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An intravenous (IV) infusion rate — usually expressed in cubic centimeters (cc) or milliliters (ml) per hour — is part of a physician's prescription for the fluid or medication to be administered. In US hospitals, most IV fluids are infused with a computerized IV pump to ensure accuracy. IV pumps, however, do not forcibly pump fluid into the bloodstream. Rather, they allow infusion of the medication at the prescribed intravenous infusion rate despite the relative height of the IV bag, and sound an alarm to notify nursing staff if it is unable to instill that amount. Many factors can affect the prescribed or actual intravenous infusion rate, including the IV cannula gauge, the location of the IV cannula, the condition of the patient's veins, and the patient's physical condition.
The IV cannula gauge, or catheter diameter, can limit an intravenous infusion rate. Larger cannula gauge numbers, with smaller diameters, have smaller maximum infusion rates than do large bore cannulae. For this reason, large bore cannulae are routinely placed in trauma patients, surgical cases and transplant patients who regularly require large infusions of IV fluids. For patients who require a large amount of IV fluid very quickly, large cannulae can easily handle a liter or more of fluid infused in minutes with an inflated cuff around the IV bag to force a fluid infusion beyond what gravity and an open line would instill. In the absence of an IV pump, gravity can influence an IV infusion rate as measured by the height of the IV bag above the patient's heart.
Another factor that can influence an intravenous infusion rate is the location of the IV cannula. The more peripheral the IV placement, the slower the maximum infusion rate as the veins are smaller further away from the heart. Thus, an IV placed in the hand can handle less fluid volume than can one placed in the antecubital fossa, also known as the inner elbow. Peripheral IVs in the hands or arms also can cause intermittent infusion interruptions when patients use their arms and crimp the blood vessels or the IV catheter is inadvertently placed against a vein valve. Central lines, such as those placed in the subclavian vein close to the front clavicles or collarbones, can safely accept a higher intravenous infusion rate than peripheral lines with fewer chances of interruption.
A patient's diagnosis can also limit a prescribed intravenous infusion rate in order to avoid risky complications. Patients suffering from congestive heart failure (CHF), kidney disease or other conditions necessitating fluid limitations require slower IV infusion rates. Finally, some IV medications — such as chemotherapy solutions — can only be infused at certain rates for the body to safely tolerate them.