ICU Patient Velocity Model

breed [care-givers care-giver]
breed [beds bed]
breed [patients patient]


globals [
  overflow ;;holds overflow count
  patient-arrival-chance ;; List containing probability of arrival for each hour
]

patients-own [initial-apache apache acuity TTL LOS stable-ticks my-caregiver recieving-care? care-count death-prob bed-number ]
beds-own [occupied?]
care-givers-own [my-patients treat-count acuity-score]

to setup
  ca
  
  ;;;;;;;;;;;;;;;
  ;;Setup Layout
  ;;;;;;;;;;;;;;;
  
  ask patches with [pycor > 10 and pycor < 40] [set pcolor white]
  ask patches with [pycor < 10 and pxcor < 20] [set pcolor cyan]
  ask patches with [pycor < 10 and pxcor > 20] [set pcolor cyan]
  
  
  ;;;;;;;;;;;;
  ;;Setup Beds
  ;;;;;;;;;;;;
  
  ask patches with [pycor = 20 or pycor = 30 and pxcor > 5 and pxcor < 35 and pxcor mod 3 = 0] [set pcolor 99]
  ask patches with [pycor = 21 or pycor = 31 and pxcor > 5 and pxcor < 35 and pxcor mod 3 = 0] [set pcolor 99.1]
  set-default-shape beds "square"
  ask patches with [pcolor = 99] [sprout-beds 1 [set size 1 set color 99 set heading 0]]
  
  ;;;;;;;;;;;;;;;;;;;;
  ;;Setup Care-Givers
  ;;;;;;;;;;;;;;;;;;;;
  
  set-default-shape care-givers "person"
  ask n-of n patches with [pcolor = white] [sprout-care-givers 1 [
    set size 2
    set color blue
    set my-patients[]
  ]]
  set-default-shape patients "person"
  
  
  
  ;;;;;;;;;;;;;;;;;;;;;;;;
  ;;Setup Initial Patients
  ;;;;;;;;;;;;;;;;;;;;;;;;
  let initial-patient random-normal initial-patient-mean 2 ;; normal intitializtion of how many patients there are. Initial conditions likely affect system performance.
  if initial-patient > count beds [set initial-patient 20] 
  ask beds [set occupied? false]
  ask n-of initial-patient beds [hatch-patients 1 [set color red set size 2 set bed-number [who] of myself  ] set occupied? true]
  ask patients [ 
    set-apache                                 ;; based off of Naved et al. (2011) - APACHE-II Score Correlation with Mortality and Length of Stay in an ICU
    set-ttl 
    set my-caregiver nobody
    set recieving-care? false
    set-death-prob
    set-patient-color 
  ] 
  assign-patient
  ;;Patient Arrival Probability List
  set patient-arrival-chance [ 12 12 10 10 11 15 18 15 15 13 11 10 ] ;; Assuming that more patients come in the middle of the day. in two hour blocks 
  reset-ticks
end 

to go
  ask beds [
    if not any? patients-here [set occupied? false]  
  ]
  patient-inflow
  assign-patient
  treat-patients
  ask patients [advance-health] ; patients either improve or get sicker depending on quality of care
  ask patients [if random-float 1 < death-prob [remove-patient] ]       ;;patients can randomly die according to their accuity
  ask care-givers [clean-list]
  discharge-patients 
  ask care-givers [clean-list]
  ask patients [set LOS LOS + 1]
  ask patients [set-patient-color] ;; to visualize how sick patients are
  
  tick
end 






;; admits patients if there are available beds. Patients arrive based on the defined patient arrival probability list with added noise

to patient-inflow
  if random 100 < random-normal 0 2 + item (remainder ticks 12) patient-arrival-chance [
    ifelse any? beds with [occupied? = false]  [admit-patient] [overflow-patient] ] ;; each tick, patients either flow in or are overflowed
end 


;; Creates the patient on an open bed

to admit-patient
  ask one-of beds with [occupied? = false] [hatch-patients 1 [
    set color red
    set size 2
    set-apache                                 
    set my-caregiver nobody
    set recieving-care? false
    set-apache
    set-ttl
    set-death-prob
    set bed-number [who] of myself
    set-patient-color
    
