Fluids Flashcards
Replacement fluids
Typical fluid
0.9% saline (crystalloid)
Replacement fluids
Exceptions (2)
Hypernatraemic or hypoglycaemic:
- 5% dextrose
Has ascites:
- Human-albumin solution (saline would worsen ascites)
Replacement fluids: how fast?
- If tachycardic/hypotensive, give 500 mL bolus immediately (250mL if HF), then reassess HR, BP and urine output
- If only oliguric (and not due to urinary obstruction), give 1L over 2-4 hrs then reassess HR, BP and urine output
Replacement fluids: how depleted is someone?
Use their obs:
- Reduce urine output (oliguric if < 3mL/hr, anuric if 0ml/hr) indicated 500 mL of fluid depletion
- Reduced urine output plus tachycardia indiciated 1L of fluid depletion
- Reduce urine output plus tachy plus shocked indicates 2L+ of fluid depletion
Fluids
% of intracellular fluid?
65%
Fluids
% of extracellular fluid?
35%
25% in interstitial and 10% in intravascular
Fluids
Intracellular fluid composites
- High potassium concentration
- Low sodium concentration
- Intracellular solute concentrations remain more or less constant
Fluids
Extracellular fluid composites
- High sodium concentration
- Low potassium concentration
Fluids
What is Starling’s hypothesis?
The fluid movement due to filtration across the wall of a capillary is dependent on the balance between the hydrostatic pressure gradient and the oncotic pressure gradient across the capillary
- Water moves between intra- and extra-cellular compartments through osmosis
- Distribution of water is determined largely by extracellular sodium ion concentration
- Extracellular solute concentration determines intracellular water quantity and consequently cell vol
- Gradient is maintained by sodium-potassium ATPase pump
Fluids
Urine output of a) healthy person b) fluid replacement aim
a) 1 ml/kg/hr
b) Aim for 0.5ml/kg/hr
Fluids
Sources of fluid loss (6)
- Urine
- GI (approx 100ml/day lost via faeces)
- Insensible losses (500-800 ml per day on average). Can increase if sweating, febrile, tachypnoeic, open cavity surgery.
- Surgical (biliary drain, pleural and peritoneal drain output)
- Bleeding
- Burns
Fluids What is lost in: a) Sweat b) Diarrhoea/increased stoma output c) Vomiting d) Insensible los
a) Sodium
b) Sodium, potassium, bicarbonate
c) Potassium, chloride and hydrogen ions (hence picture of hypochloraemic metabolic alkalosis, sometimes with mild hypokalaemia)
d) Pure water loss
Fluids
What are crystalloids
Essentially mineral salts
Fluids
What are colloids?
Examples
Distribution
Contain larger water-insoluble molecules such as complex branched carbohydrates or gelatin
- Blood
- Dextrans
- Gelatin (e.g. gelofusine)
- Human albumin solution
- Hydroxyethyl starch (HES)
Distribution: All stays in intravascular compartment
Fluids
Things to consider when choosing type of fluid
- Type of fluid loss
- Renal function
- Cardiac function
- Concomitant electrolyte abnormalities
What should you assess before prescribing fluids?
- BP
- Cap refill
- Fluid balance charts
- Response to straight leg raise
- Skin turgor
- Weight
Fluids
Isotonic crystalloids
Definition and example
- Stay almost entirely within the extracellular compartment, 25% to intravascular and 75% to interstitial
- E.g. NaCl 0.9%
Fluids
Hypertonic crystalloids
Definition and example
- Increase plasma tonicity and draw fluid out of cells
- E.g. NaCl 3%, mannitol
Fluids
Hypotonic crystalloids
Definition and example
- Lower serum osmolarity and are not commonly used
- NaCl 0.45%
Fluids
How does 1L of glucose 5% distribute?
2/3rds intracellular
1/3rd extracellular
Approx 80mls will stay in the intravascular compartment
Define distributive shock?
3 causes
Results in a relative hypovolaemia
Causes: sepsis, anaphylaxis, neurogenic shock
Hypovolaemia shock
3 causes
Most common form of shock encountered
Causes: hemorrhage, burns or any cause of substantial fluid loss
Grading of shock
15%/750ml
- Grade 1
- Mild resting tachycardia, slight delayed CPT 3 secs
15-30%/750-1500mL
- Grade 2
- Cool peripheries, tachycardic, decreased pulse pressure, delayed CRT 5 seconds
30-40%/1500-2000mL
- Grade 3
- Marked tachycardia and tachypnoea, low systolic BP, narrow pulse pressure, oliguria, low vol pulse, a postural drop of 20-30, confusion/agitation
50-50%/2000-2500mL
- Grade 4
- Low GCS/unconscious, minimal or no urine output, thready pulse, very tachycardic, very low immeasurable BP, cold skin
Cardiogenic shock
Causes (4)
- Relative or absolute reduction in cardiac output due to primary cardiac disorder
- Circulatory collapse occurs as a result of pump failure
- May also have raised JVP or cardiac arrhythmias
Causes: ischaemia, heart failure, arrhythmias, cardiomyopathy
Obstructive shock
Causes (2)
- Physical impedance to blood flow
Causes: PE, cardiac tamponade
Fluids
What is the passive leg raise
- Mimics fluid bolus by tipping pt. to redirect fluid to heart
- One minute after measure HR, BP and stroke vol
- Return patient to original position and check again - should return to baseline
Fluid resus
500 ml of Sodium Chloride 0.9% over less than 15mins
- Review MAP, urine output, CRT
- These are in addition to calculated maintenance fluids
Maintenance fluids
- Matched the patient’s ideal body weight
- Total vol divided by 24 to give hrly rate
- Prescribe less for older adults, frail, renal/cardiac failure, malnourished, risk of refeeding syndrome
Replacement fluids
- Adjust to account for existing fluid and/or electrolyte deficits or excesses, ongoing losses (e.g. diarrhea, fever) or abnormal distribution
Tx of fluid overload
- Stop IV fluids
- Furosemide
- Sublingual nitrate
- IV nitrate
- CPAP
Maintenance fluids: which fluids and how much?
- General rule = adults 3L IV per 24 hrs
- Elderly 2L
- Adequate electrolytes are provided by 1L of 0.9% saline and 2L of 5% dextrose (1 salty, 2 sweet)
How can you provide potassium?
KCl in:
- 5% dextrose (not replacement)
or
- 0.9% saline
How much potassium?
- Guided by U&Es
- Normal K+ - give roughly 40 mmol KCl per day (20 mmol in 2 bags)
Max rate of potassium
- Max is 10mmol/hr
Max concentration of potassium
- Max is 40mmol/litre
Maintenance fluids: how fast?
a) 3L
b) 2L
a) 3L per day = 8-hourly bags
b) 2L per day = 12-hrly bags
NICE guidelines for maintenance fluids?
25-30 ml/kg of water
- 1 mmol/kg/day of potassium, sodium and chloride
- 50-100 g/day of glucose to limit starvation ketosis
When should you NOT give dextrose/
- In a stroke due to risk of cerebral oedema
- With KCl in replacement of K+
