Back Off The Tethered Infusion Pump! Preventing Dosing Errors In Animal Studies
Posted on Feb 01, 2012 by SolomonScientific
Complications from an occlusion in a tethered infusion pump animal model include either an inadvertent bolus after resolving the occlusion or a dose over-reporting error. Modern syringe driver devices sold for human use all have a “back off” feature (also called “anti-bolus”). When the occlusion alarm is activated and pumping stops, the back off feature reverses the driver direction until the pressure is reduced to a normal level. This feature is necessary because the pressure buildup leading to an occlusion alarm activation will result in a bolus of pressurized test article when the occlusion is cleared (i.e., by straightening kinked tubing).
In addition to preventing an inadvertent bolus, the back off feature assures accurate dose delivery data in toxicology and safety pharmacology animal studies. For not only does the back off feature prevent a bolus, it also deducts the indicated amount of fluid infused when it reverses. Note that syringe pumps calculate fluid infused according to the distance the driver travels. Pumps using older technology (i.e., like the Baxter AS-50) which do not have the anti-bolus feature continue to record dose delivery during the interval between the occlusion start time and the occlusion alarm activation time. In slow rate scenarios, this interval can be some hours. During this interval, the pump “thinks” it is pushing fluid into the animal when in fact this fluid is simply accumulating in the tubing proximal to the occlusion point.
In the case of older technology tethered infusion pumps, one post-occlusion result is the animal receives an unintended bolus. The other result is that, after the syringe driver is manually backed off, the indicated amount of fluid infused is greater than the actual amount of fluid infused. The result is an over-reporting of the dose delivery. In the case of a low volume push at a slow rate, the percent variation may be dramatic.
Toxicology drug studies involving rats, dogs, and monkeys (nonhuman primates) routinely depend on tethered infusion pump models using either syringe drivers or other administration devices. These same devices are used for to treat humans during inpatient and outpatient treatment. In both animal and human use, the most common complication of pump use is the occlusion alarm. The back off feature in new technology pumps solves the bolus and over-reporting dose errors which occur in old technology pumps (i.e., like the Baxter AS-50).
