CARTOGRAFÍA DEL RIESGO

The previous chapter gave an overview of the normal parameters of swallowing in the younger and older population. It reports that penetration and aspiration of oral intake (food, drink and saliva loaded with oral flora) does not, in the healthy individual, lead to pneumonia, owing to the characteristics of the bolus that is aspirated and the host clearing systems.

Consideration is given in this chapter to the circumstances where aspiration, defined as material entering the airway below the level of the vocal folds (Logemann et al., 1999), may precipitate infection, deterioration in chest status, and pneumonia. The

relationship between aspiration, as determined by videofluoroscopy, and the

development of pneumonia has been reported elsewhere in different client groups i.e. patients with head and neck cancer (Eisbruch et al., 2002). This chapter details the routes for development of aspiration pneumonia; the risk factors and the requisite features that predispose individuals to develop pneumonia as a consequence of aspiration; the effects and potential consequences of aspiration in stroke patients; individual clinical determinants of aspiration, and how these could be the focus of any future swallow screening tool.

3.1 Route for the development of aspiration pneumonia

Aspiration of refluxed gastric secretions may result in pneumonitis, the clinical presentation of which, may be confused with aspiration pneumonia resulting from aspiration of anaerobic bacteria, (found in oropharyngeal flora) in an individual that is susceptible to aspiration (Bartlett et al., 2010).

Refluxed gastric secretions and contents (pH<2.5) may be aspirated and burn the lung membrane. These gastric secretions carry with them anaerobic flora from the gut. The lung defence system is unable to clear volumes of aspirate exceeding 0.3 ml/kg of body weight, typically 20-25 ml in adults (Varkey, 2006), causing inflammation of gravity-dependent lung tissue (Huxley et al., 1978; O‟Connor, 2003) and subsequent chemical pneumonitis. Pneumonia arising from aspirated reflux may be the cause of

treatment. Whereas aspiration pneumonia, as a result of repeatedly aspirated material from the oropharynx, requires ongoing identification and management.

The previous chapter reports that oral intake and oropharyngeal flora is present and may be aspirated in a healthy population without consequence. However, this chapter portends that in certain circumstances, or with a combination of requisite conditions, aspiration of material and oropharyngeal flora may precipitate aspiration pneumonia.

The majority of anaerobes are unable to survive or grow in the presence of oxygen (Cruickshank, 1970); hence it is aerobic bacteria that are usually associated with respiratory infection. To cause infection, bacteria need to either possess specialist mechanisms that enable them to attach to epithelial cells, or to grow only when there is a reduction in host immune defences. Aerobic gram-negative bacilli (AGNB) are the most frequently isolated microorganism considered to be the cause of aspiration pneumonia (Marik, 2001). Therefore aspiration of aerobic flora originating in the oropharyngeal secretions in compromised patients may result in bacterial pneumonia (Shay, 2002).

3.2 Risk factors for aspiration pneumonia in stroke

Aspiration alone, as identified in the previous chapter, is not sufficient to cause

aspiration pneumonia in the absence of one or more predisposing risk factors. Several factors that increase the risk of patients acquiring aspiration pneumonia have been identified in the literature and are presented below.

Bolus characteristics

The risk of developing aspiration pneumonia is determined by bolus characteristics; quantity, acidity, consistency and the infective bacterial state of the bolus aspirated (Varkey, 2006).

Host defence systems

The risk of developing aspiration pneumonia is compounded if the patient‟s immune status is compromised (Johnson and Hirsch, 2003) particularly if the patient‟s respiratory clearing system is impaired (Kikawada et al., 2005). In the healthy population, aspiration is cleared by mucociliary and by macrophage action (Mims, 1979). If the individual has a poor or compromised defensive clearing system, the aspirated bolus is not removed and the individual becomes susceptible to pneumonia. Indeed the most severe clinical symptoms of aspiration pneumonia are usually seen in

those individuals with chronic illness and those who are immuno-compromised (Shay, 2002).

Poor oral hygiene

The oro-pharyngeal mucosa in healthy individuals is not receptive to pathogenic aerobic gram-negative bacteria (AGNB) (Mobbs et al., 1999). AGNB are subsequently cleared within three hours of colonisation (LaForce et al., 1976). Patients with

increased dependency for oral care (Brady et al., 2007) and tooth decay are at increased risk of aspiration pneumonia (Burke, 2010). Poor dental hygiene and periodontal disease exacerbates the colonisation of potentially pathogenic respiratory tract bacteria in the dental plaque and gingival crevices (Marik, 2001; Shay, 2002; Johnson and Hirsch, 2003; Azarpazhooh and Leake, 2006) which increases the risk of aspiration pneumonia in immuno-compromised individuals (Kikawada et al., 2005). Furthermore, there is evidence of increased colonisation of bacteria in the oral cavity in hospitalised acute stroke patients (Millns et al., 2003). A systematic approach to

improving oral hygiene in patients resident in nursing homes has been shown to reduce the rate of pneumonia (Yoneyama et al., 2002). A reduction in oro-pharyngeal bacteria in patients with a high rate of aspiration has been affected by daily oral hygiene, and regular dental care has been shown to be a cost-effective means of reducing morbidity (Tran and Mannen, 2009). Aspiration of oro-pharyngeal bacteria is thus a common cause of morbidity.

Dependency

Dependency for oral care (Scannapieco et al., 1992; Brady et al., 2007) and feeding (Brady et al., 2007), have been identified as predictors for the development of aspiration pneumonia (Langmore et al., 1998).

