pneumonia aspirasi

12 JMAJ, January 2003—Vol. 46, No. 1

Introduction

Progressive aging of the society poses theproblems of susceptibility of a significant sec-tion of the population to infections associatedwith age-related multiorgan dysfunction, andof dealing with the seriousness and refracto-riness of the infections complicating variousunderlying diseases in this subject population.

This article is a revised English version of a paper originally published inthe Journal of the Japan Medical Association (Vol. 125, No. 7, 2001, pages 1018–1022).

Aspiration becomes clinically evident whenthe patient chokes or has a fit of coughing dur-ing a meal. In contrast, a less obvious form ofaspiration, which may sometimes be associatedwith mild coughing but is more often largelyasymptomatic, is called micro-aspiration. Whenfood or drink, saliva containing oral flora, orregurgitated gastric acid is aspirated into theairway, severe inflammation of the lower respi-

Aspiration and Aspiration PneumoniaJMAJ 46(1): 12–18, 2003

Tsuyoshi NAGATAKE

Professor, Department of Internal Medicine,Institute of Tropical Medicine, Nagasaki University

Abstract: It is not rare for aspiration to occur in association with a severe parox-ysm of coughing in elderly people. In such cases, a depressed cough reflex mayresult in severe aspiration pneumonia. Aspiration becomes clinically evident whenthe patient chokes or has a fit of coughing during a meal. In contrast, a less obviousform of aspiration, which is almost asymptomatic, is called micro-aspiration. Whenfood or drink, saliva containing oral microbial flora, or regurgitated gastric acid isaspirated into the airway, severe inflammation of the lower respiratory tract andlung parenchyma occurs. Since aspiration can cause pneumonia and seriousairway damage, the prevention of aspiration is important, particularly in elderlypeople. Pathogenic microorganisms are more likely to colonize the oral cavity inpatients with swallowing disorders. Thus, when patients with swallowing disordersare admitted to a hospital, they are at a higher risk of encountering nosocomialpathogens, i.e., multidrug-resistant bacteria. Therefore, protection against aspi-ration and prevention of lower respiratory tract infection by ensuring good oralhygiene may be the most practical and effective means for the prevention ofpneumonia in the elderly.

Key words: Aspiration pneumonia; Hospital-acquired pneumonia;Depressed cough reflex; Anaerobic infections

�Medical Care for the Elderly

JMAJ, January 2003—Vol. 46, No. 1 13

ratory mucosa occurs, often complicated bypneumonia. Although aspiration by itself is oneof the most important risk factors for pneu-monia, the situation is obviously more seriouswhen nosocomial multidrug-resistant patho-gens, which cause hospital-acquired pneumo-nia, are contained in the aspirate.

Intensive effort to protect against aspirationand encourage maintenance of good oralhygiene in elderly patients could be expectedto result in a reduction in the incidence ofnosocomial pneumonia. How thoroughly canwe take these preventive measures in the clini-cal setting in Japan? In this study, we attempt todiscuss the clinical presentations of aspirationpneumonia and the measures adopted in Japanto prevent this condition, from the prevailingclinical setting.

Lower Respiratory Tract InfectionCaused by Pathogenic BacteriaOriginating from the UpperRespiratory Tract

1. Decreased swallowing ability increasesthe risk of colonization of the upperrespiratory tract by pathogenic bacteria

Cough is an important clinical manifestationof pneumonia. The cough reflex is, however,often compromised in elderly individuals. Wepreviously examined whether colonization ofthe upper respiratory tract by pathogenic micro-organisms is more frequently associated withthe onset of lower respiratory tract infection inbedridden patients in geriatric hospitals.1–5)

The results indicated that the frequencyof pharyngeal colonization by Staphylococcus

Table 1 Risk Factors for Nosocomial Respiratory Tract Infections3)

Parenteral alimentation Oral alimentationP-valuegroup (n�26)* group (n�54)

