13 Fluids

Saline: e.g. 0.9% saline, 0.18% saline in 4% glucose.

Glucose: e.g. 5%, 10%, 20%, 50%.

Sodium bicarbonate: e.g. 1.26%, 8.4%.

Higher concentration glucose infusions may be used to prevent hypoglycaemia.

Crystalloid fluids may contain potassum chloride supplements.

Sodium bicarbonate may be used to correct metabolic acidosis, for urinary alkalinisation, etc.

As most plasma substitutes are carried in saline solutions, any additional salt containing crystalloid infusion is only needed to replace excess sodium losses.

The sodium content of 0.9% saline is equivalent to that of extracellular fluid. Therefore, salt‐containing solutions distribute throughout the extracellular fluid space.

Ringer's lactate or Hartmann's solution avoid hyperchloraemic acidosis caused by the relative excess chloride infused with 0.9% saline. Hyperchloraemic acidosis may adversely affect coagulation and renal function though human data are lacking.

A daily requirement of 70–80mmol sodium is normal although there may be excess loss in sweat and from the gastrointestinal tract. This can be provided as saline or balanced electrolyte solution.

5% glucose is used to supply intravenous water requirements. Since there are no electrolytes to favour distribution to one space or another, water distributes uniformly throughout the extracellular and intracellular spaces. The 50g/L glucose content ensures an isotonic solution, but only provides 200Cal/L. Normal requirement is approximately 1.5–2L/d.

Water loss in excess of electrolytes is uncommon but occurs in excess sweating, fever, hyperthyroidism, diabetes insipidus, and hypercalcaemia. 5% glucose is an appropriate replacement fluid for water loss.

Potassium chloride must be given slowly since rapid injection may cause fatal arrhythmias. No more than 40mmol/h should be given and even this may be dangerous in some patients. Up to20mmol/h is safer. The frequency of infusion is dictated by plasma potassium measurements.

Hypertonic sodium bicarbonate 8.4%.

Alkalinisation of urine, e.g. for salicylate overdose, treatment of rhabdomyolysis.

Alkalinisation of blood, e.g. for treatment of tricyclic antidepressant overdose.

The hypertonic (8.4%) solution (1mEq HCO₃  ^–/mL) is rarely required in intensive care practice to raise blood pH in severe metabolic acidosis.

Bicarbonate therapy is inappropriate when tissue hypoperfusion or necrosis is present.

Administration may be indicated as either specific therapy (e.g. alkaline diuresis for salicylate overdose) or if the patient is dyspnoeic in the absence of tissue hypoperfusion (e.g. renal failure).

The PaCO₂ may rise if minute volume is not increased.

Bicarbonate cannot cross the cell membrane without dissociation so the increase in PaCO₂ may result in intracellular acidosis and depression of myocardial cell function.

A decrease in plasma ionised calcium as a result of alkalinisation may also cause a decrease in myocardial contractility. Significantly worse haemodynamic effects have been reported with bicarbonate compared to equimolar saline in patients with severe heart failure.

Convincing human data that bicarbonate improves myocardial contractility or increases responsiveness to circulating catecholamines in severe acidosis are lacking. Acidosis secondary to myocardial depression is related to intracellular changes that 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.

Sodium bicarbonate 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.

Dextran: e.g. 6% Dextran 70.

Gelatin: e.g. 3.5% polygeline, 4% succinylated gelatin.

Hydroxyethyl starch: e.g. 6% hetastarch, 6% hexastarch, 6 and 10% pentastarch, 6% and 10% tetrastarch.

Medium‐term volume expansion (albumin, pentastarch, tetrastarch).

Long‐term volume expansion (hetastarch, hexastarch).

Anaphylaxis.

Interference with blood crossmatching (Dextran 70).

Nephropathy (high dose hydroxyethyl starches).

Albumin is the main provider of COP in the plasma and has a number of other functions. There is no evidence that maintenance of plasma albumin levels, as opposed to maintenance of plasma COP with artificial plasma substitutes, is advantageous.

Hyperoncotic colloids can be used where salt restriction is necessary. This is rarely necessary as plasma volume expansion relates to weight of colloid infused rather than concentration. Artificial colloids used with ultrafiltration or diuresis are just as effective in oedema states.

