IV therapy focus CONTINUING PROFESSIONAL DEVELOPMENT Fluid management By reading this article and writing a practice profile, you can gain The use of intravenous therapy 47-52 ten continuing education points (CEPs). You have up to a year to Multiple-choice questions send in your practice profile. Guidelines on how to write and and submission instructions 54 Practice profile submit a profile are featured immediately after the continuing assessment guide 55 professional development article every week. Practice profile 27 The use of intravenous therapy NS98 Hand H (2001) The use of intravenous therapy. Nursing Standard. 15, 43, 47-52. In brief Date of acceptance: October 10 2000. Author Helen Hand BSc(Hons), between different body compartments, as well as Aims and intended learning outcomes MA(Ed), RGN, is Lecturer, knowledge of the actions of the various solutions School of Nursing and The aim of this article is to increase your under- available. Midwifery, University of standing of fluid and electrolyte homeostasis, and Sheffield. Email: provide the rationale for the care and manage- [email protected] Body fluid compartments ment of patients undergoing intravenous fluid therapy. After reading this article, you should be The total amount of water in a male weighing Summary able to: 70kg is around 40L. Almost two thirds by volume Nurses have a professional I Describe different body fluid compartments. (25L) is contained in the intracellular fluid (ICF) and legal responsibility to I Define the principles of osmosis, diffusion and compartment, which consists of trillions of cells. understand the rationale for the use of prescribed fluids. filtration in relation to the movement of water The remaining one-third (15L) is found in the Safe administration requires and solutes between compartments. extracellular fluid (ECF) compartment (outside an understanding of the role I Differentiate between hypotonic, isotonic and the cells). The ECF compartment is divided into of electrolytes and water and hypertonic solutions. two sub-compartments: the plasma (3L), the of the mechanisms of I Understand the role of electrolytes in fluid fluid portion of blood in the blood vessels, and movement between different balance. the interstitial fluid (12L) which bathes the body body compartments. I Identify the signs and symptoms of fluid and cells. electrolyte imbalance. There are numerous other examples of ECF Key words I Explain the different reasons for commencing that are distinct from blood plasma and inter- I Intravenous therapy I intravenous fluid therapy. stitial fluid (ISF), such as cerebrospinal fluid, Nursing: care I State the different types of intravenous fluid synovial fluid, lymph, serous fluid and secretions These key words are based and give a rationale for their use. from the gastrointestinal (GI) tract. on subject headings from the I Analyse the nurse’s role in observing and sup- The fluid compartments are separated from British Nursing Index. This porting the patient undergoing intravenous one another by semi-permeable membranes. article has been subject to fluid therapy. Water and small molecules pass through the double-blind review. membrane, whereas larger colloid substances Introduction and proteins are confined to the intravascular space. The composition of each compartment is Knowledge of different parenteral fluids and maintained by the selectivity of its membrane. their method of action is essential to the safe The intravascular fluid (IVF) is separated from the delivery of infusion therapy. Nurses have a profes- ISF by the capillary membrane, and between the Online archive sional and legal responsibility to understand ISF and the ICF is the cell membrane. The con- For related articles visit our the rationale for the use of specific prescribed trolled movement of fluids and solutes between online archive at: fluids and the desired and untoward effects of these spaces ensures that vital nutrients can pass www.nursing-standard.co.uk administration. Safe administration demands an from the IVF to the cells, and that waste prod- and search using the key understanding of the role of electrolytes and ucts can move out of the cells and into the IVF. words above. water and of the mechanisms of movement The body fluid compartments are maintained at CONTINUING PROFESSIONAL DEVELOPMENT Fluid management Fig 1. Osmosis energy. In the body, the diffusion of substances takes place across a selectively permeable plasma membrane and will only occur if the molecules Semi-permeable membrane are small enough to pass through. Facilitated diffusion This makes use of highly selective ‘carrier molecules’ situated in the cell membrane. This is used by large lipid insoluble molecules, such as glucose, to gain rapid entry into cells. If the carriers became saturated, diffusion will be reduced even though a diffusion gradient still exists. Higher concentration Lower concentration TIME OUT 1 Using an anatomy and physiology text, list at least five substances that move across the cell membrane by diffusion. Filtration