While this subject is addressed in detail in other chapters, a brief review here is important to fully understand the basis of pulmonary care in the elderly especially following injury. The respiratory system consists of two fundamental elements: (1) a gas exchange mechanism in the lung that leads to inspired oxygen being transferred from the alveolus into the blood and carbon dioxide being transferred in the opposite direction and (2) the pump consisting of the rigid rib cage, respiratory muscles, and the neural mechanisms that govern the act of breathing including the brain stem that responds to levels of oxygen and carbon dioxide in the blood [3]. Both elements of the respiratory system change with age in a manner that reduces reserve and our ability to increase the delivery of oxygen to the tissues following injury. In the lung, while the total lung volume remains relatively constant, there is a decrease in vital capacity primarily caused by an increase in residual volume [4]. This directly limits the degree to which minute ventilation can be increased to facilitate greater oxygen delivery and removal of carbon dioxide. At the same time, the closing volume increases, so even minor chest trauma leads to alveolar collapse and increased shunting resulting in ventilation/perfusion (V:Q) mismatch [5]. On the pump side, respiratory muscles participate in the overall decline in muscle mass with aging, limiting the ability to take deep breaths and effectively clear the airways of secretions [6]. Also the sensitivity of the brain stem to hypoxemia and hypercarbia is diminished leading to decreased respiratory drive. In addition to these age-related physiological changes, older patients may also have pulmonary comorbidities that further diminish respiratory reserve. Finally, all narcotic analgesics used for pain control diminish respiratory drive even more [7]. In summary, there is less drive, diminished strength, and poorer gas exchange setting the stage for respiratory failure.

Certain principles apply to any elderly patient admitted to the hospital for any reason but may especially apply after injury. These are:

Gas exchange in the lungs is dependent upon ventilation of the alveolus and perfusion of the ventilated alveolus or V/Q matching. Over time, there is an age-related decrease in the partial pressure of oxygen in arterial blood (PaO₂) of 4 mmHg per decade without any change in the partial pressure of alveolar oxygen (PAO₂) or partial pressure of arterial carbon dioxide (PaCO₂) [8]. This is due to decreased efficiency of gas exchange across the respiratory membrane caused by increased thickness and reduced surface area, decreasing from nearly 75 m² at age 20–60 m² by age 70 [9].

Simple measures that maintain V/Q matching go a long way in ensuring adequate V/Q matching. These include:

Aspiration is a common cause of respiratory failure among the elderly and occurs with oropharyngeal and/or gastric contents that may carry pathogens. Aspiration results in a sterile chemical pneumonitis that damages type I pneumocytes impeding gas exchange, reduces surfactant causing alveolar collapse, and makes the patient prone to the development of microbial pneumonia – usually bacterial but sometimes viral or fungal. Risk factors contributing to aspiration include the positioning of the head of the bed <30°, presence of a nasogastric tube, enteral feeds (especially in the presence of a nasogastric tube), mechanical ventilation >7 days, Glasgow Coma Score <9, and burns [20–24].

Measures to prevent aspiration include:

Respiratory infections are common in the elderly and contribute to significant morbidity and mortality, especially in the presence of underlying comorbidities [31, 32]. These are usually caused by bacteria, and less often by viruses, other atypical pathogens, or fungi. The body has numerous mechanisms of clearing potentially infected material from the upper airways – mucociliary escalator, cough reflex, etc. All of these are diminished with age and hence the elderly are more prone to the development of pulmonary infection. The problem is more pronounced in the intubated and ventilated patient as the protective mechanisms are completely bypassed and there is pooling of oropharyngeal and eructed gastric secretions just above the balloon of the endotracheal tube that is a source of frequent micro-aspiration [33]. The gastric secretions very often are colonized since in the elderly acid production is diminished with age or drugs (proton pump inhibitors, Histamine receptor-2 blockade). Studies have shown that this supraglottic pool has potentially pathogenic organisms and that the upper airway of the ventilated patient gets colonized by such organisms within 3–5 days of endotracheal intubation.

