In this video from MedCram, Dr. Seheult discusses how low sodium can affect the brain. If you were to look at the BMP or chem 7 which we have on our MedCram series, normal values are between 135-145 in the blood for sodium. If it is less than 135, this is called hyponatremia. We will be discussing how to correct hyponatremia safely because if you do it too quickly, it can cause osmotic demyelination syndrome and lead to brain injury and even death.
Low sodium is not technically caused by not having enough salt in your diet. Dr. Seheult had a patient that he had admitted to the hospital where she came in with a sodium level of 104. That is extremely low and when it reaches this level, one of the concerning issues is an increased risk for seizures. The treatment in this case is to get the sodium level up so that you can avoid potential for neurological complications.
How do you safely treat hyponatremia?
However, the question that is of utmost importance is how do you get the sodium up in a quick and safe manner without over correcting too quickly. If you overcorrect the sodium too quickly, this can equally cause serious injury. We have neurons in our brain and on each neuron there is a sheath of myelin that coats this neuron, and this prevents any type of electrical conduction in this area. If you have a situation where the sodium concentration is low on the outside and the inside of the cell has equilibrated and then you suddenly raise the outside sodium concentration you are going to get a movement of water from inside the cell to outside the cell. The concentration of sodium is now higher and what will then happen is that it will disrupt this membrane, the myelin sheath, and cause damage to it. So what is defined as increasing the sodium too quickly? The current guidelines recommend no more than an increase of 6 points per 24 hour period. If you can see that your rate is over correcting faster than it should, then you may need to use means to try and lower the sodium again. This is something you are going to have to follow closely with lab work every 3-4 hours.
You can increase sodium with 3% normal saline which is a super concentrated solution of salt water. The normal fluid sodium concentration is 0.9%. The 3% needs to go through a central line. A concentration of 2.3% can still go through a peripheral IV. To decrease the sodium you can do this with free water but this can’t go through an IV, so D5W or dextrose is used for this purpose instead. You can also use regular NaCl especially if you are also trying to correct volume.
The brain and hyponatremia
In the brain in the posterior pituitary, there is a hormone that is secreted called vasopressin which is also known as ADH or desmopressin. In the kidney’s collecting tubule the molecules of vasopressin cause reabsorption of free water. There are two things that will cost stimulation of vasopressin to be secreted from the pituitary. The first is a high sodium concentration. The other stimulus is low volume. With this patient, in this scenario, who presented with nausea and vomiting and was found to have low electrolytes,she had also been drinking free water and this was further diluting everything. So in this patient, her vasopressin levels are expected to be elevated as she was volume depleted. She was vomiting sodium and water, but only replacing the water.
In the ER, the patient was given normal saline, but now as soon as the saline is given, the patient is volume resuscitated. You have now removed the stimulus for vasopressin production. So now you are going to see a massive output of free water from the kidneys. The body realizes it has too much free water and now needs to get rid of excess water. As the sodium starts to rapidly go up due to the excess diuresis of water you’re going to see that the sodium is going to shoot up very quickly and overshoot past the recommended six points in 24 hours. So you can give free water to replace the free water the patient is losing, however the kidney can still excrete free water faster than you can replace it. In this situation, it is actually recommended to give the patient a dose of desmopressin 1 mcg IV q12 hours. This causes the body to continue to hold onto the free water. Then you start the patient on 3% normal saline and can allow the sodium to correct slowly up to around 120 and then can back off on the desmopressin to allow the body to try and continue to self correct the sodium.
If the sodium is corrected too quickly and osmotic demyelination syndrome occurs it can result in permanent paralysis.
If you need a refresher course on hyponatremia or other electrolytes please visit the MedCram website