Section 3: Anesthesia Management
Part B: Monitoring
Chapter 30: Cardiovascular Monitoring

ARTERIAL BLOOD PRESSURE MONITORING

As with heart rate, blood pressure is a fundamental cardiovascular vital sign, which reflects the force that derives perfusion of the body. In addition, blood pressure is the most important determinant of left ventricular afterload, the workload of the heart. Consequently, frequent measurement of arterial blood pressure is a critical part of monitoring anesthetized or seriously ill patients. The importance of monitoring this vital sign is underscored by the fact that standards for basic anesthetic monitoring mandate measurement of arterial blood pressure at least every 5 minutes in all anesthetized patients. 3 

Techniques for measuring blood pressure fall into two major categories: indirect Riva-Rocci cuff devices and direct arterial cannulation and pressure transduction. These methods differ in nearly every respect, notably in terms of the physical process being monitored and in the level of invasiveness of their application. In clinical practice, blood pressures measured by different techniques often yield significantly different values. 22  So common are these inconsistencies that some investigators have declared: “Blood pressure is a function of the way it is measured.” 23 

Studies comparing different blood pressure monitoring techniques usually use direct arterial pressure measurement as the reference standard against which another method is judged. However, there are many ways in which direct arterial pressure measurement can yield spurious results (see the section Technical Aspects of Direct Blood Pressure Measurement ). In view of these considerations, Gorback‘s 24  comments provide a valuable guide: “It is preferable to understand the strengths and weaknesses of the various techniques and expected relative values, since they do not measure the same event.” In the end, the clinician must acquire sufficient understanding of the performance characteristics of these monitors to become the arbiter of measurement discrepancies by integrating all available data.

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