“Maybe CNN is just like an emergency room.”


That is what a longtime CNN employee theorized last year, during one of the channel’s predictable defeats in the Nielsen ratings.


When elections and explosions happen, people tune in to CNN, the same way they hurry to a hospital when they think they are having a heart attack. But people tend not to linger in either place — a reality that was reaffirmed for CNN this week when Nielsen ratings showed that April was the channel’s lowest-rated month in 10 years.


CNN, with its vast news-gathering resources and a heap of international channels, is set to make nearly $600 million in operating profit this year, a record high, for its parent company, Time Warner. But the downward ratings trend for CNN/U.S., its flagship channel in the United States, has stirred discontent within CNN and Time Warner. Performance of CNN/U.S. drives public perception — and employee pride — and declines there may gradually damage CNN’s networks as a whole.


Jeffrey Bewkes, the Time Warner chief executive, has made his dissatisfaction about the CNN/U.S. ratings known to his lieutenants and expects them to make changes, according to some of the 15 current and former CNN employees interviewed for this article. Those people, representing a wide cross-section of the channel, spoke on the condition of anonymity because they were not authorized by their bosses to talk to a reporter.


One of the employees said that Jim Walton, who oversees all of the CNN networks, and his boss, Philip I. Kent, who runs the Turner Broadcasting division of Time Warner, were under “intense pressure” to raise the ratings this spring.


In a statement, CNN said: “Despite the perennial ratings stories and quotes from anonymous sources, CNN continues to deliver quality journalism which is uniquely valuable to audiences, advertisers and distributors. In fact, CNN is on track to deliver its highest profits in its history and continues to reach more people on more platforms than any other TV network.”


CNN embarked on a series of programming changes in late 2010 and continued making them through early this year, effectively remaking the weekday schedule. Among other changes, Soledad O’Brien is now the morning host, Erin Burnett is the 7 p.m. host and Piers Morgan is the 9 p.m. host. Executives were hoping for an overall ratings lift, but have been disappointed.


Further programming changes may take place at the channel. But “first we need better execution of the current programming,” said a Time Warner executive.


CNN’s programming problem may date back to 1980, the year it was started, creating the concept of cable news. In periods of major breaking news, viewers flock to CNN, but only a small fraction stick around after, causing big swings in the channel’s ratings from day to day and month to month.


In April 2011, CNN had an average of 451,000 viewers at any given time, more than the cable news channel MSNBC’s 428,000. The month included the much-watched royal wedding in Britain. But this April, an unusually quiet month in the news business, CNN had an average of 357,000 viewers, its lowest monthly average since August 2001. MSNBC held steady with 425,000.


CNN long ago ceded the No. 1 position among cable news channels to Fox News. But now CNN seems to be ceding the No. 2 position to MSNBC. In prime time, the most lucrative part of the day, CNN has had fewer viewers than MSNBC for 22 of the last 24 months. (CNN usually has more viewers than MSNBC during the day, however.)


“They were first in, and established the genre,” said a cable news executive who insisted on anonymity to speak candidly about the competition. “But they got too comfortable. They just made so much money that they didn’t have to change.”


MSNBC, on the other hand, did change. Like Fox News, MSNBC now has hosts with clear political points of view at key times of the day. CNN promotes itself as the top source for nonpartisan news on television.