Archives
Osmoles, osmolality and osmotic pressure: Clarifying the puzzle of solution concentration
Martin Caon
Senior Lecturer in Biophysical Science, School of Nursing and Midwifery, Flinders University, Adelaide SA
Abstract
Nurses are routinely involved in the collecting and testing of urine and plasma, dialysis, the administration of intravenous fluids and the treatment of osmolar disorders, all of which require an understanding of solution concentration.
This article discusses the various ways in which the concentration of solutions are stated, how they differ and why the different ways of expressing concentration are useful in human physiology. It also explains the similarities and differences between the terms used to describe solution concentration: tonicity, percentage concentration, density, specific gravity, molarity, osmolarity, osmolality and osmotic pressure.
The terms osmolarity, osmolality and osmotic pressure appear routinely in textbooks used in undergraduate nursing courses but often are used incorrectly as synonyms. The usefulness and the appropriate context to use the different ways of expressing solution concentration is discussed. Osmolality (or osmolarity) should be used instead of osmotic pressure to describe the movement of water between compartments while the use of osmotic pressure should be reserved for situations where filtration and osmosis are operating together.
Keywords
solution concentration, osmolarity, osmolality, osmotic pressure, tonicity, nursing
References
Bayer Corporation (1992) Multiple reagent strips for urinalysis. Package insert for MULITSTIX 10 SG (#2300)
Caon M and Hickman R (2003) Human Science: Matter and Energy in the Human Body 3rd edn, Crawford House Australia, Adelaide.
Craven R and Hirnle C (2000) Fundamentals of Nursing: Human Health and Function 3rd edn, Lippincott, Philadelphia.
Crisp J and Taylor C (2005) Potter and Perry’s Fundamentals of Nursing 2nd edn, Elsevier, Sydney.
Guyton A and Hall J (2006) Textbook of Medical Physiology 11th edn, Elsevier Saunders, Philadelphia.
Guyton A (1991) Textbook of Medical Physiology 7th edn, WB Saunders, Philadelphia.
Jenkins GW, Kemnitz CP and Tortora GJ (2007) Anatomy and Physiology: From science to life. Wiley, Hoboken.
Lewis S, Heitkemper M and Dirksen S (2004) Medical Surgical Nursing: Assessment and management of clinical problems 5th edn, Mosby, St Louis.
Marieb E and Hoehn K (2007) Human Anatomy and Physiology 7th edn, Pearson Benjamin Cummins, San Francisco.
Martini FH (2006) Fundamentals of Anatomy and Physiology 7th edn, Pearson Benjamin Cummins, San Francisco.
Silverthorn DU (2007) Human Physiology: An integrated approach, 4th edn, Pearson Benjamin Cummins, San Francisco.
Worthley LIG (1999) Osmolar Disorders, Critical Care and Resuscitation 1: 45-54, accessed at http://www.jficm.anzca.edu.au/pdfdocs/Journal/Journal1999/J1999%20(a)
%20March/Osmolar%20disorders.pdf on July 19 2007.
eContent Home