Fluid Administration

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Questions Received:

  1. Is there any evidence of benefit, and what is the physiology of sub-cut fluid administration of such fluids to immobile eldery patients?

  2. Over what length of time can sub-cut fluids be used where the patient is unable to tolerate oral thickened fluids? At what point should long-term parenteral feeding be considered?

  3. Hello, I am a student nurse, could you help me please understand what crystalloids and colloids are and what is the difference between them, ie. why would you use one rather than the other. Hope you can help.

Responses:

Is there any evidence of benefit, and what is the physiology of sub-cut fluid administration of such fluids to immobile eldery patients?

9th May 1999

The technique by which solutions are infused into the subcutaneous tissues is known as hypodermoclysis. This procedure is adopted if a person's oral fluid intake is deficient and other methods for meeting fluid and electrolyte needs are not feasible. It may be undertaken, for example, if the intravenous route is inappropriate because of fragility or sclerosis of the veins, or if the person is not be able to tolerate or fully co-operate with an intravenous approach. It has to be remembered that absorption of fluid subcutaneously will be quite slow, especially in an immobile person, and therefore the infusion will run more slowly than an intravenous infusion. The fluid enters the extracellular tissue fluid and is either drained by the lymphatic system or enters the blood plasma at the venous ends of capillary networks in the subcutaneous tissues.

The need to provide a subcutaneous infusion might arise because of an acute illness that results in dehydration (e.g., flu, diarrhea), or dehydration linked with advanced cancer. Administering fluids parenterally is a substitute for the preferred oral (enteral) route, and the decision should be made on the basis of a careful assessment taking into account the problems related to dehydration, the potential risks and benefits of fluid replacement, and the patient’s and family’s wishes (Steiner and Bruera, 1998).

The rate at which subcutaneous fluids will be administered is likely to be in the region of 500 ml over 12-16 hrs. Normally only crystalloid solutions are used. The site will need to be checked regularly, and the infusion re-regulated if absorption is delayed. As the total volume administered over 24 hrs will be unlikely to exceed 1 litre, it can be appreciated that subcutaneous fluid administration acts as a supplement to oral intake and does not replace it.

Hypodermoclysis is an effective method of giving fluid to elderly people and in recent years has been used more commonly (Lipschitz et al, 1991; Noble-Adams, 1995; Mansfield, Monaghan, and Hall, 1998). It has the advantage that it can be administered in a chronic care setting (Worobec and Brown, 1997), and this reduces the need to transfer the elderly client to an acute care hospital, which might be a stressful experience. The main problem with this technique is the possible occurrence of fluid imbalance in subjects with existing homeostatic disorders (Dutertre and Constans, 1991). For this reason, hypodermoclysis should not be used in emergencies.

References

Over what length of time can sub-cut fluids be used where the patient is unable to tolerate oral thickened fluids? At what point should long-term parenteral feeding be considered?

21st June 2000

In theory subcutaneous fluid/s could be administered indefinitely, provided that the potential problems of localised infection and the possibility of tissue necrosis could be overcome. In practice, though, subcutaneous fluids are usually administered for limited periods. It is important to keep in mind that the subcutaneous route is normally used to supplement fluid/s that are being consumed orally, or to provide fluid over the short term until other routes become available. An exception might be when it is administered to a person during the terminal stages of their illness as an attempt towards preventing dehydration.

Examples of the fluids normally administered are glucose 5%, sodium chloride 0.9% and sodium chloride 0.18% with glucose 4%. Potassium chloride may be given, as prescribed, in association with any one of these solutions.

Such preparations enable fluid and electrolyte requirements to be met and up to 3 litres may be given to the average adult over a twenty four-hour period. (The average water requirements for an adult over a 24-hour period is in the region of 1.5 to 2.5 litres.) However, such a regime will not contribute towards meeting a person's nutritional and metabolic needs, and after approximately seventy-two hours, depending on a person's weight, age and sex, a catabolic state would ensue. Therefore it is necessary to plan and implement procedures that will meet the person's nutritional requirements, for example a fine bore naso-gastric tube, a jejunostomy feeding line, or Total Parenteral Nutrition (TPN).

Suggested Reading

Hello, I am a student nurse, could you help me please understand what crystalloids and colloids are and what is the difference between them, ie. why would you use one rather than the other. Hope you can help.

12th May 2004

Intravenous fluids are widely used in treatment, especially in the intensive care unit. Prompt administration of a crystalloid or colloid solution can save lives by restoring fluid balance, maintaining cardiac output, and promoting the delivery of oxygen and nutrients to the tissues and removal of waste products. However, there is an ongoing debate about which type of fluid to use. Before looking at the evidence, it will be helpful to be clear about what crystalloids and colloids are, and why they are given during fluid replacement.

