Cannulating in difficult circumstances
Cannulation in the Emergency situation isn't always straight forward. The difficulty for you as a Paramedic is that you will almost certainly be doing this in a patients home or workplace so you've got to take care not to spill any blood. The other main problems are convulsions, profuse sweating, aggression/agitation, peripheral venous shut down, lighting and environmental conditions.
A Patient suffering a convulsive episode will prove pretty difficult cannulate as the arms are usually bent rigid and the patient's body is shaking. Any Patient with internal rotation of the arms can be cannulated more easily by placing them on the ambulance trolley first. Gently straighten out one of the patients arms and tape the wrist to the side bar of the trolley. Access to the dorsum of the hand and to the Ante Cubital Fossa is greatly improved. Turn the side bar of the trolley down to 90° for even better access. Make sure the tape is not too tight as this sometimes affects venous return and this will affect your cannulation attempt. When you've finished cannulating secure the cannula and then release the tape. Another method is to put the patients hand under the trolley bar, curl their fingers up around the bar as if they were gripping it and put a piece of tape around their fingers to secure in position.
Some patients will sweat profusely. Keeping an IV cannula in-situ is difficult with standard iv tape dressings. In these cases put two circumferential wraps of tape around the dressing. One at the distal end of the cannula and one around the end cap. make sure the end cap is secure before you do this. If you are going to give IV fluids do the same around the cap after you have attached the IV line. Another option is to secure the cannula in place with a small dressing. Cut off any absorbent or gauze section and wrap the dressing around the cannula site and tape down to secure.
In Cardiac arrest
In cardiac arrest get the patient on to the trolley asap and raise the legs (trendellenburg position), or if you cannot gain access with a trolley, raise the legs with whatever you can this auto-transfusion will flood the upper veins and give you a better chance at a successful cannulation. It also gives a better patient arm position as the patients arm will naturally fall downwards and externally rotate giving a good view of the Ante Cubital area.