Vital signs:
- Blood pressure 89/65 (MAP 55)
- Heart rate 105 bpm
- Respiratory rate 18/min
- Temperature 38.3C
Initial labs:
- Serum sodium 105 mmol/L
- Lactate 4 mmol/L
What is the safest way to volume resuscitate a hyponatremic, hypovolemic patient?
Likely the first instinct is to provide an isotonic fluid bolus of 20-30 mL/kg for septic shock. However, in chronic, severe, symptomatic hyponatremia, sodium correction should not exceed 0.5-1 mEq/L/h with a goal of 8-12 mEq/L/d to reduce the risk of central pontine myelinolysis (also known as osmotic demyelination syndrome).1,2 Acutely symptomatic (<48 hours) patients can be corrected safely at a faster rate with goal of increasing sodium by approximately 1-2 mEq/L/hr for 3-4 hours.
This is a nuanced case of fluid management, but can have long-term implications for an acutely ill patient. The ideal fluid choice would allow for adequate fluid resuscitation without rapid overcorrection of the sodium concentration.
Options for fluid resuscitation
| Fluid | Na+ (mEq/L) | Cl- (mEq/L) | K+ (mEq/L) | Ca++ (mEq/L) | Mg++ (mEq/L) | Buffer | pH | Osmolality (mOsm/L) |
|---|---|---|---|---|---|---|---|---|
| 0.9% NaCl | 154 | 154 | – | – | – | – | 5.7 | 308 |
| Lactated Ringers | 130 | 109 | 4 | 3 | – | Lactate (28) | 6.4 | 273 |
| 3% saline | 513 | 513 | – | – | – | – | 5.0 | 1026 |
Trick of the Trade: Lactated Ringers may be the safest choice
Compared to normal saline, Lactated Ringers provides twice the volume expansion for the same degree of correction of sodium due to the lower sodium concentration per liter.
This was calculated using MDCalc, which was derived based on a great NEJM review paper.3 For example, the amount of fluid needed to increase the serum sodium by 1 mmol/L/hr for an elderly female with an estimated weight of 60 kg and an initial sodium concentration of 105 mmol/L:
| Lactated Ringers: | 1240 mL/hr |
| 0.9% Normal Saline: | 633 mL/hr |
| 3% Saline: | 76 mL/hr |
The exact amount of volume that can be given for an expected 1 mmol/L/hr increase in serum sodium will change depending on your patient’s age, sex, weight, and starting sodium value and should be calculated for each individual patient.
Bottom Line
Be concerned about rapid sodium correction in a patient with symptomatic hyponatremia. Twice the amount of volume resuscitation with Lactated Ringers can be given compared to normal saline for the same degree of sodium correction.
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