Director, Center for Acute Care Nephrology Cincinnati ...ipna-online.org/Media/Junior Classes/2014 -...

Hypo/Hypernatremia

Stuart L. Goldstein MD

Director, Center for Acute Care Nephrology Cincinnati Children’s Hospital

The Center for Acute Care Nephrology

Objectives

• Understand Fluid cellular shifts

• Understand “maintenance” fluid and calculations

• Understand hyponatremic, isonatremic and hypernatremic dehydration and therapy


The Cell Has a Limited Repetoire

K+140 meq/L

280 milliosmoles/L

H20 moves passively

Across cell membrane

According to the osmotic

gradient

Na+140 meq/L

280 milliosmoles/L


High Osmolality Outside The Cell=Shrinkage

Na+150 meq/L

300 milliosmoles/L

K+140 meq/L

280 milliosmoles/L

H2O


Low Osmolality Outside The Cell=Swelling

K+140 meq/L

280 milliosmoles/L

H20

Na+120 meq/L

240 milliosmoles/L

RUPTURE


ECF Na & ICF K+ Concentration, TBW distribution and body fluid osmolality

A B

C D

280mosm/L

H2O

K+=140

28L

270mosm/L

H2O

K+=135

29L

290mosm/L

H2O

K+=145

27L

280mosm/L

H2O

K+=140

28L

280mosm/L

H2O

Na+=140

14L

290mosm/L

H2O

Na+=145

15L

270mosm/L

H2O

Na+=125

14.5L

280mosm/L

H2O

Na+=140

15.5L

Intracellular

Intracellular

Intracellular

Intracellular

Extracellular Extracellular

Extracellular Extracellular

Normal Conditions 210 mM NaCl added to ECF

1.5 L H20 added to ECF 1.5 L 0.9% NaCl added to ECF


HUMANS

• Lose insensible (unmeasured) water through skin and lungs at a predictable rate according to metabolic rate and size. – Infant- 50-60cc/kg/24hr

– Adult- 15-20cc/kg/24hr

• This insensible water is almost always electrolyte free and therefore, every body requires replacement of “free water”. – If you give solute, there is obligatory urine output

– 1400 milliosmoles per 1000cc urine


HUMANS cont.

• Small amounts of electrolytes are lost in stool and urine

• “Maintenance intake” is the amount of water and electrolytes needed to keep humans, and therefore, their cells in a stable state of adequate circulation and normal osmoles.


TABLE I INSENSIBLE WATER CALCULATIONS

Age Weight Surface H2O

Area Expenditure

(kg) (M2) (cc/kg/24hr) Newborn 2.5-4 0.2-0.23 50

1 Week -

6 Months 3-8 0.2-0.35 65-70

6-12 Months 8-12 0.35-0.45 50-60

1-2 Years 10-15 0.45-0.55 45-50

2-5 Years 15-20 0.6-0.7 45

5-10 Years 20-35 0.7-1.1 40-45

10-16 Years 35-60 1.5-1.7 25-40

Adult 70 1.75 15-20


TABLE II Electrolyte Concentration of Various Body Fluids

Fluid Na K Cl Protein (mEq/l) (mEq/l) (mEq/l) (g/dl) Gastric 20-80 5-20 100-150 - Pancreatic 120-140 5-15 40-80 - Small Bowel 100-140 5-15 90-130 - Bile 120-140 5-15 80-120 - Ileostomy 45-136 3-15 30-115 - Diarrhea 10-90 10-80 10-110 - Burns 140 5 110 3-5 “3rd Space” Fl. 140 5 110 Variable Urine <10 <5 <10

Variable


TABLE III Holliday Segar calculation of maintenance

fluids and electrolytes

Water Electrolytes

(cc/kg) (per 100cc H2O)

1st 10kg body weight 100 Na 3mEq

2nd 10kg body weight 50 Cl 2mEq

Each additional kg 20 K 2mEq

through 70k

Therefore: 10kg = 1000cc/24hr

20kg = 1500cc/24hr

70kg = 2500cc/24hr


TABLE IV Composition of commonly used IV solutions*

Solution Ionic Concentration mEq/l Total

[Na+] [K+] [Ca2+] [Cl-] [HCO3-] mosmol/l

5% Dextrose - - - - - 278

in water

Isotonic Saline 154 - - - - 308

(0.9%,normal)

Dextrose in Saline

5% in 0.22% 38.5 - - - - 355

5% in 0.45% 77 - - - - 432

Lactated Ringers 130 4 3 109 28 272

*Adapted from A.Arieff, Clinical Disorders of Fluid and Electrolyte Metabolism,

2nd ed.,M.H Maxwell and R. Kleeman (eds.). McGraw-Hill, New York, 1972.


