Intravenous infusion
Intravenous (IV) infusion refers to a medical process wherein a medical staff delivers medications and fluids to the bloodstream and other body compartments using infusion sets or IV sets.
Some of the drugs administered through the IV infusion include analgesics (for pain), sedatives (to calm the patient), antibiotics, chemotherapy agents (drugs for cancer), vasodilators (for dilating blood vessels), hormones, anesthetics (to put the patient to sleep), parenteral nutrition (infusion of nutrients), crystalloid solutions, and blood products.1
Medical experts classify infusions in the form of either intermittent or continuous. Some medical doctors administer an antibiotic intermittently. Medical workers infuse a specific dose of the medicine every 6 hours. On some occasions, a medical staff infuses an antibiotic continuously for severe or deep-seated infections.2
In some, the duration is short. Examples include the delivery of anesthetic agents and drugs for cardiac catheterizations (inserting a catheter into the patient’s heart). Anesthesiologists continue to infuse the drugs only during surgical operations. Cardiac surgeons and anesthesiologists only administer the needed medications while doing heart catheterizations. After the procedures, the medical staff terminates the infusion. Medical workers do all of these procedures only once and in a short time.
It is not repeated; hence, it is not intermittent or continuous. In some cases, the administration takes an indefinite duration, such as administering insulin for diabetic patients and infusing intravenous vasodilators to treat pulmonary hypertension.1 Medical expert considers this, too, as continuous infusion.
Components of an intravenous infusion system
Reservoir
Reservoir refers to the bag or big syringe containing the fluid and medications infused by the medical worker. The medical procedure requires using an infusion set if a bag serves as the reservoir. On the other hand, the medical staff uses a winged infusion set or scalp vein set if a syringe serves as the reservoir.1 In addition, medical workers may also use a winged infusion set with an IV set to administer infusion in children.
Tubing
Tubing refers to the transparent and flexible tube that connects the reservoir to the catheter. It delivers the content of the fluid bottle to the patient.1
Flow regulator
The flow regulator regulates the flow rate. Often, device manufacturers use a roller flow regulator or a roller clamp to perform this vital function.1
Percutaneous device
The percutaneous device, such as the hypodermic needle, pricks the venous blood vessel of the patient. It connects and anchors the infusion set to the patient.1
Driving forces for infusions
Gravity-driven
The force that propels the infusion comes from the gravitational pull. Thus, the location of the reservoir must be higher than the insertion site of the catheter.1
A mechanical pump propels the fluid infused by creating a positive displacement by consuming electrical energy. Hence, manufacturers of medical instrumentations define mechanical infusion pumps as equipment intended to regulate the flow of liquids into the patients under the influence of positive pressure generated by the pump.
The pump performs the following: to provide continuous flow only, non-continuous flow only, only discrete delivery of a bolus, or combinations of continuous, non-continuous, and bolus delivery.1
Factors affecting the flow rates
Variations in infusion sets
Medical staff and workers monitor and check the flow rate of a gravity-driven infusion by counting the drops seen in the drip chamber over one minute. This method assumes that the drop size is independent of other factors and the rate per minute remains the same throughout the infusion. This method poses a danger because, based on one study, the sizes and the number of drops/ml of an infusion set coming from different manufacturers vary. Thus, the flow rate from one infusion set differs from another.1
The vertical height of the reservoir
The height of the reservoir directly affects the flow rate. The higher the height is, the faster will be the flow rate.1
Resistance to flow
Gravity-driven infusion
Roller clamp
The roller clamp provides resistance to the fluid flow. IV set manufacturers installed such part on the infusion tubing to regulate the flow rate by rolling it up or down. However, the competence of this part varies over time. Consequently, it unintentionally allows different rates of drug and fluid delivery.1
Catheter’s diameter
The flow resistance is inversely proportional to the diameter of the catheter. Poiseuille’s Law governs this principle. This Law implies that the wider the diameter is, the faster the fluid flow because flow resistance is lower. The reverse is also true: the narrower the diameter, the slower will be the fluid flow because flow resistance is higher.1
Catheter’s length
The longer the catheter’s length is, the slower will be the fluid flow. This principle also arises from Poiseuille’s Law.1
The viscosity of drugs and fluids
Viscosity measures the ease by which fluid flows along a tube. Liquids with higher viscosity have a slower flow rate. Fluids with lower viscosity have a faster flow rate.1
Co-infused fluids
The presence of rapidly flowing co-infused fluid directly affects the flow rate. The greater the number of co-infused fluids is, the slower the flow rate will be.1
Mechanical pump infusion
Mis-programming
Mis-programming the mechanical pump poses a great danger to the lives of patients. The error alters the following: the flow rate, dose units, concentration of the drug, and dose. Any alteration in any of these very vital treatment parameters endangers the lives and safety of patients.1
Changing the vertical height
Changing the vertical height of the syringe pump alters the rate of delivering the fluid. Reduction of dose delivery occurs when medical staff lowers the syringe from the starting position. Bolus delivery happens when the medical worker raises the syringe pump to its original height.1
Drug adsorption
Sticking some drug molecules in a flexible tube, fluid bag or bottle, semi-flexible container (burette), or soft wall bag reduces the delivery of the fluid-containing medications. As much as 30% of the expected drug delivery fails to reach the patient’s systems.1
Syringe changeover
The reservoir of the drug in a syringe completely empties its content after some time. Accurate and uniform delivery of drugs discontinues if medical staff fails to provide prompt replacement or replenishment.1
Manifolds and infusion system dead volume
Multiple fluids flow
The simultaneous infusions of several fluids and drugs coming from the mainline and secondary lines slow down the flow rate.1
Configurations
Simultaneous infusions, consisting of the mainline, secondary line, and manifold use, slows down the flow rate. Manifold—a device interposed into the infusion system—provides additional sites for connecting other infusions.1
Dead volume
Medical experts define dead volume as the product of the distance between the point of entry into the primary infusion up to the distal tip of the intravascular catheter and the cross-sectional area of the tube. The longer the distance is and the wider the tube is, the greater will be the dead volume. If the fluid flow rate is low and the dead volume is significant, the delivery time will be longer. If the fluid flow rate is high and the dead volume is small, the delivery time will be short.1
Risk of an unintended drug bolus
The dead volume serves as a potential reservoir of drugs and fluids under infusion. Specifically, the drug accumulates in the dead volume if the fluid flow is interrupted. If the interruption is so prolonged, much medication gets collected that when the medical staff re-starts the flow, a bolus of the drug enters the patient’s system, possibly harming the patient.1
2 thoughts on “Critical Factors Affecting Flow Rate of Intravenous Therapy”
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Hi there,
Would changing from pvc bag to non-pvc bag has any impact on infusion flow rate?