BOLUS: A Clinical Framework for Predicting Adverse Events from Aspiration

Co-author: Aaron Padilla, MS, CCC-SLP, BCS-S

Literature supports that aspiration alone does not independently lead to an adverse event such as aspiration pneumonia (Bock et al., 2017; Langmore et al., 1998; Palmer & Padilla, 2022). When aspiration occurs, the host’s response is linked to the individual’s defense mechanisms and physiologic responses. Ideally, in a healthy individual, if material is aspirated the elimination process begins. This multifactorial process engages several levels of removal of the aspirated material. If aspiration of water occurs, aquaporins (i.e., ion channels in the lungs) help transport the fluid from the lungs into the capillaries. When non-water contents are aspirated, clearance may be achieved through an enzymatic process where phagocytes engulf the inoculum, or through mucociliary clearance which assists in elevating the invader upward and out of the lungs, concluding with an expelling cough. When one has diminished host defenses or when the defense mechanisms are overburdened by the amount of aspiration, immigration into the lungs may exceed elimination from the lungs, and an adverse event may occur.  

Effective management of aspiration is crucial given that it can result in varied outcomes ranging from minor to life-threating consequences (Mandell & Niederman, 2019; Marik, 2001).  While aspiration itself may not always result in a negative outcome, the significance lies in the impact of the potentially detrimental consequences, especially considering the essential role that eating and drinking plays in our daily lives and in cultural customs (Padilla, Palmer, & Rodriguez, 2019). Given the high stakes and varied outcomes associated with aspiration, how can dysphagia clinicians identify and assess risk, determine when the risk is acceptable, discern which risk factors are modifiable, and ultimately make evidence-based decisions regarding care. 

Over the past 30 years, there has been a body of literature dedicated to identifying and clarifying variables that impact the risk of adverse events associated with aspiration. Yet, the integration of this evidence into clinical practice is inconsistent. This aligns with the fact that it can take up to 17 years from time of publication to implementation of evidence into clinical practice (Bauer et al., 2015). 

To aid the dysphagia clinician in aspiration risk stratification, a comprehensive framework, referred to as BOLUS (Fig. 1). was created. It draws upon current evidence to encapsulate the risk of an adverse event from aspiration within the context of holistic patient care.  

Figure 1. Schematic of Bolus Framework

Table 1. Resources to support understanding of host defenses and the proposed framework.  

The BOLUS Framework 

Each letter in the BOLUS framework is associated with a distinct risk category that contains a series of guiding questions to support clinical decision making (Fig. 2). As noted in Figure 1, B stands for bolus variables, O stands for oral care and oral health, L stands for lifestyle and ability to perform activities of daily living, U stands for unintended or iatrogenic risk factors, and S stands for general system status such as other comorbidities. 

Figure 2. Questions associated with BOLUS framework

B: Bolus variables and response.

B represents risks linked to bolus variables such as volume, frequency, pH, or viscosity of aspirated material, and the associated physiologic response to aspiration of these materials. In general, aspiration of varying viscosities yields different outcomes, where (a) solids and thicker liquids have a greater likelihood of an adverse event (Langmore et al., 1998, Nativ-Zeltzer et al., 2018, 2020; Robbins et al., 2008), (b) aspiration of acid laden contents increases the odds of pneumonitis (Marik 2001), and (c) frequent aspiration increases the odds of a secondary opportunistic infection if elimination of aspiration is suboptimal as may be the case in individuals with lung disease, current smoking, or bedbound status. In fact, in a recent rapid review (Palmer & Padilla, 2024), there was strong evidence supporting the relationship between aspiration of dense material and the incidence of medical complications (e.g., UTI, dehydration). However, there was insufficient evidence to determine if aspiration of thick or dense material was linked to pulmonary sequalae or death. 

Cough, important for aiding in airway clearance, may be a modifiable factor for the individual with dystussia (Hutcheson et al., 2018; Kim & Sapienza, 2005), or for an individual with silent aspiration. That is, even if the reflexive cough is not engaged upon invasion of the bolus into the airway, a cued cough can be employed. In fact, if a patient silently aspirates, or aspirates with an unsuccessful sensate response, targeting cough would be a useful intervention. Targeting sensory motor training for airway protection has been shown to improve both reflexive and cued cough (Troche et al., 2022).  It has been postulated that completing cough intervention after mealtimes may assist with airway clearance (L. Wennerholm, personal communication, March 13, 2024).