Gram-negative bacilliRate of colonization of the upper respiratory tract(number of specimens with positive results/the number 61% (106/175) 3.6% (4/111) 0.001of specimens tested)Number of episodes of respiratory infections 31 (average, 1.2) 1 (average, 0.02) 0.001

MRSARate of colonization of the upper respiratory tract(number of specimens with positive results/the number 47% (83/175) 5.4% (6/111) 0.001of specimens tested)Number of episodes of respiratory infections 17 (average, 0.64) 3 (average, 0.06) 0.001

Total number of episodes of respiratory infections/month 1.5 0.2 0.001

Injectable penicillin 7.2 0.86 0.001Second-generation cephalosporins 8.9 0.44 0.001

Doses of antimicrobials Third-generation cephalosporins 9.1 0.37 0.001(g/month) Other �-lactams 3.2 0.08 0.001

Minomycin® 0.16 0.01 0.02Aminoglycosides 0.13 0.002 0.01

Hemoglobin (g/dl) 8.6 11.8 0.01Serum total protein (g/dl) 5.9 6.5 0.02

Presence of decubitus ulcers 25 (96%) 5 (9%) 0.001

* including 4 patients with tracheostomy.Note: Preliminary testing revealed that the MRSA and Gram-negative bacilli colonization rates of the upper respiratory tract

were higher in the parenteral alimentation group than in the oral alimentation group, and that the use of antimicrobialswas more frequent in the former.

(This survey was conducted from February 1991 to September 1991 in a geriatric hospital)

ASPIRATION PNEUMONIA


almost nil in adults and the elderly, except inthose who frequently came in contact with chil-dren (mothers, school staff, etc.). On the otherhand, the frequency of pharyngeal colonizationby pathogenic organisms was about one andhalf to two times higher in children belongingto the acute upper respiratory tract inflam-mation group than in the children assigned tothe healthy group. Pharyngeal colonization bypathogenic organisms, although at a low per-centage, was also confirmed in adults and olderadults assigned to the acute upper respiratorytract inflammation group.

These findings indicate that in healthy adults,systemic and local immune mechanisms mightprevent colonization of the pharynx by patho-genic organisms with the help of the barrierestablished by the resident microbial flora onthe surface of the pharyngeal membrane. How-ever, when the defense of the membrane isweakened by viral infection, pathogenic organ-isms can easily establish themselves on the air-way membrane and cause lower respiratorytract infection and pneumonia, especially in theimmunocompromised elderly.6)

3. Destruction of the barrier of indigenousmicrobial flora on the pharyngolaryngealmucosal epithelium by pathogenicorganisms

Indigenous microbial flora is believed toblock adhesion of pathogenic organisms tothe pharyngolaryngeal mucosal epithelium inhealthy adults. Adhesion factors and receptorsare known to be closely linked to the adhesionof bacteria to the host epithelium; the under-lying molecular processes, however, remain tobe elucidated in detail.

We previously clarified that the adhesion fac-tors of Haemophilus influenzae and Moraxella(Branhamella) catarrhalis are sugar chains, andthat several drugs effectively prevent thesepathogenic bacteria from adhering to themucosa of the respiratory tract. Easy adhesionof pathogenic bacteria to the pharyngeal epi-thelium may increase the risk of lower respira-

aureus strains, particularly methicillin-resistantStaphylococcus aureus (MRSA) and Gram-negative bacilli, was significantly higher inpatients on parenteral alimentation than inthose on oral alimentation. Furthermore, theincidence of lower respiratory tract infectioncaused by MRSA and Gram-negative bacilliwas also higher in the parenteral alimentationgroup than in the oral alimentation group(Table 1). Both the frequency of MRSA coloni-zation of the pharynx and the incidence oflower respiratory tract infection were about 10times higher in the parenteral alimentationgroup than in the oral alimentation group.

These findings indicate that pathogenic bac-teria are more liable to persist and grow in theoral cavity of patients with depressed swallow-ing function. It is also indicated that normaldeglutition and salivary secretion may facilitatethe smooth swallowing of saliva as well as foodand drink, and act as self-cleansing mecha-nisms of the oral cavity.

