Page 250 - Encyclopedia of Nursing Research

HeMODyNAMIc MONITOrING n 217

disorders and to facilitate early identification Doppler monitors measure aortic blood flow
of sepsis and organ dysfunction. and assess stroke volume (SV) and heart rate–
The tip of the catheter is positioned in the adjusted cardiac output via a probe placed H
distal pulmonary artery (pA) and attached to within a nasogastric tube. exhaled cO 2 tech-
a pressure transducer system that converts nology measures blood flow from exhaled
physiologic/mechanical signals to electrical cO 2 , and cardiac output is derived using a
signals and provides a continuous display modified Fick equation. clinical application
of pulmonary systolic, diastolic, and mean requires use of controlled ventilation and has
pressures. The distal balloon port is used primarily been limited to the operating room
to measure the pA wedge (occlusive) pres- setting.
sure, an indirect measure of left ventricular A new less invasive device uses arterial
end diastolic pressure. The proximal lumen pressure–based SV to derive cardiac output
is used to monitor right atrial pressures and measurements. It is based on the Stewart–
used as an injectate port for cardiac output. Hamilton equation but uses a dilution curve
The catheter’s thermistor port provides a from an arterial tracing via a sensor attached
continuous display of the blood (core) tem- to an existing arterial line. The device mea-
perature. Additional enhancements include sures SV variation to guide fluid adminis-
specialized catheters for continuous mon- tration and is considered a more sensitive
itoring of cardiac output, fiber optic moni- indicator compared with traditional static
toring of mixed venous oxygen saturation measures of preload using the pA catheter
(SvO 2 ), right ventricular end diastolic volume (Headly, 2005, 2006). SV is derived from the
and ejection fraction, and intracardiac atrio- arterial line waveform using an equation
ventricular sequential pacing. (SV = K × pulsatility). The constant takes
Hemodynamic indices are obtained by into account the vascular resistance, arterial
the critical care nurse and used in conjunc- compliance (based on sex, height, weight,
tion with derived parameters such as sys- and age and pulse pressure waveform char-
temic vascular resistance and pulmonary acteristics), and pulsatility (based on an
vascular resistance. Nurses make assess- analysis of the contour of the arterial pres-
ments and in collaboration with physician sure waveform; Manecke, 2005). This tech-
colleagues institute goal-directed therapy to nology has limitations, and many factors
optimize the heart rate, preload, afterload, affect the accuracy. The majority of research
and contractility to improve overall cardiac was done under controlled situations with
output and tissue perfusion. Nurses must the patients on controlled ventilation and
be trained with the requisite knowledge and specific tidal volume settings (Bridges, 2008).
skills to work with these invasive devices and The accuracy of this technology requires that
hemodynamic monitoring remains a funda- the patient is intubated with fixed tidal vol-
mental component of critical care nursing ume and respiratory rate. Irregular rhythm
curriculum. with variability in heart may affect accuracy.
Historically, the gold standard for hemo- There is great opportunity for future nurs-
dynamic monitoring has been the use of the ing research to examine the risks versus
pAc for the assessment and management of benefits of the new less invasive options and
critically ill patients. Questions continue to to examine the impact of nurse-driven goal-
be raised in medical journals and within the directed therapy to optimize patient out-
critical care community about the relative comes. clinical outcomes such as decreased
risks versus benefits of the using the invasive number of ventilator days and reduced blood
catheter. As a result, there is a distinct trend stream infection using noninvasive methods
toward minimally invasive and noninvasive are important outcome measures. Decreased
methodology in the last decade. esophageal number of intensive care unit days and a