Lecture 4 - Acid/Base Abnormalities Flashcards
Describe acidosis and alkalosis
processes that tend to change pH in a given direction
Describe academia and alkalemia
resultant pH of blood
Acid-base homeostasis maintains an arterial pH within a range of ____ to ____
- 35 to 7.45
* ideally we say 7.4 but it fluctuates
what pH defines acidemia
pH < 7.4
what pH defines alkalemia
pH > 7.4
What are 3 sites of acid-base regulation
- chemical buffers
- lung
- kidney
What defines metabolic acidosis?
serum bicarbonate < 24 mEq/L
normal range 18-24 mEq/L
What defines metabolic alkalosis?
serum bicarbonate > 24 mEq/L
What defines respiratory acidosis?
pCO2 > 40 mmHg
normal range 35-45 mmHg
What defines respiratory alkalosis?
pCO2 < 40 mmHg
What marker for metabolic acidosis or alkalosis?
serum bicarbonate
What marker for respiratory acidosis or alkalosis?
pCO2
One primary acid-base disturbance = _____ disorder
simple
What is the major buffering system?
bicarbonate/carbonic acid system
What is pH dependent on?
pH is dependent on the relative ratio between carbon dioxide (acid source) and bicarbonate (base)
Normally, there are ___ parts of bicarbonate (HCO3-) to 1 part of carbonic acid (H2CO3)
20
If this ratio of 20:1 is altered, then what happens?
an acid-base abnormality!
Describe the respiratory regulation of CO2 elimination
Respiratory center: medullary chemoreceptors activated by cerebral arterial CO2
Lungs compensate for metabolic disturbances
if HCO3 decreases, what disorder is present?
metabolic acidosis
*pH will also decrease
Acidosis stimulates the _____ center
respiratory
*rate and depth of respiration increases which allows for a greater quantity of CO2 to be eliminated by the lungs
respiratory response to the metabolic acidosis is called a _______ _______
compensatory response
What does a compensatory response do?
allows for the 20:1 ratio to be closer to normal and therefore the pH is not affected as greatly
_____ reabsorb filtered HCO3- and eliminates H+
kidneys
In the presence of respiratory acidosis, how do the kidneys compensate?
the kidneys excrete hydrogen ions and conserve bicarbonate ions
In the presence of respiratory and metabolic alkalosis, how do the kidneys compensate?
they kidneys retain hydrogen ions and excrete bicarbonate ions
Respiratory acidosis:
Describe compensatory response in mmol
For every 10mmHg increase in pCO2, HCO3 increases by 1 mmol
Respiratory alkalosis:
Describe compensatory response in mmol
For every 10mmHg decrease in pCO2, HCO3 decreases by 2 mmol
Metabolic acidosis:
Describe compensatory response in mmol
For every mmol decrease in HCO3, the pCO2 decreases by 1 mmHg
Metabolic alkalosis:
Describe compensatory response in mmol
For every mmol increase in HCO3, the pCO2 increases by 0.7 mmHg
What indicates the presence of a second primary acid-base disorder (i.e. a mixed acid base disturbance) ?
absence of expected compensatory response!
Anion Gap allows for ____ _____ to be divided into two forms
metabolic acidosis
What are the two options for anion gap for metabolic acidosis?
- High Anion Gap
- Normal Anion Gap
What is the law of electroneutrality ?
the net positive and negative charges of the serum must be equal
Unmeasured cations
calcium and magnesium
Unmeasured anions
phosphate, sulfate, albumin, ketons, and organic acids (eg. lactic acid)
Sodium and potassium = ____% of extracellular cations
95
Chloride and bicarbonate = ___% of extracellular anions
85
Anion gap formula
AG = Na - (Cl + HCO3)
Why is K+ taken out of anion gap formula?
K+ is largely intracellular cation and rarely alters the anion gap, it is often deleted from the equation of simplicity
What is a normal anion gap
12 +/- 4 mEq/L
What does a high anion gap mean?
increased unmeasured anions or decreased unmeasured cations
Standard range for:
Na+
135-145 mEq/L
Standard range for:
K+
3.5-5.0 mEq/L
Standard range for:
Cl-
98-106 mEq/L
Standard range for:
HCO3-
18-24 mEq/L
Standard range for:
Lactate
<2 mEq/L
Standard range for:
pCO2 (arterial)
35-45 mmHg
Standard range for:
pO2 (arterial)
90-100 mmHg
Standard range for:
pH
7.35-7.45
Anion gap is useful to diagnose the underlying cause of ____ ______
metabolic acidosis
Describe high AG metabolic acidosis
- generation of an acid which titrates the bicarbonate with an unmeasured ion (ex. lactic acid)
- chloride concentration remains normal
- *normochloremic acidosis
high AG metabolic acidosis = _____chloremic acidosis
normo
Describe normal AG metabolic acidosis
- processes that cause bicarbonate loss and chloride retention (ex. diarrhea)
- absolute or relative chloride concentration higher than normal
- *hyperchloremic acidosis
normal AG metabolic acidosis = ______chloremic acidosis
hyper
What are some causes of high anion gap metabolic acidosis? (normochloremic acidosis)
- Renal failure (accumulation of endogenous acids)
- Lactic acidosis
- Ketoacidosis (diabetic, alcoholic, starvation)
- Drugs and Toxins (salicylates, caffeine, ibuprofen, theophylline)
What are some causes of normal anion gap metabolic acidosis? (hyperchloremic acidosis)
1) Drugs (acetazolamide, acidifying agents, cholestyramine)
2) Gastrointestinal bicarbonate loss (diarrhea)
3) Chloride retention (renal acidosis)
