Vital Signs Part 1: Blood Pressure

     The classic vital signs of blood pressure, pulse, respiration and temperature have been the backbone of EMS since its inception. Vital signs give EMS providers insight to what's going on inside our patients, and let us evaluate their responses to our interventions. This multipart series will take a fresh look at these vital signs and what they actually tell us in terms of changing our prehospital treatment, predicting the severity of presenting problems and even predicting survival. This article will examine blood pressure.

     "The cuff of Riva-Rocci is placed on the middle third of the upper arm; the pressure within the cuff is quickly raised up to complete cessation of circulation below the cuff. Then, letting the mercury of the manometer fall, one listens to the artery just below the cuff with a children's stethoscope. At first no sounds are heard. With the falling of the mercury in the manometer down to a certain height, the first short tones appear; their appearance indicates the passage of part of the pulse wave under the cuff. It follows that the manometric figure at which the first tone appears corresponds to the maximal pressure. With the further fall of the mercury in the manometer, one hears the systolic compression murmurs, which pass again into tones (second). Finally, all sounds disappear. The time of the cessation of sounds indicates the free passage of the pulse wave; in other words, at the moment of the disappearance of the sounds, the minimal blood pressure within the artery predominates over the pressure in the cuff. It follows that the manometric figures at this time correspond to the minimal blood pressure."

     With those 190 words, spoken in an address to the Imperial Military Academy in 1905, Russian physiologist Nikolai Korotkoff introduced the classic technique of obtaining systolic and diastolic blood pressure with the use of a sphygmomanometer and stethoscope.

     Korotkoff actually described five types of sounds, now named after him. The first is the snapping sound first heard at the systolic pressure. The second is the murmuring heard for most of the area between the systolic and diastolic pressures. The third and fourth, at pressures within 10 mmHg above the diastolic blood pressure, are described as "thumping" and "muting." The fifth sound is silence as the cuff pressure drops below the diastolic blood pressure. It is recorded as the last audible sound.

     Traditionally, the systolic blood pressure is taken to be the pressure at which the first Korotkoff sound is first heard, and the diastolic blood pressure is the pressure at which the fourth Korotkoff sound is just barely audible. There has been disagreement in the past as to whether the fourth or fifth Korotkoff sound should be used for recording diastolic pressure, but phase IV tends to be even higher than phase V when compared against the true intra-arterial diastolic pressure, and is more difficult to identify. There is now general consensus that the fifth phase should be used, except in situations in which the disappearance of sounds cannot reliably be determined because sounds are audible even after complete deflation of the cuff—for example, in pregnant women and patients with arteriovenous fistulas (e.g., for hemodialysis) or aortic insufficiency.¹ All providers must be using the same criteria, Korotkoff V, in establishing the diastolic pressure.