1. The Physic of Flow in Relation to Intravenous Access’s Size Selection.
Muhamad Na’im Bin Ab Razak, M.D USM
In emergency setting, the crucial part in managing patient is delivering of fluids or medication
through the Intravenous (IV) Access. Many factors
serve the purpose of the treatment.
In order to select the proper size of IV access, we need to understand the physic of flow. From
the physic, the Hagan-Pouseille equation is derived.
To understand the derived formula, we need understand about the concept of flow. It is being
defined as the quantity of the fluid that passes a point per unit. The fluid may also exist in form
of gas, liquid or vapor.
Flow: (F) = Quantity (Q) / Time (t)
Or also known as Rate of change of mass or volume (
There are two type of flow which are 1) Laminar, and 2) turbulent.
In case of flow through IV access, it is represented by the laminar flow and hence will be
discussed here. Laminar flow occurs when fluid flows through a tube and the rate of flow is low.
In laminar flow, the molecule of fluids will be moving in a numer
velocity.
www.jacknaimsnotes.com
The Physic of Flow in Relation to Intravenous Access’s Size Selection.
Muhamad Na’im Bin Ab Razak, M.D USM
In emergency setting, the crucial part in managing patient is delivering of fluids or medication
through the Intravenous (IV) Access. Many factors will influence the selection of the IV size to
serve the purpose of the treatment.
In order to select the proper size of IV access, we need to understand the physic of flow. From
Pouseille equation is derived.
The Hagan-Pouseille equation
To understand the derived formula, we need understand about the concept of flow. It is being
defined as the quantity of the fluid that passes a point per unit. The fluid may also exist in form
(Q) / Time (t)
Or also known as Rate of change of mass or volume (∆Q)
There are two type of flow which are 1) Laminar, and 2) turbulent.
In case of flow through IV access, it is represented by the laminar flow and hence will be
discussed here. Laminar flow occurs when fluid flows through a tube and the rate of flow is low.
In laminar flow, the molecule of fluids will be moving in a numerous layer with different
www.jacknaimsnotes.com
The Physic of Flow in Relation to Intravenous Access’s Size Selection.
In emergency setting, the crucial part in managing patient is delivering of fluids or medication
will influence the selection of the IV size to
In order to select the proper size of IV access, we need to understand the physic of flow. From
To understand the derived formula, we need understand about the concept of flow. It is being
defined as the quantity of the fluid that passes a point per unit. The fluid may also exist in form
In case of flow through IV access, it is represented by the laminar flow and hence will be
discussed here. Laminar flow occurs when fluid flows through a tube and the rate of flow is low.
ous layer with different

2. If the mean velocity of the flow is v, then the molecules at the center of tube are twice the
velocity (2v) and the flow of molecules at the side of the tube is stationary.
In order for the flow to take place
of a tube. The greater the pressure gradient, the greater flow would be.
Resistance will occur between the fluid and the opposing vessel wall against the flow. This
resistance is constant.
Resistance (R) = ∆P / ∆Q
Factors affecting the flow
1) Tube diameter.
a) Flow is directly proportionate to d
reduced to 1/16.
b) This will explain why fluids flow more rapidly through the large bore
14, 16 and 18 gauze branulla is selected during resuscitation.
2) Length
a) If the length is doubled, then the flow is halved. Flow is inversely proportionate to the
length of tube.
b) This explains why the fluids flow slower through central
access even though the internal diameter is similar.
3) Viscosity
a) As the viscosity increases, the flow decreases proportionately.
b) Due to this fact, I prefer crystalloid during the initial phase of resuscitation of
trauma patient followed by colloid and blood product.
www.jacknaimsnotes.com
If the mean velocity of the flow is v, then the molecules at the center of tube are twice the
velocity (2v) and the flow of molecules at the side of the tube is stationary.
In order for the flow to take place, we need a different pressure gradient (∆P) between the ends
of a tube. The greater the pressure gradient, the greater flow would be.
Resistance will occur between the fluid and the opposing vessel wall against the flow. This
Flow is directly proportionate to d4
. If the diameter of the tube is halved, then the flow is
This will explain why fluids flow more rapidly through the large bore IV Access and size
14, 16 and 18 gauze branulla is selected during resuscitation.
If the length is doubled, then the flow is halved. Flow is inversely proportionate to the
This explains why the fluids flow slower through central line compared to peripheral IV
access even though the internal diameter is similar.
As the viscosity increases, the flow decreases proportionately.
Due to this fact, I prefer crystalloid during the initial phase of resuscitation of
nt followed by colloid and blood product.
www.jacknaimsnotes.com
If the mean velocity of the flow is v, then the molecules at the center of tube are twice the
∆P) between the ends
Resistance will occur between the fluid and the opposing vessel wall against the flow. This
. If the diameter of the tube is halved, then the flow is
IV Access and size
If the length is doubled, then the flow is halved. Flow is inversely proportionate to the
line compared to peripheral IV
Due to this fact, I prefer crystalloid during the initial phase of resuscitation of

3. www.jacknaimsnotes.com
4) Pressure gradient
a) As being explained before, the greater the pressure gradient, the greater flow
would be.
b) The higher the height of the gravity system, the greater flow would be.
c) Manually compressing the lower drip chamber and usage of pressure bag will
increase the flow of fluid during the resuscitation.
5) Multi lumen extension
If you attach the multi lumen extension into the large bore IV branulla and run multiple
fluids spontaneously, it will reduce the flow up to 76%.
IV Vascular Access in Emergency Department
Pediatric intraosseous line for difficult IV Access in pediatric group.
EZ-IO Drill and Needle.

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Second Generation Bone Injection Gun (B.I.G)
A: Triple Lumen Central Venous Line, B: Single Lumen Central Venous Line, C: Single lumen
Central Venous line
24 gauze branulla for neonate age group. It provides about 23 ml/min fluids.

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22 Gauze branulla for pediatric size. It provides about 36 ml/ min fluids
20 gauze size branulla. It provides about 61 ml/min fluids
18 gauze size branulla. It provides about 96 ml/min fluids

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16 gauze size branulla. It provides about 196 ml/min fluids
14 gauze size branulla. It provides about 300 ml/min fluids
14 gauze size Angiocath. It provides about 210 ml/min fluids. Note that even though the internal
diameter is 14 gauze similar to the branulla, but the length is more than branulla, hence reducing
the flow of the fluids.

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In short, the selection of IV Access
a) Large bore branulla for pediatric size is 22, 20 and 18
b) Large bore branulla for adult size is 18, 16 and 14
c) Most of the antibiotics are irritant to the vessel; hence selecting the smaller size branulla will
reduce the complication.
d) Central venous access may be obtained if failed to get peripheral line. It is preferable to use
angiocath rather than triple lumen/short line or long line
Reference
D.M Levine, A.L Garden, H.T Truong et al, "Influence of multi-lumen extensions on fluid flow
through intravenous cannulae", Anaesthesia, The Association of Anaesthetists of Great Britain
and Ireland, 2013
M. D. S TONEHAM, "An evaluation of methods of increasing the flow rate of i.v. fluid
administration", British Journal of Anaesthesia 1995;75: 361–365.
Anesthesiology note.