From: AAAI Technical Report SS-94-01. Compilation copyright © 1994, AAAI (www.aaai.org). All rights reserved.
NEONATAL WORKSTATION FOR INSPIRED OXYGEN CONTROL
AND CLINICAL MONITORING
Yao Sun MD,Isaac Kohane MD,Phi)
Children’s Hospital, Harvard University Medical School, Boston, MA
designed to advise clinicians about ventilator
management. Some recent examples include:
VentPlan, a ventilator managementadvisor that
interprets patient data within a physiological model
to predict the effect of proposedventilator changes;
(11) ESTER, a program which assesses the
patient’s pathophysiological state using modified
APACHE-II
criteria, then offers suggestions for
weaning from intermittent mandatoryventilation;
(6) WEANPRO,
a program designed to help wean
postoperative patients from ventilators; (15) and
KUSIVAR, a program which describes
a
comprehensive system for respiratory management
during all phases of pulmonary disease. (10)
Background
Although many such expert systems have been
Oxygentoxicity plays a role in the developmentof described, few have been tested in clinical patient
chronic lung disease in newborninfants requiring care.
mechanical ventilation. (12,16,17) In premature
infants, oxygentoxicity is also implicated in the Other investigators have studied direct computer
developmentof retinopathy of prematurity. (1,7,8) control of specialized aspects of ventilator
Therefore,
minimizing oxygen exposure of management.(14,18) For example, studies
ventilated newborninfants has becomea priority in computer-controlled optimization of positive endneonatal intensive care.
expiratory pressure, and computerizedprotocols for
managementof adult respiratory distress syndrome
By constantly monitoring the signals from cardiac have been explored by East. (3,4) A computerized
and pulse oximetry monitors and correlating these ventilator weaning system for post-operative
signals, a computer system has been designed to patients has beentested by Strickland. (13)
control the inspired oxygen concentration (FIO2)
delivered to mechanically ventilated newborn Experience in computer controlled ventilation in
infants. This computer-controlled FIO2 delivery infants, however, is limited. In one of the few
system can continuously adjust oxygendelivery to reports available in the literature, Morozoffand
the minimumamount needed to achieve a target Evans showedthat a computerized FIO2 controller
oxygensaturation.
could maintain the oxygensaturation of a ventilated
newborn infant at least as well, and sometimes
physiological data received by the computerfrom a better than manual FIO2 control. (9) They
patient monitoring system is readily available for described their FIO2controller as a "differentialselective storage and analysis. Thesedata could be feedback" controller. This description matches the
utilized in several ways. The information for an general class of controllers knownas "proportional
individual patient could be analyzed and plotted to integral derivative" (PID) controllers. For best
need to be
detect trends in clinical
improvement or response, most PID controllers
deterioration.
By comparing data from many optimized for the system that they will be used in.
neonates, we might also elucidate physiological This maylead to degradation of performanceif the
system changes.
trends and patterns associated with particular
pulmonary diseases. Displaying the data in a
selective and informative waywill also benefit the Clinical monitoring systems have also been
clinician by facilitating the analysis of enormous described previously. Examplesinclude Guardian,
quantities of raw information.
a "proof of concept"of an intelligent agent designed
to coordinate a range of reasoningtasks in intensive
Investigation into computer-controlledor computer- care monitoring, (5) and Simon, a series of semiassisted mechanicalventilation is expanding. One independent modules designed to collect and
form of computerassistance is an "expert system" analyzeclinical data whileinterpreting patient status
Introduction
The regulation of oxygen delivery to acutely ill
infants requiring mechanicalventilation is a vital
process in neonatal intensive care medicine. We
have designed a microcomputer based system to
automatically and continuously control the inspired
oxygeff-" concentration (FI02) delivered
mechff~ically ventilated newborn infants. In
addition, wewill utilize this computerplatform to
collect and analyzeclinical data (such as heart rate,
respiratory rate, arterial blood pressure, and oxygen
saturation) in newborn infants with pulmonary
disease.
156
and predicting
parameters. (2)
the evolution
of monitored
The present system incorporates a new FIO2
controller in the context of a system designed to
collect, store, and display the physiological
monitored data for mechanically ventilated newborn
infants.
System description
The system consists of a microcomputer, a
ventilator with electronic signal outputs, a clinical
monitor with signal outputs, and the patient.
Software currently exists that enable clinical
monitors to accept input signals from a ventilator
indicating ventilator parameters such as the FIO2.
The clinical monitor also collects patient
physiological data such as heart rate, respiratory
rate, and oxygen saturation. Using these data
inputs from the clinical monitor, the computerwill
execute an algorithm to makechanges in the FIO2
to achieve a target oxygensaturation. The computer
will also continuouslyrecord the clinical data input
for later retrieval and analysis.
that response.
Thesystem’s user interface allows the clinician to
enter identifying patient information and critical
alarms limits for the oxygensaturation, heartrate,
mean blood pressure and respiratory rate. The
clinician also sets the target oxygensaturation for
the systemto maintain.
