Weight estimation in pre-hospital paediatric emergencies is often required for the calculation of drugs dosages, endotracheal tube size, fluid therapy and defibrillation. For a number of varying reasons, the ‘gold standard’ of actually weighing the patient in the pre-hospital field is not feasible. Previous work conducted by a number of researchers suggests that weight estimation by medical staff is of moderate accuracy, with other health care professionals estimates being grossly inaccurate (Greig et al, 1997; Uesugi et al, 2002; Hall et al, 2004; Menon and Kelly, 2005; Partridge et al, 2009). Research suggests paramedics are the least accurate of all health professionals (attending physicians, residents, interns, nurses, medical students and paramedics) (Hall et al, 2004). Parents’ estimates of their child's weight are reasonably accurate (Wald et al, 2007; Partridge et al, 2009) however they are not always available in the unpredictable pre-hospital environment, and thus weight-based formulae are a crucial component in the pre-hospital management of a paediatric patient.
The overwhelming majority of emergency medical service (EMS) providers use the advanced paediatric life support (APLS) weight estimation formula for children aged from 1–10 years of age (Weight(kg)=age × 2+4) (Geduld et al, 2010). At the time of inception, the APLS formula was accurate in terms of average weight at a particular age, however recent statistics have shown that the average weight of children is increasing with the percentage of overweight children increasing from 4.2 % in 1990 to 6.7 % in 2010 (de Onis et al, 2010). As a result of this, as children now weigh more on average, there is a need to assess whether the APLS formula is still valid and reliable. The ability to accurately estimate a child's weight allows for accurate treatment of the patient's presenting problem such as effective pain management, or sedation without underdosing or overdosing the patient. It allows the accurate delivery of defibrillation joules, accurate calculations for critical replacement and maintenance of fluid following a significant burn injury, and for accurate dosage calculations of a wide variety of other pharmacological agents (Tintinalli et al, 2004).
In the recent decade a variety of different weight estimation methods have been devised in addition to the APLS formula. These include; the ‘best guess’ weight estimation formula (Casey and Borland, 2010), the Broselow tape weight estimation formula (Theron et al, 2005), the Australian Resuscitation Council (ARC) weight estimation formula (Thompson et al, 2007), and the Argall weight estimation formula (Nguyen et al, 2007).
The ‘best guess’ weight estimation formula is divided into age groups with different formulas for each age group (Casey and Borland, 2010) and is considered to an accurate weight estimation method:
The Broselow tape method requires the use of a specially marked tape measure that has weight calculations pre–written on it based upon the height of the patient (Casey and Borland, 2010) and is commonly used in hospital emergency departments when dealing with paediatric patients that are unable to be weighed. The ARC weight estimation formula is a modified weight estimation formula of the APLS methods by being age-based with patients aged 1–9 years. The formula is weight (kg)=2 × age in years +4, and for those aged 10 years and above weight (kg)=3.3 × age in years (Thompson et al, 2007). Finally, the Argall weight estimation method is another weight estimation formula based on the patient's age with weight (kg)=(age in years + 2) × 3 (Nguyen et al, 2007). However, this formula is not commonly used due to the need to assign a body habitus in order to use the formula.
The objective of this study was to identify a paediatric weight estimation formula relevant to the pre-hospital setting.
Methods
A literature review was undertaken using the electronic medical databases Ovid Medline, EMBASE, CINAHL Plus, Cochrane Systematic Review, and Meditext from their commencement date until the end of May 2012.
The search strategy used the following MeSH terms and keywords: ‘weight estimation’, ‘drug calculations’, ‘pediatric’, ‘paediatric’, ‘EMS’, ‘EMT’, ‘paramedic’, ‘emergency medical service’, ‘emergency medical technician’, ‘pre-hospital’, ‘out-of-hospital’, and ‘ambulance’. These search terms were used individually or in combination. The reference list of retrieved articles was reviewed to ascertain if articles were missed during the initial search process.
