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Intravenous Fluids: Types of IV fluids

Clinical Practice, Disease Management, Emergency Medicine | 8 comments

Intravenous fluids are commonly used in hospitals and emergency departments. There are many different types of IV fluids, which are used both as IV boluses as well as maintenance fluids. Understanding the difference between the types of IV fluids can be challenging, but as a nurse, it is important to understand.

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Indications for Intravenous Fluids

Intravenous fluids are very commonly used in healthcare settings. Most frequently, IV fluids are used to hydrate those with dehydration. Additionally, they can be used to support blood pressure in those with hypotension or sepsis.

IV fluids can also be used as maintenance fluids for those who are not able to intake enough hydration throughout the day.

In the ER, I commonly order Intravenous fluid to those with nausea and vomiting, diarrhea, dehydration, acute kidney injury, abdominal pain, headaches, bleeding, or infections.

Maintenance Fluids vs IV Bolus

Maintenance fluids are intravenous fluids that are run at a slower rate, usually to account for decreased PO intake or expected fluid losses. Patients who are NPO (nothing by mouth) are commonly ordered maintenance fluids, as well as those with ongoing fluid losses.

Maintenance Fluids

Ongoing fluid losses commonly occur with various medical conditions. Fevers commonly require increased maintenance fluid, as they cause “insensible water losses” from sweating and overall increased metabolism.

Those experiencing frequent vomiting or diarrhea require increased fluid to account for their ongoing water losses in their vomit or stool. The same goes for those with drains experiencing significant drainage.

Those with burns or pancreatitis often require a large volume of fluids.

Those admitted with dehydration, mild hyponatremia, or acute renal failure will usually require maintenance fluids in order to slowly correct their hydration, sodium levels, and renal function.

When a patient is NPO, maintenance fluids keep the patient hydrated. To calculate maintenance fluids when a patient is NPO, you can take the patient’s body weight in Kilograms, and use the following equation: (Kg – 20) + 60 = mL/hr. (Ref).

Please note that this is not a hard rule. Those with ongoing fluid losses and various medical conditions may require a faster rate, and those who are older or with CHF may require slower rates.

Clinical Note: Just because a patient is NPO after midnight does not mean that they need maintenance fluids ordered. Do you usually drink water in the middle of the night while you sleep?

IV Bolus

IV boluses are intravenous fluids given rapidly over a short amount of time. This is most frequently used within acute care settings such as the ER or the ICU in those who are unstable with low blood pressure. Giving an IV bolus helps support blood pressure and correct hypotension.

It is common for a 1 liter IV bolus to be ordered on patients initially presenting to the ER, as fluids can help many different conditions. You will commonly see between 1-3 Liters of IV boluses, for conditions such as dehydration, sepsis, shock, migraines, abdominal pain, and n/v/d.

In sepsis, 30ml/kg boluses are commonly ordered. If a bolus is ordered, hang the bolus (usually 1L bags) by gravity and open the clamp wide open. Make sure the patient keeps their arm straight if the IV is in the AC, otherwise the bolus won’t flow.

Clinical Note: If using a pump, run the fluid at 999ml/hr. Please note that in true emergencies this may not be fast enough, and using gravity and/or a pressure bag will infuse the fluid more quickly.

Important Fluid Concepts to Understand

Before diving into the different types of IV fluids, there are a few important underlying concepts we need to understand.

Tonicity, Osmolarity, and Osmosis

Tonicity refers to a fluid’s ability to move fluid into or out of cells and is related to osmolarity – which is the total concentration of solutes within a solution. The more solutes, the higher the osmolarity.

In the body, water shifts into or out of our cell through a semi-permeable membrane – the cell wall. This means water freely flows through it, but larger solutes do not such as our electrolytes (sodium, chloride, potassium, etc).

Osmosis occurs, which is when water flows from a higher osmolarity to a lower osmolarity to “balance” out the concentrations of each side, in this case inside and outside of the cell.

Isotonic, Hypotonic, and Hypertonic Fluids

Isotonic fluids are IV fluids that have nearly the same osmolarity as intracellular fluid. This means that this IV fluid should not cause any significant net fluid shifts into or out of cells.

Hypotonic fluids are IV fluids that have a lower osmolarity than inside the cells, which causes net fluid shifts into the cells. This leads to cellular swelling, which can be deadly in certain conditions like severe head injuries and increased Intracranial Pressure (ICP).

Hypertonic fluids are IV fluids that have a higher osmolarity than inside the cells, which causes net fluid to shift out of the cells. This leads to cellular dehydration and shrinking.