2. Pharyngeal colonization by pathogenicbacteria following viral infection(common cold syndrome)

In another study, we investigated the coloni-zation of the pharynx by pathogenic organismsin healthy subjects, from children to the elderly.Healthy subjects were defined as people whohad rarely consulted a physician, except forcommon cold, and in the case of adults andthe elderly, also those who had no underlyingdisease that might predispose to infection, suchas diabetes mellitus or chronic respiratorydisease. The subjects were classified into twogroups: those presenting with the common coldsyndrome, including pharyngolaryngeal painand running nose, within the week prior tocommencement of the study (the acute respira-tory tract inflammation group), and those with-out any symptoms of common cold during thecorresponding period (the healthy group).

In the healthy group, the frequency of pha-ryngeal colonization by pathogenic bacteriawas substantially higher in children and was

T. NAGATAKE


tory tract infection. Thus, proper gargling isuseful in the prevention of adhesion of patho-genic bacteria to the upper respiratory tract.The aforementioned drugs can also be used todecrease the frequency of episodes of lowerrespiratory tract infections.7)

On the other hand, various types of non-pathogenic bacteria adhere to and grow onthe surface membrane of the upper respiratorytract in healthy adults. The barrier formed bythe non-pathogenic microbial flora inhibits theadhesion of pathogenic organisms to the sur-face membrane of the respiratory tract. Thesenon-pathogenic bacteria strongly adhere to themembrane of the respiratory tract and theirrate of proliferation is much higher than thatof pathogenic bacteria.

Accordingly, destruction of the barrierformed by the resident microbial flora wouldbe expected to increase the chances of patho-genic bacteria adhering to the airway mem-brane. Damage to the membrane of the respi-ratory tract by orotracheal and nasotrachealcatheters, and decreased or increased oropha-ryngeal secretions related to advanced age orunderlying disease, may directly or indirectlyinduce the adhesion of pathogenic bacteria tothe surface membrane of the respiratory tract.

Mechanisms by which AspirationCauses Severe Pneumonia

Aspiration pneumonia is often a progressiveor refractory disease. The following factors maybe involved.1. Aspirated saliva, gastric acid, and food

debris injure the airway membrane anddamage the mucociliary clearance system.

2. Microorganisms originating in the oralmicrobial flora can easily invade the lowerrespiratory tract and grow there.

3. Although aspiration induces infections byvarious types of pathogens, if the initial anti-biotic treatment is inappropriate, multidrug-resistant bacteria, anaerobes, and fungi sur-vive and exert pathogenicity.

4. Aspiration of regurgitated gastric acid,because of its strong acidity, frequentlycauses severe chemical pneumonitis.

5. Repeated aspiration, whether it is micro-aspiration, or a frank large-volume incidentduring a meal (macro-aspiration), causesinflammation that is often prolonged andrefractory.

The lung segments involved greatly dependon the posture of the patient during the aspira-tion, and most often include the dorsal seg-ments bilaterally. Extensive lobar pneumonia,pulmonary abscess, and pleural empyema mayoccur in severe cases. Airway obstruction byfood debris or other materials in combinationwith aspiration pneumonia may manifest asatelectasis and obstructive pneumonitis, witha poor prognosis.

The following factors may influence theseverity of aspiration pneumonia:1. The number of episodes of aspiration. The

more frequent the aspiration, the moresevere the complications.

2. The degree of airway obstruction by the aspi-rated material and the amount of airway-injurious substances contained in the aspi-rate, such as gastric acid.

3. Aspiration of massive amounts of indige-nous microbial flora alone, or of a mixtureof pathogenic organisms, is associated withincreased severity of complications.

4. Failure of initial therapy, including drain-age procedures or the antibacterial chemo-therapy, is associated with refractorycomplications.

