approach to diagnosis of hypokalemia

7/26/2019 Approach to Diagnosis of Hypokalemia

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Dr Chaitanya Vemuri

Approach to Diagnosis of

Hypokalemia


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Most abundant cation in human body

Regulates intracellular enzyme function and helps to determine

neuromuscular & cardiovascular tissue excitability.

9 !of total body "# $ %ntracellular

predominantly in muscle '

( ! $ )xtracellular fluid

* ( ! $ +lasma

Introduction : Potassium


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Ratioof extracellular "# to %ntracellular "# $ determines

the membrane potential

,he acuity of changesin serum potassium concentration& membrane potential determines clinical symptoms and

underlying signs

+lasma concentration varies from -. to ./ mmol0l


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1igh intracellular concentration of "# is maintained by

several factors that govern "# upta2e & release from

intracellular compartment

"# upta2e into cells $ actively driven by 3a#"#4,+ase

5ea2bac2 into )C6 $ opposed by electrical gradient

Physiology Of PotassiumHomeostasis


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4cid base status

+ancreatic hormones $ insulin 7 glucagon

Catecholamines

4ldosterone

+lasma 8smolality

)xercise

Cellular "# content

Factors modifying transcellular K+distribution


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4l2alemiapromotes "# upta2e by cells

4cidemia diminishes "# upta2e by cells

4cute respiratory al2alosis7 incontrast increase plasma "#

by . mmol0l per .( p1 unit

d0t increased adrenergic activity

Acid ase !tatus


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%nsulinstimulates cellular upta2e of "# by activating

3a#"#4,+ase decreasing plasma "# '

%nsulin affects "# transport independently of glucose

upta2e

:lucagon increase plasma "#independently of changes

in plasma glucose 0 insulin

Pancreatic Hormones


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;eta adrenergic activity < hypo2alemia

4lpha adrenergic antagonists < hypo2alemia

"atecholamines


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%nvitro studies4ldosterone stimulates 3a#"#4,+ase and thereby

activating 3a # influx

Aldosterone


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1yperosmolality Mannitol infusion 0 hyperglycemia in

DM ' $ increase plasma "#

)ach ( m8sm 0 "g rise in plasma osmolality7 increases

plasma "# by ./ mmol0l

Osmolality


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Recurrent contraction increases "# egress from muscle

Modest exercise $ high "# in )C6 in local environment

produces vasodilatation & thereby increased regional blood

flo=

>evere exercise $ increase plasma "# modestly

+hysical training increases 3a#"#4,+ase activity in s2eletal

muscle =hich helps s2eletal muscle to ta2e up "# again

#$ercise


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%ntracellular "# affects intra to extracellular "#

?ith "# depletion 7

"# loss from )C6 @ %C6 losscausing increased "i # 0 "e#

"# depletion $ hyperpolarization

"# retention $ depolarization

"ellular K+ "ontent


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"idney is dominant in sustaining "# balance

@9 ! "# $ excreted in urine

Remainder through feces

Decrease in :6R7 "# excretion via feces increased

:% 5oss $ "# secretion by proximal & distal colon

K+ alance


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%enal Handling of K+:lomerulus$ freely filtered

+C,7 ,hic2 4s limb 581 $

reabsorbed


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"ortical "ollecting Duct


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Defined as plasma concentration of "# * -.A m)B05

Mild 1ypo2alemia $ -. < -.A m)B05 $ asymptomatic

1ypo2alemia * -. m)B05 $ symptomatic

Clinical manifestations of hypo2alemia vary greatly

bet=een individual patients&

their severitydepends on degree of hypo2alemia

Hypokalemia


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Clinical features

%nvestigations

Diagnosis


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Mild hypo2alemia $ generally asymptomatic

%ncreased ris2 of mortality for pts =ith cardiovascular disease < trigger ventricular

tachycardia 0 ventricular fibrillation

decrease "# $ d0t sympathetic stimulation'

Digitalis induced arrhythmias < can occur =ith normal drug levels if hypo2alemia is

present

Diuretic induced hypo2alemia & hypomagnesemia must be avoided in pts on drugs

that prolong , interval $ as it predisposes topolymorphic V, 0 ,orsade de pointes

