Fluids and Electrolytes
Bruce R. Wall, MD, FACP
Texas Health Dallas Presbyterian
October 14th, 2010
RBF=1000ml/min; RPF=600ml/min
GFR=120ml/min or 172.8L/day
Key Concepts
• Volume status (EABV) “think” saline in ECF
• Cannot be measured in the lab…
• TBW (Total Body Water) “think” [Na+ mEq/L]
Laboratory result… must examine the patient
• IV FLUID orders: Volume - Water - K+ - Acid/base
3 Key Concepts in Fluid and Electrolyte
Physiology
• Cell membrane permeability
• Osmolality
• Electroneutrality
Cell Membrane Permeability
Osmolarity vs Osmolality
• Osmolarity is defined as the concentration of the
solute per liter of solution
• Osmolality is concentration of the solute/kg
solvent (usually plasma or urine)
• Sodium accounts for 97-98% of plasma osmolality
(range 287  7 mOsm/Kg)
• mOsm/kg = 2X[Na+ mEq/L] + (glucose mg/dL)/18 + (BUN mg/dL)/2.8
Electroneutrality
• Primary extracellular cation is SODIUM
• Primary intracellular cation is POTASSIUM
• Plasma (ECF) is the only compartment readily accessible
Body Fluid Compartments
• Adult humans are 50% - 70% water
• Women and the elderly have higher % of body fat
than young men, and thus less water.
• For all practical purposes, assume that
TBW = 0.60 X WT (kg)
Body Fluid Compartments
• 70 kg male (TBW=0.6 X wt)
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IntraCellFluid
ECF
Extravascular
Intravascular
28L (70 kg X 40% = 28)
14L (70 kg X 20% = 14)
10.5L (70 kg X 15% = 10.5)
6.3L (70 kg X 9% = 6.3)
Distribution of Sodium
Extracellular Na+
16%
81%
3%
Intracellular
*Plasma
EABV
Body Fluid Compartments
• The composition of the ECF is roughly the same
as the interstitial space with the exception of
proteins which are trapped within the vascular
lumens.
• The distribution of fluid between these two spaces
is determined by Starling Forces.
Volume Homeostasis
• ECF Volume is linked to total body sodium
• Important: Total body sodium is not concentration
• Concentration depends not only on amount of
sodium but also the amount of water
• Total body sodium is regulated by the kidneys
• Input minus output equals accumulation…
Volume Depletion
(a.k.a Hypovolemia)
• Decreased ECF volume is always sensed as a decrease in
the “Effective Arterial Blood Volume (EABV)”
• The EABV signals the kidney whether to reabsorb or excrete
sodium.
• No direct measure of the EABV, it is determined by blood
volume, cardiac output, and systemic vascular resistance
• Decreased “EABV” results in Na+ retention and
expansion of ECF volume
Clinical Signs of Hypovolemia
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Orthostatic hypotension
Tachycardia
Flat neck veins
Dry mucous membranes
Absent axilliary sweat
Decreased skin turgor
Decreased CVP
Common IV Fluids
Solution
Glucose
Na+
K+
Ca++
Cl-
Lactate
PO4=
Mg++
D5W
50
0
0
0
0
0
0
0
NS
0
154
0
0
154
0
0
0
D5NS
50
154
0
0
154
0
0
0
D5½NS
50
77
0
0
77
0
0
0
LR
0
130
4
3
109
28
0
0
Management of Hypovolemia
• The primary fluid prescribed for hypovolemia is
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Normal Saline
In the management of hypovolemia, there is no
place for ½NS or D5W….
Transfusion
Albumin
Hetastarch (Hespan ®) or Plasmanate ®
IV fluids: continued
• Addition of an isotonic fluid (0.9% NaCl)
expands the ECF but doesn’t change the
IntraCellularFluid
• Addition of a hypotonic fluid (D5W) will cause
movement of water into the cells.
• Addition of a hypertonic fluid (3% saline) will
cause movement of water out of the cells.
Why is Normal Saline the “drug of
choice”?
• If you give 1 Liter of Normal Saline (0.9% NaCl),
the NaCl is restricted to the ECF, therefore the
entire liter stays in this space. 75% (750 ml) in
the interstitial fluid and 25% (250 ml) in the
intravascular space.