Types of IV Fluids

There are many different types of IV fluids that can be ordered, and knowing the difference between them is important. Certain intravenous fluids are useful for certain situations, and others can be harmful.

As a nurse, it is important to know the basics. As a nurse practitioner, you will be responsible for ordering these fluids so this becomes even more necessary to understand.

Normal Saline (0.9% NS)

Normal Saline, NS, or NSS is the standard fluid given in both boluses and as maintenance fluids. Normal saline contains sodium chloride (NaCl) and is isotonic. This means when given through the IV, there should be no net movement of fluid or electrolyte into or out of the cells.

This ensures that there is no unnecessary swelling or shrinking of the cells when infused. Normal saline is the cornerstone intravenous fluid because it can be given for most situations, including:

  • Hydration
  • Maintenance Fluids
  • Hyponatremia
  • Hypotension or Shock
  • Sepsis
  • with Blood transfusions

Normal saline is cheap and does not result in allergic reactions, and almost all medications are compatible.

Use caution with heart failure or end-stage renal disease, and those on dialysis or in acute fluid overload should probably not receive IV fluids.

A large amount of Normal Saline (3-5+ liters) can cause significant hyperchloremic non-anion gap metabolic acidosis, especially if the patient has renal failure. This can worsen their outcomes within the hospital.

As with any IV fluid, continually monitor fluid status by making sure the patient is not having worsened lower extremity edema or new rales/crackles in the lungs.

If the patient develops sudden shortness of breath during IV fluid administration, consider fluid overload and flash pulmonary edema as a potential cause, especially with a history of heart failure.

You should always be assessing for IV infiltration as well. If there is significant swelling, blanching, and coolness near the IV site – you probably need to remove it and start a new IV.

Related articles:

Lactated Ringers (LR)

Lactated Ringers (LR) is another isotonic fluid that is commonly given. LR is the fluid of choice by surgeons, and some consider LR to be slightly better than NS, but the general consensus is that ‘One is not better than the other’.

Lactated Ringers differ from NS in that it not only has sodium chloride, but also has sodium lactate, potassium chloride, and calcium chloride.

So why choose LR over NS? LR is buffered and won’t cause the hyperchloremic metabolic acidosis that large volumes of NS can. Some studies showed improvement in renal function in critically ill patients who were on LR as opposed to NS, but the evidence is mixed.

LR can be given for all of the indications that NS can be given, including:

  • Dehydration
  • Maintenance Fluids when NPO
  • Ongoing fluid losses
  • Sepsis
  • Allergic Reactions

LR is preferred over NS in certain situations, including:

  • Pancreatitis
  • Burns
  • Surgical patients (surgeon preference)
  • Sepsis

LR should be avoided in:

  • Severe liver or renal failure
  • Metabolic alkalosis > 7.5
  • Hyperkalemia or Hypercalcemia
  • Blood transfusions (If run in the same line can cause precipitation)

As with any fluid administration, be on the lookout for fluid overload as well as local site reactions including infiltration or phlebitis.

Side Note: LR contains sodium lactate, not lactic acid. However, giving LR during sepsis can mildly influence the lactic acid level (about .9 mmol/dL), but this does not actually worsen the sepsis, and has actually giving LR has been shown to indicate lower mortality overall. Interestingly enough, NS also seems to elevate Lactic levels within in the blood. 

Intravenous Fluids IVF - Isotonic fluids

Half Normal Saline (0.45% NS)

Half normal saline (.45% NS) has half the tonicity of Normal saline. This means Half-NS is hypotonic, so the IV fluid has a lower osmolarity than the fluid inside the cells.

This means that half normal saline will cause fluid to shift inside the cells, causing the cells to swell. This can be good in certain situations, and very bad in others.

Half-Normal Saline is rarely given alone, but usually in combination with Potassium or dextrose. However, you may see slower rates given in conditions which cause significant cellular dehydration, such as with:

  • Hypernatremia
  • Severe DKA

Half-Normal saline, when run alone, is typically the wrong choice for most other scenarios as it can deplete intravascular volume and cause cellular edema. Hypotonic fluids are especially bad when it comes to:

  • Head injuries or increased ICP
  • Trauma
  • Burns
  • Liver disease

When given, make sure the patient’s sodium levels are monitored daily, as this can cause hyponatremia.

Intravenous Fluids IVF - Hypotonic fluids

Hypertonic Saline (3% NS)

Hypertonic saline is given with severe hyponatremia or with increased intracranial pressures.

