Fluid management is essential for peri-operative patient care and impacts outcomes. Three key considerations for fluid prescription include the purpose of the fluid, the patient's weight and comorbidities, and laboratory values. Crystalloids are commonly used for volume resuscitation while colloids provide more sustained plasma expansion but risk allergic reactions. Proper fluid status assessment and strict input-output monitoring are important to avoid overhydration or dehydration.

1. Fluid Management
In Peri-operative patients
A guide to successful fluid prescribing.
Hooman Rowshan, M.D. MSc

2. Introductory
Remarks
Introduction
Effective fluid and haemodynamic management is central to
peri-operative patient care and has been shown to have a
significant impact on post-operative morbidity and the length of
hospital stay.
It is essential to gain a firm understanding of the physiology
of fluid balance and the compositions of each fluid being
prescribed.
It’s important to think about why fluids should be prescribed in
the first place.
Add fluids for resuscitation, maintenance, and
replacement
01
02
03
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3. Key Consider ations
01
Is the aim of the fluid for resuscitation,
maintenance, or replacement ?
What is the weight of the patient?
The fluid requirements of a frail 45kg 80yr female
and a healthy 100kg 40yr male will be
significantly different

4. Significant Comorbidity
02
heart failure or chronic kidney disease

5. P a t i e n t ’ s H i s t o r y
03
Underlying reason for admission
Labratory numbers
Most importan to check is the electrolytes
septic patients
bowel obstruction
septic patients or patients in bowel obstruction will
need aggressive fluid

6. Fluid Compartments
2/3rd of total body weight is water, which is further divided
2/3 of body water is distributed in to the intracellular fluid and the remaining 1/3 is distribute to the extracellular fluid
The fluid in the extracellular space, around 1/5th or 20% stays in the intravascular space
4/5th or 80% of the extracellular space is found in the interstitium
If a patient receives 1.5 litres of 5% dextrose, how much of this will remain in the intravascular compartment?
Work out the problem on your own: Correct Answer is 300 ____ fill in the correct unit
We will solve this problem step-by-step during the presentation

7. Normal Physiology
It is important to understand the different types of pressures that exists in the vascular space
In normal physiological state,the net effect of these pressures serve to retain fluid in the intravascular space
Capillary hydrostatic pressure (PC) is the pressure that drives fluid out of the capillary (i.e., filtration), and is
highest
at the arteriols and the lowest at the venular end
Capillary Plasma Oncotic Pressure is the pressure that keeps the fluid in the vascular space and is the function of
plasma proteins. Albumin generates about 70% of the oncotic pressure.The oncotic pressure increases along the
The oncotic pressure increases along the length of the capillary

9. Septic Patients
Septic patients lose large volume of intravascular fluid volume
It is often necessary to give relatively large volumes of intravenous fluid to maintain the intravascular
volume, even though the total body water may be high. Close monitoring of the fluid balance will be required
sepsis is a serious condition in which the body responds improperly to an infection
infection-fighting processes turn on the body, causing the organs to work poorly
Sepsis may progress to septic shock. Septic shock is a severe drop in blood pressure
Progression to septic shock increases the chances of death
Discribe the normal and the pathophysiological mechanisms of action?

10. Fluid Input
Only 3/5th of our fluid input comes through fluids via the enteric route. The rest comes
from both food and metabolic processes. When a patient is NPO, nil by mouth (NBM), it
is important that all sources are replaced via the parenteral route.
Fluid Output
Losses from non-urine sources are termed insensible losses
insensible losses will rise in unwell patients. The exmples are following:
febrile
tachypnoeic
Increase bowel secretion

11. Assessment of Fluid Status
In the fluid depleted patients, one should be looking for:
Dry mucous membranes and reduced
skin turgor
Decreasing urine output (should target >0.5 ml/kg/hr)
Orthostatic hypotension
Increased capillary refill time
Tachycardia
Low blood pressure

12. fluid overloaded
In patients who may be fluid overloaded, one should be looking for:
Peripheral or sacral oedema
Pulmonary oedema
Raised JVP
Ensure that the patient has a fluid input-output chart and daily weight chart commenced;
Also ensure to monitor the patient’s urea and electrolytes (U&Es) regularly, for any evidence of dehydration,
renal hypoperfusion, or electrolyte abnormalities

13. Daily Requirements
Patients do not just require water, they also need Na+, K+, and glucose replacing too
This is especially true if they are NPO
The current guidlines are as follows:
Water: 25 mL/kg/day
Na+: 1.0 mmol/kg/day
K+ 1.0 mmol/kg/day
Glucose: 50g/day

14. IV Fluids
IV fluids can be broadly categorised in to two groups, crystalloids and colloids
Crystalloids – Crystalloids are more widely used than colloids, with research supporting the idea that neither is
better
A crystalloid fluid is an aqueous solution of mineral salts and other small, water-soluble molecules. Most
commercially available crystalloid solutions are isotonic to human plasma. These fluids approximate
concentrations of various solutes found in plasma and do not exert an osmotic effect in vivo.
Colloid fluids are crystalloid electrolyte solutions with a macromolecule added that binds water by its colloid
osmotic pressure. As macromolecules escape the plasma only with difficulty, the resulting plasma volume
expansion is strong and has a duration of many hours.
We will now go over examples of these fluids used in clinical practice

15. Crystalloids
Crystalloid fluids are the first choice for fluid resuscitation in the presence of hypovolemia, hemorrhage, sepsis,
and dehydration
acting as a solution for intravenous medication delivery
blood pressure management
increasing diuresis
saline (0.9% NaCl solution)
0.45% NaCl (hypotonic solution
3% NaCl (hypertonic solution)
5% Dextrose in water
10% Dextrose in water

