Adverse environmental conditions cause infrastructure systems to deteriorate (e.g., loss capacity) over time. Modeling system deterioration is essential to define optimum design strategies, and inspection and maintenance (intervention) programs. In particular, the main purpose of maintenance is to increase the system availability by extending the life of the system. Most strategies for maintenance optimization focus on defining long term strategies based on the system's condition at the decision time (e.g., <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> =0). However, due to the large uncertainty in the system's performance through life, an optimal maintenance policy requires both permanent monitoring and a cost-efficient plan of interventions. This paper presents a model to define an optimal maintenance policy of systems that deteriorate as a result of shocks. Deterioration caused by shocks is modeled as a compound Poisson process, and the optimal maintenance strategy is based on an impulse control model. In the model, the optimal time and size of interventions are executed according to the system state, which is obtained from permanent monitoring.