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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. 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 School of Nursing and The aim of this article is to increase your under- available. Midwifery, University of standing of fluid and 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 Describe different body fluid compartments. (25L) is contained in the intracellular fluid (ICF) and legal responsibility to 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 Differentiate between hypotonic, isotonic and the cells). The ECF compartment is divided into of and water and hypertonic solutions. two sub-compartments: the plasma (3L), the of the mechanisms of Understand the role of electrolytes in fluid fluid portion of in the blood vessels, and movement between different balance. the interstitial fluid (12L) which bathes the body body compartments. Identify the signs and symptoms of fluid and cells. . There are numerous other examples of ECF Key words Explain the different reasons for commencing that are distinct from blood plasma and inter- Intravenous therapy intravenous fluid therapy. stitial fluid (ISF), such as , Nursing: care 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 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 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 insoluble molecules, such as , 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 Osmosis that allows only certain substances to cross (Fig. 1). blood to supply nutrients and raw materials to Diffusion Pores in the membrane allow the movement of the cells for use in metabolic processes. Filtration Facilitated diffusion water molecules, from an area of low solute is also important in urine formation. The hydro- Filtration concentration to an area of high solute static pressure at the nephron causes water and Active transport concentration. For example, if a glucose 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 Prolonged diuretic use the bloodstream is returned by the lymphatic eventually burst. Excessive diaphoresis system, which drains the interstitial space. (sweating) Prolonged / Plasma protein concentration is, therefore, an TIME OUT 2 diarrhoea important factor in the maintenance and distri- Make a list of the intravenous Extensive bution of fluid extracellular compartments. infusion solutions commonly Renal disease Active transport Where no electrical or used in your clinical area. 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 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. Syndrome of inappropriate triphosphate (ATP), to move substances antidiuretic hormone (ADH) against a pressure or concentration gradient. The Adrenal impairment sodium- pump on the cell membrane Cirrhosis Electrolytes that is responsible for maintaining intracellular Congestive cardiac failure , such as intravenous fluid volume best illustrates this concept. Sodium It is important when nursing patients with fluid , is actively pumped out of the cell, against a and electrolyte imbalance and those receiving carbamazepine, concentration gradient, while potassium is infusions, to understand the role of electrolytes in amitriptyline, ecstacy allowed in (Dougherty and Lamb 1999). body fluids, the reason why and how their levels Addison’s disease are maintained within homeostatic limits, and the problems that can arise as a result of the (Malster 1999) Tonicity imbalance. Because the electrolyte content of Understanding tonicity is vital to comprehend ECF differs from that of ICF, it is customary to the mechanisms involved in fluid and electrolyte measure the electrolytes in ECF, chiefly plasma. imbalance and their management with intra- Plasma electrolyte concentrations can be used to venous fluid and electrolyte therapy. assess and manage patients with a diversity of Many intracellular molecules, particularly electrolyte imbalances. Although some tests proteins and selected ions, are prevented by are performed on serum, the terms ‘serum’ and their size from diffusing through the plasma ‘plasma’ are used interchangeably. membrane. Consequently, any change in their Sodium Sodium plays a vital role in concentration produces changes in water maintaining the concentration and volume of concentration on either side of the membrane ECF. It is the main cation (positively charged ion) and results in net loss or gain of water by the of ECF and, therefore, the major determinant of cell. This osmotic movement of water in and out the osmotic pressure of ECF. The normal of cells is influenced by the tonicity of the solu- concentration of sodium is 135-145mEq/L. tions to which they are exposed. Tonicity is: ‘... the Sodium is also important in maintaining irri- ability of a solution to change the tone or shape tability and conduction of nerve and muscle of cells, by altering their internal water volume’ tissue, and assists with the regulation of acid- (Marieb 1998). base balance. Average daily intake of sodium A solution with the same concentration of far exceeds the body’s normal requirement. The non-penetrating solutes (unable to cross the kidneys excrete excess sodium and are capable membrane) as body cells is isotonic, or the same of conserving sodium in times of extreme sodium tonicity. If a cell is placed into an isotonic solution restriction. Sodium concentration is maintained (such as 0.9% or 5% glucose), the cell will via regulation of water intake and excretion. If not change its shape or tone. serum sodium falls