SM_173a: Acid Base Flashcards
The major buffer pair in bodily fluids is ______ and _______
The major buffer pair in bodily fluids is bicarbonate and carbonic acid
CO2 + H2O <-> H2CO3 <-> HCO3- + H+
What is the Henderson-Hasselbach equation?
pH = 6.1 + log10 ( [HCO3-) / [H2CO3] ) = 6.1 + log10 ( [HCO3-) / (0.03 PaCO2) )
Increased minute ventilation causes PaCO2 to _____, which _____ pH
Increased minute ventilation causes PaCO2 to decrease, which raises pH
(minute ventilation: V·E = RR *VT)
(HCO3- changes require renal compensation which requires time)
Normal [H+} is ____, which corresponds to pH of ____
Normal [H+} is 40 nEq/L, which corresponds to pH of 7.4
What is the simplified version of the Henderson-Hasselbach equation?
X = 24 (PaCO2 / HCO3-) with the last two digits of pH equal to 80 - X
- Example: if [H+] is 40 nEq/L then 80-40 = 40 so pH is 7.40
- Example: if [H+] is 50 nEq/L then 80-50 = 30 so pH is 7.30
What does each space in the electrolyte tree represent?
How do you calculate the anion gap?
AG = Na - (Cl + HCO3-)
Normal anion gap is ____ mEq/L
Normal anion gap is 10 ± 2 mEq/L
______ or ______ increases the anion gap
Increase in unmeasured anions (such as with acid accumulation) or decrease in unmeasured cations increases the anion gap
(unmeasured means that the electrolyte or protein involved is not Na, Cl, or HCO3)
______ or ______ decreases the anion gap
Decrease in unmeasured anions (such as with hypoalbuminemia) or increase in unmeasured cations decreases the anion gap
(unmeasured means that the electrolyte or protein involved is not Na, Cl, or HCO3)
If pH and PaCO2 are on _____ sides of normal, think respiratory process
If pH and PaCO2 are on opposite sides of normal, think respiratory process
In respiratory acidosis, pH is ____ and PaCO2 is ____
In respiratory acidosis, pH is decreased and PaCO2 is increased
(7.32/50 and 7.24/60)
In respiratory alkalosis, pH is ____ and PaCO2 is ____
In respiratory alkalosis, pH is increased and PaCO2 is decreased
(7.48/30 and 7.56/20)
For every change in PaCO2 of _____ mmHg, the pH changes in the _____ direction by _____
For every change in PaCO2 of 10 mmHg, the pH changes in the opposite direction by 0.08
In response to a respiratory process, _____ compensation increases or decreases _____ so pH approaches normal
In response to a respiratory process, renal compensation increases or decreases serum bicarbonate so pH approaches normal
(can take 3 days)
(example of fully compensated respiratory alkalosis: patient / PE and increased minute ventilation for 3 days has 7.46/20 (14) on day 3 and 7.50/20 (16) on day 2)
When pH and PaCO2 are on the ____ side of normal, think metabolic process
When pH and PaCO2 are on the same side of normal, think metabolic process
In metabolic acidosis, pH is _____ and PaCO2 is _____ if there is expected respiratory compensation
In metabolic acidosis, pH is decreased and PaCO2 is decreased if there is expected respiratory compensation
(low serum bicarbonate)
In metabolic alkalosis, pH is _____ and PaCO2 is _____ if there is expected respiratory compensation
In metabolic alkalosis, pH is increased and PaCO2 is increased if there is expected respiratory compensation
(high serum bicarbonate)
Low serum bicarbonate suggests ______
Low serum bicarbonate suggests metabolic acidosis
High serum bicarbonate suggests _____
High serum bicarbonate suggests metabolic alkalosis
For metabolic acidosis, quick compensatory _____ elevates pH
For metabolic acidosis, quick compensatory hyperventilation elevates pH
(example of metabolic acidosis with appropriate respiratory compensation: 7.20/20 (8) - with compensation the last 2 digits of pH roughly equal PaCO2)
The two types of metabolic acidosis are _____ and _____
The two types of metabolic acidosis are elevated anion gap and non-elevated anion gap
Winter’s formula provides expected _____ when _____ is present
Winter’s formula provides expected PaCO2 when metabolic acidosis is present
PaCO2 = 1.5 (bicarbonate) + 8 ± 2
Metabolic acidosis follows ____ accumulation or ____ loss
Metabolic acidosis follows acid accumulation or bicarbonate loss
In metabolic acidosis, acid accumulation increases _____ and therefore the _____
In metabolic acidosis, acid accumulation increases unmeasured anions and therefore the anion gap
Ex: patient with alcoholic ketoacidosis
7.20/20 (8) 135 | 119
8
AG = 135 - (119+8) = 27
Anion gap ≥ 20 mEq/L is highly suggestive of metabolic acidosis from _____
Anion gap ≥ 20 mEq/L is highly suggestive of metabolic acidosis from acid accumulation
