PaediCalc.org

This is an ongoing collaboration project by a team of anaesthetists, paediatric intensivists, AED physician, pharmacist and IT experts in Prince of Wales Hospital, Chinese University of Hong Kong. Our mission is to make these drug and equipment calculations as simple as possible. Originally developed as a paediatric body-weight based calculator for anaesthesia in 2017, the project has now branched off into Anaesthetic and PICU versions of the calculator. This project received the Best Research Award in the Korea-Anaesthesia Meeting 2018.

The core function of the calculator is to calculate doses based on body weight. The Javascript function calculate(x) receives x as the body weight from the user input. Using atropine as an example, the data used to calculate the atropine dose is coded within the HTML span tag, as data attributes:

<span id="atropine" class="field" data-type="dose" data-multiply="0.02" data-dp="2" data-max="0.5" data-min="0.1" data-conc="0.6" data-ML-dp="2">

The multiplication factor is 0.02 (i.e. 0.02mg/kg), number of decimal places is 2, max dose 0.5mg, min dose 0.1mg, drug concentration 0.6mg/ml. The calculate function then uses for loops to iterate through drug dose fields, retrieving data-attributes for each field, then performs the dose calculation given by the formula: output = BW * multiplication factor, further, the dose volume is given by the formula: output = dose / drug concentration.
All the output data are written to arrays and the last part of the calculate(x) writes the arrays to the DOM. The following is the calculate(x) function.

function calculate(x) {
  var listdosefield = document.querySelectorAll('[data-type="dose"]');
  var i;

  for (i=0; i<listdosefield.length; i++) {
    var factor = listdosefield[i].getAttribute('data-multiply');
    var dp = listdosefield[i].getAttribute('data-dp');
    var max = listdosefield[i].getAttribute('data-max');
    var min = listdosefield[i].getAttribute('data-min');
    var output = x * factor;
    var conc = listdosefield[i].getAttribute('data-conc');
    var dp2 = listdosefield[i].getAttribute('data-ML-dp');
    var idML = listdosefield[i].id + "ML";
    var output1;
    var output2;

    if ((max != null) && (output > max)) {
      output1 = max;
      if (dp2 === "1") {
        output2 = Math.round(max / conc * 10)/10;
      } else if (dp2 === "2") {
        output2 = Math.round(max / conc * 100)/100;
      }
    }
    else if ((min != null) && (output < min)) {
      output1 = min;
      if (dp2 === "1") {
        output2 = Math.round(min / conc * 10)/10;
      } else if (dp2 === "2") {
        output2 = Math.round(min / conc * 100)/100;
      }
    } else {
      if (dp === "1") {
        output1 = Math.round(output * 10)/10;
      } else if (dp === "2") {
        output1 = Math.round(output * 100)/100;
      }
      if (dp2 === "1") {
        output2 = Math.round(output / conc * 10)/10;
      } else if (dp2 === "2") {
        output2 = Math.round(output / conc * 100)/100;
      }
    }
    arrDOSES.push([listdosefield[i].id,output1,idML,output2,factor,dp,max,min,conc,dp2]);
  }

  var listvolfield = document.querySelectorAll('[data-type="vol"]');

  //for volume only elements
  for (i=0; i<listvolfield.length; i++) {
    var factor = listvolfield[i].getAttribute('data-multiply');
    var dp = listvolfield[i].getAttribute('data-dp');
    var max = listvolfield[i].getAttribute('data-max');

    var output = x * factor;
    if ((max !=null) && (output>max)) {
      output1=max;
    } else {
      if (dp === "1") {
        output1 = Math.round(output * 10)/10;
      } else if (dp === "2") {
        output1 = Math.round(output * 100)/100;
      }
    }
    arrVOLUMES.push([listvolfield[i].id,output1,factor,dp,max]);
  }
  

  var listprepfield = document.querySelectorAll('[data-type="prep"]');
  //populate prep fields for 1 level
  for (i=0; i<listprepfield.length; i++) {
    var cutoff = listprepfield[i].getAttribute("data-lookup").split(",");
    if (cutoff.length === 4) {
      listprepfield[i].innerHTML = (x < cutoff[1]) ? cutoff[2]:cutoff[3];
    }
    if (cutoff.length === 6) {
      listprepfield[i].innerHTML = 
        (x < cutoff[1]) ? cutoff[3]:
        (x < cutoff[2]) ? cutoff[4]:
        cutoff[5];
    }
    if (cutoff.length === 2) {
      listprepfield[i].innerHTML = cutoff[1];
    }
  }

  var listinf = document.querySelectorAll('[data-type="inf"]');
  
  for (i=0; i<listinf.length; i++) {
    arrINF.push(calcinf(listinf[i]));
  }

  //write HTML innerHTML
  
  for (i=0; i<arrDOSES.length; i++) {
    document.getElementById(arrDOSES[i][0]).innerHTML = arrDOSES[i][1];
    document.getElementById(arrDOSES[i][2]).innerHTML = arrDOSES[i][3];
  }
  for (i=0; i<arrVOLUMES.length; i++) {
    document.getElementById(arrVOLUMES[i][0]).innerHTML = arrVOLUMES[i][1];
  }
  
  for (i=0; i<arrINF.length; i++) {
    document.getElementById(arrINF[i][0]).innerHTML = arrINF[i][1];
  }
  
}
        

The calculation of infusions is slightly more complex. The data attributes of the infusion are contained in the select tag for desired dosing rate user input option box, for example for dopamine:

<select id="dopamineSELECT" class="inlineselect" onchange="calcinfTHIS(this);" data-type="inf" data-factor="3" data-dp="1">

The infusion dilution/preparation is calculated based on the body weight, for example, lower body weight results in a less concentrated preparation. Depending on the drug infusion, there are two or three levels of dilution. For dopamine, 0-<30kg: 150mg in 50ml; >=30kg: 300mg in 50ml. This data is contained in the span tag for the corresponding preparation field.

<span id="dopaminePREP" class="field" data-type="prep" data-lookup="0,30,150,300">

The Javascript function calcinf is called to calculate the final infusion rate based on the value of the select object. The formula is: output = BW * desired rate * multiplication factor / drug concentration. This Javascript function is as follows:

  var name = object.id.slice(0,-6);
  var setrate = object.value;
  var x = document.getElementById("BW").value;
  var prep = document.getElementById(name + "PREP").innerHTML;
  var factor = object.getAttribute("data-factor");
  var output = Math.round(x * setrate * factor / prep * 10)/10;
  var arr = [name + "RATE", output]
  return arr;
            

You can view the source code on the calculator websites. This work is licensed under a Creative Commons BY-NC 4.0 License.