AKUFFO QUARDEINTERN (PEDIATRICS, TEMA GEN. HOSP)
Fluid and Electrolyte ManagementPhysiology of water homeostasisBody Fluid CompartmentsMaintenance Fluid RequirementsDehydration and Fluid therapyOral Rehydration TherapyPractical Examples
Physiology of Water HomeostasisTo understand that disorders of sodium balanceare related to conditions that alter extracellularfluid volumeTo recognize clinical signs and symptoms ofthe different forms of dehydration.To appreciate that the management ofhypernatremic dehydration differs from that ofisonatremic/hyponatremic dehydration.
Physiology of Water HomeostasisOsmotic Shifts of water between body fluidcompartments is dependent on the soluteparticles within individual body compartments.Effective osmolarity of body fluid compartmentsis contributed to by unique properties of the cellmembranes ( difference in permeability to waterand solutes)The difference in concentration of impermeableparticles across cell membranes determinesthe osmotic movement of water. (effectiveosmolarity)
Physiology of Water HomeostasisIn a steady state the osmolarity of bothintracellular and extracellular compartments willremain the same. (approx. 300MOsm)There is a delicate interaction betweenosmolality and water balance.(movement of water in the initial phase ofcompensation for osmolar changes, is to resetosmolarity either at a higher level or lower level.i.e. Osmolarity of both intracellular andextracellular fluids should remain the same
Physiology of Water HomeostasisA complex set of homeostatic mechanisms areat play, which regulate water intake and waterexcretion.The hypothalamus and surrounding braincontrol the sense of thirst and the productionand release of arginine vasopressin (AVP), theantidiuretic hormone (ADH)It is the osmolality of plasma and extracellularfluid which is “sensed” by osmoreceptors in theanteromedial hypothalamus.
Physiology of Water HomeostasisNon-osmotic stimuli will also cause AVP to bereleased. (atrium / large vessels in the chest)A reduction in “effective circulating volume”[blood loss, hemorrhage, ECF volume depletion(dehydration, diuretics, etc.), nephroticsyndrome, cirrhosis, congestive heartfailure/low cardiac output]
Neonatal PhysiologyAt birth renal function is generally reduced,particularly in premature neonates.GFR increases progressively during gestationparticularly in the third trimester. By 1 to 2years, GFR, Urea clearance and maximumtubular clearances would have reached adultlevels.
Neonatal PhysiologyAVP has been measured in amniotic fluid andis present in fetal circulation by mid-gestation.At birth, vasopressin levels are high butdecrease into “normal” ranges within 1–2 daysIn neonates, AVP responds to the same stimulias older children and adults. However, theability to concentrate urine to the maximumachieved by older children or adults does notoccur.
Neonatal PhysiologyWhy a low urine concentrating ability inneonates?Decreased glomerular filtration rate (decreasedrenal blood flow)reduced epithelial cell function in the loop ofHenle and collecting ductreduced AVP receptor number and affinityreduced water channel number or presence onthe cell surface
Neonatal PhysiologyNeonates have increased non-urinary waterlosses (skin and respiratory) as a function ofweight/BSA, which are greater compared toolder children and adults.The net effect is that neonates are at greaterrisk of dehydration either due to inadequatewater provision or to high osmolar loadsRisk of volume overload (hyponatremia/hypo-osmolality) if fluids are given too rapidly
Body Fluid CompartmentsWater accounts for 60% of TBW in men and50% in women while infants have a higherproportion of water, 70–80% (due to the lowerproportion of muscle in comparison to adipose)The higher proportion of TBW to whole bodyweight in younger children is mainly due to thelarger ECF volume when compared to adults.disproportionate weight of brain, skin, and theinterstitium in younger children contributes tothe variability in the ECF volume.
Body Fluid CompartmentsWater is distributed between two maincompartments, the intracellular fluidcompartment (ICF) and extracellular fluidcompartment (ECF)The intracellular compartment makes upapproximately 2/3 of the TBW. The ECFconstitutes 1/3 of the TBW composed ofplasma and interstitial fluid
Maintenance Fluid RequirementsMaintenance requirements are related tometabolic rate and affected by bodytemperature.Insensible losses account for about half ofmaintenance requirements.Volume must rarely be exactly determined, butgenerally should aim to provide an amount ofwater that does not require the kidney tosignificantly concentrate or dilute the urine.
Maintenance Fluid RequirementsThe Holliday-Segar method remains thesimplest in approximating maintenance fluidrequirements.It is based on caloric requirement each day andthe amount of fluid needed based on caloricexpenditure.
Maintenance Fluid RequirementsTable 3Caloric, Water, and Basic Electrolyte Requirements Based on WeightSodium Chloride PotassiummEq/100 mEq/100 mEq/100Body weight (kg) Calories Water mL H2 O mL H2 O mL H2 O3–10 kg 100/kg 100/kg 3 2 211–20 kg 50/kg 1000 mL + 3 2 250 mL/kg foreach kg above>20 kg 20/kg 1500 mL + 3 2 220 mL/kg foreach kg above20
Maintenance Fluid Requirements5% dextrose is provided to deliver 5 g ofcarbohydrate per 100 mL of solution or 50 g/LFor a limited period of time (generally under 5–7 days) this amount of carbohydrate will besufficient to prevent protein breakdown.If it is anticipated that there will be a need forprolonged parenteral therapy, a higher dextrosesolution will be required.
Intravenous FluidsIntravenous fluids that are safe to administerparenterally based on their osmolalityEach solution is selected based on the clinicalstatus of the patient. Solutions without dextrose(0.45% isotonic saline) or without electrolytes5% dextrose in water are only administeredunder special clinical situations.
