hyponatremia 1

7/27/2019 Hyponatremia 1

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Hyponatremia

Overview

Fluid compartments and solutes

Define hypoNa

Epidemiology

Normal physiology preventing hypoNa

Pathophysiology of hypoNa

Manifestations

Work-up & Differential Diagnosis

Treatment


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Hyponatremia

Fluid Compartments/Solutes

Distribution of water- due to osmotic forces

Na is mainly extracellular, K is intracellular

Serum osmol = 2(Na)+ BUN/2.8 + Gluc/18 Sodium is the primary determinant

Serum osmol tightly regulated (275 290)

Mechanisms for regulation If osmol 1. thirst mechanism, 2. ADH

Effective circulating volume also ADH


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Hyponatremia

Hyponatremia

Definition: Commonly defined as a serum sodium concentration

135 meq/L

Hyponatremia represents a relative excess of water inrelation to sodium.


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Hyponatremia

Hyponatremia

Most often due to retention of free water

2ndary to impaired excretion of free water

Occ. due to Na loss exceeding water loss

i.e. thiazide-induced hypoNa (elderly women)


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Hyponatremia

Hyponatremia

Epidemiology:

Frequency

Hyponatremia is the most common electrolyte

disorder

incidence of approximately 1%

prevalence of approximately 2.5%

surgical ward, approximately 4.4%

30% of patients treated in the intensive care unit

ocw.jhsph.edu
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Hyponatremia

Hyponatremia

Epidemiology Cont.

Mortality/Morbidity

Acute hyponatremia (developing over 48 h or less)

are subject to more severe degrees of cerebraledema

sodium level is less than 105 mEq/L, the mortality is over

50%

Chronic hyponatremia (developing over more than48 h) experience milder degrees of cerebral

edema

Brainstem herniation has not been observed in patients

with chronic hyponatremia


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Hyponatremia

Hyponatremia

Epidemiology Cont.

Age

Infants

fed tap water in an effort to treat symptoms ofgastroenteritis

Elderly patients with diminished sense of thirst,

especially when physical infirmity limits

independent access to food and drink


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Hyponatremia

Hyponatremia

Physiology

Serum sodium concentration

regulation:

stimulation of thirst

secretion of ADH

feedback mechanisms of the renin-

angiotensin-aldosterone system

renal handling of filtered sodiumwww.daviddarling.info
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Hyponatremia

Hyponatremia

PhysiologyCont.

Stimulation of thirst

Osmolality increases

Main driving force

Only requires an increase of 2% - 3%

Blood volume or pressure is reduced

Requires a decrease of 10% - 15%

Thirst center is located in the anteriolateral centerof the hypothalamus

Respond to NaCL and angiotensin II


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Hyponatremia

Hyponatremia

PhysiologyCont.

Secretion of ADH Synthesized by the neuroendocrine cells in the

supraoptic and paraventricular nuclei of thehypothalamus

Triggeres: Osmolality of body fluids

A change of about 1%

Volume and pressure of the vascular system

Increases the permeability of the collecting duct towater and urea


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Hyponatremia

Hyponatremia

PhysiologyCont

renin-angiotensin-aldosterone Renin

Stemuli are perfusion pressure, sympathetic activity, andNaCl delivery to the macula densa

Increase in NaCl delivery to the macula decreases theGFR by decrease in the renin secretion

Aldosterone

Reduces NaCl excretion by stimulating its resorption Ascending loop of Henle

Distal tubule

Collecting duct


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Hyponatremia

Normal Physiology

Excretion of free water requires: 1. generation of free water by reabsorption of

NaCl w/o water in ascending Loop of Henle

2. excretion of this water by maintenance of

impermeability to water in collecting duct (No

ADH)

Remember that ADH leads to retention of water via

pores


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Hyponatremia

Hyponatremia

www.merricks.com/tech_electrolyte_new.htm
http://www.merricks.com/tech_electrolyte_new.htmhttp://www.merricks.com/tech_electrolyte_new.htm


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Hyponatremia

Pathophysiology

Simply, hyponatremia is due to inability tomatch water excretion with water ingestion

1. Defect in water excretion

SIADH (inappropriate ADH release)

Hypovolemic state(appropriate ADH release)

Hyperglycemia (draws water into plasma)

Advanced renal failure 2. System overwhelmed (water ingestion)

i.e. primary polydipsia


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Hyponatremia

Clinical Manifestations

most patients with a serum sodium

concentrationexceeding 125 mEq/L are

asymptomatic

Patients with acutely developing

hyponatremia are typically symptomatic at a

level of approximately 120 mEq/L


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Hyponatremia

Clinical Manifestations (cont.)

Most abnormal findings on physical

examination are characteristically neurologic

in origin

Mild Sx: anorexia, nausea, lethargy

Mod Sx: disoriented, agitated, neuro deficit

Sev Sx: seizures, coma, death


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Hyponatremia

Differential Diagnosis/Work-Up

First test to obtain: serum osmolality

Helps exclude two easier to remember

causes of hyponatremia

1. HyperosmolarhypoNa (osmo > 295)

2. Iso-osmolarhypoNa (280-295 osmo)


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Hyponatremia

HyperosmolarhypoNa

Water shifts from the intracellular to theextracellular compartment, with a resultant

dilution of sodium. The TBW and total body

sodium are unchanged.

