FLUID AND ELECTROLYTE MANAGEMENT IN CHILDREN

FLUID AND ELECTROLYTE MANAGEMENT IN CHILDRENBY

DR G I McGIL UGWUCONSULTANT PAEDIATRIC NEPHROLOGIST DELSUTHOUTLINE OF PRESENTATIONPRE-TEST FOR FLUID THERAPYLEARNING OBJECTIVEINTRODUCTIONNORMAL BODY FLUID AND ELECTROLYTESMAINTENANCE THERAPYREPLACEMENT/DEFICIT THERAPYCONCLUSIONTAKE HOME POINTSREFERENCESPRE-TEST FOR FLUID THERAPYIn the fetus and newborn,Extracellular fluid (ECF) is smaller than Intracellular (ICF)Postnatal diuresis causes decrease in the ICF Both NA+ and water are predorminantly lost during postnatal diuresisPremature babies have higher total body water/weight than term neonates.

Concerning ECF and ICF,By one year of age, the amount of ECF and ICF are largely equalIn adulthood, ECF constitutes 10-20% while ICF constitutes 20-25%Females have higher ICF than malesThe increase in ICF is largely due to cell growth in an individual.

Concerning ECF and plasma,plasma is part of ICFplasma volume is greater than ECFvolumeplasma water is about 10% of the body weightblood volume is about 8% of the body weight

4.Intestitial fluid A Is part of ECFBIs part of ICFCConstitutes about 13% of the total body weightD Can be increased by acsitis and pleural effusion

Based on the caloric expenditure model, each calorie expended requires provision of water in the ratio of:2ml/1cal/day at rest1ml/1cal/day at rest1ml/2cal/day at rest2ml/2cal/ady at restAlso according to the caloric requirement, the ranges of Na+ nd K+ required is3mEq of Na+/100ml of water and 2mEqK+/100ml of water4mEq of Na+/100ml of water and 4mEq of K+/100ml of water1mEq of Na+/100ml of water and 1mEq of K+/100ml of water2.5mEq of Na+/100ml of water and 2.5mEq/100ml of waterConcerning plasma and intestitial fluid,plasma is the same as intravascular fliudhydrostatic pressue drives fliud int the plasma from the intestitial fluidOncotic pressure drives fluid from the plasma to the intestitial fluidOncotic pressure retains fluid in the intestitial fluidIn the composition of the ECFand ICFNa and Cl are the predominant cation and inion in the ECFK. Proteins and phosphates are the predominant cation and inion in the ECFThe amount of K in the ICF is about 10x that in the ECFICF fluid is governed by the balance of hydrostatic and oncotic pressuresConcerning Maintenance fluidThis is the amount of fluid and electrolytes rquired required for dly excretion of waste productsThere ia a wide variation in the daily intake of electrolytes and water in childen60% of total excreted water is lost in the urine, 35% through the lungs and skin and 5% in the stool40% is lost in the urine 35% thfough the lungs and skin and 25% in the stoolA child of 4yrs who weighs about 16kg will require about 1.2litres of fluid/day1.5litres of fluid/day1.3litres of fluid/day2litres of fluid./day

The gaols of maintenance fluid areprevent dehydrationprevent electrolyte imbalanceprevent ketoacidosisprevents protein degradation

Maintenance fluid should contain glucose so as tominimize carbohydrate metabolism5g of glucose/100ml of fluid gives about 10Cal of energy5g of glucose /100ml gives about 17Cal/l5g of glucose/100ml represents about 20% of the daily calorie requrementConcerning maintenance fluid againChildren can be maintained on maintenance fluid for upto two weeks10% dextrose is enough for the maintenance in the 1 day old newbornThe recommended fluid for a 6 and a yr old child is 4.4% in 1/5 salineThe recommended for the 6 and a old child is saline in 5% dextrose Maintenance fluid requirement in a newborn is60ml/kg/day on day onefollowed by 10ml/day increamentfollowed by 20ml/day increamentfollowed by 30ml/day increamentMaintenance fluid requirement in a newborn is60ml/kg/day on day onefollowed by 10ml/day increamentfollowed by 20ml/day increamentfollowed by 30ml/day increament

Deficit fluidis the fluid lost over a timecan be expressed as a % of the body weightIn GI losses, K and HCO3 are lost predominantly through diarrhoeathe most lost solute diarrhoea is Na

