Ventilometer

A ventilometer, also referred to as a respirometer, is a device used to measure tidal volume and ultimately minute volume within the anesthesia circuit. It is placed on the expiratory side of the circuit where the expiratory breathing tube attaches to the anesthesia machine.  The device can be used on both rebreathing and non-rebreathing circuits.

There are many different types of respirometers available on the market. One of the original versions is the Wright’s respirometer (Mark 8), which is a mechanical device that detects volume of flow as air passes through the unit. The Mark 8 contains both a small and a large gauge, which indicate volume of flow in the range of 0-1 liters and 0-100 liters, respectively. The original Wright’s respirometer is a simple device that has no power supply making it lightweight and portable between different anesthesia machines. Another type of ventilometer is the electronic digital version with an LCD readout display such as the model 295. This model requires an electrical power source or battery to operate.  Opinions seem to vary among veterinarians and veterinary technicians on the usefulness of the device. One advantage to having a ventilometer is to help check and/or calibrate the volume of gas that is delivered to a patient by a ventilator. This can be especially useful when determining the proper tidal volume for a smaller patient.

One disadvantage to using a ventilometer is that when used in conjunction with an ETCO2 monitor the two pieces of equipment may add too much resistance and dead space to the circuit. Therefore, it may be difficult to justify the usefulness of a ventilometer if the veterinary clinic already has an ETCO2 monitor and has the ability to perform arterial blood gases. Another down side is the cost of the unit. For example, the original Wright’s respirometer can cost anywhere from $1000-1400 whilethe electronic device costs around $600.