Feline Anesthesia Oxygen Flow Calculator
kg
lbs
Non-Rebreathing (Bain/Mapleson) – Standard for Cats
Rebreathing (Circle) – Maintenance
Rebreathing (Circle) – Induction
Custom Rate
Standard Non-rebreathing rate is 200-300 ml/kg/min.
Most vaporizers require 0.5 – 1.0 L/min for accuracy.
Calculated Requirement:
0 ml/min
Recommended Setting (L/min):
0 L/min
Note: Calculated requirement is below equipment minimum. The recommended setting has been adjusted to your minimum safety threshold.
How to Calculate Oxygen Flow Rate for Cats
Determining the correct oxygen flow rate during feline anesthesia is critical for ensuring patient safety, maintaining adequate anesthetic depth, and preventing the waste of medical gases. Because cats have smaller lung capacities compared to dogs, they often require specific breathing circuits that influence how these calculations are performed.
Safety Note: Always consult your specific anesthetic machine's manual and your veterinary protocol. While calculations provide a target, most precision vaporizers require a minimum flow (often 500ml/min or 1 L/min) to function accurately.
1. Determine the Circuit Type
The calculation formula depends entirely on the type of breathing system being used:
- Non-Rebreathing Systems (Bain, Jackson-Rees, Mapleson): These are most commonly used for cats and small patients (typically under 7-10 kg). They rely on high fresh gas flow to flush out exhaled Carbon Dioxide (CO2).
- Rebreathing Systems (Circle Systems): Occasionally used for large cats. These use chemical absorbents (soda lime) to remove CO2, allowing for lower flow rates.
2. The Formulas
Once you have identified the circuit, apply the appropriate mathematical factor to the patient's weight.
For Non-Rebreathing Systems (Standard for Cats)
Because there is no CO2 absorber, the flow rate must be high enough to prevent the cat from re-inhaling exhaled gases. The standard formula relies on the Minute Volume (MV).
- Formula: Weight (kg) × 200 to 300 ml/kg/min
- Example: A 4 kg cat on a Bain circuit.
Calculation: 4 kg × 200 ml/kg/min = 800 ml/min (0.8 L/min).
For Rebreathing Systems (Maintenance)
If using a circle system for a larger animal, the flow rate is significantly lower during the maintenance phase.
- Formula: Weight (kg) × 20 to 40 ml/kg/min
- Example: A 9 kg Maine Coon on a circle system.
Calculation: 9 kg × 30 ml/kg/min = 270 ml/min.
*Note: This is likely below the vaporizer's minimum accuracy threshold, so you would likely set the flow to 0.5 L/min or 1.0 L/min despite the calculation.
3. Minimum Flow Safety Rule
Regardless of the mathematical calculation, hardware limitations dictate a "floor" for flow rates. Most modern anesthetic vaporizers require a minimum gas flow to vaporize the liquid anesthetic agent accurately.
Standard Guideline: Never run the flow meter below 500 ml/min (0.5 L/min), and many anesthesiologists prefer a minimum of 1.0 L/min for non-rebreathing circuits to ensure ample CO2 washout.
4. Unit Conversions
Veterinary dosages are almost exclusively calculated in Metric units (kg and ml). If you weigh your patient in pounds (lbs), you must convert to kilograms first.
Conversion: Weight in lbs ÷ 2.2046 = Weight in kg.