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Dear Sir/ Editor,
Dr Smith makes relevant and interesting points regarding the terminology used for fluids, which can be used for both “resuscitation” purposes and “maintenance” therapy, and we thank him for his interest and response.
The purpose of this clinical question was to review the current evidence for paediatric patients in relation to “ balanced fluids”, a term emerging in the medical literature. NICE recommends using any isotonic crystalloid, which covers a wide range of sodium concentration from 130 to 154mmol/L (reference 1 in the article).
The loss of electrolytes, either from the gut or as a result of renal impairment, needs regular clinical review. We observe that repeated bicarbonate measurements are not regularly undertaken after initial assessment or following admission and it is important to remind trainees to consider these losses, hence our recommendation of daily monitoring of electrolytes. By following this approach, appropriate individualised adjustments can be made to the fluid prescription of patients as necessary.
Our conclusion from this question highlighted that research needs to be undertaken in the paediatric population of bicarbonate/ lactate containing fluids to determine whether this may affect acute kidney injury and other specific clinical outcomes. We agree attention to detail is always necessary when caring for infants and children receiving intrav...
Our conclusion from this question highlighted that research needs to be undertaken in the paediatric population of bicarbonate/ lactate containing fluids to determine whether this may affect acute kidney injury and other specific clinical outcomes. We agree attention to detail is always necessary when caring for infants and children receiving intravenous fluids of any type.
Dr Patel & Dr Hulton
Having just read this article I am concerned about the terminology used as I am not sure it truly reflects the clinical problem posed. The article refers to "maintenance" fluids but the question asked relates more to “resuscitation” fluids.
It is important to be clear as to the aim of treatment in the individual patient when prescribing fluids rather than just following a guideline. The paper debates the relative merits of 0.9% sodium chloride and balanced fluids as “maintenance” fluids. To my mind “maintenance” fluids are administered to patients who have a replete extracellular fluid (ECF) volume. If ECF volume is low then “resuscitation” fluids are required. “Maintenance” and “resuscitation” fluids have different roles and therefore might be expected to have different characteristics.
As the article refers to “maintenance” fluids I will deal with these first. This fluid is needed to replicate the fluid that the patient would normally be drinking but for a variety of reasons may not be able to ingest. It should be differentiated in turn from "replacement" fluid which is the fluid given on top of the "maintenance" fluid when patients have fluid losses in excess of those normally anticipated. This includes diarrhoea, vomiting and fluid from surgical drains. The fluid used for "replacement" needs to match the composition and volume of the fluid being lost. Once "resuscitation" and "replacement" fluid...
As the article refers to “maintenance” fluids I will deal with these first. This fluid is needed to replicate the fluid that the patient would normally be drinking but for a variety of reasons may not be able to ingest. It should be differentiated in turn from "replacement" fluid which is the fluid given on top of the "maintenance" fluid when patients have fluid losses in excess of those normally anticipated. This includes diarrhoea, vomiting and fluid from surgical drains. The fluid used for "replacement" needs to match the composition and volume of the fluid being lost. Once "resuscitation" and "replacement" fluids have been taken care of and the ECF compartment is full, "maintenance" fluid needs to be prescribed. This equates to insensible water losses and urine output and will be the same as the fluid and electrolytes we take in orally each day. Current guidelines propose the use of a fluid containing 154 mmol/l of sodium. This article questions whether this should be accompanied by chloride or a mix of chloride and potential bicarbonate. However none of us would dream of drinking such a fluid and the recommended sodium intake for infants is around 3 mmol/kg/day which for a 10 kg child given the standard 1 litre of maintenance fluid equates to a solution containing 30 mmol/l or 0.18% sodium chloride. This is the sodium concentration you will find in total parenteral nutrition (TPN). Using 0.9% sodium chloride gives 154 mmol of sodium or 15.4 mmol/kg! The concern about using hypotonic solutions as “maintenance” fluid centres around the notion that the syndrome of inappropriate anti-diuretic hormone secretion (SIADH) is a common phenomenon and administration of hypotonic solutions will cause hyponatraemia. However SIADH is overdiagnosed and when ADH levels are raised it is almost always appropriate i.e. ADH is being produced in response to ECF volume contraction. In that situation an isotonic solution is required. Once ECF volume has been restored ADH production will almost always be switched off and continuing use of isotonic solutions will risk causing hypernatraemia.
The question that should have been asked was which fluid was more appropriate for “resuscitation” purposes? In the scenario described it is the administration of a 20ml/kg bolus of 0.9% sodium chloride that has led to a hyperchloraemic metabolic acidosis. We have recently had this discussion in our department and as in this article, have had to look primarily at evidence from adult studies. At this meeting the use of isotonic crystalloid as "maintenance" fluid was questioned and subsequently we have seen three cases of hypernatraemia as a result of 0.9% sodium chloride “maintenance” therapy.
"Resuscitation" fluid is given to restore ECF volume. To achieve this it would make sense to use a fluid that matches the composition of ECF and unfortunately 0.9% saline only goes part of the way to achieving this. ECF contains 140 mmol/l of sodium, 4 mmol/l of potassium, 113 mmol/l of chloride and 26 mmol/l of bicarbonate and as a result, when using 0.9% sodium chloride to correct a deficit there is an excess of chloride and a lack of bicarbonate. This creates a metabolic acidosis. It therefore makes sense to use balanced fluids containing potential bicarbonate. The studies quoted in this article are primarily related to severely ill patients many with sepsis in whom ongoing problems with ECF volume will be an issue and cannot be extrapolated to children on a general paediatric ward.
In summary, prescription of intravenous fluids should only be made after a careful assessment of the patient, in particular their ECF volume status. If that is reduced an isotonic solution should be administered. A balanced solution makes more sense physiologically but the evidence supporting its use over 0.9% saline is limited, particularly in the paediatric population. If there are ongoing losses they should be replaced by a solution best matching the fluid being lost. If it is not possible to establish the electrolyte content of the fluid losses an isotonic solution is advised. Once ECF volume is replete then a hypotonic solution should be given and on our ward we would use 0.45% saline + 2.5% dextrose. This is still providing more sodium than is normally recommended if giving fluids orally or in TPN. Unfortunately ECF volume status is notoriously difficult to assess and if there is doubt isotonic solutions will be safer. However if 0.9% sodium chloride continues to be administered as "maintenance" fluid we will see more cases of hypernatraemia. Whatever strategy is adopted it is essential to monitor serum electrolytes at least daily in children receiving a significant (>50%) proportion of their fluids intravenously.
I have not mentioned the ongoing debate about the volume of "maintenance" fluid we should be giving children. Currently this is based on recommendations made by Holliday and Segar in the 1950’s, matching fluid requirement to energy expenditure. It is now recognised that these do not reflect the fluid requirements of unwell children lying in bed and as a result “maintenance” fluid volume prescriptions may be twice what they should be. The prescription of more water than is needed is potentially a contributing factor to hypotonic solutions producing hyponatraemia - the prescribing of too much water rather than too little sodium. It is also likely that the cases of hyponatraemia reported in the literature were the result of the prescribing of hypotonic solutions to patients who were deplete of ECF in which case isotonic solutions should have been given.