blood
colloids
crystalloids
electrolytes (potassium, bicarb, etc)
trace elements
parenteral nutrition
drugs for ketosis
Giving fluids iv is the quickest way to get them to where they are required. Some knowledge of physiology is required to get the dose right - overdosing can be fatal. Too much fluid in the circulation will increase preload on the heart. This is not good for animals with heart disease; in normal animals, signs of congestive heart failure will start to show. Pulmonary and peripheral oedema are most obvious. Pulmonary oedema is often fatal. If an animal is in shock, its veins may be difficult to find and a cut down may be necessary.
Electrolytes such as potassium and bicarbonate are needed inside cells but are given iv - it takes time for them to diffuse into cells. If the solutions are given too quickly, it is possible to have an excess in the blood at the same time as a deficit in the tissues. Since the heart is one of the organs with the best blood supply, this can lead to arrhythmias.
The circumstances in each animal will be different. The only safe way of using fluids is to monitor the effects of treatment closely. Central venous pressure measurement is very useful - at the very least you should look at the large veins to see if they are distended. CVP can be measured with an improvised water manometer (bits of giving set and a 3 way tap) connected to a central vein.
Whole blood is the fluid of choice for major blood loss but it is expensive and time consuming to collect and store. Blood is usually taken into flexible bags containing acid citrate dextrose (ACD) or citrate dextrose phosphate (CDP) (see anticoagulant notes). ACD will preserve red cells in blood stored at 4˚C for 3 weeks, CDP for 4 weeks. Clotting factors and platelets will be degraded in hours.
Indications
used where RBCs are required
acute bleeding - PCV below 20%
chronic problems - PCV below 15% (dog), 10% (cat)
Packed cells (what is left after plasma has been removed) are used where only RBCs are required and suspended in saline before use.
Fresh blood (collected using ACD or CPD but not stored) is used where RBCs and / or clotting factors and / or platelets are required. Beware of transfusion reactions (see anaesthesia notes). There is also the potential for spread of infections, parasites and tumours.
There are no satisfactory substitutes for blood yet but since there is a potentially enormous (human) military market a lot of time and money is being expended looking for a fluid which can carry oxygen, be infused without worries about reactions and has a long shelf life. The nearest so far are perfluorocarbon mixtures which do all these things but are not broken down or excreted by the body. One product is on sale in Japan but worries about long term effects mean that it has not been licensed anywhere else. Cross linked haemoglobin solutions (Oxyglobin) have recently been developed overseas and work in dogs but are not available in NZ yet.
These stay in the blood vessels where they maintain blood volume.
Fresh frozen plasma, if collected, separated and frozen immediately, is a useful source of clotting factors as well as a plasma expander. Lasts about 12 months at -80˚C or 3 months at -20. Collecting, separating and storing takes time and equipment. There is the possibility of spreading diseases by tranfusing plasma. Human plasma is sterilised to kill HIV, but this is never done in veterinary practice. Mild allergic reactions are common.
Gelatin solutions (Haemaccel, Gelofusin) are the most widely used plasma expanders overseas. Useful duration of effect 2 - 3 hours. They are ridiculously expensive in NZ, although the price is coming down. They are made from cross linked bovine gelatin from (supposedly) BSE free countries.
Hydroxyethyl starch solutions are stable, have a long plasma half life (about 8 hours), a long shelf life - ideal but very expensive.
Anaphylactic reactions to all of these have been reported in people.
Dextrans are obsolete as plasma expanders. They interfere with blood clotting and are now only used (rarely) for this purpose. Lower molecular weight dextrans (40kDa) can cause kidney failure. Avoid.
These move rapidly out of the blood vessels into the ECF, but can still be useful to expand the blood volume in emergency.
Sodium chloride 0.9% solution (normal saline) is distributed throughout the ECF. Its lack of bicarbonate or a precursor tends to lower pH, but in acidosis, increased blood volume may improve kidney blood flow and thus kidney regulation of pH leading to a reduced acidosis. Long term use will require extra potassium.
Sodium chloride 0.18% and dextrose 4% (dextrose saline) solution is a useful sodium and water maintenance solution.
Dextrose 5% solution is used as a means of supplying water. The dextrose is quickly metabolised; it is not enough to provide significant energy to the animal. Distributed throughout the body water. Do not give sc - electrolytes diffuse into the pool of dextrose solution drawing water with them and making the situation worse.
Ringer's solution is similar to normal saline but with some potassium. Also tends to lower pH. Not available in NZ.
