Background Little is known of the incidence of adverse events in the paediatric intensive care unit (PICU). Perceived incidence may be dependent on data-collection methods.

Objective To determine the incidence of adverse events by voluntary reporting and systematic enquiry.

Methods Adverse events in PICU were recorded contemporaneously by systematic enquiry with bedside nurses and attending doctors, and compared with data submitted voluntarily to the hospital's quality and safety unit. Events were classified as insignificant, minor, moderate, major and catastrophic or lethal, and assigned origins as medical/surgical diagnosis or management, medical/surgical procedures, medication or miscellaneous.

Results Among 740 patients, 524 adverse events (mean 0.71 per patient) occurred in 193 patients (26.1%). Systematic enquiry detected 405 (80%) among 165 patients and were classified by one investigator as insignificant 30 (7%); minor 100 (25%); moderate 160 (37%); major 103(25%) and catastrophic 12 (3%). The coefficient of agreement (kappa) of severity between the two investigators was 0.82 (95% CI 0.78–0.87). Voluntary reporting detected 166 (32%) adverse events among 100 patients, of which 119 were undetected by systematic reporting. Forty-nine events (9%) were detected by both methods. The number and severity of events reported by the two methods were significantly different (p<0.0001). Voluntary reporting, mainly by nurses, did not capture major, severe or catastrophic events related to medical/surgical diagnosis or management.

Conclusions Neither voluntary reporting nor systematic enquiry captures all adverse events. While the two methods both capture some events, systematic reporting captures serious events, while voluntary reporting captures mainly insignificant and minor events.