The risk factors for silent aspiration: A retrospective case series and literature review

Evidence shows that 20%-30% of patients who aspirate do so silently. Research to date has not demonstrated clear evidence to indicate which patients are at higher risk of silent aspiration. Our aim was to use univariate logistic regression analysis of retrospective case review to determine potential patterns of silent aspiration.

We conducted a retrospective analysis of 455 fiberoptic endoscopic evaluation of swallowing (FEES) reports. The patients were divided into four groups: G1 - neurological diseases (n = 93), G2 - head and neck surgery (n = 200), G3 - gastroenterological diseases (n = 94) and G4 - other patients (n = 68). Data included the occurrence or absence of saliva penetration or aspiration, of silent fluid/solid food penetration or aspiration, type of penetration or aspiration, occurrence of cranial nerve paresis, radiotherapy and tracheostomy. Univariate logistic regression was used to evaluate independent risk factors of silent aspiration in the study population. Three models with different independent variables were considered.

There is a statistically significant difference in the frequency of occurrence of silent penetration and aspiration within the groups (p < 0.001), with intraglutative being most frequent. Fluid and food penetration and aspiration correlated with saliva penetration and aspiration in all groups (p < 0.001). Cranial nerve paresis (IX and X), radiotherapy and tracheostomy correlate with saliva penetration and aspiration (p = 0.020 for cranial nerve paresis; p = 0.004 for radiotherapy; p < 0.001 for tracheostomy). One hundred and fifteen patients (45.81%) in the subgroup of patients with intraglutative aspiration had cranial nerve paresis (IX, X or IX-X).

Patients who should be prioritised or considered to be at a higher need of instrumental swallowing evaluation are those with IX and X cranial nerve paresis, tracheostomy and those who have had radiotherapy, with saliva swallowing problems, especially after paraganglioma, thyroid and parathyroid glands and middle and posterior fossa tumour surgery.

What is already known on the subject Clinical signs of penetration or aspiration include coughing, throat clearing and voice changes, while silent penetration or aspiration patients aspirate without demonstrating any clinical symptoms. The most common consequences of silent aspiration include aspiration pneumonia, recurrent lower respiratory tract infections and respiratory failure. Additionally, malnutrition and dehydration can be indicators of silent aspiration. Patients may unknowingly reduce their oral intake and lose weight. Retrospective studies have shown that 20%-30% of patients aspirate silently (e.g. patients after stroke, acquired brain injury, head and neck cancer treatment, prolonged intubation). Clinical examination of swallowing can miss up to 50% of cases of silent aspiration. What this paper adds to existing knowledge Currently, silent aspiration is often discussed in neurological literature, but its applications to head and neck surgery are limited. In this study, we identify head and neck surgery patients who should be prioritised or considered to be in higher need of instrumental swallowing evaluation due to a higher risk of silent aspiration. What are the potential or actual clinical implications of this work? Post-treatment structural changes can result in lower cranial nerve paresis (IX, X, XII) and face injury, in which vagus and glossopharyngeal nerves are injured. After tracheostomy and radiotherapy, patients with problems swallowing saliva need careful clinical examination, particularly cranial nerve examination.