Perioperative Noninvasive Blood Pressure Monitoring
The most commonly monitored variable for perioperative hemodynamic management is blood pressure. Several indirect noninvasive blood pressure monitoring techniques have been developed over the last century, including intermittent techniques such as auscultation (Riva-Rocci and Korotkoff) and oscillometry (Marey) and continuous techniques. With the introduction of automated noninvasive blood pressure devices in the 1970s, the oscillometric technique quickly became and remains the standard for automated, intermittent blood pressure measurement. It tends to estimate more extreme high and low blood pressures closer to normal than what invasive measurements indicate. The accuracy of the oscillometric maximum amplitude algorithm for estimating mean arterial pressure is affected by multiple factors, including the cuff size and shape, the shape of the arterial compliance curve and arterial pressure pulse, and pulse pressure itself. Additionally, the technique typically assumes a consistent arterial compliance and arterial pressure pulse, thus changes in arterial compliance and arrhythmias that lead to variation in the pressure pulse can affect accuracy. Volume clamping, based on the Penaz principle, and arterial tonometry provide continuous tracking of the arterial pressure pulse. The ubiquitous use of blood pressure monitoring is in contrast with the lack of evidence for optimal perioperative blood pressure targets.