In anaesthesiology, two monitors were developed and came into common use around 1985 -1990, which made anaesthesia much safer and reduced morbidity and mortality so much that for the following decade was just about the only medical specialty with falling malpractice insurance rates.
The devices are:
1) The pulse oximeter. We all know patients go blue without enough oxygen in their blood. A good anaesthesiologist under ideal conditions (well lit Caucasian patient with normal hemoglobin) can detect the change when the oxygen saturation falls to 85 per cent. The machine can measure the saturation accurate to the nearest one per cent and by default alarms at 90%. In many cases, the tone of the pulse beep becomes lower as the saturation falls. A decrease of two or three per cent from the normal value of 99 per cent is enough to be significant and require a search for possible causes. As a result, the cause is usually found, identified and corrected long before it reaches the stage of being harmful.
2) The end-tidal CO2 monitor. One of the common causes of a falling oxygen saturation is that the anaesthesiologist has incorrectly placed the breathing tube in the oesophagus, which leads to the stomach, instead of through the larynx into the trachea, which leads to the lungs. If this mistake is spotted quickly and corrected, usually no harm results. If the tube remains misplaced, eventually the patient will suffer brain damage and death due to a lack of oxygen. The end-tidal CO2 monitor measures the carbon dioxide in exhaled breath if the tube is in the correct position. Failure to show carbon dioxide coming from the tube proves that the tube is misplaced and must be removed and reinserted.
Within a short period after the technology became reliable and affordable, the use of both the pulse oximeter and the end-tide CO2 monitor became the standard of care, and anaesthesia became much safer.