Sodium Balance

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Sodium Balance




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Slide1

Sodium Balance

Pedram

Fatehi

, MD

Division of Nephrology

fatehi@stanford.edu

Slide2

Learning Objectives

ECF

volume

matches

total ECF sodium content

.

The kidney

matches sodium excretion to sodium intake in order to maintain ECF volume.

Recognize

the volume sensors and

effector

mechanisms that regulate sodium excretion (i.e. regulate ECF volume

).

Explain

why sodium saving mechanisms developed during evolution to prevent ECF volume reduction may be activated in disease, causing an increase in the ECF volume above normal.

Slide3

Salts are ionic compounds of

cations and anions. For our discussion, we’ll use the term “salt” to mean sodium chloride or just sodium.

Water follows Salt

Slide4

Maintaining the Internal Environment

What Goes In

=What Comes Out

Intracellular Fluid

290

mOsm

Na+ 10K+ 120

Extracellular Fluid290 mOsmNa+ 140K+ 4

Slide5

Bourque CW. Nature Reviews Neuroscience, 2008

Central mechanisms of osmosensation and systemic osmoregulation

Mammals ECF~300 mOsm/kg

Non-mammals ECF(vertebrates and invertebrates)42 – 1140 mOsm/kg~range of U Osm

(~290

mOsm

/kg)

Slide6

Galapagos marine iguana has nasal salt glands to excrete excess salt.

Slide7

Terrestrial elephant finds salt deposits to replete salt deficiency.

Slide8

Intake of salty foods will prompt thirst so water (and volume) will follow.

Slide9

Maintaining the Internal Environment

What Goes In = What Comes Out

High sodium diet150 mEq/day ~ 3450 mg/day

Very low sodium diet15 mEq/day~345 mg/day

Effect of abrupt changes in Na+ intake on body weight and renal Na+ excretion in a normal human. The shaded areas refer to changes in total body Na+ stores due to the difference between intake and excretion. (From

Earley

LE , Clinical Disorders of Fluid and Electrolyte Metabolism, 1972)

“Low Sodium Diet”

<100

mEq

/d ~ <2300 mg/d

Slide10

GFR ≈ 100

mL/min ≈ 150 L/day [Na] ≈ 150 mEq/LNa filtered ≈ 150 L/day x 150 mEq/L ≈ 22,500 mEq/dayNa excreted ≈ 1 to 50 mEq/day (less than 1%)

Na

+

excretion in humans

is regulated by the kidney

Slide11

In nature, salt and the water that accompanies it are hard to obtain and easily lost, eg. in fever, sweat, diarrhea, blood loss; thus, evolved responses to maintain and replete ECF volume by: Increasing sodium intake (‘salt hunger’) Restricting sodium loss in the kidneys *

Cholera Outbreak

Cameroon , 2014

Slide12

DehydratedVolume depletedHypervolemicHypovolemicEdematous

How would you describe a patient with severe diarrhea from cholera?

(may choose more than one)

Slide13

DehydratedVolume depletedHypervolemicHypovolemicEdematous

How would you describe a patient with severe diarrhea from cholera?

(may choose more than one)

Slide14

Low urine sodium concentrationLow cardiac outputHigh stroke volumeFast heart rateLow blood pressurePoor tissue perfusion

Patients with very low ECF volume (ie, low salt content or salt deficiency) will have:(may choose more than one)

Slide15

Low urine sodium concentrationLow cardiac outputHigh stroke volumeFast heart rateLow blood pressurePoor tissue perfusion

Patients with very low ECF volume (ie, low salt content or salt deficiency) will have:(may choose more than one)

CO = HR x SV

Same for diarrhea or blood loss, both

hypovolemic states.

Slide16

PO (oral) WaterIV D5W (water with 5% dextrose)IV NS (normal saline, Na/Cl, ~290 mOsm)Oral ‘Rehydration’ Therapy (Na/Cl/K/citrate/glucose, ~250 mOsm)IV LR (lactated ringers, Na/Cl/K/Ca/lactate, ~270 mOsm)

Reasonable options to manage severe diarrhea from cholera include: (may choose more than one)

Slide17

PO (oral) WaterIV D5W (water with 5% dextrose)IV NS (normal saline, Na/Cl, ~290 mOsm)Oral ‘Rehydration’ Therapy (Na/Cl/K/citrate/glucose, ~250 mOsm)IV LR (lactated ringers, Na/Cl/K/Ca/lactate, ~270 mOsm)

Reasonable options to manage severe diarrhea from cholera include: (may choose more than one)

Slide18

Intracellular Fluid

290

mOsm

Na+ 10

K+ 120

Extracellular Fluid290 mOsmNa+ 140K+ 4

Hypovolemic

states are managed with sodium-containing isotonic solutions, because Na+ is the major determinant of ECF volume.