The majority of the literature that was found in our search was conducted on paediatric populations in Australia, America, South Africa, with few being conducted in the United Kingdom.
Articles were included if they reported on the development or evaluation of a paediatric weight calculation in the pre-hospital or hospital setting. Articles were excluded if they were not in English, not featuring human subjects, or were letters to the editor.
Results
The search located 635 articles with 29 meeting the inclusion criteria. There were only two pre-hospital–based studies located. Four studies were excluded as they were based on visual estimation rather than a weight estimation formula; this included one of the pre-hospital focused papers. This left 25 articles to be reviewed, which are summarised in Table 1.
| Author, date | Study type and level of evidence NHMRC | Study size (n) | Patient age group (years) | Estimation methods examined |
|---|---|---|---|---|
| Casey et al, 2010 | Level 3(II) | 1235 | 0–14 | ‘Best guess’ weight estimation method; advanced paediatric life support (APLS) weight estimation method; Broselow tape weight estimation method. |
| Sandell et al, 2009 | Level 3(II) | 544 | 0–11 | APLS weight estimation method; an aged–based weight estimation method; a length–based weight estimation method. |
| Theron et al, 2005 | Level 3(II) | 909 | 0–10 | APLS weight estimation method; the Broselow tape weight estimation method; the Oakley resuscitation chart; the Shann weight estimation formula; Leffler weight estimation formula. |
| Thompson et al, 2007 | Level 3(III) | 1843 | 0–14 | APLS weight estimation method; Australian Resuscitation Council (ARC) weight estimation method; best guess weight estimation method. |
| DuBois et al, 2007 | Level 3(III) | 400 | 0–14 | Broselow–Luten tape weight estimation method; devised weight estimation method (DWEM). |
| Zink et al, 2008 | Level 3(III) | 127 | 0–17 | Nurse estimation; physician estimation; parent estimation; Broselow tape weight estimation method; DWEM estimation method. |
| So et al, 2009 | Level 3(II) | 1011 | 0–9 | Broselow tape weight estimation method; Leffler weight estimation formula; Theron weight estimation formula. |
| Luscombe and Owens, 2007 | Level 3 (III) | 13 | 998 0–10 | Weight(kg)=2(age+4) weight estimation formula; |
| Nguyen et al, 2007 | Level 3(II) | 410 | 0–10 | The Argall weight estimation formula. |
| Argall et al, 2003 | Level 3(III) | 300 | 1–10 | APLS weight estimation method; Broselow tape weight estimation method. |
| Cattermole et al, 2010 | Level 3(III) | 1 248 | 1–10 | APLS weight estimation formula; ARC weight estimation formula; Nelson weight estimation formula; Shann weight estimation formula; Tintinalli weight estimation formula; Tinning (‘best guess’) weight estimation formula; Argall weight estimation formula; Luscombe weight estimation formula; Theron weight estimation formula; Chinese age weight rule (3x age last birthday)+5. |
| Luscombe et al, 2010 | Level 3(II) | 9 3827 | 1–16 | Weight(kg)=2(age+4) weight estimation formula. |
| Geduld et al, 2010 | Level 3(II) | 2 832 | 1–10 | APLS weight estimation formula; Luscombe and Owens weight estimation formula; ‘best guess’ weight estimation formula; Broselow weight estimation formula |
| Black et al, 2002 | Level 3(II) | 495 | 1–18 | APLS weight estimation formula; Broselow tape weight estimation formula; DWEM; Oakley table, Traub–Johnson weight estimation formula; Traub–Kichen weight estimation formula. |
| Krieser et al, 2007 | Level 3(II) | 410 | 1–11 | APLS weight estimation formula; Broselow tape weight estimation formula; Argall weight estimation formula; ‘best guess’ weight estimation formula. |
| Kelly et al, 2007 | Level 3(III) | 410 | 1–11 | ‘Best guess’ weight estimation formula. |
| Haftel et al, 1990 | Level 3(III) | 100 | Not listed | ‘The hanging leg weight’ weight estimation formula. |
