FLUIDS AND ELECTROLYTES. INTRODUCTION The kidneys are responsible for maintaining plasma osmolality...

FLUIDS AND ELECTROLYTES

INTRODUCTION

• The kidneys are responsible for maintaining plasma osmolality within a narrow range.

• Water is the most important solvent in the composition of the living systems.

• Total body water is a percentage of the body weight.

• TBW decreases with age.• TBW consists of the ICF and ECF.

INTRODUCTION CTD

• At birth TBW is 78% of body wt• Drops dramatically within 1st month of life• Equals adult level of 55%-60% at 1yr• ECF drops after birth due to neonatal diuresis.• ICF increases to achieve adult ratio.• Obligatory water loss refers to the minimum

intake necessary to maintain fluid balance.

TBW AND AGE

Age Body water % ECF% ICF%

Term 75 35-44 33

4-6mo 60 23 37

12mo 60 26-30 37

Puberty 60 20 40

Adult 50-60 20 40

ECF

• Constitutes 20-25% of body wt• Consists of plasma water which is 5% of body wt interstitial water dat is 15% of body wt• Differs btw males and females at puberty• Monitored by low( cardiac atria) and high

pressure (aortic arch, carotid sinus,JGA)• Regulated by the RAA,ANF,ADH.

ICF

• Represents the difference btw TBW and ECF

• Forms 30-40% of body wt• It is the sum of fluids in different locations

of the body with different functions.

OTHERS

• Trans-cellular and other slowly exchangable compartments are of lesser importance under normal conditions.

• Forms 8-10% of body wt • Found in the bone, connective tissue and

cartilage• It is not accessible to body fluid regulatory

mechanism

OTHERS CTD

• Trans-cellular fluid are located in the cerebrospinal, intra-occular, pleural, peritoneal and synovial fluids

• Transcellular fluid is influenced by trans epithelial transport.

• Also described as extracoporeal.

REGULATION OF BODY WATER

• Body water balance is regulated by intake and excretion

• Excretion is the most important in the regulatory mechanism

• Plasma osmolality is 285-295mosmo/kg H20 is the concentration of solute particles and this is constant irrespective of fluctuation of solutes and water intake

INTAKE REGULATION

• Thirst is a major defense against fluid depletion.• Regulated by a center in the mid

hypothalamus• Change in plasma osmolality as littlle as 1-2% or

ECF depletion by 10% stimulates thirst• Osmoreceptors located in the hypothalamus,

pancreas and hepatic portal vein but the mechanism by which volume depletion induces thirst are not understood.

EXCRETION

• Losses of water occurs thru lungs ,skin, git, kidneys.

• Insensible loss are those lost thru evaporation and is proportionate to the surface area of the body and influenced by enviromental temp, resp

• Insensible loss must be taken into consideration in fluid management in children

• Urinary water excretion is an obligatory one that is needed in body homeostasis

• Obligatory loss is important in osmolality regulation.

EXCRETION CTD

• Urinary loss is regulated by ADH and its receptors activity in the collecting duct and the medullary concentration gradient where there is passive re-absorption of water

• ADH is an octapeptide released from the posterior pitutary fossa in response to stimuli from the hypothalamus.

FLUID THERAPY

• Fluid therapy when employed orally or parenterally is to maintain or restore volume or composition of body fluids.

• The goal of fluid therapy is to normalize the ICF and ECF chemical environment for cell and organ to function well.

• Fluid requirement consists of three categories viz i) maintenance ii) deficit iii) supplementary or ongoing loss

MAINTENANCE THERAPY

• This is a function of metabolic rate changes of which affect h20 production.

• It replaces usual body losses of fluid and electrolyte.

• Includes usual insensible loss and the urinary output ml for ml

• Calculation is based on 100ml/100 cal on the assumption of negligible fecal loss .

• It is also assumed dat this will also address the renal water loss.

MAINTENANCE CTD

• Requirement is as followsBody wt in kg Fluid requirement/day0-10 100ml/kg11-20 100ml/kg+50ml/kgAbove 20 100ml/kg+50ml/kg+ 20ml/kg *** any wt above 20kg subsequently needs

20ml/kg in addition.

EXAMPLE

• What is the maintenance fluid requirement of a 2year old with a weight of 20kg

• 1st 10kg =100*10……1000ml

+2nd 10kg = 50*10……..500ml

Total fluid = 1500ml

EXAMPLE CTD

• Calculate the fluid requirement of a child with a weight of 30kg

1st 10kg=100*10=1000ml

2nd 10kg= 50*10= 500ml

3rd 10kg= 20*10= 200ml

Total = 1700ml

DEFICIT THERAPY

• This includes losses due to disease e.g vomiting ,diarrhea

• Calculation is based on body weight loss• This loss is based on clinical assessment.

DEGREE OF LOSS

• Mild dehydration

loss of 3% - 5% of body weight

loss of 30ml/kg - 50ml/kg of body weight

• Moderate dehydration

loss of 7%-10% of body weight

loss of 70ml/kg – 100ml/kg of body weight

DEGREE OF LOSS

• Severe dehydration

loss of 10%-15% of body weight

loss of 100ml/kg-150ml/kg of body weight

CLINICAL FEATURES OF FLUID DEFICIT

MILD DEHYDRATIONLoss of 3-5% body weightThere is mild thirstDry mucus membraneNo sunken eyesSkin tugor returns normallyBP, HR normalMental status intactUrine output normal

MODERATE DEHYDRATION

• Loss of 7-10% of body weight• Thirst is marked• Absence of tears• Dry mucus membrane• Sunken eyes and fontanelle• Skin tugor goes back slowly• Reduced urine output• HR ↑,BP↓• Irritable mental state

SEVERE DEHYDRATION

• Loss of 10-15% of body weight• Severe thirst • Parched mucus membrane• Very sunken fontanelle• Anuria• Hypotension• Delayed capillary refill• Lethargy or coma

MANAGEMENT OF DEHYDRATION

• Mild and moderate dehydration can be corrected orally.

