After reading this chapter,1 you should know the answers to these questions:
● What is patient monitoring, and why is it done?
● What are the primary applications of computerized patient-monitoring systems in the
intensive-care unit?
● How do computer-based patient monitors aid health professionals in collecting,
analyzing, and displaying data?
● What are the advantages of using microprocessors in bedside monitors?
● What are the important issues for collecting high-quality data either automatically or
manually in the intensive-care unit?
● Why is integration of data from many sources in the hospital necessary if a computer
is to assist in critical-care-management decisions?
What Is Patient Monitoring?
Continuous measurement of patient parameters such as heart rate and rhythm, respiratory rate, blood pressure, blood-oxygen saturation, and many other parameters have become a common feature of the care of critically ill patients. When accurate and immediate decision-making is crucial for effective patient care, electronic monitors frequently are used to collect and display physiological data. Increasingly, such data are collected using non-invasive sensors from less seriously ill patients in a hospital’s medical-surgical units, labor and delivery suites, nursing homes, or patients’ own homes to detect unexpected life-threatening conditions or to record routine but required data efficiently. We usually think of a patient monitor as something that watches for—and warns against—serious or life-threatening events in patients, critically ill or otherwise. Patient monitoring can be rigorously defined as “repeated or continuous observations or measurements of the patient, his or her physiological function, and the function of life support equipment, for the purpose of guiding management decisions, including when to make therapeutic interventions, and assessment of those interventions” (Hudson, 1985, p. 630). A patient monitor may not only alert caregivers to potentially life-threatening events; many also provide physiologic input data used to control directly connected lifesupport devices. In this chapter, we discuss the use of computers to assist caregivers in the collection, display, storage, and decision-making, including interpretation of clinical data, making therapeutic recommendations, and alarming and alerting. In the past, most clinical data were in the form of heart and respiratory rates, blood pressures, and flows, but today they include integrating data from bedside instruments which measure blood gases, chemistry, and hematology as well as integrating data from many sources outside the intensive-care unit (ICU). Although we deal primarily with patients who are in ICUs, the general principles and techniques are also applicable to other hospitalized patients. For example, patient monitoring may be performed for diagnostic purposes in the emergency room or for therapeutic purposes in the operating room. Techniques that just a few years ago were used only in the ICU are now routinely used on general hospital
units and in some situations by patients at home.
A Case Report
We will use a case report to provide a perspective on the problems faced by the healthcare team caring for a critically ill patient: A young man is injured in an automobile accident. He has multiple chest and head injuries. His condition is stabilized at the accident scene by skilled paramedics using a microcomputer-based electrocardiogram (ECG) monitor, and he is quickly transported to a trauma center. Once in the trauma center, the young man is connected via sensors to computer-based monitors that determine his heart rate and rhythm and his blood pressure. Because of the head injury, the
patient has difficulty breathing, so he is connected to a microprocessor-controlled ventilator. Later, he is transferred to the ICU. A fiberoptic pressure-monitoring sensor is inserted through a bolt drilled through his skull to continuously measure intracranial pressure with another computer-controlled monitor. Clinical chemistry and blood-gas tests are performed in two minutes at the bedside with a microcartridge inserted into the physiologic monitor, and the results are transmitted to the laboratory computer system and the ICU system using a Health Level 7 (HL7) interface over a standard Ethernet network. With intensive treatment, the patient survives the initial threats to his life and now begins the long recovery process. Unfortunately, a few days later, he is beset with a problem common to multiple trauma victims—he has a major nosocomial (hospital-acquired) infection and develops sepsis, adult respiratory distress syndrome (ARDS), and multiple organ failure. As a result, even more monitoring sensors are needed to acquire data and to assist with the
patient’s treatment; the quantity of information required to care for the patient has increased dramatically. The ICU computer system provides suggestions about how to care for the specific problems, provides visual alerts for life-threatening situations, and organizes and reports the mass of data so that caregivers can make prompt and reliable treatment decisions. The patient’s physicians are automatically alerted to critical laboratory and blood gas results as well as to complex physiological conditions by detailed alphanumeric pager messages. His ARDS is managed with the assistance of a computer-monitored
Patient Monitoring in Intensive-Care Units
There are at least five categories of patients who need physiological monitoring:
- Patients with unstable physiological regulatory systems; for example, a patient whose respiratory system is suppressed by a drug overdose or anesthesia
- Patients with a suspected life-threatening condition; for example, a patient who has findings indicating an acute myocardial infarction (heart attack)
- Patients at high risk of developing a life-threatening condition; for example, patients immediately after open-heart surgery or a premature infant whose heart and lungs are not fully developed
- Patients in a critical physiological state; for example, patients with multiple trauma or septic shock.
