60 Arterial Pressure–Based Cardiac Output Monitoring 525

PROCEDURE Arterial Pressure–Based Cardiac 60 Output Monitoring Susan Scott PURPOSE: Arterial pressure–based cardiac output monitoring is a minimally invasive technology that can be used to obtain hemodynamic data on a continuous basis. PREREQUISITE NURSING • The difference between the systolic and diastolic pressures KNOWLEDGE is called the pulse pressure, with a normal value of 40 mm Hg. • Arterial pressure is determined by the relationship between • Knowledge of the anatomy and physiology of the cardio- blood fl ow through the vessels (cardiac output), the com- vascular system is necessary. pliance of the aorta and larger vessels, and the resistance • Knowledge of the anatomy and physiology of the vascu- of the more peripheral vessel walls (systemic vascular lature and adjacent structures is needed. resistance). The arterial pressure is therefore affected by • Understanding of the pathophysiologic changes that occur any factors that change either cardiac output, compliance, in heart disease and affect fl ow dynamics is necessary. or systemic vascular resistance. • Understanding of aseptic technique is needed. • The average arterial pressure during a cardiac cycle is • Understanding of the hemodynamic effects of vasoactive called the mean arterial pressure (MAP). It is not the medications and fl uid resuscitation is needed. average of the systolic plus the diastolic pressures, because 1 • Understanding of the principles involved in hemodynamic at normal heart rates systole accounts for 3 of the cardiac 2 monitoring is necessary. cycle and diastole accounts for 3 of the cardiac cycle. • Knowledge of invasive cardiac output monitoring is needed. The MAP is calculated automatically by most patient • Knowledge of arterial waveform interpretation is needed. monitoring systems; however, it can be calculated manu- • Knowledge of defi nitions and norms for cardiac output, ally using the following formula: cardiac index, systemic vascular resistance, stroke volume, Systolic pressure +×()diastolic pressure 2 stroke index, preload, afterload, and contractility and stroke volume variation is necessary. 3 • Arterial pressure represents the forcible ejection of blood from the left ventricle into the aorta and out into the arte- • MAP represents the driving force (perfusion pressure) for rial system. During ventricular systole, blood is ejected blood fl ow through the cardiovascular system. MAP is at into the aorta, generating a pressure wave. Because of its highest point in the aorta. As blood travels through the the intermittent pumping action of the heart, this arterial circulatory system, systolic pressure increases and dia- pressure wave is generated in a pulsatile manner (see stolic pressure decreases, with an overall decline in the Fig. 59-1 ). The ascending limb of the aortic pressure wave MAP (see Fig. 59-2 ). (anacrotic limb) represents an increase in pressure because • Arterial pressure–based cardiac output (APCO) is obtained of left-ventricular ejection. The peak of this ejection is from an arterial catheter. 10–12 the peak systolic pressure, which is normally 100 to • APCO technology measures the rate of fl ow (cardiac out- 140 mm Hg in adults. After reaching this peak, the ven- put). 10–12 tricular pressure declines to a level below aortic pressure • Stroke volume and heart rate are key determinants of cardiac and the aortic valve closes, marking the end of ventricular output. systole. The closure of the aortic valve produces a • Although systemic vascular resistance affects cardiac out- small rebound wave that creates a notch known as the put, the location of that effect is global and not limited dicrotic notch. The descending limb of the curve by location of that measurement because cardiac output is (diastolic down slope) represents diastole and is character- measured as fl ow per minute throughout the body. Man- ized by a long declining pressure wave, during which the ufacturers of the arterial pressure–based cardiac output aortic wall recoils and propels blood into the arterial systems have factored in variance for both radial artery network. The diastolic pressure is measured at the lowest catheters and femoral artery catheters. 9 point of the diastolic down slope and is normally 60 to • Ultrasound guidance is recommended to place arterial 80 mm Hg. catheters if the technology is available. 