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ICU Surge Capacity Model

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Learning Objective

Analyze how admission rate, mean length of stay, and surge capacity decisions interact to determine whether an intensive care unit breaches capacity during a respiratory pandemic, and identify the threshold at which the system tips from manageable to overwhelmed.

Specification

The full specification below is extracted from Chapter 18: Simulation Design.

Type: microsim
sim-id: icu-surge-capacity
Library: p5.js
Status: Implemented

Display a stock-and-flow simulation of ICU bed occupancy with the following layout:

Top section — Stock-and-Flow Diagram (visual):
- A large blue rectangle labeled "ICU Bed Occupancy" with a fill level that animates up and down
- Red line at 100% capacity with label "CAPACITY BREACHED"
- Orange line at 85% with label "Crisis Standard of Care Threshold"
- Left arrow (green) labeled "Admissions/day" flowing in
- Right arrow (red) labeled "Discharges + Deaths/day" flowing out

Middle section — Controls (p5.js built-in controls):
- Slider: Admission Rate (0–50 patients/day, default 10)
- Slider: Mean ICU Length of Stay (3–21 days, default 10)
- Slider: Baseline ICU Beds (50–500, default 200)
- Checkbox row: Surge Options (each adds beds when checked):
  - "Convert step-down units (+40 beds)"
  - "Regional overflow site (+60 beds)"
  - "Field hospital (+100 beds)"
- Button: "Reset / Restart Simulation"
- Button: "Pause / Resume"

Bottom section — Time-Series Chart:
- Line chart of ICU occupancy over 90 days
- Y-axis: 0 to 150% of baseline capacity
- Horizontal bands: green (<85%), yellow (85-100%), red (>100%)
- Current day marker (vertical dashed line)

Simulation logic: each "day" (one animation frame at reduced speed), new patients =
admission_rate; discharged patients = current_occupancy / mean_los. Stock updates:
new_occupancy = current + admitted - discharged. When the red band is entered, a
banner "CRISIS STANDARDS ACTIVATED" flashes. When the simulation ends (day 90),
display summary statistics: peak occupancy %, days above capacity, total patients
admitted.

How to Use

  1. Adjust the Admission Rate slider and watch the tank fill or drain.
  2. Lower Mean ICU Length of Stay to see how faster discharges reduce occupancy.
  3. Check the Surge Capacity Options boxes to add beds during a crisis.
  4. Click Reset / Restart to begin a new 90-day run.
  5. Find the threshold where the system tips from green to red. This is the lesson Little's Law teaches: occupancy ~ admission rate x mean length of stay.