Whether complication is life-threatening, or causes disability or death.

Invasiveness of intervention required to address complication.

Length of stay.

50 postoperative complication types (specific to vascular surgery) were identified from a database and grouped into 9 categories (e.g., vascular, cardiac, pulmonary).

Complications unrelated to vascular surgery (e.g., shoulder pain from pneumoperitoneum) not included.

Each complication type (e.g., pneumothorax) was stratified into 4 severity grades (mild, moderate, severe, death) based on their physiologic significance.

Grading system was used only to help orient the expert panel, who determined the score for each complication using a range from 0 (no complication) to 100 (death); mean score was used.

Reasoning behind the classification was subjective: if this complication were to happen to the experts as a patient, how would they rate it in terms of physiologic stress?

For composite score, individual severity scores are summed.

All possible system-based adverse events are identified by multiple multidisciplinary committees, and their severity is graded from 1 to 5 based on

• ⋄ Symptoms

• ⋄ Treatment modality used

• ⋄ Effects on functionality/activities of daily living

• ⋄ Life-threatening or disability-inducing

Modifications to 1992 Clavien–Dindo system.

Length of stay no longer a criterion for grading owing to differences across centres.

Life-threatening complications have higher grades associated with them.

Disability no longer a grade on its own but is now highlighted by the suffix “d” (for disability). Thus, any grade of complication may be supplemented with this information.

Utility weighting used for calculating severity (useful for aggregating multidimensional scales into a single unified measure of overall impact; severity = utility × duration).

Panel of surgical experts employed to derive a set of severity weights for the grades of the Accordion Severity Grading system between 0 and 100. The average of these scores was then associated to each grading level as its severity weight.

Composite score for each procedure (Postoperative Morbidity Index) is then calculated with the following formula:

Similar to Clavien–Dindo 2004, which considers interventions to treat complications.

Also incorporates length of stay, resource use (home care) and disability.

Team consisting of pediatric anesthetist, cardiac intensivist and cardiac surgeon drew up a list of conditions or diseases that can affect patients in the course of congenital heart surgery or increase costs of hospital stay.

Conditions/diseases were assigned a severity score between 1 and 4 (need for mechanical ventilation for more than 7 days) according to estimated severity or costliness. If no complication, score of 0.5 assigned.

Complication scores are added linearly; if the sum is more than 5, score of 5 is assigned.

Developers chose to not include hospital death among complication as they believed that concepts of mortality and morbidity should not be mixed and that complications leading to death should be evaluated separately.

Complications arising from congenital heart surgery at IWK Health Centre over 3 years were compiled.

Each complication was weighted by assigning a severity coefficient of 1, 2 or 3 according to expert consensus, where 1 = mild or temporary deficit predicted to affect patient’s course minimally, and 3 = severe or permanent complication predicted to impair patient’s outcome significantly and possibly precede death.

Morbidity burden or total magnitude of complication for a given procedure calculated as follows: ∑ (frequency x severity).

Clinical experts and patients assign severity score of 0–100 to complication scenarios involving all grades of Clavien–Dindo system.

Severity of a given grade is calculated by means of operation risk index analysis by multiplication of the median severity graded by patients and physicians (a summative approach is not used because it ignores the gravity of high-grade complications).

Raw composite score obtained by summation of severity ratings for complications for a given patient.

To facilitate clinical applicability of Comprehensive Complication Index, the developers tested different mathematical transformations of the raw composite score in 3 years of cohort data to find a distribution of the index that is closest to normal distribution, which would give the CCI a set limit between 0 and 100.

The following is the mathematical transformation that worked (where MRV = median reference value):