| Ramarajan et al, 2008 | Level 3(II) | 548 | Not listed | The Broselow tape weight estimation formula. |
| Tinning and Acworth, 2007 | Level 3(II) | 70 181 | 0–14 | APLS weight estimation formula; simple age–based weight estimation formulas. |
| Rosenberg et al, 2011 | Level 3 (III) | 372 | 0–14 | Visual weight estimation by blinded physicians in comparison to the use of the Broselow tape weight estimation method. |
| Park et al, 2012 | Level 3 (III) | 124 095 | 0–14 | New formula compared to APLS, ‘best guess’ formula, Shann formula, Leffler formula, Nelson formula and Broselow tape. |
| Nieman et al, 2006 | Level 3 (III) | 7500 | 0–12 | Actual weight in comparison to the weight estimated using the Broselow tape. |
| Luscombe, Owens and Burke, 2011 | Level 3 (II) | 93 827 | 1–16 | Comparison of APLS formula and Weight=3(age)+7 |
| Bourdeau, Copeland and Milne, 2011 | Level 3 (III) | 243 | 1–10 | Broselow tape method. |
| Heyming et al, 2012 | Level 3 (II) | 572 | 10–49 months | Comparison of the Broselow tape in the pre–hospital field, in the emergency department (ED) and the scales used in the ED. |
Table 2 includes the National health and Medical Research Council's (NHMRC) evidence hierarchy used in Table 1 (National Health and Medical Research Council, 2012).
A more comprehensive version of Table 1, including an assessment of the key findings and limitations of each study included in this study is available on request from the editor (jpp@markallengroup.com).
| Level | Intervention |
|---|---|
| 1 | A systematic review of level II studies. |
| 2 | A randomised controlled trial. |
| 3 (I) | A pseudo-randomised controlled trial (i.e. alternative allocation or some other method). |
| 3 (II) | A comparative study with concurrent controls: non-randomised, experimental trial, cohort study, case–control study, interrupted time series with a control group. |
| 3 (III) | A comparative study with concurrent controls: non–randomised, experimental trial, cohort study, case–control study, interrupted time series with a control group. |
| 4 | Case series with either post-test or pre-test and post-test outcomes. |
Discussion
It was difficult to draw a conclusion of which weight estimation formula has the highest level of accuracy and was best suited for the pre-hospital field. However, it was clear that the currently accepted ‘gold standard’, the APLS weight estimation formula, frequently underestimates the weight of paediatric patients (Black et al, 2002; Theron et al, 2005; Luscombe and Owens, 2007; Thompson et al, 2007; Tinning and Acworth, 2007; Luscombe et al, 2009; Sandell and Charman, 2009; Casey and Borland, 2010; Cattermole et al, 2010). There is evidence to suggest that other weight estimation formulas or methods such as the Broselow tape (Theron et al, 2005; DuBois et al, 2007; Zink et al, 2008) are also continually underestimating the weight of paediatric patients as the average weight of children continues to trend upwards (de Onis et al, 2010). To highlight the variance among the weight estimation methods, a comparison is shown in (Table 3) using midazolam 0.1 mg/kg as the calculated drug dose.
| Age/formula | APLS 1–10 years (age × 2 + 4) | Broselow tape (females) | Broselow tape (males) | Best guess: |
Argall 1–10 years (age + 2) × 3 |
|---|---|---|---|---|---|
| 6 months | N/A | 0.7 mg | 0.7 mg | 0.75 mg | N/A |
| 1 year | 0.6 mg | 0.9 mg | 1.0 mg | 1.2 mg | 0.9 mg |
| 5 years | 1.4 mg | 1.7 mg | 1.9 mg | 1.7 mg | 1.8 mg |
| 10 years | 2.4 mg | 3.3 mg | 3.3 mg | 4.0 mg | 3.6 mg |
| 14 years | N/A | N/A | N/A | 5.6 mg | N/A |
NB. Above dosages have been calculated using a midazolam dose of 0.1mg/kg. Broselow tape height measurements were taken from the Victorian State Government's Department of Education and Early Childhood Development website (Child Health Records, 2007) and was based on 50 th percentile heights.