- Mother and baby during the labor and delivery process.
Care of the critically ill patient requires prompt and accurate decisions so that lifeprotecting and life-saving therapy can be appropriately applied. Because of these requirements, ICUs have become widely established in hospitals. Such units use computers almost universally for the following purposes:
● To acquire physiological data frequently or continuously, such as blood pressure readings
● To communicate information from data-producing systems to remote locations (e.g., laboratory and radiology departments)
● To store, organize, and report data
● To integrate and correlate data from multiple sources
● To provide clinical alerts and advisories based on multiple sources of data
● To function as a decision-making tool that health professionals may use in planning the care of critically ill patients
● To measure the severity of illness for patient classification purposes
● To analyze the outcomes of ICU care in terms of clinical effectiveness and cost effectiveness
Historical Perspective
The earliest foundations for acquiring physiological data date to the end of the Renaissance period.2 In 1625, Santorio, who lived in Venice at the time, published his methods for measuring body temperature with the spirit thermometer and for timing the pulse (heart) rate with a pendulum. The principles for both devices had been established by Galileo, a close friend. Galileo worked out the uniform periodicity of the pendulum by timing the period of the swinging handelier in the Cathedral of Pisa, usinghis own pulse rate as a timer. The results of this early biomedical-engineering collaboration, however, were ignored. The first scientific report of the pulse rate did not appear until Sir John Floyer published “Pulse-Watch” in 1707. The first published course of fever for a patient was plotted by Ludwig Taube in 1852. With subsequent improvements in the clock and the thermometer, the temperature, pulse rate, and respiratory
rate became the standard vital signs. In 1896, Scipione Riva-Rocci introduced the sphygmomanometer (blood pressure
cuff), which permitted the fourth vital sign, arterial blood pressure, to be measured. A Russian physician, Nikolai Korotkoff, applied Riva-Rocci’s cuff with a stethoscope developed by the French physician Rene Laennec to allow the auscultatory measurement3 of both systolic and diastolic arterial pressure. Harvey Cushing, a preeminent U.S. neurosurgeon of the early 1900s, predicted the need for and later insisted on routine arterial blood pressure monitoring in the operating room. Cushing also raised two questions familiar even at the turn of the century:
(1) Are we collecting too much data?
(2) Are the instruments used in clinical medicine too accurate? Would not approximated values be just as good? Cushing answered his own questions by stating that vitalsign measurements should be made routinely and that accuracy was important (Cushing, 1903). Since the 1920s, the four vital signs—temperature, respiratory rate, heart rate, and
arterial blood pressures—have been recorded in all patient charts. In 1903, Willem Einthoven devised the string galvanometer for measuring the electrocardiogram (ECG), for which he was awarded the 1924 Nobel Prize in physiology. The ECG has become an important adjunct to the clinician’s inventory of tests for both acutely and chronically
ill patients. Continuous measurement of physiological variables has become a routine part of the monitoring of critically ill patients. At the same time that advances in monitoring were made, major changes in the therapy of life-threatening disorders were also occurring. Prompt quantitative evaluation of measured physiological and biochemical variables became essential in the decisionmaking process as physicians applied new therapeutic interventions. For example, it is
now possible—and in many cases essential—to use ventilators when a patient cannot breathe independently, cardiopulmonary bypass equipment when a patient undergoes open-heart surgery, hemodialysis when a patient’s kidneys fail, and intravenous (IV) nutritional and electrolyte (e.g., potassium and sodium) support when a patient is unable to eat or drink.
