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Weight estimation guidelines


When a child is picked up by paramedics or brought into an emergency department, we don’t know their weight.

Many research teams have been trying to find the best method to estimate a child’s weight, so medication can be dosed safely and equipment sized appropriately.

So what weight estimation guidelines are we supposed to use?

Traditionally, we’ve used age-based formulae, but these are inaccurate. More reliable methods are available. However, all require more information than age, whether height, mid-arm circumference, a parent estimate or a smartphone image.

Currently, we still use age-based formulae in Australia, and although inaccurate, there are some advantages to using such formulae.

Why use age-based formulae?

They are very quick. Most prescribers use these formulae with resuscitation aids, emergency manuals or clinical practice guidelines. This means they do not need to remember the formula or do the calculation themselves as they are given a table with corresponding weight to age.

Given that age-to-weight conversion are often provided, staff do not need to be trained to gather the estimate.

They do not require additional equipment, which may be hard to find if an ambulance or emergency department rarely sees paediatric critical cases.

You can predict the weight of the child that is about to arrive by ambulance if you have their age. This means you can draw up any critical medications in advance.

The impact of cognitive load on medication errors

Extrinsic cognitive load is a key risk factor for committing a human error in paediatric critical events. Mistakes include significant medication errors like ten-fold errors (where 10x the medication is prescribed or administered because the decimal point is moved or the concentration is incorrectly calculated). These cause significant patient morbidity and mortality.

Gathering more information to make the weight estimate more accurate (e.g. measuring the child, taking a sufficient quality image, or finding a parent) increase the complexity of the weight estimation phase. This increased complexity increases cognitive load and the risk of human error at all phases of the dosing process.

What is the ideal weight estimation tool?

We need to find something that can be used by anyone who might need to manage a critical paediatric event. This includes paramedics, junior medical staff and adult emergency department personnel that may need to manage patients before they reach a tertiary children’s hospital or paediatric emergency department.

We need clear, easy-to-follow guidelines and associated training that can be rolled out broadly. We must keep the cognitive burden as low as possible, as many prescribers will be in an unfamiliar, stressful situation.

Future protocols may also differ based on the paediatric emergency expertise and training available in that setting, so this needs to be considered. For example, a paediatric emergency department may choose a more accurate method with a higher cognitive load than an ambulance service.

Another crucial factor is the time delay associated with each weight estimation strategy. When it comes to events that require weight estimation, time is of the essence. It is essential to consider the time required to obtain the estimate and the time needed to locate the appropriate equipment, perform subsequent dose calculations, and prepare the medication for administration. There is a significant advantage if emergency departments can prepare medications in advance, even before the child arrives. Pre-calculating and pre-preparing doses would significantly reduce the time delay in administering the drugs, which is paramount in emergencies.

In light of the increasing prevalence of childhood obesity, finding a weight estimation strategy that can accommodate various body types and medication requirements is crucial. Different drugs necessitate dosing based on different factors, such as ideal body weight (IBW) or total body weight (TBW), depending on their pharmacokinetic characteristics. Dosing medication based on TBW in obese children can potentially result in overdosing.

Sydney Children’s Hospital has provided a comprehensive overview of the necessary adjustments for specific medications, which is highly valuable. However, in pediatric emergencies, weight adjustments for each medication can further burden healthcare providers with additional cognitive load.

Regrettably, available data on patient outcomes is scarce to provide clear guidance. Existing studies examining the impact of weight errors focus on incorrectly recorded weights, such as instances where the wrong unit (e.g., pounds instead of kilograms) or decimal point placement was used. None of these studies specifically investigate the harms resulting from weight estimation errors.

There is no suggestion that using the original APLS formula in Australia is causing harm to patients. However, there is also a lack of evidence to definitively prove otherwise. Therefore, the overarching goal should always be to minimize errors.

Nonetheless, it is important to consider that increasing the complexity of weight estimation methods could heighten the cognitive load on healthcare providers, increasing the risk of more significant errors. Hence, it is crucial to strike a balance between accuracy and practicality.

Getting an accurately dosed drug into a critically ill or injured child is complex.

Unfortunately, there is a lack of high-quality evidence to guide our practice regarding weight estimation and drug dosing. We have limited knowledge about the consequences of dosing errors and the appropriate doses for many medications.

We can take two perspectives. One is to argue that accurate weight estimation doesn’t matter since there is no evidence showing its impact on outcomes. The other is to advocate for maximum accuracy to minimize potential drug dosing errors, which is the more ethical option.

Fortunately, recent evidence supports the idea that accurate weight estimation is crucial. A significant medication error is likely in at least one-third of clinically stable children. The situation becomes even more concerning for children needing resuscitation.

We should focus on weight estimation errors and consider the cumulative impact of other errors in weight-based drug dosing. These are known as compounded errors. These can occur during medication preparation and administration. Medication preparation and administration errors may match or surpass the weight estimation error. Moreover, drug concentration errors can contribute an additional 10 to 15% error. Therefore, a 20% weight estimation error, combined with a 20% administration error and a 10% concentration error, quickly becomes a potential 50% error.

Let’s use adrenaline as an example. The “low” indicates the maximum potential underdosing and the “high” the maximum potential overdosing at each step of the compounded error.

*An adrenaline/epinephrine solution must contain 90% to 115% of the labelled amount to meet United States Pharmacopeia standards (Epinephrine injection. The United States Pharmacopeia: The National Formulary. United States Pharmacopeial Convention, Rockville, MD; 2013).

So, what is the solution? We need to use accurate weight estimation systems and ensure appropriate, goal-directed training in preparing and administering emergency medications. Errors should be minimised at every step of the drug dosing-delivery process.

