobin dissociation curve
- Cardiac contractility is decreased
- There is decreased responsiveness to catecholamines
What is the equation of anion gap?
Anion gap = [Na+] - ([Cl-] + HCO3-])
What is the normal value for anion gap?
7-14
T/F: An acidosis with a high anion gap is caused by relatively strong nonvolatile acids.
TRUE
What are some substances that cause a high anion gap?
- Uremia
- Diabetic ketoacidosis
- Lactic acidosis
In a high anion gap the __ ion consumes HCO3- and an ____________ anion accumulates and takes the place of bicarbonate.
- H+
- accuulates
A normal anion gap acidosis the ___ takes the place of the HCO3.
- Cl-
What are some causes of normal anion gap acidosis:
- diarrhea (GI loss of bicarb)
- Renal loss or HCO3-
How would you treat metabolic acidosis?
- Treat underlying cause (Hypovolemia, anemia, cardiogenic shock)
- NaHCO3 (Do not give to patient with respiratory failure as CO2 will go up)
- Refractory acidosis may require dialysis
How would you treat alkalosis?
- IV HCl (rare cases)
- Spironolactone if increased mineralocorticoid activity
- Stop diuretics
- (Treat Hypokalemia) Hypokalemia will also augment H+ secretion
- Stop NG suction
What would be the expected level of compensation for respiratory acidosis?
Acute: 1meq/L increase in HCO3- for every 10 mmHg increase in CO2
Chronic: 4 meq/L increase in HCO3- for every 10mmHg increase in CO2
What would be the expected level of compenstion for metabolic acidosis?
- CO2 decrease 1.2 X the decrease in HCO3-
What would be the expected level of compensation for respiratory alkalosis?
Acute: 2 meq/L decrease in HCO3- for every 10 mmHg decrease in CO2
Chronic: 4 meq/L decrease in HCO3- for every 10mHg decrease in CO2
What would be the expected level of compensation for metabolic alkalosis?
CO2 increase by 0.7 X the increase HCO3-
