# Flexible-Imaging-Fiber-Guided Intrratracheal Intubation in Rodents
## 4 Discussion
With precise administration using a small endoscope, researchers can reduce variability and ensure consistent dosing. Finally, the use of a small endoscope can reduce the number of animals required for the study. With precise administration, researchers can accurately evaluate the drug's or toxic substance's effects in the same animal over time, reducing the need for additional animals. Research on the lung deposition of liquid or powder using the PennCentury DP-4M inhaler and several self-assembly devices is being actively conducted. Despite the advantages of these systems, several disadvantages have been mentioned by researchers [23]. It has been reported that the powder dispersed in the DP4M inhaler cannot reach deep into the lungs with larger than 5 \(\upmu\)m particles, and powder and liquid mass transfer is difficult in small animals, such as mice [24]. There are various devices for delivering drugs to the lungs of rodents, such as the nose and systemic inhalation chambers. However, the primary drawback is the low likelihood of drug absorption. In other words, it is reported that 80-90% of the drug is deposited [25; 26]. The drug or toxin delivery to the lungs from the nasal cavity depends on the breathing pattern of the animal. Therefore, a forced blower is required for direct delivery to the lungs in small animal models. Based on the prevalence of lung disease caused by inhalation exposure due to humidifier disinfectants in the Republic of Korea from 2006 to 2011, this study was conductedto establish and evaluate the equipment for the evaluation of toxicity in rodent models. The use of an intratracheal drug administration system based on a flexible fiber microen-doscope was proposed. PHMG was found to cause lung disease and irreversible fibrosis for one year based on the equipment offered in a previous study [27]. Based on these results, an instrument for evaluating toxic substances such as PHMG is essential. Acute toxicity tests involve exposing organisms to high concentrations of the chemical for a short period, usually 24-48 h. Chronic toxicity tests, on the other hand, expose organisms to lower concentrations of the chemical for a longer period, usually several weeks to several months. Both tests measure the effects of the chemical on the organism's mortality, growth, and reproduction. Polyhexamethylene guanidine (PHMG) is a biocide commonly used in disinfectants, and as such, its toxicity is a concern for both human health and the environment. Toxicity assessment of PHMG is therefore necessary to ensure its safe use. Toxicity assessment involves a range of tests and experiments to evaluate the potential health and environmental effects of a chemical. These tests may include acute toxicity tests, chronic toxicity tests, genotoxicity tests, and ecotoxicity tests. Toxicity assessment with PHMG has been carried out in several studies. One study conducted acute and chronic toxicity tests on two aquatic organisms: Daphnia magna and Danio rerio (zebrafish) [28]. The results showed that PHMG was toxic to both organisms, with chronic toxicity being more severe than acute toxicity. The equipment proposed in this study was a flexible-imaging-fiber-guided intratracheal administration device that can be inserted into micro-organs to administer drugs and toxic substances. In addition, Micro-sized endoscopes are feasible and have great potential for revolutionizing medical imaging and diagnosis. As technology advances, we will likely see further developments in this area, leading to new applications and improvements in medical care. Researchers who are required to test small animal models will likely find that the designed device will become a universal instrument for inhalable material delivery and monitoring at the laboratory level in the future. However, the device needs to be improved to ensure that the powder is perfectly and evenly distributed in the lungs. In animal experiments, drugs or toxic substances are often administered in powder form for several reasons.