Infusion Pump Controller

1
Infusion Pump Controller

• Requirements Definition
• A
• Decision-Table Approach

by
Richard Riehle
2
CARA

• Computer-Aided Resuscitation Algorithm
• Purpose
• Blood Pressure Monitoring
• Prevent Hypotension
• Fluid Resuscitation

3
Controlling Instrumentation

• Infusion Pump
• Physiological Monitoring Device
• arterial line
• non-invasive cuff
• pulse wave
• others may be added

4
Objective

• Use results from PMD
• Define acceptable range for BP
• Detect out of range conditions
• Activate M100 Infusion Pump
• Fluid resuscitation measures
• Log activity

5
Some General Software Guidelines

• Safety Critical Application
• Single Computer
• Single-threaded Algorithm
• Real-time
• i.e. tight timing constraints
• Must be used in Rugged environment
• Remote Communication Option
• Marginal User Expertise

6
Functional Software Guidelines

• Data Input From Sensors
• Single BP Reading
• Visual Display of Data
• User-controllable range settings
• Error Detection
• Is sensor behaving correctly?
• Is M100 behaving correctly?
• Proportional Close-loop Algorithm
• drives M100 Infusion Pump

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Software Behavioral Considerations

• Many possible conditions
• BP Readings may vary
• Possible interruption for maintenance
• e.g. change the IV Bag
• change location of infusion tube
• Relatively few possible actions
• Actions require feedback loop for error control

Question for future design Can this be a
cyclic executive design or do we need priority
preemptive scheduler?
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Approach to Requirements Definition
Real-time extensitions to Structured Analysis
Method

• Possible Approaches
• Structured Methods
• Hately-Pirbhai Boeing Method
• Buhr Machine charts
• Object Modeling
• UML and Use Cases
• Schlaer-Mellor
• CRC Cards
• Formal Methods
• State Based Modeling

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Chosen Approach

• State Based Modeling
• Why?
• Single-purpose algorithm
• Not an object-oriented problem
• Use case interesting but unnecessary
• Decision-tables Will Work Fine
• Could also use formal methods, but
• There are more conditions than actions
• Timing issues are important
• Overkill

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Why Decision Table Approach?

• Safety-critical permits no set of conditions to
  be overlooked.
• Algorithmic implementation can map well to
  decision table
• Facilitates Communication
• Easy for customer to understand
• Easy for programmer to understand

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Decision Table Model - 1
Condition-1 T T T T F F F F Condition_2
T T F F F T T F Condition-3 T F T F F T F
T Action-1 X X Action-2
X X Action-3 X X Action-4
X X X Action-5 X
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Decision Table Model - Condition Stub
Condition-1 T T T T F F F F Condition_2
T T F F F T T F Condition-3 T F T F F T F
T Action-1 X X Action-2
X X Action-3 X X Action-4
X X X Action-5 X
Condition Stub
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Decision Table Model - Action Stub
Condition-1 T T T T F F F F Condition_2
T T F F F T T F Condition-3 T F T F F T F
T Action-1 X X Action-2
X X Action-3 X X Action-4
X X X Action-5 X
Action Stub
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Decision Table Model - Condition Entry
Condition-1 T T T T F F F F Condition_2
T T F F F T T F Condition-3 T F T F F T F
T Action-1 X X Action-2
X X Action-3 X X Action-4
X X X Action-5 X
Condition Entry
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Decision Table Model - Action Entry
Condition-1 T T T T F F F F Condition_2
T T F F F T T F Condition-3 T F T F F T F
T Action-1 X X Action-2
X X Action-3 X X Action-4
X X X Action-5 X
Action Entry
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Four Step Process

• Define all the Possible Actions
• (for ActionStubs)
• Define all the Possible Conditions
• (for Condition Stubs)
• Determine which conditions are Possible
• Eliminate those that cannot ever occur
• Which Conditions trigger which actions

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CARA Actions

• Monitor Air Pump Line
• Monitor Impedance Signals
• Display Error Message
• Trigger Audible Alarm
• Set Alarm Lamp On
• Monitor EMF Line
• Keep track of infused fluids
• Calculate and Log Volume Infused
• Record when in manual/automatic mode
• Monitor Blood Pressure
• Log Blood Pressure reading
• Record Source of BP Reading
• Record time of BP Reading
• Display BP Graph
• Display Flow Rate Graph
• Display Infused Volume Graph
• Display Numerical values for BP, Infused Volume,
  etc.
• Keyboard entry of BP to which CARA with titrate

Not an exhaustive list
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CARA Conditions

• Current BP Reading in Range?
• Pulse Wave Signal Detection?
• Using Cuff Pressure?
• Arterial Line?
• Beat to Beat Source?
• Valid BP Reading?
• Cuff Frequency gt Some Value?
• Drop in BP Occurred?
• In Autocontrol Mode?
• Pause button Activated?

Not an exhaustive list
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Sample Decision Table for CARA
BP lt 60 hg T T T T T T T
T F F F F F F F F Valid BP
F F F F T T T T F F F F
T T T T BP
gt SetPoint F T T F T T F
F F F T T T T F F
Prev BP / Current BP F F T T T
F T F F T F T T F F F
Action 1
X Action 2
X Action 3

X Action 4
X
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Summary

• Decision Tables are
• Simple to Use
• Easy to read
• CARA lends itself to this approach
• Cannot afford undiscovered conditions
• Must match all actions to some conditions

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Questions?
Questions?