Thermodynamics Flashcards
What is thermodynamics?
Study of energy and how it is interconverted from one form to another
What are four fundamental laws related to thermodynamics?
Zeroth, First, 2nd and Third Law
What is the zeroth law of thermodynamics?
Systems are in thermal equilibrium if they do not exchange energy in the form of heat
If two objects, A and C, are each in thermal equilibrium with the object B, A is in ______ with C
thermal equilibrium
What is the first law of thermodynamics?
Expresses how energy can be transformed (changed from one form to another)
What is a fundamental rule regarding energy?
Energy can neither be created nor destroyed
What is the second law of thermodynamics?
Heat can only flow from a higher level to a lower level
What is the an example of the second law of thermodynamics?
When placing a blanket on top of a patient feeling cold, heat will transfer from the blanket to the patient and not from the patient to the blanket
What is required in order for heat to flow from cold to hot?
Energy
What is the third law of thermodynamics?
It is not possible to lower the temperature of an object to absolute zero
What is absolute zero?
Theoretical-(0 K, -273.15 ℃) is void of all energy
What is energy?
The exertion of force (kinetic) or the capacity (potential) to do work
How is energy expressed?
Mechanical work, chemical reactions, or heat
What is the unit of measurement is energy?
Joule
A joule is the force of ___ that moves its point of application 1 m in the direction of that force
1 N
What is potential energy?
Energy waiting to be used, stored and available to be converted to power
What is the formula for potential energy?
PE= mass x gravity x height
What is Kinetic Energy?
Energy of movement
What is the formula for kinetic energy?
KE= 1/2 the product of mass (m) x velocity (v) squared?
What is entropy?
Based on the second law of thermodynamics. underlying process promoting spontaneous and elicited movement in our everyday lives and the universe in general
Universe favors ____.
Chaos
Entropy involves the ______ of energy
equilibration
In entropy, how does energy movement?
Unidirectional. The movement of energy from a high concentration to a lower concentration unless you put in work
In entropy if you have a larger gradient how is the movement of energy affected?
Faster
What is an example of a process driven by entropy?
Diffusion
How does a difference in a gradient (entropy) influence the speed of flow?
Greater difference usually = greater flow (high to low)
When does entropy end?
When all energy is equally distributed
What is temperature?
A measure of the thermal state of an object, quantitative measurement of that energy.
What is heat?
A form of energy that can be transferred from a hotter object to a colder object
What happens when there is no net heat flowing between two objects?
The objects have the same temperature.
How will heat flow?
Always flows from the object with higher temperature to the object with a lower one (entropy)
What causes molecules to expand?
Higher energy states between molecules in a solid lead to molecules vibrating with bigger amplitude and taking up more space (expanding).
What causes the force between molecules to decrease?
Molecules move further and further apart and the force between each neighboring molecule
What causes melting?
Eventually with enough energy (heat) added to the solid, the intermolecular bonds will break
What is van der Walls forces?
In a liquid, the individual molecules still exert some degree of force (attraction)
What happens when heat is addeded to a liquid?
The movement of molecules becomes greater and eventually overcome the vdW forces to become a vapor or gas.
Name the three commonly used temperature scales.
Fahrenheit, Celsius & Kelvin
During anesthetic administration, when does the greatest decrease in core temperature occur?
First Hour
What is the freezing point of water in Fahrenheit?
32 degrees
What is the boiling point of water in Fahrenheit?
212 degrees
What is the freezing point of water in Celsius?
0 degrees
What is the boiling point of water in Celsius?
100 degrees
What is the freezing point of water in Kelvin?
273.15 degrees
What is the boiling point of water in Kelvin?
373.15 degrees
How does the body produce heat?
Metabolism and muscle movements (shivering)
What is MET?
Metabolic heat production of an average seated and resting adult individual is 1 MET (metabolic equivalent of task).
What will happen to MET during exercise?
Increase
What does a MET score of 1 mean?
Poor functional capacity
What is 4 METs mean?
Good functional capacity
What is greater than 4 Mets mean?
Excellent functional capacity
How can you assess a patients functional capacity?
Inquiring about activity tolerance and is recommended as part of cardiac risk assessment prior to anesthesia
What is are examples (2) of good functional capacity?
(1) Are you able to walk four blocks without stopping regardless of limiting symptoms?
(2) Are you able to climb two flights of stairs without stopping regardless of limiting symptoms?