Slide19

Gatorade provides (per liter):

sodium 20

mEq, potassium 3 mEq

Slide20

Ernest Starling, M.D.1866 - 1927Starling Law of the Heart Starling Forces of capillary filtration

Slide21

Net filtration pressure = Lp S [Δ hydraulic pressure – Δ oncotic pressure]

Lp

, permeability of capillary wall; S, surface area available for filtration

Slide22

Extracellular Fluid (ECF)

Volume determined by Na+ content

28 L

11 L

3 L

Plasma and interstitium are normally in equilibrium, but edema forms if altered Starling forces favor filtration into the interstitial space.

Total Body Water = 42 L (70kg x 60%)

Slide23

Kidneys and body will respond to ‘perceived’ plasma volume (not the interstitial fluid).

Intracellular Fluid

290

mOsm

Na+ 10

K+ 120

Extracellular Fluid

290

mOsm

Na+ 140

K+ 4

28 L

11 L

3 L

Slide24

(JGA)

, Aortic Arch

(Sympathetic NS)

Slide25

Slide26

Rose BD, 2001

Clinical Physiology of Acid Base and Electrolyte Disorders

(Na+ and H2O)

In altered Starling forces, kidney/body effort to restore plasma volume may improve volume deficit somewhat, but will also worsen interstitial edema.

Slide27

Ring placed at thoracic inferior vena cavaDogs fed 75 meq / day sodiumOn Day 1 : TIVC constrictionOn Day 2 : Increased constrictionOn Day 15: Release constriction

Barger’s

C

aval

Constriction

E

xperiment

Slide28

Renal

response to low effective circulating volume is sodium (volume) retention

BLOOD PRESSURE ~effective circulating volume ~effective tissue perfusion

RENIN

ALDOSTERONE

URINE SODIUM

PLASMA VOLUME

New Steady State

Slide29

BLOOD PRESSURE

RENIN

ALDOSTERONE

URINE SODIUM

PLASMA VOLUME

BODY WEIGHT

R ATRIAL PRESSURE

Renal

response to high effective circulating volume is sodium (volume) excretion

Slide30

Renal

response to high effective circulating volume is sodium (volume) excretion

Slide31

Na+ Intake: 10

mEq/day 350 mEq/day

Atrial

Natriuretic

Peptide

vs

Renin

-

Angiotensin-Aldosterone

Slide32

Case

Slide33

65M is in ED with shortness of breath; he is waiting to be seenPMHx: HTN, DM, lipids, CAD

Extracellular fluid volume and TBW are:

A.

Decreased

B.

Normal

C.

Increased

D.

Need more information

Slide34

65M is in ED with shortness of breath; he is waiting to be seenPMHx: HTN, DM, lipids, CAD

Extracellular fluid volume and TBW are:A. DecreasedB. NormalC. IncreasedD. Need more information

Slide35

65M presents to ED with progressive dyspnea and orthopnea, ran out of diuretics x 1 wkPMHx: HTN, DM, lipids, CAD

AF 70/palp 120 30 85%RATripod position, 1 word sentences+JVD, crackles; tachycardic, S3Cool extremities, 3+ LE edema

Extracellular fluid

(ECF) volume and TBW are:A. DecreasedB. NormalC. IncreasedD. Need more information

Slide36

65M presents to ED with progressive dyspnea and orthopnea, ran out of diuretics x 1 wkPMHx: HTN, DM, lipids, CAD

AF 70/palp 120 30 85%RATripod position, 1 word sentences+JVD, crackles; tachycardic, S3Cool extremities, 3+ LE edema

Extracellular fluid

(ECF) volume and TBW are:A. DecreasedB. NormalC. IncreasedD. Need more information

