When Dr. Samuels is teaching Dr. Beale to swim, they are standing in chest deep water. However, when they both go underwater, there are several feet of water both above and below them.
When performing the coronary artery bypass, Dr. Craig leaves the operating room to change scrubs leaving an intern at table side. With a patient on active bypass and an open chest this would never happen. Likewise, the surgical team would consist of several surgeons, not just an attending and intern.