The Vital Signs, Part 2: Pulse

     The classic vital signs of blood pressure, pulse, respiration and temperature have been the backbone of EMS since its inception. Vital signs give prehospital care providers insight to what's going on inside our patients and let us evaluate their responses to our interventions. This multipart series takes 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 examines the pulse.

     Pulse might seem to be the easiest of the vital signs to obtain. Evidence suggests otherwise. A 1996 study led by German physician Balthasar Eberle was among the first to conclude that recognition of pulselessness by rescuers with basic CPR training was time-consuming and inaccurate. In the study, even professional EMTs and paramedics scored poorly. In 10% of patients, an absent carotid pulse was not recognized as pulselessness, and in 45% a pulse was not identified despite the presence of a carotid pulse with a systolic pressure of 80 mmHg or more.¹ A more recent study found that only 40 of 105 healthcare students who'd completed at least BLS instruction could accurately find a carotid pulse on a computerized manikin within 10 seconds.² The American Heart Association, for its part, deleted the carotid pulse check from its 2000 CPR/ECC guidelines.

     One study in infants determined that heart rates assessed by auscultation and palpation tended to be inaccurate and underestimate the ECG heart rate by 14 and 22 beats a minute, respectively.³ Another study evaluated 28 nurses' ability to detect infants' cardiac activity. The nurses determined the infants' heart rates with five different techniques: palpation of brachial pulse, carotid pulse, femoral pulse and apical impulse, and auscultation of apical impulse with the naked ear. The authors determined that the direct auscultation technique was more rapid and accurate than any other technique to determine cardiac activity without instruments, and it was also superior to palpation of the brachial artery in cardiopulmonary resuscitation in infants.⁴ The most recent article on the subject evaluated the long-held position that the brachial artery is the best site to check for a pulse in the critical infant. Its authors concluded that femoral pulse palpation proved best for detecting heartbeat and counting heart rate in hypotensive infants.⁵

     Pulsus alternans is a cardiovascular phenomenon characterized by alternating strong and weak pulses during a sinus rhythm. No changes are apparent on ECGs. The mechanism of pulsus alternans is not entirely clear, though it is attributed to an alteration in the stroke volume with every other cardiac cycle and is typically seen in patients with advanced myocardial disease. The difference in the beats is best detected by palpating the femoral pulses rather than the brachial, radial or carotid pulses. In many cases, pulsus alternans is an ominous sign that suggests severe cardiac failure.

     Pulsus paradoxus is a physical sign of tremendous diagnostic and prognostic significance. Under normal conditions, arterial blood pressure fluctuates throughout the respiratory cycle, falling with inspiration and rising with expiration. The changes in the intrathoracic pressures during breathing are transmitted to the heart and great vessels. During inspiration the fall in the left ventricular stroke volume is reflected as a fall in the systolic blood pressure. The converse is true for expiration. During quiet respiration, the changes in the intrathoracic pressures and blood pressure are minor. The accepted upper limit for fall in systolic blood pressure with inspiration is 10 mmHg. The "paradox" refers to the fact that the heartbeat can be heard with a stethoscope, but no radial pulse is felt. This is due to an exaggeration of normal mechanisms mentioned above. Moreover, the clinical method of assessment of this "pulse" is by measurement of systolic blood pressure.⁶