Sam Platt, RGN, ENB 100.
Lead Nurse/Matron Critical Care at The Queen Elizabeth Hospital NHS Trust, Woolwich
Patients receive intravenous fluids when they are unable to maintain adequate fluid balance and need replacement therapy. This may be due to an inability to take hydration orally because of illness or surgery, or as a result of fluid depletion or loss resulting from trauma, burns or overwhelming infection. The maintenance of fluid balance is essential to ensure homeostasis.
In health fluid balance is maintained by input (from food and drink) and output (as urine and faeces). The symptoms of dehydration and hypovolaemia include hypotension, tachycardia, falling urinary output, and cooling of the peripheries. Left untreated the patient will become shocked and unable to deliver oxygen to the tissues. Fluid overload results in breathlessness, which may lead to pulmonary oedema, and generalised oedema with warming of the skin, particularly in the limbs and sacral area.
Crystalloids are solutions of ions (usually sodium and chloride) and/or sugars (glucose) contained in water. Most solutions in clinical use are isotonic with plasma and their sodium content determines their final distribution within the body. The more sodium in the chosen fluid, the more the fluid will be retained within the extravascular space. Solutions with less (or no) sodium distribute more evenly throughout the total body water. Thus, the more sodium found within your crystalloid solution, the better it will be as a plasma expander. However, care must be taken not to induce hypernatraemia.
Sodium chloride 0.9% contains 150mmol of sodium per litre. This is an isotonic solution and is useful as a plasma expander and a treatment for sodium depletion. Glucose 5% is essentially water with some calorie content. As the glucose is primarily metabolised, it produces little or no plasma expansion and is not useful as a resuscitation fluid. Solutions of glucose 4% and sodium chloride 0.18% contain 30mmol of sodium per litre. Again, this is isotonic and is a useful maintenance fluid, but may lead to dilutional hyponatraemia.
Colloids are solutions containing large molecules that contribute to the oncotic pressure at the vascular endothelium. They produce a greater volume expansion than crystalloids as they are, in the short term, mainly retained within the extravascular space. But this effect is temporary, depending on the type of colloid used.
Albumin solutions are derived from pooled donations of human serum. The usual concentrations of albumin solutions available are 4.5% (isotonic) or 20% (hypertonic). In theory giving 1g of albumin expands plasma by 18ml, and 4.5% albumin contains 4.5g in 100ml and 20% contains 20g in 100ml. The higher-strength solution also draws fluid osmotically into plasma.
Gelatins, starches and dextrans are synthetic colloids containing molecules of varying weights. Two gelatins are commonly used - Gelofusine or Haemaccel. Gelofusine has the longer duration of action due in part to its increased molecular size. Gelatins provide a minimal plasma expansion effect, similar to sodium chloride 0.9%, but slightly longer lasting. The gelatin molecules are retained more in renal impairment and so their effect may be increased in this setting. Starches have effects on clotting, both by dilution and interference with clotting factors. They can cause severe itching. The maximum volume that can be infused over 24 hours limits use.
Crystalloid or colloid solutions
The usual treatment for patients requiring fluid resuscitation has been colloid solutions. However, systematic reviews (Schierhout and Roberts, 1998, Choi et al, 1999) show an increase in mortality with their use or no apparent difference in pulmonary oedema, mortality or length of stay between isotonic crystalloid and colloid resuscitation. As colloid solutions are more expensive, their use is not cost-effective. Docherty and McIntyre (2002) recommend isotonic crystalloid solutions as the fluid replacement of choice, unless blood products are required, as crystalloid and colloid solutions dilute the existing haemoglobin (Hand, 2001). There is no risk of anaphylaxis with crystalloids.
Physical assessment enables the nurse to determine the patient’s fluid balance status. As well as observing the temperature of the patient’s limbs, and the presence or absence of oedema, capillary refill time of less than two seconds implies adequate hydration, and more than two seconds implies reduced blood flow and therefore hypovolaemia.
Abnormal vital signs tell the nurse about altered fluid balance, and require more frequent observation recording, while measures such as fluid infusion take place. Combined with physical findings, abnormal blood chemistry results such as elevated serum sodium and urea indicate dehydration, while a low level of sodium may indicate fluid overload. The chemistry results help in choice of fluid. Avoid isotonic sodium chloride if serum sodium is elevated.
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