I've mentioned elsewhere that the smell can be the grossest thing about surgery. Smell is not the most nerve wracking thing, though. Sound is. Not the sound of surgeons bellowing, but rather what is normally a quite normal sound, the pulse oximeter. For those not familiar with it, the pulse oximeter is a machine that measures the amount of oxygen carried by the blood. It does this by shining a specific wavelength of red light through a relatively thin body part, usually a finger. It then measures how much of that light is absorbed. From this it is able to calculate what percentage of the red blood cells are oxygenated. The best possible "score" is 100 (unless you are a member of Spinal Tap). Numbers above 96 are considered normal. Numbers below 90 are worrisome. The machine is also able to measure the pulse by measuring the time between each wave of freshly oxygenated blood. It has become one of the basic tools of anesthesia.
It has also has the best designed sound I have ever heard. It is the modern version of Monty Python's "machine that goes ping". Every time the curve peaks the machine makes an electronic "ping". Its the background noise of every OR. Most of the time it doesn't register on our consciousness. The genius in this sound is one feature: as the oxygen saturation decreases, the the tone of the "ping" lowers. A drop of 10 points will drop the tone over an octave. Since a decrease in saturation is often accompanied by a slowing of the pulse, the machine begins to sound like its battery is dying, which is the perfect metaphor, because that's what the patient is doing.
Believe me, a serious drop in the tone of a pulse ox will get everyone in the rooms attention.
This video shows the tone change in minor way. These tone changes wouldn't grab anyone's attention but they give an idea of what I am talking about. (Tone changes about 0:27 and 1:25)