Development of Intensive-Care Units
To meet the increasing demands for more acute and intensive care required by patients with complex disorders, new organizational units—the ICUs—were established in hospitals beginning in the 1950s. The earliest units were simply postoperative recovery rooms used for prolonged stays after open-heart surgery. Intensive-care units proliferated
rapidly during the late 1960s and 1970s. The types of units include burn, coronary, general surgery, open-heart surgery, pediatric, neonatal, respiratory, and multipurpose medical-surgical units. Today there are an estimated 75,000 adult, pediatric, and neonatal intensive care beds in the United States. The development of transducers and electronic instrumentation during World War II dramatically increased the number of physiological variables that could be monitored. Analog-computer technology was widely available, as were oscilloscopes, electronic
devices used to depict changes in electrical potential on a cathode-ray tube (CRT) screen. These devices were soon used in specialized cardiac-catheterization4 laboratories, and they rapidly found their way to the bedside. Treatment for serious cardiac arrhythmias (rhythm disturbances) and cardiac arrest (abrupt cessation of heartbeat)—major causes of death after myocardial infarctions—became possible. As a result, there was a need to monitor the ECGs of
patients who had suffered heart attacks so that these episodes could be noticed and treated immediately. In 1963, Day reported that treatment of postmyocardialinfarction patients in a coronary-care unit reduced mortality by 60 percent. As a consequence, coronary-care units—with ECG monitors—proliferated. The addition of online blood-pressure monitoring quickly followed. Pressure transducers, already used in the cardiac-catheterization laboratory, were easily adapted to the monitors in the ICU. With the advent of more automated instruments, the ICU nurse could spend less time manually measuring the traditional vital signs and more time observing and caring for the critically ill patient. Simultaneously, a new trend emerged; some nurses moved away from the bedside to a central console where they could monitor the ECG and other vital-sign reports from many patients. Maloney (1968) pointed out that this was an inappropriate use of technology when it deprived the patient of adequate personal attention at the bedside. He also suggested that having the nurse record vital signs every few hours was “only to assure regular nurse–patient contact” (Maloney, 1968, p. 606). As monitoring capabilities expanded, physicians and nurses soon were confronted with a bewildering number of nstruments; they were threatened by data overload. Several investigators suggested that the digital computer might be helpful in solving the problems associated with data collection, review, and reporting.
Development of Computer-Based Monitoring
Teams from several cities in the United States introduced computers for physiological monitoring into the ICU, beginning with Shubin and Weil (1966) in Los Angeles and then Warner and colleagues (1968) in Salt Lake City. These investigators had several motives:
(1) to increase the availability and accuracy of data,
(2) to compute derived
variables that could not be measured directly,
(3) to increase patient-care efficacy,
(4) to allow display of the time trend of patient data, and
(5) to assist in computer-aided decision-making.
Each of these teams developed its application on a mainframe computer system, which required a large computer room and special staff to keep the system operational 24 hours per day. The computers used by these developers cost over $200,000 each in 1965 dollars! Other researchers were attacking more specific challenges in patient monitoring. For example, Cox and associates (1972) in St. Louis developed algorithms to analyze the ECG for heart rhythm disturbances in real-time. The arrhythmiamonitoring system, which was installed in the coronary-care unit of Barnes Hospital in
1969, ran on a relatively inexpensive microcomputer. As we described, the advent of integrated circuits and other advances allowed computing power per dollar to increase dramatically. As hardware became smaller, more reliable, and less expensive, and as better software tools were developed, simple analog processing gave way to digital signal processing. Monitoring applications developed by the pioneers using large central computers now became possible using dedicated microprocessor-based machines at the bedside. The early bedside monitors were built around “bouncing-ball” or conventional oscilloscopes and analog-computer technology. As computer technology has advanced, the definition of computer-based monitoring has changed. The early developers spent a major part of their time deriving data from analog physiological signals. Soon the data-storage and decision-making capabilities of the computer monitoring systems came under the investigator’s scrutiny. Therefore, what was considered computer-based
patient monitoring in the late 1960s and early 1970s is now entirely built into bedside monitors and is considered simply a “bedside monitor.” Systems with database functions, report-generation systems, and some decision-making capabilities are usually called computer-based patient monitors.
Advantages of Built-In Microcomputers
Today, bedside monitors contain multiple microcomputers, with much more computing power and memory than was available in the systems used by the computer monitoring pioneers. Bedside monitors with built-in microcomputers have the following advantages over their analog predecessors (Weinfurt, 1990):
● The digital computer’s ability to store patient waveform information such as the ECG permits sophisticated pattern recognition and physiological signal feature extraction. Modern microcomputer-based bedside monitors use multiple ECG channels and pattern recognition schemes to identify abnormal waveform patterns and then to classify
ECG arrhythmias.
● Signal quality from multiple ECG leads can now be monitored and interference noise minimized. For example, the computer can watch for degradation of ECG skin–electrode contact resistance. If the contact is poor, the monitor can alert the nurse to change the specified problematic electrode.
● Physiological signals can be acquired more efficiently by converting them to digital form early in the processing cycle. The waveform processing (e.g., calibration and filtering, as described in Chapter 5) then can be done in the microcomputer. The same process simplifies the nurse’s task of setting up and operating the bedside monitor by
eliminating the manual calibration step.
● Transmission of digitized physiological waveform signals is easier and more reliable. Digital transmission of data is inherently noise-free. As a result, newer monitoring systems allow health-care professionals to review a patient’s waveform displays and derived parameters, such as heart rate and blood pressure, at the bedside, at a central station in the ICU, or at home via modem on a laptop computer.
