Paediatric WETFLAG calculations
Paediatric emergencies are high-stress situations where rapid, accurate calculations are vital.
WETFLAG is a mnemonic used in paediatric emergency medicine to quickly calculate key parameters for resuscitating a critically ill child. It’s especially useful when the child’s weight isn’t known and there isn’t time to consult a drug chart.
The mnemonic is primarily for children between 1 and 10 years of age, though some variations exist for other age groups.
Remember that there are other methods too …like length-based tapes (e.g., Broselow tape) or digital apps, which are often used in practice to simplify and reduce errors in these high-stakes situations.
WETFLAG Mnemonic Explained
Here is a breakdown of what each letter in the WETFLAG mnemonic represents, along with the standard formulas and calculations. It’s important to note that these are estimates and may vary slightly depending on the specific guidelines (e.g., APLS, Resuscitation Council UK) and local protocols.
W: Weight This is the first and most critical calculation, as all subsequent values are derived from it. When a child’s actual weight is unknown, you can estimate it using an age-based formula:
Formula: Estimated Weight (kg) =
For example, for a 5-year-old child: kg.
E: Energy (for defibrillation) This refers to the electrical energy required for defibrillation or cardioversion. The dose is calculated per kilogram of body weight.
Formula: Energy (Joules) = (kg)
For an 18 kg child: J.
T: Tube (endotracheal tube size) This calculates the approximate internal diameter (ID) of the endotracheal tube (ETT) for intubation. This formula is for uncuffed tubes, which are typically used in young children to prevent airway damage.
Formula: ETT size (mm) =
For a 5-year-old child: mm. You would select the closest size, such as a 5.0 or 5.5 mm tube.
F: Fluid bolus This is the dose for an intravenous (IV) fluid bolus, typically used to treat shock. The standard is a crystalloid solution, such as 0.9% Normal Saline.
Formula: Fluid bolus (ml) = (kg)
Note: In some cases, like trauma or suspected cardiac causes, a smaller bolus of might be used initially.
For an 18 kg child (non-trauma): ml.
L: Lorazepam This is the dosage for Lorazepam, a benzodiazepine used to manage seizures (status epilepticus).
Formula: Lorazepam (mg) = (kg)
Maximum Dose: Typically capped at 4 mg
For an 18 kg child: mg
A: Adrenaline (Epinephrine) This is the dosage for adrenaline in cardiac arrest. The concentration is crucial—the standard for pediatric cardiac arrest is a 1:10,000 solution.
Formula: Adrenaline (ml) = (kg) of 1:10,000 solution
This is equivalent to a dose of .
For an 18 kg child: ml.
G: Glucose (Dextrose) This is the dose for 10% dextrose solution used to treat hypoglycemia (low blood sugar).
Formula: Glucose (ml) = (kg) of 10% dextrose solution
For an 18 kg child: ml.
NOTE:
While WETFLAG is a valuable and widely taught tool for pediatric emergency medicine, it’s crucial to understand its limitations and potential downsides for a comprehensive lecture. The mnemonic is a heuristic, and its formulas are approximations that may not be accurate in all cases. Here are the key downsides and limitations of WETFLAG:
1. Inaccuracy of the Weight Formula
The most significant limitation of WETFLAG is the weight calculation. The formula: is an estimate and may not be accurate for all children, particularly in two specific scenarios:
-
Obese children: The formula can significantly underestimate the weight of an obese child, which may lead to under-dosing of drugs.
-
Children outside the 1–10 year age range: The formula is designed for this specific age range. Using it for infants (under 1 year) or adolescents (over 10 years) can lead to significant errors in weight estimation and subsequent drug calculations.
2. Risk of Calculation Errors
Even with a simple mnemonic, manual calculation in a high-stress, time-sensitive emergency setting can lead to errors. Studies have shown that traditional, manual calculation methods like WETFLAG are associated with a higher rate of error compared to other methods. This can be due to:
-
Mental math errors under pressure.
-
Incorrect recall of the formula itself.
-
Misunderstanding the units (e.g., mistaking mL for mg).
3. Alternative and Potentially More Accurate Methods
The medical community has developed and adopted several alternatives that are often considered more accurate and reliable, particularly in a non-out-of-hospital setting. You should mention these in your lecture to provide a balanced view.
-
Length-based tapes (e.g., Broselow Tape): This is a widely used tool that is often preferred over age-based formulas. The tape is stretched next to the child, and a color-coded system indicates the estimated weight, pre-calculated drug dosages, and appropriate equipment sizes. This method eliminates the need for manual calculations.
-
Emergency drug charts and apps: Many hospitals and pre-hospital services use pre-printed drug charts or smartphone apps. These provide drug and fluid doses for specific weight ranges, minimizing the risk of calculation errors.
4. Over-reliance on a Mnemonic
While WETFLAG is a great memory aid, a downside is that it might encourage an over-reliance on a single set of formulas without considering the patient’s individual characteristics. A critically ill child may have a known weight or a visibly different body habitus (e.g., very thin or obese), in which case a formula-based estimate should be abandoned in favor of a more accurate method.
In summary, while WETFLAG is an excellent tool for training and initial response in a dire situation with no other resources, it is a simplified approximation.
The ideal approach in pediatric resuscitation is to use the child’s actual weight if known, followed by a length-based tape or a pre-calculated drug chart. You should present WETFLAG as a crucial first-line tool, but with a clear caveat about its limitations and the existence of more accurate alternatives.