Background: Ineffective or delayed treatment of patients with blunt chest wall injury results in high rates of morbidity and mortality. A blunt chest injury care bundle protocol (ChIP) was developed and implemented to improve evidence-based care for these patients at two regional hospitals in Australia. ChIP is an early notification system to notify specialist clinician ‘responders’ to prescribe and commence treatment for patients with blunt chest injury in the emergency department (ED). A multi-pronged implementation strategy developed using the Behaviour Change Wheel (BCW), including seven intervention functions and 15 behaviour change techniques, guided implementation. Fidelity to the implementation strategy was high, with 97.5% fully or partially implemented. Implementation fidelity is the extent to which an intervention has been implemented as intended; it affects the internal and external validity of implementation. This study evaluates the fidelity of intervention delivery (fidelity, dose and reach) at two hospitals. Methods: Pre-post implementation evaluation study. The characteristics of patients, rate of ChIP activations and components of ChIP received by eligible patients were compared pre (1 July 2015 to 21 November 2017) and post (22 November 2017 to 30 June 2019) intervention. Sample medians were compared using the non-parametric median test, with the 95% confidence of the difference estimated using the Hodges-Lehmann estimate. Differences in proportions for categorical data were compared with two-sample z-test. Logistic regression was used to adjust for group differences. Results: Overall, 97.1% of eligible patients received ChIP over the 19-month post-implementation period. Compared to the pre-implementation group the post-implementation group, were more likely to receive evidence-based treatments including high flow nasal cannula (OR=6.8 (4.8,9.6)), incentive spirometry in ED (OR=7.5 (3.2,17.6)), regular analgesia (OR=2.4 (1.5,3.8)), regional analgesia (OR=2.8 (1.5, 5.3)), Patient controlled analgesia (OR=1.8 (1.3,2.4)), and multiple specialist team reviews e.g. ICU liaison (OR=10.7 (6.9,16.7)). Conclusions: High fidelity of delivery was achieved and sustained for ChIP for the implementation of a complex intervention in the emergency context with a robust implementation plan based on theoretical frameworks. Findings from this evaluation can inform future implementation of ChIP and other multidisciplinary interventions in an emergency or acute care context. Trial registration: ANZCTR: ACTRN12618001548224, approved 17/09/2018