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• Use of 0.9% saline as maintence fluid is bad medicine
  Graham C Smith
  Published on: 19 January 2018

• Published on: 19 January 2018

  Use of 0.9% saline as maintence fluid is bad medicine

  • Graham C Smith, Paediatric Nephrologist University Hospital of Wales, Cardiff

  I read with interest the review by Green and Lillie[1] of the NICE guideline (N29) on intravenous fluid therapy in children[2]. The new guideline correctly questions the routine use of the Holliday-Segar formula for calculation of maintenance fluids[3], but the recommendation of 0.9% saline as the maintenance fluid must still be questioned.

  The review opens with two contradictory statements in the first two paragraphs:

  “The prescription of intravenous fluids requires an understanding of fluid homeostasis and should be tailored to the individual, the disease and the intended therapeutic goal.”

  and, in reference to the NICE guideline:

  “…its aim was to offer a ‘standardised approach to assessing patient’s fluid and electrolyte status and prescribing IV fluid therapy in term neonates, children and young people’.”

  I agree wholeheartedly with the first statement but it does not fit with the second proposal of a “standardised” approach. The problem hinges around the idea of “replacement” and “maintenance” fluids and this was reviewed in an excellent paper by Malcolm Coulthard in 2007 when he questioned the switch from 0.18% saline to 0.45% saline as the recommended maintenance fluid[4]. The arguments he used are now doubly relevant when you move to 0.9% saline.

  Patients who need fluid “replacement” need an iv fluid matching extracellular fluid composition and 0.9% saline fits the bill. Patients who need iv “maintenance” fluid need some...

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  I read with interest the review by Green and Lillie[1] of the NICE guideline (N29) on intravenous fluid therapy in children[2]. The new guideline correctly questions the routine use of the Holliday-Segar formula for calculation of maintenance fluids[3], but the recommendation of 0.9% saline as the maintenance fluid must still be questioned.

  The review opens with two contradictory statements in the first two paragraphs:

  “The prescription of intravenous fluids requires an understanding of fluid homeostasis and should be tailored to the individual, the disease and the intended therapeutic goal.”

  and, in reference to the NICE guideline:

  “…its aim was to offer a ‘standardised approach to assessing patient’s fluid and electrolyte status and prescribing IV fluid therapy in term neonates, children and young people’.”

  I agree wholeheartedly with the first statement but it does not fit with the second proposal of a “standardised” approach. The problem hinges around the idea of “replacement” and “maintenance” fluids and this was reviewed in an excellent paper by Malcolm Coulthard in 2007 when he questioned the switch from 0.18% saline to 0.45% saline as the recommended maintenance fluid[4]. The arguments he used are now doubly relevant when you move to 0.9% saline.

  Patients who need fluid “replacement” need an iv fluid matching extracellular fluid composition and 0.9% saline fits the bill. Patients who need iv “maintenance” fluid need something that matches what they would normally be drinking. If we take a 10kg child for simplicity, assume a sodium requirement of 2.5 mmol/kg and a water requirement of 100 ml/kg this equates to 1000 ml of a solution containing 25 mmol of sodium. The nearest iv solution matching this recipe is 0.18% saline containing 31 mmol of sodium in the litre administered (still a bit too much!). If you use the same volume of 0.9% saline you will be giving 154 mmol of sodium i.e. 15.4 mmol/kg which should be considered excessive.

  The key to fluid management is being able to tailor the fluids to the individual as advocated in the first paragraph of the review. It has correctly been recognised that children do not usually need the volume of maintenance fluid previously advocated and it was this excess volume of water that led to problems of hyponatraemia not the lack of sodium.

  The syndrome of inappropriate antidiuretic hormone (SIADH) is rare and is not the reason for the development of hyponatraemia in most cases. As a medical student I was taught by Professor George Haycock at the same hospital as the authors of this review and he was an authority on this subject. He would tell us that rather than SIADH these patients would usually have “appropriate” ADH secretion. These patients would have an unrecognised fluid deficit and needed “replacement” fluid that should be isotonic and the administration of a hypotonic solutions would lead to a dilutional hyponatraemia. Once the patient is fluid replete the solution should be changed to a hypotonic one administered at an appropriate rate. A volume of 50-80% of the previous calculated routine maintenance would be reasonable. In our patients we do not use 0.9% saline as a "maintenance " fluid, instead giving 0.45% saline plus dextrose, which is still probably too much sodium. The key is regular review of the patient with daily checking of serum electrolytes. Urine electrolytes can also be useful and I am confident that very few patients will be found to be producing urine containing 150 mmol/l of sodium unless that is what they are being given as "maintenance" fluid.

  I feel that the guideline has been developed in response to the practice of poor medicine and the failure to recognise the needs of individual patients. I believe that with these guidelines poor medicine is at risk of continuing.

  References
  1. Green J, Lillie J. Intravenous fluid therapy in children and young people in hospital N29. Arch Dis Child Educ Pract Ed 2017; 102: 327–331.
  2. Intravenous fluid therapy in children and young people in hospital NICE guideline N29. nice. org. uk/ guidance/ ng29
  3. Holliday MA, Segar WE. The maintenance need for water in parenteral fluid therapy. Pediatrics 1957; 19: 823–32.
  4. Coulthard MG. Will changing maintenance intravenous fluid from 0.18% to 0.45% saline do more harm than good? Arch Dis Child 2008; 93: 335–340

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  Conflict of Interest:
  None declared.

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