06- Fluid & Electrolytes.pdf Reem Med student 👩‍🎓 graduate school

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1. 1

3. Composition of Body Fluids
Water is the most abundant compound within the human body.
The percentage of body water changes with ageand body composition.

4. TBWisdividedbetween
2maincompartments:
Intracellularfluid(ICF)
&
Extracellularfluid(ECF).Intracellular fluid (ICF)
Extracellular fluid (ECF)
40%
15%
5%
1
/
3
2
/
3

6. ❖Osmolality:
TheICFandtheECFareinosmoticequilibriumbecausethecell
membraneispermeabletowater.
oIf the osmolality in 1 compartment changes, then water movement
leads to a rapid equalization of osmolality.
TheosmolalityoftheECFusuallyequalstheICFosmolality.
Theplasmaosmolalityisnormally285–295mOsm/kg.
Osmolality= 2×[Na]+ [glucose]/18+ [BUN]/2.8.
Thecalculatedosmolalityisusuallyslightlylowerthanthemeasuredosmolality.
Hypernatremiaalwaysissynonymous
withhyperosmolality,
butHyponatremiadoesNOT
necessarilyimplyhypo-osmolality

10. Hyperglycemiacausesanincreaseintheplasmaosmolality
becauseitisnotinequilibriumwiththeintracellularspace.
Duringhyperglycemiathereisashiftofwaterfromthe
intracellularspacetotheextracellularspace.
oThis is clinically important in children with hyperglycemia during
diabetic ketoacidosis.
oThe shift of water causes dilution of the sodium in the extracellular
space, causing hyponatremia despite an elevated plasma osmolality.
Themagnitudeofthiseffectcanbecalculatedasfollows:
[Na]
corrected= [Na]
measured+ {1.6 ×([glucose] -100mg/dL)/100}

11. Normally,themeasuredosmolalityandthecalculatedosmolality
arewithin10mOsm/kg.
Thepresenceof“unmeasuredosmoles”causesthemeasured
osmolalitytobesignificantlyelevatedwhencomparedwiththe
calculatedosmolality.
Thisdifferenceistheosmolalgap.
➢When the measured osmolality exceeds the calculated osmolality by >10 mOsm/kg.
Examplesofunmeasuredosmoles:
Ethanol
Ethyleneglycol
Methanol
Mannitol

12. Regulation of Osmolality & Volume
Maintenanceofnormalosmolalitydependsoncontrolofwater
balance.
Controlofvolumestatusdependsonregulationofsodium
balance.
Whenvolumedepletionispresent,thistakesprecedenceover
regulationofosmolality,andretentionofwatercontributestothe
maintenanceofintravascularvolume.

13. ❖REGULATION OF OSMOLALITY:
Theplasmaosmolalityistightlyregulatedandmaintainedat285–295mOsm/kg.
Modificationofwaterintakeandexcretionmaintainsnormalplasma
osmolality.

14. Osmoreceptorsinthehypothalamus
sensetheplasmaosmolality.
Anelevatedeffectiveosmolalityleads
tosecretionofantidiuretichormone
(ADH).
CirculatingADHbindstoitsV
2receptorsin
thecollectingductcellsofthekidney
Whenvolumedepletionispresent,both
ADHsecretionandthirstarestimulated,
regardlessoftheplasmaosmolality.

15. InSIADH,ADHcontinues
tobeproduceddespitea
lowplasmaosmolality.
InCentralDiabetes
insipidus,ADHisabsent.Patientswithnephrogenic
DIhaveaninabilityto
respondtoADH.

16. ❖REGULATION OF VOLUME:
Anappropriateintravascularvolumeiscriticalforsurvival;bothvolumedepletionand
volumeoverloadmaycausesignificantmorbidityandmortality.
Adequatebodysodiumisnecessaryformaintenanceofintravascularvolume.
Thekidneydeterminessodiumbalance.
Normally,thekidneyexcretes<1%ofthesodiumfilteredattheglomerulus.
Therenin-angiotensinsystemisanimportantregulatorofrenalsodiumexcretion.
Volumeexpansionstimulatesthesynthesisofatrialnatriureticpeptide,whichinhibits
sodiumresorptioninthemedullaryportionofthecollectingduct,facilitatinganincrease
inurinarysodiumexcretion.
Volumeoverloadoccurswhensodiumintakeexceedsoutput.
Volumedepletionusuallyoccurswhensodiumlossesexceedintake.

17. Sodium
Sodium is the dominant cationof the ECF.
It is the principal determinant of extracellular osmolality.
Sodium is therefore necessary for the maintenance of intravascular volume.
Less than 3% of sodium is intracellular.
More than 40% of total body sodium is in bone; the remainder is in the
interstitial and intravascular spaces.

18. HYPERNATREMIA
Typicallydefinedasaserumorplasmasodium>150mEq/L.

19. Iatrogenicin
ahospital
setting.

20. developsonlyifthepatient
doesnothaveaccesstowater
orcannotdrinkadequately
becauseofimmaturity,
neurologicimpairment,emesis,
oranorexia.
Water Deficit
Nephrogenic diabetes insipidus
Central Diabetes Insipidus
Increased insensible losses:
- Premature infants
- Radiant warmers
- Phototherapy
Inadequate intake:
- Ineffective breast-feeding
- Child neglect or abuse
- Adipsia

21. Thewaterdeficit
exceedsthesodium
deficit.

22. Clinical Manifestations
Mostchildrenwithhypernatremiaaredehydrated.
Childrenwithhypernatremicdehydrationtendtohavebetterpreservationof
intravascularvolumebecauseoftheshiftofwaterfromtheintracellular
spacetotheextracellularspace.
Probablybecauseofintracellularwaterloss,thepinchedabdominalskinofa
dehydrated,hypernatremicinfanthasa“doughy”feel.
HypernatremiacausesCNSsymptomsthattendtoparallelthedegreeof
sodiumelevationandtheacuityoftheincrease.
Patientsareirritable,restless,weak,andlethargic.
Someinfantshaveahigh-pitchedcryandhyperpnea.

