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Overview of Pneumonia




Pneumonia is a fatal infection that inpatients are the most likely to contract.



悪性腫瘍  malignancy;

胃食道逆流  gastroesophageal reflux;

咽頭反射  gag reflex;

インフルエンザ菌 ... 髄膜炎や肺炎などを起こすグラム陰性桿菌の一種  Haemophilus influenza;

下気道  ... 呼吸器系のうち, 喉頭よりも肺側の気道; 喉頭から気管・気管支・細気管支・肺胞に至る部分  lower respiratory tract;

喀出する  expectorate;

感覚異常  dysesthesia;

感染の  infective;

鑑別診断  differential diagnosis;

胸部X線撮影  chest radiograph;

結核  tuberculosis;

嫌気性の  anaerobic;

嫌気性肺感染  anaerobic lung infection;

顕著な誤嚥  gross aspiration;

口腔咽頭  oropharynx;

好中球  neutrophil;

誤嚥  aspiration;

呼吸器合胞体ウイルス  ... 成人には軽度の呼吸器感染症を起こすだけだが, 子供(特に幼児)には気管支肺炎や細気管支炎の原因となる  respiratory syncytial virus (RSV);

呼吸困難  dyspnea;

錯乱  confusion;

市中感染性肺炎  community-acquired pneumonia;

触覚振盪音 ... 患者に発声させた場合に胸郭に触知できる振動  tactile fremitus;

神経疾患  neurologic disease;

心不全  heart failure;

水泡音  rale;

咳反射 ... 気道壁の刺激が迷走神経によって延髄に伝達されて起きる反射。気道の分泌物や異物を排出する  cough reflex;

繊毛  cilia;

爪床  nail bed;

大気管支  large bronchus;

代謝疾患  metabolic disease;

多糖類のカプセル  polysaccharide capsule;

痰  sputum;

チアノーゼ ... 血液の酸素化の不足によって皮膚などが暗紫色になる状態  cyanosis;

超音波撮影  ultrasound imaging;

入院患者  inpatient;

粘液繊毛エスカレーター  mucociliary escalator;

膿瘍  abscess;

肺炎連鎖球菌  Streptococcus pneumoniae;

肺実質  lung parenchyma;

肺胞  alveolus;

白血球数の測定  leukocyte count;

微小誤嚥  microaspiration;

微生物  microorganism;

飛沫  droplet;

副流煙  secondhand smoke;

マクロファージ  macrophage;

慢性閉塞性肺疾患  chronic obstructive pulmonary disease (COPD);

免疫オプソニン ... 細胞や粒状の抗原に結合して, それらが食作用をうけやすくする  immune opsonin;

モラクセラ・カタラーリス ... ヒト鼻咽頭の常在菌; まれに中耳炎や気道感染の原因  Moraxella catarrhalis;

ラ音  crackle;

レジオネラ属  Legionella species;



Not only cigarette smoke that smokers directly inhale, but secondhand smoke that bystanders indirectly inhale affects macrophage function and ciliary function.



credit:  Cigarette smoke, Nativemothering



Alcohol and drugs likely deteriorate the cough reflex and thereby prevent unnecessary debris from being removed from the respiratory tract.



Some drugs administered during and after surgery may cause aspiration and damage the cough reflex.



If a patient who has fever, cough, chest pain, shortness of breath, and increased respirations, he or she is likely to have contracted pneumonia.



Sputum may be streaked with pus or blood.  In severe pneumonia, patients may have signs of oxygen deprivation called cyanosis in which the nail beds or lips become blue. 


Category of Pneumonias



Pneumonias are largely categorized as those of infections of the lung parenchyma and those of infections limited to the trachea.  In addition, they are categorized as those acquired in the community and those that occur in institutional settings.  These pneumonias are composed of hospital-acquired pneumonia, ventilator-associated pneumonia, and nursing facility–associated pneumonia.



Aspiration of oropharyngeal contents also predisposes to pneumonia.



Community-Acquired Pneumonia



It is important to know whether the patient has predisposed to hospital-acquired pneumonia, ventilator-associated pneumonia, or nursing facility–associated pneumonia so as to identify most possible infectious agents and administer appropriate medications to him or her.





