One of the objectives of anesthesia is to provide adequate blood flow to tissue. One way to assess blood flow is to measure blood pressure (ideally mean blood pressure) and heart rate.

Most of the time, in small animal anesthesia, blood pressure is measured non-invasively. It is, however, possible to measure blood pressure invasively to obtain a more precise value. Only non-invasive blood pressure monitoring techniques are explained below. Non-invasive blood pressure can either be monitored with oscillometric devices (PetMap for example) or with a Doppler flow monitor (later call Doppler).

A Doppler only detects flow and makes sounds when the arterial flow changes during each heartbeat. When measuring blood pressure with a Doppler, the principle is to occlude arterial blood flow by inflating a cuff and then deflating it until the flow goes back to normal. When the pressure in the cuff is just below the systolic blood pressure, blood flow can pass the cuff and is detected by the Doppler probe. Heart rate can be calculated with the sounds of the Doppler.