8-21 Electrolyte CIS

Question 1

What is the formula for serum osmolality?

Answer 1

Serum Osmolality = 2Na⁺ + (glucose/18) + (BUN/2.8)

Can often estimate rapidly by 2* Na⁺

Question 2

A 35 year old female presents after 3 days of epigastric pain and vomiting. She has only been able to retain water. The patient is orthostatic and found to have poor skin turgor with skin tenting and dry mucosal surfaces. Serum sodium is 122 meq/L (normal 140 meq/L) with K of 2.5 meq/L (n = 4.5 meq/L). Cl is 88 meq/L (100) with HCO3 of 33 meq/L (25). Glucose is 60 mg/dL (60 -100). BUN is 60 mg/dL (normal 10 mg/dL) and Creatinine is 1.4 mg/dL (normal 1 mg/dL). Urine osmolality is 580 mOsm/L (specific gravity 1.030).

What is this patient’s tonicity?

Volume Status?

Sodium status?

Answer 2

Hypotonic hypovolemic hyponatremia

Question 3

What would you expect the urinary sodium to be for hypotonic hypovolemic hyponatremia?

Why?

Answer 3

Less than 10 meq/L

1. Decreased volume –> decreased baroreceptor stretch
2. increases sympathetic tone
3. activates RAAS
4. increases Na+ reabsorption in cortical collecting tubule
5. Decreased CO = decreased GFR and RBF
6. This leads to increased sodium uptake and low urinary sodium

Question 4

Why would the serum sodium be low in a hypovolemic hypotonic hyponatremic patient?

Answer 4

1. Low blood volume activates ADH secretion, increasing water retention
2. this outperforms the retention of Na+ and leads to hyponatremia
3. particularly true if patient has increased free water intake.

Question 5

Almost all cases of hyponatremial involve what?

What is the exception to this?

Answer 5

Relative excess of ADH, which may be appropriate or inappropriate.

Exception is psychogenic polydipsia

Question 6

A 35 year old female presents after 3 days of epigastric pain and vomiting. She has only been able to retain water. The patient is orthostatic and found to have poor skin turgor with skin tenting and dry mucosal surfaces. Serum sodium is 122 meq/L (normal 140 meq/L) with K of 2.5 meq/L (n = 4.5 meq/L). Cl is 88 meq/L (100) with HCO3 of 33 meq/L (25). Glucose is 60 mg/dL (60 -100). BUN is 60 mg/dL (normal 10 mg/dL) and Creatinine is 1.4 mg/dL (normal 1 mg/dL). Urine osmolality is 580 mOsm/L (specific gravity 1.030). Serum osmolality is 267 mOsm/L (n = 287 mOsm/L). Una is < 10meq/L.

What other test would indicate a low K in this patient and why is the K+ low and the HCO3- high?

Answer 6

An EKG is done on the patient and reveals flattened to inverted T waves with U waves.

Potassium is low from vomiting, volume contraction and renal wasting from secondary hyperaldosteronism.

Bicarb is high due to sodium retention, K+ and H+ secretion in the aldosterone sensitive cortical collecting tubule and alpha intercalated cells.

Question 7

A 35 year old female presents after 3 days of epigastric pain and vomiting. She has only been able to retain water. The patient is orthostatic and found to have poor skin turgor with skin tenting and dry mucosal surfaces. Serum sodium is 122 meq/L (normal 140 meq/L) with K of 2.5 meq/L (n = 4.5 meq/L). Cl is 88 meq/L (100) with HCO3 of 33 meq/L (25). Glucose is 60 mg/dL (60 -100). BUN is 60 mg/dL (normal 10 mg/dL) and Creatinine is 1.4 mg/dL (normal 1 mg/dL). Urine osmolality is 580 mOsm/L (specific gravity 1.030). Serum osmolality is 267 mOsm/L (n = 287 mOsm/L). Una is < 10meq/L.

Why is the potassium low?

Why is Bicarb high?

Answer 7

The K+ is low from vomiting, volume contraction and renal K+ wasting from secondary hyperaldosteromism.

The HCO3- is high (“contraction alkalosis”) from secondary

aldosteronism, ie Na+ retention and K+ and H+ excretion in the

aldosterone sensitive cortical collecting tubule and α intercalated cell.