below 135mEq/L (hypona- Solutions that have a higher concentration of traemia), the kidneys excrete water. Causes of non-penetrating solutes than the cell are called hyponatraemia are illustrated in Box 2. hypertonic solutions. Cells immersed in hyper- Conversely, if serum sodium levels rise above tonic solutions will lose water by osmosis, which 145mEq/L (hypernatraemia), the osmotic pressure will cause them to shrink (crenate). Solutions that of serum increases stimulating the thirst centre are more diluted and, therefore, contain less and causing the release of antidiuretic hormone non-penetrating substances than cells are called (ADH) by the posterior pituitary gland. ADH acts hypotonic solutions. Cells placed in hypotonic on the kidney to conserve water, thus diluting solutions rapidly gain water by osmosis. Distilled the sodium. CONTINUING PROFESSIONAL DEVELOPMENT Fluid management

Box 3. Causes of Aldosterone released from the adrenal cortex numbness in the extremities, a potassium level hypernatraemia also regulates serum sodium by causing the kidney below 3.5 mEq/L and a slow heart rate. to conserve sodium and water, thereby increasing Signs of hypokalaemia include malaise, skeletal Inadequate water intake ECF volume. Possible causes of hypernatraemia and smooth muscle atony, muscular cramps and Watery diarrhoea include water deprivation/loss, excessive infusion postural . Severe insensible loss of saline and diabetes mellitus. Because sodium Burns is the major determinant of the osmotic pressure TIME OUT 4 Osmotic diuretic therapy of ECF, hypernatraemia always causes a shift of Using your textbook, Hyperglycaemia water out of the cells, which leads to cellular list the possible causes of Diabetes insipidus hyperkalaemia and Near in salt water . Possible causes of hypernatraemia hypokalaemia. Hypertonic IV saline are presented in Box 3. Hyperaldosteronism (Conn’s syndrome) TIME OUT 3 Using an appropriate Other electrolytes Calcium is one of the body’s (Malster 1999) textbook, find the signs and most abundant ions. It combines with symptoms that might phosphorus to form the mineral salts of the accompany hypernatraemia and bones and teeth. Calcium exerts a hyponatraemia. effect on nerve cells and has important intracellular functions, including development of the cardiac action potential and contraction of Potassium Potassium is the main cation of ICF, muscles. Less than 1 per cent of the body’s which contains more than 98 per cent of the calcium is found in ECF. body’s total potassium. The 2 per cent found in Magnesium has an important role in enzyme ECF is kept in a narrow range of 3.5-5.0mEq/L. activity, contributing to the metabolism of carbo- Because the ratio of ICF to ECF helps determine hydrates and proteins. Serum levels should be 1.3- the resting membrane potential of nerve and 2.1mEq/L. A magnesium imbalance is common muscle cells, an alteration in the plasma in critically ill patients, although deficits can occur potassium level might adversely affect in less ill patients, such as those experiencing neuromuscular and cardiac function. Excess or withdrawal from and those receiving deficit in ICF or ECF can, therefore, cause serious, parenteral or enteral nutrition after a period of (potentially fatal) impairment of body function. starvation. Magnesium is excreted by the kidneys, The body gains potassium from food (primarily therefore, diminished renal function results in meat, fruit and vegetables) and . In abnormal renal magnesium retention. addition, ECF gains potassium any time there is Chloride is the chief anion (negatively charged ion) a breakdown of cells (tissue catabolism) or of ECF, with a plasma concentration of 97- movement of potassium out of the cells. 110mEq/L. Chloride deficiency leads to a deficiency However, elevated serum potassium does not of potassium and vice versa. There is also a loss of occur unless there is a concomitant reduction chloride with a loss of sodium. Phosphate is the in renal function (Horne and Swearingen chief anion of ICF, with a normal plasma level of 1991). Potassium is lost from the body through 1.7-2.3mEq/L. the kidneys, GI tract and skin, but the kidneys are the primary regulators. They do this by TIME OUT 5 adjusting the amount of potassium excreted in Before moving on, find out the urine. The presence of aldosterone also what the normal plasma increases the excretion of potassium. Conditions levels of the following that increase aldosterone secretion might, there- substances should be: sodium, fore, increase urinary excretion of potassium. potassium, , creatinine, High serum potassium levels (hyperkalaemia) bicarbonate, calcium, magnesium, glucose have an adverse effect on heart muscle and can and phosphate. cause cardiac arrhythmias. Hyperkalaemia is, therefore, a life-threatening emergency requiring prompt recognition of ECG changes and treat- Fluid and electrolyte replacement ment. If the potassium level rises above 5.5 mEq/L, an infusion of dextrose with Knowledge of the different parenteral fluids and might be commenced to assist the movement of their method of action is essential to the delivery potassium back into the cells. Other signs and of infusion therapy. Infusions can be separated symptoms of hyperkalaemia include tingling and into those that influence cellular fluids, and CONTINUING PROFESSIONAL DEVELOPMENT Fluid management

