This table from NEJM’s most recent publication is a handy reference. Knowing the composition of the different intravenous fluids will help us understand how they affect the electrolytes and osmolarity.
I remember asking my seniors to teach me how to choose intravenous fluids for my patients, and have always been frustrated with their answer that choosing IV fluids is “an art that you pick up with experience.” This week’s NEJM published an algorithm addressing this issue, and provides us with a good general guideline for choosing IV maintenance fluids. This is the first practical guide to choosing IV fluids that I have come across. I agree with the algorithm, although we generally prefer a non-dextrose-containing fluid for patients with CNS disease.
Some Important Notes:
- Possible consequences of normal saline administration: hypernatremia, fluid overload with edema or hypertension, hyperchloremic acidosis, renal vasoconstriction, delayed micturition, hyperkalemia, increased incidence of AKI requiring RRT
- Normal saline has the same sodium concentration as the aqueous phase of human plasma but has a supraphysiologic chloride concentration.
- Saline solutions may have a pH far lower than that of water (3.5-7.0). The low pH of normal saline may be related to the polyvinyl chloride bags in which it is packaged, since the pH of normal saline in a glass bottle is 7.0.
- Currently, no balanced electrolyte solution is perfectly matched with plasma.
- Multiple electrolytes injection, type 1, USP has a supraphysiologic buffer concentration of 50 mmol/L.
- Ringer’s lactate contains calcium and may be incompatible with blood products and some medications.
- Some dextrose-containing saline solutions are hyperosmolar to plasma but they are not hypertonic since the dextrose is rapidly metabolized on entering the bloodstream.
- The default maintenance solution for adults is 5% dextrose in a solution of 0.9 saline administered at a rate of 100-120 ml/hr.
- The common practice of adding 20 mmol per liter of potassium to maintenance IV fluids – no data supports this approach, may be unnecessary when IV fluids are administered for <48h, unless hypokalemia or malnutrition is present or diuretics are being used.
Ingelfinger, Julie R., Michael L. Moritz, and Juan C. Ayus. ‘Maintenance Intravenous Fluids In Acutely Ill Patients’. New England Journal of Medicine 373.14 (2015): 1350-1360. Web. 7 Oct. 2015.