Aqueous solutions with varying concentrations of electrolytes.The tonicity of a solution is determined by the solutes that do not enter the cell and are, therefore, osmotically active (e.g., sodium, potassium). The osmolarity of a parenteral solution takes into account the concentration of all the solutes, including those that enter cells (e.g., dextrose). The osmolarity and tonicity of a solution are not the same thing! Administering solutions with inappropriate tonicity can lead to life-threatening fluid and electrolyte imbalances. Higher than the intracellular compartmentĬan be hypertonic, isotonic, or hypotonic Describes what will happen to the equilibrium of a cell when it is placed in a certain solutionĮquivalent to the intracellular compartment.Reflects the osmotic effect of particles that cannot easily pass cell membranes, i.e., the effective osmotic pressure gradient.Tonicity: the capacity of an extracellular fluid to create an osmotic gradient that will cause water to move into or out of the intracellular compartment cannot be measured and has no units.Takes into account all osmotically active particles, including those that enter cells (e.g., glucose, urea).Preferred term to describe the osmotic pressure of parenteral fluids. Osmolarity: the concentration of solutes per unit volume of solvent (mOsm/ L) often used interchangeably with osmolality in clinical practice.Osmolality: the concentration of dissolved particles per unit mass of solution (mOsm/ kg) preferred term to describe the osmotic pressure of biological systems.Balanced IV fluid solutions: crystalloids or colloids that do not significantly alter the homeostasis of the extracellular compartment.Colloids: solutions that contain larger molecular weight solutes (e.g., albumin and starch).Crystalloids: solutions that contain small molecular weight solutes (e.g., minerals, dextrose).Example: A 35 kg child minimum hourly fluid intake would be: (4x10) + (2x10) + (1x15) = 75 cc/hour.20 cc/kg/24 hours= 1 cc/kg/hour for the remaining weight.50 cc/kg/24 hours= 2 cc/kg/hour for the 2nd 10 kg of the patient's weight.100 cc/kg/24 hours= 4 cc/kg/hour for the 1st 10 kg of the patient's weight.Fluid requirements per hour: Daily fluid requirements are divided into approximate hourly rates which gives the "4-2-1" formula often used to calculate hourly infusion rates of IV fluids.50 cc/kg for the 2nd 10 kg of the patient's weight.100 cc/kg for 1st 10 kg of the patient's weight.Clinicians should be aware of clinical signs of dehydration and respond appropriately.The Holliday-Segar Method provides a formula for calculating fluid requirements (Holliday-Segar 1957) - contemporary articles support continued use of this method with modifications based on overall health of the child with individualized rates of IV fluids "accounting for enteral fluid intake, IV medication fluids, and fluid loss (Alexander 2022). In patients who have had tonsillectomies or other procedures affecting their ability to swallow, their daily fluid requirements should be calculated prior to discharge to determine if they will be able to stay adequately hydrated with PO intake once they are no longer receiving IV fluids. Pediatric patients have weight-based minimum fluid intake requirements.See also: Tonsillectomy and Adenoidectomy Maximum allowable blood loss
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