MUDPILES: methanol, uremia, diabetic ketoacidosis, propylene glycol, isoniazid, lactic acidosis, ethylene glycol, salicylates
Causes of metabolic acidosis from acid accumulation are described by the mnemonic _____
Causes of metabolic acidosis from acid accumulation are described by the mnemonic MUDPILES
M: methanol
U: uremia
D: diabetic ketoacidosis
P: propylene glycol
I: isoniazid
L: lactic acidosis
E: ethylene glycol
S: salicylates
Metabolic acidosis caused by _____ involves NO anion gap increase and instead involves an increase in _____
Metabolic acidosis caused by bicarbonate loss involves NO anion gap increase and instead involves an increase in chloride
(hyperchloremic b/c chloride has increased)
Example: patient with diarrhea and loss of bicarbonate-rich fluid
7.20/20 (8) 137 | 119
8
AG = 137 - (119+8) = 10
Non-elevated anion gap is highly suggestive of metabolic acidosis from _____
Non-elevated anion gap is highly suggestive of metabolic acidosis from bicarbonate loss
(increased chloride)
(USED CARS: uretero-enterostomy w/ bicarb-rich ostomy fluid, saline administration, endocrine disorders such as adrenal insufficiency, diarrhea, carbonic anhydrase inhibitors such as acetazolamide, ammonium chloride, renal tubular acidosis, spironolactone)
Causes of metabolic acidosis from bicarbonate loss are described by the mnemonic _____
Causes of metabolic acidosis from bicarbonate loss are described by the mnemonic USED CARS
U: uretero-enterostomy w/ bicarb-rich ostomy fluid
S: saline administration
E: endocrine disorders (e.g. adrenal insufficiency)
D: diarrhea
C: carbonic anhydrase inhibitors (acetazolamide)
A: ammonium chloride
R: renal tubular acidosis
S: spironolactone
Metabolic alkalosis with appropriate respiratory compensation involves _____ in both pH and PaCO2 and is primarily caused by _____
Metabolic alkalosis with apprpriate respiratory compensation involves increase in both pH and PaCO2 and is primarily caused by elevated serum bicarbonate
(causes hypoventilation, which increases PaCO2 and drops pH closer but completely to normal)
Example: 7.47/47 (34) 140 | 96
34
The two types of metabolic alkalosis are _____ and _____
The two types of metabolic alkalosis are chloride responsive and chloride non-responsive
Chloride responsive metabolic alkalosis is associated with _____
Chloride responsive metabolic alkalosis is asssociated with decreased extracellular volume
_____ can cause chloride responsive metabolic alkalosis
Vomiting w/ volume depletion can cause chloride responsive metabolic alkalosis
Volume depletion signals the kidney to reabsorb NaCl and H2O:
- If patient is chloride depleted from vomiting HCl, then NaHCO3 is reabsorbed with H2O to restore intravascular volume at the cost of alkalosis
- Body chooses to restore volume over maintaining normal pH -> urine output low, urine Na and Cl and FeNa low
Chloride unresponsive metabolic alkalosis results from _____
Chloride unresponsive metabolic alkalosis results from excess aldosterone or hypokalemia
- Excess aldosterone causes H+ secretion in renal epithelial cells by activating Na/H exchange
- Hypokalemia causes intracellular shift of H+ for K+
If each mEq/L of acid is titrated by the carbonic acid buffer system, serum bicarbonate will drop by ____
If each mEq/L of acid is titrated by the carbonic acid buffer system, serum bicarbonate will drop by 1 mEq/L
(example: if acid elevates AG to 22 mEq/L from 10 mEq/L, serum bicarobnate should drop from 24 mEq/L to 12 mEq/L)
Delta anion gap should ____ delta bicarbonate unless other conditions are present
Delta anion gap should equal delta bicarbonate unless other conditions are present
If serum bicarbonate is significantly lower than expected by delta-delta analysis, consider ______
If serum bicarbonate is significantly lower than expected by delta-delta analysis, consider a concurrent bicarbonate wasting condition (i.e. a non-elevated anion gap metabolic acidosis)
If serum bicarbonate is significantly higher than expected by delta-delta analysis, consider ______
If serum bicarbonate is significantly higher than expected by delta-delta analysis, consider a concurrent bicarbonate excess state (i.e. a concurrent metabolic alkalosis)
Delta-delta analysis is most helpful when anion gap is _____ because it allows one to identify a ______
Delta-delta analysis is most helpful when anion gap is elevated because it allows one to identify a concurrent non-elevated anion gap metabolic acidosis or metabolic alkalosis
What are the steps for interpreting acid base problems?
- Check electrolytes
- Calculate anion gap
- Perform delta-delta analysis
