Hemodynamic monitoring is the use of advanced technology and application of physio-logical principles to clinically assess the cardiac function and circulatory system in critically ill patients. The pulmonary artery catheter was first introduced in 1970 by Dr. Jeremy Swan (Swan et al., 1970), and continues to be a frequently used tool in the critical care setting. The catheter tip is positioned in the distal pulmonary artery and is used to monitor pulmonary artery systolic, diastolic, and mean pressures, and to obtain blood samples to determine mixed venous oxygenation. The distal balloon port is used to measure the pulmonary artery wedge pressure (PAWP)when the balloon port is inflated with 1.5 cc of air.
Additional hemodynamic parameters and data are obtained from other ports and lumens of the catheter, such as right atrial pressure, cardiac output measurements, blood (core) temperature, and saturation of venous oxygenation (SvO2). Using data obtained at the bedside from the pulmonary artery catheter and other physiologic indices such as cardiac output, heart rate, preload, afterload, and contractility, critical care nurses and physicians are able to make rapid assessments and determinations about the clinical status of the critically ill patients. The catheter enables clinicians to assess ventricular function, diagnose complications following acute myocardial infarction, differentiate shock states, cardiac and pulmonary disorders, manage high-risk cardiac surgical patients, and monitor unstable patients with complexities such as sepsis and multiple organ dysfunction. The original balloon-tipped, flow-directed thermodilution catheter has evolved since 1970 and has added enhancements such as saturation of venous oxygenation (SVO2), right ventricular volumes and ejection fraction, continuous monitoring of cardiac output, and intracardiac atrioventricular sequential pacing.
Newer technologies to monitor cardiac output using noninvasive methodology include the Esophageal Doppler monitor and the Exhaled Carbon Dioxide (CO2) monitor. The Esophageal Doppler monitor measures cardiac output via a probe placed within a nasogastric tube that measures aortic blood flow, enabling the clinician to assess stroke volume and heart rate adjusted cardiac output. A second technology, Exhaled CO2, Isa noninvasive method of cardiac output monitoring that measures blood flow from exhaled CO2 using a modified Fick Equation. Its clinical application is limited to the operating room setting since the technology requires measurement of blood flow from exhaled CO2 under controlled ventilation, but it has great potential for the future when the technology can be used for different modes of mechanical ventilation with or without spontaneous breathing. Examining the impact these new technologies may have on patient outcomes is an important area for future nursing research.
Hemodynamic monitoring has great relevance to nurses in critical care because of the important role it plays in the care of critically ill patients. Critical care nurses are responsible for continuous monitoring, interpretation, and trending of hemodynamic indices and for communicating critical information to physician colleagues. Understanding the implications of subtle changes in pressures and parameters will directly impact a patient’s response to complex therapeutic interventions such as fluid administration and manipulation of vasoactive drips. Utilizing research to examine existing practices and to change practice is vital to ensure research-based practice and positive patient outcomes. The majority of nursing research on hemodynamic monitoring has been focused on the technical and clinical variables affecting accuracy of pulmonary artery pressure monitoring. Because many variables affect accuracy, this topic is particularly relevant for nurses caring for critically ill patients. The standard in critical care has traditionally been to reference (level the air/fluid interface stopcock at the phlebostatic axis) and zero the catheter system a minimum of once per shift and at times more often, to offset zero drift, and to ensure accuracy. The results of one nursing study suggested that zeroing disposable transducers may be required only once during hemodynamic monitoring, before initial readings are obtained (Ahrens, Pennick, & Tucker, 1995). These findings encourage practitioners to reevaluate a long-held critical care nursing standard and demonstrate the value of keeping pace with new technology.
Replication studies are needed in this area to validate this practice. A major focus in recent nursing research has been to study hemodynamic pressures in various backrest elevations. There is considerable nursing research supporting accurate and reliable measurement of hemodynamic pressures in backrest elevations from 0° to60° if the air/fluid interface (zeroing stop-cock) is leveled or referenced at the phlebostatic axis. Lateral positioning may be used if the air/fluid interface is leveled at the phlebostatic axis, but the patient must be at a 90° side position with the backrest flat to ensure accuracy. The phlebostatic axis in the right lateral 90° position is the fourth intercostal space at midsternum, compared to the fourth intercostal space at the left sternal border in the left lateral 90° position (Paolella, Dorfman, Cronan, &Hasan, 1988). The question of accuracy and reliability of measurements in lateral positioning other than 90° has been the subject of two recent nursing studies. In one study, pulmonary artery (PA) pressures were obtained with patients in the 60° lateral position (Aitken, 2000). The dependent midclavicular line at the level of the fourth intercostal space was used as the zero reference level. Statistically significant differences were found and the author concluded that PA pressures cannot be obtained with patients in the 60° lateral position. Another group of researchers studied the effect of 30° lateral recumbent position on PA and PAWP pressures (Bridges, Woods, Brengelmann, Mitchell, & Laurent-Bopp, 2000). Using an angle-specific left atrial reference point, the investigators found a statistically significant difference between measurements of PA pressures with the patient supine and those obtained in 30° lateral position. Mean differences were small and the author considered the measures clinically equivalent to those of patients in supine position. The optimal reference point for lateral positions other than 90° with backrest flat continues to be an area that will require further study and validation in future research studies.
Recent studies have examined cardiac output technology in patients with low cardiac output. Continuous cardiac output technology was found to be more precise than measurements using the bolus technique in one study of patients with low-cardiac output (Albert, Spear, & Hammel, 1999). The practice of using room-temperature injectate versus iced solution was supported in another study examining traditional thermodilution methods of cardiac output in patients with low cardiac output (Kiely, Byers, Greenwood, Carroll, & Carroll, 1998).To ensure accuracy and reliability, all hemodynamic pressures are read at end expiration in ventilated patients as well as those breathing spontaneously. Numerous studies continue to support the use of a strip chart recorder to provide more reliable and accurate hemodynamic readings than do digital data (directly off the monitor) in both ventilated and spontaneously breathing patients.
Since the advent of the pulmonary artery catheter, technology in hemodynamic monitoring has advanced at a rapid pace. Future studies must continue to keep pace with the ever-changing technology. Technical difficulties in measurement, as seen in patients with severe respiratory variation, in ventilated patients on high levels of positive end expiratory pressure (PEEP), and in the presence of large “v” waves on the hemodynamic waveform, are examples of clinical issues that continue to confound critical care nurses. Critically evaluating the use of both new and traditional technology is essential to the provision of good patient care.
The potential risk versus benefit of pulmonary artery catheterization is an important ethical consideration in hemodynamic monitoring. Questions have been raised within major medical journals and the media about the safety and efficacy of pulmonary artery catheterization. As a result of the controversy, organizations such as the Society of Critical Care Medicine have intensified efforts to conduct large randomized controlled trials to evaluate critically the safety and effectiveness of PA catheters in critically ill patients.
The results of studies on the clinical competency of critical care nurses’ knowledge of PA catheters have been less than impressive, and underscore the need to provide ongoing training and competency assessments of nursing staff to ensure safe and quality patient care. Hemodynamic monitoring is a valuable tool if used judiciously by specially trained and competent medical and nursing professionals.