The complication rate is a key performance metric in surgical practice. It quantifies the proportion of procedures resulting in adverse outcomes such as infection, hemorrhage, device malposition, or neurological deterioration.

In the context of CUSUM analysis, the complication rate serves as the primary outcome variable, coded as:

• 0 for success (no complication)
• 1 for failure (any complication)

This binary format allows direct integration into cumulative sum calculations.

Accurate complication tracking:

• Ensures accountability and transparency.
• Supports quality assurance programs.
• Enables early detection of safety issues.
• Guides training needs and protocol adjustments.

The observed complication rate is compared to a predefined acceptable target (e.g., 10%). An actual rate consistently higher than target may signal issues in:

• Surgical technique
• Patient selection
• Team communication
• Postoperative care

If a surgeon performs 20 ICP monitor placements with 3 complications:

• Observed rate = 3/20 = 15%
• Target rate = 10%
• The CUSUM chart will reflect a net upward trend, prompting further review.

Setting clear definitions of what constitutes a complication is critical for data consistency across operators and institutions.