Version May 2024
| Primary physiologic process/parameter targeted | Monitoring equipment | Principle | Derived information | Additional function | |
| Oxygenation | Inspired gas O2 content | O2 analyzer (with a low-limit alarm in use) | Paramagnetic sensor, fuel (galvanic) cell, polarographic (Clark) electrode, mass spectroscopy, or Raman scattering. | Inspired/expired O2 concentration when placed downstream from fresh flow control valves | A low-level alarm is automatically activated by turning on the anesthesia machine |
| Blood oxygenation | Pulse oximeter | The Beer-Lambert law applied to tissues and pulsatile blood flow. The relative absorbency at wavelengths of 660 and 940 nm is used to estimate saturation, which is derived from the ratio of oxyhemoglobin to the sum of oxyhemoglobin plus deoxyhemoglobin. | Hemoglobin saturation, pulse rate, relative pulse amplitude displayed on plethysmography waveform | Continuous evaluation of circulation, variable pitch pulse tone, and audible low-threshold alarm | |
| Ventilation | Exhaled CO2 | Capnograph | CO2 molecules absorb infrared radiation at 4.26 micrometers, proportionate to the CO2 concentration present in the breath sample. | ETCO2, inspired CO2, diagnostic waveforms, respiratory rate, apnea detection | Instantaneous information about:
|
| Integrity of ventilation system during mechanical ventilation | Disconnection alarm | Detects the cyclical changes in airway pressure in the normal range. | Alarms if a significant decrease in rate or pressure occurs | Alarms if high pressures are sensed | |
| Pulmonary mechanics (volume, flow, pressure) | Pulmonary flow and pressure sensors | Volume of gas proportional to a drum movement, changes in differential pressure (near the Y-connector) or in electrical resistance (hot wire housed in a monitor or ventilator). | Inspired and expired volume, flow, and airway pressure | Pressure volume and flow volume loops | |
| Circulation | Cardiac activity | ECG | The ECG monitor detects, amplifies, displays, and records the ECG signal. | Heart rate and rhythm | ST segment depression/elevation and trend over time, with an audible alarm warning of significant arrhythmias or asystole |
| Arterial BP | Noninvasive BP monitor | Oscillometric devices automatically inflate and deflate the cuff, and have electronic pressure sensors that record the pressure oscillations of the arteries. The pressure at which maximal oscillations occur as the cuff is deflated corresponds with MAP. Proprietary algorithms are used to calculate systolic and diastolic BP. | Arterial BP | Indicator of organ perfusion | |
| Temperature | Temperature monitor | Devices with a semiconductor, electrical resistance decreases as temperature decreases. | Core or peripheral temperature | A greater than 2°C core-to-periphery temperature gradient is indicative of low cardiac output | |
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