The Advanced paediatric life support (APLS) weight estimation formula
At the time of inception, the APLS formula was accurate in terms of average weight at a particular age. However, recent studies have shown that the average weight of children is increasing (de Onis et al, 2010) and, the APLS weight estimation formula is providing increasingly inaccurate weight estimations (Black et al, 2002; Theron et al, 2005; Luscombe and Owens, 2007; Thompson et al, 2007; Luscombe et al, 2009; Sandell and Charman, 2009; Casey and Borland, 2010; Cattermole et al, 2010; Luscombe et al, 2011; Park et al, 2012). These studies showed that the APLS weight estimation formula had a tendency to underestimate the weight of paediatric patients (Black et al, 2002; Argall et al, 2003; Theron et al, 2005; Thompson et al, 2007; Sandell and Charman, 2009; Casey and Borland, 2010; Cattermole et al, 2010). This could lead to under resuscitation and incorrect drug dosages, which could be detrimental to the patient's wellbeing. In large sized studies conducted by Tinning and Acworth (2007); Luscombe and Owens (2007) and Luscombe et al (2009; 2011), it was demonstrated that the APLS weight estimation formula significantly underestimates the weight of paediatric patients, with inaccuracy increasing as the patient becomes older in age.
In a study conducted on 13 998 paediatric patients by Luscombe and Owens (2007), it was shown that the APLS weight estimation formula underestimated weight by a mean of 18.8 % (Luscombe and Owens, 2007). In another study conducted on 93 827 paediatric patients by Luscombe et al it was demonstrated that the APLS weight estimation formula underestimated weight by a mean of 33.4 % (Luscombe et al, 2009). The findings in both of Luscombe's studies are supported by the findings Argall et al, who also found that the APLS weight estimation method tended to underestimate the weight of paediatric patients on a mean average of 3.52 kg (Argall et al, 2003). The findings of the three aforementioned studies suggests that the underestimation of a paediatric patient varies on average between 18.8 % and 33.4 %. This raises potentially serious patient safety questions.
Despite the recent concerns of the APLS weight estimation formula it remains accurate in specific sub-populations. For example, in a study conducted by Geduld et al, it was shown that the APLS weight estimation formula was accurate for paediatric patients presenting to a major receiving hospital in the Western Cape, South Africa (Geduld et al, 2010). On average, the paediatric patients that presented to the major receiving hospital in the Western Cape, weighed less than their western counterparts (Geduld et al, 2010)—potentially explaining why the APLS weight estimation formula was accurate in this particular sub-population. In contrast to the high level of accuracy in this sub-population, a study conducted by Theron et al (2007), demonstrated that the APLS weight estimation formula significantly underestimated the weight of Maori and Pacific Islander children (Theron et al, 2005) who weigh more on average than their western counterparts. This demonstrates the contrast between the average weight of sub-populations and the effects this has on the accuracy of paediatric weight estimation formulas—indicating that it is possible that paramedics may require a range of weight estimation formulas for a variety of different sub-populations if accurate weight estimation is to be achieved. The articles examining the APLS method were limited by the fact that they are conducted on one population and in one geographical location, reducing their ability to be generalised. In addition, population bias was another limitation as paediatric patients that had life-threatening conditions were excluded from most studies.
The Broselow tape weight estimation method
The Broselow tape weight estimation method is based upon a specially marked tape measure that has weight calculations pre-written on it based upon the height (or length) of the patient and is an accepted alternative to the APLS weight estimation formula. The Broselow tape weight estimation method has been proven to be accurate at the time of introduction into widespread use. However, there is some doubt over whether it remains accurate as the average weight of children continues to trend upwards (Nieman et al, 2006; de Onis et al, 2010).
