Blood pressure is a fundamental health measurement, representing the force exerted by circulating blood against the walls of the body’s arteries. It is a routine vital sign assessed by healthcare professionals, including nurses, to gauge a patient’s overall cardiovascular well-being. Regular monitoring of blood pressure helps in identifying potential health concerns, as deviations from normal ranges can indicate underlying conditions that may require medical attention.
Understanding Blood Pressure Readings
Blood pressure readings consist of two numbers: systolic and diastolic pressure. The systolic pressure, the higher number, reflects the pressure within the arteries when the heart contracts and pumps blood out into the body. This measurement captures the peak force exerted on arterial walls during each heartbeat. Diastolic pressure, the lower number, indicates the pressure in the arteries when the heart is at rest, between beats, as it refills with blood. Both values are presented in millimeters of mercury (mmHg), indicating the heart’s pumping efficiency and vascular resistance.
The Essential Tools
Manual blood pressure measurement relies on two instruments: the sphygmomanometer and the stethoscope. A sphygmomanometer, also known as a blood pressure cuff, consists of an inflatable cuff, a pressure gauge (manometer), and a bulb with a valve for inflation and deflation. This device temporarily restricts blood flow in the artery, allowing for pressure readings.
The stethoscope is a medical device used to listen to internal body sounds. It has a chest piece with a diaphragm and a bell, connected to earpieces. For blood pressure measurement, the stethoscope enables the nurse to hear specific sounds produced by blood flow in the artery, which are used to determine the systolic and diastolic values.
The Measurement Process: Hearing the Sounds
To begin, the nurse ensures the patient is relaxed, seated with their back supported and feet flat on the floor, with the arm supported at heart level. An appropriately sized cuff is then placed snugly around the upper arm, one inch above the elbow, aligning the artery marker with the brachial artery. The stethoscope’s diaphragm is positioned over the brachial artery in the antecubital fossa, just below the cuff’s edge.
The cuff is rapidly inflated to a pressure 20 to 30 mmHg above the patient’s estimated systolic pressure, or until the radial pulse is no longer palpable. This temporarily stops blood flow. The nurse then slowly deflates the cuff at a steady rate of about 2 to 3 mmHg per second, listening through the stethoscope. As the pressure in the cuff drops, blood begins to flow turbulently through the partially constricted artery, producing Korotkoff sounds. These sounds change as the cuff pressure falls, signaling different phases of blood flow.
Identifying Systolic and Diastolic Values
The nurse interprets the changing Korotkoff sounds to determine the systolic and diastolic pressures. The first appearance of tapping sounds (Korotkoff Phase I) indicates the systolic blood pressure. At this point, the cuff pressure has fallen enough to allow blood to spurt through the artery with each heartbeat, creating audible turbulence. The number on the sphygmomanometer gauge at this moment is recorded as the systolic reading.
As the cuff continues to deflate, the sounds progress through different phases, becoming softer, then crisper, and eventually muffled. The point at which the sounds completely disappear marks the diastolic blood pressure (Korotkoff Phase V). This disappearance signifies that blood flow through the artery has returned to its normal, smooth, non-turbulent state, and the pressure in the cuff is no longer constricting the vessel.