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Anaesthesia

Updated 09 January 2018

The equipment - the monitor screen

On top of the anaesthetic machine or built into it is the anaesthetic monitor. This is like a computer screen, and the most up-to-date models have a colour display.

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A vast amount of information is displayed on the screen, both as numbers and as waveforms. A modern monitor will thus contain most or all of the following:

  • A continuous ECG as a waveform, and the number of heart beats per minute. The more sophisticated machines will also give a warning message regarding irregularities of the heartbeat and whether the heart muscle shows electrical signs of inadequate oxygenation.
  • Blood pressure measurements, including the systolic, diastolic and mean values.
  • A waveform of the arterial oxygen saturation, and also a digital reading of the peak readings.
  • A capnogram waveform showing the carbon dioxide concentrations throughout the breathing cycle, with digital readings of the value during inspiration and the highest reading at the end of expiration.
  • The patient’s temperature if a temperature probe has been applied.
  • If a central venous pressure catheter is been used, a waveform of the pressures on a beat-to-beat basis with readings of systolic, diastolic and mean values.
  • If an arterial catheter is been used, a waveform of the pressures on a beat-to-beat basis with readings of systolic, diastolic and mean values.
  • If a neuromuscular monitor is being used, the values of the muscle strength in response to an electrical stimulus applied to the nerve supplying that muscle. This assists the anaesthesiologist in deciding when to give more muscle relaxant and when to reverse the relaxant.
  • The concentrations of the volatile agent in each breath at the beginning of inspiration and at the end of expiration.
  • If the ventilator is being used, readouts of the breaths per minute, the volume of each breath, the volume of gas breathed per minute, the pressures at each stage of the breathing cycle, and a number of other respiratory parameters. If the patient’s breathing circuit becomes blocked or disconnected an alarm will sound and an alarm message will be displayed. In most instances these values are displayed on a separate screen that is part of the ventilator, but the more sophisticated machines have these values on a screen next to the main monitor screen.

In addition to displaying the values of all these vital signs, the machine has built-in alarms that will sound if any particular value reaches a dangerous or abnormal level.

 

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