Types of fluids and routes of administration Flashcards
Osmosis
The diffusion of water molecules, from a region where the water molecules are in higher concentration to a region where they are in a lower concentration, through a semi permeable memebrane
Osmotic pressure
The amount of pressure required to stop osmosis, the greater the concentration difference the higher the osmotic pressure.
Higher the conc gradient the higher the osmotic pressure needed to stop osmosis
Colloid osmotic pressure
Type of osmotic pressure caused by very large molecules that don’t readily cross a semi permeable membrane. albumin/ proteins in the capillaries help to pull fluid back into the blood.
Colloids in cappilarys will displace water molecules creating a relative water molecule deficit with water molecules moving back into the circulatory system within the lower venous pressure end of the capillaries.
Fluid movement from arteries/ arterioles and veins/ venules
Artery = fluid out
- High hydrostatic pressures f the arterial system pushes fluid out - the fluid proving cells with nutrients in the capillary bed
Veins = pulls fluid back in
- The high colloid oncotic pressure of the remain fluid within the venues ‘pulls’ fluid back in - in blood = albumin
- fluid previously in tissues will go back into veins
Crystalloid products
Can be:
Hypertonic, isotonic, hypotonic
Hypertonic = 7.2% NaCl
Isotonic = 0.9%NaCl OR Hartmann’s
Hypotonic = 0.18% NaCl or 4% glucose
Colloid products
All isotonic
Natural or synthetic
Natural = Plasma - blood transfusion products
Synthetic = e.g. Gelatin
Crystalloids…
- Solutions containing small molecules such as electrolytes dissolved in water
- They readily move out of the blood stream through the capillary membrane
- Cheap and widely available
- They do not exert any colloid osmotic pressure
- Tonicity is variable (hypertonic, isotonic or hypotonic)
Colloids…
- Solutions contain large molecules
- The molecules do NOT readily move out of the blood stream - sits in the blood stream for longer
- They are generally more expensive and difficult to acquire
- They are isotonic but DO exert osmotic pressure - will very due to size and number of larger molecules within the solution
What is tonicity?
The capability of a solution to modify the volume of cells by altering their water content
What does hypertonic mean?
Means having a higher concentration of solutes. Water will flow out of the cell into the extracellular fluid - the cell will shrink up until the two concentrations become equal
What does isotonic mean?
Means having the same concentration of solutes - there will be not net shifts of fluid
What does hypotonic mean?
Means having a lower concentration of solutes. Water will flow into the cell from the extracellular fluid- in this case the cell will swell (and possibly burst)
Isotonic crystalloids?
- They are commonly used and widely available in practice
- They mimic intravascular electrolyte concentrations
- This means they are high in sodium and low in potassium
- They are indicated for dehydrated and hypovolaemic patients
- They can be used to replace ongoing losses
Comparison of 0.9% NaCl and Hartman’s
0.9% NaCl has a higher concentration of sodium
Hartmann’s had potassium (so won’t give if patient is hyperkalemic) and 0.9% NaCl has no K
0.9% NaCl has more chloride
Hartmann’s has calcium (might not want to give to patient who is hypercalcemic) - 0.9% does not
No magnesium in either
No dextrose in either
Hartmann’s has a lactate buffer - may be good if a patient is acidotic
Higher osmolarity in 0.9%
0.9% has a higher pH so more acidic
Neither have any colloid osmotic pressure as crystalloid
No clinically significant difference between the two - just ensure you know wether the cat is dehydrated or hypovalemic so know whether to give a bolus or slowly
Hypotonic crystalloids
- Very rarely used
- will contain less Na and Cl than isotonic
- Can be indicated for the management or hypernatraemia (high concentration of Na in the blood, from drinking too much sea water, churns disease, very rare)
- If used inappropriately can cause acute hyponatraemia
- Acute hyponatraemia > cerebral oedema > death
Hypotonic crystaloids mechanism in the body
Administration of hypotonic fluid causes a net shift of fluid from the intravascular to the extravascular space. Brain cells are least tolerant of this change in cell volume.
