Emergency & Critical Care : Fluid Therapy 2: Introducttion to Fluid Therapy and Fluid Therapy Types
Abstract
This lecture is the second in the series of Fluid Therapy lectures by Louise O Dwyer and introduces fluid therapy and fluid therapy types. Beginning with the history of fluid therapy and then moving on to look at parenteral fluid types available it gives an interesting and in depth introduction to fluid therapy. It then looks at indications for and contraindications against using different fluid types. It then ends with a short discussion of subcutaneous fluid therapy.
Learning Outcomes
- Knowledge of the history of fluid therapy
- An understanding of different fluid types and using fluid therapy
Course Notes
Parenteral fluids:
•Biologically compatible sterile solutions in water, designed for injection rather than oral administration. Two main routes:
•Intravenous
•Subcutaneous
Types:
Crystalloids:
Isotonic High Sodium Fluids
Hypotonic Low Sodium Fluids
Hypertonic Saline Solution
Colloids:
Synthetic
Natural
Crystalloids:
Indications for high sodium fluids (Replacement fluids)
•Replace extracellular fluid lost to:
•Vomiting, diarrhoea and wound drainage
•Resuscitate patients with hypovolaemia
•Expand plasma volume following loss due to:
•Haemorrhage and drainage
•Extracellular fluid movement to a third space (sequestration)
•Administered rapidly to restore circulation
•Rate of administration depends on each patient’s specific condition
•Administered slow to replace extracellular fluid lost due to non-life threatening isotonic dehydration
•Used to replace normal on-going fluid losses in animals that can tolerate their sodium content
Contraindications for high sodium fluids
Do not use to replace on-going fluid losses in patient’s with:
•Heart disease
•Renal disease
•Inflammation
•Oedema
Examples of High Sodium Fluids:
•High sodium fluids with high potassium concentrations added:
•Often used to treat dehydration from GI losses
•If potassium concentration exceeds 5 mEq/L the fluid must not be infused rapidly because it can cause hyperkalaemia
Low Sodium Fluids:
•Short term support of water and electrolyte homeostasis
•Replaces normal on-going losses in patients withheld from normal fluid intake
•Administration rate is based upon body size and does not change from day to day
Indications for low sodium fluids
•Continuous IV administration of:
•Analgesics• Antiemetics
•Antibiotics• Much more!
•Hypertonic dehydration in patients with a normal total body sodium content
•Dog with hyperthermia and no access to drinking water
•Animals unable to maintain hydration orally, e.g CKD
Contraindications for low sodium fluids
•Never use in patients requiring rapid infusions for resuscitation from shock
•Rapid infusions would:
•Rapidly reduce the extracellular fluid sodium concentration
•Cause problems due to the rapid reduction in osmolality
Hypertonic saline
•Resuscitation from hypovolaemic shock using small volumes
•Especially useful in larger patients
•Administered once, early in treatment
•Concentration of 3%-7.6%
•Resuscitation from hypovolaemic shock using small volumes
•4-6ml over 2-3 minutes
•As effective as high sodium crystalloids
•Can be administered in less time than high sodium crystalloids
•Do NOT use in patients with
•Heat failure
•Hypovolaemia from severe dehydration
Colloids:
Mixture containing one substance that is easily dispersed in another.
It generally does not diffuse through a semi permeable membrane.
•Natural colloids include:
•Albumin
•Whole blood products
•Plasma
•Haemoglobin based products
Contraindications for Colloids
•Patients with active uncontrolled bleeding
•Interferes with platelet function and may aggravate haemorrhage
•Produce volume overload and pulmonary oedema at lower volumes than high sodium crystalloids
Electrolyte Supplementation
•When restoring homeostasis in patients with pathological GI and urinary losses
•Identify the patient’s electrolyte abnormalities:
•History
•Physical findings
•Serum chemistry results
Commonly added electrolytes:
Provided as a constant rate for normal on-going loss replacement to avoid inadvertent overdosage
If volume of all additives exceeds 50ml:
Remove equivalent volume of fluid from bag before adding electrolytes
Subcutaneous Fluid Therapy
•Best to administer most fluids intravenously, but in some situations, subcutaneous administration is appropriate
•Isotonic, high sodium crystalloid fluids are most often used:
•Lactated ringers solution
•0.9% NaCl
•Volume is limited by the distensibility of the subcutaneous tissues
•Substantial patient variation
•Fluid osmolality should not exceed 450 mOsm/kg
•Potassium concentration should not exceed 40 mEq/L
•Sodium concentration should be at least 40 mEq/L