Polygeline is a 3.5% solution and contains calcium (6.25mmol/L). The calcium content prevents the use of the same administration set for blood transfusions. Succinylated gelatin is a 4% solution and does not contain calcium.

Hydroxyethyl starch solutions are protected from metabolism due to a high degree of substitution (proportion of glucose units substituted with hydroxyethyl groups—DS) or a high C2:C6 ratio of carbon atoms substituted. Prolonged itching related to intradermal deposition, coagulopathy, and nephropathy are complications if excessive doses of higher molecular weight hydroxyethyl starches are used.

Pentastarch and tetrastarch provide only a short‐term volume expanding effects.

Hydroxyethyl starches in balanced electrolyte solutions are available. These avoid the problem of hyperchloraemic acidosis in higher doses. There is also some evidence of less coagulation disturbance.

Free radical scavenging.

Binding of toxins.

Inhibition of platelet aggregation.

High DS and high C2:C6 ratio protect hydroxyethyl starch from metabolism.

All artificial colloids are polydisperse (i.e. there is a range of molecular sizes).

Potassium load—potassium returns to cells rapidly, but hyperkalaemia may be a problem if blood is stored at room temperature.

Jaundice—haemolysis of incompatible or old blood.

Pyrexia—immunological transfusion reactions to incompatible red or white cells or platelets or blood products

DIC—partial activation of clotting factors and destruction of stored cells, either in old blood or when transfusion is incompatible.

Anaphylactoid reaction—urticaria is common and probably due to a reaction to transfused plasma proteins; if severe, it may be treated by slowing the transfusion and giving chlorpheniramine 10mg IV/IM. In severe anaphylaxis, in addition to standard treatment, the transfusion should be stopped and saved for later analysis. A sample should be taken for further crossmatching.

Transmission of disease—including viruses, parasites (malaria), prions.

Transfusion‐related acute lung injury (TRALI) and other immune reactions.

A multicentre trial suggested liberal transfusion in the critically ill produced less favourable outcomes, particularly in younger, less sick patients, than using a trigger haemoglobin of 7g/dL. This was performed with non‐leukodepleted blood; the validity with leukodepleted blood now in common use is uncertain.

Platelets.

Concentrates of coagulation factors, e.g. cryoprecipitate, factor VIII concentrate, factor IX complex, Octaplex.

Recombinant technologies, e.g. factor VIIa, factor VIII.

Haemophilia (cryoprecipitate, factor VIII, recombinant factor VIIa).

von Willebrand's disease (cryoprecipitate).

Fibrinogen deficiency (cryoprecipitate).

Christmas disease (factor IX complex).

Platelet concentrates are viable for three days when stored at room temperature. Viability decreases if they are refrigerated. They must be infused quickly via a short giving set with no filter.

Indications for platelet concentrates include platelet count <10×10⁹ or <50×10⁹ with spontaneous bleeding or to cover invasive procedures and spontaneous bleeding with platelet dysfunction. They are less useful in conditions associated with immune platelet destruction (e.g. ITP).

A 15mL vial of cryoprecipitate contains 100U factor VIII, 250mg fibrinogen, factor XIII, and von Willebrand factor and is stored at –30°C.

In haemophilia, cryoprecipitate is given to achieve a factor VIII level >30% of normal.

Factor VIII concentrate contains 300U factor VIII per vial. In severe haemorrhage due to haemophilia, 10–15U/kg are given 12‐hourly.

Recombinant factor VIIa is indicated for control of bleeding in patients with haemophilia with inhibitors to factors VIII or IX, or congenital factor VII deficiency. It forms complexes with exposed tissue factor and is not dependent on the presence of factors VIII or IX. It has been shown to reduce blood transfusion requirements in major blunt trauma. Success has been reported in cases of uncontrollable intra‐operative bleeding (90mcg/kg repeated every 2–3h until bleeding stops).

Octaplex is a prothrombin complex concentrate for the substitution of factors II, VII, IX, and X in treatment or prophylaxis of hereditary and acquired coagulation factor disorders, e.g. warfarin overdose.