Arterial catheterization is one of the most frequently performed invasive procedures performed on critically ill patients. It is generally considered to be a safe procedure with few serious complications and a major complication rate ranging between 1% and 5%.1,2,3,4 Although arterial catheterization was traditionally performed by physicians, contemporary practice in many organizations allows credentialing for this procedure to be performed routinely by nonphysician providers including nurse practitioners, certified registered nurse anesthetists, and physician assistants. Arterial line placement remains a readily acceptable intervention for unstable patients requiring continuous monitoring of blood pressure, frequent blood sampling, and blood gas analysis.1,3,4,5 Newer technologies for hemodynamic monitoring such as measurement of stroke volume variation and cardiac output are also facilitated by the presence of an arterial line. This chapter will review general principles of arterial line placement, monitoring, and care.
INDICATIONS FOR ARTERIAL CANNULATION
In the majority of hospitalized patients, non-invasive indirect monitoring of blood pressure by auscultation of Korotkoff sounds is sufficient. However, in critically ill and hemodynamically unstable patients indirect techniques may underestimate blood pressure1; thus the need for more intensive blood pressure monitoring via arterial catheterization may be beneficial. Historically, the indications for placement of arterial lines included: (1) continuous beat-to-beat monitoring of blood pressure; (2) frequent sampling of blood for laboratory analysis and monitoring of ventilatory impairment; (3) arterial administration of drugs such as thrombolytics; and (4) use of an intra-aortic balloon pump.1,3 These remain compelling indications for placement of arterial catheters, however technological advances in contemporary design of catheter and monitoring systems now allow arterial lines to be used for more advanced hemodynamic monitoring, including real-time calculation of cardiac output, stroke volume, and evaluation of fluid responsiveness in suspected hypovolemic states.1 The modern practitioner requires adequate knowledge of new technologies and data interpretation in order to effectively use these new modalities to enhance patient care and delivery.
ARTERIAL WAVEFORM ANALYSIS
The waveform seen on bedside monitors is a visual representation of intravascular fluid dynamics as a result of rhythmic pulsation of blood generated by cardiac systole. Changes in intravascular pressure are transmitted through rigid, fluid-filled tubing that propagates the pressure wave to a transducer. This transducer converts the pressure wave from a mechanical process (displacement of fluid) into an electrical signal that is, in turn, amplified, processed, and represented on the monitor as a readily recognizable and characteristic wave. As a result of different pressures through arteries of varying circumference and distance from the heart, the visual representation of the waveform on the monitor will be different based on which artery the catheter has been placed (see Figure 89–1).