The rationale for pulse oximetry and capnometry in anaesthesia and sedation.

The monitoring of sedated or unconscious patients always requires a trained clinician. Extra vigilance and information can be provided by numerous electronic aids that also introduce error, distraction and cost. Particularly for pulse oximetry and capnography, however, these negative factors are offset by the benefits of accurate blood-gas information obtained continuously and non-invasively. The photometric principles common to pulse oximetry and infrared capnometry are examined in detail. Accuracy and sources of error are discussed and applications and limitations outlined. Evidence of the beneficial impact of these two instruments is presented from published experience with both unconscious and sedated patients.