73 y/o F w/ hx of hyperlipidemia, IDDM, and prior smoking hx presents with her daughter reporting weakness in the setting of 1 week of nausea and vomiting. She is also reporting difficulty with motor functions including walking and picking up objects such as the morning paper and her afternoon teacup. Her exam is significant for global weakness and ataxia, however the pt is noted to be conversing normally with her daughter in the room.
What's the diagnosis and what treatment do you want to initiate?
Hyponatremia; first treatment is to DO NOTHING and obtain additional labs to determine the etiology of the hyponatremia (hypovolemic hyponatremia, euvolemic hyponatremia, hypervolemic hyponatremia, SIADH, medication related (thiazides), drugs (ecstasy), psychogenic polydipsia, potomania, etc…). You first need to determine the etiology of the hyponatremia and if you initiate treatment before obtaining these labs then it'll make it difficult to determine the cause. Also, initiating aggressive treatment turns off ADH and can lead to massive over diuresis, which can cause a sharp rise in serum sodium levels and potentially result in osmotic demyelination (i.e. locked-in syndrome, severe neurologic morbidity, death). Lastly, normal saline can actually worsen the hyponatremia in a patient with SIADH, therefore the etiology of the electrolyte abnormality needs to be elucidated BEFORE treatment. This is especially true in asymptomatic patients. If a patient is presenting with severe neurologic symptoms, then the risks/benefits need to be assessed when considering treatment.
Is the patient hypovolemic, euvolemic, or hypervolemic? How can you tell?
Hypovolemic: The Inferior vena cava (IVC) is seen completely collapsing with respirations, which suggests a volume depleted state. The IVC should normally, in a euvolemic patient, collapse by about ~50% with respirations. An IVC that doesn't collapse at all with respirations is usually seen in a well-resuscitated patient OR fluid overloaded patient while an IVC that completely collapses suggests volume depletion. The parasternal long and parasternal short echocardiogram views shown display a hyper dynamic, tachycardic heart, which in the right clinical setting can indicate hypovolemia. (note, there is decent literature to support using IVC diameter to determine fluid states in conjunction with clinical status, however there isn't comparable data for a hyper-dynamic tachycardic heart, it's just an interesting finding that you might find, especially in patients suffering from septic or hemorrhagic shock).
Charge nurse calls: no beds are available in the hospital and none are anticipated to be ready until 7 am (7 hours from now).
You decide to initiate treatment for this patient's condition. What do you give and what's your target goal?
The labs (and echocardiogram) above support the diagnosis of hypovolemia hyponatremia (serum osm < 280, urine Na+ < 20 suggesting the patient is dehydrated and the kidneys are attempting to retain sodium/water, and the urine osm isn't egregiously low which would have suggested severe malnutrition (beer potomania).
Best course of action is to do nothing and fluid restrict, however if the patient is showing signs of severe neurologic dysfunction and boarding in the ED then you can consider correcting the Na+ SLOWLY. Different sources recommend different rates of correction, but it's better to be more conservative and never correct more than by 6 mmol/L in first 6 hours in the ED. If you find yourself boarding a hyponatremic patient beyond this initial correction, nephrology should be consulted to help guide care (of course, in an academic setting, you might be consulting nephrology from the beginning). The following equation can be used to predict the rise in Na+ based on the fluid initiated: Change in serum Na+ = infusate Na+ – serum Na+ / (total body water + 1) (Adrogue HJ, Madias NE. Hyponatremia. N Engl J Med 2000; 342:1581). The infusate Na+ for 3% Na+ solution is 513 mmol/L and the infusate for NS is 154 mmol/L. To calculate total body water try MD calc: http://www.medcalc.com/tbw.html. The rate of infusion can be calculated based on the Na+ concentration chosen and the desired Na+ increase over a given time period. Check serum sodium every hour.
Before initiating treatment, the patient begins to have a tonic-clonic seizure. What do you give?
The seizure is likely due to the hyponatremia, therefore rapid Na+ infusion is the best treatment: 100 cc of 3% Normal Saline, which increases Na+ by 2 mmol/L, given over 10 mins. Wait 10 mins, then give a second dose if they continue to seize. This can be given peripherally assuming you have a decent line. You can also give benzos concurrently, but not as effective in these hyponatremic seizures. Check the sodium level after these two doses before giving more, consult nephrology, and of course explore other etiologies of the patient's seizure.