Body Fluid Compartments
• 70 kg male (TBW=0.6 X wt)
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IntraCellFluid
ECF
Extravascular
Intravascular
28L (70 kg X 40% = 28)
14L (70 kg X 20% = 14)
10.5L (70 kg X 15% = 10.5)
6.3L (70 kg X 9% = 6.3)
IV Fluids: what about 0.45% saline?
• Think of 0.45% NaCl as 500ml of saline and 500 ml of
water.
• The saline distributes to the ECF compartment alone.
75% (375 ml) in the interstitial space and 25% (125
ml) in the intravascular space.
• The water distributes 66% (330 ml) to the intracellular
space & 33% (170 ml) to the ECF. Of the 170 ml to
ECF, only 25% or 42.5 ml stays in the intravascular
space.
Fluid Prescriptions
Thus of our 1L 0.45NaCl, only 125 + 42.5 =
167.5 ml stays in the intravascular space
When should you use hypotonic
solutions?
• If there is a need to administer water to the patient
(because of a water deficit state)
• Maintenance fluids (not volume replacement)
• D5W, D5¼NS or D5½NS may be used in
combination with bicarbonate if there is a need to
administer base.
Clinical Signs & Symptoms of Volume
Expansion
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Jugular venous distension +/- S3 gallop
Dyspnea
Ascites – this could be debated
Pulmonary edema
Pleural effusions
Peripheral edema (remember hypoalbuminemia)
Management of Hypervolemia
• Goal of treatment
• Removal of extracellular fluid
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Loop Diuretics
Salt restriction (PO and IV)
Dialysis/CVVHD
Phlebotomy
Rotating tourniquets
Pathways of Water Balance
Calculate the Water Deficit…
• [0.6] x (wt in Kg) X [{Na/140} – 1]
The water deficit should be fixed in the form of water (D5W or tap
water).
Water repletion is over and above the maintenance fluids which may be
either isotonic or hypotonic.
How do you write IV Fluid orders?
Input – output = accumulation
• Volume balance
• Water balance
• Potassium (deficit, CKD, Mg++, presence of
acidosis or alkalosis)
• Acid base (administration of bicarbonate or HCl)
Case I: Mild Hyponatremia
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65 yo WF smoker @ small cell carcinoma
No evidence of CHF on physical exam
Na+ 122 mEq/l K+6.1
Mild respiratory acidosis GFR normal
No dyrenium, amiloride, or aldactone
Positive history for Lovenox (DVT) for 2 weeks
Case I: hyponatremia - continued
• PE: normal vitals (no tilt) comfortable at rest
extremities - no edema
no confusion
• Random U Na+ elevated at 40 mEq/L
• Uosm 600
TSH is WNL
• 1) Differential Diagnosis
• 2) IV fluid orders (NPO for cardiac evaluation)
Patient receives saline
• Diagnosis = SIADH
• IV saline administered: 1 liter = 300mosm
• Urine 600 mosm, provides for excretion of 300
mosm of sodium chloride in 500ml of urine
• Allows patient to “keep” 500 ml of water
• Sodium falls to 119 mEq/L
Case II: HIV possible sepsis
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25 yo male with HIV
Admitted with streptococcal sepsis with meningitis
History of IVDA with baseline CKD
ARF = BUN 80mg% creatinine 2.5mg%
Volume depletion on exam
NPO (unresponsive) Mild metabolic acidosis
Sodium 133 mEq/L
IV fluids?
Case III: history of CHF
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70 yo diabetic, known CHF, mild CKD
Admitted with acute coronary syndrome
NPO for cardiac cath
Recent increase in diuretics caused acute deterioration in
GFR: BUN > 110
creat 2.2mg%
• Euvolemic on exam (maybe a little dry?)
• Na+ 125mmole/L
• IV Fluids?
