Head injury – the 4-hour observation clock…

You have just seen a 3-year-old boy who, one hour earlier, was running along the street, fell over and hit his head. There was no loss of consciousness, no vomiting, and he’s running around the Emergency Department (ED) completely unaware of ‘social distancing’ practices. On examination, he’s got a small forehead abrasion but nothing else concerning. The parent was initially concerned (so they came to ED) and now wants to go home.

You think this is sensible and speak to your senior, who advises that you observe him for 4 hours post-injury. You think he’s got a trivial head injury with no risk factors and ask why they need to wait three more hours in ED.


‘That’s what we do’, comes the reply…

Paediatric head injuries, arguably, make up a significant proportion of children attending hospitals. It’s been suggested and subsequently shown that a fair proportion could be sent home by a competent nurse at triage even during a worldwide pandemic…

PREDICT have done some wonderful work recently with their ‘Guideline for Mild to Moderate Head Injuries in Children – Algorithm’ (2021) – answering questions I have often wondered myself. However, I personally feel the two most ground-breaking of all these recommendations appear to have been glossed over. This may be because they are so obvious, simplistic and pragmatic, but that makes me love them even more…

Trivial head injuries

‘Children with trivial head injuries do not need to attend hospital for assessment; they can be safely managed at home’. 

• How many children in your own experience fall (boom boom) into this category and attended for review?
• How much money and time (the families and the health services) could be saved if these children stayed at home?

‘A lot’ would be the assumption for both of these questions. However, this is currently an evidence void in need of answers.

Extended observation OR discharge

It is made very clear that children who do not fall into one of the assorted risk categories have ‘no need for observation’ aka discharge home.

• No need to stop, pass go or take up sacred ED seating until 4 hours after their medically innocuous injury (agreed, to a parent, an injury may not have been innocuous but by medical head injury rules, it is).
• The child stays no longer than it took to see and assess them. This may be a hard practice to change in many EDs.

Another 4-hour rule?

How many paediatric head injuries in your own clinical practice do you or someone else say/write the immortal words “Observe 4 hours from injury’? 

Do all the children observed for 4 hours across the world require this?

How many children that you have seen in your practice have deteriorated?

Why does this practice exist, and what is the evidence base?

Well, there is a consensus on who should be observed for 4 hours from injury. In the UK, the National Institute for Health and Care Excellence (NICE) Head Injury: assessment and early management CG176, 2014 – – suggests children with the following require observation for at least 4 hours from the injury:

The latest PREDICT guideline is slightly more prescriptive (especially around age groups) and suggests those with the following risk factors need observation for up to 4 hrs…

But why 4 hours? Why not 3 hours, as someone previously suggested, with wheeze?  Why observe them at all and just CT the lot? Well, at the end of the day, this is all about risk stratification. A CT scan is not without risk (that small thing called radiation?), and the actual number of abnormal CTs (ciTBI/TBI-CT) is quite low (2.3%) in a large group (19 920) of children with head injuries.  We want to scan those children deemed ‘high risk’ who are more likely to have an abnormal scan, not those deemed medium/low risk who are less likely to have an abnormal scan.

The evidence for four hours

What evidence is 4 hrs observation based on? Umm, not a lot. Like many practices in medicine, it’s based on consensus and pragmatism. Many institutions follow a 4-hour target for patients to be admitted or discharged from the emergency department. Children with asthma/wheezing seem to require inhalers every 3-4 hours until discharge, too, and there are, no doubt, countless other examples within the medical world. Four hours of observation post-injury is the consensus view and currently established practice from experts with specialist knowledge in this field. It probably came about when you had to sell your kidney to the Radiologist for a CT scan, and radiation doses delivered per scan were much higher than present ‘modern’ machines. It was easier to observe the child, and if they deteriorated, you could more easily argue for a scan. This is my best guess but it is probably not far from the mark. Could this time be shortened in these at-risk groups? Probably. But trying to research this would, no doubt, be an ethical minefield.

The clock is ticking…

A small select group of children with head injuries require a period of observation post-injury, as suggested by national guidelines, decision rules and clinical gestalt. I would argue that many children in EDs worldwide that are observed for ‘4 hours post-injury do not fall into any of the categories mentioned above, and the root cause for observation is clinician preference based on defensive or outdated practice. This is understandable in those who see children infrequently, but should this be accepted going forward?

In the COVID-era we are living through, I believe there will be an increased focus on reducing unnecessary hospital footfall, ED crowding and time in a potentially risky environment. One potential quality improvement project would be to look at your own institution – how many children stay ‘4 hours post-injury and how many needed to…?