An 82-year-old female is brought into the Emergency Department by family for a several day history of progressive altered mental status. You initiate a broad workup. However, soon after initial evaluation, you are called back into the room. The patient’s vitals are as follows and concerning for septic shock and an alarming serum sodium level.
- Blood pressure 89/65 (MAP 55)
- Heart rate 105 bpm
- Respiratory rate 18/min
- Temperature 38.3C
- 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
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.
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.
Expert Peer Review
The clinical condition of an undifferentiated hyponatremic AND hypotensive patient poses a rare but significant clinical dilemma. While Early Goal Directed Therapy (EGDT) demands rapid correction of hypovolemia when sepsis is suspected, there exists a significant risk of cerebral demyelination from overly aggressive sodium correction.
Remarkably, based on the MDCalc application (derived from Adrogué HJ, Madias NE. Hyponatremia. NEJM, 2000.), seemingly mild differences in the sodium and potassium content of Ringer’s lactate, allows for infusion of much larger crystalloid volumes compared to Normal Saline for the same degree of serum sodium increase. In this case, a “typical” 2 liter bolus of Normal Saline would be expected to increase the serum sodium concentration almost 2.5 mmol/L which is already about a quarter of the recommended daily sodium change in hyponatremia. Ringer’s Lactate (or other “balanced” crystalloid solutions such as Plasma-Lyte) would be expected to cause HALF of this effect on serum sodium.
While some might argue that the sodium increase from a single 2 liter bolus of Normal Saline has minimal significance a hyponatremic patient’s immediate morbidity and mortality, I would argue that there are still compelling reasons to change practice. For one, as described, Ringer’s Lactate is a clearly superior crystalloid compared to Normal Saline in these circumstances. Two, we ought to be mindful of how our decisions in the ED have downstream effects. In such a complicated patient, we should attempt to optimize the conditions for success of our ICU colleagues and the patient over the ensuring hours and days of care. It is not hard to imagine the massive deliberation needed to balance the needs of multiple continuous IV infusions, volume resuscitation, and careful sodium titration in this patient. Why make it more difficult for our ICU colleagues? Finally, it is really in these critically-ill patients, where single, sometimes seemingly minor decisions, can have major impacts on their ultimate morbidity and mortality.
As an aside, for me, the most striking aspect of this trick of the trade is how it exposes the danger of using automated behaviors (a form of anchoring) irrespective of individual patient conditions. Rapid volume resuscitation is an EGDT cornerstone, which has been ingrained as gospel in medical trainees, and as strict policy at many emergency departments/ intensive care units. Additionally, use of Normal Saline as the crystalloid of first choice is largely the result of convenience and routine, rather than superiority to other crystalloid formulations. For me, this trick of the trade teaches me that I shouldn’t always use a 2 Liter bolus of Normal Saline just because it’s on my medication order “quick list.”
In summary, it is ideal to use Ringer’s lactate (or other “balanced” crystalloid solutions) as the initial choice for volume resuscitation in the undifferentiated hyponatremic, hypotensive patient, until more definitive diagnosis and disease-centric treatments can be initiated.
Expert Peer Review
Thank you for writing up this pearl. Both of the reviewers bring up great points.
- I agree with Dr. Zuckerman\'s point #4 as I am unable to find an outcome specific study in fluid resus between the usual standard care (NS 20-30 ml/kg bolus vs LR) with patient-specific safety outcomes. Based on the math, it theoretically should be a safer choice for a carefully selected cohort of patients. Please consider stating \"may be the safest choice,\" rather than \"[it] is the safest choice.\"
- The second small change is to be consistent with your units. (cc/kg -->ml/kg).
- From an emergency department perspective, differentiating acute vs chronic hyponatremia can be very challenging. Perhaps majority of our patients will have chronic hyponatremia, and in cases where the onset period is unknown (and there are no life-threatening symptoms), it may be best to assume chronic hyponatremia, rather than treat aggressively with NS or higher osmolality fluids. Regardless of the strategy, it would be wise to recommend close and frequent monitoring of Na (every 2 to 4 hours), starting in the emergency department while these patients continue to wait for a bed. Repeat Na can be easily overlooked during a busy shift.
Thank you again for this great pearl!