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?

HYPONATREMIAPlasma Osmolality

(285-295)

High•Hyperglycemia•Mannitol

Normal•Hyperproteinemia•Hyperlipidemia•Bladder irrigaton

LowTrue Hyponatremia

MaximallyDilute urine

Singer, 2001

HYPONATREMIA

Maximally dilute urine

Uosm < 100

No Yes

Primary polydipsiaReset osmostat

ECF Volume

Singer, 2001

HYPONATREMIA

Increased Normal Decreased

ECF Volume

CHFCirrhosisRenal failureNephrosis

HypothyroidHypoadrenalSIADH

Urine Na

Singer, 2001

HYPONATREMIA

Urine Na

UNa < 10 meq/L UNa > 20 meq/L

Extrarenal Na lossRemote diureticsRemote vomiting

Na wasting nephropathyHypoaldosteronismDiureticsVomiting

Singer, 2001

Fluid and Electrolytes Part II

Question # 3: What is the most likely cause of hyponatremia in this patient?

A. Congestive heart failureB. DiureticsC. HypothyroidismD. 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?

HYPERNATREMIAECF Volume

Increased Not increased

Administration of Hypertonic NaCl andNaHCO3

Minimum volumeof maximallyconcentrated urine(Uosm)

Singer, 2001

HYPERNATREMIA

UOsm > 800

No Yes

Insensible H2O lossGI H20 lossRemote renal H2O loss

Urine osmolarexcretion rate

Singer, 2001

HYPERNATREMIAUrine osmolar excretionrate > 750 mosm/day

YesNo

Osmotic diuresisDiuretic

Renal responseto desmopressin

UOsm Uosm no

Central DI 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.