a report by

S t e v e Ma r t i n

Assistant Professor, Physician Assistant Program,

College of Allied Health and Nursing, Nova Southeastern University

I n t r a v e n o u s D e v i c e s

There are many types of intravenous (IV) needlesand catheters:

S t e e l N e e d l e s

An example of a steel needle is the butterfly catheter(see Figure 1), named after the wing-like plastic tabsat the base of the needle. They are used to deliversmall quantities of medicines, to deliver fluids via thescalp veins in infants and, sometimes, to draw bloodsamples (although not routinely, since the smalldiameter may damage blood cells). These are small-gauge needles (i.e. 23-gauge).

Over-the-needle Catheters

An example of an over-the-needle catheter is theperipheral-IV catheter (see Figure 2). A close-up viewof the catheter/needle tip is provided in Figure 3.

Ins ide-the-needle Catheters

Figure 3 depicts an inside-the-needle catheterarrangement.

G a u g e s

Catheters (and needles) are sized by their diameter,which is called the gauge. The smaller the diameter,the larger the gauge. Therefore, a 22-gauge catheteris smaller than a 14-gauge catheter. Obviously, thegreater the diameter, the more fluid can be delivered.To deliver large amounts of fluid, a large vein shouldbe selected and a 14- or 16-gauge catheter used. Toadminister medications, an 18- or 20-gauge catheterin a smaller vein will suffice (see Figure 4).

I V F l u i d s

IV fluids are usually provided to achieve thefollowing:

• provide volume replacement;• administer medications, including electrolytes; and• monitor cardiac functions;

An example of this is a patient who comes into anaccident and emergency department withgastroenteritis and is dehydrated from vomiting anddiarrhoea. Acutely, the patient receives a fluid bolusto expand his/her intravascular volume. Thepatient’s blood chemistry shows that his/herelectrolytes are outside of the normal parameters, sothe IV fluid is adjusted to bring them within normalparameters. The patient is also given medication fornausea via his/her IV and will remain onmaintenance IV fluids until he/she is able to drinkadequate amounts of fluids.

There are three main types of fluids:

• isotonic fluids;• hypotonic fluids; and• hypertonic fluids.

I s o t o n i c F l u i d s

Isotonic fluids are close to the same osmolarity asserum. They remain inside the intravascularcompartment, thus expanding it. They can be helpfulin hypotensive or hypovolemic patients, however,they can also be harmful. There is a risk of fluidoverloading, especially in patients with congestiveheart failure and hypertension. An example isprovided in Figure 5.

H y p o t o n i c F l u i d s

Hypotonic fluids have less osmolarity than serum (i.e.less sodium ion concentration than serum). It dilutesthe serum, which decreases serum osmolarity. Wateris then pulled from the vascular compartment intothe interstitial fluid compart-ment. As the interstitialfluid is diluted, its osmolarity decreases, which drawswater into the adjacent cells.

Hypotonic fluids can be helpful when cells aredehydrated, such as those of a dialysis patient ondiuretic therapy. They may also be used forhyperglycaemic conditions such as diabeticketoacidosis, in which high serum glucose levelsdraw fluid out of the cells and into the vascular andinterstitial compartments.

In t ravenous Therapy

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Reference Section

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Steve Martin is the AssistantProfessor of the Physician Assistant

Program in the College of AlliedHealth and Nursing at Nova

Southeastern University. He is alsothe Associate Program Director of

the Master of Medical ScienceProgram and the Director of thePhysician Assistant PostgraduateProgram in Family Medicine at

Nova Southeastern University, wherehe also lectures on the clinicalprocedure of intravenous (IV)

therapy. Mr Martin is a fellow andmember of the American Academy

of Physician Assistants and amember of American Academy of

Physician Assistants. He has been aphysician assistant since 1996 and

has had clinical experience atPlains Medical Center, Colorado, and

Aiken Regional Medical Center,South Carolina. He is currently

studying for a PhD in InternationalHealth at Touro University

International College of HealthSciences, and completed his MastersDegree in Physician Assistant Studies

at the University of NebraskaMedical Center in 1999.