Intravenous FluidsSolutions Used for Intravenous AdministrationOsmolality Sodium Potassium Chloride DextroseSolution mOsm/L mEq/L Eq/L mEq/L mOsm/L0.9% Isotonic saline 308 154 154(normal saline)0.45% Isotonic saline 154 77 77∗(1/2 Normal)5% Dextrose in Water 2785% Dextrose + 0.33% 378 50 50 278isotonic saline5% Dextrose + 0.45% 432 77 77 278isotonic saline∗ The lowest intravenous solution that can be used safely is 0.45% isotonic saline with anosmolality of 154 mOsm/L or approximately 50% of plasma. Any solution with an osmolalityunder this value will result in cell breakdown with a large potassium load to the extracellularspace resulting in severe hyperkalemia leading to cardiac arrhythmias and possibly death.
Dehydration and Fluid TherapyDehydration is significant depletion of bodywater and electrolytesDehydration usually due to gastroenteritisremains a major cause of morbidity andmortality in infants and young childrenworldwhile.Infants are particularly susceptible on accountof their greater baseline fluid requirementsand higher evaporative losses. (High surfacearea) and their inablity to communicate thirst.
Dehydration and Fluid TherapyAetiology and PathophysiologyIt results from increased fluid loss or adecrease intake or bothFluid is always lost with accompanyingelectrolytes, in varying concentrations.Common causes include (gastroenteritis, DKA,burns, 3rdspace losses eg. I/O)
Dehydration and Fluid therapySymptoms and SignsThey vary based on the fluid deficit.Dehydration without hemodynamic changesrepresents mild dehydration (5% body weightor 3% bw in adolescents)Tachycardia represents moderate dehydration.(10% body weight or 6% bw in adolescents)Hypotension with impaired perfusion meanssevere dehydration. (15% body weight ininfants or 9% in adolescents)
Dehydration and Fluid TherapySeverity of DehydrationCharacteristicsInfants Mild – 1–5% Moderate – 6–9% Severe – >10%(=> 15% =shock)Older Children Mild – 1–3% Moderate – 3–6% Severe – >6% (=>9% = shockPulse Full, normal Rapid Rapid, weakSystolic BP Normal Normal, Low Very LowUrine output Decreased Decreased Oliguria(<1 mL/kg/h)Buccal mucosa Slightly dry Dry ParchedAnt fontanel Normal Sunken Markedly sunkenEyes Normal Sunken Markedly sunkenSkin turgor/capillary refill Normal Decreased MarkedlydecreasedCool, mottling,Skin Normal Acrocyanosis
Dehydration and Fluid TherapyTreatmentTreatment is best approached by consideringan estimated fluid deficit, ongoing losses andmaintenance requirementsThe volume, composition and rate of infusion ofreplacement fluids differs for each.Most importantly, monitoring the vital signs,clinical appearance and urine output, serves asan appropriate guide.
Dehydration and Fluid TherapyTreatmentChildren with evidence of circulatorycompromise – severe dehydration, should begiven IVFs in the initial resuscitationThose unable or unwilling to drink or havingrepetitive vomiting should receive fluids IV,through an NG tube or by administeringrepeated small amounts orally.
Dehydration and Fluid TherapyResuscitationPatients with symptoms and signs ofhypoperfusion, should receive fluidresuscitation with boluses of isotonic fluid (e.g.0.9% Saline or Lactated Ringers)Resuscitation phase should reduce moderateor severe dehydration to a deficit less than 8%body weight.20ml/kg (2% body weight) is given IV over 20-30 minutes.
Dehydration and Fluid TherapyMost importantly response of the patient toresuscitation determines the endpoint of fluidresuscitation.This includes (Restoration of tissue perfusionand BP and return of increased heart ratetoward normal)
Dehydration and Fluid TherapyDeficit ReplacementThe resuscitation phase should have reducedmoderate or severe dehydration to a deficit of /about 8%.The remaining deficit can be replaced byproviding 10ml/kg (1% body weight) per hourover the next 8hours.Deficits in total body potassium is usuallybegan after urine output has improved (restoredtissue perfusion) . 2-3mEq/24hrs
Dehydration and Fluid TherapyOngoing lossesVolume of ongoing losses should be measureddirectly (eg. NG tube aspirates, catheter ,stools) or estimated e.g. 10ml/kg per diarrhealstool.
Oral Rehydration TherapyOral Fluid Therapy is effective, safe,convenient and effective compared with IVtherapy.It should be used for children with mild tomoderate dehydration who are accepting fluidsorally.Contraindications to ORT is incessant copiousvomiting, surgical abdomen, I/O.Soda, juice and fizzy drinks generally have toolittle sodium and too much carbs.
Oral Rehydration TherapyORS is effective in patients with dehydrationregardless of age, cause or type of electrolyteimbalance. [in the presence of unimpaired renalfunction]If ORS is unavailable, a sodium/glucosesolution can be used.SSS are prepared by adding 1tbsp of sugar to½ tsp of salt in 1L of water. Though lesseffective, it can be used for treating diarrhea.
Oral Rehydration TherapyAdministrationMild dehydration – 50ml/kg over 4hoursModerate dehydration – 100ml/kg over 4hours10ml/kg for each diarrheal stool (up to a max of240mls)Patient should be reassessed after 4hours.N.B – Patients with cholera may require manygallons of fluid per day
Oral Rehydration TherapyVomiting is not a contraindication to oralrehydration. Small frequent volumes should begiven. (e.g 5ml every 5mins and increasedgradually as tolerated)Importance of encouraging oral feeds.