18 Intravenous Fluids
Solutions of electrolytes and water are given intravenously, to meet normal fluid and electrolyte requirements or to replenish substantial deficits or continuing losses, when the patient is unable to take adequate amounts by mouth, e.g. nauseous, vomiting, haemorrhaging, dehydrated or ketotic.
The causes and severity of the electrolyte imbalance must be assessed from the clinical history and biochemical investigations. Sodium, potassium, chloride, magnesium, phosphate and water depletion can occur singly and in combination with or without disturbances of the acid–base balance. Actions must be taken to ensure that circulatory overload does not occur as a result of intravenous fluid therapy, as overloading will result in pulmonary oedema and breathlessness, which may cause respiratory arrest. Hence a record of all fluids infused is essential.
Plasma volume expanders are used for the treatment of circulatory shock, e.g. massive obstetric haemorrhage or where there is a sudden acute blood or plasma loss leading to a fall in blood pressure and resulting in blood cells collapsing while trying to redress their balance. They restore vascular volume, stabilizing circulatory haemodynamics and maintaining tissue perfusion.
Drugs should NOT be added to infusions of sodium bicarbonate, amino acids, mannitol, blood products or specially prepared fat emulsions, such as those used in neonatal intensive care units for feeding neonates (total parenteral nutrition) via the intravenous route.
Instructions regarding storage and degradation of solutions should be noted, and any deviation either from instructions or within the solution should indicate that the infusion should not be commenced, or, if in progress, should be discontinued.
Additive labels should be used to indicate what has been added to the solution, time, strength and, if relevant, expiry time/date, as well as patient identity and the signature of the practitioners checking the infusion. The practitioner must also be aware of the suitability of the additive to the electrolyte solution and where to refer any enquiries.
NB: All fluids should accurately reflect daily requirements, and close monitoring is required to avoid fluid and electrolyte imbalance.
Intravenous fluids are commonly described as crystalloids and colloids.
Crystalloids
These are solutions with small molecules that flow easily from the bloodstream into the cells and tissues. They contain similar concentrations of osmotically active particles to extracellular fluid, so fluid does not shift between the extracellular and intracellular areas. Crystalloids can be described as:
Isotonic – with a concentration of dissolved particles equal to that of intracellular fluid. Osmotic pressure is therefore the same inside and outside the cells, so they neither shrink nor swell with fluid movement.
Hypotonic – less concentrated than extracellular fluid, so fluid moves from the bloodstream into the cells, causing cells to swell
Hypertonic – more highly concentrated than extracellular fluid, so fluid is pulled into the bloodstream from the cells, causing cells to shrink.
Intravenous crystalloid fluids in common use
Sodium chloride 0.9%
This isotonic solution provides the most important extracellular ions in near physiological concentrations and is indicated in sodium depletion, used in fluid replacement and electrolyte balance, as an IV infusion, as a carrier for injections in which the prescribed drug requires reconstitution, or as a ‘flush’ for IV cannulae.
Cautions: impaired renal function, cardiac failure, hypertension, peripheral and pulmonary oedema, toxaemia of pregnancy.
Side effects: administration of large doses may give rise to sodium accumulation, oedema and hyperchloraemic acidosis.
NOTE: The term ‘normal saline’ should not be used to describe sodium chloride intravenous infusion 0.9%; the term ‘physiological saline’ is satisfactory, but it is preferable to state the actual composition of the fluid, i.e. sodium chloride intravenous infusion 0.9%.
Glucose solutions
These are used mostly to replace water deficit and should not be given alone as they may lead to hyponatraemia and other electrolyte disturbances.
Sodium chloride and glucose
These hypertonic solutions are indicated when there is combined water and sodium depletion. A 1 : 1 mixture of isotonic sodium chloride and 5% glucose allows some of the water (free of sodium) to enter body cells, which suffer most from dehydration, while the sodium salt with a volume of water determined by the normal plasma Na+ remains extracellular.
Glucose 5%
This is used as an isotonic intravenous infusion (IVI) for fluid replacement, dehydration and when there is an insulin infusion for the prevention of diabetic ketoacidosis, i.e. during diabetic labours and to provide energy. NB: There are a number of different concentrations, i.e. 2.5% and 4% glucose in sodium chloride.
Hartmann’s solution (compound sodium lactate solution)
This isotonic solution, used as an IVI to replace fluid and restore electrolyte balance, can be utilized instead of isotonic sodium chloride solution during or after surgery, or in the initial management of the injured or wounded; it may reduce the risk of hyperchloraemic acidosis. Often used in obstetrics as a carrier for syntocinon infusions or for ‘preloading’ before and during epidural analgesia.
Intravenous potassium
Potassium directly affects how well the body’s cells, nerves and muscles function, hence maintaining its balance is essential.
