Acids & bases highlights Flashcards
1) What is anion gap?
2) What is it made of?
3) What is high AG?
1) difference between measured cations and measured anions in the extracellular space
2) AG = Na+– (Cl−+ HCO3−)
3) >12
Measured cations normally outnumber measured anions; the difference is made up by what?
The anion gap
As your anion gap goes up, what goes down?
Bicarb and chloride (measured anions)
1) What does the anion gap measure?
2) When does it increase?
1) Represents unmeasured anions
2) With accumulation of acid anions (e.g., lactate, acetoacetate)
1) What is the anion gap useful in?
2) Explain
1) Useful in narrowing down the cause of metabolic acidosis
2) AG >12 = HAGMA
AG ≤12 = NAGMA
1) What is the principal unmeasured anion usually responsible for the anion gap?
2) When must the anion gap be corrected?
1) Albumin
2) Hypoalbuminemia
How do you differentiate between acute and chronic respiratory acidosis?
<3 days or >3 days
What can the anion gap look like in metabolic acidosis?
Normal anion gap (NAGMA) or high anion gap (HAGMA)
Differentiate between compensation by the kidneys and lungs
1) Kidneys: metabolic via HCO3 level changes; slower
2) Lungs: respirations change pCO2 levels; faster
With metabolic acidosis:
1) What happens to pH and bicarb?
2) What happens to alveolar ventilation? What does this do?
3) What does this do to pH?
1) Low; low
2) Increases; decreases pCO2
3) Returns pH close to normal
In compensation, the HCO3 and pCO2 move in what direction(s)?
In the same direction
Mixed acid-base disorder: give 1 reason to suspect this
Changes in pCO2 and HCO3 are in opposite directions
What are the 3 potential causes of metabolic acidosis?
1) Increased acid generation
2) Loss of bicarbonate
3) Diminished renal acid excretion
True or false: In compensation, the HCO3 and pCO2 move in the same direction
True
What is the hallmark of metabolic acidosis?
Decreased HCO3– (<22 mEq/L so pH < 7.35)
What are the 3 classifications of metabolic acidosis?
Classified by anion gap:
1) Decreased (<6 mEq)
2) Increased (>12 mEq) (aka, high AG, HAGMA)
3) Normal (6-12 mEq) (aka, hyperchloremic, nongap, NAGMA)
Metabolic acidosis and is associated with too much of what ion? (each can cause the other)
Potassium (hyperkalemia)
What are the 4 main causes of HAGMA?
1) Ketoacidosis (diabetic/alcohol/starvation)
2) Uremia (severe renal dysfunction)
3) Lactic acidosis
4) Toxins (ethylene glycol [antifreeze], methanol, salicylate OD, many others)
In compensation, what 2 things move in the same direction
HCO3 and pCO2
Lactic Acid (Lactate):
1) Primarily produced by _________________ of glucose (glycolysis) in tissues
2) Buildup of lactic acid (via overproduction and/or reduced metabolism) leads to what?
1) anaerobic metabolism
2) Lactic acidosis (LA) – a HAGMA
1) Lactic acidosis is usually due to what?
2) Elevated lactic acid potentially indicates __________ tissues.
1) Impaired tissue oxygenation leading to increased anaerobic metabolism
2) hypoxic
Lactic Acidosis (HAGMA)
1) What are elevated?
2) Define lactic acidosis numerically
3) Lactic acidosis produces decreased ____ and usually elevated _____
1) Lactate levels
2) >4 mmol/L
3) pH; AG
List and describe the 2 kinds of L-lactate acidosis
1) Type A (hypoxic): from decreased tissue perfusion and hypoxia; leads to anaerobic glycolysis; more common
1) Type B: not due to decreased tissue perfusion/hypoxia; from metabolic causes (DM, kidney dz, etc) or toxins
1) Type A (hypoxic) L-lactate acidosis results from what?
2) What kind of glycolysis does it lead to?
3) Which type of L-lactate acidosis is more common?
4) Which type can be due to metabolic causes (like DM or kidney dz) or toxins?
1) Decreased tissue perfusion and hypoxia
2) Anaerobic
3) Type A
4) Type B
What are the 3 major causes of NAGMA? Give examples of each
1) HCO3–loss from GI tract (ex. diarrhea)
2) Defects in renal acidification (ex. renal tubular acidosis (RTA), which may be due to hypoaldosteronism or other causes; impaired renal excretion of H+ or reabsorption of HCO3)
3) HCO3- dilution (ex. NS IVF)
In NAGMA, a compensatory increase in _____________ (hyper______________) maintains a normal anion gap
serum chloride (hyperchloremia)
Metabolic Alkalosis:
1) What is the hallmark?
2) Give an example of why that is
1) High HCO3
2) e.g., due to loss of H+ or gaining/inadequate secretion of HCO3-
Metabolic Alkalosis: What 2 things is it most often due to?
1) Excess loss of H+ ions and Cl- from GI tract (e.g., vomiting) or urine (e.g., mineralcorticoid excess/hyperaldosteronism, diuretics)
2) H+ ion movement into cells (e.g., hypokalemia)
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Alkali administration (e.g., antacids)
ECF volume contraction around relatively constant amount of extracellular HCO3 (“contraction alkalosis”)
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Metabolic alkalosis and hypokalemia are associated (each can cause the other)
Metabolic alkalosis is also associated with hypochloremia (inhibits renal HCO3 secretion)
Metabolic alkalosis Causes include (LAVA-UP):
Loop (and thiazide) diuretics: multifactorial, induce secondary hyperaldosteronism
Antacid use: alkaline
Vomiting: loss of HCl (H+ ions and Cl-)
Aldosterone increase (“A-UP”): Na+ and water reabsorbed, K+ and H+ secreted into urine; loss of H+ causes metabolic alkalosis
Respiratory Acidosis:
1) What does it result from?
2) What is acute respiratory failure?
1) hypoventilation & hypercapnia (increased pCO2)
2) Acute respiratory failure
Respiratory Alkalosis:
1) What does it result from?
2) When is metabolic compensation greater, in chronic or acute form?
1) Hyperventilation (reduces PCO2, increases pH)
3) Chronic
Salicylates (e.g., aspirin)
Suspect aspirin toxicity if both respiratory alkalosis + HAGMA (particularly with alkalemia)
PAST PH Respiratory Alkalosis
(gerber doesn’t find this mnemonic very helpful)
Panic attacks
Anxiety attacks
Salicylates
Tumor (CNS)
PE (and other pulmonary diseases)
Hypoxemia (high altitude, etc.)
List the 6 steps of acid-base diagnosis
1) Determine whether the primary disorder is an acidosis or alkalosis by reviewing the pH
Determine whether the primary acidosis or alkalosis is metabolic or respiratory by reviewing the HCO3− and PaCO2
Evaluate magnitude of compensation
Calculate Anion Gap (AG)
If metabolic acidosis exists and the AG is increased, compare ΔAG and ΔHCO3− (delta ratio)
Establish the clinical diagnosis
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Define delta AG/delta HCO3 ratio
2)
1) compare the increase in AG to the decrease in the HCO3 concentration
2) Assume normal AG = 12, normal HCO3 = 24
Delta AG/delta HCO3 Ratios: What suggests HAGMA + metabolic alkalosis?
> 2
