Physical Principles of Temperature PDF

PHYSICAL PRINCIPLES  Temperature  Matter may change form with the addition of greater heat energy. An example we see every day is the melting of an ice cube into liquid water, and the transformation of liquid water into water vapor with the addition of greater heat energy. Liquid water, wit...

PHYSICAL PRINCIPLES  Temperature  Matter may change form with the addition of greater heat energy. An example we see every day is the melting of an ice cube into liquid water, and the transformation of liquid water into water vapor with the addition of greater heat energy. Liquid water, with the addition of heat energy, expands.  Temperature is the measurement of the thermal state of an object. Heat is thermal energy; temperature is the quantitative measurement of that energy. Several temperature scales exist: Fahrenheit, Celsius, and Kelvin. Conversion among temperature scales is as follows: Celsius to Kelvin:°K = °C + 273 Celsius to Fahrenheit: °F = 1.8(°C) + 32 Fahrenheit to Celsius: °C = (°F − 32)/1.8 Standard temperature is 273.15 K (0°C)  Heat Loss Heat and energy are the same. Heat loss (energy loss) of a system, as discussed previously, is unidirectional from the higher concentration to the lower concentration, from hotter to less hot. Even ice possesses heat (energy). Remember absolute zero, 0°K (−273.15°C or −459.67°F), is the absence of all energy and therefore the absence of all heat The human body is a system that contains energy. Much of this energy is in the form of heat. Our bodies continually exchange heat with the environment from a high concentration to a lower concentration. On a very hot day or in a very hot room, we could become hyperthermic. Similarly, in a cool room, our bodies could become hypothermic, Core Temperature Redistribution A patient’s core temperature can drop quickly due to the vasodilating actions of anesthetics, with the greatest decrease occurring in the first hour after anesthetic adminsitration. Covering all exposed areas of a patient minus the surgical site, wrapping the head in blankets, and warming the operating room all decrease heat loss. The use of forced warm air devices is effective at decreasing heat loss in the operating room environment.  Blood flow to our body’s surface encourages heat loss by four primary processes. In decreasing order, they are: 1. Radiation 2. Convection 3. Conduction 4. Evaporation  RADIATION Radiation is the most significant mechanism by which our bodies lose heat, especially in patients under anesthesia. Radiation of the infrared electromagnetic wavelength transfers heat energy from our warm bodies to the less warm operating room environment (walls, ceiling, equipment, etc.)  Convection Convection is the process by which heat creates air currents. 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.  Conduction Conduction is the transfer of heat by physically touching a less warm object. Where two objects are in direct contact, heat exchange occurs from the higher concentration to the lower concentration. An example would be holding a cold soda can. The sensation of cold is the direct loss of heat from your hand to the can  Evaporation Evaporation is not usually a large contributor to patient heat loss. Heat loss from evaporation includes moisture evaporation from the patient’s skin, as well as exhaled water vapor. The process of evaporation, which is the phase change from liquid to gas, requires energy THANK YOU