Sodium Disturbances

Question 1

Most common electrolyte abnormality following SAH

Answer 1

Hyponatremia

May be due to EITHER CSW or SIADH

Volume status is the best way to differentiate these two.

Question 2

When does hyponatremia become symptomatic?

Answer 2

When it is acute (< 48 hours)

OR

When Na is < 120 mEq/dL

Question 3

If you correct hyponatremia too fast, you are at risk for ___.

If you correct hypernatremia too fast, you are at risk for ___.

Answer 3

If you correct hyponatremia too fast, you are at risk for central pontine myelinolysis.

If you correct hypernatremia too fast, you are at risk for cerebral edema and herniation.

Question 4

Why do hypotensive patients become hyponatremic?

Answer 4

ADH release in order to defend the blood pressure

Remember, ADH prioritizes pressure over electrolyte balance

Question 5

As a quick rule of thumb, whenever the sodium goes down. . .

Answer 5

. . . the brain will start to swell

This includes the general pathology of hyponatremia as well as the complications of reversing hypernatremia too quickly.

Question 6

What is the first thing you measure once you determine that a patient is hyponatremic?

Answer 6

Serum osmolality

In hyponatremic patients, it may be hypotonic, isotonic (pseudohyponatremia), or hypertonic. The only way to know is to check.

Question 7

Isotonic hyponatremia

Answer 7

aka pseudohyponatremia

Caused by:

• Severe hypertriglyceridemia
• Hypercholesterolemia
• Paraproteinemia

Question 8

Management of hyponatremia depending upon patient volume status

Answer 8

Hypovolemic hyponatremia: Depletional hyponatremia, such as CSW. May be caused by renal or extra-renal sodium loss. Volume repletion is generally sufficient to correct the sodium, as this will allow ADH to autoregulate the sodium independent of blood pressure.

Euvolemic hyponatremia: Many causes, but SIADH is most common. Correct slowly with hypertonic saline (< 10-12 mEq/dL in 24 hours, < 18 mEq/dL in 48 hours) and transition to water restriction when symptoms resolve or at 120 mEq/dL.

Hypervolemic hyponatremia: Caused by clinical entities of volume overload (CHF, nephrotic syndrome, cirrhosis, etc). Correct slowly with hypertonic saline (< 10-12 mEq/dL in 24 hours, < 18 mEq/dL in 48 hours) and transition to water restriction when symptoms resolve or at 120 mEq/dL.

Question 9

What is the goal sodium for the acute correction of hyponatremia?

What is the goal sodium for the acute correction of hypernatremia?

Answer 9

Hyponatremia: 120 mEq/dL or resolution of symptoms in the acute phase. Then just restrict free water until it corrects the rest of the way.

Hypernatremia: 145 mEq/dL. This should be the goal sodium used in the free water deficit equation. Give free water (with or without diuresis) until this sodium is reached.

Question 10

While actively correcting sodium levels, how frequently should you check a BMP?

Answer 10

Every 2-4 hours

This is necessary to ensure that you are not correcting too fast

Question 11

Hyponatremia 1 liter infusate equation

Answer 11

ΔNa_serum = (Na_infusate - Na_serum) / (Weight + 1)

This equation assumes that you are giving 1 liter of infusate.

Question 12

Free water deficit equation

Answer 12

FWD = 0.6 x Weight x [( Na_serum - Na_goal ) / Na_goal]

Where Na_goal = 145 mEq/dL in most cases

Question 13

Total nonfood fluid limit for fluid restriction in hyponatremia

Answer 13

500 mL/day + daily average urine volume

Note that this is total fluids, including from medications, etc

Question 14

Correcting hypervolemic hyponatremia may require. . .

Answer 14

. . . concurrent dilute water administration and diuresis

This is totally fine. Think of it like this: Free water treats the electrolyte abnormality, diuresis treats the fluid overload with little effect on electrolyte balance,