those that expand the intravascular volume. Various combinations of dextrose and saline Infusions that influence cellular fluids exist. The saline component aids maintenance in water is primarily a source of or expansion of ECF volume, whereas glucose fluid and electrolyte, with different percentages aids cellular hydration as it is metabolised, and available to reflect changes in the patient’s provides a small amount of energy. Glucose 4% sodium balance. Sodium 0.9% is isotonic to with sodium chloride 0.18% is commonly used normal body fluid, and will not, therefore, alter to supply calories, water and moderate amounts the osmotic movement of water across cell of sodium and chloride, while glucose 5% with membranes (unless ICF is more or less sodium chloride 0.9% supplies fluid, nutrients and concentrated than normal). Isotonic crystalloid electrolyte replenishment. Hypotonic solutions solutions are rapidly dispersed into ECF, so large such as dextrose 2.5% with saline 0.45% drive volumes need to be infused to substitute for fluid from the plasma into the interstitial space intravascular losses (Waschke and Frietsch 1999). and are, therefore, used to rehydrate body cells. Sodium 9% is generally used to sustain ECF The third most commonly infused electrolyte is volume by compensating for losses due to potassium. Ideally potassium should be replen- dehydration, urinary excretion of sodium, or fluid ished slowly by diet, however, patients with drains following . It is also indicated at the severe hypokalaemia might require an infusion. initiation and termination of blood transfusions Potassium solutions administered intravenously so that haemolysis of red blood cells that occurs have value as a source of water and electrolytes, with dextrose in water is avoided. and those with glucose are also a valuable Hypertonic saline (3% and 5%) is also avail- source of nutrients. Infusion is, therefore, indi- able. This is used to expand intravascular volume cated when dietary measures are not feasible by moving endothelial and intracellular water and when replenishment of fluids and electrolytes into the intravascular space. It is also used in is required. severe sodium depletion when rapid restoration Conditions that might result in potassium defi- of electrolyte balance is important. It is often ciency include vomiting, diarrhoea, use of potent used in conjunction with to prolong the diuretics, , some forms of renal dis- intravascular volume effect. Hypertonic solutions ease and metabolic acidosis. Excess potassium contain higher concentrations of particles when can lead to cardiac arrhythmias and even death. compared to plasma. This causes fluid to leave Therefore, potassium levels need to be checked the cells and enter the plasma, and has the regularly and carefully controlled. potential, therefore, to cause fluid overload. If potassium is added to an infusion manually, it Hypertonic solutions also have the potential to should be carefully checked and the bag agitated irritate peripheral and administration to ensure thorough mixing. Failure to do this should be slow and carefully monitored. might result in a of potassium being Hypotonic saline (0.45%) is used as an electrolyte administered accidentally. The most frequently replenisher and maintenance solution, preferred used method of potassium administration, over isotonic saline where there is a question over according to Malster (1999), is potassium chlo- the amount required. The complications of saline ride in an isotonic solution. Careful consideration administration include overhydration, sodium over- should be given to the infusion rate as rapid infu- load and potassium deficit. sion can lead to irritation of the veins. Surrounding Dextrose 5% in water is isotonic but, unlike tissues are also at risk if the solution extravasates normal saline, glucose will penetrate cells and and central lines are, therefore, the preferred be metabolised, in effect leaving behind the method of administration. Over correction must infused water. It is, therefore, a useful means of also be avoided because of the consequences of replacing or maintaining fluid volume without hyperkalemia. altering electrolytes. It also provides calories, Other infusion fluids used include Ringer’s 1L of 5% dextrose provides the patient with solution and Hartmann’s solution. Ringer’s solu- 170 calories. Hypertonic solutions such as 10% tion contains the primary electrolytes found in glucose will yield 340 calories and are useful for plasma (with the exception of magnesium and providing calories for patients unable to tolerate chloride) and is, therefore, a source of electrolyte large quantities of water (for example, those with and . Hartmann’s solution is simi- renal insufficiency). Concentrations higher than lar to plasma, with the exception of magnesium. 5 per cent can irritate veins and rapid infusion It is modified by the addition of sodium lactate, can cause dehydration by promoting osmotic which is metabolised by the liver to bicarbon- diuresis, again highlighting the need for careful ate. This is useful in certain conditions, such as patient observation. metabolic acidosis. CONTINUING PROFESSIONAL DEVELOPMENT Fluid management

