Guidance [Health Devices Oct 1992;21(10):374-9]
The primary purpose of apnea monitoring is to ensure adequate warning of
certain life-threatening respiratory and cardiac events, often in infants monitored at
home. However, parents often become frustrated by frequent alarms, and others may not use
the monitor at all. Unfortunately, ECRI has received a number of incident reports in which
infants have died while not connected to their monitors or where a failure to monitor was
suspected. We believe that some of these deaths may have been prevented if monitoring had
been used properly.
The most important step that parents can take to achieve effective
monitoring is to faithfully follow the directions of their doctor. In an effort to ensure
parental compliance, documentation capability has been added to many of today's monitors.
In addition, those involved in providing patient care, especially the prescribing
physicians, durable medical equipment (DME) providers, report scorers, interpreting
physicians, and other clinicians, should carefully review their monitoring programs and
the available documentation monitoring systems to determine how they can best meet their
patients' needs. Below, we discuss the factors to consider when contemplating documented
apnea monitoring and when selecting a documented monitoring system.
The Use of Documented Monitoring
Advantages of Documentation Systems
Documented monitoring offers distinct advantages over nondocumented
monitoring. Its most important benefit is that it can be used to confirm parental
compliance and reveal whether steps must be taken to improve it. It also provides evidence
of the time and type of alarms, and the tabular and waveform reports provide physicians
with information about a patient's condition that would not be verifiable with
conventional apnea monitors. Waveform documentation helps physicians to more accurately
distinguish true from false alarms and assess the severity of events.
Documentation can also provide early warnings of monitoring problems, as
well as vital information for investigations and research in the event of an infant death.
And the use of documentation systems has the potential to reduce the cost of patient care
by providing additional criteria for admission to and discharge from apnea programs and
also through reduced trips to patients' homes to resolve problems. However, no studies
have yet verified that either conventional apnea monitors or documentation systems improve
the quality of patient outcome.
Safety Features and Practices
Purchasers should inventory their existing monitors to determine whether
they have the essential safety features: heart-beat detectors with heart-rate alarms,
remote-alarm capability, power-loss alarms for non-battery-operated units, and electrodes
that cannot be plugged into electrical cords or outlets. Any monitor being considered for
purchase or currently in use that does not meet these minimum criteria for safety should
be replaced as soon as possible.
ECRI recommends that, at a minimum, compliance monitoring be used during
the first few weeks of the monitoring period for all patients, and we prefer that
documented monitoring be used throughout the monitoring period. In many cases, physicians
prescribe full-time compliance monitoring (i.e., monitor on and off times) only when
compliance is questionable, rather than routinely prescribing it for every patient.
However, if money is an issue and no problems are found, switching to nondocumented
monitoring is reasonably safe, as long as compliance and reporting are ensured. In
hospitals, compliance monitoring is not as critical because hospital staff will more
reliably follow the physician's orders. Unfortunately, we are not aware of any simple,
low-cost add-on device that can be used in conjunction with existing conventional apnea
monitors to add basic documentation capabilities, such as compliance monitoring.
Selection Factors for Apnea Documentation Monitors
Because no exact method or standard criteria for apnea monitoring yet
exist (see Health Devices
Oct 1992;21(10):339-41), ECRI believes that greater
monitoring capabilities and features (i.e., more channels and complete waveform and
tabular documentation) provide clinicians with greater flexibility, which may lead to
better patient management. Although greater capabilities may allow more information to be
collected, this is an advantage only if the information will be used. Purchasers should
therefore consider the available resources and anticipated use of these capabilities when
making purchasing decisions. Below, we discuss various selection factors for apnea
documentation systems and the relative merits and shortcomings of various capabilities and
features. Also see "The FDA Apnea Monitoring Standard" at the end of this
Most home apnea monitoring programs are limited to infants. However, some
programs include older children and adults. The needs of older patients, especially
adults, are different from those of infants, and these needs should be considered in the
purchasing process. For example, some adults are monitored at home because they are
receiving patient-controlled analgesia (PCA), and some PCA drugs are respiratory
suppressants that can significantly slow breathing. Also, many patients (usually adults)
are sedated while in the hospital. In these cases, units that alarm and document slow
breathing have advantages over other systems.