16. Crystalloids Mechansim of action
Crystalloid fluids function to expand intravascular volume without disturbing ion concentration or causing significant
fluid shifts between intracellular, intravascular, and interstitial spaces.
Hypertonic solutions such as 3% saline solutions contain higher concentrations of solutes than those found in
human serum. Because of this discrepancy in concentration, these fluids are osmotically active and will cause fluid
shifts.
Their primary indication is for emergent replacement of serum solutes, such as in hyponatremia with neurologic
symptoms.
In an acute setting, the clinical situation may indicate a rapid infusion of crystalloid fluids. For example in fluid
resuscitation
Fluids should be administered, preferably via large-bore peripheral lines (18-gauge or larger) or through central
access
Patients should receive a fluid challenge of 20 mL/kg over the first 30 minutes of treatment. Subsequent volume
dosing should depend on the severity of hypovolemia and should be adjusted in increments of 500 mL, aiming for
an ultimate central venous pressure of 8 to 12 mmHg. This may be required in septic patients

17. Maintenance Fluids
The fluid requirements of patients were determined to be related to a patient's caloric demand. Now we use a mass
based formula. The mass-based formula uses what is known as the "4-2-1" rule
4 ml/kg for first 10kg, 2ml/kg for the next 10kg, 1 ml/kg for every 1kg over 20.
Infusion rate = total fluid volume per day ÷ 24 hour
Example of Calculation:
for a 70kg person: 4×10=40; 2×10=20; 1×50=50. Total=110 ml/hr
Additional formulas for fluid administration have been developed for specific clinical scenarios (e.g., the Parkland
formula for fluid maintenance in burn patients (look up on your own, Also known as rule of 9s)
Volume expansion with crystalloid fluids may cause iatrogenic fluid overload. The risk of this complication
becomes particularly elevated in patients with impaired kidney function.Patients with congestive heart failure are
at elevated risk for serious adverse effects of crystalloid fluid administration. Fluid overload can cause life-
threatening pulmonary edema and the worsening of diastolic or systolic heart failure,

18. Contraindications
Hypertonic saline is contraindicated in all clinical settings except in patients with severe hyponatremia and
neurologic sequelae. Rapid correction of hyponatremia may cause central pontine myelinolysis, a devastating
neurologic condition.
Hypotonic solutions are also contraindicated in patients with or at risk of developing cerebral edema.
Crystalloids containing potassium (Lactate Ringer's solution) are relatively contraindicated in patients with
hyperkalemia since these may exacerbate their condition, which in turn can lead to ventricular dysrhythmias.
Avoid using crystalloids containing dextrose (D5%W, D10%W, D5% 0.45% NS, etc.) in patients with hyperglycemia.
Ringer's lactate solution contains calcium ions. Calcium can induce coagulation of the blood products in the IV
tubing and therefore inhibit their effective delivery. In patients who require a blood transfusion, blood products should
utilize a separate IV setup.
Frequent clinician and nursing staff monitoring should be emphazied in order to minimize the complications of
fluid administration.

19. Colloids
Colloids can be man‐made (e.g. starches, dextrans, or gelatins), or naturally occurring (e.g. albumin or fresh frozen
plasma (FFP)), and have bigger molecules, so stay in the blood for longer before passing to other parts of the
body.
Colloids, which are suspended in crystalloid solutions, are similarly given for the purpose of volume expansion.
All colloids have a larger molecular weight than crystalloids and do not cross the endothelium into the interstitial
fluid easily.
This means that they stay in the intervascular space for longer than crystalloids, provide the benefit of rapid plasma
expansion, and can correct colloidal osmotic pressure
colloids are a good option when administration of crystalloids has not reversed the patient’s shock
Colloids, on the other hand, may (rarely) trigger an anaphylactic reaction.
Low dose colloids typically preserve hematocrit and coagulation factor levels
When replacing blood loss, you need to administer approximately 3x estimated blood loss volume when using a
crystalloid solution. In the acute setting, you can replace blood loss with an equal volume of colloid solutions;
however, as the half-life of all colloids is relatively short, patients will eventually require a greater volume of colloid

20. Take Away
Fluids are given intravenously and so enter the intravascular space. However, depending on the osmolality, the fluid
will be distributed across the various fluid compartments (intravascular, interstitial, intracellular) to different extents.
The aim of fluid resuscitation in hypovolaemic patients is to expand the intravascular volume by administering fluids
that stay in the intravascular space, such as, 0.9% saline and colloids.
for a 70kg patient, maintenance regimens need to provide approximately 2.5L fluid, 70-140mmol Na+, and 35-
70mmol K+).
Pre-existing fluid deficit (replaced using STAT boluses)
Ongoing losses (prescribe fluids to replace future losses as they are likely to occur)

21. Fluid Prescribing Sample
let us say that our patient is a 70kg healthy male. we know in total, we need to prescribe fluids over 24 hours that
provide 1750mL of water (70kg x 25mL/kg/day), 70mmol of Na+ (70kg x 1.0mmol/kg/day), 70mmol of K+ (70kg x
1.0mmol/kg/day), and 50g (50g/day) of glucose.
First bag: 500mL of 0.9% saline with 20mmol/L K+ to be run over 8 hours
This provides all of their Na+, ~1/3rd of their K+, and a quarter of their water
Second bag: 1L of 5% dextrose with 20mmol/L K+ to run over 8 hours
This provides a further 1/3rd of their K+, and half of their water, as well as glucose
Third bag: 500mL of 5% dextrose with 20mmol/L K+ to run over 8 hours
This provides the remaining 1/3rd of their K+, and a quarter of their water, as well as glucose

22. Thank you
Hooman Rwoshan, M.D. MSc