Biomedical Engineering Reference
In-Depth Information
The admission of a patient to an ICU is often (but not
always) prompted by compromises or threats to cardiac
and/or respiratory function. Insufficiencies in these areas
must be addressed rapidly. The delivery of oxygenated
blood to body tissues is therefore the first concern of the
ICU staff. ECG, pulse oximetry, and noninvasive blood
pressure (NIBP) are physiological measurements that
can be obtained immediately and noninvasively upon
connection of the patient to the monitoring equipment.
Monitoring and therapy at this point become pro-
gressively more invasive with the addition of vascular
access to measure internal blood pressures on both the
arterial and venous side of the circulatory system.
Catheters can be inserted into the pulmonary artery to
obtain thermodilution cardiac output information
(Trautman, 1988) as well as measurement of patient fluid
load. Vascular access also provides a convenient site for
obtaining blood samples for a variety of laboratory tests.
Although attempted for many years, a practical and eco-
nomical indwelling blood gas analysis catheter remains to
be developed.
Additional diagnostic tools are often available in the
ICU as well. It is common to find ultrasonic scanning
and imaging systems as part of the unit's armamentar-
ium. Although 12-lead ECG acquisition is often part of
thebedsidemonitor,aseparateECGmachineisalso
available. Depending on the ICU size and census, the
ICU also can own items such as dedicated, portable
X-ray machines and blood gas analyzers. Because of the
volatility of the patient's medical condition, and the
need to respond quickly to sudden changes, point-
of-care blood chemistry machines, which are small
enough to be positioned at a patient's bedside, have
been developed.
Bedside physiological data is often routed to a central
station for display, printing, and alarm monitoring. In
recent years, the importance of the central station as
a location to be carefully watched for adverse patient
events has diminished. Staffing in the ICU environment
usually involves a high nurse-to-patient ratio. Most alarm
events are recognized at the bedside, with the central
station serving more as workstation for archival retrieval
of alarm history and analysis of trends. The availability of
inexpensive computer hardware has made possible the
implementation of full disclosure systems that permit
the archiving of all waveforms for a period of up to sev-
eral days for all of the beds in the ICU. These are often
packaged as software within the central station monitor.
A consequence of the capabilities has been a reduction in
the need and use of strip-chart recorders at the bedside
or central station. There is little need to sift through
yards of paper strips to find the event of interest because
the full disclosure or alarm history record can be printed
at will. The laser printer has become the
de facto
hard-
copy device of choice.
Monitoring &
Diagnostics
Information Collection and
Clinical Information Systems
Therapy
Interpretation
Figure 4.2-1 Four elements required for effective management
of patient care.
Impedance based respiration
One to three invasive blood pressures
Noninvasive blood pressure
Pulse oximetry (SaO
2
)
Two temperatures
Thermal dilution cardiac output
The following additional monitoring functions are also
available as separate units or modules that can be relevant
to the management of ICU patient:
End tidal CO
2
Continuous cardiac output (CCO)
Impedance based cardiac output
Metabolic monitoring
Real-time blood gas monitoring
Mass spectrometry
Although provided as part of the therapeutic aspect of
the ICU, the life-support ventilator provides a full range
of pulmonary monitoring parameters as well.
Figure 4.2-2 Physiological monitoring at the central station.