Although it is currently the only active control
function, the FIO2controller is incorporated in a
processing loop that includes data collection,
diagnostic analysis, and data storage. This general
architecture will enable expansionof the system to
accommodatefuture diagnostic and therapeutic
options, such as the implementation of total
ventilator control and diagnosis of pulmonary
disease.
System Testing
Thesystemhas been tested on the data set of patient
physiological information provided for this
symposium.For the purposes of FIO2 control, the
only data that need processing are the oxygen
saturation, the "arterial heartrate", the ECG
Currently, the system is designed to operate by (cardiovascular monitor) heartrate, and the FIO2.
displaying suggested FIO2changesto the clinician, The other patient information is gathered and
rather than to control the ventilator directly. This stored.
ensures medical safety until the system is fully
tested for clinical efficacy.
Since the data set represents static information, it
did not test the FIO2controller’s response to a
The algorithm to be tested in this system has two dynamically changing system. The system
features that differ from a standard PIDcontroller. performsthe followingactions correctly for the data
First, changes in the FIO2 will be based on the set:
hemoglobin-oxygendissociation curve. This builds 1) For the target oxygen saturation set by the
in a "predictive" componentto the controller based
clinician, the controller will suggest FIO2
on the expected changes in oxygen saturation for
changes in the appropriate direction (higher or
given changes in partial pressure of oxygen. As
lower) with appropriate adjustments in the
patient oxygensaturation values are collected by the
magnitude of FIO2 changes based on the
system, these values are mappedto a corresponding
difference
between the measured oxygen
portion of the hemoglobin-oxygen dissociation
saturation and the target.
curve. If the oxygensaturation mapsto a steeper 2) Validation of the oxygensaturation is performed
portion of the curve, smaller changes in FIO2will
by comparingthe "arterial heartrate" with the
be made, and correspondingly larger changes in
ECGheartrate.
The arterial
saturation is
FIO2will occurfor flatter portions of the curve(i.e.
presumedto be an artifact if the two heart rates
at high oxygensaturation values).
do not correlate within 5 beats/minute.
3) The system correctly displays alarm messages
Secondly,the algorithm will dynamicallyadjust the
whenthe physiological information represents
magnitudeof the changes in FIO2 dependingon the
valuesoutsidethe limits set by the clinician.
individual patient’s
responses. This will 4) All the patient data is stored in a file for later
compensate for changes in a patient’s clinical
retrieval and analysis.
condition over time, and also allow the system to be
used with different patients without the need to Subsequent clinical trials of the FIO2 control
modifythe system for each patient. The adjustment system will test the effectiveness of the controller
algorithm works by examining the patient’s past in maintainingpatient oxygensaturations. Data will
response to FIO2 change and regulating the be analyzed to compare the oxygen exposure of
magnitude of subsequent FIO2 changes based on patients during "open loop" computer control vs.
157
during manual FIO2 control. If the data analysis 6) Hernandez-Sande C, Moret-Bonillo
V,
reveals that the computer FIO2 control system
Alonso-Betanzos A.
provides lower patient oxygen exposure without
ESTER:an expert system for management of
compromise
in tissue oxygenation,a clinical trial of
respiratory weaningtherapy.
direct computercontrol of ventilator FIO2will be
IEEE Tl.ans Biomed Eng 1989; 36: 559.
conducted.
7) Kinsey VE.
Retrolental fibroplasia: cooperative study of
Summary
retrolental fibroplasia and the use of oxygen.
The implementation of this system to control FIO2
Arch Ophthalmol 1956; 56: 481.
in mechanically ventilated newborns may have 8) LenmanJT, GuyLP, Dancis J.
important clinical implications for reducing the
Retrolental fibroplasia and oxygen therapy.
development of chronic lung disease and
JAMA1954; 155: 223.
retinopathy of prematurity. In addition, the data 9) Morozoff PE, Evans RW.
collection functions of the system will allow
Closed-loop control of Sa02 in the newborn
analysis of physiological variables in multiple
infant.
ways. As the system evolves, concurrent selective
Biomed Instl’um Technol 1992; 26:117.
display of realtime data will also enable clinicians to 10) RudowskiR, Frostell C, Gill H.
assimilate and process raw information in an
A knowledge-based support system for
efficient manner.
mechanical ventilation of the lungs. The
KUSIVARconcept and prototype.
Currenttesting with static clinical data verifies that
Comput Methods Programs Biomed
the FIO2 control algorithms will produce
1989; 30: 59.
appropriate recommendations to increase or 11) Rutledge G, ThomsenG, et al.
decrease the FIO2 while observing the alarms and
VentPlan: a ventilator-management advisor.
limits imposed by the clinician user. Further
Proc Annu Symp Comput Appl Med
dynamictesting in the neonatalintensive care setting
Care 1991: 869.
will evaluate the ability to respond to changing 12) Saugstad OD.
patient clinical conditions.
Oxygentoxicity in the neonatal period.
Acta Paediatr Stand 1990; 79: 881.
13) Strickland JH, Hasson JH.
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