1ypo2alemia * - m)B05 $ >ymptomatic

"linical Features


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Digitalis %ntoxication $ ventricular extrasystoles

ventricular tachycardia

ventricular fibrillation

partialcomplete 4V bloc2bradycardia

atrial flutter

atrial fibrillation

Ventricular arrhythmias $ tachycardia 0 fibrillation

"ardiac


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6atigue

Myalgia

Muscular =ea2ness involving lo=er limbs

>evere 1ypo2alemia $

+aralysis extremities '

?ea2ness of respiratory muscles dyspnea '

Rhabdomyolysis exercise induced'

&euro'muscular


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Constipation

+aralytic ileus

(astro'intestinal


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Chronic interstitial nephritis

d0t functional decrease in renal blood flo= , >egment

development of prominent u =aves

>evere hypo2alemia $ increased amplitude of p =ave

increased R> duration

>.+otassium

asic In*estigations


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In*estigations ) etiologyErinary "#

,,":

Erinary Chloride

C;C+eripheral >mear

4;:

)chocardiogram

Cardiac )nzymes

>erum aldosterone

>erum renin

E>: 4bdomen

C, 0 MR% 4bdomen

6;> 0 ++;> 0 Erine "etones

,>1 0 free ,- 0 free ,

Colonoscopy 0 8:Dscopy


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:rossly due to

Decreased net inta2e

>hift into cells

%ncreased net loss

Diagnosis ) #tiology


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8ccurs in patients =ith extreme leu2ocytosis

eg $ in myeloproliferative disorders

%nvitro ?;C upta2e potassium =ithin the test tube

3ot associated =ith any internal 0 external potassium

balance

!purious Hypokalemia


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>tarvation

Clay ingestion binds to dietary "# & %ron '

Decreased Intake


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4cid < ;ase >tatus $Metabolic 4l2alosis

1ormonal $ %ncreased %nsulin

%ncreased ;eta 4drenergic activity

Drugs $ ;eta agonists

,heophylline

;arium %ntoxicationChloroBuine

Calcium Channel ;loc2ers

ranscellular shifts


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Catecholamine release associated =ith $

4sthma

C8+D < exacerbations

1eart failure

Myocardial infarction 0 angina

Drug =ithdra=al syndrome < alcohol 0 narcotics 0 barbiturates

ranscellular shift


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%nsulin administration < for treatment of D"4

Refeeding >yndrome

1ypo2alemic +eriodic +aralysis

,hyrotoxic +eriodic +aralysis

,reatment of anemia $ Vit ;( 0 6olic acid deficiency

Ese of :M < C>6 in patients =ith 3eutropenia

ranscellular shift


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Decreased total body "#Decreased inta2eRenal loss of "#)xtra renal loss of "#


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Erinary "#$ @ m)B05< Renal loss

Erinary " # $ * m)B05< )xtrarenal loss

,,": $ ,ranstubular +otassium :radient

Erine "# 0 +lasma "# '

Erine 8sm 0 +lasma 8sm '

,,": $ Renal loss $ @

)xtra renal loss $ *

%enal ,s #$tra renal loss


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#$tra %enal -ossErinary "# * Metabolic 4cidosisMetabolic 4l2alosis


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Erinary loss "# @ Metabolic 4cidosisErinary chloride levelErinary chloride levelMetabolic 4l2alosisErinary chloride level

%enal -oss


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4mphotericin ; $ tubular damage

increased excretion of "#

4minoglycosides $ renal =asting of "#

,hiazides7 6urosemide7 4cetazolamide $ renal loss "#

Cisplatin

1F+8M4:3)>)M%4 $ >ignificant renal "# =asting

%enal loss ' Drugs

%enal -oss + .etabolic


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Erinary Chloride

%enal -oss + .etabolicAlkalosis


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1igh $ ;artter71igh $ ;artter71,3 7 %ncreased )C61igh $ ;artter71igh $ ;artter7

%enal loss +/rine "l 0 12 m#34-


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RENIN HIGHALD HIGH

RENIN LOWALD HIGH

LOW RENINLOW ALD

R4> +rimary 1yperaldosteronism 38RM45 C8R,%>85 $

Malignant 1,3 :lucorticoid remediable 1,3 )xogenous mineralocorticoid

Renin >ecreting ,umor 5iddles syndrome

58? C8R,%>85 $

4drenogenital syndrome

1%:1 C8R,%>85 $

6amilial :lucocorticoidResistance


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HA&K 5O/

approach to diagnosis of hypokalemia

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