What is an example (2) of poor functional capacity?
The inability to climb two flights of stairs or walk a short distance is indicative of poor functional capacity and is associated with an increased incidence of postoperative cardiac complications in noncardiac surgery
What should occur to patients with patients with moderate to poor functional capacity (less than 4 METs)?
Further assessed to identify cardiac risk factors.
Patients with good functional capacity (more than 4 METs) may proceed for surgery provided patients with cardiac risk factors are properly managed with _____and ______ therapy as described later in this section
Statin & Beta-blocker therapy
What affect can sustained shivering have on heat production?
Augment the metabolic heat production by 50-100% in adults
What affect does shivering have on oxygen consumption and CO2 production?
This increases oxygen consumption and CO2 production by 100-200%
What medication can be used to treat unwanted shivering?
Meperidine
Does shivering occur in children?
Shivering does not occur in newborn infants and is not fully effective until children are several years old
What is metabolized to promote nonshivering thermogenesis?
The metabolism of brown fat, which is located in the interscapular space, thorax, and abdomen
Nonshivering Thermogenesis Increases metabolic heat production without producing ________.
Mechanical work
Nonshivering Thermogenesis is most effective in which patient population.
Infants, Has minimal (if any) effect in adults
What causes nonshivering thermogenesis?
Primarily controlled by norepinephrine released from beta-adrenergic nerve terminals
What are methods for promoting heat disposal?
The body can dispose of heat by sweating, vasodilation, and breathing, but production remains the same.
What is the relationship between heat and energy?
are the same
What process drives heat loss?
Entropy, Heat loss (energy loss) is unidirectional (hotter to less hot)
What does most of the energy take the form of in the body?
Heat, Our bodies continue to exchange heat with the environment
What protective mechanisms exist to prevent heat loss?
Clothes, hair, skin, and fat insulate us
What physiological causes a reduction in heat loss from our bodies?
Vasoconstriction of peripheral vessels slows heat loss from our bodies
What promotes heat loss when overheating?
Vasodilation
What thermoregulatory mechanism is dsrupted under anesthesia?
Vasoconstriction and vasodilation
What encourages heat loss?
Blood flow to our body’s surface encourages heat loss by four primary processes (core temperature redistribution).
What is the four primary processes of heat loss?
Radiation
Convection
Conduction
Evaporation
Which process is the most significant sight of heat loss?
Radiation, especially under general anesthesia
What is radiation?
Infrared radiation from bodies is greatest in areas of highest blood flow.
How does radiation occur in the OR?
Radiation of the infrared electromagnetic wavelength transfers heat from warm bodies to the less warm OR environment (walls, ceiling, equipment, etc
What body part loses the greatest amount of heat & why?
Heads- due to high percentage of blood flow
How does an increase in blood flow to the head increase heat loss from radiation?
Blood carries body heat, and the greater amount of blood and heat transported to the head, the greater the amount of heat loss to radiation.
What is the quickest way to increase heat in the OR?
Increase the temperature
What is convection?
Our bodies transfer kinetic energy to air molecules on the surface of our skin. The heated air molecules then move about with greater kinetic energy, rise, and are replaced by colder (less kinetic energy) air molecules.
Our bodies then transfer more kinetic energy to these molecules, which rise and are again replaced by cooler air molecules
What does convection create?
Air currents
What causes conduction?
Transfer of heat by physically touching a less warm object
What is conduction?
Where two objects are in direct contact, heat exchange occurs from the higher concentration to the lower concentration (entropy)
What is an example of conduction in the OR?
A patient on a cold operating room table will conduct their heat to the less warm table by physical contact
What patient population is conduction more significant in?
Pediatric-who have a large body surface area compared to overall mass
What is evaporation?
Specific process of vaporizing liquids
What has the least contributor to heat loss?
Evaporation
What is an example of heat loss through evaporation?
The patient’s skin and exhaled water vapor
Where does the source of energy come from during evaporation?
Surrounding environment
What relation do IV fluids have to heat loss?
One unit of refrigerated blood or 1 liter of crystalloid at room temperature will drop the core temperature by 0.25 ℃
What can help to reduce heat loss from IV fluids?
Fluid warming
What must be done to dry gasses before being administered to the patient (2)?
need to be warmed and humidified by the body before reaching the alveoli
How much of the total heat loss can occur from dry anesthesia gases?