Despite the recent questioning about the accuracy of the Broselow tape method, it is still a widely used method of weight estimation and appears to be relatively accurate, especially in certain sub-populations, and may be a suitable alternative when actual weighing is impossible and no parent is present (Krieser et al, 2007). In studies conducted by Black et al (2002) and more recently Casey et al (2010), it was demonstrated that the Broselow tape estimation method is accurate, and is particularly more accurate than emergency physician estimation (Rosenberg et al, 2011), a finding also supported by So et al (2009). However, it was revealed that the accuracy of the Broselow tape decreased rapidly once a child's weight was greater than 25 kg. The accuracy of the Broselow tape estimation method was also validated in the sub-population in the Western Cape of South Africa, however, this paediatric sub-population has a lower average weight than the world wide paediatric weight average (Geduld et al, 2010).
In the only pre-hospital study conducted by Heyming et al (2012), it was shown that Broselow tape had a high inter-rater reliability between emergency physicians and paramedics. It was also shown by Heyming et al (2012) that there was a strong correlation between the weight that was estimated on the Broselow tape and the actual weight of the patient, and it has become evident from this literature review that there is conflicting evidence on the accuracy of the Broselow tape, and it is yet to be seen if the Broselow tape will be able to cope with the rise in the average weight of children (Nieman et al, 2006; Park et al, 2012).
In studies conducted by Argall et al (2003); Nieman et al (2006); Dubois et al (2007); Zink et al (2008); Bourdeau (2011) they were able to demonstrate that as the average weight of children is rising, the accuracy of the Broselow tape weight estimation method is declining. The aforementioned studies found that the Broselow tape estimation method underestimates the weight of patients. The inaccuracy of the Broselow tape weight estimation method was more evident in sub-populations, with the Broselow tape estimation method underestimating the weight of Maori and Pacific Islander children (Theron et al, 2005) much in the same manner as the APLS method. In a study conducted by Ramarajan et al (2008), it was revealed that the Broselow tape estimation method overestimates the weight of Indian children by 10 % (Ramarajan et al, 2008). The inaccuracies of the Broselow tape method in sub-populations such as Maori and Pacific Islander children further indicate that a single weight estimation formula may not be sufficient for paramedics and other health care professionals. Similar to the studies conducted on the APLS weight estimation formula, the majority of studies were conducted in a single geographical location and on a single population, leading to a reduction in generalisability of the results. In some studies, children with a life-threatening illness were excluded and there was no set acceptable over or underestimation percentage.
The ‘best guess’ weight estimation formula
The ‘best guess’ weight estimation formulas are a set of three formulas that are based upon the age of the patient and is one of the few methods that can actually be used on patients that are younger than one year old.
As health care clinicians search for alternative weight estimation formula to the APLS formula, the ‘best guess’ estimation formula appears to be a suitable substitute. In studies conducted by Kelly et al (2007); Thompson et al (2007); Casey et al (2010) it was found that the ‘best guess’ estimation formula was more accurate than the currently accepted ‘gold standard’ APLS formula, and the Broselow tape estimation method in the 1–4 years age group (Casey and Borland, 2010). However further, large scale studies are required to validate the ‘best guess’ formula and to determine if this method is able to remain accurate across the weight ranges of all children.
Despite the accuracy reported by Kelly et al (2007), Thompson et al (2007) and Casey et al (2010), there is some doubt over the ability of the ‘best guess’ formula to accurately estimate the weight of selected sub-populations of paediatric patients. In a study conducted by Geduld et al (2010), it was shown that the ‘best guess’ weight estimation formula tended to overestimate the weight of children. Casey et al also discovered that once a patient was older than 4 years of age the ‘best guess’ formula tended to overestimate the weight of patients with 33 % of patients aged 5–10 having their weight overestimated by over 20 % (Casey and Borland, 2010). It is possible that with the increasing average weight trend (de Onis et al, 2010), that this overestimation will be balanced out, however further research is required to determine if the ‘best guess’ formula should become more widely accepted. As is normative practice for studies conducted on weight estimation methods, most studies were conducted in a single geographical location, upon a single population—something which can lead to an inability to generalise results to other populations. There was also a lack of an acceptable under or over estimation percentage, making it difficult to interpret what is an acceptable over or under weight estimation.
