Heat, thermodynamics and states of matter

Abstract

The physical principles of heat and states of matter influence diverse areas of anaesthetic practice. They relate to patient care (e.g. the maintenance of body temperature) and the performance of equipment (e.g. the function of bimetallic strips and the behaviour of compressed gases). This article briefly explains some of the physical principles that govern thermal energy systems and the behaviour of matter within such systems. It relates these principles to clinical practice using examples. The principles of calorimetry and the laws of thermodynamics that often affect biological systems are explained, with examples of where they may influence practice, and where heat energy may be harnessed to derive work. Also described are the principles that govern states of matter and the events that occur at a molecular level when that state changes. Finally, the influence of dissolved particles on a solution’s response to thermal energy is described, with examples of their use in clinical measurement.