Question 8

A 35 year old female presents after 3 days of epigastric pain and vomiting. She has only been able to retain water. The patient is orthostatic and found to have poor skin turgor with skin tenting and dry mucosal surfaces. Serum sodium is 122 meq/L (normal 140 meq/L) with K of 2.5 meq/L (n = 4.5 meq/L). Cl is 88 meq/L (100) with HCO3 of 33 meq/L (25). Glucose is 60 mg/dL (60 -100). BUN is 60 mg/dL (normal 10 mg/dL) and Creatinine is 1.4 mg/dL (normal 1 mg/dL). Urine osmolality is 580 mOsm/L (specific gravity 1.030). Serum osmolality is 267 mOsm/L (n = 287 mOsm/L). Una is < 10meq/L.

Why is the BUN elevated?

Answer 8

Urea is passively reabsorbed in the proximal tubule. Thus, if volume is

low and BUN concentration high, there will be increased reabsorption

according to the higher BUN gradient. Also, more urea is reabsorbed at

low tubular flow rates than at high tubular flow rates.

In addition, low effective plasma volume creates a resultant increased

ADH with the latter effecting more collecting tubule reabsorption of

BUN in order to create the gradient for water reabsorption.

Question 9

So dehydration has what effect on BUN?

Answer 9

It will be elevated

Question 10

What does a BUN/Creatinine ratio of 60:1.4 mean?

Answer 10

Prerenal azotemia

•due to the decreased GFR with avid Na and H2O and BUN (passive) reabsorption in the proximal tubule. At the same time creatinine is actually secreted in the proximal tubule since the kidney is functioning normally. The result is a high BUN/creatinine ratio.

Question 11

The causes of elevated bun/creatinine ratio include:

1. high protein intake or breakdown
2. prerenal disease
3. post renal disease

Give examples of each

Answer 11

1. high protein intake or breakdown

• catabolic state
• catabolic drugs (steroids)
• GI bleed

2. prerenal disease

• Dehydration
• CHF
• Shock
• Glomerulonephritis

3. post renal disease

• Prostatic obstruction
• ureteral obstruction

Question 12

What does a bun/creatinine ratio of 10/1 indicate?

What if it were 40/4?

Answer 12

BUN/creatinine of 10/1 indicates either normal renal function (when creatinine is 1 or less) or intrinsic renal disease (when the creatinine is > 1), ie. BUN of 40 and creatinine of 4 = 40/4 = I0/1

Question 13

What does a BUN/Creatinine ratio of less than 10/1 indicate?

Answer 13

10/1(non-renal), ie low BUN seen in liver failure, malnutrition, overhydration, pregnancy, SIADH

He said for us to just consider this related to Liver failure.

Question 14

A 35 year old female presents after 3 days of epigastric pain and vomiting. She has only been able to retain water. The patient is orthostatic and found to have poor skin turgor with skin tenting and dry mucosal surfaces. Serum sodium is 122 meq/L (normal 140 meq/L) with K of 2.5 meq/L (n = 4.5 meq/L). Cl is 88 meq/L (100) with HCO3 of 33 meq/L (25). Glucose is 60 mg/dL (60 -100). BUN is 60 mg/dL (normal 10 mg/dL) and Creatinine is 1.4 mg/dL (normal 1 mg/dL). Urine osmolality is 580 mOsm/L (specific gravity 1.030). Serum osmolality is 267 mOsm/L (n = 287 mOsm/L). Una is < 10meq/L.

Labs on the above patient show:

Na+ 122 meq/L, K+ 2.5 meq/L

Cl- 88meq/L, HCO3- 33 meq/L

BUN 60 mg/dL, Creatinine 1.4 mg/dl

Spot Una+ < 10 meq/L, FeNa < 1%

Serum osm = 267 mOsm/kg, Urine osm = 580 mOsm/kg

At this point we can assume that the patient has:

A.acute tubular necrosis.
B.glomerulonephritis.
C.acute interstitial nephritis.
D.chronic renal failure.
E.pre renal azotemia.

Answer 14

E. Prerenal Azotemia

Question 15

A 35 year old female presents after 3 days of epigastric pain and vomiting. She has only been able to retain water. The patient is orthostatic and found to have poor skin turgor with skin tenting and dry mucosal surfaces. Serum sodium is 122 meq/L (normal 140 meq/L) with K of 2.5 meq/L (n = 4.5 meq/L). Cl is 88 meq/L (100) with HCO3 of 33 meq/L (25). Glucose is 60 mg/dL (60 -100). BUN is 60 mg/dL (normal 10 mg/dL) and Creatinine is 1.4 mg/dL (normal 1 mg/dL). Urine osmolality is 580 mOsm/L (specific gravity 1.030). Serum osmolality is 267 mOsm/L (n = 287 mOsm/L). Una is < 10meq/L.

