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Marion McRae is a clinical nurse III in the Cardiothoracic ICU at UCLA Medical Center.
This column is designed to provide the latest research findings in patient care in a format that is easy to understand and integrate into clinical practice. The information is drawn from individual protocols in the various Protocols for Practice series available from AACN, which cover research-based practice protocols in detail.
With the advent of disposable pressure transducer technology, accuracy affecting intra-arterial pressure readings is now limited to patients’ clinical conditions and clinicians’ knowledge and skills in the use of the intra-arterial pressure monitoring device. Some of the most common elements affecting accuracy of intra-arterial pressure readings include anatomical sites, peripheral vascular diseases, and use of vasoactive medications. The knowledge, experience, and skills of clinicians in leveling and zeroing pressure transducers; variations in patient position relative to the transducers; and waveform configurations also need to be considered in ongoing intra-arterial pressure measurement.
ANATOMICAL SITES
Intra-arterial pressure monitoring is designed to measure systemic pressure as close to the heart as possible. The best way to measure true systemic pressure is through the use of a central aortic pressure catheter, which can only be accomplished during cardiac surgery or with an intra-aortic balloon catheter. As arterial pressure monitoring sites go from central to peripheral, changes in waveform configurations and readings occur (Figure 1
). When arterial pulse waveforms are recorded from sites distal to the central aorta (for example, the dorsalis pedis), the systolic portion (anacrotic limb) becomes peaked and narrowed with increased amplitude. As a result, the systolic blood pressure in distal sites will be significantly higher than that recorded from a more central site. The diastolic portion of the waveform may display a secondary (reflectance) wave, as the monitoring site becomes more distal to the central aorta. The dicrotic notch becomes less defined as the monitoring site is moved toward the periphery. These changes could also be intensified with significant doses of vasodilators or vasopressors. With vasodilators, the waveform takes on a more central appearance (for example, the femoral arterial waveform). With vasoconstrictors, the systolic pressure component becomes exaggerated due to enhanced resistance in the peripheral arteries. In infants, however, the change in waveform from central aortic to peripheral sites may not be as pronounced due to age and shorter limbs.
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Advanced technology in disposable transducer systems ensures accurate calibration and low drift from zero. Transducer failures are rare. There are, however, steps nurses can take to ensure precision and accuracy of the intra-arterial pressure monitoring system:
). The goal is to measure central aortic pressures, even if the catheter is located in a distal artery. This leveling approach depends on patient position (ie, head of bed elevation or lateral positioning); erroneous pressure readings may be obtained if the transducer is not releveled with position changes.
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This article is based on the protocol "Arterial Pressure Monitoring" by Flerida Imperial-Perez and Marion McRae. It was taken from the Hemodynamic Monitoring series of AACN’s Protocols for Practice. Protocols can be obtained from AACN, 101 Columbia, Aliso Viejo, CA 92656-1491, (800) 899-AACN, (949) 362-2000. $11.01, AACN members; $12.95, nonmembers
Note
This article was first published in CRITICAL CARE NURSE April 1999.
Bibliography
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