4-19. MEASURING BLOOD PRESSURE
Blood pressure is usually measured indirectly using a stethoscope and an
instrument called the sphygmomanometer. The most common site is the arm just above
the antecubital area, using the brachial artery. Blood pressure may be measured directly
by means of a catheter or probe inserted into a blood vessel or the heart.
a. Direct Measurement.
(1) One means of direct blood pressure measurement is to place a special
tube in a vein and monitor central venous pressure (CVP). Central venous pressure may
be used to determine fluid needs in shock, hemorrhage, or severe burns, to detect
pulmonary edema, and to determine the extent of circulatory overload.
(2) Another method of direct blood pressure measurement is internal or
invasive monitoring. A large, flexible catheter, such as a Swan-Ganz catheter measures
pressures within the heart itself.
b. Indirect Measurement. The sphygmomanometer (often called a blood
pressure apparatus) includes a wide, cloth-covered rubber cuff with two rubber tubes
extending from it. One tube is connected to a bulb air pump that has a valve, which can
be opened or closed. The other tube is connected to a glass cylinder containing mercury
(mercury manometer) or to a dial (aneroid manometer), which attaches to the arm wrap.
You obtain the indirect blood pressure reading with the manometer by listening to the
heartbeat with a stethoscope.
(1) Cleanse the stethoscope and earpiece with an alcohol wipe before and
after the procedure (unless you use your own stethoscope).
(2) Have the patient lie down or rest comfortably in a chair with the arm
supported and the palm turned upward to expose the brachial artery on the inside of the
(3) Let the air out of the cuff. Wrap the cuff firmly around the arm, just far
enough above the elbow to leave the space over the brachial artery free, and fasten the
clip or Velcro closure.
(4) Find the pulse in the artery and place the stethoscope over the spot where
you can feel the strongest pulsations.
(5) Pump the manometer bulb to 20 mm above a possible systolic pressure.
Release the valve on the manometer bulb to gradually release air from the cuff.
(6) Note the level on the mercury column or dial at which you first hear a
heartbeat. This is the systolic pressure.