In assessing dehydration in a child less than 2yrsmild dehydration = 3% body weightModerate dehydartion= 5% body weightSevere dehydration = 8% body weightmild dehydration=5% body weightModerate dehydration= 7% body weightSevere dehydration= 10% body weightdeficit is replaced is replaced over 1-6hoursdeficit is replaced over 12hoursDehydrationcan be isonatremic, hyponatremic and hypernatremicThe amount of Na given is 0.5Meq/L/Hr or 12mEq/L /dayin correcting dehydration, hypernatremic dehydration it is advisable to use Na free solutionshypernatremic dehydration is corrected over 24hoursIn correcting shock0.9% saline in 5% dextrose is the fluid of choicefluid is given over 30mins-1hrthe amount of fluid is 40ml/kgthe amount given is subtracted from the calculed fluid loss and given over the remaing hours of correctionConcerning On-going lossfluid is replaced ml for mlabout 10ml/kg/loose stool is adequate replacement fliudthe choice choice of fluid should be appropriately the maintenance fluid for the chids age/weightnormal can with or without K can be used

On-going loss is assessed every 4hrsevery 8hrsevery 1hrevery 12hrs

The following considerations should be borne in mindhyponatremia may develop anytime during the course of therapythe electrlytes should be checked every 24hoursin elctrolyte values are abnormal they should be checked every 8hoursa reduced urine output always indicates renal failureOral rehydration therapyis prefered for uncomplicated moderate dehydration for mild dehydration, 50ml/kg over 4hours is adequate90ml/kg for moderate dehydration over 4hours is adequateboth mild and moderate dehydration are foolowed with 100ml/kg/dayFeeding must be continued while ORT is onORT can be used to correct severe dehydrationThe current WHO packs contain less solutes than the previous packsORS is contraindicated in a child with vomitingINTRODUCTIONWater is the most plentiful constituent of the human bodyTotal body water varies from age to age, being highest in the youngest, with the preterm baby having the highest.TBW is divided into ICF and ECF.In the fetus and the newborn, ECF is larger than the ICFThe normal postnatal diuresis causes a decrease in the ICFCoupled with the increse in ICF due to cell growth, by one yr of life, the ratio of ICF to ECF almost equals that in adulthood where ECF constitutes 20-25% of the body weight and ICF 30-40%, close to twice the ECF volume.With puberty, the increased muscle mass in males makes them to have higher ICF than femalesThere is however no significant diff in the postpubertal ECF of males and females.The ECF is further divided into plasma water and the intestitial water. The plasma water is 5% of the body weight and with a hematrocit of 40%, blood volume is usually 8% of the body weight. This is however higher in the newborn and infact it is 10% in pretermsThe volume of plasma water is altered by pathological conditions such as dehydration, anaemia, plycythaemia, haert failure, abnormal plasma osmolality and hypoalbuminaemia.The intestitial fluid, normaly 13% of body weight, can increase drmatically with edema, such as heart failure, protein losing enteropathy, liver failure, nephrotic syndrome and sepsis.An increase in interstitial fluid also occurs in ascitis and pleural effusion.There is always a delicate equilibrum betwee the intravascular fluid (plasma) and the interstitial fluid, which is governed by the hydrstatic and oncotic pressure.While the hydrostatic pressure drives fluid from the intravascular space to the interstitial fluid, oncotic pressure prevents fluid from moving from the intravascular compactment to the interstitiumThe composition of the solutes in the ICF and ECF are diff.Na and Cl are dorminant cation and anion in the ECF respectively and are much lower in the ICF.K is the most abundant cation in the ICF and its ICF content is about 30% that in the ECF. Proteins, organic anions and pphosphate are the most plentifull anions in the ICFBased on the caloric expenditure model, each calorie expended requires provision of water in theratio of 1ml/cal metabolized/day at rest.Also according to the caloric expenditure model, Na and K ranges/100ml of maintenance fliud is 3mEq/100ml and 2mEq/100ml respectively.NORMAL ELECTROLYTES IN CHILDRENElectrolyte composition