7 523 524 Unit II Cardiovascular System EQUIPMENT PATIENT ASSESSMENT AND PREPARATION • Invasive arterial catheter and insertion kit • Specialized sterile transducer and sensor kit (manufac- Patient Assessment turer specifi c) • Obtain the patient ’ s medical history, including a history • Intravenous (IV) pole and transducer holder (manufac- of peripheral vascular disease, diabetes, and hypertension. turer specifi c) Rationale: These conditions increase the patient ’ s risk for • Pressure-transducer system, including fl ush solution rec- arterial or venous insuffi ciency. ommended according to institutional standards, a pressure • Obtain the patient ’ s medical history for peripheral vascu- bag or device, pressure tubing with transducer, and fl ush lar disease, vascular grafts, arteriovenous fi stulas or device shunts, arterial vasospasm, thrombosis, or embolism. In • Pressure module and cable for interface with the monitor addition, obtain the patient ’ s history of coronary artery • Normal saline-fl ush solution bypass graft surgery in which radial arteries were removed • Monitoring system (central and bedside monitor) for use as conduits. Rationale: Extremities with any of • Special monitor to interface with the bedside monitor for these problems should be avoided as sites for cannulation trending and display of hemodynamic values (manufac- because of the potential for complications. turer specifi c) • Assess the neurovascular and peripheral vascular status of • Dual-channel recorder the extremity to be used for the arterial cannulation, • Indelible marker including color, temperature, presence and fullness of • Nonvented (noninjectable) caps pulses, capillary refi ll, presence of bruit, and motor and • Leveling device (low-intensity laser or carpenter level) sensory function (compared with the opposite extremity). • Sterile and nonsterile gloves Note: A modifi ed Allen ’ s test may be performed before Additional equipment, to have available as needed, includes cannulation of the radial artery (see Fig. 81-3 ). Rationale: the following: This assessment may identify neurovascular or circulatory • Heparin if prescribed impairment, so potential complications related to radial • 3-mL syringe artery cannulation may be avoided. • Dressing supplies • Assess the patient ’ s vital signs and compliance factors • Tape (e.g., age, gender, height, weight). Rationale: This assess- • Sterile ultrasound probe cover ment provides baseline data. The compliance factors • Sterile ultrasound gel allow for the individual variables that ultimately dictate pulse pressure and its relevance (proportionality) to stroke PATIENT AND FAMILY EDUCATION volume. • Explain the rationale for arterial line insertion, including Patient Preparation how the arterial pressure is displayed on the bedside • Verify that the patient is the correct patient using two monitor. Rationale: This explanation may decrease patient identifi ers. Rationale: Before performing a procedure, the and family anxiety and increase understanding. nurse should ensure the correct identifi cation of the patient • Explain the standard of care to the patient and family, for the intended intervention. including insertion procedure, alarms, dressings, and • Ensure that the patient and family understand preproce- length of time the catheter is expected to be in place. dural teaching. Answer questions as they arise, and rein- Rationale: This explanation encourages the patient and force information as needed. Rationale: Understanding family to ask questions and voice concerns about the of previously taught information is evaluated and procedure and may decrease patient and family anxiety. reinforced. • Explain the patient ’ s expected participation during the • Ensure that informed consent has been obtained. Ratio- procedure. Rationale: Patients will know how they can nale: Informed consent protects the rights of the patient help with the procedure. and makes a competent decision possible for the patient. • Explain the importance of keeping the affected extremity • Perform a preprocedure verifi cation and time out, if non- immobile. Rationale: This explanation encourages patient emergent. Rationale: Ensures patient safety. cooperation to prevent catheter dislodgment and ensures • Validate the patency of IV access. Rationale: Access may a more accurate waveform. be needed for administration of emergency medications • Instruct the patient to report any warmth, redness, pain, or fl uids. numbness, or wet feeling at the insertion site at any time, • Place the patient ’ s extremity in the appropriate position including after catheter removal. Rationale: These symp- with adequate lighting of the insertion site. Rationale: toms may indicate infection, bleeding, or disconnection of This placement prepares the site for cannulation and facil- the tubing or catheter. itates an accurate insertion. 60 Arterial Pressure–Based Cardiac Output Monitoring 525 Procedure for Arterial Pressure–Based Cardiac Output Monitoring Steps Rationale Special Considerations Initiating the Procedure 1 . HH 2 . PE 3. If the radial artery is to be used, The modifi ed Allen ’ s test has been The modifi ed Allen ’ s test does not perform the modifi ed Allen

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