In t ravenous Therapy

Hypotonic fluids can be dangerous to use because ofthe sudden fluid shift from the intravascular space tothe cells. This can cause cardiovascular collapse andincreased intracranial pressure in some patients. Anexample is provided in Figure 6.

H y p e r t o n i c F l u i d s

Hypertonic fluids have a higher osmolarity thanserum. They pull fluid and electrolytes from theintracellular and interstitial compartments into theintravascular compartment and can help stabiliseblood pressure, increase urine output and reduceoedema. They are rarely used in the pre-hospitalsetting and care must be taken with their use.Hypertonic fluids can be dangerous in the setting ofcell dehydration. An example is provided in Figure 7.

There are two main groups of fluids:

• crystalloid; and• colloid.

C r y s t a l l o i d

Crystalloids are isotonic and remain isotonic andare, therefore, effective volume expanders for ashort period of time. However, both the water andthe electrolytes in the solution can freely cross thesemipermeable membranes of the vessel walls (but not the cell membranes) into the interstitialspace and will achieve equilibrium in two to three hours. They are ideal for patients who needfluid replacement.

When using an isotonic crystalloid for fluidreplacement to support blood pressure from bloodloss, it should be borne in mind that threemillilitres of isotonic crystalloid solution are neededto replace one millilitre of patient blood. This isbecause approximately two-thirds of the infusedcrystalloid solution will leave the vascular spaces byabout one hour.

Generally, a good rule of thumb is that initialcrystalloid replacement should not exceed three litresbefore whole blood is instituted. Continued use ofcrystalloids runs the very real risk that the fluid thathas leaked into the interstitial space will result inoedema, primarily in the lungs (pulmonary oedema).Examples are Lactated Ringer’s, normal saline.

C o l l o i d

Colloids contain molecules (usually proteins) that aretoo large to pass out of the capillary membranes andtherefore remain in the vascular compartment. Thelarge protein molecules give colloid solutions a veryhigh osmolarity. As a result, they draw fluid from the

interstitial and intracellular compartments into thevascular compartment. They work well in reducingoedema (as in pulmonary or cerebral oedema) whileexpanding the vascular compartment.

Colloids can produce dramatic fluid shifts and placethe patient in considerable danger if they are notadministered in a controlled settings. Examples arealbumin and steroids.

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Figure 1: Butterfly Catheter

Figure 2: Inside-the-needle Catheter

Figure 3: Midline and Extended-dwell Catheters

Figure 4

V e i n S e l e c t i o n

Generally speaking, the vein section with thestraightest appearance should be selected. A vein thathas a firm, round appearance or feel when palpated

should be chosen and areas where the vein crossesover joints should be avoided.

If the IV treatment is for a life-threatening illness orinjury, choice may be limited to an area thatremains open during hypoperfusion. Otherwise, IVaccess needs to be limited to the more distal areas ofthe extremities.

D o r s a l D i g i t a l V e i n s

Dorsal digital veins flow along the lateral portion ofthe fingers and are joined to each other bycommunicating branches. They are available for IVsaccommodating a small-gauge IV catheter (22- or24-gauge) and need to be properly supported with atongue blade or hand board. Dorsal digital veins areusually not very stable and not a primary site choice.

M e t a c a r p a l V e i n s

Metacarpal veins are formed by the union of digitalveins (dorsal venous area) and are ideally positionedfor IV use – primary choice IVs. Venipuncture

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Reference Section

Figure 5: Lactated Ringer’s, Normal Saline or 0.9%

Saline in Water

Isotonic fluids contain an approximately equal number of molecules (blue dots) as

serum so the fluid stays within the intravascular space. Fluid flows from an area of

lower concentration of molecules to an area of high concentration of molecules

(osmosis) to achieve equilibrium (fluid balance). In this example, there is no fluid

flow into or out of the intravascular space.

Hypotonic fluids contain a lower number of molecules than serum so the fluid shifts from the intravascular space to the interstitial space (represented by the green arrows).

This decreases the interstitial space osmolarity (because of the increase of fluid and constant number of molecules within it), which then causes fluid to move into the cells.

