I have had a few emails from nurses asking how they should best select the location to place a cannula. Here are some tips based on my own personal experience. You may well disagree with them, or you may have some better ideas of your own. Lets have a look.


I think 80% of the trick in performing a successful cannulation is in taking time to prepare your equipment and selecting the best available site.


  • Long and Large: You want to pick a a large vein and then put a large cannula into it. In the emergency department setting we often need to deliver large volumes of fluid over short times. The larger the vein and the larger the cannula, the less resistance to rapid flows.
  • Pure and Pink:There should be no evidence of thrombosis or damage to the valves from previous attempts at cannulation. The target area should be well perfused. It should not be in a zone of acute burns, wounds or infection. You should avoid attempting to cannulate over a bony prominence.
  • Safe and secure: You should also consider both the security of the cannula and the comfort of the patient when considering placement. A cannula placed at the cubital fossa is likely to kink off every time the patient bends their arm. It can also be quite uncomfortable. Similarly, a cannula placed in the back of the hand is also likely to kink with movement of the hand. For some reason placing cannulas in the back of a patients dominant hand seems to be a favorite site for junior doctors.

scope the lay of the land.

OK. Before we begin machete-ing our way into the circulation, let us tighten up the tourniquet and give the veins a little time to fill. Some people swear by using an inflated BP cuff instead of a tourniquet to really buff up those veins. Other tricks used to get a little vein-o-erection include placing warm towels over the area, briskly tapping or slapping the area, letting the arm hang down over the edge of the bed (before applying tourniquet) , and even using vasodilatory creams such as Nitrobid paste ( this sounds a little dicey to me). Start by inspecting the non-dominant arm, but if you cant find anything jumping out at you, check the other arm. Don’t forget to inspect the entire surface of the arm. Quite a few times I have battled to get a line in only to find veins the size of a garden hose on the underside of their arm. Never underestimate the importance of palpating. More experienced cannulators will probably tell you that they rely more on feel than on sight when searching for a vein.

ground zero.

Once the veins are on show… look to see if you have one that bifurcates ( like the inverted Y pictured). These veins are simply begging to be cannulated, and its a simple matter of inserting your needle through the bifurcation and up into the root vein. Sweet. One mistake many people make when attempting to access a straight vein is to approach from above. More often than not the vein will *roll* away from the needle. Particularly in older patients with more, well, older connective tissues. Approach from the side whilst at the same time stabilizing the vein with your other hand by applying gentle traction to the skin. Over time you can develop quite a sensitivity to the actual layers of resistance. The skin will often require some force to pierce, but don’t push too hard. Once through the skin the needle will advance easily until you feel a subtle ‘pop’ as you enter the vein. Advance the needle slowly to avoid skewering right through the vein. Known as pranging the vein. [Related articles: Zen and the art of cannulation. How to secure a cannula. Needle stick injuries. ]

8 Responses to “where to place a cannula.”

  1. This is a wonderful and very revealing piece. As an A&E Nurse, I have had some occasions where setting up a line seem like eternity. Like the writer rightly puts it, the larger the vein the easier your access and the faster the flow. One key to effectiveness and proficiency in cannulation is consistent practice. The more you cannulate, the better you become.

  2. [...] posts: Where to put a cannula. How to put a cannula. How to secure a [...]

  3. If your patient has “bad veins”:

    1) Go for the forearm. Forearm veins, however, don’t usually just pop right out at you (they do on young males sometimes). If it’s purple, straight, and you can see it, go in at a low angle with a #20 or #18 until you get flashback. At least in my facility, floor nurses are scared of forearm veins. It’s like there’s nothing between the hand and the AC, so many of these veins are virgins. YOU DON’T NEED TO BE ABLE TO FEEL IT TO STICK AN IV IN IT.
    2) If there are no forearm/hand/AC veins, look up in the biceps or near the shoulder. I’ve found a few ginormous veins up there on people who have told me that “anesthesia” normally puts their IVs in.
    3) Look in the watch area. Remove the watches. There are ginormous wrist veins hiding under there. You’d be violating the “don’t put an IV in over a bony prominence” rule. Yeah, it’s a crappy spot, but it’s better than nothing.
    4) Last ditch effort. Carefully go for the #22 in all those squiggly veins near the radial artery. Usually one of them is straight enough for something. This is more for a medical patient who doesn’t need rapid infusion.
    5) I’ve found hidden veins using the double tourniquet. One tourniquet is good, two tourniquets is better if you can’t find a vein.

  4. Glad to read that slapping is passe, I don’t get much from watching the poor victim pump their fist either.
    Hanging the arm down seems to be the only trick, taking about the footie weather or something else irrelevent helps as well (and practice)

  5. The only thing I’d add to this, from my IV therapy nurse experience, is to ditch the tourniquet on the most elderly patients – especially anyone with very fragile skin and significant bruising from previous IV access attempts.

    On those patients, I use my non-dominant thumb to occlude the vein while I pull the skin taut. As soon as I see a flash, I loosen the pressure or remove the thumb entirely and slide the cannula off the stylet into the vein. If you’ve got the limb (usually the arm) below the level of the heart, the vein will stay filled long enough.

  6. Thanks Molly and Jen, some great points. Maybe I should have said tap not slap. Slapping should only be used on doctors…I’m kidding.
    And the point about getting comfortable yourself is very important. How many times have you seen someone crouched over in a stress position whilst they attempt to get a line in?
    Thanks for the tips.

  7. I agree, ban slapping forthwith, bad habit, not necessary and does’t work.
    Here are some simple alternatives, don’t bother to try IV cannulation on a cold arm / hand, unless of course its an emergency.
    Getting the client to hold a hot pack and wrap the whole limb in a towel should be enough to perfuse. I have got clients to soak in hottish water and that really gets them pumpin’.
    After the limb is warm and dry, hang the arm as low as you can for at least a minute BEFORE putting on tourniquet above elbow. Then bring arm up, palpate, plan then puncture last of all, and don’t forget to warn the client of imminent ‘sting’ so they inhale, not jump away from you. Try to be in a comfortable position yourself, this is most important.

  8. Ian, I have to get on my soapbox here about the slappers. I have watched nurses slap or flick people’s veins and seen the patient wince (or sometimes even say “OW!”), and the nurse responds with “Sorry, honey, I have to get the vein up.” I’ve also seen nurses do this with patients on anticoagulents or with other coagulopathies and watched as the arm bruised up, ruining any chance of getting a site anywhere. The patient comes to us to be cared for, not roughed up. Were I in the patients’ position, I’d slap the nurse back!

    Vigorously rubbing, swabbing with alcohol, hanging the limb down (gravity works!) have all worked just as well in my experience.

    Off soapbox now.

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