Acid Base Balance

Question 1

What are examples of volatile acids & what type of metabolism do volatile acids use?

Answer 1

Volatile acids include carbonic acid and uses aerobic metabolism

Question 2

What are examples of nonvolatile acids & what type of metabolism do nonvolatile acids use?

Answer 2

Nonvolatile acids include lactic acid & hydrogen phosphate and use anaerobic metabolism

Question 3

How are body acids generated?

Answer 3

Through aerobic metabolism with volatile acids and anaerobic metabolism with nonvolatile acids

Question 4

What does it mean to be an acid?

Answer 4

An acid is a compound that contains hydrogen and reacts with water to form hydrogen ions

Question 5

Strong acids…

Answer 5

readily & irreversibly give up hydrogen ions

Question 6

Define acidemia

Answer 6

ph <7.35 and is the net effect of all the primary processes and compensatory mechanisms on pH

Question 7

Why is pH important for normal physiology?

Answer 7

-affects ionization
Responsible for the movement of certain
molecules in & out of cells
-Can affect enzyme activity
-Can alter the degree of ionization of proteins & drugs
-pH & PCO2 demonstrate fairly predictable changes in pathological conditions
-Changes in ventilation, perfusion, and electrolyte composition can rapidly alter [H+] & the acid based balance

Question 8

What are the physiological effects of acidemia?

Answer 8

-Pushes carbonic acid equation to the right
-Net effect is inhibitory
-Coronary system dilates & respiratory system constricts
-decreased SVR, contractility–> hypotension
-vasculature less responsive to endogenous
catecholamines
- threshold for vfib is decreased
-tissue hypoxia despite rightward shift of hgb affinity for O2
-Progressive hyperkalemia (increase of 0.6 mEq/L for 0.1 drop in pH)—> results in lethal dysrhythmias
-Increased CBF & intracranial HTN- “CO2 narcosis”
-CNS depression (affect is greater than what the epi & norepi can do to help fix it)

Question 9

Using general terms, how does kidney function alter acid base balance?

Answer 9

• Control reabsorption of bicarb
• Form new bicarb
• & excrete H+ in the form of titratable & ammonium acids

Question 10

What does the kidney do during acidosis?

Answer 10

Increase reabsorption of bicarb, increased excretion of H+ through titratable & ammonium acids

Question 11

What does the kidney do during alkalosis?

Answer 11

excretes large amounts of bicarb
Metabolic alkalosis is commonly associated with increased mineralcorticoid activity even in the absence of sodium & chloride depletion

Question 12

Define respiratory acidosis, compensatory measures, and determination of acute vs. chronic

Answer 12

pH <7.35, CO2 >45; compensatory mechanism bicarb <22; for acute vs. chronic would need pt history or if fully compensated and pH not 7.4 then most likely chronic

Question 13

Define respiratory alkalosis, compensatory measures, and determination of acute vs. chronic

Answer 13

pH >7.45, CO2 <35; compensation: bicarb >26; would need pt history or if fully compensated and pH not 7.4 then most likely chronic

Question 14

What are the possible mixed disorders?

Answer 14

1. pH 7.4, PCO2 and Bicarb are opposite of each other
2. pH <7.35, PCO2 high & bicarb low
3. pH >7.45, PCO2 low and bicarb high

Question 15

What is metabolic acidosis?

Answer 15

pH <7.35, bicarb <22, compensation: CO2 >45

Question 16

What can anion gap tell us about the source of metabolic acidosis?

Answer 16

If it is high anion gap acidosis then MUDPILES is the answer

If it is normal anion gap acidosis then FUSEDCARS is the answer- lead to reduced bicarb & increased chloride

Question 17

How is anion gap calculated?

Answer 17

[Na+]-[HCO3-]-[Cl-]

anion gap of 12 is normal

Question 18

What is the normal range of base excess?

Answer 18

-2 to +2

Question 19

How do you calculate base excess?

Answer 19

BE= calculated bicarb- 24 (normal bicarb)

Question 20

What does a BE of >+2 indicate?

Answer 20

excess base

Question 21

What does a BE of >-2 indicate?

Answer 21

reduced base

Question 22

What is the “base” in base excess?

Answer 22

the sum of weak acids including hemoglobin, plasma proteins, phosphate, and bicarb

Question 23

What does base excess signifiy?

Answer 23

Helps to quantify the metabolic acidosis

Question 24

What is metabolic alkalosis?

Answer 24

pH >7.45, bicarb >26, compensation: CO2 <35

Question 25

What happens to the base excess in metabolic alkalosis?

Answer 25

the base excess increases in metabolic alkalosis

Question 26

Describe the strength & efficiency (timing) of the acid based buffer systems in the body.

Answer 26

1. Buffers- immediate- weakest
2. Respiratory- hours to 24 hours- middle
3. Renal-3-5 days- strongest

Question 27

List the anesthetic considerations of acidemia:

Answer 27

• Potentiates CNS depressant effects of most sedatives & anesthetic agents
• increased sedation & depression of airway reflexes (predispose to aspiration)
• direct circulatory depressant effects of anesthetics may be exaggerated
• Anesthetic agents that rapidly decrease sympathetic tone can indirectly produce unopposed circulatory depression
• Avoid succ d/t hyperkalemia

Question 28

List the anesthetic considerations of alkalemia:

Answer 28

• combination of alkalemia & hypokalemia can precipitate dysrhythmias
• general ischemia can occur with decreased CBF (particularly in the presence of hypotension)
• Respiratory alkalosis prolongs the duration of opioid induced respiratory depression