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Fluids (CRYSTALLOIDS
Water soluble crystalline substance capable of…
Fluids
CRYSTALLOIDS
- Water soluble crystalline substance capable of diffusion through a semi-permeable membrane e.g. Na, K, Glucose, Ca, Cl
- Can infuse rapidly in large volumes
- Readily available
- Cheap
- Equilibrate with large fluid compartments
- Short duration in circulation
- Risk of over perfusion / pulmonary oedema
0.9% NaCl
- 0.9g/100ml
- 154mmol Na, 154mmol Cl per litre
- 4.7L = 1L increase in plasma volume
- All in ECF - 25% intravascular, 75% interstitial
- Contains chloride > HYPERCHLORAEMIC ACIDOSIS
Hartmann's
- Balanced: Na+, Cl-, K+, Ca2+, Lactate
- Similar distribution to 0.9% NaCl
- Lactate = gluconeogenic
5% Dextrose
- Water and dextrose
- Distributes throughout body water
- 14L = 1L increase in plasma volume
4% Dextrose / 0.18% Saline
- Dex-Saline
- Similar distribution to 5% Dextrose
- Free water, dilution, risk of hyponatraemia
Electrolyte distribution
Positively charged electrolytes
- Sodium (Extracellular 142, Intracellular 10)
- Potassium (Extracellular 5, Intracellular 100)
- Calcium (Extracellular 5)
- Magnesium (Extracellular 2, Intracellular 123)
- Total positive ions = 154 Extracellular, 205 Intracellular
Negatively charged electrolytes
- Chloride (Extracellular 105, Intracellular 2)
- Bicarbonate (Extracellular 24, Intracellular 8)
- Proteins (Extracellular 16, Intracellular 55)
- Phosphate (Extracellular 2, Intracellular 149)
- Sulphate (Extracellular 1)
- Total negative ions (Extracellular 154, Intracellular 205)
Water balance
LOSSES
- Skin 500ml
- Lungs 400ml
- Gut 100ml
- Kidneys 500ml
Total 1500ml
SOURCES
- End product of metabolism 400ml
- Diet 1100ml
Total 1500ml
COLLOIDS
- A dispersion or suspension of finely divided particles in a continuous medium - NOT a solution
- Fluid stays in circulation
- All contain NaCl
- No oxygen carrying ability
Gelatins
- Gelofusine, Haemaccel, Volplex
- Contains modified gelatine
- Plasma half life 2-3 hours
- Small risk of allergic reactions
Albumin
- HAS = Human Albumin Solution
- Pooled human plasma
- Stays in intravascular space
- 1-2hour effect
Definitions
- Solute = a dissolved substance
- Solvent = a liquid which is able to dissolve a solute to form a solution
- Semipermeable membrane = freely permeable to the solvent but not the solute
- Diffusion = movement of a solute down a concentration gradient
- Osmosis = movement of water from a less concentrated solution to a more concentrated solution
- Osmotic pressure = proportional to the number of particles in a solution
- Osmolarity = concentration of osmotically active particles in the solution (milliosmoles)
Daily requirements
- WATER 30-40ml/kg
- ENERGY 30-40kcal/kg
- Sodium 1-2mmol/kg
- Potassium 1mmol/kg
- Chloride 1.5mmol/kg
- Phosphate 0.2-0.5mmol/kg
- Calcium 0.1-0.2mmol/kg
- Magnesium 0.1-0.2mmol/kg
Water and sodium homeostasis in illness/injury/starvation
- Water - non-physiological ADH release, water retention, dilution hyponatraemia
- Sodium - renin release, sodium and water retention, fluid overload
Fluid depletion
- Decreased intake: elderly, dysphagia, unconsciousness, fasting
- Increased loss: fever/sweating, hyperventilation, diarrhoea/vomiting, renal loss, diuretics, third space losses!
- Increased requirements: trauma, burns, post-operative
BLOOD
- Colloid - ideal replacement for acute blood loss
- Expands intravascular volume
- Oxygen carriage
- Packed red cells ~300ml
- Transfusion reactions, infection risk, expensive
Assessment of fluid deficit
- MILD = loss of 4% body weight, loss of skin turgor, dry mucous membranes
- MODERATE = loss of 5-8% body weight, oliguria, tachycardia, hypotension
- SEVERE = >8% body weight, profound oliguria, CVS collapse