• Therefore in a 22kg 4-year-old, the maintenance fluid could be calculated by:

• 10kg X 100cc/kg = 1000cc

• 10kg X 50cc/kg = 500cc

• 2kg X 20cc/kg = 40cc

• Total H2O = 1540cc

Na = 3mEq/100cc = 45 mEq in 1.5 liters = 30mEq/liter

K = 2mEq/100cc = 30mEq in 1.5 liters = 20mEq/liter

These calculations can be made with a maximum weight of 70kg or a total volume of 2500cc/24hr


• In order to utilize prepared IV solutions, you round off the electrolyte requirements to the closest solution available. All orders must be written with the quantities “per liter” as a standard. This makes it easy to compare the IV solution to what you know is in plasma water. You know D5.2NaCl contains 38mEq of NaCl per liter, so this is an effective solution to use.

• For the 22kg boy, your order would read: D5.2NaCl with 20mEq/KCl/liter @ 64cc/hr.


The Rules of the Road

• Cells require adequate circulation (vascular volume) and a stable iso-osmotic milieu to function

• Maintenance fluid has been calculated by understanding :

– Metabolic rate

– Body size

• It assumes:

– All homeostatic mechanisms are intact

– Lungs and kidneys are functional and there is adequate circulating volume


• If these assumptions are not met, you must:

– Calculate insensible loss

– Calculate fluid and electrolyte loss

– Calculate rate based on previous slides


DEHYDRATION

• Measured by weight loss and clinical signs and symptoms

•Mild 4-5%

•Moderate 6-10%

•Severe 10%

•Death >25%


TABLE V Estimates of probable water and electrolyte deficits

in individuals with approximately 10% dehydration

Hellerstein 1993

Condition H20 Sodium Potassium Chloride (ml/kg) (mEq/kg)

Hypotonic 20-100 10-15 8-15 10-12 [Na]<130mEq/L

Isotonic 100-120 8-10 8-10 8-10 [Na]=130-150mEq/L

Hypertonic 100-120 2-4 0-6 0-3 [Na]>150mEq/L


TABLE VI Correction of symptomatic electrolyte disturbances a. Formula: mEq required = (CD-CA) x fD x Wt CD = concentration desired (mEq/l) CA = concentration present (mEq/l) fD = distribution factor as fraction of body wt Wt = baseline weight prior to illness (kg)

b. Apparent distribution factor (D): Electrolyte fD

HC03- 0.4-0.5

Cl- 0.2-0.3

Na- 0.6-0.7

** Correction of free H2O Deficit = 4cc/kg for every mEq that the serum Na exceeds 145mEq/l


Types of Dehydration

• Isonatremic – cells neutral

• Hypernatremic – cells shrunken/and can have rebound

• Hyponatremic – cells swollen


HYPERNATREMIA (Na > 150 MEq/L)

• ALWAYS means

Serum osmolality is above normal


HYPONATREMIA

• USUALLY means

• Serum osmolality is below normal

except for:

- Hyperlipidemia

- Hyperglycemia/mannitol – which adds osmoles


mg/dl mg/dl

Serum osmolality = Serum Na+ X 2 + BUN + Glucose

2.8 18

• Urea – moves passively across cell and therefore does not cause an osmotic “gradient” hyperosmolar but not hypertonic

• Glucose – in diabetes cannot move intracellularly and therefore is an osmotic gradient and “dilutes” the sodium effect is hypertonic


TYPES

• ISONATREMIC

80% of all dehydration

Proportional loss of salt and water

Treatment

- Calculate deficit from decreased weight

- Replace intravascular volume with isotonic solution such as lactated ringers

- From tables calculate estimate of water, sodium and potassium deficit


ORDERS STANDARD

• Isotonic rehydration 10-20 cc/kg (more important is to restore vascular volume)

