Fluid management & anesthesia

FLUID MANAGEMENT – DEC 2018
MATERNITY
DASHT-E BARCHI
Dr. Sandro Zorzi
References:
http://teachmesurgery.com/perioperative/preoperative/fluid-management/
MSF guidelines

2
Fluid management is a major part of hospital activity prescribing; whether working
on a surgical firm with a patient who is nil-by-mouth or with a dehydrated patient on a
care of the elderly firm, this is a topic that who is working in the hospital utilises on a
regular basis.
Ensuring considered 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.
Hence it is essential to gain a firm understanding of the physiology of fluid balance
and the compositions of each fluid being prescribed.

3
Around 2/3rd
of total body weight is water (‘total body water’). Around 2/3 of this
distributes in to the intracellular fluid and the remaining 1/3 will distribute in to the
extracellular fluid.
Of that fluid in the extracelular space, around 1/5th
stays in the intravascular space
and 4/5th
of this is found in the interstitium, with a small proportion in the
transcellular space.
For the general maintenance of hydration, it is necessary for fluid to distribute into
all compartments. However, if the aim is to fluid resuscitate a patient (improving
tissue perfusion by raising the intravascular volume), it is more important these fluids
stay within the intravascular space. This concept will help us understand why
different fluids are available and for what purpose they might be used.

9
Note that these figures are the average for a 70kg man.
The actual amount varies considerably depending on physiological status and body weight (which in adult patients can vary from around
40kg to 200kg).

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INPUT?
Only 3/5th
of our fluid input comes through fluids via the enteric route, with the remainder from both food and
metabolic processes. Hence, when a patient is nil by mouth (NBM), it is important that all sources are
replaced via the parenteral route.
OUTPUT?
Losses from non-urine sources are termed insensible losses; insensible losses will rise in unwell patients,
who may be febrile, tachypnoeic, or having increased bowel output. These factors should be taken into
account when deciding how much fluid a patients needs replacing.
When patients start to clinically improve, their vascular permeability returns to baseline state. They
therefore often “correct themselves” and urinate out the excess fluid that was previously required to maintain
their intravascular volume and tissue perfusion. In such patent, monitor the electrolytes and allow this
correction to occur, as this is normal and is to be expected (rarely will supplementary IV fluids will be
warranted in such cases).

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It is essential to utilise various clinical parameters to continually assess the patient’s fluid status. A doctor’s
first assessment is, of course, the patient’s clinical 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
● In worsening stages:
○ Increased capillary refill time
○ Tachycardia
○ Low blood pressure
In patients who may be fluid overloaded, one should be looking for:
● Raised JVP
● Peripheral or sacral oedema
● Pulmonary oedema

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Patients do not just require water, they also need Na+
, K+
, and glucose replacing too,
particularly if they are nil by mouth. You will find numerous ways of calculating the
daily requirements of these 4 components and they are invariably based on the
patient’s weight. Current NICE guidelines suggest the following:
● Water: 25 mL/kg/day
● Na+
: 1.0 mmol/kg/day
● K+
: 1.0 mmol/kg/day
● Glucose: 50g/day
Based on these required, it is necessary to consider the fluids that are available for
prescription and what exactly they contain, to be able to prescribe appropriately….

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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 superior in replenishing intravascular volume for
resuscitation purposes. Therefore, crystalloids are used very commonly in the acute
setting, in theatres, and for maintenance fluids.
Colloids – Colloids have a high colloid osmotic pressure and theoretically should raise
the intravascular volume faster than their crystalloid counterparts, yet clinical trials have
not shown any significant benefit or effect in practice so their use in many hospitals is
decreasing

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5% dextrose solution is a hypotonic (and isosmotic) fluid containing only dextrose
and water. Dextrose, the D-isomer of glucose, is rapidly taken up into cells to be
metabolised, leaving the remaining free water component to equilibrate across all
the body compartments.
Only 7% of the fluid therefore stays in the intra-vascular space. This means that 5%
dextrose has no role in fluid resuscitation of a patient, only in fluid maintenance
regimes. The main advantage* of dextrose is being able to maintain hydration
without administering an excess of electrolytes, and it can also be prescribed with
supplementary potassium if required.
*The energy produced by the metabolism of the dextrose is relatively negligible and should not be considered to have any
substantial calorific or nutritional value, dextrose used only as a means of hydration.

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As an example, let us say that our patient is a 70kg healthy male*. From the above section, 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. Consequently, a typical fluid maintenance regimen is as follows:
● 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.
*Providing the patient’s renal function is adequate and they are clinically euvolemic, these do not have to be replaced exactly but should be
targeted, to permit ease of prescribing
In MSF we follow the 4:4:2 rule or the clinical guideline table:
(4ml/kg for the first 10kg) + (2ml/kg for kg 11-20) + (1ml/kg for every kg above 20) = hourly rate

31
● Fluid management is a major part of prescribing across many specialities
● Aims of fluid prescription can be divided into Resuscitation, Maintenance,
Replacement
● A knowledge of the composition of each fluid type prior to their
prescription is essential
● Ensure to regularly examine the patient following administration of fluids
and reassess their requirements

Fluid management & anesthesia

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