The United States spends more on healthcare than any other country in the world. How should healthcare managers reduce healthcare costs and healthcare spending?

When trying to minimize cost in any system, especially one as complex as the healthcare industry, it is a good idea to first break down exactly where costs are accrued.
The United States owes its inflated cost of healthcare to two main agents. The first is the pharmaceutical industry (colloquially titled "big pharma"), which is made up of companies who pay scientists to invent new drugs, pay marketing teams to induce a consumer demand, and patent the drugs as their own intellectual property. All of these factors work together to let the patent-holding company of a given drug set the prices as high as they wish, which oftentimes approaches oligopolistic and even monopolistic market behavior.
The pharmaceutical industry's monopoly on healthcare in the United States makes it incumbent on another entity—the US government—to make the costs affordable to ordinary citizens. In its current political state, the US government does not guarantee healthcare as a right for its people. I would argue, also, that it does not work to break down the monopolistic corporations that control "big pharma"; instead, it uses taxpayers' money to unevenly allocate resources to third-party programs that collude with pharmaceutical companies to get package reductions on medicine.
Though healthcare managers can exert little real power to undo price-setting behavior, they can often choose to source non–name-brand versions of a given drug or find reasonable alternatives to drugs that are too expensive for patients at a given hospital.