Hypernatremia - Mucksavage (Exam 2)

What is a normal sodium value?

135-145 mEq/L

How do we define hypernatremia?

> 145 mEq/L

What is the most typical cause of hypernatremia?

Usually a total body water deficit

Is hypernatremia always a hyperosmolar state?

Yes!

What does moderate hypernatremia manifest as?

Muscle weakness, restlessness, nausea, vomiting

What does severe hypernatremia manifest as? (160 mEq/L +)

Confusion, lethargy, irritability, stupor, coma

What is classic manifestation of hypernatremia?

Intense thirst!

What are our 3 buckets of hypernatremia?

- Low ECF (meaning their total body water is significantly decreased, total body sodium might actually be slightly decreased as well)

- Normal ECF (meaning their total body water is decreased, but the total body sodium remains the same)

- High ECF (meaning their total body water is increased, but their total body sodium is significantly increased)

We put patients into one of 3 buckets based on their ECF!

Low ECF = ____ volemia

HYPO

Normal ECF = ____volemia

EU

High ECF = ___volemia

HYPER

What is the typical cause for hypervolemic hypernatremia?

Iatrogenic (meaning we induced it) --> e.g. sodium overload with 3% NaCl, excessive Na+ ingestion, antibiotic containing Na+, hypertonic dialysis

What are some less common causes of hypervolemic hypernatremia?

- Hyperaldosteronism

- Cushing's syndrome

What are a few causes of euvolemic hypernatremia?

- Renal water loss due to diabetes insipidus (i.e. you either are not secreting AVP or you have lost responsiveness to AVP)

- Non-renal water loss due to fever and hyperventilation

What are some signs and symptoms of diabetes insipidus?

- Polyuria (peeing a lot)

- Polydipsia (excessive thirst)

- urine sp gr < 1.005 (this is dilute)

What is normal sp gr of urine?

1.010 (ten-ten)

What is common etiology of central DI?

Head trauma, surgery (pituitary), drugs (phenytoin, ethanol) --> causes lack of production or release of AVP

Usually normal ECF due to thirst mechanism! (we can drink water to keep up)

What is common etiology of nephrogenic DI?

Renal disease, hypercalcemia, hypokalemia due to medications such as lithium, demeclocycline, amphotericin B, foscarnet, clozapine, cimetidine, VRA

What are common causes of hypovolemic hypernatremia?

- Renal loss due to osmotic diuresis, loop diuretics, or acute/chronic renal disease

- Non-renal loss due to diarrhea, vomiting, fistulas, excessive sweating, burns

Why can't we rapidly treat hypernatremia?

- Hypertonic state in the plasma

- Brain is losing water, flowing to the plasma

- Brain accumulates electrolytes + organic osmolytes

- Too much water too quick

- Brain has no time to adjust

- Water will travel into the brain

- Cells start to swell, leading to cerebral edema

What is the maximum correction rate for acute hypernatremia? (acute means less than 48 hours)

1 mEq/L/hr

What is the maximum correction rate for chronic hypernatremia? (chronic means more than 48 hours)

0.5 mEq/L/hr

What is the maximum decrease in serum sodium in 24 hours?

10 mEq/L/24hr

How often should we be monitoring serum Na+?

every 2-4 hours

What is the goal serum sodium when managing hypernatremia?

145-150mEq/L

What fluids would you use to treat hypernatremia?

0.45% NaCl or D5W

What equation can you use to predict what 1L of infusate will do to serum sodium?

(infusate Na+ - serum Na+) / (TBW + 1)

- TBW = 0.6 for men, 0.5 for women, 0.5 for elderly men, and 0.45 for elderly women

How do we calculate free water deficit?

- TBW Deficit = Normal TBW * (1 - [140/Na])

- Normal TBW = BW x % water

How do we use free water deficit to our advantage?

You should replace 1/2 deficit over the first 24 hours then replace the remainder in the next 24-72 hours

Let's do an example! Calculate free water deficit for a 70kg young man with serum sodium of 158.

70kg (0.6L/kg) * (1-[140/158])

= 4.8L

= 2.4L/24hr --> 100mL/h x 24h for replacement

What are units for doing fluids? (for the final rx)

Rate per hour!

How do you treat iatrogenic hypervolemic hypernatremia?

- d/c offending agent

- diuretics to eliminate Na/H2O excess

- hemodialysis if renal failure

- replace free water deficit

Why is treatment for hypervolemic hypernatremia unique?

You are administering water BUT you are also administering diuretic to pee off excess

How do we manage euvolemic hypernatremia?

Depends on type of symptoms. Also depends if they have DI/ what type of DI.

Mild/moderate --> replace free water deficit po or IV

Severe --> replace free water deficit with 0.45% NaCl or D5W IV

If the patient has CDI, administer vasopressin or desmopressin

If the patient has NDI, administer HCTZ, amiloride, or indomethacin

What is the drug of choice to treat central diabetes insipidous?

Desmopressin

What are dosage forms of desmopressin?

- Nasal spray (0.1 mg/mL) where 1 spray = 10 mcg (max 4 sprays per day, can be dosed QD or TID)

- Rhinal tube

- IV 4 mcg/mL (0.25-1mcg every 12-24h IV or SC)

- Oral tablet (0.1 mg or 0.2 mg) (0.1-0.8mg daily dosed either BID or TID)

What are ADRs for desmopressin nasal spray?

Rare, include conjunctivitis, HA, nasal congestion, abdominal pain (if large doses, HTN and angina)

What are ADRs for IV desmopressin?

Pain at the injection site, HA, abdominal pain (if large doses, HTN, angina, MI)

What are ADRs for oral desmopressin tablet?

Well tolerated (HA most common)

How do we treat hypovolemic hypernatremia?

Depends on symptoms.

Mild-moderate: Replace free water deficit PO or IV

Severe: They are in hypovolemic shock. You need to do 0.9% NaCl 500-1000 mL over 30-60 min (you would go with 0.9% NaCl because this will go into ECF - no ICF - which will go into IVF), then replace free water deficit with 0.45% NaCl, D5W IV