INTERACTIVE CASE
DISCUSSION
Fluid and Electrolyte
Disorders
Part II
Fluid and Electrolytes Part II
CASE # 1:
• 60 y/o male with ischemic cardiomyopathy and
CHF. Admitted because of orthopnea.
• 150/60, HR=120/min, RR = 38/min
• JVP = 20 (); bibasal inspiratory crackles
• S3 gallop; ascites; pedal edema
• Na = 125meq/L ()
• Posm = 270 mosm/kg ()
• Uosm = 500 mosm/kg
Fluid and Electrolytes Part II
Question # 1: Describe the patient’s
fluid and electrolyte status.
A. Na deficit, water deficit
B. Na deficit, water excess
C. Na excess, water deficit
D. Na excess,water excess
Fluid and Electrolytes Part II
Answer #1: Na excess, water excess
• Hyponatremic (Na=125) hence he has
water excess.
• Hypervolemia on physical
examination ( BP, JVP,crackles,
ascites, edema ) hence he has Na
excess.
Fluid and Electrolytes Part II
REMEMBER !
Serum Na  Na balance
Serum Na = Water balance
Volume status = Na balance
Fluid and Electrolytes Part II
Question # 2: How will you approach
the problem of hyponatremia?
HYPONATREMIA
Plasma Osmolality
(285-295)
High
•Hyperglycemia
•Mannitol
Normal
•Hyperproteinemia
•Hyperlipidemia
•Bladder irrigaton
Low
True Hyponatremia
Maximally
Dilute urine
Singer, 2001
HYPONATREMIA
Maximally dilute urine
Uosm < 100
No
ECF Volume
Yes
Primary polydipsia
Reset osmostat
Singer, 2001
HYPONATREMIA
ECF Volume
Increased
CHF
Cirrhosis
Renal failure
Nephrosis
Normal
Hypothyroid
Hypoadrenal
SIADH
Decreased
Urine Na
Singer, 2001
HYPONATREMIA
Urine Na
UNa < 10 meq/L
UNa > 20 meq/L
Extrarenal Na loss
Remote diuretics
Remote vomiting
Na wasting nephropathy
Hypoaldosteronism
Diuretics
Vomiting
Singer, 2001
Fluid and Electrolytes Part II
Question # 3: What is the most likely
cause of hyponatremia in this
patient?
A. Congestive heart failure
B. Diuretics
C. Hypothyroidism
D. Syndrome of Inappropriate ADH
secretion (SIADH)
Fluid and Electrolytes Part II
Answer # 3: Congestive heart failure
• Low Posm excludes pseudohypoNa.
• Uosm > 100 (500) hence not primary
polydipsia or reset osmostat
• Volume status increased (Na excess)
• Compatible with CHF
Fluid and Electrolytes Part II
CASE # 2: 30 y/o 70kg male suffered a skull
fracture due to MVA.
• 86/60,HR=110/min.
• JVP = 4, poor skin turgor
• Dry mucosa, no edema
• Na = 168 meq/L
• Posm = 350mosm/kg; Uosm = 80mosm/kg
• 24 hr urine output = 4 liters
Fluid and Electrolytes Part II
Question # 4: Describe the patient’s
fluid and electrolyte status.
A. Na deficit, water deficit
B. Na deficit, water excess
C. Na excess, water deficit
D. Na excess, water excess
Fluid and Electrolytes Part II
Answer # 4: Na deficit, water deficit
• Hypernatremic ( Na = 168) hence he
has water deficit.
• Hypovolemic on physical
examination ( BP,  JVP,poor skin
turgor, drymucosa) hence he has Na
deficit.
Fluid and Electrolytes Part II
REMEMBER !
Serum Na  Na balance
Serum Na = Water balance
Volume status = Na balance
Fluid and Electrolytes Part II
Question # 5: Calculate the amount of
water deficit in this patient.
Fluid and Electrolytes Part II
Answer # 5: 7 liters
Water deficit
= Plasma Na – 140/140 X ( 0.5 X BW )
= 168 – 140/140 X ( 0.5 X 70 )
= 7 liters.
Fluid and Electrolytes Part II
Question # 6: How will you approach
the problem of hypernatremia?
HYPERNATREMIA
ECF Volume
Increased
Administration of
Hypertonic NaCl and
NaHCO3
Not increased
Minimum volume
of maximally
concentrated urine
(Uosm)
Singer, 2001
HYPERNATREMIA
UOsm > 800
No
Urine osmolar
excretion rate
Yes
Insensible H2O loss
GI H20 loss
Remote renal H2O loss
Singer, 2001
HYPERNATREMIA
Urine osmolar excretion
rate > 750 mosm/day
No
Renal response
to desmopressin
 UOsm
Central DI
Yes
Osmotic diuresis
Diuretic
Uosm no 
Nephrogenic DI
Singer, 2001
Fluid and Electrolytes Part II
Question # 7: What is the most likely
cause of the patient’s hyperNa?
A. Diabetes insipidus
B. GI water losses
C. IV hypertonic NaCl
D. Osmotic diuresis
Fluid and Electrolytes Part II
Answer # 7: Diabetes insipidus
• Not hypervolemic hence not IV hypertonic
NaCl.
• Uosm < 100 (dilute) hence not extrarenal
water losses (GI losses).
• Urine osmolar excretion rate = Uosm X U
volume; 80mosm/kg x 4 liters/d = 320
mosm/d (< 750mosm/d); hence not
osmotic diuresis.
Fluid and Electrolytes Part II
Question # 8: The patient was given a
dose of desmopressin (ADH
analog). The Uosm after the dose is
800 mosm/kg. What is the cause of
the diabetes insipidus?
A. Central diabetes insipidus
B. Nephrogenic diabetes insipidus
Fluid and Electrolytes Part II
Answer # 8: Central DI
• The Uosm increased after the
desmopressin dose. The Uosm will
not change even after repeated
desmopressin doses in patients with
nephrogenic DI.