Sodium lactate infusion (Hartmann's solution, lactated Ringer’s, ) is commonly used for ECF replacement as it contains lactate (metabolised to bicarbonate). Will tend to raise the pH.
Sodium chloride 7% solution (hypertonic saline) (3% or 5% are sometimes used) is used as a plasma volume expander. It draws water out of the ECF into the circulation which increases cardiac output and tissue perfusion in hypovolaemia. It may also have a direct stimulant effect on the heart. Effects only last 20 - 30 mins so normal crystalloids and / or colloids must be given as well. The small volume of injection makes hypertonic saline (4ml/kg iv followed by normal fluids) useful as a first aid measure in large animals. It is used for first line treatment of hypovolaemia - more dilute solutions / water to drink must be given afterwards; and in head and lung injuries (draws oedema fluid into the circulation). It should not be used in severe dehydration.
Potassium chloride solution comes in several strengths which must be diluted before use. They are usually mixed into a bag of crystalloid. Note that injecting potassium into a bag is not the same thing as mixing it with the bag's contents - a bolus of potassium will rapidly stop the heart. Longer term fluid therapy (>12 hours) usually requires potassium supplementation. Make sure that you label the bag in an obvious way.
Hyperkalaemia can be treated by correcting acidosis, giving insulin in 5% dextrose to promote uptake of potassium by cells and by giving calcium borogluconate to oppose the cardiac effects of potassium.
Sodium bicarbonate is used to correct acidosis. Treatment should be guided by a blood gas sample. An 8.4% solution is usually used because it contains 1mmol/mL which makes the sums easier. If you come across other concentrations you will have to do some more maths. For instance, a 5% solution contains 50g/L. The molecular weight of sodium bicarbonate is 84, so a 5% solution contains 50/84 = 0.6mol/L (mmol/mL).
Bicarbonate must be mixed with other solutions before use. Normal saline is the fluid usually used - bicarbonate is incompatible with anything containing calcium (many other solutions and most drugs) (calcium carbonate is insoluble and precipitates out). Bicarbonate is distributed throughout the body water but administration is calculated to replace the circulating deficit, since correcting the acidosis will lower plasma potassium levels. A blood gas sample is taken and the amount of bicarbonate required is obtained by multiplying the base excess (a negative number in acidosis!) by the blood volume (roughly 10% of body weight).
Beware of overdose - this will cause a paradoxical acidosis in the CNS. Give too little bicarbonate and reassess the animal rather than giving too much.
Calcium (boro) gluconate solutions (the boron is added only to improve solubility) are used in cows and ewes for milk fever (40% solution) and in bitches for eclampsia (10% solution). The amount of calcium given to cows does not correct the deficiency; the aim is merely to tilt the balance in favour of homoeostasis. Administration of calcium salts sc causes intense vasoconstriction and sometimes necrosis of the overlying skin so give them iv.
Magnesium sulphate / chloride solutions are used in cows for grass staggers. Intravenous administration causes muscle paralysis and can stop the heart - it should be given sc.
Compound calcium / magnesium / phosphorous mixtures are often given iv to cows where it is not clear which mineral or combination of minerals is deficient. Given iv in grass staggers followed by magnesium solution sc.
Usually given as an oral supplement to ruminants. Remember that animals only need a trace - any more will probably be toxic. Selenium is very easy to overdose - beware of Se injections in animals which have been dosed orally or been on pasture with Se supplemented fertiliser.
Avoid if at all possible! Consider enteral feeding by nasogastric or pharyngostomy tube before embarking on parenteral feeding. A dedicated catheter into a central vein is required; maintenance of this catheter and prevention of phlebitis and infection is tricky.
Lipid emulsions and amino acid mixtures are used. Both are expensive, are ideal bacterial growth media and can be irritant. Care is required with iv glucose since it causes an osmotic diuresis.
Ketosis occurs when there is a sudden increase in demand for energy, e.g. at the start of lactation in dairy cows or towards the end of pregnancy with twins in beef cows and ewes. The liver becomes depleted of glycogen and undergoes fatty change which leads to anorexia which exacerbates the problem. Glucocorticoids are sometimes used to promote gluconeogenesis but can cause premature parturition. Prevention by sorting out the diet is better than cure.
Propylene glycol, sodium propionate and glycerol are all rapidly metabolised to glucose in cows and ewes. Dose varies with the preparation / severity of the condition. These drugs are given orally as glucose precursors to break the vicious cycle - not to provide all the energy requirements of the animal.