  ]
    set occupied? true]
  ask care-givers [clean-list]
end 

;;Increases the overflow count variable

to overflow-patient
  set overflow overflow + 1
end 

;; This procedure holds the logic for treating patients

to treat-patients
  ;; Aiken et al, 2002: increase in one patient to nurses assignment increases mortalilty rate 7%
  
  
  let dedicated-care-givers care-givers with [length my-patients = 1 and item 0 my-patients != nobody] ;; select care-givers that only have one patient
  ask dedicated-care-givers [
    ifelse random 100 < care-time [
      move-to item 0 my-patients
      fd 2
      set treat-count treat-count + 1
      ask item 0 my-patients [
        set recieving-care? true
        set care-count care-count + 1 ;; increasing by ten with each tick?
        set recieving-care? false
      ]
    ]
    [
      ask dedicated-care-givers [move-to one-of patches with [pcolor = cyan]] 
    ]
  ]
  
  
  
  
  
  let multi-care-givers care-givers with [length my-patients > 1]
  ask multi-care-givers [
    ifelse random 2 = 0 [
      ifelse random 100 < care-time [
        move-to item 0 my-patients
        fd 2
        ask item 0 my-patients [
          set recieving-care? true
          set care-count care-count + 1 ;; increasing by ten with each tick?
          set recieving-care? false
        ] ] 
      [move-to one-of patches with [pcolor = cyan]]
    ][
    ifelse random 100 < care-time [
      if item 1 my-patients != nobody [ ;; ensure that the care-giver has a second patient
        move-to item 1 my-patients
        fd 2
        ask item 1 my-patients [
          set recieving-care? true 
          set care-count care-count + 1
          set recieving-care? false
        ]
      ]
    ]
    [move-to one-of patches with [pcolor = cyan]
    ]
    ] 
  ]
end 


;;Patients that are stable are discharged  starting at 7am

to discharge-patients
  ;; every morning at 7 am patients are discharged
  ifelse strict-discharge? [
  if remainder ticks 24 = 7 [
    ask patients with [ stable-ticks > stable-hours-needed ] [
      remove-patient
    ] ]]
  [ask patients with [ stable-ticks > stable-hours-needed ] [
      remove-patient]
  
  ]
end 

;; This procedure abstracts quality of care into how often the care-giver treats the patient. 
;; If the quality of care is high the patient is more likely to improve their health.

to advance-health
  if LOS > 0 [
    let quality-of-care (care-count / LOS) + random-normal 0 .1              ;; patient-centric quality of care plus a little noise
    if random-float 1 < quality-of-care [improve-health] ;; 
    
    
    if random-float 1 < 1 - quality-of-care [worsen-health] ;; includes error rates like nonsocomial infections, falls, HAI, and others
    
                                                            ;;If patient is low acuity, they add to a stability counter which determines if they are ready for discharge
    ifelse apache < stable-apache [set stable-ticks stable-ticks + 1] [set stable-ticks 0]]
  set-death-prob
end 




;;;;;;;;;;;;;;;;;;;;               
;; Helper Methods ;; Methods that are called throughout the model
;;;;;;;;;;;;;;;;;;;;

;; a patient procedure to remove the patient from the ICU

to remove-patient
  if my-caregiver != nobody [ 
    
    ask my-caregiver [ set my-patients remove myself my-patients]
  ]
  die
  ask beds [
    if not any? patients-here [set occupied? false] 
  ]
end 


;; decreaing apache score is equivalent to reducing acuity

to improve-health
  set apache apache - random-normal .2 .05
end 

;; increasing apache is equivalent to increasing patient acuity

to worsen-health
  set apache apache + random-normal .2 .05
end 

;;larger number the darker the color: 

to set-patient-color
  if acuity = "high" [
    set color scale-color red apache 60 25
  ]
  
  if acuity = "medium" [
    set color scale-color yellow apache 50 0
  ]
  
  if acuity = "low" [
    set color scale-color green apache 20 -10 
  ]
end 


;; sets the death probability for each patient group which defines how likely it is that a patient will die during that tick.

