Figure 2.

Maximum number of manageable COVID-19 cases per day on the basis of resource constraints in the Ontario health care system.

The figure shows the COVID-19 patient-flow dynamics in the Ontario health system when each resource (acute care beds, critical care beds, and mechanical ventilators) available to patients with COVID-19 is in full use and at steady state. In this example, 2847 COVID-19 cases per day would result in 761 of those cases being admitted or transferred to acute care (“patients in”), assuming that 26.7% of all COVID-19 cases require acute care. Assuming that 8378 acute care beds are available for patients with COVID-19, with an average stay of 11 days in acute care, we can expect 761 patients with COVID-19 to leave acute care per day (“patients out”) when at capacity (either by transfer, discharge, or death). If the province of Ontario reaches 2847 new COVID-19 cases per day, the acute care system would be at capacity and steady state, because the number of patients with COVID-19 entering and exiting the acute care system would be equal at 761 (patients in = patients out). Also shown are the same steady-state scenarios for critical care beds and mechanical ventilators for Ontario. The calculation can be broken down into 3 steps to estimate the maximum number of manageable COVID-19 cases per day that can occur for each resource (acute care beds, critical care beds, and mechanical ventilators). First, calculate the daily turnover of a resource when in maximal use: TO_res = N_res/LOU_res, where TO_res is the number of resource units that become available per day (turnover) for patients with COVID-19, N_res is the total number of units of that resource available for patients with COVID-19, and LOU_res is the mean length of use of that resource for patients with COVID-19. Second, calculate the proportion of COVID-19 cases that require a resource:

 

, where P_res is the proportion of COVID-19 cases that require that resource, P_i is the proportion of COVID-19 cases that are within age group i of N age groups, and P_i,res is the proportion of COVID-19 cases within age group i that require that resource. Third, calculate the maximum number of new COVID-19 cases per day that can occur such that the daily number of COVID-19 cases requiring a resource is equal to the daily turnover of that resource: C_max,res = TO_res/P_res, where C_max,res is the maximum daily number of COVID-19 cases that can occur for that resource and TO_res and P_res have been defined previously.

* Number of existing acute or critical care resources for patients with COVID-19.