• Calculate deficit from tables – Give ½ over 8 hours

– Give ½ over 16 hours

• Calculate maintenance – Run piggyback

• Calculate ongoing losses – Replace hourly


ORDERS IN REALITY

• Emergency Room – isotonic rehydration 10-20cc/kg or until looks better

• Home on oral rehydration solution 5cc/minute = 300cc/hour


ORAL REHYDRATION: What You Need to Know

• Works well with vomiting and diarrhea

• Inappropriate with shock

• 5cc given every minute = 300cc/hour


APPROPRIATE FLUIDS

CHO/mmol/L Na K Base Osmo

WHO Formula 140 45 20 48 265

Pedialyte 140 45 20 30 250

Not appropriate

Cola 700 2 0 13 750

Apple Juice 690 3 32 0 730

Chicken Broth 0 250 8 0 500


HYPONATREMIC DEHYDRATION

• 5% of all dehydration

• Usually occurs with a patient who has high GI losses accompanied by water replacement (jello/ pop, etc)

• Water shifts into the intracellular space to balance osmoles, so patient looks sicker since ECF is compromised

• Causes significant neurological problems as brain swells

** if Na<120mEq/l – can cause permanent myelinolysis


If Na is above 120mEq/l

• Replace intravascular volume with isotonic solution

• Calculate Na Deficit

– 135 mEq/l – measured Na X TBW

– TBW = 0.6 X body weight

• Use D5 ½ NaCl = 75mEq/l of Na to replace deficit

– ½ over 8 hours

– ½ over 16 hours

– Add in maintenance = potassium

– Do not change serum more than 1 mEq/hour


If Na<120mEq/l, Assess Hydration very Carefully

• If dry, give 20cc/kg of Isotonic solution

• You may use hypertonic saline if CNS signs are evident = 3%NaCl

– 514 mEq/l = 1028 mosm/l or

– 0.5 mEq NaCl per cc

• Risk of seizures


Calculate Deficit of Sodium to Get You to 120

• In a 10kg child with sodium of 110

– (CD-CA) X 0.6 wt/kg

– (120-100) X 0.6 X 10

– 10 X 0.6 X 10 = 60mEq

• 60 mEq NaCl = 120 cc of 3% NaCl

• Give over 1-2 hours rechecking Na+ every 30 minutes


HYPERNATREMIC DEHYDRATION

• 15% of all dehydration

• Seen in patients with deprivation of water

– Breast-feeding failure

– Patients with lossed replaced by high sodium foods (broth, etc)

– Elderly without adequate thirst mechanism

• Water moves out of the intracellular space and the ICF is compromised

• Na+>160mEq/l causes CNS effects

• With shrinking of the brain there can be tearing of bridging blood vessels causing subarachnoid or subdural bleeds


TREATMENT – SLOW!!! • If patient is stable and hypernatremic and got

that way over weeks, you may take a week to correct it

• If patient is in shock, give isotonic solution 10-20cc/kg to get out of shock

• Calculate Water deficit

– 0.6L/kg*(SNa/145-1)*weight

– Replace deficit to correct SNa by 15mmol/L/day


• Example: A 10kg child arrives with a history of

dehydration. He now weighs 9.4kg. You give him 20cc/kg of L/R or 200cc. Labs return showing his lytes are: 160 130

4.2 18

• You want this child’s Na to drop from 160 to 145 in 24 hours

• His water deficit is:

0.6*(160/145-1)*9.4 = 583cc


• The safest way to give the “water” deficit is by using D5 1/2 NS. One liter of this solution contains 500cc of “free water” and 500cc of isotonic solution, so you have to give 1200cc of this solution for 600cc of “free water”. He will also have total body K+ depletion, but his serum K is OK so you can simply give him that in his maintenance fluids.

