Lecture 2: Fluids/Solutions Study Guide for Quiz Flashcards
What are two types of fluids?
Liquids and gases
Fluids take the ___
Shape of their container
What does Pascal’s principle state about pressure?
Pressure is exerted equally regardless of the size of the container—i.e.: arterial blood pressure monitoring
What do hydrometers measure?
Density of fluids
What is hydrodynamics?
The study of fluids in motion
What is laminar flow?
Flow that is smooth, orderly
What is turbulent flow?
Flow that is chaotic, always changing
In anesthesia, we strive for ___ flows
Laminar flows
What is the venturi flow meter?
- Venturi flow meter was originally used to measure speed in a pipe—they found that the speed was greatest at the narrowest part of the pipe
- Today, Venturi flow meters are the basis behind nebulizers
What is Pouisielle’s Law?
The laminar flow rate is proportional to the fourth power of the pipe’s radius
Pouiseuille’s Law applies to ___ flow only
Laminar flow only
What two things have the greatest effect on laminar flow?
Radius and length
What are 3 possible ways to increase the fluid flow rate through a catheter or needle (based on Poiseuille’s Law)?
- Raise IV bag height or add a pressure bag
- Use a large gauge IV catheter
- Use a shorter length IV catheter
What is Bernoulli’s Principle?
Pressure of a fluid varies inversely with speed—as the speed of a fluid increases, the pressure exerted by the fluid decreases
Bernoulli’s principle—an increase in speed = a ___ in pressure
Decrease
Bernoulli’s principle—a decrease in speed = ___ in pressure
Increase
According to Bernoulli, pressure is ___ in the narrow part of the tube
Lower (because speed increases in the narrow part of the tube)
Bernoulli’s principles are seen in the ___
Venturi tube flowmeter
What is viscosity?
Measure of a fluid’s resistance to flow
Fluids with a high viscosity…
Do not flow very readily (i.e.: honey)
Fluids with a low viscosity…
Flow more easily (i.e.: water)
The closer a molecule is to a wall, the ___ it moves
Slower (speed is essentially zero)
Molecules in the center move…
The fastest (parabolic shape, laminar flow)
Less viscosity =
Better flow
How does length affect flow?
More length = less flow
Shorter = more flow
Speed of fluid vs. cross-sectional area
Speed of fluid is INVERSELY proportional to the cross-sectional area
Flow rate =
Volume/time (i.e.: 3L/min)
Flow is directly proportional to the ___ power of the radius
Fourth power
If you double the radius of your tube (i.e.: ETT, IV tubing), you would increase the flow by ___
16 (2^4)
If you triple the radius of your tube, you would increase the flow by ___
81 (3^4)
What has the most dramatic effect on flow?
A change in radius
How does the length of a tube affect flow?
- Shorter tube has more flow through it
- Longer tube has less flow through it
Viscosity of blood
Blood is viscous; flows slowly
Increase in viscosity =
Decrease in flow
Decrease in viscosity =
Increase in flow
Viscosity is related to ___ flow
Laminar flow
Density is related to ___ flow
Turbulent
What increases when flow becomes turbulent?
Resistance
What can you do to lessen turbulent flow?
Change the density when you have turbulent flow—decrease the density to make the flow less turbulent (i.e.: heliox is less dense than oxygen, makes the flow less turbulent)
What is Reynold’s number?
The measure of the tendency for turbulence to occur
When Reynold’s number rises above ___, turbulence will usually occur
2000
Even in a straight, smooth vessel!
Reynold’s number is directly proportional to ___
Velocity (how fast it’s flowing), density, and diameter
Reynold’s number is INVERSELY proportional to ___
Viscosity
What is a solution?
A homogeneous mixture that consists of one or more solutes uniformly dispersed throughout a medium known as a solvent
What is a solvent?
Part of a solution; present in the larger amount
What is a solute?
Part of a solution; present in the smaller amount
Molality (m)
Moles of solute / kg solvent
Molarity (M)
Moles of solute / L solution
More applicable to our profession
Molality and molarity…
NEVER equal each other
What is solubility?
The amount of solute that will dissolve in a given amount of solvent
Lipid solubility is related to the ___ of a drug
Potency
Drugs with a greater lipid solubility have a ___ potency
Greater potency
Protein-binding is related to…
Duration of action of drugs (i.e.: local anesthetics)
Solubility deals with the ___ of a drug
Potency
Protein-binding deals with ___
Duration of action of a drug, particularly for local anesthetics
Drugs with decreased solubility (i.e.: desflurane)
Faster induction, faster wake up…because blood and other tissues aren’t taking up the drug, the drug is going right to the target site (brain)
Increased solubility of drugs =
Slower induction, slower wake up…because every place along the path is taking some of that drug, less is going to the brain
Blood solubility of a drug determines…
The speed of induction (less soluble = faster, more soluble = slower)
As temperature goes down, solubility ___
Increases
Gas is more soluble at ___ temperatures
Cold temperatures
Solubility =
Potency
How does cardiac output relate to anesthetic gas?
Slow cardiac output = more anesthetic delivered to the brain because there’s more time for the gas to jump onto the alveoli, and then the blood takes it up to the brain
Tonicity
Relative concentration of solutes in osmotic systems
Isotonic
Equal concentration of particles
Hypertonic
Greater concentration
Hypotonic
Lower concentration
Osmosis
Diffusion of water
Diffusion occurs from ___ to ___
High concentration to low concentration