It is well recognized that impedance pneumography (IP)-based apnea
monitors are unable to detect obstructive apnea. Unfortunately, because most adult apnea
is obstructive, techniques other than, or in addition to, IP must be used to effectively
monitor and record apneic events in adults. Two possible methods are nasal airflow and
pulse oximetry (see below).
Monitor Performance and Impedance Pneumography
Although monitoring performance was not the focus of this evaluation of
IP-based systems, as it was in our previous study (Health Devices 16[3-4], Mar-Apr
1987), we noted that monitor performance does not appear to have changed significantly
over the past five years. As in our last evaluation, most of the monitors in this study
worked well most of the time. However, some more than others easily went into or out of
alarm status in the presence of aberrant signals. The most serious limitations of IP are
that it cannot detect the loss of airflow (obstructive apnea), and it may interpret
thoracic movements and other artifacts unrelated to respiration as breaths. However, IP
apnea monitoring is still the easiest, most practical method of detecting apnea in the
Although the Event mode of recording is a useful compromise between the
need for patient data and the need for memory conservation, it is subject to the
shortcomings of IP. Apnea monitors using IP technology do not detect all significant
patient events and do not work 100% reliably on all types of patients. Therefore,
documentation is not always an accurate representation of patient conditions.
Because some clinicians may tend to trust computer-generated hard-copy
information more than they do the parent's log or other account, the documentation now
produced by apnea systems may offer a false sense of security in monitor performance that
never existed in the past. Tabular data (without waveforms) provides only a thorough
chronology of alarms and events; it does not allow the user to verify the accuracy of the
recording of the event (e.g., to determine whether an apnea alarm was due to a valid
apneic episode or to an artifact). Neither tabular nor waveform Event mode recording can
ensure that a patient event was not missed. However, for those well versed in the
applications of IP in apnea monitoring, documentation has helped to heighten their
awareness of the shortcomings of this technology by giving them insight into what occurred
Memory Management and Capacity
Memory management and memory capacity should be fully investigated and
understood before selecting a documentation system. Monitoring system memory management
methods must be in agreement with the view of data priority adopted by the apnea program.
Because of electronic memory limitations and the associated cost factors, each monitor
manufacturer has to compromise the duration, quantity, and types of events kept in memory.
The waveform-documentation systems manage memory in one of three ways:
- First-in-first-out (FIFO). These systems keep the most recent data and overwrite the oldest
data. ECRI believes that this helps to maintain trending information that is
the most relevant to the patient's current condition; this is in agreement
with the general philosophy of trend monitoring. We prefer this approach.
- Halted recording. These
systems stop recording waveforms when the memory fills. These systems are an
alternative to FIFO systems and present no increased risk of inappropriate
data loss with sufficient memory capacity; also, some physicians prefer to
retain the data obtained at the start of the monitoring session.
- Prioritization. These systems keep events
that satisfy specific criteria based on the duration of events. This is the
least appropriate method of maintaining patient data, primarily because
longer heart-rate events are not necessarily the most severe. Although,
theoretically, longer respiratory events can be the most significant, this
is not always true because of the shortcomings (e.g., changes in
transthoracic impedance [TTI] due to body movements) of IP-based apnea
monitoring in the home.
Note that routinely downloading data will ensure that the effects of any
memory management method will cause minimal loss of data.
Total waveform time (TWT) is not an absolute measure of which memory
system will record more events on a given patient. Actual recording durations vary in the
clinical setting. However, during our testing of waveform-logging systems, we did find
that TWT is a general indication of recording duration because those systems with the
smallest TWT capacities consistently filled first.
During our discussions with clinical users, we found that event and
waveform memory-related problems and inconveniences are rare. However, all of the
currently available methods of memory management are subject to the loss of data.
Trade-offs must be made between the type (i.e., tabular or waveform) of documentation,
number and duration of events, system cost, system speed, and memory capacity. Again, the
method of memory management selected should be consistent with the goals of the specific
apnea monitoring program.