The concentration of the major cations and anions in the intracellular space and the plasma, expressed in mEq/L.MAINTENANCE THERAPYCan be given orally or intravenously for patients who cannot tolerate orallyThis is the amount of fluid electrolytes required for the dialy metabolism and also corrects the fluid necessary for obligate excretion of wiaste products esp solutes (see above)Usually there is a wide variation in the daily intake of water and electrolyes.Only exceptions are children who receive fixed amount of fluids such as in SIADH secretion, also children who receive f;luids via N/G tube, or as intravenous total parentheral nutritionMaintenance fluids are most commonly necessary in preoperative and postoperative surgical patientsThere are however nonsurgical conditions that require maintenance fluid calculationMost important thing is to recognize when to commence maintenance therapyThe goals of maintenance fluids arePrevent dehydrationPrevent electrolyte disordersPrevent ketoacidosisPrevent protein degradationMaintenance are generally composed of a solution of water, glucose, Na+, K+. Other electrolytes are such as Ca2=, PO4- etcAddition of glucose of a minimum of 5gm/100ml (5%dextrose, to the fluids provides about 17kcal/100 which is about 20% of the daily requirement but is enough tominimize tissue catabolism to the point that protein stores are spared from providing substrate for gluconeogenesis. Ketosis from fat metabolism is also prevented.(remem our goals)However patients will lose weight on this regimen. That is why patients are started on total parentheral nutrition just after a few days on maintenace fluids.Also maintenance fluids lack essential requirements such as proteins, fat, vitamins and minerals.The maintenance values are calculated as a guide based on the body weght of the child.Body weight method for calculating maintenance is as follows:Body Weigth Fluid per day0-10kg 100ml/kg11-20kg 1, 000ml + 50ml/kg each kg >10kg >20kg 1, 500ml + 20ml/kg for each kg >20kgAs a guide of fluid loss from the bodyUrine accounts for 60%Insensible loss from skin and lungs accounts for 35%Stool accounts for 5%These are however very variable as it also depends on certain extrenous factors , such as humidity,temperature hyperventilation drugs etcSolution available maintenace therapy (the commecially available fluids):

Solution Composition Normal saline(0.9%NaCl) 153mEq Na+/LOne-half saline(0.45%NaCl) 77mEqNa+/LOne-third saline (0.33%NaCl) 57mEqNa+/LOne-quarter saline(0.2%NaCl) 38.5mEq Na+/LOne-fifth saline(0.18%NaCl) 30.8mEqNa+/L5gm of glucose/100ml (5% dextrose) to any of the solution provides a calorie of about 20.5Kcal/100ml.One-fifth saline normally comes with 4.3% dextrose (17.6Kcal/100ml)Ringers lactate 130mEqNa+/L(Also contains 4mEqK+/L, 109mEq/L Cl-, 28mEqHCO3-/L and 3mg/dl of calciumHartmans solutionChoice of fluid(1) First-Line choice for children above 20-25kg is 0.45% saline (1/2 saline) with 5%dextroseConsider adding KCl, up to 40mmol/L once plasma concentration is known(2) Second-Line choice0.9% saline(normal saline) in 5% dextroseChildren more than one month but 20-25kg( 1)1/4saline in 5% dextrose. They do best with this because of thgeir high water needs /Kg Second-Line choice1/5th saline in 4.3% dextrose(3) Third-Line saline ff normal saline , each in 5% dextrose salineSummary as follows:Weight ml/kg/24hrsml/kg/hour10kg or less 100 4 Additionally for each kg >10 upto 20kg 50 2Additional ly for each kg>20kg thereafter 20 1

Maximum maintenance2000ml per 24hrs for girls2500ml per 24hrs for boysNeonates ,1month and 150ml/kgThat is 30ml/kg increament /day till day4

The reason for the daily increament sep in sick term babies is that the GFRonly improves as from day 3, and in preterms, respiratory outcome are likely to be worse if Na+ is added before naturesis which starts as from birth, and weight loss has started.Do not automatically add electrolytes on day 2; check the serum electrolytes first.

NOTE: Above regimen for the neonates may be altered:(i) Gestation- very premature babies have very high insensible loss and may require higher amount of fluidIncubator humidity is very important in these babies(ii) Clinical state-eg edema (reduce fluids or increase more slowly), dehydratiom (may require more fluids)Perinatal asphyxia- may need to reduce ml/kg/dayWeight- dly weighing are required in NICU babies. Beware of increasing the fluid or consider reduction in a baby in NICU if there is weight gain in the first one week of life.Serum sodium- the best guide to hydration in the first few days of life, especially in preterm, hypernatremia; hypernatremia indicates dehydrationRESTRIC FLUID TO 2/3RD MAINTENANCE FOR ALL CHILDREN IF BRONCHIOLITIS/PEUMONIA/MENINGITIS/ENCEPHALITISREPLACEMENT THERAPYBroadly divided in two major parts: Correcting or replacing deficit, and replacing On- going lossDeficit TherapyGI tract is a potential losss of considerale amount of water and electrolytes and so lead to intravascular contraction and electrolyte imbalance.GI losses are often associated with loss of K+ leading to hypokalemia. The stool also contains a heavy amount of HCO3-, so diarrhoea leads to metabolic acidosisIn the absence of vomiting, diarrhoea or NG drainage, GI losses are usually minimal, but when ever losses occur, its usually considered eccessive and increase in the water requirement is equal to the volume lostBecause GI water and electrlyte losses can be precisely measured, it is possible to use an appropriate replacement fluid.Deficits are usually replaced within1-6hrs, depending on the rate of loss.Diarrhoea is a common cause of fluid loss in children and lead to dehydrationThe first step in caring for a child with dehydration is to acceess the degree of dehydration clinically.Clinical Evaluation of DehydrationMild Dehydration (3-5%): normal or increased pulse, decrease urine output, thirsty, normal physical examination.(5% for infants or20kgNoderate Dehydration (7-10%): tachycardia, little or no urine output, irritable/lethargic, sunken eyes and fontanel, decreased tears, dry muccuos membranes, mild tenting of the skin, delayed capillary refill, cool and pale.Severe Dehydration (10-15%): rapid and weak pulse, decreased blood pressure, no urine output, very sunken eyes and fontanel, no tears, parched muccuos membranes, tenting of the skin, very delayed capillary refill, cold and mottled.These are however estimates and infact all physical characteristics used to describe differing degrees of dehydration are really measures of the integrity or relative degree of expansion of the extracellulr fluid space.

