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Hyponatremia & Hypernatremia- For Nursing Students
The final electrolyte imbalance in our fluid and electrolyte series is hyponatremia and hypernatremia. I think I am just as happy as you to be finishing up this fluid and electrolyte series. It is quite a bit to sort through!
We will review the causes, signs and symptoms, treatments, and nursing considerations.
Once you have read all the information in this post, be sure to download this printable PDF cheat sheet.
Let us begin by breaking down the words hyponatremia and hypernatremia.
Hypo= low natr=sodium emia= in the blood
Hyper= high natr= sodium emia= in the blood
Hyponatremia= low sodium in the blood
Hypernatremia= high sodium in the blood
The normal sodium lab value= 135-145 mEq/L
Therefore, hyponatremia <135 mEq/L and hypernatremia= >145 mEq/L
Sodium
Sodium is a particularly important electrolyte as it has a close relationship with water. Essentially, sodium determines where water is located; where salt goes, water follows.
Sodium is important in excitable cells that cause skeletal muscle contraction, cardiac contraction, and nerve impulse transmission.
Sodium is regulated by the kidneys.
When sodium levels are low
- Antidiuretic hormone (ADH) and natriuretic peptide (NP) secretion is inhibited
- Aldosterone secretion is triggered
When sodium levels are high
- Aldosterone secretion is inhibited
- ADH and NP secretion is stimulated
Hyponatremia
Lab value= <135 mEq/L
Causes:
Hyponatremia can come in a couple different forms. One of those is an actual sodium deficit, in which sodium levels have been depleted after excess loss. There is also a relative sodium deficit due to dilution. Dilution occurs when the fluid volume increases but the sodium levels do not.
(Actual deficit):
Excessive diaphoresis– sweating will cause a loss of water and sodium which in excess can lead to hyponatremia.
Diuretics– sodium is excreted with diuretic therapy so the risk of developing hyponatremia is high.
GI wound drainage, NGT suction– gastric secretions are rich in sodium, so an excess loss of these fluids leads to hyponatremia.
(Dilution):
Psychogenic polydipsia– this is a psychological condition in which an individual compulsively drinks water in excess which leads to water intoxication. This causes the fluid volume to increase but the sodium level does not, which leads to hyponatremia.
Nephrotic syndrome– this syndrome causes fluid to be retained, which will lead to dilution of the blood
Syndrome of inappropriate antidiuretic hormone secretion (SIADH)- this is a condition in which ADH is excreted in excess. ADH causes water to be retained, therefore it will cause dilution of the blood, leading to hyponatremia.
Heart failure– heart failure causes an increase in water retention. This extra water dilutes the blood thereby decreasing the concentration of sodium .
Signs/symptoms:
*Remember, hyponatremia causes reduced excitability and cellular swelling. This swelling can be dangerous as it reduces cellular function*
Behavioral changes, altered LOC– the changes that are seen in cognition are correlated to the cerebral edema that results from the swelling of the cells.
Generalized weakness, diminished DTRs– the decreased excitability of skeletal muscles will cause patients to be weak and have diminished or absent deep tendon reflexes.
Increase intestinal motility– the increased intestinal motility can cause vomiting, diarrhea, and abdominal cramping.
Rapid and weak pulse- in patients who are hypovolemic (fluid deficit). Blood pressure will be decreased. This is due to the loss of fluid volume in the body.
Full and bounding pulse- in patients who are hypervolemic (fluid overload). Blood pressure will be increased. This is due to the fluid excess in the body.
Treatment:
DC diuretic therapy- diuretic therapy should be discontinued to prevent excess water and sodium excretion.
IV saline solution (for fluid deficit)- if the patient is hypovolemic, then a hypertonic solution may be used to rehydrate them. These hypertonic solutions will pull the fluid out of the cells and into the bloodstream, thereby increasing the sodium level
Conivaptan, tolvaptan- for patients with hypervolemia, these ADH antagonists can be used to decrease the amount of fluid retention, thereby reducing the dilution causing the hyponatremia
Demeclocycline- the mechanism of action for this medication is not well understood, but you can check out this article if you would like to learn more about the existing studies.
Increased sodium intake- if the sodium deficit is low, then it can be helpful to encourage patients to eat foods that are high in sodium
Hypernatremia
>145 mEq/L
Causes:
As with hyponatremia, the causes of hypernatremia can be caused by an actual loss of sodium or a relative loss.
(Actual)
Cushing’s disease, Hyperaldosteronism- aldosterone plays an important role in conserving sodium in the body. If too much aldosterone is being secreted, then there will be an increase in the amount of sodium that is retained in the bloodstream.
Kidney failure- hypernatremia can result due to the kidneys’ inability to filter the blood properly
Diabetes insipidus- DI is a condition in which there is a lack of ADH. This deficiency in ADH causes excess water to be excreted. The concentration of sodium increases due to this loss of fluid volume.
(Relative)
Hyperventilation
Diarrhea – the excess loss of fluid causes the bloodstream to become more concentrated with sodium
Signs/symptoms:
*Remember, hypernatremia causes increased excitability. This can cause an over response to stimuli. *
Alterations in LOC can vary. If decreased fluid volume= agitation, confusion, seizures. Increased fluid volume= confusion, lethargy, stupor
Muscle twitching, muscle contractions- the increased excitability of skeletal muscles will cause muscle twitching and inappropriate muscle contractions. If the hypernatremia is severe or in the late stages, then then DTRs will become absent and the patient will experience severe muscle weakness.
Faint pulses and hypotension if the patient is hypovolemic.
Bounding pulse, increased blood pressure, and distended neck veins if the patient is hypervolemic.
Treatment:
Diuretics- such as furosemide or bumetanide can help decrease sodium levels by excreting excess sodium through the urine
Hypotonic IV solution (0.225% NaCl)- these hypotonic solutions will cause sodium to be shifted into the cells, which will decrease the concentration in the bloodstream.
Restrict sodium intake- teach patients to avoid foods that are high in sodium.
Nursing Considerations
Monitor the respiratory system of individuals with hyponatremia and severe hypernatremia as they could experience respiratory failure due to severe muscle weakness.
Patients who receive hypotonic IV solutions should be monitored closely for neurological changes. Cerebral edema could occur due to the shift of volume into the cells.
Educate patients on foods that are high in sodium. Teach patients with hyponatremia to increase consumption of healthy foods that are high in sodium; teach patients with hypernatremia to restrict consumption of foods that are high in sodium.
I hope this was helpful for you nursing students out there learning about fluid and electrolytes!
If you haven’t already checked out my other posts on the other fluid and electrolyte imbalances, you can click the links below to be taken to each of the individual posts. Each of them have a downloadable cheat sheet so be sure to grab those!
- Hypokalemia & hyperkalemia
- Hypocalcemia & hypercalcemia
- Hypomagnesemia & hypermagnesemia
- Hypophosphatemia & hyperphosphatemia
Be sure to also check out my tips on how to study and pass nursing exams in nursing school, so you can pass your fluid and electrolyte exam with flying colors!
As always, feel free to contact me if you have any questions!
Happy Nursing!