While a capacious memory may seem highly desirable, it is not usually
necessary. Apnea monitoring in the home requires personal attention from DME providers.
Memory should be considered sufficient if it can record without losing valuable data
between visits by the DME; memory capacity limitations should not result in the need for
more frequent visits. The frequency of home visits should be based on patient and family
needs, independent of documentation features. Documentation should not be viewed as either
a substitute for or a cause for increasing the periods between routine home visits. Remote
downloading and alarm and event-limit control are useful features when long distances or
time limitations may make it more efficient to carry out these functions from a central
Reimbursement and System Configuration
Cost factors, especially reimbursement, will have a significant effect on
which, if any, documentation systems are acquired. Those responsible for apnea monitoring
programs must have a clear understanding of reimbursement in their area before making
purchasing decisions. Some DMEs receive additional reimbursement for documentation
monitors over that received for nondocumentation monitors. Some receive no additional
reimbursement, and others receive reimbursement for only nondocumented monitoring when
periodic documentation studies are performed as proof of the need for monitoring.
Reimbursement also varies from region to region. Where reimbursement levels are high, DMEs
tend to convert a large percentage of their monitor line to documentation systems; as
reimbursement levels degrade, so does the willingness or ability to convert to these
One approach to updating apnea monitoring equipment in light of limited
reimbursement is to minimize the major cost factors. For example, for systems that require
a computer, purchasing an IBM clone, upgrading an existing underutilized computer, or
sharing an existing office computer may help to reduce the computer-related expenses.
Also, the DME's labor costs can be reduced by reducing the amount of data recorded after
the initial monitoring period; for example, some monitors allow portions of the memory to
be turned off. Another approach is to distribute the cost over an extended period. For
example, tabular-logging systems are generally less expensive to purchase and operate than
waveform-logging systems. Tabular reports may provide enough documentation to satisfy
insurance companies' requirement for proof of the need for monitoring and to verify
compliance. If physicians prescribe waveform-documentation systems, DMEs can acquire them
gradually. It is also important to anticipate upgrading or expanding the documentation
capabilities of an apnea program. Some manufacturers offer a trade-in value for their own
nondocumentation monitors toward the purchase of documentation monitors. Time and money
can be saved when purchasing tabular- and waveform-logging monitors that can be used with
the same computer software.
Some systems can directly print tabular event reports without a computer
and its associated costs. Before purchasing a computer for use with a documentation system
or a documentation system for use with an existing computer, purchasers must confirm that
they are compatible.
Some manufacturers of documentation systems also offer nondocumenting
apnea monitors. Existing nondocumenting monitors in inventory may influence a DME's
decision about which documentation systems to obtain. Apnea programs that are already
using one manufacturer's apnea monitors will have to consider whether purchasing
documentation monitors from another manufacturer will affect parents by creating confusion
in learning and becoming familiar with new monitors. Also, the DME's learning curve,
confidence level, physician familiarity, and costs must be considered.
Levels of Documentation
Systems with the most documentation capabilities have the potential to be
the most clinically useful and are preferred, especially in areas where reimbursement is
Four levels of waveform documentation are available:
- Level 1. The most
complete level of documentation is event recording of respiration and ECG
waveforms and heart-rate trend during respiration and heart-rate events.
- Level 2. These systems
contain the same channels as level 1, but ECG waveforms are recorded only
during a maximum of 10 heart-rate events.
- Level 3. ECG waveforms
are recorded for only a 15 sec portion of heart-rate events.
- Level 4. These systems contain the least
amount of documented waveform data currently available—respiration
waveforms and heart-rate trend.
As noted above, although waveform systems can be used to satisfy clinical
preferences and answer many questions, they may be more expensive to purchase and operate.
Alternatively, tabular documentation systems may cost less initially and can be less
complex to operate. They meet the basic needs of compliance, in some cases without a
computer, and allow verification of the presence of alarms (although not their validity)
without having to rely entirely on the parents' log. However, the initial cost difference
between waveform and tabular documentation systems may be under $500, which may not be
significant when distributed over the life of the device.