Case IV: DKA
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45 yo WF IDDM X 20 yrs
Non-functional glucometer…
N&V for 18 hrs… indigestion/pain for 2 hrs
No dyspnea No blood in emesis or stool
‘too sick’ to administer insulin
PMH - DM HBP Lipids CKD
DKA: continued
• 130/60 tilting to 95/50 P110 R24 Afebrile
Neck: veins impossible to assess
Lungs: few rales, WOB increased
Cor: I/VI m, soft S3, increased HR
Abd:benign, non-distended Ext: 1+edema
• WBC 12K Hct 35% 2+proteinuria 5-10
WBC/HPF
• EKG: 2mm ST elevation III and AVF
DKA: continued
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Na+ 131
K+ 3.2
Cl- 104
HCO3 5mEq/l BUN 70 Creat 2.0
anion gap 22 mEq
pH 7.18 pCO2 18 pO2 80
(1.5)(HCO3) + 8 [+/- 2mEq] = pCO2
Dx? Volume status? Na+? K+?
acid/base issues? IV fluids?
Case V: Rhabdomyolysis
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24 yo SWAT team member of GPD
August 1998 “106 degrees in the shade”
full gear running drill - collapse in field
BP 100/60 P 130 T 102.8 rectal
Skin warm Neck veins: nl Lungs: clear
Cor: increased HR MS: tender back/gluteal
region, no edema
Rhabdo: continued
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Urine looks red… scant volume… heme +
U Na+ <10 FeNa+ low Na+ 149
K+ 5.9 Anion gap 22 Bun 15 Creat 2.4
Ca++ 6.5 Phos 8.5 CPK 50,000
“As you rapidly cool down the patient:”
Diagnosis? Volume status?
Cause of Hyperkalemia?
IVF orders?
Case VI: Ascites
• 65 yo retired engineer with known cirrhosis
• ETOH exposure Hx GIB/varices
• Meds: Beta blocker Aldactone Furosemide
(no NSAID’s)
• Decreased intake for several days; increasing abd
pain - severe, diffuse, no radiation; minimal
emesis no gross hemorrhage in stool
Ascites: continued
• PE: barely awake confabulates barely follows
• tremulous T 101.8 BP 90/60 red palms spider
angiomata muscle wasting massive ascites very
tender abdomen guaiac positive stool 1+ edema 2+
ankles
• Lab: WBC 20K Hct 34% Bili 4 albumin 2.4 INR
2.5 AG 12 Na+128 K+ 5.0 FeNa<1; ascites with
3000 WBC and positive gram stain
• BUN 80 Creat 3mg%
Decreased U Na+ < 15
Ascites: continued
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Differential diagnosis?
Volume status?
Acid base status?
IV fluids? (TPN?)
Case VII – Metabolic acidosis
• Patient with recurrent diarrhea complains of
muscle weakness
• No carpopedal spam, Trousseau’s of Chvostek’s
• EKG reveals ST-segment and T-wave changes
and PVC’s compatible with hypokalemia
Case VII: continued
• Plasma [Na+] = 140 meq/L
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[K+] = 1.3 meq/L
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[CL-] = 117 meq/L
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[HCO3] = 10 meq/L
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[albumin] = 4.1 g/dL (3.5 – 5 g/dL)
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[Ca++] = 6.3 mg/dL (8.8 – 10.5 mg/dL)
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arterial pH = 7.26
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pCO2 = 23 mm Hg
• Correction MA effect K+? Correct hypo Ca++?
Case VIII: Chronic Li+
• 40 yo female NPO X 48 hours post complicated
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cholecystectomy
Admission [Na+] = 146 mmoles
Developes profound hypotension requiring
transfer to ICU (without myocardial infarction)
Current [Na+] = 175 mmoles
IV fluid orders?
Case IX: AKI
• 60 yo attorney ANURIC AKI SEPSIS
• MSOF: lungs, cardiac, liver, renal, bone marrow,
nutrition, skin, CNS
• Intermittent HD
• [Na+] 130 [K+] 3.3 BUN 40 mg% Creat 5mg%
• IVF orders?
TPN?
Tube feeds?
Case X: acute water intoxication
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20 yo SMU student brought to ER by fraternity
Unresponsive hypothermic hypotensive
Sodium 106 mEq/L Mild azotemia
Calculated water load > 8 liters…
IVF?
Summary
• Most common error in writing IV Fluid orders:
• 1) administration of NS in pts with SIADH
• 2) inadequate volume replacement in sepsis or
pre-renal azotemia
Questions?
Next month: hemodialysis therapy…
Treatment of Hyponatremia
Hyponatremic Patient
Symptomatic
Acute
(<48 hrs)
Chronic
(>48 hrs)
Risk Factors for
Neurologic
Complications?
