Fluid Management Flashcards
What are the main reasons for fluid prescriptions?
Resuscitation - improving tissue perfusion by raising intravascular volume)
Maintenance
Replacement
What must you consider before prescribing fluids?
Aim of fluid: rests, maintenance, replacement
Weight and size of patient
Co-morbiditis - HF/CKD
Underlying reason for admission - some surgical patients are deliberately run on the dry side
What was their most recent electrolytes
Describe the body fluid compartments.
Total body water (42L)
2/3 of body water distributes to ICF (28L)
1/3 of body water distributes to ECF (14L)
1/5 of ECF stays in intravascular space (plasma) (3L)
4/5th in interstitial water (11L)
What is the circulating blood volume? Made up of?
5L
3L plasma
2L red cells
What is the difference of fluid distribution required for maintenance and resuscitation?
For general maintenance - fluid to distribute into all compartments
For resuscitation - fluid to stay within intravascular space
Why is it necessary to give lots of fluid in sepsis?
Capillary junctions become leaky and vascular permeability increases so lots of fluid required to maintain intravascular volume
What is haematocrit?
Proportion of blood that consists of RBCs
Usually 2L/5L so 40%
At rest the HR is 70 bpm and SV is 70ml so CO at rest is 4900ml/min ~ 5L/min
So total blood volume circulates once per minute
How is fluid gained and lost from the body? How much?
Intake:
Drinking (1.5L)
Food (0.5L)
Metabolic (0.5L)
Output: Urine (1.5L) Respiration (0.4L) Sweating (0.5L) Faeces (0.1L)
Actual amount varies depending on physiological status and body weight
What are insensible losses of fluid?
Losses from non-urine sources - faeces, sweating respiration.
This will rise in unwell patients - febrile, tachypnoeic, increased bowel motions
OE, what should you look for in fluid depleted patients?
Dru mucous membranes Reduced skin turbot Urine output (should be 0.5ml/kg/hr) Thirst Increased cap refill time Tachycardia Hypotension
What should you look for in a fluid overloaded patients?
Raised JVP Peripheral oedema Pulmonary oedema Tachycardia Tachypneuoa/hypoxia
What are essential tools to monitor fluids?
Input/output chart
Daily weight
U&Es regularly checked
What are the daily requirements for water sodium, potassium and glucose?
Water - 25ml/kg/day
Na - 1mMol/kg/day
K - 1mMol/kg/day
Glucose - 50g/day
What is osmolality?
The concentration of particles in a solution
The higher the osmolality, the greater the concentration of particles in a solution.
Particles move from areas of higher osmolality to lower osmolality (due to osmotic pressure)
What causes increased urine osmolality?
More concentrated urine Dehydration Renal disease Congestive hear failure DM/hyperglycaemia Hypernatraemia Addison's
What causes decreased urine osmoliaity?
Diabetes insipidus - large amounts of dilute urine and increased thirst due to lack fo ADH (Central), kidneys not responding to ADH (nephrogenic)
What causes decreased serum osmoliaity and increased urine osmolality
Syndrome of Inappropriate ADH secretion
Excessive release of ADH from posterior pituitary
Urine is not dilute - water is retained
Serum less concentrated
What causes decreased serum osmolality and urine osmolality
Overhydration
Hyponatraemia
What are the 2 groups of IV fluids?
Crystalloids:
Cheaper and more commonly used
Colloids:
Have high colloid osmotic pressure so theoretically should raise intravascular volume faster than crystalloids but no benefits demonstrated
What are the 3 main types of colloid? Crystalloids?
Colloids:
Gelatins
Albumin
Blood products
Crystalloids:
0.9% NaCL saline
5% dextrose
Hartmann’s solution
How much sodium and chloride in 1L of 0.9% NaCl?
How much glucose in 1L of 5% dextrose?
What does dextrose-saline contain?
150mmol of sodium, 150mmol of chloride
50g of glucose in 1L dextrose
1/5th normal saline: 1L water, 40g dextrose, 30mmol of sodium and 30mmol of chloride
How much water/sodium/potassium/glucose is required for a 70kg normal healthy male?
1750ml water
70mmol Na
70mmol K
50g glucose
Give a maintenance fluid regimen for a 70kg man who has adequate renal function and is not overloaded
1: 500ml of 0.9% saline with 20mmol/L K over 8 hours
All Na, 1/3rd of K and 1/4 of water
2: 1L of 5% dextrose with 20mmol/L K over 8 hours
1/3rd K and half of water and all glucose
3: 500ml of 5% dextrose with 20mmol/L K over 8 hours
Remaining 1/3rd of K and 1/4 of water as well as glucose
Which patients cannot be safely prescribed typical maintenance regimens?
Renal impairment - normal kidneys correct any minot errors of fluid/electrolyte administration. However patients with renal compromise must be planned
Cardiac impairment
Elderly, frail, cachectic patients
What is reduced urine output? How should this be managed?
<0.5ml/kg/hour
Fluid challenge and urine output subsequently rechecked, also checking catheter is not blocked or patient is not in retention
What is a fluid challenge for decreased urine output?
250ml/500ml Hartmann’s over 1 hour depending on patient size and comorbidities
What are reasons patients may be in fluid/electrolyte deficit?
Vomiting, fistulae, bleeding, perotinitis
What should be assessed for excess fluid loss?
Third space losses - to bowel lumen (obstruction) or retroperitoneum (pancreatitis) Diuresis? Tachypneoic? Febrile so sweating more? Passing more stool/high output stoma Losing electrolyte rich fluid? Dehydration? Raised haematocrit and raised Urea:creatinine ratio (raised serum urea) Vommitting (Low K, low Cl and alkalosis) Diarrhoea (Low K and acidosis)