The Scottish chemist Thomas Graham discovered in the 1860s that certain substances (for example: glue, gelatine, or starch) could be separated from certain other substances (for example sugar or salt) by dialysis. He gave the name ‘colloid’ (colloid means ‘glue’ in Greek) to substances that do not diffuse through a semipermeable membrane such as parchment or cellophane, and the name ‘crystalloid’ to those which do diffuse and which are therefore in true solution.

In a true solution the particles of dissolved substance are much smaller than colloidal particles. So the main distinction is one of particle size - tiny particles form true crystalloid solutions, while slightly larger particles such as large, non-dissociated organic molecules form colloidal solutions.

A colloid consists of two materials - one is a fluid or gas in which the other material is dispersed as small particles (an alternative name is ‘emulsion’). The colloid looks evenly dispersed but is generally rather murky or opaque to the naked eye because the particles scatter light - think for example of fog and milk. In a clinical setting the colloidal particles are generally large molecules such as proteins or carbohydrates suspended in water. Although the particles are larger than those in a true solution, they are still small enough to remain evenly dispersed without settling. (If the particles are still larger than those in colloids, the mixture is referred to as a ‘suspension’. In this case, the particles will tend to separate out after a while, either sinking to the bottom or floating to the top.)

Fluid Compartments

Recall that the body has three major fluid compartments - intracellular fluid (the fluid within cells), interstitial fluid (fluid between cells), and blood plasma. These fluids are ‘salty’, meaning that they contain ions of sodium, potassium, and chloride, but there are differences in exact composition between the compartments. The movement of water between the compartments will be driven by osmotic and hydrostatic differences. All dissolved substances will contribute to the osmotic pressure of a fluid. However, solutes such as sodium chloride which dissociate into ions when they dissolve in water will exert a proportionately greater osmotic effect than non-dissociating molecules such as starch or proteins.

In normal plasma, the plasma proteins are the major colloids present. Plasma proteins are important in capillary fluid dynamics because they draw most of the fluid back into the distal ends of capillaries after it has been pushed out into the interstitial spaces by the hydrostatic pressure of the blood entering the capillary. (The remaining excess fluid will be collected by the lymphatics.)

Crystalloids

In a clinical setting the most commonly-used crystalloid solutions include normal saline (a solution of sodium chloride in water), lactated Ringer's solution, and dextrose in water. Normal saline and lactated Ringer’s solution are considered first-line agents for restoring extracellular electrolyte and volume deficits. Dextrose in water is thought of as ‘free water’ - the dextrose is rapidly metabolised and the water is freely distributed to both intracellular and extracellular compartments; it does not specifically increase plasma volume.

Colloids

Colloid solutions are made up with large molecular-weight substances such as proteins (eg: albumin, gelatin) or carbohydrates (eg: starch, dextran). Colloids remain in the blood plasma longer than crystalloids. They do not readily cross capillary walls and can draw water from the interstitial space into the plasma, increasing its volume. Some colloids are made up of evenly-sized molecules, for example, albumin, while others have a variety of different molecule sizes and shapes, for example, starch.

Which to Use?

Crystalloids are well tolerated and easy to administer. They have low cost, are easy to store and are readily available. There will be no religious objections to their use. The most common adverse reaction is peripheral oedema resulting from administration of too much fluid. The primary limitation of crystalloids is the amount of fluid needed to replace plasma volume - it is estimated that 5 litres of crystalloid would replace only 1 litre of blood loss because of dispersal of the crystalloid into the interstitial compartment.

Proponents of colloid resuscitation argue that colloids lead to a more rapid and effective correction of the intravascular volume and do not cause the peripheral oedema that can be caused by crystalloids. However, opinions differ as to which colloid is best. Different colloids vary in their molecular weight and therefore in the length of time they remain in the circulatory system. Because of this and their other characteristics, they may differ in their safety and efficacy (Bunn, Alderson, and Hawkins, 2004). From this review, there is no evidence that one colloid solution is more effective or safe than any other. The two main problems associated with the use of colloid solutions are their higher cost compared with crystalloid solutions and the small but significance incidence of adverse reactions, especially anaphylactoid reactions.

So when to use crystalloids and when to use colloids? There is a great deal of controversy on which fluids should be used during the acute resuscitation phase to deal with hypovolaemia. The controversy remains despite multiple meta-analyses of published studies (Bellomo, 2002). There appears to be no evidence from randomised controlled trials that resuscitation with colloids reduces the risk of death compared to the use of crystalloids in patients with trauma, burns, and following surgery (Alderson et al, 2004). Colloids such as dextran and hydroxyethyl starch are more effective than crystalloids at increasing intravascular volume, but they carry an increased risk of complications and mortality (Lighthall and Pearl, 2003).

References

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