Infusions that expand intravascular volume outcome and, according to findings by the There are a variety of infusions used to expand Cochrane Institute of Albumin Reviewers (1998), it vascular volume and blood cell count. The might actually increase mortality by increasing choice lies between crystalloids, blood and its interstitial oedema, especially in the lung. blood derivatives and artificial colloids. Artificial colloids These include , hy- Blood and its derivatives Infusion of whole droxyethyl starch (HES) and derivatives. blood and plasma is undertaken to replace Dextrans are polydispersed solutions available as volume lost by haemorrhage caused by or 40, 70 (low molecular weight dextrans) surgery where blood loss exceeds 20 per cent of and 110 (high molecular weight dextran). total blood volume (Clark et al 1997). Whole Dextran 40 acts as a hypertonic solution ex- blood contains cells (red, white and platelets), panding rapidly on infusion, whereas dextran 70 plasma and electrolytes. , therefore, acts isotonically. Interference with blood clotting, replaces fluids, electrolytes and oxygen- allergic reaction and cross-matching difficulties carrying capacity. are problems associated with dextrans (Collis Packed cells are the result of the removal of 1984, Josephson 1999, Waschke and Frietsch platelet-rich plasma from whole blood. One unit 1999). of contains the same are complex carbohydrate molecules amount of oxygen carrying red blood cells as too large to pass out of the capillaries or vascular a unit of whole blood. The danger of circula- walls, so are restricted to the vascular space. They REFERENCES tory failure is lessened because of the reduced generate osmotic forces that cause water to Boltd J et al (1991) Cardiorespiratory responses to hypertonic saline solu- volume. It is, therefore, appropriate for patients enter blood vessels, thereby expanding the plas- tion in cardiac operations. Annals of with heart failure or renal failure. ma volume. This is the main reason why they are Thoracic Surgery. 51, 4, 610-615. Plasma is the content remaining after used in preference to crystalloids. Because the Clark J et al (1997) Pharmocological Basis of Nursing Practice. St Louis, Mosby. the red cells have been removed. It contains electrolytes present in the solution contain calci- Cochrane Group Albumin Reviewers water, electrolytes, proteins, globulin and coag- um, blood and gelatin cannot be mixed or (1998) Human albumin administration ulation factors. contains all infused down the same line, as the calcium will in critically ill patients: systematic review of randomised controlled trials. the normal components of blood plasma, initiate clotting. British Medical Journal. 317, 7153, including clotting factors and fibrinogen. It is HES is available as high molecular weight and 235-240. beneficial to patients with clotting deficiencies or medium molecular weight starch. HES solutions Collis R (1994) The effect of HES and other plasma volume substitutes on bleeding disorders. It is an isotonic volume are primarily eliminated from the body by filtra- endothelial cell activation: an in vitro expander, therefore, patients receiving multiple tion through the kidney. Research has shown study. . units must be observed for signs of fluid overload. that treatment with HES in patients with burns 21, 1, 37-41. Dougherty L, Lamb J (Eds) (1999) It should not be used for volume expansion – this (Waxman et al 1989), and following cardiac sur- Intravenous Therapy in Nursing is better done with crystalloid or colloid solutions. gery (Boldt et al 1991), led to more favourable Practice. Edinburgh, Churchill Albumin comprises 40 per cent of the plasma outcomes compared to treatment with albumin Livingstone. Horne M, Swearingen P (1991) Fluid, protein and can be purified from raw plasma. It 5%. HES was also found to produce less allergic Electrolyte, and Acid Base Balance: is naturally synthesised in the liver and is respon- reactions than dextrans. A Case Study Approach. St Louis sible for maintaining plasma oncotic pressure. MO, Mosby. Albumin is available for infusion as 4.5% and Josephson D (1999). Intravenous Infusion Conclusion Therapy for Nurses. Practice and 20%. The 4.5% albumin is isotonic and can be Principles. London, Thomson used in the treatment of low serum albumin levels By working through this article, you should be Learning. Malster M (1999) Fluid and electrolyte and hypovolaemia to expand the plasma volume. aware of the importance of undertaking obser- balance. In Dougherty L, Lamb J (Eds) Albumin 25% is hypertonic and depends on vations on patients undergoing infusion therapy Intravenous Therapy in Nursing additional fluids either drawn out of the tissues, and able to provide a rationale for the choice of Practice. Edinburgh, Churchill Livingstone. or administered separately for its maximum fluid, based on your knowledge of fluid move- Marieb E (1998) Human Anatomy and osmotic effect. It must be administered with cau- ment and the function of electrolytes Physiology. Fourth edition. California, tion as rapid infusion can cause an increase in Benjamin Cummings Science Publishing. intravascular oncotic pressure, resulting in circu- Waschke K, Frietsch M (1999) Selection latory overload. Albumin is mainly indicated to TIME OUT 6 of adequate substitutes for treat in cases of burns, haemorrhage, intravascular volume replacement. surgical losses and trauma (Josephson 1999). Now that you have completed International Journal of Intensive Care. the article, you might like to 6, 4, 135-143. There does not appear to be any convincing think about writing a practice Waxman K et al (1989) Haemodynamic evidence that albumin is better than synthetic and oxygen transport effects of profile. Guidelines to help you pentastarch in burns . colloids for volume replacement. Several studies have are on page 55. Annals of Surgery. 209, 3, 341-345. failed to show that treatment with albumin improves