O: Oral care.

There is an abundance of literature on the topic of oral care and oral health, and its strong role in reducing the odds of pulmonary and medical sequelae (Palmer & Padilla, 2024). This literature is well summarized in the recent review by Ashford (2024). For patients who aspirate and have good oral care, the likelihood of a negative consequence is lower (Langmore et al., 1998; Gosney et al., 2006; Quinn et al., 2014; Palmer & Padilla, 2024). Notably, good oral care should include debridement of plaque through brushing to prevent dysbiosis (Dyck et al., 2012). Soft oral swabs are insufficient for adequate oral care.  Rather, a toothbrush is advantageous given the increased friction and increased ability to debride pathogens. 

L: Lifestyle and ability to perform activities of daily living. 

Risks associated with aspiration may be influenced by one’s lifestyle choices and their ability to independently perform activities of daily living. Lifestyle choices such as chemical use (i.e., smoking and drinking) can impact functionality and effectiveness of lung clearance in the event of aspiration. Mobility, which may not be a clear lifestyle choice, such as in the case of orthopedic injuries, is an important aspect of pulmonary clearance and pulmonary hygiene. Although the data are limited for individuals who are bed bound, low levels of mobility have been linked to greater odds of pulmonary consequences in the event of aspiration (Karagiannis et al., 2011; Langmore et al., 2002). Individuals who aspirate and depend on others for feeding and daily activities face higher risks of an adverse event (Langmore et al., 1998). It’s reasonable to infer that individuals reliant on caregivers for tasks like oral care may have reduced frequency and completion rates of these essential routines. More data are needed in this area to strengthen these conclusions (Palmer & Padilla, 2024).

U: Unintended or iatrogenic risk factors.

Unintended or iatrogenic risk factors occur when a treatment improves one system but causes other adverse events. For example, although feeding tubes are used to provide life-sustaining nutrition and hydration as a part of supportive care, the presence of the tubes introduces a risk factor that increases with longer duration of tube placement (Freytag et al., 2003; Ickenstien et al., 2005; Juan et al., 2020). In fact, the presence of feeding tubes can result in decreased swallow frequency, reduced clearance of secretions from the aerodigestive tract, and increased bacterial harboring (Pisegna & Langmore, 2018). Although the individual with a feeding tube who is nil per os will have adequate nutrition and hydration parenterally, the effect on the pharyngeal musculature is disadvantageous. That is, as swallowing frequency is reduced, disuse atrophy of the pharyngeal musculature is observed

In addition to feeding tubes, other supportive care has been shown to increase the likelihood of an adverse event, such as the presence of a tracheotomy tube (Nativ-Zeltzer et al., 2022). Evidence strongly links the presence of tubes in the oropharynx to increased odds of pulmonary sequalae, particularly for individuals with compromised swallow safety (Palmer & Padilla, 2024). 

Another unintended risk factor would be the side effects of medications. Medications aimed to provide essential support may negatively impact immune function, saliva production, or cognitive status. For example, immune suppression is a common side effect for individuals who are on chronic high dose corticosteroids or are receiving chemotherapy. 

S: System status and comorbidities.

System status refers to any conditions that could impair host response. Such conditions can be either chronic (e.g., an individual with dementia) or acute (e.g., individuals with an acute confusional state). System status includes variables such as co-morbidities (e.g., pulmonary disease, or GI disease), cognitive function, frailty, chronic immune deficiency (e.g., diabetes), Chronic or progressive conditions that impact cognitive function can lead to an increased risk of aspiration (Jo et al., 2017; Rösler et al., 2015).  Individuals who are frail and also have dysphagia, have a higher likelihood of pulmonary events when aspiration occurs (Bock et al., 2017). Further, individuals who are frail will have more difficulty increasing muscle mass if they are experiencing protein calorie malnutrition. 

