03 fluids & electrolytes

8/7/2019 03 Fluids & Electrolytes

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Fluids & Electrolytes(Background Information: Physics)


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5 Considerations5 Considerations

Volume of fluidVolume of fluid

TonicityTonicity

Specific ElectrolytesSpecific Electrolytes

AcidAcid--base balance (impact)base balance (impact) Caloric influenceCaloric influence

FLUIDS & ELECTROLYTESFLUIDS & ELECTROLYTES


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Volume of WaterVolume of Water

2-3 liters/day

1 liter: insensible

Rest: urinary output



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Insensible LossesInsensible Losses

600 mL: respiration

200 mL: feces

200-400mL: perspiration/evaporation thru

skin (little minimum flexibility)



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Urinary output can adjust to a fluid ration short of2-3 liters.Normal dietary intake: 1,200 mOsm

Good kidney: 1,400 mOsm / L

Patient with renal problem: flexibility is lost Ex: chronic renal disease = stage of diuresis

Plasma osmolality vs. kidney's concentrating ability

Maximum water intake: can go beyond the usual 2- 3liters/day



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2 Mechanisms2 MechanismsHypotonicity

Hypothalamus

ADH secretion

Action or lack of action of Aldosterone (Naretention or excretion): water goes with it



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Acute Renal Failure/Terminal ChronicAcute Renal Failure/Terminal Chronic

Renal FailureRenal Failure

endogenous water (oxidation of fats /

metabolism of muscle)

1 cc / 10 cal burned

300 gms loss/day if not eating (fat andmuscle)



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Maintenance FluidMaintenance Fluid

should be scaled down for smaller than

average adults & children

Body surface

a satisfactory indicator of lean tissue mass calculated from height and weight better reflection of the body size

1,500 cc/m2 of body surfaceAverage adult: 1.7 m2 (2 liters/day)



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TonicityTonicity

definition

body fluid

not composed of water alone

different compartments has differentindividual solutes

total number of particles remarkably

constant (300 mOsm/L)



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PlasmaPlasma tonicity mostly attributable to electrolytes (280

mOsm/L) - sodium other half

anions (Chloride and bicarbonate)

modest share crystalloids (CHO, urea, creatinine)

Protein: 2 mOsm

Sodium is responsible for tonicity but not with metabolism(ADH mechanism)



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What happens to the regulation of tonicity ifthe normal supply of solutes (mainly

Sodium) drops down to zero?

in some situations, volume conservationoverrides tonicity regulation

regulation is much easier if Sodium intake ismaintained at somewhat similar to diet (100-150mEq/day)



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To Provide Daily RationTo Provide Daily Ration

different IV fluid choices

water without salt

water with salt

sugar is added to water without saltsolution (5% - roughly isotonic to plasma)



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Specific ElectrolytesSpecific Electrolytes volume and tonicity

Potassium (K+): only one needed to be given daily daily dietary K+ intake: 75 to 100 mEq (KCl, KPO4, K

Acetate)

sudden administration: cardiac arrest (impact on ICU

management) (if sugar is added, safe limit: 10 mEq/hour (max: 20

mEq/hr)

Note: not wise to have >40 mEq/L (catch-up game)Calcium (Ca++), Phosphorus (P), Magnesium (Mg++) = has plenty ofstores



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Time for AdditionTime for Addition

Vit. B

requirement if CHO is the entire caloric supply

Vit. C

peace of mind surgeons (scurvy)

cheap, non-toxic, water soluble



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Acid Base BalanceAcid Base Balance given adequate water and electrolytes, kidney

will take care of acid base balance rather nicely 2 issues has to be raised = basis

proportion of Na+ and Cl- in IV fluids 0.9%NaCl = not exactly the proportion in plasma

Normal individuals / impaired renal function / patients proneto acidosis

balanced solution: better source of Na+

most balanced solutions in the market haveproportions of Na+ and Cl- similar to plasma

complemented by bicarbonate, lactate or acetate

Ringer's lactate (Hartmann's solution) undisputed



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Question: ability of the body tometabolize lactate

pH of the existing IV fluids in the

market



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pH 5 (1000 x more acid than the blood)

Relax: scarcely a drop in the bucket

value gained from volume expansionoutweighs very minor blood buffersexpenditure even so, still ask: why not

make it with more physiological pH*unstable

= neutralizing solution (5 mg Heparin + 0.1

mg Prednisolone/liter bottle)



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Caloric IntakeCaloric Intake 2,500 cal/day (average adult) 1,500 ca/day (completely inactive)

4,000 5,000 cal/day (severe stress / athletes) 0.5 to 1 gram/kg body weight/day = minimum protein requirement IV fluids:50 g glucose /L (4 cal/gram) 200 cal/L (x3)

600 cal/day starvation = converted to semi-starvation modest amount of calories, spare protein breakdown and lose

weight gracefully rather than catastrophic catabolism glucose: tonicity and protein sparer

total parenteral nutrition early start of feeding = cost consideration oral absorption



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Problem Oriented ApproachProblem Oriented Approach Pediatric patients new admission (kidney status)

ward Adult patients with cardiac problems / state of congestion pneumonia patients (SIADH)

electrolyte imbalance Critically ill Sepsis Dengue shock syndrome DIC

Crystalloids Colloid


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