Care must be taken when administering potassium as it is toxic to the heart and so must be given slowly except in extreme circumstances. Hypokalaemia may result if there is renal impairment. Careful patient monitoring is required. Intravenous pumps should be used to control the rate of administration.
Potassium chloride + glucose
This is used in severe electrolyte depletion – exact regimen specified by the prescriber.
Potassium chloride + sodium chloride
As above. Where possible, premixed infusion solutions should be used or, alternatively, potassium chloride concentrate, as ampoules containing 1.5 g (K+ 20 mmol) in 10 mL, is mixed thoroughly with 500 mL sodium chloride 0.9% intravenous infusion. NB: Ensure additive label applied.
Colloids
These are also known as plasma expanders/expanders of the intravascular space. They pull fluid into the bloodstream and are used if the circulatory blood volume does not improve. The main concern with colloids is that they may enter the interstitium, resulting in the osmotic gradient being increased and thereby pulling additional water into the interstitium. Increased risk of endothelial injury and capillary leak are linked to thromboembolism, anaphylaxis and disseminated intravascular coagulation (DIC), conditions that often necessitate colloid therapy.
There are four main colloids: albumin, dextran, starches and gelatin.
Albumin
Albumin is derived from human plasma. It is used to maintain normal oncotic pressure and to act as a carrier of some metabolites. Natural colloid, prepared from whole blood, contains soluble proteins and electrolytes but no clotting factors, blood group antibodies, or plasma cholinesterases. Albumin can be given without regard to the recipient’s blood type.
Albumin solution (human albumin solution)
This is a solution containing protein derived from plasma, serum or normal placenta; at least 95% of the protein is albumin. The solution may be isotonic (containing 3.5–5% protein) or concentrated (containing 15–25% protein).
Indications: usually used after the acute phase of illness, to correct a plasma volume deficit.
Cautions: history of cardiac or circulatory disease.
Contraindications: cardiac failure, severe anaemia.
Side effects: hypersensitivity reactions (including anaphylaxis) with nausea, vomiting, increased salivation, fever, tachycardia, hypotension and chills reported.
Isotonic solutions: human albumin solution 4.5%, human albumin solution 5%, Albunorm® 5%, Octalbin® 5% and Zenalb® 4.5%.
Concentrated solutions (20%): human albumin solution 20%, Albunorm® 20%, Flexbumin® 20%, Octalbin® 20%, Zenalb® 20%.
Dextran
This is derived from glucose: Dextran 70 (BNF non-proprietary), RescueFlow® (Dextran 70 intravenous infusion 6% in sodium chloride intravenous infusion) – avoid in pregnancy.
Gelatin
Gelatin is derived from a bovine source: Gelofusine®, Geloplasma® (manufacturer of Geloplasma recommends avoid at the end of pregnancy), Isoplex® and Volplex®.
Starches
Hydroxyethyl starch (HES) is derived from amylopectin (a soluble polysaccharide).
NB: It is not within the remit of this book to discuss blood products but it MUST be remembered that blood products are drugs and therefore the normal processes in relation to drug administration must be followed alongside the additional requirements set down in Trust policies and procedures.
References and Recommended Reading
. Centre for Maternal and Child Enquiries 2011 Saving Mothers’ Lives: Reviewing Maternal Deaths to Make Motherhood safer: 2006–2008. The 8th Report of the Confidential Enquiries into Maternal Deaths in the United Kingdom. Available http://www.oaa-anaes.ac.uk/assets/_managed/editor/File/Reports/2006-2008%20CEMD.pdf [accessed 2 March 2012]
Hofmeyr G.J., Neilson J.P., Alfreirevic Z., Crowther C., Duley L., Gulmezoglu M., Gyte G.M., Hodnett E.D. Pregnancy and Childbirth – A Cochrane Pocketbook. London: Wiley Cochrane Series; 2008.
Joint Formulary Committee. British National Formulary (BNF) 62. London: Pharmaceutical Press; 2011.
Jordan S. Pharmacology for Midwives: The Evidence Base for Safe Practice, second ed. Basingstoke: Palgrave Macmillan; 2010.
Roberts J., Bratton S. Colloid volume expanders: problems, pitfalls and possibilities. Drugs. 1998;55:621–630.
Royal College of Nursing (RCN). Right Blood, Right Patient, Right Time: RCN Guidance for Improving Transfusion Practice. London: RCN; 2006.
Royal College of Obstetricians and Gynaecologists (RCOG). Blood Transfusion in Obstetrics. London: RCOG; 2007. Greentop Guideline No. 47
Rubin P.C., Ramsey M. Prescribing in Pregnancy, fourth ed. Oxford: BMJ Books/Blackwell Publishing; 2007.
Scott W. Fluids and Electrolytes Made Incredibly Easy!. London: Lippincott Williams and Wilkins; 2010.
Volans G., Wiseman H. Drugs Handbook 2012–2013, thirty third ed. Basingstoke: Palgrave Macmillan; 2012.