The above patient is diagnosed with pancreatitis, placed NPO and treated with fluid replacement with slight overall improvement. However, three days later, urine output is 20 cc/hr with labs as follows:

Na+ 138 meq/L, K+ 4.5 meq/L

Cl- 100 meq/L, HCO3- 16 meq/L

BUN 40 meq/L Creatinine 4 meq/L

Calcium 7.8 meq/L (8-11), Phosphorus 5 meq/L (2.4-4.1)

Spot Una+ > 20 meq/L, FeNa > 2%, Uosm 280 mOsm/L (SG 1.010).

• Now we see the casts in the urine that are shown in the picture. What are these casts?
• What does the BUN/Creatinine ratio indicate?
• Why has the HCO3 decreased from 35 to 16 meq/L?
• Why has the Una increased from < 10 meq/L
• to > 20 meq/L?
• What does all this mean for our patient?

Answer 15

• Granular, or “muddy brown” casts and renal tubular epithelial casts
• Intrinsic renal failure
• Anion gap acidosis led to decreased bicarb
• Urinary Na+ increased because of loss of tubular function
• Patient has developed ATN

Question 16

What is pathognomonic for ATN?

Answer 16

Urine sediment with pigmented granular casts and renal tubular epithelial cells

Question 17

What are the causes of ATN?

Ischemia - 5

Exogenous toxins - 4

Endogenous toxins - 4

Answer 17

Ischemia

• Post operative
• Shock
• Sepsis
• Pancreatitis
• hypophosphatemia

Toxins

• Exogenous
  
  • Aminoglycosides
  • vancomyocin
  • cyclosporine
  • radiographic contrast media
• Endogenous
  
  • myoglobinuria
  • hemoglobin
  • hyperuricemia
  • Bence Jones protein

Question 18

A 65 year old male cirrhotic with severe peripheral edema and ascites presents with a sodium of 120 meq/L and serum osm of 245 mosm/L. Urine sodium is < 10 meq/l. Bilirubin is 5 mg/dL (n = 0.2-1.4 mg/dL), albumin is 1.4 mg/dL (n= 3.5-5gm/dL), protime is 16 sec (n=12 sec). Glucose is 110 mg/dL. BUN is 2 mg/dL.

What is the term that describes this hyponatremic condition?

Answer 18

Hypotonic Hypervolemic Hyponatremia

Question 19

In hypotonic hypervolemic hyponatremia, why is the urine Na+ low?

Answer 19

Hypoalbuminemia and decreased effective plasma volume

with increased sympathetic tone,

decreased RBF and GFR, and

increased RAAS

Question 20

Hypotonic hyponatremic dehydration can be associated with a hypervolemic state. What sign should you be thinking of with this condition? What diseases?

Answer 20

Hypotonic hyponatremic hypervolemic state = EDEMA

Think edematous states:

CHF

Liver disease

Nephrotic Syndrome/renal Na+ retention

Advanced kidney disease (Una >20 meq/L)

Question 21

Hypotonic hyponatremic dehydration is also associated with a euvolemic state. What is a classic example of this?

Answer 21

SIADH - (Uosm >200mOsm/L)

Question 22

What other diseases are associated with hypotonic euvolemic hyponatremia?

Answer 22

Post-op hyponatremia
Psychogenic polydipsia – 4% (Uosm < 100)
Hypothyroidism
Beer potomania (Uosm < 100)
Idiosyncratic drug reaction – 7% (thiazide diuretics, ace inhibtors, NSAIDs*, SSRIs**)
Endurance Exercise
Adrenocorticotropin deficiency – 2% (↓cortisol = ↓free water clearance)
Stress
HIV
Idiopathic hyponatremia of the elderly - (reset osmostats- Uosm < 100 mOsm/L)

Question 23

A 36 year old male alcoholic is found unconscious in a road side gutter. He has been without food for four days. An IV of Dextrose 5% in 0.45 NaCl is started in the ER. The patient rouses slightly but is markedly agitated and confused. He complains of pain in the muscles and bones. He develops alveolar hypoventilation and requires a respirator. The next day labs show Hb of 10 gm with increased LDH, increasing BUN and creatinine and elevated CPK to 40,000 IU/L (normal = 8-150)

Urine: dipstick positive for “hemoglobin”

Microscopic urine: no RBCs.

The urine will also be positive for:

Answer 23

myoglobin

Question 24

A 36 year old male alcoholic is found unconscious in a road side gutter. He has been without food for four days. An IV of Dextrose 5% in 0.45 NaCl is started in the ER. The patient rouses slightly but is markedly agitated and confused. He complains of pain in the muscles and bones. He develops alveolar hypoventilation and requires a respirator. The next day labs show Hb of 10 gm with increased LDH, increasing BUN and creatinine and elevated CPK to 40,000 IU/L (normal = 8-150)

Urine: dipstick positive for “hemoglobin” Microscopic urine: no RBCs.

