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Hospital Surge Model Version 1.3: Description

Public Health Emergency Preparedness

This resource was part of AHRQ's Public Health Emergency Preparedness (PHEP) program, which was discontinued on June 30, 2011, in a realignment of Federal efforts.

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Chapter 2. Smallpox

This chapter describes the assumptions for the smallpox scenario, including:

  • The severity categories.
  • The arrival pattern of casualties at the hospital(s).
  • The length of stay by hospital unit (i.e., ED, ICU, and the floor).
  • The path probability within the hospital(s) and the length of stay.
  • The overall outcome probabilities (i.e., probability of discharge and probability of death).
  • The assumed level of resource consumption per patient per day per hospital unit.

Footnotes in the text of a particular section refer to references at the end of the section. In the absence of specific references, parameter estimates were obtained from general references listed in the Hospital Module section.

2.1 Severity Categories

For the smallpox scenario, all patients arrive at the hospital(s) at the onset of mild, generalized symptoms.

2.2 Casualty Arrival Pattern

Casualties are assumed to present at the hospital(s) when symptoms appear. For this scenario, we assume the hospital receives casualties with the same overall arrival pattern as the greater epidemic. To estimate arrival, we calculated inhalation of smallpox by individuals exposed to the attack. Above a certain minimum exposure, all of these individuals were assumed to develop smallpox and were normally distributed around the average onset time. Each casualty was then assumed to infect three other individuals prior to hospitalization. The resulting time curve, taking into account time to development of symptoms and increasing numbers of those exposed, shows a characteristic first wave followed by a second wave peaking one to two weeks after.

2.3 Length of Stay (LOS) By Hospital Unit

The assumed average lengths of stay (in days) of patients in the ED, in the ICU, and on the floor2,7 are:

Average LOS by Hospital Unit Smallpox Case
ED 1
Floor, not via ICU 14
Floor, via ICU 7
ICU 7

2.4 Combined Path Probabilities and Lengths of Stay

The table below shows the assumed probabilities of different "paths" through the hospital(s)2,7 listed at the end of this section). The table shows, for example, that a patient presenting with a case of smallpox has a 19 percent chance of being transferred from the ED to the ICU and then dying in the ICU.

Path Smallpox Case
ED → Discharge 0%
ED → Death 0%
ED → Floor → Discharge 54%
ED → Floor → Death 7%
ED → Floor → ICU → Death 6%
ED → Floor → ICU → Floor → Discharge 3%
ED → Floor → ICU → Floor → Death 1%
ED → ICU → Death 19%
ED → ICU → Floor → Discharge 9%
ED → ICU → Floor → Death 2%

The breakdown of length of stay by patient type summed over all paths is:

Average LOS by Patient Outcome Smallpox Case
Survivors 15.29
Fatalities 7.00
Average Combined 12.43

2.5 Overall Outcome Probabilities

Based on these inputs,5 the overall discharge and death probabilities are:

Outcome Smallpox Case
Discharge 66%
Death 34%

2.6 Resources Consumed Per Patient Per Day

The assumed level of resource consumption per patient per day is shown in the table below:

Resource Units Category Subcategory Lambdaa Onset
ED ICU Floor
Med/Surg Bed Unit of Use Capacity Floor 1 0 0 0
ICU Bed Unit of Use Capacity ICU 1 0 1 0
Operating Room Unit of Use Capacity OR 1 0 0 0
Airborne Isolation Room Unit of Use Capacity Isolation 0.9 0.167 1 1
Intensivists (CCM) FTE Staff CCM 0.7 0.042 0.042 0
Critical care nurses (CCN) FTE Staff CCN 1 0.167 0.33 0
Surgeons FTE Staff Surgeon 0.3 0 0.083 0
Non-intensivists (MD) FTE Staff MD 0.9 0.083 0 0.021
Non-critical care nurses (RN/LPN) FTE Staff RN 1 0 0 0.146
Respiratory Therapists (RT) FTE Staff RT 0.7 0.083 0.083 0
Radiology machines Machine Time Lab/Radiology Radiology 0.3 0.021 0.021 0
Radiologic Technicians FTE Staff Rad Tech 0.3 0.021 0.021 0
Pharmacists (PharmD/RPh) FTE Staff Pharmacist 0.7 0.021 0.083 0.042
Mechanical ventilator Machine Time Capacity Ventilator 0.9 1 1 0
Ventilator equipment Unit of Use Equipment Vent Tubing 0.9 1 1 0
Oxygen (O2) Unit of Use Supplies Oxygen 0.9 1 2 0
Oxygenation monitoring equipment Machine Time Equipment O2 Monitoring 0.9 0.083 1 0
Surgical supplies Unit of Use Supplies Surgical 0.3 0 0.25 0
Radiology supplies Unit of Use Supplies Radiological 0.3 1 1 0
Antibiotics for secondary pneumonia Assorted Pharmacy Antibiotics 1 0 1 0
Antibiotics intravenous infusion set Unit of Use Supplies IV set 1 1 0.5 0.5
Hemodynamic medications Unit of Use Pharmacy Hemodynamic 0.7 1 1 0
Intravenous fluids Unit of Use Pharmacy IVF 0.7 1 1 1
Intravenous infusions set Unit of Use Supplies IV Set 0.7 1 1 1
Laboratory machines Machine Time Lab/Radiology Laboratory 0.7 0.02 0.042 0.021
Laboratory supplies Unit of Use Supplies Laboratory 0.7 0.5 1 0.5
Temperature monitoring equipment Machine Time Equipment Temperature 1 0.083 1 1
Thromboembolism prophylaxis Unit of Use Pharmacy DVT Prophylaxis 1 0 1 0
Urine output monitoring equipment Unit of Use Equipment U/O 1 0 1 0
Universal precautions PPE Unit of Use PPE Universal 1 1 1 1
Waste disposal Unit of Use Waste Mgmt Decon Waste 0.3 1 1 1
Enteral feedings (3/day/patient) Unit of Use Nutrition Enteral 1 0 0.5 0
Oral food (3 meals per day per patient) Unit of Use Nutrition Oral 1 0 0.5 1
Sheet change Unit of Use Housekeeping Laundry 1 1 1 1
Patient infection control FTE Epidemiology Infection Control 0.5 0.083 0.083 0.083
Engineering FTE Engineering Facility 0.7 0.042 0.083 0.042
Janitorial/Housekeeping FTE Housekeeping Janitorial 1 0.125 0.125 0.083
Nutrition FTE Nutrition Counseling 0.5 0 0.083 0.083
Psychological support FTE Ancillary Psychologist 0.5 0 0 0.042
Mortuary FTE Mortuary Morgue 0.1 0 0.083 0.042

a. Lambda captures the resource requirement decay rate for a resource. Lambda = 1 implies no decay; the patient requires a constant amount of the resource while s/he is hospitalized. Lambda <1 implies that less of the resource is required each day the patient is hospitalized. Go to section 2.2 for details.

2.7 References

1. Binder P, Attre O, Boutin JP, et al. Medical management of biological warfare and bioterrorism: place of the immunoprevention and the immunotherapy. Comp Immunol Microbiol Infect Dis 2003;26(5-6):401-21.

2. Breman JG, Henderson DA. Diagnosis and management of smallpox. N Engl J Med 2002;346(17):1300-8.

3. Ferguson NM, Keeling MJ, Edmunds WJ, et al. Planning for smallpox outbreaks. Nature 2003;425(6959):681-5.

4. Gani R, Leach S. Transmission potential of smallpox in contemporary populations. Nature 2001;414(6865):748-51.

5. Henderson DA, Inglesby TV, Bartlett JG, et al. Smallpox as a biological weapon: medical and public health management. Working Group on Civilian Biodefense. JAMA 1999;281(22):2127-37.

6. Lane JM. Smallpox and smallpox vaccination. N Engl J Med 2002;347(9):691-2.

7. Legrand J, Viboud C, Boelle PY, et al. Modelling responses to a smallpox epidemic taking into account uncertainty. Epidemiol Infect 2004;132(1):19-25.

8. Robinson-Dunn B. The microbiology laboratory's role in response to bioterrorism. Arch Pathol Lab Med 2002;126(3):291-4.

9. Stephenson J. Monkeypox outbreak a reminder of emerging infections vulnerabilities. JAMA 2003;290(1):23-4.

10. Yetman RJ, Parks D, Taft E. Management of patients exposed to biologic weapons. J Pediatr Health Care 2002;16(5):256-61.

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