Slide37

65M presents to ED with progressive dyspnea and orthopnea, ran out of diuretics x 1 wkPMHx: HTN, DM, lipids, CAD

AF 70/palp 120 30 85%RATripod position, 1 word sentences+JVD, crackles; tachycardic, S3Cool extremities, 3+ LE edema

Effective circulating volume is:

A. DecreasedB. NormalC. IncreasedD. Need more information

Slide38

65M presents to ED with progressive dyspnea and orthopnea, ran out of diuretics x 1 wkPMHx: HTN, DM, lipids, CAD

AF 70/palp 120 30 85%RATripod position, 1 word sentences+JVD, crackles; tachycardic, S3Cool extremities, 3+ LE edema

Effective circulating volume is:

A. DecreasedB. NormalC. IncreasedD. Need more information

Slide39

65M presents to ED with progressive dyspnea and orthopnea, ran out of diuretics x 1 wkPMHx: HTN, DM, lipids, CAD

AF 70/palp 120 30 85%RATripod position, 1 word sentences+JVD, crackles; tachycardic, S3Cool extremities, 3+ LE edema

Sympathetic nervous system and RAAS activity

are:A. DecreasedB. NormalC. IncreasedD. Need more information

Slide40

65M presents to ED with progressive dyspnea and orthopnea, ran out of diuretics x 1 wkPMHx: HTN, DM, lipids, CAD

AF 70/palp 120 30 85%RATripod position, 1 word sentences+JVD, crackles; tachycardic, S3Cool extremities, 3+ LE edema

Sympathetic nervous system and RAAS activity

are:A. DecreasedB. NormalC. IncreasedD. Need more information

Slide41

65M presents to ED with progressive dyspnea and orthopnea, ran out of diuretics x 1 wkPMHx: HTN, DM, lipids, CAD

AF 70/palp 120 30 85%RATripod position, 1 word sentences+JVD, crackles; tachycardic, S3Cool extremities, 3+ LE edema

Urine sodium concentration is likely

A. low, < 10 mEq/LB. high, > 50 mEq/L

Slide42

65M presents to ED with progressive dyspnea and orthopnea, ran out of diuretics x 1 wkPMHx: HTN, DM, lipids, CAD

AF 70/palp 120 30 85%RATripod position, 1 word sentences+JVD, crackles; tachycardic, S3Cool extremities, 3+ LE edema

Urine sodium concentration is likely

A. low, < 10 mEq/LB. high, > 50 mEq/L

Slide43

Rose BD, 2001

Clinical Physiology of Acid Base and Electrolyte Disorders

(Na+ and H2O)

In altered Starling forces, kidney/body effort to restore plasma volume may improve volume deficit somewhat, but also worsen interstitial edema.

Slide44

Slide45

Learning Objectives

ECF

volume

matches

total ECF sodium content

.

The kidney

matches sodium excretion to sodium intake in order to maintain ECF volume.

Recognize

the volume sensors and

effector

mechanisms that regulate sodium excretion (i.e. regulate ECF volume

).

Explain

why sodium saving mechanisms developed during evolution to prevent ECF volume reduction may be activated in disease, causing an increase in the ECF volume above normal.

Slide46

Questions

fatehi@stanford.edu

Slide47

Slide48

Angiotensinogen

ACE

Renin

-

Angiotensin

-

Aldosterone

System

(RAAS)

Slide49

Renin - Angiotensin - Aldosterone System(RAAS)

Slide50

ENaC

Principal Cell

Palmer BF, NEJM, 2004

Managing HyperK Caused by Inhibitors of the RAAS

Volume Regulation

Baro

-receptors

Sympathetic NS

RAAS

Natriuretic

Peptides

Slide51

Levin ER, et.al. NEJM, 1998

Natriuretic Peptides

Natriuretic PeptidesPhysiologic effects of increased venous return (hypervolemia)

/ ADH

Slide52

Consequence of low effective circulating volume

If we performed the IVC constriction experiment on an unsuspecting 70 kg medical student, and he ate the recommended daily intake of sodium (2400 mg) for 3 days. Approximately how much would his weight increase?

(HINT, 2400 mg of Na+ = ~ 100

meq

Na+)

2 liters

0.2 liters

20 liters

Slide53

Slide54


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