Hyponatremia: Quick & Dirty

Clinical Manifestations

Serum [Na] > 125 mmol/L

Usually asymptomatic

Serum [Na] 125-130 mmol/L

Predominantly GI symptoms (nausea, vomiting)

Serum [Na] <>

Lethargy, headache, ataxia, psychosis,weakness

Severe cerebral edema - seizures, coma, brain stem herniation, respiratory depression, death

Physiological Manifestations

↓ Serum [Na]

(in the presence of ↓ tonicity)

Shift of water from ECF → ICF

Water enters brain cells

Cerebral edema

Really good article

Adroque HJ, Madias NE. Hyponatremia. NEJM 2000, 342(21): 1581-9.

1. Figure out their volume status
1. Hypovolemic (thirsty, + orthostatics, dry mucus membranes, BUN/Cr)- diuretics, hypoaldosterone, salt-wasting nephropathy

Treat with fluids, hormones, salt

2. Hypervolemic (edema in legs, pulmonary edema)- CHF, Liver disease, nephrotic syndrome

Treat by diuresing, water restriction

3. Euvolemic (none of the above problems)- SIADH

inappropriately secretes ADH, so body doesn’t want to lose water, have very concentrated urine (urine osm- high, urine Na- high), so water stays in the body (serum osm- low)

need to make sure nothing is wrong with thyroid and adrenals (check TSH, cortisol)

treat by free water restriction and sometimes need to replace sodium, if chronic- demeclocycline

psychogenic polydipsia- need to drink 12-20 L a day and urine osm will be low

2. How to Treat
1. Too rapid- central pontine myelinosis
2. Rate of increase should not exceed 0.5 mEq/L/hr
3. In the case of neurologic emergency

Awesome Website

http://www.medcalc.com/sodium.html

Adrogue Formula:
Change in serum Na+ =	(infusate Na+ + infusate K+) - serum Na+
	_____________________________
	total body water + 1

Use the above formula to estimate the effect of 1 liter of any infusate containing sodium and potassium on serum sodium

Infusate Infusate Na+ (mmol/L) 5% NaCl 855 3% NaCl 513 0.9% NaCl (NS) 154 Lactate Ringer's 130 0.45% NaCl (½ NS) 77 0.2% NaCl (¼ NS) 34 5% Dextrose in water (D5W) 0

Total Body Water (in liters) : Children 0.6 x weight Women 0.5 x weight Men 0.6 x weight Elderly Women 0.45 x weight Elderly Men 0.5 x weight

Example

45 yr old 70 kg man, Na 110

Using 3% NS

Change in serum Na= (infusate Na + infusate K) – serum Na/ total body water + 1

= 513- 110/ 0.6 (70) + 1

= 403/ 43

= 9.7

So, 1 liter of 3% NS will bring up this patient’s serum Na by 9.7

Let’s use 0.9% NaCl

= 154 – 110/ 43

= 44/43

= 1

So, 1 liter of 0.9% NS will bring this patient’s serum sodium up by 1