What is the most appropriate initial therapy for a 40-year-old man who has been trapped under wreckage, presenting with multiple bruises and elevated creatine kinase levels?

In the context of a patient who has been trapped under wreckage and presents with multiple bruises along with elevated creatine kinase levels, the situation raises concerns for rhabdomyolysis, which can occur due to muscle injury from compression. One of the primary complications of rhabdomyolysis is acute kidney injury, which can result from the release of myoglobin and other muscle cell contents into the bloodstream.

The most appropriate initial therapy in this scenario is the infusion of 0.9% saline. This intervention is critical because adequate hydration helps to maintain urine output, dilutes nephrotoxic substances, and promotes the excretion of myoglobin, thereby potentially preventing or mitigating acute kidney injury. Early aggressive fluid resuscitation is essential for supporting renal function and reducing the risk of complications.

Other interventions may be necessary as the patient's condition evolves, including possibly administering diuretics if oliguric renal failure develops, but the initial step is to ensure adequate volume status and promote renal perfusion through the administration of intravenous saline.