to set-death-prob
  if acuity = "low" [ 
    set death-prob abs ( random-normal .1 .05 / ttl) ;; based on Naved Et al. results .1 is the mortality % divded by the number of days the patient is expected to stay in the ICU
  ]
  
  if acuity = "medium" [
    set death-prob abs (random-normal .4 .25 / ttl)
  ]
  
  if acuity = "high" [
    set death-prob abs ( random-normal .85 .05 / ttl )
  ]
end 



;; This procedure sets the apache score for each patient
;; Imputed from Naved et al. (2011) - APACHE-II Score Correlation with Mortality and Length of Stay in an ICU

to set-apache
  if initial-apache < 10 [set initial-apache random-normal 25 12 set apache initial-apache]
  group-apache
  if initial-apache < 10 [set-apache]    ; makes sure no patient has a negative apache or very small apache
end 


;;groups each patient based on the apache score.

to group-apache
  if apache <= 10 [ set acuity "low"] ;; 10% death
  if apache >= 30 [ set acuity "high"]  ;; 85% death
  if apache > 10 and apache < 30 [ set acuity "medium"] ;; but around 40-50% death More randomness with these patients
end 

;; sets the Time to Live of each patient

to set-ttl
  set ttl abs (random-normal 69 93 )           ;; this is length of stay data from literature                
end 


;;;;;;;;;;;;;;;;;;;;;
;;;Patient Assignment
;;;;;;;;;;;;;;;;;;;;;

to assign-patient
  
 
  let sick-patients patients with [ my-caregiver = nobody and acuity = "high"] ;; find high acuity patients without a care-giver 
  let dedicated-caregivers care-givers with [ length my-patients = 0] ;; find care-givers that don't have yet assignment
  ask dedicated-caregivers[
    set my-patients fput one-of sick-patients my-patients ;; adding one of the sick patients to the front of my-patients list
    if item 0 my-patients != nobody[                      ;; accesing first item in list
      ask item 0 my-patients [ set my-caregiver myself]   ;; I ask my patient to set their caregiver to me.
    ]
  ]
  
  
  ;; Assigns remaining care-givers that do not have any patients
  let remaining-patients patients with [(acuity = "medium" or acuity = "low") and my-caregiver = nobody]
  let remaining-empty-caregivers care-givers with [length my-patients = 0 or my-patients = [nobody]] ;; assign rest of caregivers that don't have a patient first
  if any? remaining-patients and any? remaining-empty-caregivers [
    ask remaining-empty-caregivers [
      set my-patients fput one-of remaining-patients my-patients
      ask item 0 my-patients [set my-caregiver myself]
    ]
  ]
  
  
  ;this assignment heuristic makes sure that no patient is left un-cared for
  let leftover-patients patients with [my-caregiver = [] or my-caregiver = nobody ]
  ask care-givers [
    clean-list
    set acuity-score 0
    foreach my-patients [set acuity-score acuity-score + [apache] of ?] ; add up the apache scores of your patients
  ]
  
  ;; asks the neccesarry amount of caregivers with the lowest agregate acuity to take care of the left over patients
  ask min-n-of (count leftover-patients) care-givers [acuity-score]  [    
    set my-patients fput one-of leftover-patients my-patients
    ask item 0 my-patients [set my-caregiver myself]
  ] 
end 


;;this makes sure that the my-patient list doesn't have nobody in the list.
;;this code is called throughout the model

to clean-list
  set my-patients remove nobody my-patients
end 








;;;;;;;;;;;;;;;           
;;Reporters 
;;;;;;;;;;;;;;;



;; census is taken at 7am every morning

to-report census
  report count patients
end 

to-report mean-apache
  report mean [apache] of patients
end 

to-report bed-utilization
  report count beds with [occupied? = true] / count beds
end 

to-report caregiver-patient-ratio
  report precision (count care-givers / count patients) 2
end 


;; add in monitors if need be. These measures are useful for adding on new features and debugging

to-report empty-patients
  report count patients with [my-caregiver = [] or my-caregiver = nobody ]
end 

to-report empty-caregivers
  report count care-givers with [my-patients = []]
end