Key Points in the Treatment ofAspiration Pneumonia

The first step in the treatment of aspirationpneumonia is proper respiratory care and pre-vention of respiratory failure. Food debris andother materials that may cause airway obstruc-tion should be removed through transbronchialsuctioning or other appropriate methods at theearliest. After securing the airway, proper oxy-



genation (proper intervention, varying fromnasotracheal intubation to mechanical ventila-tion, may be required, depending on the sever-ity of the disease) should be ensured in patientswith respiratory failure or hypoxia. In regardto antibiotic treatment, a broad-spectrum anti-microbial agent (�-lactam as the first choice)should first be administered intravenously.

The selection of antibiotics should be basedon a consideration of the following points:1) broad spectrum of activity (preferably cover-ing both Gram-positive cocci and Gram-negativebacilli), 2) stability against �-lactamase, 3) aware-ness of the fact that more and more strainsof bacteria are acquiring resistance that doesnot depend on the production of �-lactamases(e.g., alteration of penicillin-binding protein),4) the extent of drug penetration into airwayfoci (confirmed by the sputum levels of thedrug), and 5) the severity of adverse effects.In patients with severe airway damage causedby gastric acid or other injurious substances,however, the medication administered shouldalso provide coverage for less virulent specieswithin the hospital environment, includingGram-negative bacteria such as Pseudomonasaeruginosa, Serratia, Citrobacter, enterococci,Staphylococcus aureus, and Staphylococcusepidermidis.

Before the commencement of therapy witha �-lactam antibiotic in elderly patients, it isessential to check the renal and liver functions.In principle, the drug dose should be decreasedto 1/2 to 1/3 in the elderly, while ensuring thattherapeutic concentrations are achieved at thefoci of damage.

The efficacy of the initial treatment shouldbe determined on the 3rd day of treatment. Ifneither clinical nor radiographic improvementis noted, the medication should be modifiedbased on a consideration of the following:1) If no improvement in oxygenation is

observed, it must be ascertained that theairway is patent; the necessity of thoroughdrainage should also be considered.

2) When the disease has advanced to the stage

of lung abscess or pleural empyema, theinvolvement of tissue-invasive bacteria,such as Staphylococcus aureus and Strepto-coccus pneumoniae, or anaerobes should besuspected. In the case of anaerobic infec-tion, combined therapy with clindamycin iswidely adopted.

It should be noted that if proper specimencollection, be it sputum or bronchial aspirate,has been ensured, and the causative bacteriahave been appropriately identified, the drug ofsecond choice will be self-evident even if theinitial therapy has failed.

Most elderly patients with aspiration pneu-monia have underlying cerebrovascular dis-ease. Therefore, as described in the section onthe mechanism of development of aspirationpneumonia, measures to prevent reinfectionand superinfection should be adopted in con-cert with antimicrobial chemotherapy.

Measures to Prevent AspirationPneumonia

It is known that a depressed deglutitionreflex or cough reflex often predisposes elderlyindividuals to aspiration, including micro-aspiration. Sasaki et al. reported that damageof the cerebral cortex by cerebrovasculardisease impairs the synthesis of substance P,which is distributed to the pharynx and airwaythrough sensory nerves, associated with sup-pression of the deglutition and cough reflexes.They indicated that Symmetrel® (amantadinehydrochloride), an antiparkinsonian drug thatstimulates the synthesis of substance P, as wellas ACE inhibitors, which inhibit neutral endo-peptidase known to be involved in the degrada-tion of substance P, are helpful in reducing thefrequency of aspiration.8,9)

We previously reported that measures forthe prevention of nosocomial infections focus-ing on a thorough cleaning of the oral/nasalcavity with povidone iodine in patients dra-matically decreased the incidence of hospital-acquired pneumonia caused by MRSA and

T. NAGATAKE


Gram-negative rods in a geriatric hospital(Fig. 1).10) Sasaki and associates also empha-sized the importance of good oral hygiene inthe prevention of aspiration pneumonia in eld-erly patients.11)

The method of feeding may need to bemodified in patients with normal appetite whohave repeated episodes of aspiration. It isimportant to balance the patient’s nutritionalstatus and the measures needed to reduce therisks of aspiration and infection. Gastrostomyhas been considered as an alternative for theprevention of aspiration in several institutions.