● Selected data can be retained easily if they are digitized. For example, ECG strips of interesting physiological sequences, such as periods of arrhythmias, can be stored in the bedside monitor for later review. Today’s monitors typically store all of the waveform data from multiple leads of ECG and blood pressure transducers for
at least 24 hours and sometimes for even longer.
● Measured variables, such as heart rate and blood pressure, can be graphed over prolonged periods to aid with detection of life-threatening trends.
● Alarms from bedside monitors are now much “smarter”and raise fewer false alarms. In the past, analog alarm systems used only high–low threshold limits and were susceptible to signal artifacts (Gardner, 1997). Now, computer-based bedside monitors often can distinguish between artifacts and real alarm situations by using the information derived from one signal to verify that from another and can confidently alert physicians and nurses to real alarms. For example, heart rate can be derived from either the ECG or the arterial blood pressure. If both signals indicate dangerous tachycardia (fast heart rate), the system sounds an alarm. If the two signals do not agree, the monitor can notify the health-care professional about a potential instrumentation or medical problem. The procedure is not unlike that performed by a human verifying possible problems by using redundant information from simpler bedside monitor alarms. Despite these
Data Acquisition and Signal Processing The use of microcomputers in bedside monitors has revolutionized the acquisition, display, and processing of physiological data. There are virtually no bedside monitors or ventilators marketed today that do not use at least one microcomputer. Now Patient Monitors can shows a block diagram of a bedside monitor. Physiological signals such as the ECG are derived from sensors that convert biological signals (such as pressure, flow, or mechanical movement) into electrical signals. In modern computerized monitors, these signals are digitized as close to the patient as possible.
Arrhythmia Monitoring—Signal Acquisition and Processing
Although general-purpose computer-based physiological monitoring systems are now being more widely adopted, computer-based ECG arrhythmia-monitoring systems were accepted quickly (Weinfurt, 1990). Electrocardiographic arrhythmia analysis is one of the most sophisticated and difficult of the bedside monitoring tasks. Conventional
arrhythmia monitoring, which depends on people observing displayed signals, is expensive, unreliable, tedious, and stressful to the observers. One early approach to overcoming these limitations was to purchase an arrhythmia-monitoring system operating on a time-shared central computer. Such minicomputer-based systems usually monitored 8 to 17 patients and cost at least $50,000.
The newest bedside monitors, in contrast, have built-in arrhythmia-monitoring systems. These computers generally use a 32-bit architecture, waveform templates, and realtime feature extraction in which the computer measures such features as the R-R interval and QRS complex width; and template correlation, in which incoming waveforms are compared point by point with already classified waveforms (Weinfurt, 1990). Using signals from four ECG leads the computer has correctly classified a rhythm abnormality—in this case, a premature ventricular contraction (PVC). The bedside monitor also retains an ECG tracing record in its memory so that at a later time a health professional can review
the information.
Wave Form Classification
Computer algorithms for processing ECG rhythms take sampled data, and extract features, such as the amplitude and duration of the QRS complex (Weinfurt, 1990). In most schemes, each time the QRS detector is tripped, it signals a beat classification subprogram, which receives four channels of ECG data at the same time. Such a beat-classification scheme compares the waveform of each incoming beat with that of one or more clinically relevant waveform classes already established for the patient. If the new waveform matches any of those already classified, the “template” of that waveform class is updated to reflect any minor evolutionary changes in the shape. Most beat-classification schemes have the capacity to store up to 30 templates. The performance of these multilead monitors has been dramatic; however, such
arrhythmia monitors are still not perfect. Detecting and identifying pacemaker signals poses special problems for digital
computer-based monitoring systems. Pacemaker signals do not reliably traverse the analog acquisition circuitry, and the pacemaker “spikes” are very narrow such that they can occur between data samples and be missed entirely. As a result, special analog “injection” methods are used to enhance the pacemaker “spike” so that it can be more easily detected (Weinfurt, 1990).
Full-Disclosure and Multilead ECG Monitoring
Contemporary central monitors combine the advantages of digital waveform analysis as described above with high-capacity disk drives to store one or more days worth of continuous waveform data, including ECG. Some of these monitors can support recording full disclosure or synthesis of the entire 12-lead ECG on a second by second basis.
Figure 17.9 shows a run of ventricular tachycardia in a portion of a 24-hour full disclosure ECG display. Now a bedside physiologic monitor displaying a Web page view of a full 12-lead ECG with computerized interpretations.