Additional Capabilities and Considerations
Blood (hemoglobin) oxygen saturation, or SpO2, can
be used by physicians to help determine the severity of a patient's condition. Pathologic
conditions related to low blood oxygen saturation may in some cases be related to apnea.
Oxygen saturation can be monitored noninvasively using a pulse oximeter. Some of the apnea
monitor manufacturers offer their own pulse oximeters, and most apnea monitors are
compatible with pulse oximeters from other manufacturers. However, at this time, pulse
oximetry should be given limited weight when selecting a documentation system.
The oximetry-derived oxygen saturation of hemoglobin value can be
documented as a number (SpO2), or it can be represented by a line
indicating SpO2 over time (i.e., a trend). One difficulty in
documenting pulse oximeter data is the errors that can occur from signal artifact (e.g.,
from probe movement) and frequent alarms due to excessive motion, which can rapidly fill
the monitor's memory. To partly compensate for these problems, all of the evaluated
monitors provide some indication of pulse oximeter artifact if an error is suspected. This
increases the utility of this SpO2 documentation. Oximetry-derived
pulse waveforms may be used to verify the validity of oximeter alarms through a manual
comparison of ECG and pulse waveforms.
Although oxygen saturation is valuable data, especially in view of the
shortcomings of the IP technology, monitoring SpO2 is expensive and
is difficult to reliably obtain on infants in the home because of its susceptibility to
false alarms. In addition to unnecessarily upsetting parents, false alarms may fill event
memory, requiring more frequent data downloads or loss of important events.
Systems that perform error checking on the SpO2 data
are the only type that should be considered for home use. Systems that can be triggered to
alarm or record events by the oximeter are preferred; several of the manufacturers
participating in our study offer these features with their own oximeter.
Pulse oximetry should be used only in cases when not having the SpO2
data will do more harm than the possibility of false alarms. SpO2 is
typically used in 10% or less of home monitoring applications with IP. Although some
clinicians prefer pulse oximetry data, ECG waveform data is currently the most practical
and cost-effective additional data that can be obtained in apnea monitoring programs.
As noted above, the ability to document ECG waveforms is a significant
advantage. Some clinicians use ECG waveforms to help determine the validity of patient
events and to determine the nature of aberrant signals. However, ECG waveform data is not
generally viewed as a direct indicator of event severity (SpO2 is a
better indicator of severity than ECG, but ECG is easier to detect reliably in the home;
see below). It also consumes much memory and can increase the time required to download,
transmit, and print waveform reports, and it requires more time for analysis. ECG data
also increases the frequency of downloading monitor memories. The ability to select ECG
waveform recording or to turn it off is therefore an important option for this feature.
Periodic Breathing (PB)
Some apnea monitoring programs and monitoring devices identify and
classify PB as a specific type of respiratory event. Breathing is classified as periodic
if it contains three or more pauses of greater than 3 sec that are separated by less than
20 sec of normal respiration. However, this is a strict definition, and, as with most
patient data, PB must be evaluated on an individual basis.
Alarming on and documenting PB is not generally considered useful,
primarily because individual breathing patterns vary widely. PB is more useful with
waveform capture so that clinicians can evaluate the event for themselves. However, few
clinicians use the PB function. Also, PB is a long event and consumes much memory, which
limits the amount of other waveform information that can be stored; therefore, it may be
useful to be able to turn off this feature.
The ability to detect and document slow breathing rates is a valuable tool
for treating patients (usually adults) undergoing drug therapy, whether using PCA at home
or being sedated in the hospital, that can cause respiratory suppression. Therefore, the
ability to document slow breathing waveforms is a preferred feature in adult applications.
However, slow breathing alarms can be excessive in infants and can cause the memory to
Today , auxiliary input channels for airflow temperature, CO2,
and pH are seldom used in the home because of their limited practicality Separate
electronic modules (i.e., nasal thermistors, capnometers, and esophageal probes) are
required, and these usually do not have alarms. Although data from these separate modules
can be documented on some systems, they can trigger an alarm or event recording only if
they have the appropriate output signals and the monitor has separate inputs.