An EKG is done on the patient and shows a prolonged PR

interval with peaked T waves, indicative of:?

Answer 24

hyperkalemia

Question 25

testing shows: Na+ 142 meq/L (140 meq/L), K+ 5.9 meq/l (4.5) Cl- 106 meq/L (100), HCO3- 15 meq/L (25) Spot Una+ > 20 meq/L, FeNa > 2% BUN 30 mg/dL, Creatinine 2.5 mg/dL Phosphate 0.9 mg/dL (2.2-4.8) Calcium 8.5 mg/dL (8-11 mg/dL) uric acid 8.7 mg/dL (3.5 – 7.7).

What is the acid base disturbance?

Answer 25

anion gap metabolic acidosis - from lactic acidosis

(compensatory resp alkalosis)

Question 26

A 36 year old male alcoholic is found unconscious in a road side gutter. He has been without food for four days. An IV of Dextrose 5% in 0.45 NaCl is started in the ER. The patient rouses slightly but is markedly agitated and confused. He complains of pain in the muscles and bones. He develops alveolar hypoventilation and requires a respirator. The next day labs show Hb of 10 gm with increased LDH, increasing BUN and creatinine and elevated CPK to 20,000 IU/L (normal = 8-150)

Spot Una+ > 20 meq/L, FeNa > 2%

BUN 30 mg/dL, Creatinine 2.5 mg/dL

Is this pre, post or intrarenal failure?

Answer 26

prerenal and intrarenal failure – BUN/Cr is close to 10:1, 15:1 now.

Patient likely had >20:1 previously

Question 27

Spot Una+ > 20 meq/L, FeNa > 2%

What does the spot Una indicate?

Answer 27

Tubular damage from hypoxia and myoglobin with dysfunction and loss of Na.

Question 28

Additional lab review shows:Na+ 142 meq/L (140 meq/L), K+ 5.9 meq/l (4.5) Cl- 106 meq/L (100), HCO3- 15 meq/L (25) Spot Una+ > 20 meq/L, FeNa > 2%

BUN 30 mg/dL, Creatinine 2.5 mg/dL

Phosphate 0.9 mg/dL (2.2-4.8) Calcium 8.5 mg/dL (8-11 mg/dL)

uric acid 8.7 mg/dL (3.5 – 7.7).

Urine shows pigmented granular casts and renal tubular epithelial cells.

What is the diagnosis in this patient and what must one watch out for in phosphate replacement?

Answer 28

This patient has renal ATN due to rhabdomyolysis from starvation and alcohol related hypophosphatemia and subsequently decreased 2,3 DPG with oxygen starvation and tissue hypoxia.

Phosphate replacement should be done slowly to avoid hypocalcemia.

Question 29

K+ 5.9 meq/l

Phosphate 0.9 mg/dL (2.2-4.8) Calcium 8.5 mg/dL (8-11 mg/dL)

uric acid 8.7 mg/dL (3.5 – 7.7).

Urine shows pigmented granular casts and renal tubular epithelial cells.

How does this compare to “garden variety” rhabdomyolysis, as from seizures, crush injuries, hypothermia, statins, etc?

Answer 29

Classic crush injury rhabdomyolysis would cause massive release of phosphate, uric acid and potassium with decreased calcium due to Ca x P precipitation in tissues. In that type of situation, one would not want to administer calcium as with improvement it will be released from the tissues.

Question 30

What is pathognomonic for ATN?

Answer 30

Urine sediment of pigmented granular casts and renal tubular epithelial cells

Question 31

What are some ischemic causes of ATN?

Answer 31

post op

shock, sepsis

pancreatitis

hypophosphatemia

Question 32

What are the toxic causes of ATN?

Answer 32

aminoglycosides

vancomycin

cyclosporine

radiographic contrast media

myoglobinuria

hemoglobin

hyperuricemia

Bence Jones protein

Question 33

A mild case of ATN has happened, and now that person is developing polyuria. Why?

Answer 33

As the renal tubular epithelium regenerates, as the double nucleus (arrow) in this photomicrograph testifies to, the kidney begins to produce large amounts of very dilute urine. The reason for this is that the complicated brush border cells do not come back immediately, they are first replaced by low cuboidal epithelium, which does little in the way of resorption of water. Thus large quantities of dilute urine (polyuria) are produced by the patient. Eventually, the epithelium differentiates into the more complex brush border type, and normal urinary production is restored.