There are three important considerations when evaluating weight estimation systems: their accuracy, usability, and ability to integrate with a drug dosing system.

Accuracy of weight estimation guidelines

Regarding accuracy in weight estimation, our goal is straightforward: we want the most precise system available, as long as it’s not excessively costly. However, given the increasing prevalence of childhood obesity, we now face the challenge of needing a system that can estimate both total and ideal body weights. This flexibility allows us to optimize drug dosing for each specific medication and each patient.

While there is limited data on the outcomes of incorrect dosing in obese children, there is enough evidence to raise concern. Therefore, it is crucial to establish a minimum accuracy target. 95% of weight estimates should lie within 20% of the actual weight for any system we use. The PAWPER tape, the Mercy method, and potentially parental estimates are the approaches that come closest to meeting this standard.

Usability of weight estimation guidelines

In addition to accuracy, the usability of weight estimation systems plays a crucial role. This encompasses two important aspects: ease of use and vulnerability to human and patient factor errors. A system’s usability not only affects its accuracy but also impacts its practicality. Striking a balance between usability and accuracy is essential to minimize healthcare providers’ stress during emergencies.

The ideal weight estimation system should be accurate and help reduce cognitive burden. We have carefully considered the usability factor in designing the PAWPER tape. This system is designed to be quick and easy to use without adding to the cognitive load of healthcare providers. On the other hand, the Mercy method is a bit more complex to use and is more vulnerable to human and patient factor errors.

Finding a weight estimation system that is both accurate and user-friendly is vital in ensuring effective and efficient weight estimation, especially in time-sensitive situations. By prioritizing usability, we can enhance the usability-accuracy balance and better support healthcare providers in delivering optimal care during pediatric emergencies.

The ability of a weight estimation system to contribute to the accuracy of downstream processes needs to be considered. This refers to how it can improve the accuracy of drug dosing by how well the system integrates with a drug dosing guide. The best example (in a good way) is an App that can generate an accurate weight estimate automatically used for drug dosing calculations with limited further user input. The worst system is one with no integration, such as parental weight estimates or age-based formulas. Colour-coded systems and other length-based tapes with precalculated drug doses fall in the middle.

Having identified the most appropriate weight estimation system for your setting, the next step is to use it optimally. There are valid arguments about ensuring the system is maximally usable with a low cognitive load, but no system is completely cognitively neutral. However, complexity during emergencies is the reason that emergency medicine specialists exist. Our training and learning need to prepare us to practise effectively during emergencies, and the fact that treatment occurs during an emergency should not excuse a diminished quality of care. These circumstances should not excuse potentially harmful practices. 

In summary

Weight estimation systems must be evaluated according to their accuracy, usability and ability to be integrated with a drug dosing guide.

The cumulative medication errors resulting from weight estimation errors and drug preparation and administration can be significant and potentially cause patient harm.

Appropriate training in weight estimation systems and emergency drug preparation and administration is essential. The incorporation of this practice into simulation training is likewise essential.

Healthcare providers specialising in providing care during emergencies must be competent at managing the cognitive loads experienced during emergency care. This can be achieved through appropriate teaching and training. The emergent nature of the presentation should not excuse a diminished quality of care or the use of inaccurate or inappropriate adjuncts (including weight estimation tools).

Some degree of complexity is inevitable in many aspects of emergency care and adds to the cognitive load. The answer is to limit the complexity as much as possible without negatively affecting patient care and ensure that training is adequate to reduce the effects of the cognitive load.

Selected References

Doherty C, McDonnell C. Tenfold medication errors: 5 years’ experience at a university-affiliated pediatric hospital. Pediatrics. 2012;129(5):916-24. Available from:

Khoo TB, Tan JW, Ng HP, Choo CM, bt Abdul Shukor INC, Teh SH. Paediatric in-patient prescribing errors in Malaysia: a cross-sectional multicentre study. Int J Clin Pharm. 2017;39(3):551-9.

Foster M, Tagg A, Klim S, Kelly AM. Accuracy of parental estimate of child’s weight in a paediatric emergency department. Emerg Med Australas. 2019; in press.

Hirata KM, Kang AH, Ramirez GV, Kimata C, Yamamoto LG. Pediatric weight errors and resultant medication dosing errors in the Emergency Department. Pediatric Emergency Care. 2017. 10.1097/PEC.0000000000001277

Murugan S, Parris P, Wells M. Drug preparation and administration errors during simulated paediatric resuscitations. Archives of Disease in Childhood. 2019;104:444-450.

National Academy of Medicine. Preventing medication errors: Quality Chasm Series Washington 2006 [Accessed 7 July 2018]. Available from:

Shaw KN, Lillis KA, Ruddy RM, Mahajan PV, Lichenstein R, Olsen CS, et al. Reported medication events in a paediatric emergency research network: sharing to improve patient safety. Emerg Med J. 2013;30(10):815-9. Available from:

Sutherland A, Ashcroft DM, Phipps DL. Exploring the human factors of prescribing errors in paediatric intensive care units. Arch Dis Child. 2019;0:1-8. Available from:

Wells M, Goldstein L, Bentley A. The accuracy of emergency weight estimation systems in children – a systematic review and meta-analysis. International Journal of Emergency Medicine. 2017;10(29):1-43.

Wells M, Goldstein LN, Bentley A. The accuracy of emergency weight estimation systems in children – a systematic review and meta-analysis. Int J Emerg Med. 2017;1:1. Available from:


  • A medical student who spends her free time listening to Harry Potter audiobooks and trying to keep her indoor plants alive.


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