Equipment. Blood pressure is measured with a blood pressure cuff, a sphygmomanometer, and a stethoscope. The blood pressure cuff consists of a rubber bag that can be inflated with air. It is called the bladder. It is usually covered with cloth and has two tubes attached to it. One tube connects to rubber bulb that inflates the bladder. When turned counterclockwise, a small valve on the side of this bulb releases the air in the bladder. When the valve is tightened (tuned clockwise), air pumped into the bladder remains there. The other tube is attached to a sphygmomanometer.
The sphygmomanometer indicates the pressure of the air within the bladder. There are two types of sphygmomanometers: aneroid and mercury. The aneroid sphygmomanometer is a calibrated dial with a needle that points to the calibrations. The mercury sphygmomanometer is a calibrated cylinder filled with mercury. The pressure is indicated at the point to which the base of meniscus of the mercury rises, that is, the point where the meniscus touches the side of the glass tube.
Some agencies use electronic sphygmomanometers, which eliminate the need to listen to the sounds of the client’s systolic and diastolic blood pressure through a stethoscope. With some electronic sphygmomanometers, as the pressure in the cuff is lowered, light flashes to indicate the systolic and diastolic pressure.
Ultrasound Doppler stethoscopes are also needed to assess blood pressure. These are of particular value when blood pressure sounds are difficult to hear, such as an infants, obese clients, and clients, and clients in shock. The nurse applies transmission gel to a transducer probe, places the probe over the pulse point, and measures the blood pressure. A systolic blood pressure assessed with Doppler stethoscope is recorded with a large D, for example, 85 D. Systolic pressure may be only blood pressure obtainable with some ultrasound models.
Blood pressure cuffs some in various sizes, because the bladder must be the correct width length for the client’s arm. If the bladder is too narrow, the blood pressure reading will be erroneously low. The width should be 40% of the circumference, or 20% wider than the diameter of the midpoint of the limb on which it is used. The bladder dimensions by arm circumference, not the age of the client, should always be used to determine bladder size. The nurse can also determine whether the width of a blood pressure cuff is appropriate: Lay the cuff lengthwise at the midpoint of the upper arm, and hold the outermost side of the bladder edge laterally on the arm. With the other hand, wrap the width of the cuff around the arm, and ensure that the width is 40% of the arm circumference.
The length of the bladder also affects the accuracy of measurement. The bladder should be sufficiently long almost to encircle the limb and to cover at least two-thirds of its circumference.
The length of the bladder also affects the accuracy of measurement. The bladder should be sufficiently long almost to encircle the limb and to cover at least two-thirds of its circumference.
Blood pressure cuffs are made of nondistensible material so that an even pressure is exerted around the limb. Most cuffs are held in place by hooks, snaps, or Velcro. Others have a cloth bandage that is long enough to encircle the limb several times: this type is closed by tucking the end of the bandage into one of the bandage folds.
Sites: The blood pressure is usually assessed in the client’s arm using the brachial artery and a standard stethoscope. If the arm is very large or grossly misshapen and the conventional cuff cannot be properly applied, leg or forearm measurements can be taken. To obtain a leg blood pressure, a standard sized cuff is applied over the lower leg with the distal border of the cuff at the malleoli. Auscultate blood pressure sounds over the posterior tibial or dorsalis pedis arteries. To obtain a thigh blood pressure, apply an appropriate-sized cuff to the thigh, and auscultateted the pulsations of the blood over the popliteal artery. To obtain a forearm blood pressure, apply an appropriate sized cuff to the forearm 13 cm (5in) below the elbow. Blood pressure sounds then can be heard over the radial artery.
Recommended Bladder Sizes of Blood Pressure CuffsAssessing the blood pressure on a client’s thigh is usually indicated in these situations:
• The blood pressure cannot be measured on either arm (eg, because of burns or other trauma).
• The blood pressure in one thigh is to be compared with blood pressure in the other thigh.
Blood pressure is not measured on client’s arm, or thigh in the following situations:
• The shoulder, arm, or hand (or the hip, knee, or ankle) is injured or diseased.
• There is a cast or bulky bandage on any part of the limb.
• The client has had breast or axilla (or hip) surgery on that side.
• The client has an intravenous infusion or blood transfusion running.
• The client has an arteriovenous fistula (eg, for renal dialysis.)
Procedure in Assessing Blood Pressure
Selected Sources of Error in Blood Pressure Assessment
