FLUIDS - Fluid transport and Fluid Administration Flashcards
What is diffusion?
Movement of solutes from a high to low concentration down their electrochemical gradient
What are the methods of solute diffusion across a membrane?
Diffusion across the lipid bilayer
Diffusion through protein channels
Facilitated diffusion
What is Ficks law?
Ficks law defines the rate of diffusion using the solubility of the solute, the fluid concentration on either side of the membrane and membrane thickness
What is Net flux?
Diffusion is actually a two way process, net flux describes the movement of solutes down their concentration gradient
What is active transport?
An energy dependent process where the solute is moved against its electrochemical gradient
Describe the method of primary active transport
- Solute binds to an ATPase dependent protein
- ATP breaks down into ADP+P, causing a conformational change in the protein
- Solute is moved across the membrane against its concentration gradient
Describe the method of secondary active transport
The solute moves in association with another molecule/ion that is moving down its concentration gradient, utilising its stored chemical energy
What is bulk flow?
A passive process in which large numbers of ions, molecules and particles which have dissolved within a fluid, move together in the same direction down a pressure gradient
What is the Donnan’s effect?
The presence of a charged insoluble solute causes an uneven distribution of permeable solutes across a semi-permeable membrane
What is osmosis?
Osmosis is the net water movement from a low impermeable solute concentration to a high impermeable solute concentration across a semi-permeable membrane (movement of water down its concentration gradient)
What is osmolarity and how is it measured?
Osmolarity is the measure of solute concentration in a solution (the number of solute particles per litre of solution)
What is osmolality?
Osmolality is the number of solute particles per kg
What determines tonicity/tone?
The tone exerted by a solution is determined by the concentration of impermeable solutes in the solution, determining the net water movement across a semi-permeable membrane
Describe an isotonic solution
When the concentration of impermeable solutes between two solutions is the same (regardless of the concentration of permeable solutes); no net water movement
Describe a hypertonic solution
When comparing two solutions, a hypertonic solution contains more impermeable solutes than the other solution; net water movement into the hypertonic solution
Describe a hypotonic solution
When comparing two solutions, a hypotonic solution contains less impermeable solutes than the other solution; net water movement from the hypotonic solution
What are the percentages of total body water in animals and how does this differ with age and condition?
Neonatal: 75% total body water
Adult: 55-60% total body water
Old/obese: 45% total body water
Why does the percentage of total body water change with age and weight gain?
Total body water changes depending on fat distribution
Describe the distribution of fluid between the main body fluid compartments
Intracellular fluid (2/3 of body fluid)
Extracellular fluid (1/3 of body fluid)
What are the two major electrolytes contributing to the osmolarity of the intracellular fluid compartment?
K+
PO3-
What are the two major electrolytes contributing to the osmolarity of the extracellular fluid compartment?
Na+
Cl-
What is the function of Starling’s forces?
Starling’s forces act on all water molecules and regulate the fluid movement across the capillary wall
Describe the four Starlings forces
- Capillary hydrostatic pressure: moves water out of the capillary
- Interstitial hydrostatic pressure: moves water into the capillary
- Osmotic pressure: a pressure gradient generated by interstitial fluid proteins pulling water out of the capillary
- Oncotic pressure: a pressure gradient generated by plasma proteins pulling water into the capillary
Describe net filtration and net absorption
- At the arterial end of the capillaries, capillary hydrostatic pressure pushes fluid out of the capillaries into the interstitial space (net filtration)
- At the venous end of the capillaries, oncotic pressure moves fluid back into the capillaries from the interstitial space (net absorption)
Why is there such minimal interstitial hydrostatic pressure?
Fluid in the interstitial space is collected by lymphatic vessels and eventually returned to the bloodstream by the lymphatic system, resulting in a minimal build up of pressure in the interstitial space
How do imbalances in Starling’s forces result in fluid shifts and oedema?
A drop in oncotic pressure causes oedema due to the increase in net filtration and decrease in net absorption - causing a build up of fluid in the interstitial space
What are the clinical signs of oedema?
External swelling
Enlarged internal organs
List eight causes of oedema
Increased cardiac output
Inflammation
Exercise
Heart disease
Venous obstruction
Liver disease
Kidney disease
Protein malnutrition
What is dehydration?
A decreased volume of total body fluid
What is hypovolaemia?
A decreased volume of circulating plasma
What are the three clinical signs of dehydration?
