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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 the physic, the
Hagan-Pouseille equation is derived.
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| 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 of gas, liquid or vapor.
Flow: (F) = Quantity (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 velocity.
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 resistance is
constant.
Resistance (R) = ∆P / ∆Q
Factors
affecting the flow
1) Tube diameter.
a) Flow is directly proportionate
to d^4. If the diameter of the tube is halved, then the flow is reduced to
1/16.
b) 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.
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 line compared to peripheral IV 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.
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. |
 |
| Second Generation Bone Injection Gun (B.I.G) |
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| A: Triple Lumen Central Venous Line, B: Single Lumen Central Venous Line, C: Single lumen Central Venous line |
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| 24 gauze branulla for neonate age group. It provides about 23 ml/min fluids. |
 |
| 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 |
 |
| 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. |
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.
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