The pulmonary health of an individual is particularly critical, as those with pulmonary disease or current smoking status are at an increased risk for an adverse event given the compromised pulmonary defenses (Bock et al., 2017; Langmore et al., 1998, 2002). Additionally, GI diseases, such as extra-esophageal reflux, can increase the odds of adverse events (Bock et al., 2017) as aspiration of acid laden contents increase the odds of pneumonitis, adult-onset asthma, or pulmonary fibrosis (Marik, 2001, 2010).   If aspiration pneumonia does occur and the system is compromised by disease or through iatrogenic causes, the immune response may be suboptimal. 

Case Study 

Application of the BOLUS framework supports clinical management by aiding in clear identification of risk factors that may lead to an adverse event and strengths that may reduce risk.Once risk factors and strengths are identified, the clinician can focus on reducing risk by identifying modifiable factors and educating the patient and caregivers as to the modifiable risk factors and strengths that should maintained if possible.  Treatment may be geared towards improving functions so risk factors are reduced. 

Consider an individual (referred to here as PD) with COPD who does not require supplemental oxygen and presents to your local hospital with nausea, vomiting, and diarrhea. Nursing staff observes that the patient coughs during oral intake. Speech-language pathology is consulted. Upon clinical examination, the patient’s wife reported that PD has been coughing during meals for at least a year. Videofluoroscopy revealed incomplete laryngeal vestibule closure during the swallow with no oropharyngeal residue after the swallow. PD had a Penetration-Aspiration Score (PAS) of 7 with thin and mildly thick liquids during the swallow. Aspiration was refractory to compensatory measures. PD is dentate and has excellent oral care; he was ambulatory without assistance prior to admission. There is no iatrogenic disease. Medical history is significant for hypertension and hyperlipidemia. Peak flow rate is at 310 L/min. 

Given the level of aspiration combined with the pulmonary disease, the dysphagia clinician considers the risk associated with oral intake. At first glance, one might suspect that this patient would be at increased odds for sequelae secondary to dysphagia. However, guided by the BOLUS framework, the clinician also notes that dysphagia is chronic without previous history of an adverse event, the patient is not aspirating solids, has no oxygen needs, has good oral care, adequate mobility (pre hospitalization) and adequate peak flow.   

Once risks and strengths have been identified, one considers modifiable factors. Given that PD’s peak flow rate exceeds 300 L/min, which is linked to a decreased likelihood of pneumonia (Bianchi et al., 2012), recommendations include continuation of oral alimentation while avoiding intake of acidic and viscous liquids to minimize the caustic effects associated with aspirating a bolus of increased density and lower pH (higher acidity). PD should maintain his excellent oral hygiene and increase oral care from twice to three times daily to further decrease oropharyngeal bacterial burden. Ongoing speech-language pathology care can aim to restore swallow function and address physiological alterations that result in airway invasion.  Sensory motor training for airway protection may be timed to occur after mealtimes to assist with not only cough function, but pulmonary clearance. Frequency of oral care can be monitored by nursing staff. Laboratory values, temperature and chest imaging should be monitored to detect signs of an adverse event.  Medical nutrition can be consulted for dietary optimization given hospital acquired weakness. Further, consultations from OT and PT may provide benefits by increasing PD’s mobility which is limited as an inpatient. Upon discharge, it is recommended that PD follow up in the outpatient speech pathology clinic.

In this hypothetical scenario, adopting a holistic approach enabled PD to avoid a nil per os status,and placement of a feeding tube. Focusing solely on aspiration for clinical decisions risks iatrogenic consequences such as oropharyngeal muscle weakening and reduced quality of life.   Educating PD and caregivers on risk factors and strengths facilitates informed decision-making post discharge.  By targeting modifiable factors, engaging the medical team, and multiple consultative services, PD avoided a nosocomial infection, and the modifications and interventions that were implemented were chosen  through patient centered shared decision making. 

Co-author Biography:

Aaron Padilla is an acute care speech pathologist with Presbyterian Healthcare Services at Rust Medical Center in Rio Rancho, New Mexico. He is a board certified specialist in swallowing and swallowing disorders and enjoys bridging the gap between the research lab and clinical world through implementation science. He has been a member of the Swallow Disorders Research Lab in collaboration with Dr. Palmer, at the University of New Mexico since 2012.  During this time projects have included: cultural considerations, swallow diagnostics and the development and implementation of the BOLUS framework, a multifaceted tool to assist in clinical decision making.

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