Checking and Monitoring Circulation

We talk a lot about circulation in first aid and it is indeed an important thing for us to monitor on a casualty, so in this post we’re going to look at circulation a bit more deeply to give you a better understanding of what it is we’re checking for and monitoring.

What is Circulation?

When we talk about circulation in first aid, we are talking broadly about the body’s ability to effectively circulate blood around the circulatory system. Put another way, is the blood that is being pumped around the blood vessels by the heart, reaching all the parts of the body that it needs to?

Circulation can be affected by numerous things: Heart Problems or other conditions such as high cholesterol, Blood Loss, Crushing or Suspension Trauma, Temperature, and lots more. We’ve covered these issues elsewhere in the blog (click the links to learn more!) so here we’ll concentrate on the actual circulation itself.

Simply put, circulating blood around the body, via the millions of blood vessels that we have inside us, provides our muscles and other organs with all the things they need to function. Mostly, this is oxygen, but our blood contains many more important ingredients as well.

If these muscles or other organs are denied that constant supply of oxygen, this causes problems – initially an inability to function properly, leading eventually to catastrophic failure. Depending on the muscle or organ, this can be catastrophic for our ability to survive. Really the most important muscle is our heart, which needs it’s own supply of blood to work, and our brain, the organ without which we definitely cannot survive.

the circulatory system

If these muscles or other organs are denied that constant supply of oxygen, this causes problems – initially an inability to function properly, leading eventually to catastrophic failure. Depending on the muscle or organ, this can be catastrophic for our ability to survive. Really the most important muscle is our heart, which needs it’s own supply of blood to work, and our brain, the organ without which we definitely cannot survive.

The circulatory system is made up of blood vessels that get progressively smaller in diameter as the get further away from the heart. A good analogy is that of a tree – initially the blood vessels are large like the trunk. As they branch off to supply blood to different parts of the body, they become smaller by necessity, finally becoming extremely small as they reach the extremities.

Checking Circulation on a Casualty

There are multiple ways to check circulation on a casualty and we can readily practice these on ourselves. The first and easiest is Capillary Refill, but we can also consider the ‘windows to the circulatory system’ (more on this below!).

Checking Capillary Refill

Capillaries are the tiny blood vessels just under the skin. If we apply pressure to them by squeezing underneath our finger, we momentarily prevent the circulation and the area should become pale. Once the pressure is released, we should see the colour return in a few seconds. That is the capillaries refilling.

It is easiest to try this by squeezing a nail bed, or knuckle – any bony part of the body will suffice. Squeeze for 5 seconds, and then count how many seconds it takes for the colour to return.

This gives us a way of monitoring the circulation in a specific part of the body, if the time to refill is becoming longer, we know that the circulation is compromised in some way. This is particularly useful following the application of a bandage to a bleed, or supporting an injured limb. Remember that comparing the capillary refill in the injured limb against the other uninjured limb is a really good way of defining wether the circulation in the injured limb is ‘normal’ or not.

Capillary Refill is not only applicable to the extremities. It can equally be applied to any accessible part of a casualty’s body – for example their forehead if they are all wrapped up to keep warm. However, if capillaries are refilling promptly in the fingers or toes, we can be sure that the circulation to the more important parts of the body is working effectively too. If the body feels under threat, it will quickly shut off the less important areas and divert blood flow to the core. This is a survival process called ‘shunting’.

One note of caution – people with very dark brown or black skin will not tend to display the colour change required to monitor Capillary Refill effectively, however the nail beds normally display a colour change, so capillary refill can still be an effective monitoring too.

Checking Eye Lids and the Mouth – Windows to the Circulatory System

A further easy way of checking circulation is to check the colour of a casualty’s mouth, specifically inside their lower lip or their tongue, or by checking inside their eye lids. If you do this yourself in front of a mirror, you’ll see that each is a ‘pink-ish’ colour, and in fact all humans on the planet should display a similar pink-ish colour in these places if their circulatory system is functioning correctly.

The pink-ish colour shows us that oxygenated blood is flowing to these places. Given that the mouth and eyes are very close to the brain, this gives us confidence that the brain is also receiving oxygenated blood, which is important for our survival!

If the colour of the lips, tongue or eye lids changes, this could indicate a variety of issues:

  • Pale – could indicate a lack of blood flow – due to lots of reasons as mentioned above.
  • Blue – could indicate a lack of oxygen in the blood – due to asphyxiation (choking). Blueness of the lips is often a sign of other problems too, usually to do with the airway, circulation, or being too cold.
  • Cherry Red – could indicate overheating, a fever, carbon monoxide poisoning, and much more.

Checking and Monitoring Colour, Sensation and Movement

As mentioned above, monitoring the circulation in an injured limb is especially important. To do this we can use Capillary Refill, alongside checks for Colour, Sensation and Movement. If any of these are giving cause for concern, it could indicate that an injury is particularly serious and the circulatory or nervous system are compromised.


Often an injured limb can present with different colours due to bruising. However in this case we are more concerned about the colour if it is particularly flushed – which could indicate internal bleeding, or pale possibly with blue tinge to the fingers or toes – which could indicate a lack of circulation.


If the casualty reports a loss of sensation in the injured limb, i.e. that they can’t feel their fingers or toes, or the limb itself, this is possibly due to nerve damage or impairment. Often accompanied by a sensation of tingling or ‘pins and needles’.


A loss of the ability to move a limb, hand or foot, or digits is an indicator of muscle function loss. This again could be caused by nerve damage or impairment, or damage to soft tissue during the incident.

Any of these giving cause for concern should be treated as a medical emergency and professional medical help should be sought as soon as possible. In the meantime, ensure that the injured limb is carefully stabilised and supported and that you are able to continue monitoring for any changes.

Casualty Assessment and Monitoring Tips

Here are a few tips that can help the lay first aider when assessing a casualty, or performing further monitoring checks.

  • Compare and Contrast – This is something we do during a damage assessment, or secondary survey, and it is equally applicable here. As mentioned above, use the unaffected limb as a guide to what ‘normal’ looks or feels like for the casualty and compare and contrast it against the injured limb.
  • Capillary Refill – Make a note of where you checked a casualty’s capillary refill so that you can use the same place each time. Better still draw a circle on their skin with a pen, or even some dirt if that’s all you have.
  • Checking Colour – A good way of comparing one monitoring check against another is to take a photo each time. This provides a much more objective way of seeing a colour change, and provides a time stamp. Try to use the casualty’s phone if possible though, the emergency services may want to use the evidence you’ve collected which means if you’ve used your phone, it has to go with the casualty to hospital, possibly without you!
  • Write it all down – Use casualty monitoring card to write it all down – this provides a really valuable overview for the emergency services when they arrive as to what has happened over time. You can download our free casualty monitoring card here, print it out on waterproof paper and remember to pack it and a pen into your kit!
What is Capillary Refill?

Capillary Refill is a way of checking circulation where we apply pressure to the skin or a nail bed to briefly prevent circulation in the capillaries (minor blood vessels). We can then measure the time taken for the capillaries to refill but watching the colour change.

What is Circulation?

Simply put, circulation is another word for blood flow. When checking or monitoring circulation we are assessing whether blood is flowing around the body correctly. If not, muscles or other organs could become compromised as they depend on effective circulation to supply them with a constant supply of oxygen.

What does C.S.M. stand for?

Colour, Sensation, and Movement. These are things we should be checking and monitoring in an injured limb. A change of colour (other than bruising), or loss of sensation or movement could indicate a serious injury and should be considered as a medical emergency.

Scroll to Top