Monitoring During Anaesthesia

 

When a patient has a general anaesthetic, they are completely asleep and unable to tell the medical team how they feel. Because of this, anaesthetists and operating theatre staff rely on monitoring equipment to constantly check how the body is functioning during surgery.

The Royal College of Anaesthesia outline the typical minimal monitoring required during anaesthesia.

Monitoring allows the anaesthetist and theatre team to spot problems early and make adjustments immediately. Modern operating theatres use several types of monitoring to keep patients safe.

Below are some of the most important things that are monitored during anaesthesia.

 

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Oxygen Levels (SpO₂)

One of the most important measurements is oxygen saturation, often written as SpO₂.

This tells the team how much oxygen is in the patient’s blood.

A small device called a pulse oximeter is placed on the patient’s finger. It shines a light through the skin and calculates the oxygen level in the blood. 

Healthy oxygen levels are usually 95 to 100 percent.

If oxygen levels begin to fall, the anaesthetist can quickly adjust the patient’s breathing or oxygen supply.

Even with modern technology it is sometimes hard to accurately monitor your oxygen saturation if you have acrylic nails or polish. Please try and take these off before your surgery.

 

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Carbon Dioxide (CO₂)

Carbon dioxide, written as CO₂, is the gas we breathe out after our body has used oxygen.

During anaesthesia, a monitor measures the amount of carbon dioxide in the patient’s breath. This is called capnography.

This helps the team confirm that:

• The patient is breathing properly

• The breathing tube is in the correct place

• The lungs are working effectively

 

We use the phrase - No trace, wrong place. Which basically means if we can't see a CO₂ trace on our monitor it likely means that the tube we use to delivery oxygen has been put in the wrong place.

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Heart Rate (HR)

Heart rate, often written as HR, is how fast the heart is beating.

Sticky dots are placed on the patient’s chest which measure the electrical activity of the heart. This is called an ECG (electrocardiogram).

Monitoring heart rate helps detect if the heart is beating too fast, too slow, or irregularly during surgery.

 

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Blood Pressure (BP)

Blood pressure, often written as BP, measures how strongly blood is being pumped around the body.

A cuff is placed around the arm, similar to the one used during a GP appointment.

Blood pressure monitoring helps the anaesthetist ensure that the patient’s organs are receiving enough blood and oxygen during the operation.

 

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Breathing Rate (Respiratory Rate)

The respiratory rate simply means how many breaths the patient takes per minute.

During a general anaesthetic, breathing is often supported by a ventilator, which is a machine that helps move air in and out of the lungs.

Monitoring breathing helps ensure the lungs are working properly throughout the operation.

 

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Vapouriser Rate

Many anaesthetics are maintained using special anaesthetic gases.

These gases are delivered through a device on the anaesthetic machine called a vapouriser. The vapouriser controls how much anaesthetic gas is given to keep the patient asleep.

The anaesthetist carefully adjusts this level throughout the surgery.

 

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Gas Monitoring

Operating theatres also monitor the gases the patient breathes in and out.

This includes measuring:

• Oxygen levels

• Carbon dioxide levels

• Anaesthetic gases

This monitoring ensures the patient is receiving the correct mixture of oxygen and anaesthetic during the procedure.

 

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Airway Pressure

Airway pressure measures the pressure inside the breathing system while the ventilator is helping the patient breathe.

This helps the anaesthetist detect problems such as:

• Blockages in the breathing tube

• Lung stiffness

• Issues with the breathing machine

Monitoring airway pressure helps protect the lungs during surgery.

 

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Why Monitoring Is So Important

All of this monitoring allows the anaesthetic team to continuously watch how the body is responding to surgery and anaesthetic drugs.

If anything begins to change, the team can act immediately to correct it.

Modern monitoring technology has played a huge role in making anaesthesia one of the safest areas of modern medicine.

If you would like to learn more about how anaesthesia works, you can read our guide explaining What a general anaesthetic is.

You can also learn more about the professionals who assist the anaesthetist in theatre by reading our article about Operating Department Practitioners (link to ODP blog).

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