This condition occurs with hyperglycemia(100mg1.6 Na) or Administration of

mannitol
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Hyponatremia

Iso-osmolarhypoNa (nl serum

osmo)

Pseudohyponatremia (with old

machines) The aqueous phase is diluted by excessive

proteins or lipids. The TBW and total body

sodium are unchanged. hypertriglyceridemia

multiple myeloma

N.B. problem resolved with the new electrolytes

measuring electrodes


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Hyponatremia

DDx / Work-up

Hypo-osmolarhypoNa (most common) Three types (based on volume status)

Hypervolemic (congested states)

CHF, cirrhosis, nephrotic syndrome, ARF / CRI Hypovolemic (appropriate ADH secretion)

renal loss (diuretics, nephropathy, hypoAldosteron)

GI loss (vomiting, diarrhea, NGT)

Skin loss (sweating, burns, cystic fibrosis)

Peritonitis or sepsis


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Hyponatremia

DDX / Work-up

Euvolemic (normal volume state)

SIADH

Pain and nausea can cause non-osmotic ADH

release

Post-op state, especially TURP

Hypocortisolism or hypothyroidism

Psychogenic polydipsia (water intoxication)

Reset osmostat(pregnancy, psych disorders)

In this case, body thinks normal is lower-> no Tx


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Hyponatremia

DDX / Work-Up Next lab value: Urine osmolality

Is free water excretion, or ability to dilute

the urine, intact in the face of hypoNa?

Remember: problem is too much water Normal physiologic response = excrete water

If Uosm < 100, means appropriate

excretion ofdilute urine

Psychogenic polydipsia or reset osmostat

If Uosm > 200, reflected impaired water

excretion (usu due to inability to stop ADH)


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Hyponatremia

DDx / Work-Up

Final lab value: Urine sodium

UNa < 30 implies hypovolemic or reduced

effective circ volume (CHF, nephrotic,

cirrhosis)

Kidneys reabsorb solutes to retain water and

volume

UNa> 30 seen in the euvolemic type SIADH, diuretics


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Hyponatremia

Hyponatremia

Other helpful Laboratory tests:

Uric Acid Level < 4 mg/dl consider SIADH

FeNa

Help to determine pre-renal from renal causes


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Hyponatremia

Hyponatremia

Treatment

four issues must be addressed

Asyptomatic vs. symptomatic

acute (within 48 hours)

chronic (>48 hours)

Volume status

1st

step is to calculate the total body water total body water (TBW) = 0.6 body weight

(0.5 for females)

H t i


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HyponatremiaHyponatremia

Treatment Cont.

next decide what our desired correction rateshould be

Symptomatic

immediate increase in serum Na level by 8 to 10

meq/L in 4 to 6 hours with hypertonic saline is

recommended

acute hyponatremia

more rapid correction may be possible 8 to 10 meq/L in 4 to 8 hours

chronic hyponatremia

slower rates of correction

12 meq/L in 24 hours


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Hyponatremia

Hyponatremia

Symptomatic or Acute

estimate SNa change on the basis of theamount of Na in the infusate

SNa = {[Na + K]inf SNa} (TBW + 1)

SNa is a change in SNa

[Na + K]inf is infusate Na and K concentration in 1 liter ofsolution


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Hyponatremia

Hyponatremia

IV Fluids One liter of Lactated Ringer's Solutioncontains:

130 mEq of sodium ion = 130 mmol/L

109 mEq of chloride ion = 109 mmol/L

28 mEq of lactate = 28 mmol/L

4 mEq of potassium ion = 4 mmol/L

3 mEq of calcium ion = 1.5 mmol/L

One liter of Normal Saline contains:

154 mEq/L of Na+ and Cl

One liter of 3% saline contains:

514 mEq/L of Na+ and Cl


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Hyponatremia

Hyponatremia

Asymptomatic or Chronic

SIADH

sodium handling is intact in SIADH

administered sodium will be excreted in the urine,

while some of the water may be retained

possible worsening the hyponatremia


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Hyponatremia

Hyponatremia

Asypmtomatic or Chronic

SIADH

Water restriction

0.5-1 liter/day

Salt tablets

Demeclocycline

Inhibits the effects of ADH

Onset of action may require up to one week

H t i
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HyponatremiaHyponatremia Example:

a 60 kg women with a plasma sodium of 110meq/L

Formula:


What is the TBW?

How high will 1 liter of normal saline raise the

plasma sodium?

Answer:

TBW is 30 L

Serum sodium will increase by approximately

1.4 meq/L for a total SNa of 111.4 meq/L

H i


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Hyponatremia

Hyponatremia

Example: 85 y/o male with weakness and head ache

SNa is 118 mEq/L

Plasma osmolality is 254 mosmol/kg

Urine osmolality is 130 mosmol/kg

Urine sodium >20 mEq/L

Uric acid is 3mg/dl

What type of hyponatremia does thispatient have?

H t i


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Hyponatremia

Hyponatremia Example:

63 y/o female at 75 Kg with N/V/D for 4 days

SNa is 108 mEq/L

She has had one seizure in the ambulance

Plasma osmolality is 251 mosmol/kg Urine osmolality is 47 mosmol/kg

Uric acid is 6mg/dl

What type of hyponatremia does this

patient have?

H t i


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Hyponatremia

How will you Tx her?

Calculate the total body water

0.5 x weight = 37.5 L

What rate of correction do you want?

8 to 10 mEq/L in 6 to 8 hours

What fluid will you use? 3% Saline

How will you calculate the amount of sodium

to give her? SNa = {[Na + K]inf SNa} (TBW + 1)

How will her sodium increase after 1 liter of

3% saline?

By 10.8 mEq/L to 118.8 mEq/L

H t i


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Hyponatremia

Hyponatremia

What other medication will she need?

Lasix and a foley

Her sodium increases to 118.8 mEq/L over

the next 8-10 hours. How will you continue

to correct her hyponatremia?


SNa = 154mEq/L 118.8mEq/L 38.5L = 0.9

mEq/L

So 2 liters of normal saline over the next 14

hours

H t i


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Hyponatremia

Hyponatremia

The End

Questions????

hyponatremia 1

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