Technique and equipment
While it is possible to maintain an intravenous (IV) infusion through a well-secured hypodermic needle, the general practice is to use a flexible catheter. There are two basic types, catheter-over-needle and catheter-in-needle.
For routine infusion in adults, the needle gauge -- the larger the number, the smaller the diameter -- is 18 or 20 gauge. In critical care or emergency situations, "large bore" access (16 or 14 gauge) is needed to transfer large volumes; multiple large-bore accesses often are established very early in trauma, since veins may not be accessible with fluid loss and declining blood pressure.
The basic technique of entering a vein is similar whether the intent is to draw a blood sample, administer an intravenous bolus of medication, or to insert an infusion catheter. Details are in a separate article.
In general, however, the technique involves first finding a suitable vein, often the antecubital or median basilic in the proximal forearm. A tourniquet is first applied, with enough pressure to stop venous return but not arterial flow. Palpation is often more reliable than appearance in locating the vein. While simple cleansing is adequate for the quick procedure, the site used for an infusion is prepared with the techniques of surgical skin sterilization.
The operator then holds the needle, attached to a syringe or other suitable holder, pulls the skin taut, positions the needle at an angle of 10 to 20 degrees from the skin surface, and pushes it gently but quickly into the vein. When the vein is successfully entered, blood will flow into the syringe, tubing, or other equipment. Experienced operators will sense a "pop" as the venous wall is entered, and usually flatten the angle of entry to be more in line with the vessel and not go through the far side.
A variation on the needle technique is a "cutdown", where a catheter is introduced through a small incision.
The choice of fluids has been reviewed with network meta-analysis which concluded that balanced crystalloids (lactate and acetate solutions) or albumin might be best. PlasmaLyte is an example of an acetate solution and Hartmann's and Lactated Ringer's are examples of lactate solutions. Solutions lower in chlorides such as Hartmann's solution and Lactated Ringer's solution, may cause less acute kidney injury when administered to adults in intensive care. Likewise hydroxyethyl Starch should be avoided.
Complications are not reduced by routinely changing catheters.
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