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:
- IV cannulas: IV cannulas consist of short, flexible tubing doctors place into a vein.
- Nasal cannulas: Nasal cannulas consist of flexible tubing that sits inside the nostrils and delivers oxygen.
The purpose of the cannula varies according to its type.
Common uses of IV cannulas include:
- blood transfusions or draws
- administering medication
- providing fluids
According to UTMB Respiratory Care Services, doctors use nasal cannulas to:
- decrease work required to breathe
- decrease strain on the heart
- treat hypoxia or hypoxemia
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:
- They will ask the person to lie or sit down with one of their arms exposed and extended by their side.
- They will choose an insertion point in the person’s arm. This will usually be the person’s non-dominant side and will involve an area where the person’s veins are the clearest.
- They will clean this area with an alcohol wipe.
- They will tie a tourniquet above this area. A tourniquet is a band that doctors tie tightly to limit the flow of blood. It might feel uncomfortable, the doctor or nurse will only keep it in place for about a minute.
- They will inform the person they will feel a scratch, and they will insert the needle into the vein.
- The needle only serves to puncture the skin and vein so the cannula can be inserted into the vein. Once in the vein, the needle is withdrawn as the cannula slides over the needle and into the vein.
- The cannula is then secured in place with medical tape or a dressing, such as a wrap or special bandage.
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:
- They will ask the person to sit up straight, if possible, to expand their lungs.
- They will insert the flow meter into a power source and attach a nozzle.
- They will turn the flow meter on and check that the oxygen is coming through properly.
- They will place the nasal cannula into a person’s nose; the prongs on the cannula help it stay in place just inside a person’s nostrils.
- They will loop the tubing around a person’s ears and position the plastic slider under their chin so it stays stable.
- They will check the person is comfortable, and check the pressure of the cannula on the skin every 2 hours. They will check the flow rate every 4–8 hours.
At home nasal cannulas
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:
Peripheral IV cannula
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.
Central line IV cannula
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.
Sizes and flow rates
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.
Sizes and flow rates
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
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:
- Cannula: A cannula typically refers to a small plastic tubing that is inserted into part of the body with the aid of a needle that punctures the vein or vessel. The needle is then removed, leaving the cannula in place for easy access to withdraw or inject anything into the vessel.
- Catheter: A catheter is typically referring to a larger plastic tubing that is inserted into an area of the body that already has an opening, such as the bladder or an open wound that need needs assistance in draining.
IV cannulas and nasal cannulas can pose different risks.
IV cannulas present minor risks to a person. Some potential risks include:
- mild pain at the insertion site
- blood clot formation
- infection at the insertion site
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.