Reflux

Reflux and subsequent aspiration of gastric contents and oro-pharyngeal flora may be exacerbated by the presence of naso-gastric tubes and bridles (Marik and Kaplan, 2003). Impairment of the upper aerodigestive tract by naso-gastric tubes promotes pathogenic colonisation of the oro-pharynx (Li et al., 2000), as naso-tubes can become dislodged (Johnson and Hirsch, 2003) and can further compromise the integrity of the lower oesophageal sphincter, promoting reflux of gastric contents (Ferrer at al., 1999). Reflux and subsequent aspiration of mixed aerobic-anaerobic bacteria may give rise to aspiration pneumonia in the elderly hospitalised patient (Bartlett, 1993).

Neurological damage

Confounding factors that increase the risk for aspiration are neurological damage (Langmore et al., 1998; Nakagawa et al., 2000; Marik and Kaplan, 2003; Burke, 2010) and subsequent reduced consciousness (Johnson and Hirsch, 2003; Bartlett, 2010) which in turn can lead to an impaired cough reflex and reduced breathing and swallow co-ordination. Impairment of dopamine metabolism as a result of a basal ganglia stroke affects both the glossopharyngeal and vagus nerves thereby impairing the cough reflex (Kikawada et al., 2005) and so the inability to remove penetrated bolus from the larynx. Stress responses to neurological damage may also reduce the production of saliva and increase the numbers of bacteria in the mouth (Burke, 2010) which may then be

aspirated onto the lungs.

Medication

Elderly patients in the acute hospital setting are more frequently treated with antacids, histamine blockers and/or proton pump inhibitors. These drugs result in a reduction in the pH of the gastric acid, a subsequent increase in the bacterial load in the stomach, and could subsequently be aspirated onto the lungs in the event of reflux (Bartlett, 2010). Enteral feeds, common in patients with stroke, may encourage colonisation of the oro-pharynx with gram-negative bacteria and Staphylococcus aureus (Langmore et al., 1998). Sedatives may impair the protective cough reflex (Johnson and Hirsch, 2003) and some medications result in a reduction in saliva production, which may lead to reduced swallowing, poor oral hygiene and an increase in the number of pathogenic bacteria in the oral cavity (Kikawada et al., 2005). During antibiotic treatment, the respiratory pathogens colonise the oral plaque thereby reducing commensal oral flora (Scannapieco et al., 1992); the risk of pneumonia is increased if aspiration occurs.

Aspiration

Acute stroke patients who aspirate are more likely to develop aspiration pneumonia, and are more likely to die (Holas et al., 1991; O‟Connor, 2003; Marik and Kaplan, 2003). Aspiration occurs in approximately 40-50% of stroke patients (Loeb et al., 1999; Marik and Kaplan, 2003) and is associated with impaired cough reflex, reduced

laryngeal and pharyngeal sensation, and subsequent silent aspiration (Kikuchi et al., 1994; Holas et al., 1994; Daniels et al., 1998; Ramsey et al., 2005). Swallowing also facilitates clearance of gram-negative bacteria from the oro-pharynx (Kikawada et al., 2005).The implications for the patient with impaired swallowing function following stroke, and a potential concomitant reduction in sensation and motor function in the pharynx and larynx (Smith et al., 1999), are considerable.

Hospital Setting

Acute stroke patients are a high-risk group for aspiration pneumonia as they present with combinations of concomitant risk factors outlined above. AGNB replace anaerobic oropharyngeal flora (Millns et al., 2003) after seven days (Burke, 2010) in this

population, due to a combination of change in cleaning the oral cavity, altered epithelial surfaces within the mouth, and changes in salivary flow and distribution (Millns et al., 2003).

In summary, aspiration alone is not sufficient to cause pneumonia. Aspiration

pneumonia is multi-factorial, with bolus characteristics and/or an immuno-compromised system requisite to its development.

3.3 Effects of aspiration in stroke

Stroke may disrupt function at every stage of the swallowing process resulting in significant health risks. Stroke may cause uncoordinated or delayed swallowing which may affect a person‟s nutrition and hydration by reducing the amount of food and fluids that can be taken orally, and may precipitate aspiration of food and drinks onto the lungs (Figure 2.2).

Scarring of the lung tissue is a corollary of aspiration pneumonia (Bartlett, 2010). Therefore, repeated infection from undetected and mismanaged chronic aspiration has the potential to cause a deterioration in baseline lung function and respiratory state over time making the person more prone to infection. This is exemplified by the author in Figure 3.1.

time

Figure 3.1: Effect on baseline lung tissue viability of repeated episodes of aspiration Effect of aspiration on respiratory function Lung tissue viability Resolution of infection Final baseline chest status Original

Introducing a simple, diagnostically accurate swallow screening tool may encourage nurses to utilise it in the acute stroke patient thereby preventing the possible

deterioration in viable lung tissue following repeated episodes of aspiration pneumonia.

Not only does scarring of lung tissue occur following repeated episodes of aspiration pneumonia but lung tissue and therefore lung function deteriorates during a single, acute hospital admission, where patients are aspirating a percentage of each bolus from meals or drinks throughout a 24 hour period (Figure 3.2). This reinforces the need for early detection of aspirated food and drink prior to oral intake.

1 – initial aspiration 2 – further bolus aspiration 3 – continued aspirated Figure 3.2: Aspiration events and concomitant effects on lung status

It is acknowledged that the effects on chest status of different aspirated bolus volumes and acidity varies between individuals. However aspiration does, to some extent, affect lung function in all patients, making it imperative that nurses have a bedside screening tool that is able to identify and manage aspiration at the earliest opportunity.

Consequently, aspiration and subsequent infection may compromise a person‟s respiratory status (Holas et al., 1994; Martino et al., 2000; Marik and Kaplan, 2003), nutritional status (Smithard et al., 1996; Leslie et al., 2002), hydration (Gordon et al., 1987; O‟Neill et al., 1992; Watkins et al., 1997; Whelan, 2001) and the ability to take

Episodes/