Physics for the Nurse Anesthetist~Quiz 5

Question 1

When the concentration of a reactant increases, the reaction is driven toward the production of a product. conversely, when the concentration of reactant decreases the reaction is driven toward the production of more reactants and less products. Which principle applies?

Answer 1

This is LeChatelier’s principle

Question 2

What is the Bronsted-Lowery Theory?

Answer 2

The Bronsted-Lowry theory is a theory pertaining to acids and bases wherein the acid is a proton(hydrogen ion) donor and the base is a proton(hydrogen ion) acceptor.

Question 3

What is an acid? Why is a substance called a weak acid?

Answer 3

• an acid is a hydrogen ion, or proton donor
• a weak acid is one that does not ionize 100% in solution
• strong acids, such as hydrochloric acid are 100% ionized in solution

Question 4

What agents used in anesthesia re weak acids?

Answer 4

Barbiturates

Question 5

Why is carbonic acid considered a weak acid?

Answer 5

• Carbonic acid ionizes only 0.2% in physiologic solution

- an acid that does not dissociate 100% to its ionized form is a weak acid

Question 6

What is the definition of a weak base?

Answer 6

bases that do no completely ionize in water to produce an equivalent concentration of hydroxide ion. They establish a dynamic equilibrium between the molecular form(non-ionized) and the ionized form.

Question 7

What agents used in anesthesia are weak bases?

Answer 7

• all local anesthetics
• all opioids(fentanyl, afentanil, morphine)
• benzodiazepines
• etomidate
• ketamine

Question 8

On the ph scale….the more hydrogen ions equals what in relation to acid/base?

Answer 8

the more acidosis

Question 9

On the ph scale…the more hydroxide ions equals what in the relation to acid/base?

Answer 9

the more base

Question 10

What is the pH of a liter of water?

Answer 10

7 at 24 degrees celcius

Question 11

What happens to an amount of weak acid in nonionized forms as pH falls? the amount of ionized?

Answer 11

• As pH decreases, the amount of weak acid in nonionized form increases(acid + acid = nonionized)
• Consequently, as pH decreases, the amount of weak acid in ionized form decreases(acid + acid = less ionized)

Question 12

A weak acid with a pKa of 7.8 will be more than 50% or less than 50% nonionized at pH = 7.4?

Answer 12

• more than 50% will be nonionized at pH = 7.4

- Acid + Acid = more nonionized

Question 13

Will the CNS actions of barbiturates be intensified or diminished in the patient who is acidotic? explain?

Answer 13

• The CNS actions of barbiturates will be intensified in patients who are acidotic(acid + acid = nonionized)
• More barbiturate is nonionized form at lower pH, so greater amounts will cross the blood-brain barrier.

Question 14

What happens when a weak acid is injected into an acidotic patient?

Answer 14

• More drug is nonionized; as pH falls, the nonionized fraction increases.
• Acid + Acid = nonionized

Question 15

Propofol, a weak acid has a pKa of 11.0, is propofol mostly ionized or mostly unionized at normal physiologic pH 7.4? Will the dominant form readily cross membranes or not?

Answer 15

• Since the normal physiologic pH is less than the pKa 11.0 of propofol, the body environment is an acidic environment for a weak acid propofol.
• Remember, the pKa of a given substance is “dividing mark” for acidic and basic environments.
• The mnemonic is “acids + acids = more nonionized”, therefore, propofol will be mostly nonionized at physiologic pH of 7.4.
• The nonionized form of a substance is lipid-soluble and thus readily crosses membranes

Question 16

Base + Acid = more ionized?

Answer 16

as the pH decreases the amount of weak base in ionized form increases
weak base + acid pH = more ionized

Question 17

Base + Base = nonionized?

Answer 17

as the pH increases the amount of weak base in nonionized form increases
weak base + alkaline pH = more nonionized

Question 18

What happens to the amount of weak base in ionized form as pH decreases? as pH increases?

Answer 18

• as pH decreases, the amount of weak base in ionized form increases
• base + acid = more ionized
• conversely, as pH increases, the amount of weak base in ionized form decreases
• base + base = less ionized or less nonionized

Question 19

A weak base with a pKa of 7.8 will be more than 50% or less than 50% nonionized at pH = 7.4?

Answer 19

• less than 50% nonionized

- base + acid = ionized or less nonionized

Question 20

What happens when a weak base is administered to an acidotic patient?

Answer 20

• less drug is nonionized(more is ionized)
• as pH falls, the nonionized fraction of a weak base decreases and the ionized fraction of a weak base decreases and the ionized fraction increases
• base + acid = ionized

Question 21

Do drugs that are weak acids form salts with positive ions such as sodium or negative ions such as sulfate or chloride?

Answer 21

• drugs that are weak acids form salts with positive ions(sodium, potassium, calcium, magnesium)
• Sodium pentobarbital is an example of weak acid.
• Point: A drug is a weak acid if it forms a salt with a positive ion(sodium pentothal)

Question 22

do drugs that are weak bases form salts with positive ions such as sodium or negative ions such as sulfate or chloride?

Answer 22

• drugs that are weak bases from salts with negatively charged ions(chloride, sulfate, phosphate, ect.)
• Lidocaine chloride and morphine sulfate are examples of weak bases.
• Point: A drug with a weak base if it forms a salt with a negative ion(lidocaine hydrochloride, morphine sulfate)

Question 23

A new drug, Z sulfate has a pKa = 8.0. Will this drug be more than 50% ionized, 50% ionized, or less than 50% ionized at normal body pH of 7.4?(hint: first determine if the drug is a weak acid or weak base)

Answer 23

• the new drug Z sulfate is a weak base. Weak bases use negatively charged substances(chloride, sulfate, ect.) to from salts. This drug will be more than 50% ionized at pH = 7.4.
• Recall that a weak base made more acidic will become less unionized(more ionized). The key to solving this problem is first determine if you are dealing with a weak acid or weak base.

Question 24

A new drug, sodium Z, has a pKa = 9.0. Will this drug be more than more than 50% ionized, 50% ionized, or less than 50% ionized at normal body pH of 7.4?(hint: first determine if the drug is a weak acid or weak base)

Answer 24

• The new drug, sodium Z, is a weak acid. Weak acids use positively charged substances(sodium, calcium, magnesium, ect.) to form salts. This drug will be less than 50% ionized at pH = 7.4
• Recall that a weak acid made more acidic will produce more unionized(less ionized) drug.
• The key to solving this problem is first to determine if you are dealing with a weak acid or a weak base.

Question 25

Are morphine(pKa 7.9), meperidine(pKa 8.5), fentanyl(pKa 8.4) and sulfentanil(pKa 8.0) more than 50% nonionized or less than 50% nonionic at pH =7.4? are alfentanil(pKa 6.5) and remifentanil(pKa 7.26) more than 50% nonionized or less than 50% noninionized at pH = 7.4?

Answer 25

• opioids are weak bases. Hence, opioids with pKas above 7.4(morphine, meperidine, fentanyl, and sulfentanil) will be less than 50% nonionized(more ionized) at pH = 7.4
• weak base + acid pH = more ionized*
• Opioids with pKas below 7.4(alfentanil and remifentanil) will be more than 50% nonionized at pH = 7.4
• weak base + alkaline pH = more nonionized*

Question 26

What is the major intracellular buffer?

Answer 26

Proteins(Albumin)

Question 27

When considering flow through a tube, the gradient in hydrostatic pressure(Pin-Pout=F x R) Whose law describes this relationship?

Answer 27

Ohm’s law

Question 28

How are flow and resistance related?

Answer 28

• Flow through a tube is inversely proportional to resistance.
• for example, if resistance doubles, flow is halved
• if resistance is halved, flow is doubled