CLINICAL LAB SCIENEC

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ESSENTIALS OF CLINICAL LABORATORY SCIENCE
removal of the device. If collection of arterial blood is required (this is rare for
medical laboratory workers), an arterial line used to measure a patient’s blood
pressure continuously and accurately may be in place. Blood may be used from
this device for blood gas determinations as it would provide arterial blood.
Some patients have shunts where a surgical procedure is used to attach an
artery and a vein. These can be felt easily by palpating the skin over the site.
This vascular rearrangement is often done when a patient is required to undergo
kidney dialysis on a regular basis. A tourniquet should never be applied to an
arm with a shunt and blood should never be drawn from this arm. Heparin or
saline locks are present when a winged or butterfly apparatus is to be left in a
patient’s vein for up to 48 hours. The heparin and saline are necessary to prevent
clotting around the site. Blood may be drawn from this device, but only after
removing approximately 5 mL of fluid and discarding it before collecting the
sample. This should not be attempted unless one is trained and experienced in
the procedure. There are other indwelling lines from which blood may be drawn
if necessary, but again, fluid must be removed and discarded before obtaining the
testing sample. Only those skilled and experienced
in the procedure should perform this task.
Basilic
Cephalic
Median Cubital
Median
Choosing a Puncture Site
Veins are found throughout the body. However, the
majority of blood specimens are obtained in the
bend of the elbow. It is also possible to obtain venous
access in the hands, toes, neck, and elsewhere, but
the easiest site and the one with the least trauma
and potential for causing harm to the patient is the
inside of the elbow region. Figure 11-10 depicts
the most favorable sites where blood can be easily
obtained from the majority of patients. They include
the median cubital, the basilic, and the cephalic vein
in each arm. Obese patients, burn patients, and
those with amputations pose additional challenges
to obtaining an adequate sample of blood.
Initiating the Venipuncture
After gaining experience, the phlebotomist or
laboratory worker will become comfortable with
the procedure. Many of the following steps will
become automatic, and the worker will adopt his
or her own particular manner of performing a
phlebotomy procedure.
FIGURE 11-10 Veins commonly used for venipuncture.
Source: Delmar/Cengage Learning.
Applying the Tourniquet
The tourniquet should be properly placed on the
patient’s arm while selecting a site for venipuncture.
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