Monitoring variables affecting positron emission tomography measurements of cerebral blood flow in anaesthetized pigs

Preclinical Imaging Studies: Protocols, Preparation, Anesthesia, and Animal Care

Today preclinical PET imaging connects laboratory research with clinical applications. Here PET clearly bridges the gap, as nearly identical imaging protocols can be applied to both animal and humans. However, some hurdles exist and researchers must be careful, partly because the animals are usually anesthetized during the scans, while human volunteers are awake. This review is based on our own experiences of some of the most important pitfalls and how to overcome them. This includes how studies should be designed, how to select the right anesthesia and monitoring. The choice of anesthesia is quite crucial, as it may have a greater influence on the results than the effect of the tested procedures. Monitoring is necessary, as the animals cannot fully maintain homeostasis during anesthesia, and reliable results are dependent on a stable physiology. Additionally, it is important to note that rodents, in particular, are prone to rapidly becoming hypothermic. Thus, the selection of an appropriate anesthetic and monitoring protocol is crucial for both obtaining accurate results and ensuring animal welfare. Prior to imaging, catheters for tracer administration and, if necessary, blood sampling should be implanted. The administration of tracers should be done in a manner that minimizes interference with the scans, and the same applies to any serial blood sampling. The limited blood volume and organ size of rodents should also be taken into consideration when planning experiments. Finally, if the animal needs to be awakened after the scan, proper care must be taken to ensure their welfare.

Effects of Long-term Anesthesia, Blood Sampling, Transportation, and Infection Status on Hearts and Brains in Pigs Inoculated with Staphylococcus aureus and Used for Imaging Studies

Laboratory animals are widely used in imaging studies, including infection, heart, and brain research. Compared with rodents, pigs are especially useful because of their large organ sizes, ability to tolerate long-term anesthesia, and substantial blood volume, which allows repeated blood sampling. These factors are particularly important in positron emission tomography studies of potential new radioactive tracers, because the scans often are prolonged; in addition, kinetic studies involving repeated blood sampling may be performed to establish the optimal scan time. However, protracted studies may affect the cardiovascular system, brain, and other organs. This raises the question of how to monitor and counteract the effects of longterm anesthesia in pigs in a typical experimental setting yet prevent introducing bias into the experiment. To address this question, we investigated the effects of long-term anesthesia (maximum, 18 h), repeated blood sampling (maximum of 20 mL blood per kilogram body weight), and road transportation (as long as 1.5 h between 2 imaging centers) on key variables of lung, heart, and brain function in the context of a well-established pig model of Staphylococcus aureus infection. Pulse rate, oxygen saturation, body temperature, arterial pressure of CO₂, and urine production were stable during anesthesia for at least 16 h, whereas blood glucose slowly decreased. Hct and leukocyte count decreased due to repeated blood sampling. During road transportation, blood lactate levels increased 5 fold and arterial pressure of O₂ decreased by 50%. Repeated CT scans, necropsy results, and histopathology findings documented progressive lung changes and acute cardiac necrosis. No lesions indicative of hypoxia were found in brain. The study data show that the typical monitoring parameters do not fully depict the cardiovascular state of pigs during prolonged anesthesia. We recommend streamlining experimental protocols for imaging studies in pigs to avoid organ pathology.