Fluids and Nutrition Flashcards
Body composition of water?
Total water: 60% of 70kg = 42L
2/3 intracellular = 28L
1/3 extracellular = 14L
- Plasma 3L, Interstitial 10L, transcellular 1L
what is osmotic pressure?
pressure which needs to be applied to prevent the inflow of water across a semipermeable membrane
ie. ability of solute to attract water
what is oncotic pressure?
form of osmotic pressure exerted by proteins
what is hydrostatic pressure?
pressure exerted by fluid at equilibrium due to the force of gravity
third spacing of fluids leads to decrease in?
extracellular fluid
ie. bowel obstruction -> decreased fluid reabsorption -> 3rd space loss
peritonitis -> ascites -> 3rd space loss
minimum urine ouput should be?
0.5 ml/ kg/ h = 30 ml/kg for 60kg human
what is the Na daily requirement?
1.5- 2 mmol/kg/day = 120 mmol/ day for 60 kg
140 mmol/ day for 70 kg
what is the minimum K requirement for the day?
1 mmol/kg/ day = 60 mM/ day for 60kg
what is the average fluid daily requirement for a 60-70 kg human?
e.g. 1L 0.9% NaCl + 2L dextrose with 20mM K+ in each bag
each bag over 8h = 125 ml/h
replacing 3L, 154mM Na+ (around 120) and 60 mM of K+
what are sources of fluid losses that one should replace?
diarrhoea and vomiting
NG tube
drains
fever (+500mL for each degree increase)
Tachpnoea
High output stomas
CVP monitoring
- what is this measuring?
indicates RV preload and depends on venous return and cardiac output
causes of raised CVP?
High circulating volume
Low Cardiac Output: ie. pump failure
Causes of reduced CVP?
low circulating volume
what is a normal central venous pressure?
5-10 cm H2O
what does it mean if CVP does not change despite fluid challenge?
hypovolaemic
what does it mean if CVP increases and reverses after 30 min of fluid bolus?
pt euvolaemic
what does it mean if CVP is sustained above 5cm H2O after fluid challenge/
fluid overload/ pump failure
contents of 0.9% normal saline?
154 mM NaCl
used for normal daily fluid requirements + replace losses
*need to add K+
contents of Hartmanns’/ Ringer’s Lactate solution?
Na: 131 mM
Cl: 111 mM
K: 5mM
Ca: 2.2 mM
Lactate/ HCO3: 29mM
use in resus for trauma pts
alkalinising solution as lactate is a conjugate base
(lactate metabolised in liver -> HCO3 production)
what is a colloid/
contains large molecular weight molecules
e.g. gelatin, dextrans
to preserve oncotic pressure -> remains intravascular -> preferential increase in intravascular volume
e.g.s of colloids
albumin, blood
gelofusin
problems w colloids
increased risk of anaphylaxis
can interfere with cross matching -> take blood for x match before using
How to assess fluid status before examining pt?
History: thirst, surgery, other losses (D+V)
look at fluid balance chart
impression: pt drowsy?
Assessing pt fluid status on examination?
inspection: drips, drains, stomas, catheters, CVP
central CRT, HR, BP lying and standing
JVP
skin turgor, mucous membranes
oedema?
Urine Output, Urea/ creatinine
What to consider when prescribing fluids post op?
Post op:
raised ADH/ cortisol/ aldosterone -> Na + H20 conservation
raised K+: tissue damage, transfusion, stress hormones
solutions:
use UO to guide fluid replacement but may decrease maintenance fluids to 2L first 24h post op
Avoid K+ supplementation for first 24h post op
what are some problems to consider in cardiac or renal failure when prescribing fluids?
RAS activation -> Na and H20 retention
solution: avoid fluids w Na -> give 5% dextrose
mx of high output ileostomy?
Loperamide
codeine
causes of reduced UO post op?
post renal: commonest
- blocked/ malsited catheter
- acute urinary retention
pre-renal: hypovolaemia
renal: NSAIDs, gentamicin
mx of blocked catheter?
flush w 50 mL Normal saline and aspirate back
mx of hypovolaemia causing low UO post op?
fluid challenge
500mL bolus over 15 min
look for CVP or UO response within minutes
definition of refeeding syndrome?
life-threatening metabolic complication of refeeding via any route after a prolonged period of starvation
what electrolytes are abnormal in refeeding syndrome?
low K+, Mg2+, PO4-
Hypophosphataemia may lead to?
Rhabdomylolysis
Resp insufficiency
Arrhythmias
Shock
Seizures
risk factors for refeeding syndrome?
malignancy
anorexia nervosa
alcoholism
GI surgery
starvation
mx of refeeding syndrome?
liase w dietician
parenteral and oral PO4 supplementation
tx complications
caloric requirements?
20-40 kcal/ kg/ day
indications for enteral nutrition?
catabolic: sepsis, burns, major surgery
coma/ ITU
malnutrition
dysphagia: stricture, stroke
complications of Ng tube for enteral nutrition?
nasal trauma
malposition -> aspiration pneumonia
tube blockage
complications following enteral nutrition?
refeeding syndrome
aspiration
electrolyte imbalance
feed intolerance -> diarrhoea (build up feeds gradually to prevent diarrhoea)
indications for parenteral nutrition?
prolonged obstruction or ileus (>7d)
high output fistula
short bowel syndrome
severe crohns/ malnutrition/ pancreatitis
unable to swallow
how is parenteral nutrition delivered?
centrally as high osmolality toxic to veins
- short term: via CV catheter
- long term: via Hickman or PICC line
sterility is essential: use line ONLY for PN
complications of parenteral nutrition?
line related:
line sepsis, cardiac arrhythmia, pneumo/haemothorax, central venous thrombosis
feed related:
villous atrophy of GIT
electrolyte disturbances - refeeding syndrome
hyperglycaemia and reactive hypoglycaemia
vitamin and mineral deficiencies
