Accurate non-invasive blood pressure (NIBP) measurements in small animals rely on a good blood supply to the tail. If you are struggling to get pressure outputs from the ADInstruments CODA unit, firstly rule out any technical issues associated with the unit and tail cuffs by following the troubleshooting guide in the manual here. Assuming all is well with the hardware, there are other physiological considerations when measuring NIBP in anesthetised animals, as detailed below.
Temperature
Homeothermic warming of the animal is recommended, but especially for this application, as the warming pad will increase or decrease its temperature to help the animal maintain a stable core temperature. The probe can be inserted into the rectum of the anaesthetised animal or placed between the animal and the pad. Keeping the tail covered can also help keep it warm without necessarily affecting core temperature. The use of heat lamps or similar devices to try and directly warm the tail is NOT recommended; this increases the risk of burns and can shorten the lifespan of the latex bladders. Ensure tail temperature has reached 32 to 35 degrees Celsius (°C) before taking any measurements. You can measure and confirm the temperature at the base of the tail using the provided Non-Contact Infrared Thermometer.
Anesthesia
All anesthetics induce vasoconstriction in the extremities, including the tail. Lower doses of inhalant anesthetics tend to be easier for the animal to “fight off”. It is hard to see pressure readings if more than 2.5% isoflurane is used. 2% is at the upper end of where it is still expected to receive readings; if possible, lower closer to 1-1.5% assuming you still have the desired plane of anesthetic.
Animal Age
It may be harder to get consistent readings from older animals. These naturally have less blood flow in their tails. Increasing the time between cycles can help blood vessels recover from compression and encourage blood flow. This is programmed on the CODA unit as follows:
Menu>interval>select time between measurement cycles
Please also consider anything in your experimental protocol that may cause Vasoconstriction such as pharmacological agents or handling.
For further technical assistance with this or any other issue, please contact ADInstruments Technical Support by clicking HERE.