Sensor Oximetry Reflectance R/E Small Reflectance Sensor - for most animals, wet and part the hair at the ventral tail base and wrap in place with a cohesive type bandage (not adhesive tape or any tape that will tightly constrict). It may be necessary to shave a small spot on the ventral tail base in patients with a thick undercoat such as a Husky. For dogs or cats, if the sensor is inserted rectally the red light should be shining on the sphincter muscle. Do not insert the entire length of the probe in the rectum. For equine this sensor is most effectively used along the gum line or cheek. Experience will quickly tell you which sensors work best under different conditions, Fur, dark pigmentation, poor perfusion and movement can all affect the sensors ability to obtain readings. Well perfused sites with little or no hair are preferable. It is important to note that some anesthetic drugs can affect peripheral pulse pressures causing very weak pulsations.