Water deficit can be determined by subtracting the patients current weight from his/her weight just before dehydration.

However it is usually determined as above by clinical criteria is a percentage estimate of the total amount of body weight lost as water.The amount of loss and so amount needed to replace can be calculated by multiplying the current weight(kg) by the estimated % dehydration yeilding a figure that represents the estimated water loss in litres. If the weight is expressed as grammes, the estimated water loss will be in ml. This formular takes into account that 1ml of water weighs 1gm.Na+ is the solute most lost in diarrhoea as its the predorminant cation in the ECFThe loss may be relatively equal (isotonic), larger (hypotonic) or smaller (hypertonic), to the loss of water from the ECF

Below is the summary of management of various types of dehydrationSUMMARY OF FLUID AND SOLUTE CALCULATIONS (SEGAR BOX) FOR 1 DAYH2ONa+K+Maintenance (Daily fluid and electrolyte requirement)100 ml/kg-first 10 kg1000 ml + 50 ml/kg 10-20 kg1500 ml + 20 ml/kg - >20kg3 mEq/100 ml of maintenance fluids/day12 mEq/100 ml of maintenance fluids/day1

+(plus) Total Deficits

-(minus) pure free water deficit if hypernatremic2Total deficit (ml) = weight (gm) X % estimated dehydration

(ECF loss = 60% of H2O deficit) (ICF loss = 40% of H2O deficit)ECF deficit (in liters) X 140mEq/L = isotonic Na+ deficit from the ECFECF deficit (in liters) X 140mEq/L = isotonic Na+ deficit from the ECFH2ONa+K++(plus) pure free water deficit (for hypernatremia only)5Soduim3 145 x 4 ml4 2 kgX wt (kg) = pure free water deficit (ml)(MAX = 12 mEq/L decline/day)7BLANKBLANK+(plus) Excess solute losses (for hyponatremia only)BLANK

135 Sodium6 x 0.6 x wt (kg) = amount of sodium (mEq) needed to raise the serum sodium to normal(MAX = 12 mEg/L rise/day)7TOTALAcceptable ranges for maintenance of Na+ and K+/100ml of maintenance fliuds/day is 2.5-3mEq for Na+ and 2-3mEq for K+Research and clinical experience provide us with data that substantiate a maximum safe rate for Na+ change (either from high to normal or low to normal). That rate of change is 0.5mEq/L/hr or 12mE/L/day.Choice of fluidThese are actually the second line maitenance fluids. (0.9%Na+ with 5% dextrose).

The fluids are also suitable in the following conditionsModerate- Severe dehydration/intravascular volume depletionSignificant hyponatremia (serum Na+ 150mEq/L)NOTEIf shock is present, administer 0.9%NaCl, 20ml/kg (10ml/kg in the setting of trauma), given over 30min-1hr.Repeat if necessar and call for help.

Remember to subtract any volume used to treat shock from total calculated for deficit replacement.Hyponatremia may develop as complication of an fluid regimen.Symptomatic hyponatremia is a medical emergency.ONGOING LOSSThis is replaced volume for volume (ml for ml), as this occurs in your presence. It presupposes that you have been measuring amount of fluid lost and its electrlyte contentsOn-going loss is reassed every 4hrsFluids used should ideally reflect the electrlyte composition of the fluid being lost.0.9% NaCl is appropriate in most cases (with or without the additon of K+)For diarrhoeal diseases, a rough estimate of replacing on going loss is 10ml/loose stool/kgMONITORING Check plasma electrolytes before commencing the infusion, except prior tothe majority of elective surgeryMonitor plasma glucose if glucose-free solutions are used during surgeryCheck plasma electrlyes every 24hrs whilst intravenous fluids are being administered if plasma electrlytes are abnormal, consider rechecking every 4-6hrs, but definitely if plasma Na+