The use of intravenous hyperalimentation(IVH) immediately after aspiration may some-times be unavoidable for the prevention of theonset of aspiration pneumonia, since the clini-cal course of aspiration pneumonia is moreprolonged than that of other bacterial pneumo-nias. Thus, a patient care program that incorpo-rates preventive measures against aspiration asan integral part of the management should beimplemented in elderly patients in both institu-tional care and home care.

Conclusion

Aspiration pneumonia occurs mainly in eld-

P.aeruginosa�Others

MRSA�Others

MRSA�P.aeruginosa

P.aeruginosa

MSSA

MRSA

90

80

70

60

50

40

30

20

10

0Before the

implementationof preventive

measures91.1�91.12

One year after theimplementationof preventive

measures92.4�93.3

2 years after theimplementationof preventive

measures93.4�94.3

(Number of episodes of infections)

Fig. 1 The usefulness of measures adopted to prevent nosocomial pneumonia10)

erly people, particularly in those with underly-ing disease, such as cerebrovascular disease.Although the case-fatality rate is very high,patient care embracing preventive measuresagainst aspiration can reduce the risk of pro-tracted and refractory disease.

REFERENCES

1) Nagatake, T., et al.: Study of causative bacteriaof bacterial pneumonia and decubitus infec-tions in a geriatric hospital (the first report)—MRSA as nosocomial pathogen. Chemotherapy1986; 34: 240–249. (in Japanese)

2) Matsumoto, K. and Takahashi, J.: I. Biology(epidemiology) of MRSA. 5. The present sta-tus of MRSA infections. Nihon Naika GakkaiZasshi 1992; 81: 1609–1614. (in Japanese)

3) Rikitomi, N.: IV. Management of patients withserious condition for the prevention of noso-comial infections 1. In the case of tracheotomy(endotracheal intubation). Nihon Naika Gak-kai Zasshi 1993; 82: 1215–1220. (in Japanese)

4) Sakamoto, A.: MRSA respiratory infectionand the usefulness of the preventive measuresin hospital environments of a geriatric hospitalfocusing on the mechanism of the onset of thedisease and changes in pathogens over timebased on the types of coagulase after carefulselection of antimicrobial chemotherapeutic



agents. Chemotherapy 1993; 41: 239–249. (inJapanese)

5) Masaki, H. et al.: Decrease in the incidenceof bacteremia and nosocomial pneumonia andchanges in causative organisms in a geriatrichospital after the implementation of measuresto prevent nosocomial infections. Kansen-shogaku Zasshi 1995; 69(4): 390–397. (inJapanese)

6) Nagatake, T. et al.: The involvement of virusesand bacteria in respiratory infection. NihonNaika Gakkai Zasshi 1997; 86: 491–495. (inJapanese)

7) Nagatake, T. and Nakayama, T.: Preventionof infections 1. Pharyngeal sterilization. Anti-biotics & Chemotherapy. 1991; 7: 90–98. (inJapanese)

8) Sekizawa, K. et al.: Lack of cough reflex inaspiration pneumonia. Lancet 1990; 335:1228–1229.

9) Nakagawa, T. et al.: High incidence of pneu-monia in the elderly patients with basal gan-glia infarction. Arch Intern Med 1997; 157:321–324.

10) Nagatake, T. et al.: Fundamentals and clinicalpractice for the prevention of nosocomialinfections focusing on the minimization ofthe incidence of respiratory infection in eld-erly patients. Nihon Saikingaku Zasshi 1996;51(3): 871–876. (in Japanese)

11) Itabashi, S. and Sasaki, H.: Features of pneu-monia in elderly patients and signs to causecaution. Rinsho To Kenkyu 2000; 77: 6–10. (inJapanese)

T. NAGATAKE

pneumonia aspirasi

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