Principals of fluids and electrolytes management

Ram Elazary, MDGeneral Surgery Department

Hadassah Hebrew University Medical CenterCampus Ein-Kerem, Jerusalem

Total Body Waterbody weight% Total body

water%

Total 60 100Intracellular 40 67Extracellular 20 33Intravascuar 5 8Interstitial 15 25

Composition of Fluidsplasma interstitial intracellular

CationsNa 140 146 12K 4 4 150Ca 5 3 10Mg 2 1 7AnionsCl 103 104 3HCO 24 27 10SO4 1 1 -HPO4 2 2 116Protein 16 5 40

Control of VolumeKidneys maintain constant volume and composition of body fluids

– Filtration and reabsorption of Na

– Regulation of water excretion in response to ADH

Water is freely diffusible– Movement of certain ions and proteins

between compartments restricted

Control of VolumeEffective circulating volume

– Portion of ECF that perfuses organs

– Usually equates to Intravascular volume

Third space loss– Abnormal shift of fluid for Intravascular

to tissues eg bowel obst, i/o, pancreatitis

Normal Water ExchangeMean daily (ml) Minimal daily (ml)

SensibleUrine800-1500 600Intestinal up to litersSweat up to liters 500

InsensibleLungs/Skin 600-900 600-900( 10%/1 o rise in Temp)

Normal source of water

~2000ml - 1300 free water intake

700 bound to food

additional water from catabolism

Water and Eletrolytes ExchangeSurgical patients prone to disruption:

• NPO• anaesthesia• Trauma (surgery)• sepsis

Fluid and Electrolytes Therapy

Surgical patients need: •Maintenance volume requirements•On going losses•Volume excess/deficits•Maintenance electrolyte requirements•Electrolyte excess/deficits

1 .Volume Deficit • vital signs changes

– Blood pressure– Heart rate– CVP

• Peripheral temperature and capillary filling time

• urine output low

1 .Volume Deficit •Decreased skin turgor•Sunken eyes•Oliguria•Orthostatic hypotension•High BUN/Creatine ratio•Plasma Na may be normal

Fluids resusitation

• Adults:1000 ml

• Pediatrics:20 ml/kg

Fluids of crystaloids (NS or RL)Repeated dose

2. Maintenance RequirementsThis includes: insensible loss

urinarystool losses

Body weight Fluid required0-10Kg 100ml/kg/dnext 10-20Kg 50 ml/kg/dsubsequent Kg 20ml/kg/d

15ml/Kg/d for elderly

70 Kg Man Needs

1st 10kg x 100mls = 1000mls

2nd 10kg x 50mls = 500mls

Next 50kg x 20mls= 1000mls

TOTAL 2500 mls /d

Maintenance Electrolyte Requirements

Na 1-2mEq/Kg/d K 0.5 - 1

mEq/Kg/d• Usually no K given until urine output is adequate• Always give K with care, in an infusion slowly - never bolus

(max 0.2% KCL through peripheral IV)

• Na 1gr = 17 mEq• K 1gr = 13.6 mEq

• 70 KgH2O 2500ml Na 70*2 =140 mEq = ~ 9grK 70*1 =70 mEq = ~ 5gr

2500 0.45NS + 0.2%KCl 100ml/h

fluids composition

3 .On Going Losses• NGT

• drains

• fistulae

• third space losses

4 .Volume Excess• Over hydration• Mobilization of third space losses

Signs• weight gain• pulmonary edema• peripheral edema• S3 gallop

Fluid and Electrolyte Therapy

Goals• normal hemodynamic parameters• normal electrolyte concentration

Method replace deficits

normal maintenance requirementsongoing losses

Fluid and Electrolyte Therapy

Normal maintenance requirements• use BW formula

On going losses• measure all losses in I/O chart• estimate third space losses

Deficits• estimate using vital signs• estimate using U/O

Fluid and Electrolyte Therapy

The best estimate of the volume required is the patients response

After therapy started observe • vital signs• Urine output (0.5mls/Kg/hr)• Central venous pressure

Time Frame for Replacement

• Usually correct over 24 hours

• For ill patients calculate over shorter period and reassess e.g. 1, 2 hours or 3 hours for e op cases

• Deficits - correct half the amount over the period and reassess

Postoperative Fluid Therapy

• Check IV regimen ordered in op form

• Assess for deficits by checking I/O chart and vital signs

• Maintenance requirements calculated

• Usually K not started

• Monitor carefully vital signs and urine output

Postoperative Fluid Therapy• Urine specific gravity may be used (1.010 -

1.012)

• CVP useful in difficult situations (5-15 cm H20)

• Body weight measured in special situation e.g. burns

Concentration Changes• changes in plasma Na are indicative of

abnormal TBW

• losses in surgery are usually isotonic

• hypoosmolar condition usually caused by replacement with free water