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Know limitations of weight estimation tools
Weight may be underestimated
Two commonly used tools may underestimate a child's weight in the ED, according to a new study. Researchers obtained weight estimates with the Broselow-Luten tape and the devised weight estimation method (DWEM), and compared them with actual weights of 100 children.1
The Broselow-Luten tape underestimated weights in all weight classes, and the DWEM underestimated weights for children weighing more than 20 kg.
Unfortunately, a child's weight can't always be measured in the ED, notes Steven T. Baldwin, MD, an ED physician at Children's Health System in Birmingham, AL, and one of the study's authors. "Some interventions have a sufficiently small therapeutic index such that even modest errors in estimating a patient's size can significantly increase the risk of harm due to undertreating or overtreating the patient," he says.
The dramatic increase in numbers of obese children may lead to an increased risk, he notes.
However, the biggest risk is to infants, says Baldwin. He gives the example of incorrectly estimating body weight by 2 kg for a 5-kg baby vs. a 100-kg adolescent. "The relative error is 40% of the patient's body weight for the baby but is only 2% for the older child," he says.
To reduce risks, know each method's limitations for obese children or those who have other conditions that may make weight estimates incorrect, says Baldwin. One example is a condition that may change the usual relationship between body height and weight, such as limb deformities or amputations, he says. "Although such cases are infrequent, advance consideration should be given to developing a strategy for dealing with such cases when they require emergent interventions," Baldwin says.
He recommends increasing the weight estimated by a length-based tool by 25% for moderately obese patients and by 50% for profoundly obese patients. "Similarly, the estimated weight could be reduced by 25% for a severely malnourished patient," says Baldwin.
Another option for very obese patients is to plot the child's age on a growth chart and then use the weight at or above the 95th percentile line, says Baldwin.
If he child has a condition which makes measurement of body length difficult, then a flexible tape measure may be useful to get a more accurate measurement, says Baldwin. "If the issue is a condition that invalidates the usual relationship between body length and body weight, then perhaps a crude but tolerable estimate can be made by trying to estimate a correction factor that compensates for the patient's condition that is invalidating the usual length vs. weight relationship," he add.
You also can alter the estimated value for a patient's weight up or down based on their clinical response to interventions, says Baldwin. "Awareness of interventions that have a narrow therapeutic index will allow providers to pay particular attention to the risk of a weight estimation error," says Baldwin. "It will often be best to start low and titrate upward if the weight estimate may be a significant issue."
ED nurses at Children's Medical Center Dallas use the Broselow-Luten tape for any child who cannot be weighed on a scale due to an emergency, says Lanie St. Claire, RN, ED nurse and pre-hospital liaison at Childrens Medical Center Dallas. "All weight is written in kilograms," says St. Claire.
Be familiar with the use of the tool and its limitations, she advises. "Many times drug dosage mistakes occur because the concentration of the drug utilized is not the same as the one on the Broselow," says St. Claire. "It should be not be used as a quick drug reference guide unless you have taken the time to learn how to use it."
For more estimation about weight estimation tools, contact:
To download a free educational packet on the Broselow-Luten tape, go to the Duke University Medical Center's "Duke Enhancing Patient Safety" web site at www.dukehealth1.org/deps. Click on "Clinical Education," and then "Study Packet (Version 2) on the Correct Use of the Broselow Pediatric Emergency Tape."