Table 1 Microcosting in the Calgary zone, Alberta Health Services

To determine how costs differ between treatment arms in this analysis, we will use microcosting [12] data from hospitals in the Calgary Zone of Alberta Health Services. Resources used in the management of each patient will be enumerated, valued, and summed to create a highly precise cost-of-care for each individual. Less intensive methodologies using average patient costs for similar groups would be insensitive to the differences in cost between the open abdomen and primary fascial closure arms.

Microcosting is made possible by patient-specific resource use data collected by Alberta Health Services and calculated in accordance with national Management Information Systems guidelines [13]. First, the quantity of physical materials and diagnostics necessary for the care of each patient are tracked. These include medications, blood products, patient-traceable disposables, radiologic investigations, and laboratory tests. The quantity of each is multiplied by the unit cost (estimated annually) to provide a total cost estimate and these are summed. The direct human resources required for care including nursing and support staff are quantified and similarly costed. Physician billing fees are added to this to create a total cost of labor. The indirect costs of the spaces and systems of care (e.g., ICU bed or OR time) are then apportioned to each patient [12]. Costs across these domains are summed to create an estimate of cost for each patient encounter. Outpatient encounter data are also available to estimate the cost of follow-up with specialists, rehabilitation, and outpatient services such as dialysis.

The availability and quality of cost data reporting in Alberta is highly regarded and has previously been used in the assessment of surgical costs [14]. Our primary analysis will combine resource use data from all COOL sites with microcosting data from Calgary to create estimates of cost in each treatment arm.