Introduction to Fluid Therapy Flashcards
Volume control
RAAS system
Osmolality control
Anti-diuretic hormone
Fluid gains vs fluid loss
- gains: water and food, aerobic metabolism
- loss: sensible (2/3, urinary/fecal), insensible (1/3, skin/respiratory)
Total body water accounts for ____ body weight in dogs and cats
60%
Water movement is controlled by
- osmosis
- starling’s forces
Important clinical concepts
- water freely moves between all 3 compartments
- sodium containing fluids stay within extracellular space (interstitium and intravascular)
Pathologies in fluid homeostasis manifest in one of 2 main ways
- volume of fluid compartment changes
- tonicity of fluid compartment changes
Fluid therapy is indicated to:
- replace a deficit in a fluid compartment
- change the electrolyte concentration of a compartment
- shift fluids from one compartment to another
Other indications for fluid therapy
- shock resuscitation
- correct dehydration
- maintain hydration
- promote diuresis
- anesthesia
- increase oncotic pressure
- correct electrolyte abnormalities
- replace blood components
- nutritional support
Intravascular
Shock
- perfusion parameters
Interstitial
Dehydration
- skin turgor, mucous membrane moisture
Intracellular
Hypernatremia
- [Na]
Perfusion parameters
- mucous membrane color
- capillary refill time
- heart rate
- pulse quality
- temperature
- mentation
- bp
- lactate
Look at the stages of shock!!!
Look at the stages of shock!!!
Interstitial evaluation
If severe enough, dehydration is an intravascular problem (>10%)
- only changes the intracellular compartment if the sodium is severe affected
Interstitial parameters
- skin turgor: affected by BCS and age
- gingival moisture affected by: panting (falsely dry), nausea (falsely moist)
Estimating dehydration
- <5%: not detectable
- 5% tacky mm
- 8%: dry mm, decreased skin turgor
- 10%: retracted globes, persistent skin tent, hypovolemia
- 12-15%: hypovolemic shock
______ compartment cannot be evaluated on physical exam
Intracellular
- [Na] loosely reflects volume status of intracellular compartment
Severe hypernatremia =
Intracellular deficit
- as extracellular osmolality increases, water leaves intracellular space and cells become dehydrated
- hypotonic fluid loss –> hypernatremia –> intracellular dehydration
Fluids are categorized by _______
- particle size: crystalloids (small), colloids (large)
- tonicity: hypotonic, isotonic, hypertonic
Isotonic crystalloids
Freely distribute among extracellular spaces
- great for rehydrating interstitial space
- takes large volumes to expand intravascular space
- balanced: LR, plasmalyte
- unbalanced: 0.9% saline
Balanced isotonic crystalloids
Fluid of choice due to:
- buffer that combats metabolic acidosis
- more physiologic amounts of Na and Cl
Unbalanced isotonic crystalloids
Supra-physiologic amounts of sodium and chloride
- reserved for situations bc it is an acidifying solution that lacks a buffer
- used for metabolic alkalosis, hypercalcemia, drug incompatabilities
Hypotonic crystalloids
Distribute evenly among all fluid compartments
- only used for hypernatremia/free water loss
- isotonic in vitro but hypotonic in vivo
- sterile water is hypotonic in vitro and in vivo (NEVER give to patient)
Hypertonic crystalloids
Used to manipulate fluid shifts in the body
- increase intravascular expansion at a much lower volume –> short lived effect due to distribution between intravascular and interstitial space
- used for shock or hemorrhage
- can shift fluid out of intracellular compartment (cerebral edema)
Colloids
Fluids that contain large molecules with oncotic pull that stay within the intravascular space
- synthetic: hetastarch
- natural: whole blood, plasma, albumin
Colloid - confinement within the intravascular space provides ______
Volume expansion
- intact and functional vessel is necessary!
- improve oncotic pressure due to hypoalbuminemia
- severe shock (esp w/ hemorrhage)
- replace deficient blood product
Synthetic colloids
Advantages - inexpensive and readily available - increase volume expansion at lower doses - increase colloid osmotic pressure Disadvantages - dose dependent coagulopathy - worsens edema if escapes vasculature
Peripheral IV
Short term
- cephalic and saphenous
- fastest = largest bore and shortest lenth
- don’t perfuse a disease part of body
Intraosseous
Used when peripheral cannot be obtained
- severe shock or neonates
- trochanteric fossa, iliac crest (large dogs)
Central lines
Appropriate for long term catheterization, critical patients, multiple infusions, and extremely hypertonic fluids
- jugular, femoral extending to caudal vena cava
- permits frequent blood sampling
Treating intravascular compartment
- route: IV, IO
- rate: fast, bolus over 10-20 min
- fluid: balanced crystalloids, hypertonic saline, synthetic colloids
Shock strategies
- hypovolemic: large amounts of crystalloids, occasional use of hypertonic saline or colloids
- hemorrhage and trauma benefit from limited volume resuscitation (smaller amounts of crystalloids, concurrent use of hypertonic saline, +/- blood products)
Resuscitation goals
Continue fluid resuscitation until the following have normalized:
- physical exam perfusion parameters
- blood pressure
- lactate
Treating interstitial compartment
- route: IV, IO, SQ, PO
- rate: correct over 12-24 hrs
- fluid: balanced isotonic crystalloids
SQ fluids
Reserved for replacement of mild dehydration (5-8%)
- isotonic crystalloids (hypertonic, hypotonic, or dextrose will cause tissue necrosis)
- dose: 20-30 ml/kg
IV rehydration plan
- estimation of dehydration
- provision of maintenance fluid requirements
- estimate and replace on-going fluid losses
Estimating dehydration
Fluid deficit = % dehydration x body weight (kg)
- convert to hourly rate based on how fast you wish to correct dehydration (12-24 hrs)
Maintenance fluids
1 ml of fluid to metabolize 1 kcal of energy
- maintenance fluids should match metabolic energy requirements
- need to calculate using body surface area
Ongoing losses
GI and urinary are most common
- others: fever, drainage, burns/wounds, third spacing
- weight used to monitor trends
- urinary cath and drains allow precise measurement of fluid losses
Discontinuing fluid therapy
- underlying dz is corrected/controlled
- fluid deficits corrected
- fluid losses have stopped
- animal can consume water to stay hydrated
Treating intracellular compartment
- route: IV, PO
- rate: slow! 48-96 hrs
- fluid type: 5% dextrose in water administered IV, water consumed orally
Oncotic support
Indicated if albumin <1.5 g/dl or total protein <4.0 g/dl
- synthetic colloids (most available option)
- plasma is not ideal, albumin last resort
Diuresis
Fluids will be delivered at higher than maintenance rates to ensure perfusion and promote diuresis
Electrolyte supplementation
Potassium, calcium, magnesium
- all electrolytes affect hr and contractility if given too fast, CRI is ideal
_____ is the most common electrolyte abnormality
Hypokalemia
- skeletal muscle weakness is most common consequence
Hypokalemia
Potassium chloride may be added to any crystalloid
- be cautious above 0.5 mEq/kg/hr of supplementation
- risk for hyperkalemia and toxicity