This is a passive process; there is a Non-permeable solutes gradient on either side of the membrane, but this time it is pressure rather than solute concentration. a constant level by the homeostatic mechanisms Hydrostatic pressure forces water and small Box 1. Homeostatic listed in Box 1. dissolved molecules out of the plasma into the mechanisms Osmosis This is the movement of water through ISF. This movement occurs at blood capillary a selectively permeable membrane, that is, one level, fluids and small molecules leaving the I Osmosis that allows only certain substances to cross (Fig. 1). blood to supply nutrients and raw materials to I Diffusion Pores in the membrane allow the movement of the cells for use in metabolic processes. Filtration I Facilitated diffusion water molecules, from an area of low solute is also important in urine formation. The hydro- I Filtration concentration to an area of high solute static pressure at the nephron causes water and I Active transport concentration. For example, if a glucose solution other molecules to pass through the tubule in is separated from pure water by a membrane the first stage of urine production. that is permeable to water, but not permeable to If fluid is forced out of the capillary by hydro- large glucose molecules, water will diffuse from static pressure, it will be drawn back into the the area of high water concentration (pure blood supply at some point to maintain overall water) to the area of low concentration (the blood volume. This is achieved by the presence glucose solution), to equalise the concentration of plasma proteins in the blood which attract of the two solutions. water by osmosis. Plasma proteins, such as Diffusion Diffusion is the movement of albumin, are unable to leave the capillary, which substances from an area of high concentration means that the blood is more concentrated in to an area of low concentration. This is called a terms of plasma proteins and has a low water diffusion gradient. Because of the random concentration compared to ISF, which has a high movement of molecules and the collisions that water (and low plasma protein) concentration. result from this movement, molecules of a given Water, therefore, moves by osmosis from the type will eventually be evenly distributed area of high water concentration (ISF) to the throughout a system. This process can be seen, area of low water concentration (blood) to for example, when ink is dropped into a glass of equalise the two compartments. water or when perfume is sprayed into a room. Water is driven out of the arteriolar end of the The ink spreads evenly throughout the water capillary because hydrostatic pressure is greater and the perfume spreads evenly throughout the than the plasma oncotic pressure, generated by air in the room. The net movement of ink the plasma proteins. As water is forced out, molecules and perfume molecules is from a however, the hydrostatic pressure decreases and region of high concentration to one of low is eventually exceeded by the plasma oncotic concentration – in other words they move down pressure. This pressure difference favours the a concentration gradient. drawing back of water to the capillary from the Diffusion is a passive process, it does not require interstitial space. In this way, essential nutrition CONTINUING PROFESSIONAL DEVELOPMENT Fluid management is supplied and waste products are removed water represents the most extreme example of Box 2. Causes of from cells and brought into the bloodstream for hypotonicity as it contains no solutes at all. If a hyponatraemia excretion, and the overall blood volume is main- cell were placed into a solution of distilled tained. Any fluid that is not returned directly to water, it would continue to gain water until it I Prolonged diuretic use the bloodstream is returned by the lymphatic eventually burst. I Excessive diaphoresis system, which drains the interstitial space. (sweating) I Prolonged vomiting/ Plasma protein concentration is, therefore, an TIME OUT 2 diarrhoea important factor in the maintenance and distri- Make a list of the intravenous I Extensive burns bution of fluid extracellular compartments. infusion solutions commonly I Renal disease Active transport Where no electrical or used in your clinical area. I Over infusion of dextrose concentration gradient exists, substances are Decide whether they are 5% unable to move by simple diffusion and, isotonic, hypertonic or hypotonic I Anorexia, fasting, therefore, have to be ‘actively transported’. This and state what effect they would have on alcoholism requires the use of energy in the form of cells placed in them. I Syndrome of inappropriate adenosine triphosphate (ATP), to move substances antidiuretic hormone (ADH) against a pressure or concentration gradient. The I Adrenal impairment I sodium-potassium pump on the cell membrane Cirrhosis Electrolytes I that is responsible for maintaining intracellular Congestive cardiac failure I Drugs, such as intravenous fluid volume best illustrates this concept.