10%
Hypothermia in anesthesia develops with a __________-
characteristic pattern
What first happens to core temperature during surgery?
Initial rapid decrease, followed by a slow, linear reduction.
What eventually happens to core temperature during surgery?
stabilizes and remains virtually unchanged
What do volatile agents cause?
Vasodilation- also inhibit the thermo regulating vasoconstriction.
What is the body unable to do as a result of volatile agents?
inhibit the thermoregulating vasoconstriction.
This takes away the body’s ability to redistribute blood circulation
How much body heat will be lost in the first hour of anesthesia?
1.5 C r/t redistribution of blood
What happens to temperature during 2-4 hours in surgery?
A steady state in core temperature will occur. However, peripheral temperature will continue to decrease
What are some prevention strategies for reducing heat loss in the OR (5)?
Forced warm air devices, lower gas flow rates, humidification systems, ambient OR warming, covering/insulating patients
What is the difference between evaporation vs. vaporization?
Evaporation- takes place below the boiling temperature/Vaporization- at a point greater than the boiling point.
What is needed to convert liquid to vapor?
Energy
What is latent energy?
Refers to the “heating up” period prior to the phase change (so temperature is increasing, but no change in form).
What is latent heat of vaporization?
The amount of heat energy per unit mass required to convert a liquid into the vapor phase is the latent heat of vaporization
How much energy is needed from the environment to convert one gram of water into vapor?
2500 joules, or approximately 600 calories
What is an example of latent heat of vaporization in the OR?
Patients who have areas of their bodies surgically prepped with liquids experience heat loss by this method.
How does breathing contribute to heat loss?
Exhaled water vapor
How can you prevent exhaled water vapor (heat loss)?
Lower carrier gas flows, when appropriate, and use of an in-line humidifying apparatus
What is evaporation?
the transition from the liquid phase to the gas phase that takes place below the boiling temperature
What is vaporization?
the transitional phase of an element as it changes from a solid or liquid phase into a gas phase at a point greater than the boiling point
What does vaporization require?
Energy
How is latent heat of vaporization measured?
Kilojoules
During vaporization, what happens to the temperature of a liquid?
does not rise above boiling point, instead, the additional heat energy transforms the liquid into a gas
What happens to the kinetic energy of the molecules when you heat a liquid?
increases the kinetic energy of the liquid’s molecules
What does the rate of vaporization depend on?
temperature, the vapor pressure of the liquid, and the partial pressure of the vapor above the evaporating liquid
What is vapor pressure?
As gas molecules escape the liquid, they exert a pressure
How is vapor pressure measured?
mmHg
What happens to molecular kinetic energy when heat is increased?
Increase molecular kinetic energy, which will increase the rate of vaporization
What happens to the molecules in a closed container?
Equilibrium will be achieved between molecules in the gaseous phase and those in the liquid phase.
What is a volatile liquid?
All liquids have high vapor pressure at room temperature
Vapor pressure and boiling points are _________ related
inversely
What happens to vapor pressure as the boiling point is lowered?
Increased. The higher the Vapor Pressure the lower the Boiling Point
What happens to vapor pressure as the boiling point is raised?
Decreased. The lower the Vapor Pressure the higher the Boiling Point
What is the vapor pressure of Isoflurane to make it a volatile anesthetics?
238 mm Hg
What is the vapor pressure of Sevoflurane to make it a volatile anesthetics?
160 mm Hg
What is the vapor pressure of Desflurane to make it a volatile anesthetics?
660 mm Hg
What are vapor pressures dependent on?
Temperature
What happens to liquids and vapor pressures at a given temperature?
Different liquids exert different vapor pressures at a given temperature.
What is an important component of vaporizers?
Because different volatile anesthetics have different vapor pressures, vaporizers must be calibrated for each specific agent.
What happens when the wrong agent is placed into a vaporizer?
Placing the wrong agent into a vaporizer will deliver the wrong concentration.
If a high vapor pressure agent is placed in a vaporizer calibrated for a lower vapor pressure agent, the output of that vaporizer will be ______than indicated on the control dial.
higher
If an agent with a lower vapor pressure is put inside a vaporizer calibrated for a higher vapor pressure agent, the output of that vaporizer will be _______ than indicated on the control dial.
lower
What is absolute zero?
The lowest possible state of universal entropy would still possess energy, even though it would be very low.
What is absolute zero in Fahrenheit?
-460 degrees
