Cannula: Definition, types, purpose, and more

A cannula is a thin tube that doctors insert into a person's body cavity, such as their nose, or into a vein. Doctors use them to drain fluid, administer medication, or provide oxygen.

A person can use intravenous (IV) and nasal cannulas both in the hospital or at home.

This article will describe what cannulas are and explain the difference between IV and nasal cannulas. It also will describe the insertion process and risks for both types.

A cannula, pronounced "CAN-you-la," is a thin tube that doctors insert into a vein or cavity in the body.

There are two main types of cannula:

The purpose of the cannula varies according to its type.

Common uses of IV cannulas include:

Nasal cannulas provide a person with oxygen. They can be useful if a person is experiencing difficulty breathing.

According to UTMB Respiratory Care Services, doctors use nasal cannulas to:

Doctors use different methods to insert nasal cannulas and IV cannulas.

According to the Scottish Diabetes Research Network, a doctor or nurse will take the following steps to insert an IV cannula in a person's arm:

The only pain involved with fitting an IV cannula is the scratch as the needle enters the skin.

However, if a person feels faint or uneasy at any point during the process, they can talk to the doctor or nurse fitting the cannula.

A doctor or nurse will take the following steps to insert a nasal cannula:

Nasal cannulas can be portable so a person can live an independent life while receiving oxygen therapy.

The procedure for fitting a nasal cannula for home use will be the same as above, except the nasal cannula will attach to a portable oxygen supply.

The doctor or nurse will instruct a person on how to use the equipment and how often to fill the oxygen supply. They will reassure the person if they have any doubts or are feeling anxious.

The doctor or nurse will also give a person tips on caring for the cannula, such as not smoking in its vicinity.

There are several types of IV cannulas. They include:

Medical professionals use peripheral IV cannulas in the emergency room, during surgery, or when taking a radiological image.

The lines are for short-term use and attach to an IV catheter.

Doctors tape the cannula to the skin to keep it from moving.

Medical professionals may use a central line cannula for a person who needs long-term treatments that require medicine or fluids intravenously over a period of weeks or months. For example, a person receiving chemotherapy might require a central line IV cannula.

Central line IV cannulas can quickly deliver medication and fluids into the person's body via the jugular vein, femoral vein, or subclavian vein.

Doctors use draining cannulas to drain fluids or other substances from a person's body. Sometimes doctors might also use these cannulas during liposuction.

The cannula often surrounds what is known as a trocar. A trocar is a sharp metal or plastic instrument that can puncture tissue and allow the removal or insertion of fluid from a body cavity or organ.

There are several sizes of intravenous cannulas. According to a 2015 study, the most common sizes range from 14 to 22 gauge.

The higher the gauge number, the smaller the cannula.

Different sized cannulas move liquid through them at different rates, known as flow rates.

A 14 gauge cannula can pass approximately 270 milliliters (ml) of saline in 1 minute. A 22 gauge cannula can pass 31 ml in 21 minutes.

According to the American Lung Association, a standard nasal cannula is a lightweight plastic tube that is inserted just inside a person's nostrils.

The oxygen flow in a standard nasal cannula is lower than other types, including the high flow nasal cannula (HFNC).

HFNCs offer an increased flow rate of oxygen compared to standard nasal cannulas. A 2018 review explains that HFNCs can also heat the gas to 98.6oF (37oC). Colder, dryer air can lead to airway inflammation, and warmer, more humid air can help a person to breathe easily.

Some patients prefer the HFNC because it is lighter, more comfortable, and does not irritate their airways as much as a standard nasal cannula.

Nasal cannulas come in different sizes and with different flow rates. Unlike the numbered sizes of intravenous cannulas, nasal cannulas are available in sizes for adults, children and infants.

According to a 2020 study, regular flow nasal cannulas provide only up to 4–6 liters per minute of supplemental oxygen.

High-flow nasal cannula therapy systems deliver oxygen at a flow rate of up to 60 liters per minute.

Cannulas and catheters are both flexible tubes that can be inserted into veins or cavities to remove or introduce fluids, provide medication or withdraw blood.

Some medical professionals use the terms interchangeably, depending on country or region. However, there are usually distinctions drawn between the two:

Learn about the different types of urinary catheters here.

IV cannulas and nasal cannulas can pose different risks.

IV cannulas present minor risks to a person. Some potential risks include:

In a 2014 study, researchers found that humidified nasal cannulas may increase a person's risk of rainout aspiration.

Rainout aspiration occurs when the air in the oxygen tank is warmer than the air in the room.

The temperature difference can cause condensation in the tubing, which can lead to a person breathing in water through the nosepiece. This could be an unpleasant experience but could also result in a person drowning.

Standard, low flow nasal cannulas (LFNC) can lead to a greater risk of airway inflammation because of the colder, dryer air they introduce to the body. This risk is decreased with a HFNC.

Cannulas are flexible tubes attached to a person's body that can introduce or drain different things. A doctor or nurse can use an IV cannula to introduce medication or take blood, or a nasal cannula to give oxygen to a person.

IV cannulas can reduce the need for needle pricks and make it easier to deliver of medication or fluids to a person's body. Nasal cannulas can help a person who has difficulty breathing by providing them with more oxygen.

Cannulas are generally safe. There are minimal risks associated with cannulas, including a minor risk of infections and a risk of the formation of blood clots in IV cannulas.