How to insert a cannula

From WardWiki - Foundation Doctor Helper

Cannulation is a core skill for any doctor and is a relatively easy one to learn initially but can be surprisingly hard to master. It makes for an ideal DOPs and should be one of the first to be done on the first rotation. It becomes clear soon enough that venous cannulation is part of the bread and butter of ward work. Insertion of a central line is completely different skill.

Contents 1 Indcations 2 Complications 3 Preparation 4 Choosing a site 5 The procedure 6 When things become difficult 7 Cannulae guide

Indcations

All patients admitted through A&E should have a cannula sited. Patients may quickly decompensate and siting of a cannula may become unnecessary stressful and difficult if not sited early. The cannula is most commonly used to to give fluids, medication and blood products. While siting the cannula it can also be used to obtain a blood sample.

Complications

• Haematoma formation
• Infiliteration of medication into surrounding tissues
• Embolism; that can be air, thrombus, fragment of catheter breaking of and entering into blood stream
• Phlebitis; inflamation of vein

Preparation

1. Check if patient really needs a cannula
2. Prepare and assemble necessary equipment
3. Remember to bring a sharps bin
4. Check if patient needs bloods taken (relieves the patient from an extra stab with the needle)
5. Explain to the patient what you intend to do and why. Obtain verbal consent

Choosing a site

• Try to find a vein as distally as possible. That saves the proximal veins for later use
• Dorsum of the hand is useful in patients needing long term treatment. Siting may be painful and patients need pre-warning
• Antecubital fossae is the place of choice in emergencies, were a large bore needle with high fluid flow is needed. Try to avoid this area in other cases

The procedure

1. Tighten a tourniquet around he appropriate limb and identify an appropriate vein
2. Clean the insertion site with alcohol/chlorhexidine
3. Hold the cannula so that you will be able to see blood entering the transparent flashback chamber. Keep the bevel facing upwards. Stretch the skin with the thumb of your non-dominant hand
4. Insert the cannula, aiming for the vein, until you get a flashback of blood
5. Insert the cannula slightly further - remember that the plastic sleeve of the cannula does not extend right to the tip of the trocar
6. Hold the trocar still with your dominant hand and slide the plastic cannula forward with your other hand
7. Compress the vein over the tip of the cannula to prevent blood entering the cannula, withdraw the trocar and dispose of it immediately in the sharps bin
8. Continue to compress the vein and flush with 10 mls normal saline. Place a bung on the end of cannula after flushing
9. Secure the cannula in place with a transparent adhesive dressing
10. Document procedure in patients notes

When things become difficult

Do not give up after one try, you still have one left.

• Take a deep breath and take your time
• Try the other hand
• Try a more proximal vein
• Place patients arm well below level of the heart
• Try the hand in warm water trick
• Try NG spray on vein
• Try a higher gauge cannula
• Avoid feet if you can (DVT risk)
• Try not using a tourniquet (old fragile veins may pop under higher pressure)
• Learn to operate the ultrasound for guidance
• When you experience haemolysis of your blood samples taken when cannulating, you are either using a too large gauge cannula or the flow rate is to high crushing all the red blood cells. Solution may be using a smaller gauge cannula or a syringe collecting the blood so you can control the flow rate of the blood collection

Cannulae guide

Cannula size colour code

Colour code	Gauge	Ext. dia. (mm)	Length (mm)	Flow rate ml/min
Orange	G14	2.1	45	300
Grey	G16	2.1	45	172
Green	G18	1.3	45	76
Pink	G20	1.0	33	54
Blue	G22	0.8	25	31
Yellow	G24	0.7	19	14