3. Osmolality
The solute concentration in the body fluid by weight. The number of
miliosmoles (mOsm) in a kilogram (kg) of a solution.
Normal Plasma Osmolality = 275-295 mOsm/kg
6. Patient Identification
Acute presentations with vomiting or diarrhea, including intestinal
obstruction, biliary colic, gastroenteritis.
Patients who had been immobile or debilitated for a period before
presentation causing reduced fluid intake, like, pancreatitis, pneumonia,
prolonged sepsis, acute on chronic vascular insufficiency.
Drugs that impair renal response to fluid changes, like diuretics.
Patients with low body weight and with overall lower total body fluid
volume in whom similar losses have a greater effect.
7. Daily Losses
Water loss 2500ml/day (insensible losses from skin, respiratory and GI
tract, and in urine). ↑ loss in sepsis, ventilation, diarrhea, vomiting, high
output fistulas, polyuric renal failure
Na+ 100mmol/day in urine. ↑ loss in pyrexias, diarrhea, vomiting, high
output fistulas.
K+ 80mmol/day in urine. ↑ loss in pyrexias, diarrhea, vomiting, high
output fistulas.
8. Maintenance Fluid Calculation (Rules)
4/2/1 Rule
4ml/kg for first 10 kg
2ml/kg for next 10kg
1ml/kg for every next kg
Example for a 80kg patient,
10kg x 4ml/kg = 40ml
10kg x 2ml/kg = 20ml
60kg x 1ml/kg = 60ml
Maintenance rate = 120ml/hour and total fluid per day required is 2880ml
9. +40 Rule
If the patient weighs more than 40kg, add 40 to the weight and that will be
maintenance amount of fluid per hour.
Example for a 80kg patient
Adding 40 in the weight
Total maintenance fluid for this patient will be 120ml/hour.
Hence total fluid required in a day will be 2880ml by using this rule.
Electrolytes
Sodium (Na+): 1-2 mmol/kg/day
Potassium (K+): 0.5-1 mmol/kg/day
10. Calculation of IV Flow Rates
Intravenous fluids must be given at a specific rate, neither too fast nor too
slow.
The specific rate may be measured as ml/hr, litre/hr or drops/min.
To control or adjust the flow rate only drops/min are used.
Drop Factor
Drop factor is the number of drops in one milliter used in IV fluid
administration, also called drip factor.
A number of different drop factors are used but the commonest are:
Blood Set (10 drops/ml)
Regular Set (15 drops/ml)
Burette or Peadiatric Chamber (60 drops/ml)
11. Calculation of IV Flow Rates
Formula:
volume(ml) x drop factor / time(min)
Example
1500ml IV fluids are to be given over 12 hours. Using a drop factor of
15 drops/min.
1500 × 15
12 × 60
= 31 drops/minute
12. Management
The goal of fluid therapy is to maintain the urine output of
0.5 – 1.0 ml/kg/day
Avoidance of fluid overload, especially in malnutrition, heart failure, and
renal insufficiency patients.
GI losses that exceed 250ml/day should be replaced with equal volume of
crystalloids.
The minimum urine volume required to maintain normal BUN and
Creatinine is 0.24ml/kg/hr (oliguria is less than 400ml/day)
BUN to Cr ratio is helpful in assesment of hydration status,
If BUN/Cr more than 20, dry side
If BUN/Cr less than 10, wet side
13. Assessment of Volume Status
History and Examination
The dry patient. May have been NPO several days preoperatively, feels thirsty,
complains of dry mouth, dehydration could be due to diarrhea or vomiting, low
JVP, dry mucous membranes and reduced skin turgor
The over-filled patient. No thirsty feeling, raised JVP, normal skin turgor, may
have dependent edema, and evidence of pulmonary edema on auscultation
Observations Chart
The dry patient. May have falling BP, rising pulse, low CVP not rising with fluid
challenges, weight several kilos below preoperative weight.
The over-filled patient. Not usually tachycardic and has high CVP that rises
and plateaues with fluid challenges, BP falling with fluid challenges and weight
several kilos above the preoperative weight.
14. Assessment of Volume Status
Fluid balance chart
The dry patient. Usually be in several liters of negative fluid balance, possibly
over a few days, with a urine output less than 1ml/kg/hr.
The over-filled patient. Will be in several liters of positive fluid balance,
possibly over a few days. Urine output may be low because of heart failure or
renal dysfunction.
Blood results
The dry patient. ↑ sodium, potassium, creatinine, and urea
The over-filled patient. May have hyponatremia.
CXR
The dry patient. No evidence of pulmonary edema or effusions.
The over-filled patient. May have both pulmonary edema and effusions.
15. Sodium (Na+)
Normal values: 135 - 145 mEq/l
Calculation of Sodium defeict in mEq
Total body water x (Desired Na - Serum Na)
TBW (Adult Male) = 0.6 x weight (kg)
TBW (Adult Female) = 0.5 x weight (kg)
20. Management of Hyponatremia
Asymptomatic: increase the sodium level by no more than 0.5-1meq/L/h
to a maximum increase of 10meq/L per day
Symptomatic: (Na<120meq/L) Increase the sodium level by no more than
1meq/L per hour until the serum Na level reaches 130meq/L or neurologic
symptoms are improved
25. Management
Potassium removal
Kayexalate
Oral administration is 15-30g in 50-100 ml of 20% sorbitol
Rectal administration is 50g in 200 ml 20% sorbitol
Dialysis
Shift potassium
Glucose 1 vial of D50% and regular insulin 5-10 units intravenous
Bicarbonate 1 vial intravenous
Counteract cardiac effects
Calcium gluconate 5-10 mL of 10% solution
26.
27. Hypokalemia
Inadequate intake
Dietary, potassium-free intravenous fluids, potassium-deficient
total parenteral nutrition
Excessive potassium excretion
Hyperaldosteronism
Medications
Gastrointestinal losses
Direct loss of potassium from gastrointestinal fluid (diarrhea)
Renal loss of potassium (gastric fluid, either as vomiting or high nasogastric
output)
Intracellular-shift (metabolic alkalosis or insulin therapy)
29. Management
Serum potassium level <4.0 mEq/L
Asymptomatic, tolerating enteral nutrition:
KCl 40 to 100 mEq/day via entral access
Asymptomatic, not tolerating entral nutrition
Intravenous KCl at rate of 10 to 20 mEq/hour
If infused at rate >10meq then cardiac monitoring required.
Rate can be 40meq through Central lines.
Increased losses from lungs in dry atmospheres or in patients with tracheostomy, hence humidification of air is important.
This 1500ml/day urine output is warranted for normal functioning kidneys. A minimum of 400ml/day output is required to excrete the end products of protein metabolism.
D5W is considered a isotonic solution but once the dextrose is metabolized it acts as a hypotonic solution causing the fluid shifts into the cells.
LR is technically the closest fluid to serum composition.
NS is most widely used fluid. With adequate renal function NS prevents rapid cellular fluid shifts during rehydration and excess Na is excreted via kidneys. K should usually to be added only if low serum K is present.