• Orders should read D5 1/2NS – 1200 to be given at 80cc/hr x 15hr

• His “maintenance” IV can be D5 1/4 NS with 40mEq KCL/l at 40cc/hr continuously

• These can be piggybacked together and run simultaneously. Serum Na should be measured every 4 hours to watch the rate of fall and adjustments made accordingly

• Remember ongoing losses


INAPPROPRIATE ADH • Definitions:

– A state in which ADH is secreted and lowers serum osmolality despite adequate vascular volumes and hyponatremia. The following criteria must be fulfilled:

- Hyponatremia < 130

- Normal intravascular volume

- Low serum osmolality with urine osmolality that is inappropriately high

Na+ Osmolality

Serum 120 240

Urine 250 500


Diseases That Cause Inappropriate ADH

• CNS Abnormalities

(meningitis/hemorrhage/neoplasm)

• Drugs – intravenous cyclophosphamide

• Pulmonary disease

• Neoplasm

• Pain


Treatment of IADH – Depends on acuity and severity

• 1. Water restriction

• 2. Diuretics

• 3. Diuretics with saline replacement


SUMMARY • Cells need adequate circulating volume to survive:

always assess and maintain adequate vascular volume which is part of the extracellular space

• Cells are at risk with rapid shifts in osmolality. Rapid expansion should always occur with istonic fluid

• K+ is responsible for the electrochemical gradient in the cell and will cause cardiac abnormalities if too high or too low


Case #1

• A 4-year old girl presents to the emergency center with a 2-day history of fever to 104F and vomiting. She has been unable to tolerate oral liquids for 48 hours. On examination, she is irritable, photophobic and pale. Her skin turgor is poor and she has a capillary refill of > 10 seconds. Vital signs: BP 60/40, HR 160, RR 60, Temp 105F. Weight is 20 kg.

• First questions:

• What is your first course of action?

• What tests should you order?


Case #1 cont’d

• Initial labs reveal serum Na = 146, K = 3.2, Cl = 104, HCO3 = 20, BUN = 30, Cr = 1.0, CSF with bacteria, neutrophils, low glucose and high protein. After resuscitative effort, the patient now has the following vital signs: BP 110/40, HR 100, RR 45

• Second questions:

• What are you next set of fluid orders?

• How would you expect the patient’s electrolytes to change?


• After 72 hours, she becomes confused and then has a generalized tonic-clonic seizure. She is afebrile and her volume status appears normal

• Third questions:

• What is the differential diagnosis?

• What tests would you order?

• Serum electrolytes reveal: Na = 118, K= 4.0, Cl = 96, HCO3 = 20.

• Fourth questions:

• What is the cause of the patient’s hyponatremia?

• What lab tests could you order to confirm the diagnosis?

• What is the treatment?

• What are the risks of rapid correction of sodium?


Case #2

• A 5 month-old girl presents to the emergency room after a 5-minute generalized tonic-clonic seizure. A set of stat electrolytes reveals a serum Na of 183. The patient’s weight is 7.5 kg.

• First questions:

• What are the mechanisms by which patients develop hypernatremia?

• How could you distinguish between the mechanisms in this particular patient?

• What tests would you order at this time?


Case #2 Cont’d

• Physical exam revels poor skin turgor, prolonged capillary refill and vital signs reveal BP 50/20, HR 170, RR 70. The patient’s lung fields are clear to auscultation. The patient’s pupils are unequally reactive to light. Urine specific gravity is 1.005.

• Second questions:

• What are your initial fluid orders?

• What is the likely underlying cause of this patient’s hypernatremia?

• How would you assess for a peripheral versus central cause of this patient’s underlying cause of hypernatremia?


Case #2 cont’d

• The patient has been adequately resuscitated with a resultant BP of 90/50 and restoration of skin turgor. In the last 2 hours, the patient has urinated 200 milliliters. Repeat serum sodium is 179. The patient’s weight is now 7.7 kg.

• Third questions:

• What variables do you need to consider in writing this patient’s fluid orders?

• What is this patient’s free water deficit?

• What labs do you need to help guide your fluid orders?

• What is the danger of correcting the hypernatremia too quickly?


Case #2.1

• Now, let’s change the story a bit. The same aged patient presents with a serum Na of 183, but her skin appears doughy. You find on history that the patient’s mother works the late shift at night, and she has her 7 year-old daughter mix the patient’s formula

•

• Questions:

•

• What is the likely cause of the patient’s hypernatremia?

• How can you prove this?

• How would your management change?

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