Crystalloids Types Saline e.g. 0.9% saline, Hartmann’s solution 0.18% saline in 4% glucose. Glucose : e.g. 5% glucose, 10% glucose, 20% glucose. Postassium chloride Sodium bicarbonate : e.g. 1.26%, 8.4%. Uses Crystlloid fluids are used to provide the daily requirements of watr and electrolytes. They should be given to critically ill patients as a continuous background infusion to supplement fluids given during feeding or to carry drugs Higher concentration glucose infusions are used to prevent hypoglycaemia. Potassium chloride is used to supplement crystalloid fluids. Correction of metabolic acidosis (sodium bacarbonate) Routes IV

Notes Plasma volume should be maintained or replaced with colloid solutions since crystalloids are rapidly lost from the plasma. It should be noted that plasma substitutes are carried in 0.9% saline. So that the majority of critcally ill patients only require 0.9% saline infusions for excess loss. Sodium content of 0.9% saline is equivalent to that of extra cellular fluid. A daily requirement of 70-80mmol sodium is normal although there may be excess loss in sweat and from the gastrointestinal tract. Hartmann’s solution has no practical advantage over 0.9% saline for fluid maintenance. It may, however, be useful if large volumes of crystalloid are exchanged (e.g. during continuous haemofiltration) to maintain acid –balance.

5% glucose is used to supply intravenous water requirements, the 50g/L glucose being present to ensure an isotonic solution. Normal requirement is 1.5-2.0L/day. Water loss in excess of electrolytes is uncommon but occurs in excess sweating, fever, hyperthyroidism diabetes insipidus and hypercalcaemia. Potassium chlorid must be given slowly since rapid injection may cause fatal arrhythmias. No more than 40mmol/h may be given although 20mmol/h is more usual. Frequency of infusions are predicted by plasma potassium measurements.

Ion content of crystalloids (mmol/L) Na+ K+ HCO3 C1 Ca2 0.9% saline 150 150 Hartmann’s 131 5 29 111 2 0.18% saline in 30 30 4% glucose Ion content of gastrointestinal fluids (mmol/L) H+ Na+ K+ HCO3 C1 Gastric 40-60 20-80 5-20 150 100-150 Biliary 120-140 5-15 30-50 80-120 Pancreatic 120-140 5-15 70-110 40-80 Small bowel 120-140 5-15 20-40 90-130 Large bowel 100-120 5-15 20-40 90-130

Sodium Bicarbonate Type Isotonic sodium bicarbonate 1.26% Hypertonic sodium bicarbonate (1mmol/ml) 8.4% Uses Correction of metabolic acidosis Alkalinisation of urine Routes IV

Notes Sodium bacarbonate may be given as an isotonic (1.26%) solution to correct acidosis associated with renal failure or to induce a forced alkaline diuresis. The hypertonic (8.4%) solution is rearely required in intensive care practice to raise the pH to >7.0 in the serve metabolic fusion or necrosis is present Administration may be indicated as either specific therapy (e.g. alkaline diuresis for salicylate overdose), or if the patient is symptomatic (usually dyspnoeic) in the absence to tissue hypoperfusion (e.g. renal failure). The PaCO2 may rise in minute volume is not increased. Bicarbonate anot cross the cell membrane without dissociation so the increase in PaCO2 may result in intracellular acidosis and depression of myocardial cell function.

Convincing human evidence that bicarbonate improves myocardial contractility or increases responsiveness to circulating catecholamines in severe acidosis is lacking though anecdotal success has been reported. Acidosis relating to myocardial depression is related to intracellular changes which are not accurately reflected by arterial blood chemistry. Excessive administration may cause hyperosmolality, hypernatraemia hypokalaemia and sodium overload. Bicarbonate may decrease tissue oxygen availability by a left shift of the oxyhaemoglobin dissociation curve. Soidum bacarbonate does have a place in the management of acid retention or alkali loss, e.g. chronic renal failure, renal tubular acidosis, fistulae, diarrhoea, Fluid and potassium deficit should be corrected first.

Ion content of sodium bacarbonate (mmol/L) Na+ K+ HCO3 C1 Ca2 1.26% sodium 150 150 Bacarbonate 8.4% sodium 1000 1000 bacarbonate

Colloids Types Albumin: e.g. 4.5-5%, 20-25% human albumin solution Dextran: e.g. 6% Dextran 70 Gelatin: e.g. 3.5% polygeline (Haemaccel), 4% succinylated gelatin (Gelofusion) Hydroxyethyl starch: e.g. 6% hetastarch (Elo-HAES, Hespan), 6 & 10 pentastarch (Pentaspain, HAES-steril) Uses Used for maintenance of plasma volume and acute replacement of plasma volume deficit. Short term volume expansion (gelatin, dextran) Medium term volume expansion (albumin, pentastarch) Long term volume expansion (hetastarch) Routes IV Side effects Dilution coagulopathy Anaphylaxis Interference with blood cross matching (Dextran 70)

Notes Smaller volumes of colloid are required for resuscitation with less contribution to oedema. Maintenance of plasma colloid osmotic pressure (COP) is a useful effect not seen with crystalloids but they contain no clotting factors or other plasma enzyme systems. Albumin is the main provider of COP in the Plasma and has a number of other functions. However, there is no evidence that maintenance of plasma albumin levels, as opposed to maintenance of plasma COP with artificial plasma substitutes, is advantageous.

Albumin 20-25% and Pentaspan 10% are hyperonocotic and used to provide colloid where salt restriction is necessary. This use is rearely necessary in intensive care where it has been shown that plasma volume expansion is related to the weight of colloid infused rather than the concentration. Artificial colloids used with ultrafiltration or diuresis are just as effective in oedema states. Polygeline is a 3.5% solution and contains calcium (6.25 mmol/L) The calcium contents prevents the use of the same administration set for blood transfusion. Succinylated gelatin is a 4.5% solution with a larger molecular weight range than polygeline giving a slightl longer effect. This and the lack of calcium in solution make this more useful solution than polygeline for short term plasma volume expansion.

In patients with capillary leak there is onsiderable leak of albumin and smaller molecular weight colloids to the interstitum. In these caes it is probably better to use larger molecular weight colloids such as hydroxyethyl starch. Hetastarch is usually a 6% solution with a high degree of protection from metabolism. The molecular weight ranges vary but molecular sizes are large enough to ensure a prolonged effect. These are the most useful colloids in capillary leak. Pentastarch has a lower degree of protection from metabolism and therefore a shorter effect.

Unique features of albumin Transport of various molecules Free radical scavenging Binding of toxins Inhibition of platelet aggregation Relative persistence of colloid effect Albumin +++ Dextran 70 ++ Gelofusin + Haemaccel + Hespan ++++ Pentaspan ++ Elo-HAES ++++ HAES-Steril ++ Presistence is dependent on molecular size and protection from metabolism. All artificial colloids are polydisperse (i.e. there is a range of molecular sizes).