Most failed cannulations are lost before the needle comes out of its packet. The vein was
chosen badly, or it was never going to fill, or the arm was in the wrong place, or the operator was
standing somewhere that made their own hand unsteady.
This is a manual skill, and reading about it will not give it to you. What reading can do is remove the
four or five errors that account for most failures, so that the practice you get is practice at the right
thing.
Before you touch anything
- Decide what the line is forA single dose of antibiotic and a resuscitation are different
problems. Flow rises with the fourth power of the radius and falls with length, so a short wide cannula
in a proximal vein is what you want for volume, and a small cannula in a good vein beats a big one in a
bad vein for everything else.
- Get the patient warmThe single most useful thing you can do, and the most neglected.
A cold peripherally shut-down arm has no veins in it. Warm packs, warm water, a blanket for a few
minutes: the vein you could not find appears.
- Position before you prepareArm below the level of the heart, supported so the patient is
not holding it up, and the limb rotated so the vein faces you. Then set your own height and stand so your
dominant hand is not crossing your body.
- Choose with your finger, not your eyeA vein you can feel is better than a vein you can
see. Palpate for something soft, bouncy and compressible. A hard cord is thrombosed, a pulsatile one is
not a vein, and a blue line visible under thin skin may be too fragile to hold anything.
Where to go
Forearm, dorsal and volar
The best all-round choice and the most under-used. Long straight segments, well supported by
surrounding tissue, away from joints so the line survives movement, and comfortable for the patient.
Start here and work proximally.
Dorsum of the hand
Easy to see and easy to enter, but small, mobile, uncomfortable, and positional. A reasonable first
line for a short admission and a poor one for anything that must keep running.
Antecubital fossa
Big, reliable, and the right answer in an emergency or when you need volume. The cost is that it sits
across a joint, so it kinks and occludes, and it uses up a vein you may want later for a midline or a
PICC. Not a first choice in someone who will be in hospital for weeks.
Feet, and the external jugular
Both work and both have a price. Foot veins carry a higher infection and thrombosis risk and are
usually avoided in adults, particularly in diabetes. The external jugular is a legitimate peripheral
site when the arms have failed, with the patient head-down, but it is uncomfortable and easily
dislodged.
Arms that are not available
The side of a mastectomy or axillary clearance, an arm with a dialysis fistula or graft, a limb with
lymphoedema, and the affected side after a stroke. Avoid cannulating distal to a previous failed attempt
in the same vein, because the fluid will come out of the earlier hole. Ask the patient which arm people
usually use: they know, and they are almost always right.
Doing it
- Tourniquet, then wait. Firm enough to obstruct venous return but not the pulse, about
a hand's breadth above the site. Then leave it for a minute rather than five seconds. Let the arm hang,
ask the patient to open and close the hand a few times, and tap gently rather than slapping.
- Clean, and let it dry. Alcohol chlorhexidine, thirty seconds of contact, then dry
properly. Wet skin stings on puncture and the antisepsis has not worked yet. If you palpate again after
cleaning, you have to clean again.
- Anchor the vein. This is the step people skip and it is the one that decides the
outcome. Use the thumb of your non-dominant hand to put traction on the skin two to three centimetres
below the entry point, pulling towards you, and hold it there for the whole procedure. Veins roll
because nobody is holding them.
- Enter shallow. Ten to thirty degrees, bevel up, through the skin and then towards the
vein as a separate movement. Steeper than that and you go through the back wall.
- First flashback is the needle, not the cannula. When you see blood, the metal tip is
in the lumen and the plastic is still a few millimetres short. Drop the angle almost flat and advance the
whole assembly two to three more millimetres before you do anything else.
- Then advance the cannula off the needle. Hold the needle absolutely still and slide
the plastic forward with your finger. If it will not go, do not force it and do not re-advance the
needle through the cannula — that shears it.
- Release the tourniquet before you connect anything. Then press over the cannula tip,
withdraw the needle fully into its safety device, and dispose of it before your hands do anything
else.
- Flush, look, and secure. Ten millilitres of saline. It should run freely with no
swelling, no pain and no resistance. Secure it so the hub cannot move, date it, and document the site and
gauge.
The thing nobody warns you about
The flashback chamber lies to beginners. Seeing blood feels like success, and the
instinct is to stop and advance the plastic. That instinct is the single commonest cause of a cannula
that will not thread, or that flushes into the tissues. The needle is longer than the cannula by design.
Whatever your hands want to do at the moment of flashback, the answer is flatten and advance a
little further first.
The patient who is genuinely difficult
- Know it before you startIntravenous drug use, chemotherapy, dialysis, obesity, oedema,
dark skin where visual inspection helps less, chronic illness with hundreds of previous attempts, and
the very young. Recognising a hard stick in advance changes who should be doing it, not just how.
- Use the ultrasound earlier than you thinkFor deep or impalpable veins it converts a hard
procedure into an ordinary one. The basilic and the deep brachial veins are the usual targets. It needs
a longer cannula, because a standard one will fall out of a deep vein once the swelling settles.
- Two attempts, then hand overThis is a discipline, not a weakness. After two failures your
hands are less steady, the patient is less cooperative, and the next person is more likely to succeed on
their first go than you are on your third. Say so out loud and ask.
- And know when the answer is a different routeIf the patient needs access now and does not
have it, stop cannulating. That is what
intraosseous access is for, and the commonest error
with it is doing it late.
Afterwards
Phlebitis is the common one, and it rises with dwell time, with cannula size relative
to the vein, and with irritant infusions. Look at the site every shift and take it out when it is done
rather than when it fails. Extravasation is the one that causes lasting harm, and the
drugs that do the damage — vasopressors, concentrated potassium, cytotoxics, calcium —
should not be running through a peripheral line you would not defend. Infection follows
cannulas that nobody has thought about for days, which is why the date on the dressing matters.
And the line that is not being used is not harmless. If nothing has gone through it since yesterday,
ask whether it should still be there.
Challenge for you
What was the one thing that finally made your cannulation work?
Almost everyone has a moment when it stopped being luck — something somebody said, or a habit they
made you adopt. For some people it is the traction thumb. For others it is warming the arm, or waiting
longer with the tourniquet, or simply standing somewhere different. Send me yours and I will collect them
into a piece, because this is exactly the kind of knowledge that never makes it into a textbook.
Send me your one thing
The button opens a reply straight to me. If your device blocks it, write to
icuandyou@icloud.com instead.