ST segment analysis of the ECG has also become very important because ST segment displacement is indicative of ischemic episodes of the heart muscle. Changes in open-heart procedure and administration of thrombolytic therapy are predicated on ST segment analysis. Multilead monitors now offer the opportunity to monitor ST segment changes.
Bedside Point of Care Laboratory Testing
Over the past decade, laboratory chemical, hematologic, and blood gas testing processes have progressed from “wet” methods in which specific liquid reagents were mixed with blood or serum to perform analyses to a more or less “dry” phase in which analyses are performed by bringing a blood sample in contact with a reagent pack. Additional development has miniaturized both the blood-analysis cartridge and the blood-analysis machine to the point that the entire analysis system consists of a small plug-in module to a bedside physiological monitor. Many laboratory tests, including pH, PO2, PCO2, HCO3, electrolytes, glucose, ionized calcium, other chemistries, hemoglobin, and hematocrit, can be performed in 2 minutes using two or three drops of blood. Results are displayed on the bedside physiological monitor and are stored in the monitor’s database for comparison with previous results. These laboratory results obtained at the bedside are also automatically transmitted through the monitoring network and hospital’s backbone network to the laboratory computer system, and other systems as required, so that the results can be integrated into the patient’s long-term records.
Commercial Development of Computer-Based
Monitoring and Intensive-Care-Unit Information Systems
The development of central stations and integrated arrhythmia systems based on standard microcomputer-based server hardware and software platforms has led to widescale distribution in the clinical environment. These systems possess database and analysis functions previously reserved for larger systems, and well over 2000 such systems are in use in ICUs worldwide.
In recent years, the bedside monitor has become a focal point for data entry and presentation. In fact, most bedside monitoring systems sold today can also acquire and display data from clinical laboratories, bedside laboratory devices such as blood chemistry machines, and a host of other devices such as ventilators. Unfortunately each of these monitors has its own proprietary communications protocol and data acquisition scheme. As a result, the user community is faced with bedside monitors that function like “mini” patient-data-management systems. Furthermore, the desire to capture and
manage all clinical data for patients in a critical care setting (not just patient monitoring data) has resulted in development of specialized ICU information systems. It is common for hospitals to acquire computer-based bedside monitors, which must be interfaced to an ICU information system, which in turn may be interfaced with a hospital’s clinical information system. Several large, capable, and reputable manufacturers have supplied over 350 computer-based ICU information systems worldwide. Three of the major companies involved in the development of such computer-based charting and monitoring systems are Philips Medical Systems with its CareVue system (Shabot, 1997b), GE Medical Systems formerly Marqueette Electronics with its Centricity Clinical Information system, and Eclipsys (formerly EMTEK) with its Continuum 2000 computerized charting application (Brimm, 1987; Cooke & Barie, 1998).
During the time that commercially available physiological monitoring systems were being developed, imaging systems – x-ray, computed tomagraphy (CT) and magnetic resonance imaging (MRI) were also undergoing major developments and transformations. Medical imaging plays a major role in the diagnosis and treatment of the critically ill. With most medical images now available in digital format it is now convenient for care providers to have fast and convenient access to medical images via the web.
Information Management in the Intensive-care Unit
One of the goals of bedside patient monitoring is to detect life-threatening events promptly so that they can be treated before they cause irreversible organ damage or death. Care of the critically ill patient requires considerable skill and necessitates prompt, accurate treatment decisions. Healthcare professionals collect numerous data through frequent observations and testing, and more data are recorded by continuousmonitoring equipment. Physicians generally prescribe complicated therapy for such patients. As a result, enormous numbers of clinical data accumulate (Buchman, 1995; Kahn, 1994; Sailors & East, 1997; Shabot, 1995;Morris 2003). Professionals can miss important events and trends if the accumulated data are not presented in a compact, well-organized form. In addition, the problems of managing these patients have been made even more challenging by economic pressures to reduce the cost of diagnostic and therapeutic interventions. Continuity of care is especially important for critically ill patients. Such patients are generally served by teams of physicians, nurses, and therapists. Data often are transferred from one individual to another (e.g., the laboratory technician calls a unit clerk who reports the information to a nurse who in turn passes it on to the physician who makes a decision). Each step in this transmission process is subject to delay and error. The medical record is the principal nstrument for ensuring the continuity of care for patients.
Patient Monitors can shows a blood-gas report indicating the acid–base status of the patient’s
blood, as well as the blood’s oxygen-carrying capacity. Note that, in addition to the
numerical parameters for the blood, the patient’s breathing status is indicated. Based on
all these clinical data, the computer provides an interpretation. For life-threatening
situations, the computer prompts the staff to take the necessary action
