Blood Pressure (BP)
The blood pressure is the pressure in the vascular system and is reported in millimeters of Mercury (mmHg) as both the systolic and diastolic pressure. The systolic pressure is the measurement of the peak pressure in the artery generated by the contraction of the left ventricle (systole), whereas the diastolic is the residual pressure within the arteries in between contractions (diastole). The EMT is taught two methods to obtain a BP, palpated (to feel) and auscultated (to listen).
Auscultated BP method
- Select the correctly sized cuff. The cuff should wrap 1 to 1.5 times around the arm, and take up 2/3 the distance from the elbow to the armpit. Too large a cuff may give you artificially low readings, and too small a cuff can read high.
- The BP cuff should be placed directly on the skin on an uninjured arm (i.e. do not put it over clothes or proximal to an injury). Sliding a loose fitting t-shirt up so that the skin is exposed is fine. However, try not to roll tight fitting or bulky shirts up over the bicep. If you are unable to roll clothing up, have the patient remove their clothing if awake and responsive, or cut the clothing off in an unstable patient situation.
- 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.
- Turn the valve on the pumping bulb clockwise (may be counter clockwise in some cuffs) until it no longer moves. Caution should be taken to not force the valve in the open or closed position as it can become stuck. This is the position which allows air to enter and remain in the bladder.
- Slide the bell of your stethoscope under the edge of the blood pressure cuff over the site of the brachial artery (located towards the medial aspect of the antecubital fossa), and hold in place with your left hand.
- Use your right hand to pump the bulb until you have generated 150 mmHg on the manometer (or to 20 to 30 mm Hg above your previous systolic pressure if this is a repeat measurement). This is a bit above the top end of normal for SBP.
- Listen. If you immediately hear a pulsatile sound, you have underestimated the SBP. Close the valve and 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 is the return of blood through the brachial artery which is no longer being occluded by the pressure in the cuff. The needle on the manometer (gauge) 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. At the point when the sound completely disappears, you have reached the diastolic blood pressure (DBP). This is the point when the pressure within the vessel is greater than that supplied by the cuff, allowing the free flow of blood without turbulence and thus no audible sound. Your auscultated BP would be documented as systolic pressure/diastolic pressure (e.g. 110/70).
|Patient||Systolic (mmHg)||Diastolic (mmHg)|
|Adult Male||100 + age up to 40||60-85|
|Adult female||90 + age up to 40||60-85|
|Adolescent||90 and above||2/3 systolic|
|Child (1-10 yrs)||80 + (2 x age) +/- 10||2/3 systolic|
|Infant (1-12 mo)||70 and above||2/3 systolic|
To investigate the mechanism behind the different ways of obtaining a blood pressure, look at the Physiology of Blood Pressure. This may help with troubleshooting if you are having trouble obtaining an auscultated blood pressure on a patient or want more information as to how automated blood pressure machines get their results.