Physics for the Nurse Anesthetist~Quiz 5 Flashcards
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?
This is LeChatelier’s principle
What is the Bronsted-Lowery Theory?
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.
What is an acid? Why is a substance called a weak acid?
- 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
What agents used in anesthesia re weak acids?
Barbiturates
Why is carbonic acid considered a weak acid?
- Carbonic acid ionizes only 0.2% in physiologic solution
- an acid that does not dissociate 100% to its ionized form is a weak acid
What is the definition of a weak base?
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.
What agents used in anesthesia are weak bases?
- all local anesthetics
- all opioids(fentanyl, afentanil, morphine)
- benzodiazepines
- etomidate
- ketamine
On the ph scale….the more hydrogen ions equals what in relation to acid/base?
the more acidosis
On the ph scale…the more hydroxide ions equals what in the relation to acid/base?
the more base
What is the pH of a liter of water?
7 at 24 degrees celcius
What happens to an amount of weak acid in nonionized forms as pH falls? the amount of ionized?
- 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)
A weak acid with a pKa of 7.8 will be more than 50% or less than 50% nonionized at pH = 7.4?
- more than 50% will be nonionized at pH = 7.4
- Acid + Acid = more nonionized
Will the CNS actions of barbiturates be intensified or diminished in the patient who is acidotic? explain?
- 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.
What happens when a weak acid is injected into an acidotic patient?
- More drug is nonionized; as pH falls, the nonionized fraction increases.
- Acid + Acid = nonionized
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?
- 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
Base + Acid = more ionized?
as the pH decreases the amount of weak base in ionized form increases
weak base + acid pH = more ionized
Base + Base = nonionized?
as the pH increases the amount of weak base in nonionized form increases
weak base + alkaline pH = more nonionized
What happens to the amount of weak base in ionized form as pH decreases? as pH increases?
- 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
A weak base with a pKa of 7.8 will be more than 50% or less than 50% nonionized at pH = 7.4?
- less than 50% nonionized
- base + acid = ionized or less nonionized
What happens when a weak base is administered to an acidotic patient?
- 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
Do drugs that are weak acids form salts with positive ions such as sodium or negative ions such as sulfate or chloride?
- 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)
do drugs that are weak bases form salts with positive ions such as sodium or negative ions such as sulfate or chloride?
- 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)
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)
- 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.
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)
- 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.
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?
- 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*
What is the major intracellular buffer?
Proteins(Albumin)
When considering flow through a tube, the gradient in hydrostatic pressure(Pin-Pout=F x R) Whose law describes this relationship?
Ohm’s law
How are flow and resistance related?
- Flow through a tube is inversely proportional to resistance.
- for example, if resistance doubles, flow is halved
- if resistance is halved, flow is doubled