Note that the green arrows represent fluid movement, not molecule movement.

Hypertonic fluids contain a higher number of molecules than serum so the fluid shifts from the interstitial space to the intravascular space (green arrows). This increases the

interstitial space osmolarity (because of the loss of fluid and constant number of molecules within it), which then causes fluid to leak out of the cells.

Figure 6: D5NS.45 (5% Dextrose in 1/2 Normal Saline)

Figure 7: Nine Per Cent Normal Saline, Blood Products and Albumin

In t ravenous Therapy

should be started at the most distal point on theextremity and proper support is needed after IVinfusion is initiated to prevent movement of the IVcatheter. The veins are thin with inadequate tissueand muscle support in the elderly.

C e p h a l i c V e i n s

The cephalic vein flows upwards along the radialborder of the forearm producing branches to bothsurfaces of the forearm. Due to its size and location,it provides an excellent site for IV infusion. Thecephalic veins readily accommodate large-gauge IVcatheters and are available for venipuncture in theupper-arm region.

A c c e s s o r y C e p h a l i c V e i n s

The accessory cephalic vein originates from either aplexus on the back of the forearm or dorsal venousnetwork, branching off from the cephalic vein justabove the wrist and flowing back into the maincephalic vein at a higher point. Accessory cephalicveins readily accommodate large gauge IV catheters.

B a s i l i c V e i n s

The basilic vein originates in the ulnar portion ofthe dorsal venous network. It ascends along theulnar portion of the forearm, curves towards theanterior surface of the arm just below the elbow andmeets with the median cubital vein below theelbow. It is available for venipuncture above theantecubital fossa in the upper-arm region. Thebasilic vein is often overlooked because of itsinconspicuous position.

M e d i a n A n t e b r a c h i a l V e i n s

The median antebrachial vein rises from the venousplexus on the hand and extends along the ulnar sideon the anterior surface of the forearm. It empties intothe basilic vein or median cubital vein and is notalways easily seen.

M e d i a n C e p h a l i c a n d

M e d i a n B a s i l i c v e i n s

Located in the antecubital fossa, the median cephalicand median basilic veins should be a last-resort sitefor blood draws and are not a favourable site forprolonged infusions.

T e c h n i q u e

It is important to point out that starting an IV is anart form that is learned with experience accumulatedafter performing many IVs. Some patients are easy toadminister but many are difficult.

For the person administering the IV, it is imperativethat these four points are remembered:

• Do I have the right patient?• Do I have the right solution?• Do I have the right drug?• Do I have the right route?

F l ow R a t e s

Administration sets are available to calculate IV flowrates. The administration sets are available in twobasic sizes – microdrip and macrodrip.

Microdrip sets are good for medication administrationor paediatric fluid delivery, while macrodrip sets aregreat for rapid fluid delivery. Also used for routinefluid delivery and keep the vein open (KVO). Fluidsmay be ordered at a KVO rate or run in very slowly,enough to keep the vein open, but not really delivermuch volume.

At times, a faster flow rate may be desired. This isusually expressed in millilitres per hour. In otherwords, how much fluid do you want your patientto receive each hour? A common ‘maintenance’amount, for instance, would be to run it in at 125millilitres an hour, thus, the patient would receive125 millilitres of fluid every hour. Electronicpumps will deliver the fluid at precise amounts,however, if these are not used, the nurse/doctorwill need to learn how to set a flow rate. Settingthe flow rate is usually done by counting thenumber of drops that fall into the clear dripchamber on the IV administration set in oneminute. Using the following formula it is possibleto calculate the flow rate:

(volume in ml) x (drip set) = gtts(time in minutes) min.

If a patient is to receive 250 millilitres of normalsaline over a 90-minute time period and it is decidedto use a macrodrip (10gtt/millilitre) administrationset, the formula will now look like this:

(250ml) x (10 gtts/min.) = gtts(90 min.) 1 min.

which becomes:

2,500 = gtts90 1

then solving for gtts:

27.7 = gtts1

or, gtts = 28

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