Ambulatory vs Tethered
The choice between an ambulatory or tethered infusion system became possible when infusion pumps that were small, accurate and rugged enough to accomplish this feat became available. Prior to then, tethered systems using volumetric or syringe driver pumps were necessary.
Ambulatory systems allow animals unrestrained and untethered freedom of movement at all times. Long-term tethered infusion in large animals has been banned in some European countries due to the belief that untethered systems put less stress on the animal subjects. New advancements in pump technology, jacket design, catheter material, and surgical techniques and the improved demeanor of the animals, have made this the system of choice for many researchers.
In most countries it is not required that long-term continuous infusion studies in large animals be ambulatory and tethered systems are still common. No guidelines exist regarding ambulatory versus tethered systems in rodents. It is not practical to perform long-term ambulatory infusion studies in small animals unless the delivery volumes remain relatively small since the animal must carry both the pump and test formulation.
In short, there are advantages and disadvantages to both systems. Tethered systems allow constant physical contact with the pump. This is advantageous when reservoirs require frequent changes and makes it easier to monitor pump operation. Ambulatory systems require capture and temporary restraint of the animal to change reservoirs and constant monitoring can only be accomplished using telemetry or remote alarm sensors.
Tethered systems allow for delivery of higher volumes since the animal is not required to carry the reservoir. On the other hand, ambulatory systems allow the animal untethered freedom of movement which gives the appearance of a happier and less stressed animal. New pumps have recently been introduced that are small enough to carries by small cynomolgus monkeys yet are capable of delivering at the higher flow rates often encountered with short duration, restrained infusions.