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Chapter 6 - Physics and measurement

Published online by Cambridge University Press:  05 July 2014

Ari Ercole
Affiliation:
Addenbrooke’s Hospital
Jane Sturgess
Affiliation:
Addenbrooke’s Hospital, Cambridge
Justin Davies
Affiliation:
Addenbrooke’s Hospital, Cambridge
Kamen Valchanov
Affiliation:
Papworth Hospital, Cambridge
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Summary

Heat and temperature

Temperature control is clinically important. Peri-operative hypothermia, in particular, carries a significant morbidity and surgical patients are at particular risk from operative heat loss combined with impaired heat conservation caused by anaesthesia. Furthermore, effective re-warming of patients that have been allowed to become cold can be very difficult. Careful pre-operative and intra-operative management can avoid this if the mechanisms of heat loss and redistribution within the body are appreciated.

Measuring heat and temperature

Heat is a form of energy. It arises from the random jostling motion of the particles that make up the matter from which everything is made. The amount of thermal movement is measured by the concept of temperature; objects with little thermal energy having a low temperature. The Celsius/centigrade scale is commonly used in clinical practice and is defined in terms of the freezing (0oC) and boiling (100oC) points of water at standard atmospheric pressure. The SI unit of temperature, however, is the kelvin where 0 K is defined as the temperature at which thermal disorder ceases (absolute zero). A change in temperature of 1oC and 1 K are defined to be the same magnitude so that absolute zero turns out to be equal to -273.15oC.

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Publisher: Cambridge University Press
Print publication year: 2014

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References

Davey, A, Diba, A. Ward’s Anaesthetic Equipment, 5th edn. Elsevier Saunders, 2005.Google Scholar
Ercole, A. Attenuation in invasive blood pressure measurement systems. Br J Anaesth 2006; 96(5): 560–2.CrossRefGoogle ScholarPubMed
Ercole, A. Combined flow rates of venous access devices and attachments. Resuscitation 2007; 74(2): 394–5.CrossRefGoogle ScholarPubMed
Macdonald, DJ. Anaesthesia for microvascular surgery. A physiological approach. Br J Anaesth 1985; 57(9): 904–12.CrossRefGoogle ScholarPubMed
Sessler, D. Peri-operative heat balance. Anesthesiology 2000; 92(2): 578–96.CrossRefGoogle Scholar

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