23. Alertpatientsareverythirsty,eventhoughnauseamaybepresent.
Hypernatremiamaycausefever.
Hypernatremiaisassociatedwithhyperglycemiaandmildhypocalcemia.
Brainhemorrhageisthemostdevastatingconsequenceof
hypernatremia.
oAs the extracellular osmolality increases, water moves out of brain cells, resulting
in a decrease in brain volume. This can result in tearing of intracerebral veins and
bridging blood vessels as the brain moves away from the skull and the meninges.
Seizuresandcomaarepossiblesequelaeofthehemorrhage,although
seizuresaremorecommonduringcorrectionofhypernatremia.

24. Eventhoughcentralpontinemyelinolysis(CPM)isclassicallyassociatedwith
overlyrapidcorrectionofhyponatremia,bothCPMandextrapontine
myelinolysiscanoccurinchildrenwithhypernatremia.

25. Thromboticcomplicationsoccurinseverehypernatremicdehydrationand
include:
Stroke
Duralsinusthrombosis
Peripheralthrombosis
Renalveinthrombosis.
Thisissecondarytodehydrationandpossiblyhypercoagulability
associatedwithhypernatremia.

27. Na
Na
Na
Na
Na
Na
Blood Brain Cells
Osmolality

28. Na
Na
Na
Na
Na
Na
Blood Brain Cells
Osmolality

29. Inthechildwithhypernatremicdehydration,asinanychildwithdehydration,
the1
st
priorityisrestorationofintravascularvolumewithisotonicfluid.
Thedeficitreplacementfluid.
Thefollowingformulaisoftencitedforcalculatingthewaterdeficit:
Water deficit = Body weight ×0.6 (1-145/[current sodium])
Water deficit = 4 ×Body weight ×(current sodium -145)
Themostimportantcomponentofcorrectingmoderateorsevere
hypernatremiaisfrequentmonitoringoftheserumsodiumsothatfluid
therapycanbeadjustedtoprovideadequatecorrection,neithertooslow
nortoofast.

30. Aserumsodiumlevel<135mEq/L.
Hyponatremiaexistswhentheratioofwatertosodiumisincreased.
Thiscanoccurwithlow,normal,orhighlevelsofbodysodium.
Similarly,bodywatercanbelow,normal,orhigh.
HYPONATREMIA

31. Alaboratoryartifact.
Whentheplasmacontains:
Veryhighconcentrationsof
protein:
Multiplemyeloma
IVIGinfusion
Lipid:
Hypertriglyceridemia
Hypercholesterolemia

33. DiagnosticCriteriaForSIADH:
Absenceof:Renal,adrenal,orthyroidinsufficiency,
Congestiveheartfailure,nephroticsyndrome,or
cirrhosis.Diureticingestion,Dehydration.
Urineosmolality>100(usually>plasma).
Serumosmolality<280andserumsodium<135.
Urinesodium>25.

34. 3
rd
space
fluidloss

35. Na
Na
Na
Blood Brain Cells
Osmolality

36. Asbraincellsswell,thereisanincreaseinintracranialpressure.
Acute,severehyponatremiacancausebrainstemherniationandapnea.
Neurologicsymptomsofhyponatremiainclude:
Anorexia
Nausea,Emesis
Malaise,Lethargy,Confusion,Agitation
Headache
Seizures
Coma
Decreasedreflexes
PatientsmayhavehypothermiaandCheyne-Stokesrespirations.
Hyponatremiacancausemusclecrampsandweakness.
Clinical Manifestations

38. The management of all causes requires judicious monitoring and avoidance
of an overly quick normalization of the serum sodium concentration.
A patient with severe symptoms (shock or seizures), no matter the etiology,
should be given a bolus of hypertonic saline to produce a small, rapid
increase in serum sodium.
Rapid correction of hyponatremiamay cause central pontine myelinolysis
(CPM).
This syndrome produces neurologic symptoms, including confusion,
agitation, flaccid or spastic quadriparesis, and death.
it is advisable to avoid correcting the serum sodium by >12 mEq/L/day.
TREATMENT

39. Intravenous hypertonic saline rapidly increases serum sodium, and the
effect on serum osmolality leads to a decrease in brain edema.
Each mL/kg of 3% sodium chloride increases the serum sodium by
approximately 1 mEq/L.
A child with active symptoms often improves after receiving 4–6 mL/kg of
3% sodium chloride.

40. Potassium
HYPERKALEMIA
1 of the most alarming electrolyte abnormalities
because of the potential for lethal arrhythmias.

43. Clinical Manifestations
Themostimportanteffectsofhyperkalemiaare
duetotheroleofpotassiuminmembrane
polarization.
Thecardiacconductionsystemisusuallythe
dominantconcern.
Electrocardiographic(ECG)changesbeginwith
peakingoftheTwaves.

44. Peaking
of the T
waves
P-R
interval
Flattening
of the P
wave
Widening
of the QRS
complex
VF Asystole