Fluid has lower tonicity that extravascular so will move out of artery.
Hypertonic crystalloids
- Most commonly used in SA for the management of raised intracranial pressure
- commonly used in LA for rapid intravascular volume expansion (link to shock)
- Extremely dangerous if administered by mistake
Hypertonic crystalloids mechanism in the body
Hypertonic fluid administration can cause net shift of fluid from extravascular to the intravascular space
- Management of raised intracranial pressure and to suddenly increase the intravascular fluid volume
- can be easily used for hypovalemic and dehydration as don’t have the fluid in the body to move
- Due to the small molecules they can readily move from the blood stream so the effect is short lived
Colloids
- Their large molecules mean that they have an increased colloid osmotic pressure
- Stay in the intravascular space for longer so longer duration
- Can be natural e.g. plasma or synthetic e.g. gelatine, hydroxyethyl starches
- Due to staying in the intravascular space for longer a smaller volume of fluid can be used for volume resuscitation
Colloid mechanism in the body
High colloid osmotic pressure helps ‘pull’ fluid in - large molecules so they don’t readily move out of the blood stream so longer duration of action than crystalloids
Potential uses of colloids
Management of hypovolaemia
- replacing intravascular volume
- Plasma can be used for the treatment of coagulopathies as contains coagulation factors
- e.g coagulopathies = rodenticide toxicity
- NOT suitable for correction of dehydration or management of electrolyte abnormalities
The risks and reality of colloids
- Coagulopathy
- Allergic reactions
- Anaphylaxis
- Increase f death when used in human patients with sepsis
- Increase of acute kidney injury (AKI) in people
- Expensive
Routes of fluid administration
- Per os
- Subcutaneous
- Intravenous
- Central venous access
- Intra-osseous
Per os
- Via mouth, voluntary or feeding tubes
- Advantages = owners can learn how to do it, intestines are selective about how much fluids or what electrolytes they absorb
- Disadvantages = Inappropriate if loss of gag reflex, Absorption is slow, not suitable for hypovalemic or clinically moderate to severe dehydration
SC
-Fluid injected by needle, syringe or needle attached to a fluid bag
- Advantages = Cheap and easy, owners can be taught
- Disadvantages = Absorption is slow, not suitable for hypovalemic or clinically moderate to severe dehydration
- Limit to how much fluid can be administered before it becomes painful
- More loose skin= more fluid can be injected under subcutaneous space
IV
- Fluid injected directly into veins, commonly cephalic and saphenous
- Advantages = Can be administered slowly or rapidly and in large volumes, directly into intravascular compartment , appropriate for dehydration and hypovolaemia
- Disadvantages = only registered vets and veterinary nurses can use it
Central venous fluid
- Fluid injected directly into larger more central veins e.g. jugular
- Advantages = in SA life saver when peripheral venous access is impossible, ‘central lines’ also mean port for blood sampling, commonly used in LA where peripheral catheters would be impractical
- Disadvantages = in SA further training and specialist equipment is required, patients need to be very still for placement, anaesthesia commonly required
Intraosseous
- Fluid injected into medullary cavity of long bones
- Advantages =in SA life saver when peripheral venous access is impossible, in neonates, Medullary cavity is highly vascularised so allows for rapid fluid absorption, hypodermic needles can be used in neonates
- Disadvantages = For adults requires special equipment and further training required, There is a risk of causing fractures and osteomyelitis
- need special bone drills and catheters
Complications of fluid therapy
- Fluids are drugs
- There are interactions e.g. Hartman’s and bicarbonate/ blood products - can cause a clot
- Need to consider … before prescribing
Cardiac disease and heart failure
Renal disease
Respiratory disease
What does volume overload look like?
- Pulmonary oedema- tachypnoea, dyspnoea, crackles upon lung field auscultation
- Venous engorgement e.g. jugular distension or pulsations
- Peripheral oedema formation e.g. swollen limbs and chemises (swelling of conjunctiva of eye)
- Cavitary effusions e.g. pleural, peritoneal (abnormal accumulation of fluid in body cavitys)
- Serous ocular discharge - will look like crying