Dry mucous membranes
Skin tent
Sunken eyes
What are the five clinical signs of hypovolaemia?
Pallor
Weak, rapid pulse
Lethargy
Cold extremities
Prolonged capillary refill time (CRT)
Describe the clinical signs of an animal that has less than 5% fluid loss
Clinically undetectable
Describe the clinical signs of an animal that has approx. 5% fluid loss
Slightly dry mucous membranes
Mild skin tent
Describe the clinical signs of an animal that has 6-8% fluid loss
Dry mucous membranes
Moderate skin tent
Eyes begin to appear sunken
Describe the clinical signs of an animal that has a 8-12% fluid loss
Very dry mucous membranes
Marked skin tent
Obvious sunken eyes
Clinical signs of hypovolaemic shock
Describe the clinical signs of an animal that has 12-15% fluid loss
Moribund (close to death)
Why is fluid therapy used in the pre- and peri-operative period (fluid administration before anaesthetic and surgery)
Fluid therapy is used in the pre- and the peri-operative period to prevent the animal developing a fluid deficit. Fluid therapy supplements normal fluid intake, counteracts physiological changes induced by the anaesthetic and replaces fluid lost in the surgery
What are crystalloid solutions?
Solutions of electrolytes and/or glucose in water which diffuse rapidly out of the vascular compartment into the interstitial space
When are the three uses for crystalloid solutions in fluid therapy?
Replace fluid and electrolyte deficits
Treat fluid deficits complicated by metabolic alkalosis or acidosis
Maintenance of normal hydration and euvolaemia
Describe the composition of Hartmann’s solution
A balanced isotonic crystalloid solution containing anions (lactate, acetate, gluconate, citrate) which yield bicarbonate
When should Hartmann’s solution be used in fluid therapy?
Fluid and electrolyte deficits
Treat fluid deficits complicated by metabolic acidosis
Describe the composition of normal saline (0.9% saline)
An unbalanced isotonic crystalloid containing chloride ions
When should normal saline (0.9% saline) be used in fluid therapy?
Treat fluid deficits complicated by metabolic alkalosis
Describe the composition of hypertonic saline
Hypertonic crystalloid solution
When should hypertonic saline be used in fluid therapy?
Maintain normal hydration and euvolaemia
Expand normal circulatory volume when treating hypovolaemia
Can isotonic saline be used to treat hypovolaemia?
Yes but it has to be used in much larger volumes compared to hypertonic saline or colloid solutions
Describe the composition of colloid solutions
Suspensions or large molecular weight particles which cannot easily diffuse out of the vascular compartment into the interstitial space, allowing these fluids to remain in the vascular compartment for a longer period of time
When should colloid solutions be used in fluid therapy?
Rapidly increase circulating volume when treating hypovolaemia
Maintaining oncotic pressure in panhypoproteinaemia patients
Why are gelatine-based colloid solutions the only colloids available for use in the UK?
Colloid solutions can have very adverse effects due to their long prevalence in the vascular compartment. However, gelatine-based colloids have a more similar osmotic pressure to plasma and a smaller molecular weight so have a shorter prevalence in the vascular compartment compared with other colloids
What are the characteristics typically associated with oral fluid administration?
Most physiological, economical, safe, easy, can be administered by owners (useful for chronic fluid deficits), meets calorific needs
What are the characteristics typically associated with subcutaneous fluid administration?
Easy, can be injected at any rate, multiple available injection sites, slow absorption, uncomfortable for patient
What are the characteristics typically associated with intravenous fluid administration?
Rapid absorption, suitable for hypovolaemia, precise control, meets calorific needs
What are the characteristics typically associated with intraperitoneal administration?
Absorption of large volumes of fluid
What are the characteristics typically associated with intraooseous administration?
Rapid absorption, strict asepsis required
How long should fluid be administered?
Until hydration is restored and the animal can maintain their fluid balance independently
What is the basic ‘rule of thumb’ for maintenance fluid calculations
On average, maintenance fluids should be 50ml/kg/day. If an animal appears dehydrated OR in vomiting multiply this value by 2. If an animal appears dehydrated AND is vomiting, multiply this value by 3
What are the drip rates for an adult and paediatric giving set?
Adult: 20 drops per ml
Paediatric: 60 drops per ml
What is the calculation used for calculating drops per minute?
Drops per minute = (Fluid per hour (ml/hr) x drip factor) / 60 minutes
