Blood pressure measurement is a fundamental part of almost every medical assessment, providing insight into the force of blood against the artery walls. The standard method, known as auscultation, relies on a sphygmomanometer (cuff) and a stethoscope to listen for specific sounds in the artery. These sounds, called Korotkoff sounds, allow the clinician to determine both the systolic and diastolic pressures. While this technique is the most common and comprehensive, certain situations make listening for these sounds difficult or impossible, necessitating an alternative approach. This need for a non-auditory measurement leads to the use of a technique based purely on touch: the palpated blood pressure.
Defining Palpated Blood Pressure
Palpated blood pressure is a non-invasive measurement method that uses touch to determine the pressure at which blood flow resumes in an occluded artery. The technique relies on feeling the return of a pulse, rather than hearing the turbulent sounds of blood moving. This method can only accurately determine the systolic blood pressure, which represents the maximum pressure during a heart contraction.
The diastolic pressure, or the bottom number, cannot be reliably measured by palpation alone. Diastolic pressure is traditionally identified when the Korotkoff sounds completely disappear, indicating that the artery is no longer compressed and blood flow is smooth. Since the cessation of sound cannot be registered by touch, palpation provides only the systolic value. The reading is often documented with a “P” or “palp” in place of the diastolic number (e.g., 120/P).
The pressure reading obtained represents the moment the cuff pressure drops just below the maximum pressure exerted by the heart, allowing a pulse wave to push through. This momentary return of the pulse is the direct physical indicator of the systolic pressure. Palpation can also be a preliminary step before using the auscultatory method, as it helps prevent underestimating the blood pressure if an “auscultatory gap” is present. This gap is a period where Korotkoff sounds temporarily vanish, which can mislead a clinician into recording an inaccurately low systolic pressure.
The Step-by-Step Procedure
The process begins with ensuring the patient is sitting or lying comfortably with their arm supported at heart level. A correctly sized blood pressure cuff is applied to the upper arm, roughly one inch above the bend of the elbow. The clinician uses their index and middle fingers—never the thumb, which has its own pulse—to locate a distal pulse, most commonly the radial pulse at the wrist.
Once the pulse is located, the cuff is rapidly inflated until the pulse is no longer felt, indicating that the artery is fully occluded. The cuff is typically inflated about 20 to 30 millimeters of mercury (mmHg) above the pressure at which the pulse disappeared to ensure complete obliteration. The valve is then slowly opened to allow the cuff to deflate at a controlled rate, often around 2 to 3 mmHg per second.
Throughout the slow deflation, the clinician keeps their fingers firmly placed over the artery, watching the pressure gauge closely. The exact pressure reading on the manometer at the moment the pulse is first felt to return is recorded as the palpated systolic blood pressure. This reappearance confirms that the cuff pressure has fallen below the systolic pressure, allowing the first wave of blood flow to push past the compression. After noting this value, the remaining air in the cuff is quickly released.
When and Why This Method is Necessary
The palpated method becomes necessary in specific clinical and environmental situations where the standard auscultatory technique is impractical. A primary reason is excessive noise that makes hearing the faint Korotkoff sounds impossible. Environments like a moving ambulance, a busy emergency department, or a noisy construction site often require palpation to get a quick, baseline measurement.
Another scenario involves patients experiencing severe hypotension or shock, where the volume and force of blood flow are significantly reduced. In these cases, the Korotkoff sounds may be too muffled or faint to detect, even in a quiet setting. Palpation can often still pick up the pulse wave return, providing an important estimate of the systolic pressure.
Furthermore, the technique requires only the blood pressure cuff and manometer, making it useful when a stethoscope is unavailable or malfunctioning. It also serves as a check for the auscultatory gap phenomenon, ensuring the cuff is inflated high enough before listening begins.