• Severe dehydration however needs parenteral therapy cos the patient will be to weak to take enough orally and may even be in shock so iv or intra-osseous transfusion or even intraperitoneal

• Parenteral is also needed to prevent renal failure.

SEVERE DEHYDRATION

• Therapy is in stages• A --- Initial therapy• B----Subsequent therapy• C----Final

MX OF SEVERE DEHYDRATION CTD

• The goal of the initial therapy is to expand the ECF rapidly

• The patient needs 100ml/kg• 20ml -30ml/kg of IVF is given rapidly this

may be repeated if need be this is given over 30minutes or 1Hr or even longer in malnourished children

• The goal of the second or subsequent stage is to complete the existing deficit

• Require 70-80ml /kg and this is given over 5hr

• The on going loss in the case of diarrhea is commenced after completing the lost fluid.

• When the patient is able to take again then you commence the maintenance therapy.

ELECTROLYTES

• Osmolality of the body is accounted for by the electrolytes in the body.

• The electrolytes are Na, K, Cl, Hco3, urea,glucose.

• Na is the main electrolyte in the ECF alongside the Cl,Hco3, glucose urea as the anions

• K is the main electrolyte in the ICF.

ELECTROLYTES CTD

• Tonicity efers to the effective osmolality• Also reflects the concentration of impermeable

solutes in fluid.( Na, glucose)• Normal tonicity is 275-290mmol/kg• Tonicity is important in diseases where there is

inter-compartmental fluid shift • Neurologic problems are often associated with

the fluid shift.• Urea and ethanol affect osmolality while

mannitol and glycerol affects both osmolality and tonicity.

MAINTENANCE REQUIREMENTS OF ELECTROLYTES

ELECTROLYTES REQUIREMENT

Na 2-3mmol/kg/day

K 1-3mmol/kg/day

Cl 3-5mmol/kg/day

Hco3

*** New borns do not require Na,K,Cl in the 1st 24hrs

SODIUM

• Sodium is the major cation in the ECF• Responsible for maintaining intravascular and

interstitial volumes• 11% is in the plasma pool,29% in the interstitial

lymph fluid 2.55 in the icf• 43% of total sodium is in the bone and only 1/3

of this is exchangeable• ICF Na is maintained at 10meq/l while ECF

is140meq/l • Function includes nerve conduction,cellular

nutrition and BP maintenance

SODIUM REGULATION

• The amt of Na in the body is dependent on the intake and excretion.

• Regulation of Na intake is poorly understood• Different sources of intake which depends on the

source as well as age• Absorption occurs throughout the git minimally in

the stomach and maximally in the jejunum• Absorption is aided by Na-k ATPase.

Na REGULATION CTD

• Excretion of Na occurs thru sweat, urine, feces• Kidney is the principal organ regulatig Na

excretion.• The above is dependent on the glomerular

filtration and the tubular reaborption.• 67% of tub eab takes place in the PT and

LOH ,20% in the asc limb of LOH, 7% in the DT,6% in the CD

• Regulation occurs mainly thru the RAA

HYPONATREMIA

• Refers to serum conc <130meq/l• Can occur when the intake of of fluid

exceeds the excretory capacity of the kidney.

• Causes are as follows

decreased ADH

reduced gfr,polydipsia, malnutrition, thiazide.

• Increased ADH

hypovolemia---- mineralocorticoid def, excess diuretic,dehydration,cappilary leak syndrome

glucocorticoid def, hypothyroidism,

NS, CCF, hepatic cirrhosis

SIADH

CF N MX OF HYPONATREMIA

• Can be either symptomatic or asymptomatic• Often times occurs along with dehydration when

it is referred to as hypotonic dehydration • Includes nausea, vomiting,muscle twitching• Na replacement using the formular

wt* deficit *0.6• Correction done over 24hrs ½ in the 1st 8hrs and

the other ½ next 16hrs.

HYPERNATREMIA

• Serum Na >150meq/l• Results when there is excessive gain of Na

usually iatrogenic in improper mixing of infant formula

• Excessive loss of body water in diarrhea, fever• Causes include low ADH activity as seen in central DI,

nephrogenic DI high ADH activity as seen in excessive intake,

excessive loss thru sweat,adipsia

CF N MX OF HYPERNATREMIA

• **HYPERNATREMIA IS AN EMERGENCY• Lethargy ,confusion, seizures, ICH, irritability,

hypertonia, hyperreflexia,coma• ECF is preserved due to shift of water from ICF.• ***DO NOT CORRECT RAPIDLY AS RAPID

INTERCOMPARTMENTAL SHIFT IS DANGEROUS

• Rate of Na lowering is at 12meq/l/day • Correction of fluid deficit is done over 48 -72hrs.• Choice of IVF is ½ normal saline

POTASSIUM

• Potassium is the major intracellular cation• Essential for cardiac and skeletal muscle

contraction• Balance is dependent on intake, renal and

git excretion• ECF value of Kis 3.5 -5.5meq/l• Difference in K btw the two compartments

is maintained by Na-K ATPase

K REGULATION

• Regulate by two main processes 1) mechanism which responds to within minutes

to plasma changes thus promoting import or export from the icf this include insulin,βadrenergic agonist, acidosis, alkalosis, aldosterone and hyper-osmolality. This they do by inducing a secondary messenger which alters Na-K ATPase

2) mechanism responding within hrs to regulate excretion from the body.