Asymptomatic
Symptoms and Signs of Hyponatremia
Symptoms
Lethargy
Headache
Apathy
Muscle Cramps and weakness
Anorexia
Nausea
Agitation
Psychosis
Signs
Abnormal sensorium
Depressed deep tendon reflexes
Hypothermia
Pathologic reflexes
Pseudobulbar palsy
Seizures
*Tentorial Herniation
*Cheyne-Stokes respiration
*Coma
Death
Acute Symptomatic Hyponatremia
• Duration <48 hrs
• Increase serum [Na] rapidly by approximately 2 mM/L/hr until
resolution of symptoms.
• Full correction probably safe, but not necessary
• Hypertonic Saline 1-2 ml/kg/hr
• Coadministration of Furosemide
Note: The sum of urinary cations (U Na + U K ) should be less than the concentration of infused sodium
to ensure excretion of electrolyte free water.
Cerebral Adaptation to Hyponatremia
Chronic Symptomatic Hyponatremia
• Duration >48 hrs or unknown
• Initial increase in serum [Na] by 10% or 10 mM/L
• Hypertonic Saline 1-2 ml/kg/hr
• Co-administration of Furosemide
• Perform frequent neurologic evaluations; correction rate may be reduced
with improvements in symptoms
• Perform frequent measurement of serum and urine electrolytes
• At no time should correction exceed rate of 1.5 mM/L/hr, or increment of 15
mmol/day
• Change to water restriction upon 10% increase of [Na], or if symptoms resolve
Note: The sum of urinary cations (U Na + U K ) should be less than the concentration of infused sodium
to ensure excretion of electrolyte free water.
Treatment of Severe Euvolemic Hyponatremia (<125 mmol/L)
Severe Hyponatremia (<125 mM/L)
Asymptomatic
Symptomatic
Acute
Chronic
Chronic
Duration < 48 hrs
Duration > 48 hrs
Rarely < 48 hrs
Some Immediate Correction Needed
•Hypertonic Saline 1-2 ml/kg/hr
Emergency Correction Needed
•Hypertonic Saline 1-2 ml/kg/hr
•Coadministration of Furosemide
Long Term Management
•Identification and Treatment of Reversible
etiologies
•Water Restriction
•Demeclocycline 300 mg to 600 mg bid
•Urea 15 to 60g qd
•V2 receptor antagonists
•Co-administration of Furosemide
•Change to water restriction upon 10% increase of [Na],
or if symptoms resolve
•Perform frequent measurement of serum and urine
electrolytes
•Do not exceed 1.5 mM/L/hr, or 20 mM/d
No immediate
correction needed
Treatment of Asymptomatic Chronic
Hyponatremia
• Fluid Restriction
• Pharmacologic Inhibition of Vasopressin Action
• Lithium
• Demeclocycline
• V-2 receptor antagonist
• Increase solute Excretion
• Furosemide + 2-3 g of NaCl/day
• Urea 30 g/d
• Increased dietary protein intake
Management of Non-Euvolemic
Hyponatremia
• Hypovolemic Hyponatremia
• Volume restoration with isotonic saline
• Identify and correct etiology of water and sodium losses
• Hypervolemic Hyponatremia
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Water Restriction
Sodium Restriction
Substitute loop diuretics instead of thiazide diuretics
Treatment of stimulus for sodium and water retention
V2-receptor antagonist
SM Lauriat, T Berl: The Hyponatremic patient: Practical Focus on Therapy. J Am Soc Nephrol, 1997,
8(11):1599-1607.
The Hypernatremic Patient
Guidelines for the Treatment of
Symptomatic Hypernatremia
• Correct at a rate of 2 mM/L/hr
• Replace half of the calculated water deficit over the first 1224 hrs.
• Replace the remaining deficit over the next 24-36 hrs.
• Perform serial neurologic examinations - prescribed rate of
correction can be decreased with improvement in
symptoms
• Measure serum and urine electrolytes every 1-2 hrs.
Note: If U[Na] + U[K] is less than the concentration of P[Na], then there are ongoing water losses that
need to be replaced
Treatment of Hyponatremia
• Three Key Questions
• Is the patient symptomatic?
• What is the duration of Hyponatremia?
• Are there any risk factors for the development of
neurologic complications?