- Wrap the cuff around the patient's upper arm so that the line marked "artery" is roughly over the brachial artery, located towards the medial aspect of the antecubital fossa (i.e. the crook on the inside of their elbow). The placement does not have to be exact nor do you actually need to identify this artery by palpation.
Antecubital FossaThe pictures below demonstrate the antecubital fossa anatomy (surface anatomy on the left, gross anatomy on the right).
- Put on your stethescope so that the ear pieces are angled away from your head. Twist the head piece so that the bell is engaged. This can be verified by gently tapping on the end, which should produce a sound. With your left hand, place the bell over the area of the brachial artery. While most practitioners use the diaphragm of the stethescope, the bell is actually be superior for picking up the low pitched sounds used for measuring BP. It's worth mentioning that a number of different models of stethescops are available on the market, each with its own variation on the structure of the diaphragm and bell. Read the instruction manual accompanying your stethoscope in order to determine how your device works.
- Grasp the patient's right elbow with your right hand and raise their arm so that the brachial artery is roughly at the same height as the heart. The arm should remain somewhat bent and completely relaxed. You can provide additional support by gently trapping their hand and forearm between your body and right elbow. If the arm is held too high, the reading will be artifactually lowered, and vice versa.
- Turn the valve on the pumping bulb clockwise (may be counter clockwise in some cuffs) until it no longer moves. This is the position which allows air to enter and remain in the bladder.
- Hold the bell in place with your left hand. Use your right hand to pump the bulb until you have generated 150 mmHg on the manometer. This is a bit above the top end of normal for systolic blood pressure (SBP). Then listen. If you immediately hear sound, you have underestimated the SBP. Pump up an additional 20 mmHg and repeat. Now slowly deflate the blood pressure cuff (i.e. a few mm Hg per second) by turning the valve in a counter-clockwise direction while listening over the brachial artery and watching the pressure gauge. The first sound that you hear reflects the flow of blood through the no longer completely occluded brachial artery. The value on the manometer at this moment is the SBP. Note that although the needle may oscillate prior to this time, it is the sound of blood flow that indicates the SBP.
- Continue listening while you slowly deflate the cuff. The diastolic blood pressure (DBP) is measured when the sound completely disappears. This is the point when the pressure within the vessel is greater then that supplied by the cuff, allowing the free flow of blood without turbulence and thus no audible sound. These are known as the Sounds of Koratkoff.
Technique for Measuring Blood Pressure
- Repeat the measurement on the patient's other arm, reversing the position of your hands. The two readings should be within 10-15 mm Hg of each other. Differences greater then this imply that there is differential blood flow to each arm, which most frequently occurs in the setting of subclavian artery atherosclerosis.
- Occasionally you will be unsure as to the point where systole or diastole occurred and wish to repeat the measurement. Ideally, you should allow the cuff to completely deflate, permit any venous congestion in the arm to resolve (which otherwise may lead to inaccurate measurements), and then repeat a minute or so later. Furthermore, while no one has ever lost a limb secondary to BP cuff induced ischemia, repeated measurement can be uncomfortable for the patient, another good reason for giving the arm a break.
- Avoid moving your hands or the head of the stethescope while you are taking readings as this may produce noise that can obscure the Sounds of Koratkoff.
- You can verify the SBP by palpation. To do this, position the patient's right arm as described above. Place the index and middle fingers of your right hand over the radial artery. Inflate the cuff until you can no longer feel the pulse, or simply to a value 10 points above the SBP as determined by auscultation. Slowly deflate the cuff until you can again detect a radial pulse and note the reading on the manometer. This is the SBP and should be the same as the value determined with the use of your stethescope.
Technique for Measuring Blood Pressure
In order to measure the BP, proceed as follows:
