Calculation of Predicted Peak Expiratory Flow in Children with a Formula

Background: To determine whether a child has asthma exacerbation, we should obtain the value of peak expiratory fl ow. It is useful in a diagnostic procedure, in evaluation of response to therapy and following the course of asthma. The context and purpose of the study: On the basis of published relations between body height and peak expiratory fl ow in children I developed a formula for calculation of predicted peak expiratory fl ow in children according to body height. Results: Formula for estimation of predicted peak expiratory fl ow in children according to body height reads as follows: Peak expiratory fl ow [L/min] = (Body height [cm] x 5.3) – 433. Conclusions: In some situations, especially in emergency settings, the presented formula may prove useful in predicting peak expiratory fl ow knowing only a child’s body height. Research Article Calculation of Predicted Peak Expiratory Flow in Children with a Formula Matjaž Kopač* Division of Pediatrics, University Medical Centre Ljubljana, Bohoričeva 20, SI-1000 Ljubljana, Slovenia Dates: Received: 24 January, 2017; Accepted: 09 February, 2017; Published: 10 February, 2017 *Corresponding author: Matjaž Kopač, M.D., Ph.D., Assistant Professor, Division of Pediatrics, University Medical Centre Ljubljana, Bohoričeva 20, SI-1000 Ljubljana, Slovenia, Tel: +386 1 522 3842; Fax: +386 1 522 9620; E-mail:


Introduction
The peak expiratory fl ow (PEF) is defi ned as the maximum fl ow rate generated during a forced expiratory maneuver. It is effort dependent and insensitive to small airway function. It is useful in a diagnostic procedure, in evaluation of response to therapy and following the course of asthma. It is important to compare the value of measured PEF to the previous personal best value [1,2]. Most children older than fi ve years can measure PEF by using one of several available peak fl ow meters.
Reproducibility of the results depends on the patient's ability to take in a full breath and exhale rapidly with maximum force [3].

Methods
On the basis of published relations between body height and PEF rates in children, a diagram representing these data is shown in fi gure 1 [1,2]. As can be seen from the diagram, these relations are linear and a correlation coeffi cient between body height and PEF is 1. Therefore a predicted average PEF

Discussion
Measurement of PEF is one of the basic and quite simple pulmonary function tests. Objective measurement of pulmonary function is useful in the diagnostic procedure of children with respiratory symptoms as well as in monitoring the current status and therapeutic response of a child with asthma. They are valuable only if accurate and interpreted appropriately. In adition, serial measurements over time are more helpful than isolated measurements. It is also very important to compare the value of measured PEF to the previous personal best value [3]. But since children grow constantly, knowing the personal best value may be sometimes misleading, especially after a stable period of asthma without exacerbations. A child's personal best value of PEF one or two years ago may be below the predicted PEF value for present body height. In this way asthma exacerbation may be overlooked. Constant evaluation of PEF according to body height is necessary in chronic respiratory diseases, such as asthma. Nomograms and tables are available that help us to predict PEF in a child but they are not always available when we need them, especially in emergency settings. In these situations the presented formula may prove useful in predicting a child's PEF knowing only body height. Values of PEF obtained by the presented formula differ from values presented in published tables by no more than 1 % which is not clinically signifi cant. Of course the formula can be used only in children above fi ve years of age who are able to perform the PEF test. Fortunately, the relations between predicted average PEF rates in children according to body height are linear which makes the presented formula relatively simple and easy to remember.

Conclusions
Measurement of PEF is one of the basic and quite simple pulmonary function tests.
Constant evaluation of PEF according to body height is necessary in chronic respiratory diseases, such as astma.
Nomograms and tables are available that help us to predict PEF in a child but they are not always available when we need them, especially in emergency settings. In these situations the presented formula may prove useful in predicting a child's PEF knowing only a body height. To the best of my knowledge, the presented formula is the fi rst published formula for estimation of PEF in children according to body height.