The Argall weight estimation formula
A more recent weight estimation formula is the Argall formula which is an aged-based formula (weight (kg) = [age in years + 2] × 3) (Nguyen et al, 2007).
Currently there is a lack of evidence to enable the widespread use of the Argall weight estimation formula. A study conducted by Cattermole et al (2010) on 1 248 paediatric patients found that the Argall formula prediction was greater than 30 % of the actual weight of the patient on 17.1 % of occasions. In addition predictions were within 10 % of the actual weight of the patients in only 34.6 % of patients included in the study (Cattermole et al, 2010). This subsequently led to the Argall formula failing an independent validation study conducted by Nguyen et al (2007). The study conducted by Nguyen et al (2007) found that the Argall formula had poor accuracy in Australian children with 37 % of estimates being within 10 % of actual weight. It was also shown that the accuracy of the Argall formula was particularly low in the category of patients whose actual weight was greater than 35 kg.
We speculate that the Argall formula faces the same issues as the APLS and Broselow tape formula where these methods lack accuracy in the higher weight ranges of children. Numerous other weight estimation methods are available, however, there was insufficient literature available to critically review these methods and determine their accuracy and suitability for the pre-hospital field. This study has demonstrated that the current paediatric weight estimation lack accuracy, especially for use in the pre-hospital field.
Weight= 3(age) + 7
In a recent study conducted by Luscombe et al (2011) on 93 827 children aged between one and 16-years-old that presented to a major paediatric hospital emergency department showed that 3(age) + 7 was an accurate formula for estimating the weight of today's children.
This is a step in the right direction in terms of finding an accurate weight estimation method that is able to keep track with the increasing average weight of children. However, further studies may need to be conducted to validate this weight estimation method to ensure that it is able to maintain pace with the increasing average weight of children (Luscombe et al, 2011).
Limitations
This study is potentially limited by the majority of studies that were investigated being based in a single receiving hospital or a single region of a country which reduces the ability to generalise the results. Issues were also apparent in some studies of standardising the methods that were used to obtain the actual weight of the patient and how this data was actually recorded. In the studies that also included visual estimations, as well as using weight estimation methods, it was found to have only a single nurse or physician performing the visual estimation—once again, this leads to poor generalisability.
The study was also limited by the fact that no papers featuring pre-hospital weight estimation formula fitted the inclusion criteria. In most studies, critical ill paediatric patients were not included in the study, with this population of patients requiring the accurate weight estimation the most.
Other weight estimation methods were also revealed in the literature review but were deemed to be too unsuitable or too impractical for the pre-hospital field, such as the ‘Hanging leg weight’ method, studied by Haftel et al (1990).
Conclusion
Though it is perhaps rather difficult to draw a conclusion on which weight estimation formula is the most suitable for use amongst a wide variety of populations seen in the pre-hospital field—some of the key points that should be taken out of this review is that the currently accept paediatric weight estimation formula, the APLS, lacks accuracy in most of the current paediatric population. It was clear that all of the weight estimation methods examined in this literature review had decreases in accuracy as the weight of the child increases. The inability of other weight estimation methods to be accurate has made it difficult to determine an adequate replacement for the current widely accepted APLS method. Additionally, it seems that a single weight formula may not be sufficient in the pre-hospital field to counteract the variance in average weight from sub-population to sub-population.
It is evident that future research is required to determine the weight estimation formula that is best suited for the pre-hospital field.