Contents
Introduction
Intravenous fluid therapy (IV fluids) are used when the patient’s need for fluid cannot be met by the oral or enteral route. The two main scenarios where this occurs are:
- In patients are nil by mouth (NBM) – typically surgical patients before, during and also sometimes after surgery. This is often referred to as maintenance fluids
- In the acutely unwell patient for fluid resuscitation due to volume depletion.
Indications for IV fluids in the acutely unwell patient include; sepsis, dehydration (for example due to gastroenteritis, or in AKI), shock (including in trauma), correction of electrolyte imbalances (such as hypo/hypernatraemia or hypo/hyperkalaemia), during surgery, mixed with drugs for IV administration, in burns, in liver failure.
IV fluids can be divided into two main categories:
- Colloids – these contain large molecules – such as albumin or synthetic starches (gelatine [Gelofusin(R)], dextran) – and are considered to maintain the administered fluid within the circulating volume more effectively
- Crystalloids – pass more freely through a semi-permeable membrane – and include fluids such as normal saline, Hartmann’s solution (aka Ringer’s lactate), plasmalyte and glucose / dextrose solutions
Crystalloids are generally preferred in most indications, except for chronic liver disease.
If in doubt, normal saline (0.9% NaCl) is appropriate to use in the vast majority of circumstances in the acutely unwell patient – including in paediatrics. Some important exceptions are discussed below.
- Note that in paediatric patients with acute dehydration an NG (nasogastric) tube is often preferred first line instead of IV fluids
If using large amounts of fluids or if the patient if hypothermic then consider using a fluid warmer during administration.
In the past couple of decades there has been a lot of debate about crystalloids vs colloids, but the theoretical benefit of colloid based fluids remaining in the circulating volume for longer in cases of volume depletion – e.g. due to trauma or dehydration – is generally NOT supported by the evidence. There has also been a trend towards the use of LESS intravenous fluid in many critically unwell patients – probably most obvious in the instance of sepsis. IV fluid in these cases will generally provide a very short-term improvement in blood pressure, but patients are at risk of fluid overload in the following days and hours. In this scenario it is generally considered more appropriate to support blood pressure with other treatments – such as the use of vasopressors. More recent guidelines and evidence support a more judicious approach to fluid use in the critically unwell patient. – Dr Tom Leach
Crystalloids
Examples include:
- Isotonic – normal saline (0.9% NaCl), Hartmann’s solution, plasmalyte
- The most commonly used crystalloids
- Hypertonic – hypertonic saline – 3% or 7.5% NaCl, mannitol
- Generally only indicated in head injury to try to reduce intracranial pressure
- Hypotonic – dextrose 5% or 10%, hypotonic saline – 0.45% NaCl)
Contents of crystalloids
| Contents (mmol.L-1) | 0.9% NaCl | Hartmann’s | Plasmalyte |
|---|---|---|---|
| Na+ | 154 | 130 | 140 |
| Cl– | 154 | 109 | 98 |
| K+ | 4 | 5 | |
| Ca2+ | 3 | ||
| Mg2+ | 1.5 | ||
| Lactate | 28 | ||
| Acetate | 27 | ||
| Gluconate | 23 | ||
| pH | 5.0 | 6.5 | 5.5 |
Hartmann’s solution
Plasmalyte and Hartmann’s solution (aka Ringer’s lactate, or compound sodium lactate) are “balanced solutions” whose electrolyte concentrations more closely resemble that of plasma. In most situations, normal saline is the most appropriate fluid.
The main advantage of Hartmann’s or plasmalyte over normal saline is the lower chloride content – which helps to prevent hyperchloraemia when large amounts of fluids are infused. The lactate is metabolised to pyruvate and subsequently to glucose, carbon dioxide and water, with the production of bicarbonate.
- Hartmann’s should be avoided in severe liver disease as there may not be sufficient liver function to metabolise the lactate
- Cation should be applied in severe renal failure due to its potassium content
Normal saline
- The amount of sodium in 0.9% NaCl is roughly the same as the extra-cellular fluid
- When administering Normal saline, about 20% of the fluid stays in the circulating volume and the rest ends up in the extra-cellular fluid
- Large volumes of NaCl can lead to hyperchloraemia which in turn can lead to acidosis
Glucose / dextrose
Dextrose is a specific molecular structure of glucose – it is the structure that is found in nature.
- These fluids contain a solution of glucose in varying concentrations from 5% to 50%
- 5% is used as an alternative to normal saline or Hartmann’s in cases of fluid resuscitation
- Stronger strengths are used to treat hypoglycaemia
- 50% is extremely irritant to veins and ideally should not be given peripherally (only via central line) but in cases of hypoglycaemia it is sometimes still given peripherally
- In patients with thiamine deficiency (typically patients with alcohol excess), the use of glucose can precipitate Wernicke’s encephalopathy, and it should be avoided
- Administering high volumes of glucose containing fluids can also cause hyponatraemia, which can lead to hyponatraemic encephalopathy
Potassium
- Potassium is often added as an additive to other solutions – usually to normal saline
- The body typically requires 1mmol/Kg/day of potassium
- In patients receiving maintenance fluids, potassium is routinely added
- In emergency resuscitation it is only typically used if the potassium is low
- The main risk with administration of potassium is the risk of causing hyperkalaemia
- Patients with renal failure or oligouria have minimal potassium losses andare at high risk of hyperkalaemia – be wary of prescribing in these circumstances
Complications
Complications of crystalloid use include:
- APO – acute pulmonary oedema
- Hypothermia – if using large amount of fluids that have not been warmed
- Acidosis
- Tissue oedema
- Electrolyte abnormalities
- Air embolism (due to incorrect administration technique)
- Infection
Colloids
Colloids contain large osmotically active molecules – such as albumin or modified gelatin. Theoretically, these large molecules can’t diffuse out of the circulation and thus through osmotic pressure should help to maintain the circulating volume. However, in practice, in unwell patients, this has not proven to be shown clinically.
- This is probably because in critically unwell patients (i.e. in sepsis) the integrity of the capillaries is altered to make them more “leaky”
- Trials with starch-based colloids in critically unwell patients have actually shown harm and they should be avoided in this scenario.
The use of colloids clinically is generally limited to cirrhotic liver disease – where the production of albumin is impaired.
Adverse effects
Risks when using IV fluids include:
- Heart failure – can increase left ventricular filling beyond the point of maximal contractility. This is true of any IV fluid when given in sufficient quantities
- Oedema – due to the sodium content in the fluids (colloids also contain sodium)
- Allergy / anaphylaxis – can occur with starch containing colloids (Gelofusin, amongst others).
Prescribing fluids
There are some excellent NICE Guideline flowcharts on prescribing fluids for fluid resuscitation and for maintenance fluids – if you are new to prescribing fluids is strongly recommend you take a look at this.
Some basic principles of IV fluid use include:
- In the acutely unwell patient with signs of shock
- Give 500ml bolus of crystalloid at a time and monitor response and reassess
- Don’t give more than 2L without expert advice
- In patients without electrolyte disturbance who require maintenance fluids, calculate their fluid requirements and prescribe accordingly:
- Give 25-30ml/Kg/day of water
- 1 mmol/Kg/day of sodium, potassium and chloride
- 50-100g a day of glucose (e.g. 1L of 5% glucose contains 50g glucose)