Fluid management Flashcards
What volume and proportion is total body water (TBW) in a 60kg person?
42L, 60%
What volume and proportion is ICF (intracellular fluid) n a 60kg person?
28L, 40%
What volume and proportion is total ECF (extracellular fluid) in a 60kg person?
14L, 20%
What 2 componenets make up ECF and what volumes are each?
Interstitial fluid: 10L
Intravascular fluid: 4L
What happens to age/ gender related changes in total body water with age?
As a baby TBW decreases; from teenage years it decreases more rapidly in females than in males. Continues to decrease this way into old age
What are 2 broad causes of fluid shifts?
- Between body and outside world: intake and output
- Between fluid compartments: osmosis, diffusin and active transport
What is the definition of osmosis?
Movement of solvent - water - across a membrane to a region of higher concentration of solute. Rate of movement depends on the number of particles in solution
What are the definitions of osmolarity and osmolality - how do they differ?
- Osmolarity = number of osmoles per litre
- Osmolality = number of osmoles per kg
- Osmolarity is within Ls, osmalality in kgs
What do osmoles express?
Osmotic activity
1 osmole of solute dissolved in 1kg of solvent has osmolality of 1 osmol/L (often given milliosmoles/L)
What is the equation used to work out plasma osmolality?
Plasma osmolality (Posm) = 2[Na] + glucose + urea
What is the usual physiological plasma osmolality?
290 mosmol/kg
Why is there extreme hyperosmolatity in hyperglycaemic hyperosmolar state in diabetes?
Sodium, glucose and urea all go up in this state
What is the definition of tonicity?
osmolality of a solution relative to plasma
What happens to blood in a hypertonic solution?
Red cells shrink - if didn’t mix with rest of blood
When is a hypertonic solution sometimes used?
For emergency resuscitation
What is an example of a hypotonic solution?
Distilled water
What happens to blood in a hypotonic solution?
Red cells lyse - fatal if large amounts injected
What happens to red cells in an isotonic solution?
They are OK
What are 2 examples of isotonic solutions?
- 5% glucose in water
- 0.9% NaCl
Which compartment do people lose fluid from, predominantly?
Extracellular fluid
What are 3 sources of fluid influx during a normal day?
- 1.3L from drinking
- 800ml from food
- 400ml from metabolism
Total: 2.5L
What are 4 sources of fluid loss during the day?
- 500ml through skin
- 400ml through lungs
- 1500ml through urine
- 100ml through faeces
(total: 2.5L)
What are the 2 groups that IV fluids are conventionally divided into?
Crystalloids and colloids
What is a crystalloid?
Sterile mixture of water with salt or sugar, or a mixture of both salt and sugar. Contain only small molecules
What are 2 advantages of crystalloids?
- Safe; low incidence of anaphylaxis
- Cheap
What is the half life like of crystalloid solutions and how are they excreted?
Short intra-vascular half-life, excreted via kidneys
What are 3 examples of crystalloids?
- 0.9% NaCl
- 5% dextrose
- Hartmann’s (loved by anaesthetists, often used in theatre)
What happens when 0.9% NaCl is given?
Distributes entirely to the ECF
interstitial : intravascular 2:1 –> 1L expands interstial volume by 666ml, and intravacsular by 333ml
What is the sodium content of 0.9% NaCl compared with physiolgical levels?
150mmol/L in 0.9% NaCl; plasma concentration is 137-142mmol/L
What happens when 5% dextrose is given?
Distributes to all compartments following metabolism of the glucose; small impact on circulating volume
i.e. if 1L given, ICF expands by 666ml and ECF by 333ml (as ICF:ECF volume is 2:1). Within ECF, interstitial : intravascular is 2:1 so about 100ml will end up intravascularly
How does Hartmann’s solution compare to other crystalloid solutions?
much more physioogical than saline or 5% dextrose (contains sodium, chloride, lactate, potassium, calcium). Stays in circulation for around same time as saline. Often used in theatre
What are the 5 elements in Hartmann’s?
- Sodium 131mmol/L
- Chloride 111mmol/L
- Lactate 29mmol/L
- Potassium 5mmol/L
- Calcium 2mmol/L
What are colloid solutions?
Large molecular weight compounds, used for plasma expansion
What are 4 examples of colloid solutions?
- Non-synthetic (less used): human albumin serum (HAS)
- Synthetic: gelatin, dextran, starch (suspended in isotonic fluid e.g. NaCl)
How does the half life of colloids compare to crystalloids?
Longer intra-vascular half life than crystalloids
What happens when colloids are given?
1:1 volume replacement
What are 4 problems with synthetic colloids (not HAS)?
- Anaphylaxis
- Affect coagulation (anti-thrombotic)
- Deposit in reticulo-endothelial system (pruritis) - especially starches, itchy
- Renal function (starch)
What are 2 features of the patient history suggesting fluid status (partiularly dehydration)?
Protracted period of polyuria
What are 6 features of examination that can point to fluid status?
- Mucous membranes
- Skin turgor
- Capillary refill
- JVP
- Blood pressure
- Urine output (reduced if extreme change)
What are the 3 stages of dehydration and what percentage and volume are lost in each?
- Mild - 4% of TBW, 3L - reduced skin turgor, dry membranes
- Moderate - 5-8%, 4-6L - oliguria, tachycardia, hypotension
- Severe - 8-10%, 7L - CVS compromise, confusion/coma
What are 3 investigations to help determine fluid status and what can they show?
- FBC - haemoconcentration, anaemia, transfusion requirement
- U+Es = sodium and urea elevated, urea: creatinine ratio can change in dehydration and renal failure
- Creatinine - unaffected in just dehydration
Why can it be difficult to interpret FBC to work out if dehydration is present?
Difficult if blood loss and dehydration at same time - haemoconcentration may seem normal
What happens to all infused sodium in the body?
remains in ECF
What happens to water when entering the body?
Expands entire TBW
How does dehydration affect the fluid compartments in acute illness?
Almost uniform
What is the only indication for 5% dextrose/ glucose and when should it never be used?
Only indication is dehydration/prevention: do not give if bleeding as will give generalised body oedema
What is the treatment for hypovolaemia?
Rapid infusion of an isotonic solution: Hartmann’s or colloid
What is the treatment for concelealed/ sequestered fluid losses?
Replace with normal saline
How should a TBW deficit be treated?
Replace with 5% dextrose
What are the maintenance requirements for a patient who is not eating or drinking e.g. in peri-operative phase?
1.5ml/kg/hour - otherwise will become dehydrated
What are the daily sodium and potassium requirements of the average person?
Sodium: 2mmol/kg/day
Potassium: 1mmol/kg/day
What is very important to remember to give post-operatively?
Potassium: some patients not given potassium even when they have normal renal function, and become hypokalaemic
How should potassium replacement occur if a patient is asymptomatic?
Correct slowly; 20-40mmol of KCl/ L of 0.9% saline
Re-estimate U+Es frequently
How should potassium levels be kept in arrhythmias?
Aim for high normal levels
What is the management of urgent fluid therapy?
ABC approach
14g IV (orange) venflon, preferably 2
Do not delay for investigation
2000ml normal saline or 1000ml colloid STAT
Reassess fluid status
What are 7 types of blood products?
- Whole blood
- Fresh frozen plasma (FFP)
- Cryoprecipitate
- HAS (human albumin serum)
- Platelet-rich plasma
- Platelet concentrate
- SAG-M (saline adenine glucose and mannitol re-suspension of) red blood cells