Currently, there is no internationally established diagnostic standard specifically for sialorrhea in patients undergoing orotracheal intubation. Therefore, this study adopted the widely accepted metric of Unstimulated Salivary Flow Rate (USFR) for evaluation. According to Miranda-Rius et al. (8), the normal USFR for healthy adults ranges between 0.3 and 0.5 mL/min. A rate below 0.1 mL/min is indicative of salivary gland hypofunction, whereas a consistently elevated rate beyond the upper limit of normal suggests excessive salivary secretion.

In this study, a USFR > 0.5 mL/min was used as the objective diagnostic threshold for sialorrhea, defined as a salivary secretion rate significantly exceeding normal physiological levels in a resting state. All patients were assessed without any prior oral stimulation to ensure that the measurements reflected natural resting conditions. Saliva was collected using a standardized procedure: at predetermined time intervals, a 20 mL syringe was connected to a suction catheter and inserted through the central hole of a bite block or the lateral port of the endotracheal tube into the oral and pharyngeal cavity. Manual suction was used to collect the saliva. The USFR was calculated using the following formula: USFR = Volume of Saliva Collected (mL)/Time (min). Based on this criterion, patients were categorized into a sialorrhea group (USFR > 0.5 mL/min) and a non-sialorrhea group (USFR ≤ 0.5 mL/min) for comparative analysis.

The choice of manual saliva collection was primarily driven by its feasibility and cost-effectiveness in a clinical setting. This method is relatively simple to perform and does not require specialized equipment, making it suitable for use in a variety of healthcare environments, including those with limited resources. Moreover, manual collection enables immediate measurement of saliva volume, which is important in clinical contexts requiring timely evaluation and decision-making. To ensure the accuracy and consistency of saliva collection, all research staff involved in this procedure received standardized training prior to the study. Only those with at least 3 years of experience in intensive care medicine were selected to perform the saliva collection, as their expertise helps minimize potential variability in the manual suction process. Despite these measures, we acknowledge that manual saliva collection may introduce some degree of measurement error. Future studies may benefit from incorporating more automated or technology-assisted methods to enhance the precision and objectivity of saliva flow assessment.

A general information questionnaire was developed by the research team based on literature review and clinical experience to collect demographic and disease-related data. Demographic data included sex, age, educational level, body mass index (BMI), and marital status. In this study, married status referred to individuals currently in a marital relationship, while unmarried status encompassed those who were single, divorced, or widowed.

Disease-related data included primary diagnosis, Acute Physiology and Chronic Health Evaluation II (APACHE II) score, presence of oral diseases, number of concomitant organ system dysfunctions, and Glasgow Coma Scale (GCS) score. Oral diseases in this study referred to dental pulp diseases, oral mucosal diseases, oral surgical conditions, and periodontal diseases (9). The number of organ system dysfunctions referred to comorbid conditions outside of the primary diagnosis, such as cerebral infarction or hemorrhage (nervous system), respiratory failure or chronic obstructive pulmonary disease (respiratory system), and shock or hypertension (circulatory system).

As all patients in this study were undergoing orotracheal intubation and were therefore unable to speak normally, the GCS scores were calculated based only on eye-opening and motor responses, with the verbal response uniformly recorded as “T” (indicating endotracheal intubation). The depth of intubation was recorded as the distance from the patient’s incisors. All data were obtained either from the patient’s medical records or by interviewing family members.

The results of this study indicate that BMI (OR = 1.365) is a significant risk factor for the development of sialorrhea in orally intubated patients, suggesting that body weight plays a key role in the pathogenesis of this complication. Obesity not only affects systemic metabolic conditions but also alters the local oral microenvironment (13). Existing studies have shown that individuals with obesity have a higher oral microbial load compared to those with normal weight (14). This includes a greater quantity of microorganisms, as well as a more diverse range of species, particularly in terms of anaerobic bacteria and inflammation-associated strains. This imbalance in the oral microbiota may exacerbate inflammation, stimulate salivary gland secretion, or impair the mucosal barrier, thereby inducing or worsening sialorrhea (15). However, it is important to note that while our findings suggest an association between elevated BMI and increased risk of sialorrhea, the relationship between obesity-related oral microbiota changes and sialorrhea has not been causally proven. Further research is needed to explore the underlying mechanisms and establish a causal link.

To better understand the impact of BMI on sialorrhea risk, this study further utilized a restricted cubic spline model for continuous variable analysis. The results revealed that when BMI exceeds 22.785, the risk of sialorrhea significantly increases, showing a clear dose-effect relationship. This finding suggests that during the management of tracheal intubation and mechanical ventilation, clinical teams should pay special attention to patients’ nutritional status and physical condition. For patients with a higher BMI, enhanced oral hygiene and nursing interventions should be prioritized. Increasing the frequency of oral care can help prevent abnormal microbial growth in the mouth and the subsequent increase in secretions, thus reducing the incidence of sialorrhea and improving overall patient comfort and prognosis.