Pneumonia is a leading cause of death in advanced countries including Japan and is the most common fatal infectious disease.






Aspiration of Oropharyngeal Contents



The most common cause of infection of the lung with pathogenic organisms is aspiration of oropharyngeal contents.  Aspiration sometimes occurs in healthy persons while they are sleeping. 



Pathogenic organisms, such as Streptococcus pneumoniae, are colonized in the oral pharynx.  Sufficient quantities of organisms are delivered to the lung.  As a result, the lung is infected with the organisms. 



In contrast, gross aspiration occur in persons with dysesthesia, depressed level of consciousness, abnormalities in gag reflexes, or remarkable gastroesophageal reflux.



Since gross aspiration delivers many anaerobic bacteria to the lower respiratory tract, it becomes main causes of anaerobic lung infection and abscess formation.


Inhalation of Aerosol Droplets



The second most common cause of lung infection is the inhalation of suspended aerosol droplets as small as 0.5 to 1 µm containing microorganisms.



Mucociliary Escalator



When large infected droplets reach the airways, they are removed by the mucociliary escalator.  It clears entrapped droplets and carries them to the oropharynx so that they are swallowed or expectorated.



Although particles as small as 0.5 to 2.0 µm are deposited in the alveoli, microorganisms in the particles are phagocytized and destroyed by macrophages.



These macrophages also releases special proteins that are contributed to collect neutrophils from the blood stream to the alveolar spaces where they uptake and kill microorganisms.



Many infective microorganisms are cleared by the development of specific immunoglobulins as antibodies so that they bind the surface of the organisms or their polysaccharide capsule.


These specific antibodies serve as immune opsonins that greatly enhance the ability of neutrophils and macrophages to phagocytize and kill the microorganisms.



Only when microorganisms defeat or avoid these defense systems, clinically significant pneumonia occurs in the lung.



Manifestations of Pneumonia



If the patient who has respiratory symptoms such as cough, sputum, or dyspnea accompanied by fever or discontinuous lung sounds such as rales heard on physical examination of the chest, he or she is likely to have contracted pneumonia.



In aged patients and those with immunological diseases, since the initial manifestation of pneumonia is often subtle, they are likely to have nonspecific symptoms such as loss of appetite, confusion, dehydration, worsening of symptoms or signs of other chronic diseases.


Pneumonia is strongly associated with specific comorbid conditions and diseases of patients.  If they have smoking habits, chronic obstructive pulmonary disease, diabetes, malignancy, heart failure, neurologic diseases, narcotic and alcohol use, and chronic liver disease, they are likely to predispose to pneumonia.



Since the initial symptoms and signs of the patients with pneumonia are often variable, they cannot be reliably used to conduct a differential diagnosis.



In patients with lobar pneumonia, their classical physical findings include consolidation of lobar tissue, altered breath sounds, crackles, and changed tactile fremitus.



However, in many patients, the physical findings were subtler rhonchi.



When the patient is suspected to contact pneumonia, complete physical examination, chest radiographs,  (or ultrasound imaging), and a blood leukocyte count should be performed.





Even if a thorough laboratory examination is performed for the patient with pneumonia, the specific microbiologic cause can be found only in about 50% likelihood.



The probable microorganism may vary with the patient's epidemiologic factors, the severity of pneumonia, and diagnostic laboratory testing.



Bacterial Pneumonia



Lifestyle of patients may affect the risk of infection with specific microorganisms.



For instance, persons having smoking habit and patients with chronic obstructive pulmonary disease are at high risk of invasive Streptococcus pneumoniae, as well as Haemophilus influenzae, Moraxella catarrhalis, and Legionella species.  Persons having alcohol drinking habit are at increased risk for drug-resistant Streptococcus pneumoniae, anaerobic lung infection, and tuberculosis.


Viral Pneumonia



Although bacteria cause severe pneumonia, viruses can also cause serious lower respiratory tract infections.


Respiratory viruses that can cause severe pneumonia include various types of influenza viruses and respiratory syncytial virus.



Various types of influenza virus and respiratory syncytial virus can be isolated from respiratory secretions.



Influenza infections are responsible for respiratory-and circulatory-related deaths predominantly in elderly patients and those with cardiopulmonary or metabolic disease.