Hypertonic saline is carefully and selectively given, as correcting sodium too quickly can lead to osmotic demyelination syndrome, causing irreversible neural damage.

If a patient has severe hyponatremia and symptoms consistent with cerebral edema, then hypertonic saline should be administered. These symptoms include:

  • Seizures
  • Severe headaches
  • Decreased LOC
  • Tremors

The dose is usually a 100mL bolus given over 10 minutes (a rate of 600ml/hr), which can be repeated twice if needed.

Additionally, hypertonic saline can be given in the setting of severe head injury to reduce intracranial pressure.

If your patient is ordered hypertonic saline, this needs to be on a pump, and the patient needs to be hooked up to the monitor and have frequent neuro checks. Seizure precautions should also be taken if severe hyponatremia is present.

Related article: “The Cranial Nerve Assessment for Nurses”

Intravenous Fluids IVF - Hypertonic fluids

Dextrose-Containing Solutions

Dextrose can be added to any of the fluids mentioned above, as well as to water. Dextrose solution is usually ordered for:

  • Hypoglycemia
  • Maintenance fluids

Dextrose is osmotically active, meaning it does cause the fluid to increase its tonicity, and will lead to net fluid shifts out of the cells. However, dextrose is rapidly metabolized, so the effective osmolarity tends to be higher than the base fluid, but lower than the calculated osmolarity.

Common dextrose solutions include:

  • D5W: Dextrose 5% in Water
  • D10W: Dextrose 10% in Water
  • D5NS: Dextrose 5% in NS
  • D5 1/2 NS: Dextrose 5% in 1/2 NS
  • D5LR: Dextrose 5% in LR

Overall, there is little evidence that dextrose with NS has any benefit or harm when compared to saline alone. However, dextrose should probably be added in:

  • Hypoglycemia
  • Alcohol intoxication
  • Starvation ketosis

Dextrose should not be used in:

  • Hyperglycemia
  • Hypokalemia

An amp (25gm) of 50% Dextrose (D50) is often given as an IV push medication to treat profound hypoglycemia or in conjunction with IV insulin to lower potassium levels.

D5W and D10W are often used for slow correction of chronic hypernatremia, or when hyponatremia has been too-rapidly corrected. It is often commonly found mixed with certain medications.

A patient on dextrose-solution should have their blood sugar monitored, as well as their electrolytes as with any IV fluid. Dextrose-containing solutions should not be given in boluses unless as described above with D50.

Potassium-containing Solutions

Sometimes potassium may be added to each liter bag of fluids. Potassium may be added to maintenance fluid in:

  • Hypokalemia
  • Ongoing potassium losses
  • DKA or severe hyperglycemia

Potassium is as osmotically active as sodium, so this will increase the osmolarity and cause the fluid to be more hypertonic.

This means that adding potassium to an isotonic fluid will make it hypertonic, so may not be a good choice in those with cellular dehydration like in DKA.

In these instances, adding potassium to a hypotonic base fluid such as D5NS with potassium is a great alternative option.

Remember that potassium should NEVER be used as a bolus. IV administration should not exceed 10mEq/hour in most situations, or 20mEq/hour in critical situations with cardiac monitoring and preferably a central line.

Related Article: “9 Nursing Medication Errors that KILL”

Bicarbonate-containing Solutions

Sometimes Bicarb can be added to IV fluids, in order to assist with significant metabolic acidosis. This is not super common outside of the ICU.


And that sums up IV fluids! Hopefully you found this article helpful. If you have any unanswered questions, please comment down below!

References:

Rochwerg, B. et al (2014). Fluid resuscitation in sepsis: a systematic review and network meta-analysis. Annals of internal medicine161(5), 347–355. https://pubmed.ncbi.nlm.nih.gov/25047428/

Sterns, R. H. (2020). Maintenance and replacement fluid therapy in adults. In T. W. Post (Ed.), UpToDate. https://www.uptodate.com/contents/maintenance-and-replacement-fluid-therapy-in-adults

Wilkins, L. W. (2005). Fluids and electrolytes made incredibly easy. Lippincott Williams & Wilkins.

Zitek, T., Skaggs, Z. D., Rahbar, A., Patel, J., & Khan, M. (2018). Does Intravenous Lactated Ringer’s Solution Raise Serum Lactate?. The Journal of emergency medicine55(3), 313–318. https://pubmed.ncbi.nlm.nih.gov/25047428/

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