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Critical Factors Affecting IV Flow Rate

critical factors affecting flow rate of intravenous therapy

Intravenous infusion

IV therapy 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. During the infusion process, the medical staff should pay attention to the IV flow rate which is affected by the variations of IV sets, height of the reservoir, resistance, drug adsorption, syringe changeover, and dead volume.

Components of an intravenous infusion system

A complete infusion system is assembled by a reservoir, tubing, drip chamber, flow regulator, and percutaneous device. The assembly process should be carried out in a clean room of class 100,000.


Reservoir refers to the bag 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. 

Drip chamber

A drip chamber serves as a crucial component in medical systems, particularly in contexts such as intravenous therapy, where it plays a pivotal role in preventing the downstream passage of gases. Its primary function is to facilitate the upward release of gas from the liquid, ensuring a safe and controlled flow. This is especially vital in safeguarding against air embolisms, a condition wherein blood vessels can become obstructed due to the presence of gases in the circulatory system.


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 IV 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


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

Mechanical pump infusion

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 IV flow rate

Variations in infusion sets

The formula for calculating the IV flow rate (drip rate) is: Total volume (in mL) Divided by time (in min) Multiplied by the drop factor (in gtts/mL).

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 IV 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 IV 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

Tubing diameter

The flow resistance is inversely proportional to the diameter of the tubing. 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

Tubing length

The longer the tubing 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 IV 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 IV flow rate. The greater the number of co-infused fluids is, the slower the flow rate will be.1

Mechanical pump infusion


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


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

Company Introduction

Liaoning KANGYI Medical Equipment Co., Ltd was founded in 1994 and is one of the leading manufacturers of IV sets, syringes, and medical parts in China. Quality is our highest priority, and our quality assurance system is certified and meets the standards of the Chinese National Medical Products Administration, ISO 13485, and the European Union’s CE mark.

We produce over 600 million pieces per year. Our products are sold across China and exported worldwide, to destinations including Europe, South America, Russia, Africa, and the Middle East.

Our company employs over 300 staff, including 50 people working in engineering and technical management. Our premises occupy an area of 20,000 square meters, with a construction area of 15,000 square meters. This space includes a 100,000-class purification workshop that occupies 8,000 square meters.

If you want to know more about us and talk face to face, we welcome you to visit our booth in CMEF Shanghai and Hospitalar in Brazil.

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2 thoughts on “Critical Factors Affecting IV Flow Rate”

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  2. Medical Information

    Hi there,
    Would changing from pvc bag to non-pvc bag has any impact on infusion flow rate?

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