10. Fluid Therapy Flashcards
What general reasons can we use fluid therapy for?
- decreased oxygen delivery
- hypotension
- hypovolaemia
- electrolyte, metabolic and acid-base disorders
What are the 3 main causes of hypovolemia?
- haemorrhage
- shock
- dehydration
What is fluid balance?
A combination of:
- hydrostatic pressure
- osmotic pressure
- oncotic pressure
- permeability characteristics of capillaries
How is total body water broken down?
Total body water= 60% bodyweight
- Intracellular water- 40%
- Extracellular- 20% (further broken down into interstitial fluid 15% and intravascular (plasma) 5%)
What is osmosis?
net movement of water across a semi-permeable membrane
What is osmotic pressure?
pressure exerted by the particles within the solution; prevents the movement of water across the membrane
What is tonicity?
refers to the osmotic pressure of a fluid when compared with plasma
Fluid types- Why do we use Isotonic Crystalloids?
- same proportion of particles and water found in plasma
- no change in osmotic pressure
- used for dehydration, hypovolaemia, hypotension
Fluid types- Why do we use Hypotonic Crystalloids?
- has fewer particles than in plasma which decreases osmotic pressure
- pressure difference created between intravascular (low) and extravascular (high) spaces
- used if there is a free water deficit, hypernatremia
Fluid types- Why do we use hypertonic crystalloids?
- The more hypertonic solution, the larger the osmotic driving pressure and the more rapidly water will move into and expand the plasma volume
- Water moves from the interstitial and intracellular spaces (low osmotic pressure) to the intravascular space (high osmotic pressure)
- only used in emergency cases eg- hypovolaemic shock and cerebral oedema
What is oncotic pressure?
the pressure exerted by large molecular weight molecules that normally do not cross the capillary membranes
Fluid types- Why do we use colloid solutions?
- contain proteins (albumin) or starch to be used in more specific circumstances such as blood loss
- also used for hypovolemia, sepsis, hypotension, hypoalbuminemia
What are our priorities in fluid therapy?
to maintain enough oxygen delivery to vital organs to sustain aerobic metabolism
Why is fluid therapy used during anaesthesia?
- Counteract the haemodynamic effects of general anaesthetics
- Establish IV access
- Replace the insensible fluid losses and the fluid loss associated with surgery
What effects do anaesthesia have on the body?
- reduce myocardial contractibility, CO and vascular responsiveness and cause vasodilation