The study results show that smoking (OR = 8.944) is a significant risk factor for sialorrhea in orally intubated patients, indicating its considerable impact on airway management-related complications. Long-term smoking can cause persistent damage to the oral environment through various mechanisms. Nicotine, carbon monoxide, and other harmful tobacco components can significantly alter the composition of the oral microbiota, increasing the proportion of pathogenic bacteria and triggering an imbalance in the oral flora (16). Additionally, these substances can promote oxidative stress in the oral mucosal epithelial cells, leading to a chronic inflammatory state that induces conditions such as gingivitis, periodontitis, and mucosal micro-injuries. This stimulates abnormal salivary gland activity, resulting in increased salivation (17).

It is worth noting that during tracheal intubation and mechanical ventilation, patients’ ability to self-clean the oral cavity is compromised, making it difficult to eliminate oral inflammation and secretions, which further exacerbates sialorrhea symptoms (18). This study suggests that for patients with a history of smoking who undergo tracheal intubation, clinical teams should strengthen oral management strategies. This includes regular professional oral cleaning, and depending on the patient’s mucosal condition, appropriately using anti-inflammatory medications and mild mouthwashes (e.g., sodium bicarbonate, hydrogen peroxide solutions) to adjust the oral pH, inhibit bacterial growth, and maintain oral microenvironment stability (19). Such measures can effectively reduce the risk of sialorrhea.

The study results indicate that the number of combined functional impairment systems (OR = 2.844) is closely associated with the occurrence of sialorrhea in orally intubated patients, making it one of the important risk factors for this complication. An increase in the number of functional impairments often suggests a higher level of complexity in the patient’s overall condition, involving the decline or failure of multiple organ functions (20). Clinically, this requires a comprehensive assessment and the use of multiple drugs for intervention.

Many drugs commonly used in clinical support treatments, such as expectorants for the respiratory system (e.g., ambroxol, acetylcysteine), sedative-hypnotics for the central nervous system (e.g., olanzapine, clonazepam), and neurotrophic agents for post-stroke conditions (e.g., citicoline), may contribute to increased salivation or disruption of salivary gland regulation through their effects on neural control mechanisms or direct stimulation of the salivary glands (21). Furthermore, as the number of functional impairment systems increases, the probability of polypharmacy and cumulative drug doses rises, and drug interactions may exacerbate oral mucosal irritation and glandular stress responses, thereby increasing the risk of sialorrhea (22).

However, it is important to note that our study did not collect data on medication use, and thus these interpretations are speculative and based on existing literature. Future studies should include detailed data on medication use to better understand the impact of drugs on sialorrhea in orally intubated patients. Given these limitations, it is particularly important for clinical practice to be cautious in the management of patients with multiple functional impairments.

Therefore, for intubated patients with multiple combined functional impairments, it is recommended that treatment plans carefully weigh the therapeutic effects and potential side effects of medications, aiming to minimize the use of drugs that may trigger abnormal glandular secretion. Additionally, enhancing the assessment and management of oral secretions in such patients can help prevent and alleviate sialorrhea-related symptoms, improving comfort and safety during mechanical ventilation.

The study results show that the presence of combined oral diseases (OR = 2.578) is one of the significant risk factors for the occurrence of sialorrhea in orally intubated patients. This conclusion is consistent with the findings of Proctor (23), which highlighted the relationship between oral health and salivary gland function. The main mechanism behind this is that when there is chronic or acute inflammation in the oral cavity, inflammatory stimuli activate nerve endings and their associated axonal reflexes, inducing epithelial cell contraction and enhancing the secretory activity of the glands, leading to a significant increase in salivation. Additionally, damage to the barrier function of the oral mucosa further exacerbates the gland’s response to inflammatory factors, causing an imbalance in the salivary regulation mechanism, which in turn triggers or worsens sialorrhea symptoms (24).

For orally intubated patients undergoing mechanical ventilation, airway patency and oral hygiene management are closely linked. If oral inflammation is not effectively controlled, it may not only increase salivation but also raise the risk of aspiration and respiratory infections (25). Therefore, for patients with combined oral diseases, it is recommended to strengthen oral assessments and care during mechanical ventilation, carefully select appropriate antimicrobial, anti-inflammatory medications, or treatments that promote mucosal repair, and actively improve the local oral environment. This approach can help reduce the inflammatory impact on the salivary glands and prevent the occurrence and progression of sialorrhea.

The results of this study suggest that neurological diseases (OR = 4.040) are a significant risk factor for the occurrence of sialorrhea in orally intubated patients. These patients often experience disturbances in the neuro-muscular regulatory mechanisms due to damage or dysfunction of the nervous system, which interferes with the autonomic control of salivary gland secretion, leading to reflexive increases in salivation (26). Additionally, these patients often require the use of medications for cerebrovascular accidents, sedatives, and muscle relaxants during mechanical ventilation, and these medications may further exacerbate the imbalance in salivary secretion by acting on the central nervous system or peripheral nerve pathways, thereby increasing the risk of sialorrhea.

The findings of this study align with those of Naeem et al. (27), who also noted that neurological dysfunction significantly increases the incidence of sialorrhea. Based on these findings, it is recommended that healthcare providers closely monitor the oral secretion status of patients with neurological diseases undergoing orotracheal intubation. Dynamic assessment of sialorrhea risk should be conducted based on changes in salivation, and timely interventions should be implemented as necessary to enhance treatment safety and reduce the incidence of complications.