function togglePhaseVisibility() {
var circuit = document.getElementById('circuitType').value;
var phaseDiv = document.getElementById('phaseContainer');
// Non-rebreathing circuits typically use a constant high flow regardless of maintenance vs induction to prevent rebreathing CO2
// However, some protocols vary. For simplicity in this tool, we hide phase for Non-rebreathing as it relies on high flow constant.
if (circuit === 'non-rebreathing') {
phaseDiv.style.display = 'none';
} else {
phaseDiv.style.display = 'block';
}
}
function calculateFlowRate() {
// 1. Get Inputs
var weightInput = document.getElementById('dogWeight').value;
var unit = document.getElementById('weightUnit').value;
var circuit = document.getElementById('circuitType').value;
var phase = document.getElementById('anesthesiaPhase').value;
var minFlow = parseFloat(document.getElementById('minFlowSafety').value);
// 2. Validate
if (!weightInput || isNaN(weightInput)) {
alert("Please enter a valid weight.");
return;
}
// 3. Convert Weight to KG
var weightKg = parseFloat(weightInput);
if (unit === 'lbs') {
weightKg = weightKg * 0.453592;
}
// 4. Determine Flow Factor (ml/kg/min)
var flowFactor = 0;
var factorText = "";
var warning = "";
if (circuit === 'non-rebreathing') {
// Bain/T-piece typically requires 200-300 ml/kg/min to prevent rebreathing
// We will use 200 ml/kg/min as the standard calculation baseline
flowFactor = 200;
factorText = "200 ml/kg/min (Non-rebreathing)";
if (weightKg > 10) {
warning = "Note: Non-rebreathing circuits are typically not recommended for dogs over 10kg due to high gas consumption and heat loss.";
}
} else {
// Rebreathing (Circle System)
if (phase === 'induction') {
// Induction usually requires higher flow to wash in gas.
// Range 50-100 ml/kg/min. We use 50 as a standard start point.
flowFactor = 50;
factorText = "50 ml/kg/min (Induction)";
} else {
// Maintenance. Semi-closed usually 20-40 ml/kg/min.
// We use 20 ml/kg/min as standard efficient flow.
flowFactor = 20;
factorText = "20 ml/kg/min (Maintenance)";
}
}
// 5. Calculate Raw Flow in mL
var rawFlowML = weightKg * flowFactor;
// 6. Apply Minimum Flow Safety Rule
var finalFlowML = rawFlowML;
var appliedMin = false;
if (finalFlowML < minFlow) {
finalFlowML = minFlow;
appliedMin = true;
}
// 7. Convert to Liters
var finalFlowL = finalFlowML / 1000;
// 8. Display Results
document.getElementById('resWeight').innerHTML = weightKg.toFixed(2) + " kg";
document.getElementById('resFactor').innerHTML = factorText;
document.getElementById('resFlowML').innerHTML = Math.round(finalFlowML);
document.getElementById('resFlowL').innerHTML = finalFlowL.toFixed(2);
var warningEl = document.getElementById('warningMsg');
var warningHtml = "";
if (appliedMin) {
warningHtml += "Calculated flow was below the safety minimum. The result has been adjusted to " + minFlow + " mL/min.";
}
if (warning) {
warningHtml += warning;
}
if (warningHtml !== "") {
warningEl.innerHTML = warningHtml;
warningEl.style.display = 'block';
} else {
warningEl.style.display = 'none';
}
document.getElementById('resultDisplay').style.display = 'block';
}
Understanding Fresh Gas Flow Rates for Dogs
Calculating the correct Fresh Gas Flow (FGF) rate is a critical component of veterinary anesthesia. The flow rate determines how much oxygen (and anesthetic gas) is delivered to the breathing circuit per minute. The calculation depends heavily on the patient's weight, the type of breathing circuit used, and the phase of anesthesia.
1. Circuit Types
The choice of circuit dictates the mathematical formula used for flow rates:
Non-Rebreathing Systems (e.g., Bain, Ayre's T-Piece): Generally used for patients under 7-10 kg. These circuits rely on high fresh gas flow to flush out exhaled Carbon Dioxide (CO2). Because there is no chemical absorbent (soda lime), the flow rate must be high, typically 200–300 ml/kg/min.
Rebreathing Systems (Circle Systems): Used for patients over 7-10 kg. These use a chemical absorbent to remove CO2, allowing gases to be recirculated. This allows for much lower flow rates, conserving heat and moisture.
2. Anesthesia Phases (Rebreathing Systems)
If using a rebreathing system, the flow rate changes depending on the procedure stage:
Induction & Recovery: High flow rates are needed to rapidly change the anesthetic concentration in the circuit. A common calculation is 50–100 ml/kg/min (up to 3 L/min).
Maintenance: Once the patient is stable, the flow can be reduced. For a semi-closed circle system, standard maintenance flow is often calculated at 20–40 ml/kg/min.
3. The Safety Minimum
Regardless of the calculated weight-based result, most vaporizers utilize a specific minimum flow rate to ensure accuracy. A common safety rule in veterinary practice is to never run the flow meter below 500 mL/min (0.5 L/min), even for small patients, to ensure the vaporizer functions correctly and adequate oxygen is delivered.