AmSurg Corp., which operates outpatient surgery centers, said on Thursday that its first-quarter profit fell 8 percent on higher costs for refinancing credit and Medicare payment revisions.

The company said it earned $11.7 million, or 38 cents per share, during the quarter that ended March 31. That was down from $12.7 million, or 41 cents per share, during the same period last year. Revenue rose 6 percent to $179.4 million, from $169.2 million.

Analysts surveyed by FactSet were expecting a profit of 38 cents per share on revenue of $179.8 million.

Revenue at centers open at least a year — a key measure that isolates performance at older locations — remained flat. The number of procedures rose 6 percent, mostly because of nine newly acquired centers added during the past year.

Meanwhile, the company said Medicare payment revisions and high interest costs for refinancing credit cut into the results.

Looking ahead, the company expects second-quarter profit from continuing operations between 40 cents and 42 cents per share, while analysts expect 42 cents per share in profit.

For the full year, the company expects profit from continuing operations between $1.64 and $1.68 per share on revenue between $740 million and $770 million. Analysts expect 2011 profit of about $1.68 per share on $765.8 million in revenue.

Meanwhile, the company expects same-center revenue to remain flat or fall 1 percent in 2011. The company also expects to add between 18 and 20 new centers in 2011.

AmSurg shares fell 30 cents to close Thursday at $25.84.