Human Factors Design
Human factors design—including report presentation and software
operation and features—is very important in many aspects of apnea monitoring and
documentation system selection.
Tabular Report Presentation
- Tabular reports should be well organized and should also have the
— Good text print
— Patient identification,
report date, and page number on all pages;
— Complete tabular report
of patient alarms and events, equipment alarms, and time and date of
each occurrence; and
— The ability to customize
the report content (e.g., inclusion of physician's name, drug therapy,
and pie charts) may be useful for some users.
Waveform Report Presentation
- Waveform tracings and trends must have good
quality, organization, and layout and should meet the criteria for tabular
- In addition, they must also have the following:
— Horizontal scales that
permit viewing of individual breath and ECG waveforms;
— Vertical scales that can
accommodate the required range of signals;
— A minimum pre-event
waveform time equal to or greater than the alarm delays;
— Post-event waveform
selection of at least 15 sec (preferred); and
— Indicators (i.e., markers
on graph) for the start and stop of alarms and
- Event parameters should be on the page with the
waveform, including event identification or number, type, time, and
duration, as well as calculated physiologic values.
- Adjustable horizontal and vertical scale control for waveforms is
preferred to make interpretation easier.
Software Operation and Features
- The software package should be easy to install. The
entire procedure should be clearly documented.
- The system should be easy to learn and use, even
with little or no computer experience. It should not be necessary to
frequently refer to the manual for instructions.
- Help screens and prompts should be available at all
levels of the program.
- The software should supply the computer operator with all the necessary
tools to download, view, print, and store patient data efficiently.
- When packaged for transport, the monitor should not be unwieldy to
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* * *
The FDA Apnea Monitoring Standard
Scope and Status
The 1976 Medical Device Amendments to the Food, Drug, and Cosmetic Act
charge the Food and Drug Administration (FDA) with the responsibility of regulating the
safety and efficacy of medical devices and diagnostic products. One means by which this
responsibility is met is through the preparation of product standards by FDA's Center for
Devices and Radiological Health (CDRH).
Apnea monitors are in a high-priority category for standards because of
the risks and hazards associated with them. In 1986, FDA undertook efforts to establish
standards to improve the safety and effectiveness of apnea monitoring. To date , it
has issued two drafts of "The Standard for the Infant Apnea Monitor." The
standard covers requirements for all monitoring modalities in home and hospital infant
apnea monitors, including performance features, labeling, and test procedures.
The third draft of the standard is expected to be entered into the Federal
Register as a proposed rule sometime in 1992. If this does happen, it will take
several more years for finalization and phase-in. FDA estimates that the soonest the final
rule would take effect is mid-1995.
FDA and AAMI Cooperation
FDA has been working in consultation with the Apnea Monitoring Committee
formed by the Association for Advancement of Medical Instrumentation (AAMI). The committee
comprises manufacturers, physicians, and apnea professionals and is subdivided into task
groups. These groups focus on different monitoring modalities, such as impedance
pneumography (IP), inductive plethysmography, and pulse oximetry.
The committee is currently working on devising an apnea monitor test
method; this method is designed to use a database of recorded physiologic waveforms. All
meetings are open to interested parties, and participation is encouraged.
Once the standard is entered in the Federal Register and becomes a
final rule, monitor manufacturers will have about one year to phase in the required
changes to their apnea monitor systems. All monitors sold in the United States, District
of Columbia, and the Commonwealth of Puerto Rico will be affected. Devices sold before the
standard compliance deadline are not affected.
In order to make the task of complying with the FDA standard manageable,
some monitor manufacturers have been attempting to keep their apnea monitoring systems
compliant with the latest versions of the standard. Some manufacturers also have a monitor
trade-in program through which monitor purchasers can have systems updated to meet the
standard when it becomes effective.
- Apnea Monitors [12-575]
- Apnea Monitors, Recording [17-885]
- Impedance Pneumograph Monitors [12-621]