Peri-op Care: Fluid Management Flashcards
What are the 3 reasons for fluid prescription?
- Resuscitation
- Maintenance
- Replacement
What patient factors must be taken into account when prescribing fluids?
Patient size and weight
Co-morbidities, e.g. heart failure, CKD
Reasons for admission, e.g. septic or bowel obstruction patients need aggressive fluid prescribing
Recent electrolytes
Describe the distribution of total body water in terms of intracellular fluid, extracellular fluid, intravascular space and interstitial space.
- 2/3 intracellular
- 1/3 extracellular, of this:
~ 1/5 intravascular (3L plasma + 2L RBC = 5L)
~ 4/5 interstitial
Why are large volumes of IV fluids required in septic patients?
In septic patients, tight junctions between capillary endothelial cells break down and vascular permeability increases… fluid extravastion into tissues.
So necessary to give relatively large volumes of IV fluids to maintain intra-vascular volume, even though total body water may be high.
What are insensible losses and how do these change in unwell patients?
Insensible losses = fluid output from non-urine sources, e.g. respiration, sweating, faeces.
Increase in unwell patients (may be febrile, tachypnoeic, increased bowel output).
Suggest signs suggesting fluid depletion.
- Dry mucous membranes and reduced skin turgor
- Decreased urine output
- Orthostatic hypotension
In worsening stages:
- Increased capillary refill time
- Tachycardia
- Low BP
Suggest 3 signs indicating fluid overload.
- Raised JVP
- Peripheral or sacral oedema
- Pulmonary oedema
What are the recommended water, Na+, K+ and glucose values for adults?
Water = 25-30ml/kg/day
Na = 1-2mmol/kg/day
K/Cl = 1mmol/kg/day
Glucose: 50-100g/day
Describe the 2 broad categories of IV fluids.
CRYSTALLOIDS
- more widely used than colloids (cheaper)
- e.g. 0.9% saline, 5% dextrose, Hartmann’s solution
COLLOIDS
- high colloid osmotic pressure - should theoretically raise intravascular volume faster although this is not supported by clinical trials
Which 3 blood test results indicate volume depletion?
- Increased urea:creatinine
- Increased sodium (dehydration)
- Increased haematocrit
Why does serum urea increase relative to creatinine in dehydration?
Dehydration causes increased renal urea reabsorption by ADH and decreased urea excretion
Should 0.9% saline or 5% dextrose be given to a patient who is dehydrated? Who is hypotensive?
In dehydrated patient, give 5% dextrose - is distributed amongst total body water as dextrose is metabolised (hypotonic) leaving only H2O which equilibrates between compartments
In hypotensive patient, give normal saline (isotonic) - remains in ECF as contains Na+ that doesn’t enter cell.
Describe a commonly used fluid maintenance regimen.
1L normal saline over 8hrs
1L 5% dextrose + 20mmol KCl over 8hrs
1L 5% dextrose + 20mmol KCl over 8hrs
Explain why dehydration and increased haematocrit are features of small bowel obstruction, even before vomiting begins.
Fluid loss in bowel due to:
- Accumulation of fluid
- Increased fluid secretion
- Decreased fluid reabsorption
Results in isotonic hypovolaemia.
Why does severe vomiting result in hypochloremic, hypokalemic metabolic alkalosis?
Vomiting causes loss of hydrogen and chloride (HCl) ions, leading to hypochloremic metabolic alkalosis.
Renal compensation for alkalosis is to preserve H+ at expense of K+, leading to hypokalaemia.
