The primary method of respiratory support for critically ill patients in the intensive care unit (ICU) is oral tube intubation, which ensures airway patency, increases ventilation volume, and enhances lung function. However, the use of oral tube intubation may lead to oral mucosal pressure injury (OMPI) due to excessive or prolonged pressure, friction, and shear forces [1]. OMPI can increase patient pain, elevate the risk of infection, impose a financial burden on health care, increase staff workload, and even result in medical disputes. The incidence of OMPI in patients in the ICU ranges from 2.95% to 49.2%, with different fixation positions and methods of tracheal catheterization influencing its occurrence [2]. While numerous factors contribute to OMPI, including patient-related factors, physiological conditions, the use of specific medications, and nursing-related aspects, there are limited reports addressing the mechanical factors that cause OMPI [3-5]. The International Guidelines for the Clinical Prevention and Treatment of Stress Injuries suggest that finite element models can be employed to evaluate mechanical factors by assessing stress distribution characteristics within tissue structures and predicting the risk of cellular and tissue damage [6].

The purposes of this study were to use the finite element theory contact algorithm to simulate and analyze the compression process of the oral soft tissue when the endotracheal tube is fixed in different fixed positions in the oral cavity, and to explore the stress distribution characteristics of the oral soft tissue under the force of the endotracheal tube. This would help to more realistically and accurately evaluate the actual force on the oral soft tissue structure and to clarify the reasonable fixed position of the endotracheal tube when it is fixed in the oral cavity, so as to prevent the occurrence of OMPI.

The results of this study showed that when the tracheal tube was in contact with the lower lip, the equivalent stress and shear stress values of muscle tissue and mucosal tissue were the largest, followed by the upper lip, and the left and right mouth angles were lower than those of the upper and lower lip. Finite element analysis modeling is a powerful bioengineering technique employed to assess tissue loading, encompassing the interactions between tissues, objects, and medical devices. This numerical method effectively addresses mechanical problems [10]. It enables rapid and accurate stress-strain analysis of the structure, shape, load, and mechanical properties of materials in any given model [11]. Moreover, finite element analysis objectively and accurately reflects the distribution of stress, strain, and deformation, and has gained widespread application in oral biomechanics research in recent years [12].

The tracheal catheter is a critical instrument for mechanical ventilator-assisted therapy in patients in the ICU; however, the catheter itself and improper fixation methods may lead to OMPI [6]. From a biomechanical perspective, the OMPI associated with tracheal catheters primarily results from vertical pressure, shear forces, and friction [13]. Continuous mechanical loading on soft tissues is the main contributor to stress injuries, typically occurring at bony prominences or in areas contacting medical devices. When skin or deep tissue deformation persists for a certain duration owing to the pressure from medical devices, pressure injuries may develop [14]. In this study, the mechanical load originated from the force exerted by the tracheal catheter on the oral soft tissue. Contact between the tracheal catheter and the oral mucosal tissue resulted in continuous pressure, leading to tissue deformation in the mucosa. Research indicates that tracheal catheters and their fixation devices are stiffer than oral soft tissues. When the mechanical properties of these instruments do not align with those of the soft tissues, deformation occurs in the latter, concentrating mechanical stress and strain at the points of direct contact, which then gradually extends to the surrounding areas [15,16].

Continuous vertical pressure on soft tissues is a significant factor in the occurrence of stress injuries. The incidence of OMPI correlates with the intensity and duration of pressure; the greater the pressure and the longer its application, the higher the risk of developing OMPI is [17]. Furthermore, when the tracheal tube is improperly fitted and fixed too tightly, the pressure and shear force exerted will increase [14]. Shear forces applied to deep skin tissues can obstruct capillaries, leading to localized ischemia and hypoxia, which may result in deep tissue necrosis. Consequently, damage from shear forces is often undetected in the early stages and is more challenging to heal than damage from typical wounds [13]. Friction arises from the movement between the oral mucosal tissue and the surface of the tracheal tube; while it does not directly cause OMPI, it can compromise the epidermal cuticle, leading to the shedding of the mucosal surface layer and heightened sensitivity to pressure injuries. Once the compromised oral mucosal tissue is subjected to stimuli from saliva and other secretions, the risk of pressure injury escalates. Additionally, friction raises the temperature of the local mucosal tissue, disrupts the local microenvironment, alters pH levels, and increases tissue oxygen consumption, further exacerbating tissue ischemia and heightening the risk of OMPI [16].

The magnitude of the internal mechanical load required to cause tissue damage depends on the duration of the applied force and the specific biomechanical tolerance of the stressed tissue, which is influenced by factors such as age, shape, health status, and the functional capacity of the body systems, including tissue repair ability [18]. Both high loads applied for short durations and low loads sustained over extended periods can lead to tissue damage [18-20]. Continuous loading is one of the primary contributors to this damage; it refers to loads applied over prolonged periods (ranging from a few minutes to several hours or even days), also known as quasi-static mechanical loading. Research indicates that when soft tissues come into contact with the support surfaces of medical devices, pressure and shear forces are generated between the soft tissues and these surfaces [21]. This interaction results in distortion and deformation of the soft tissues under pressure, affecting both the skin and deeper tissues (including fat, connective tissue, and muscle), leading to stress and strain within the tissues [21]. Excessive internal stress in the tissues can disrupt intracellular material transport by damaging cellular structures (such as the cytoskeleton or plasma membrane) or by hindering the transport process itself (for example, by reducing blood perfusion, impairing lymphatic function, and affecting material transport in the interstitial space), which can ultimately result in cell death and trigger an inflammatory response. Concurrently, the emergence of endothelial cell spacing increases vascular permeability, leading to inflammatory edema, which further exacerbates the mechanical load on cells and tissues due to elevated tissue pressure, thus contributing to the development of pressure injuries [22-24].

According to the results of finite element analysis, the stress experienced by the lower lip is the highest, followed by the upper lip, with levels significantly exceeding those at the corners of the mouth. Therefore, in clinical practice, when fixing a tracheal catheter, it is advisable to select the mouth corner to maximize the contact surface area between the catheter and this region. Placing the tracheal catheter in the middle of the mouth minimizes the contact time between the catheter and the oral mucosa. Additionally, regular changes in the fixation position can help redistribute pressure, thereby reducing pressure, shear forces, and friction on the oral mucosa, ultimately lowering the risk of OMPI.

This study analyzed alterations in the stress experienced by oral soft tissue under pressure at various fixation positions of the tracheal catheter within the mouth, from a biomechanical perspective. It provides a theoretical foundation for preventing OMPI in patients with tracheal catheters in the ICU. While this study effectively simulates the biomechanical effects of contact between oral soft tissue and the tracheal catheter, it does not fully replicate the actual forces experienced by oral soft tissue in real-life situations, as the area of contact between the tracheal catheter and the oral soft tissue cannot be completely simulated. Additionally, the study included only one young adult male, which limits the generalizability of the findings. Therefore, it is essential to include participants of varying genders and ages to enhance the scientific validity of the research. Furthermore, improvements in the identification rate and curvature of the 3D grid of the model should be pursued to generate higher-quality 3D models, thereby enhancing data accuracy.