The following measures should be taken to prevent the development of pulmonary infection in any elderly patient admitted to the hospital:

Despite all measures, some patients, especially the elderly, admitted to the hospital after trauma, will deteriorate. In such cases, the earlier the deterioration in their condition is detected and appropriate therapy provided, the better will be the outcome. To improve the chances of rapid detection, all health-care providers caring for such patients should be aware of the subtle and not-so-subtle signs of deterioration. These include (i) alteration in mental status, caused by neurologic event or sepsis, (ii) alteration in vital signs (heart rate, blood pressure, respiratory rate, pulse oximeter saturations), and (iii) all subtle signs of stroke and myocardial infarction – the elderly may not manifest the more obvious signs/symptoms of these conditions. The use of rapid response teams has been shown to improve outcomes as from subtle signs/symptoms picked up by the nurse, a lot of resources can be rapidly brought to the bedside for quick action [42]. Lastly, specific to the respiratory system, the use of the incentive spirometer is an excellent method of not only preventing problems but also detecting them early. If the volume of air moved as shown by the incentive spirometer demonstrates a downward trend, this may be an early indicator of a developing problem and should lead to a careful evaluation of the patient [43].

Infection may present in a vastly different manner in elderly patients compared to the young due to altered physiologic reserves [44]. Elderly patients with infections may fail to illicit a fever or elevated white count. Instead, alterations in behavior including agitation and altered mentation may provide the only clues of the presence of infection. In any elderly patient manifesting subtle or overt signs/symptoms of infection, a systematic search should be instituted to identify (or rule out) the source of the infection and if detected to treat it appropriately. From a respiratory standpoint, infection could be anywhere from the larger airways – sinusitis, pharyngitis, or tracheobronchitis – to the lower respiratory tract in the form of pneumonia. If a respiratory infection is suspected, then appropriate culture specimen should be obtained and empiric antimicrobials initiated. Additionally, any unnecessary tubes in the aerodigestive tract should be removed if at all possible. For sinusitis and pharyngitis in a non-intubated patient, a sputum culture is usually an adequate specimen. The diagnosis of deep respiratory infection – pneumonia – in such patients rests on fever, leukocytosis, new or changing infiltrate on chest radiograph, and productive sputum with predominant growth of a single pathogen. If based on clinical and radiographic criteria, pneumonia is suspected, a deep tracheal aspirate should be obtained and empiric antimicrobials initiated. The choice of the empiric therapy is based primarily on whether the patient has or has not had contact with any health-care facility or use of antimicrobials over the past 90 days. Patients admitted for less than 5 days and who have not had any contact with a health-care facility or used antimicrobials over the past 90 days can be treated with standard therapy for community-acquired pneumonia. On the other hand, in a patient who has been admitted for 5 days, or who has had contact with health-care facility and/or used antimicrobials in the past 90 days, the possibility of hospital-acquired organisms should be strongly considered. In such situations, empiric therapy should cover methicillin-resistant Staphylococcus Aureus (MRSA) and hospital-acquired resistant gram-negative organisms – Pseudomonas, Enterobacter, Acinetobacter, etc.

The diagnosis of pneumonia in an elderly traumatized ventilated patient poses additional challenges. Leukocytosis and fever are nonspecific and, as noted above, may be absent in the elderly; infiltrates on chest radiograph too are nonspecific and may be due to other conditions such as cardiac pathology or pulmonary contusion; and sputum culture may be positive due to nonpathogenic colonization of the tracheobronchial tree and may not represent true pathogenic infection. In such situations, the quantitative evaluation of a clean lower respiratory specimen can offer a way of differentiating between nonpathogenic colonization and true VAP (CDC definition: pneumonia occurring in a patient who is or was on the ventilator in the previous 48 h) [45]. The clean deep respiratory specimen could be either bronchoalveolar lavage (BAL) or brush specimen and could be obtained bronchoscopically or blindly by specially designed catheters. At the authors’ institution, any patient demonstrating any two of fever, leukocytosis, changing infiltrate, or productive sputum undergoes a bronchoscopic BAL, and the specimen is analyzed quantitatively. Empiric antimicrobials are initiated immediately after obtaining the specimen. There is ample evidence that delay in appropriate antimicrobials in patients with VAP worsens outcomes [46]. If the quantitative cultures demonstrate >10⁵ microorganisms/ml of BAL fluid, the patient is labeled as having a VAP, and if <10⁵, then VAP is considered unlikely, and further search for the source of infection is continued. In either case, the empiric antimicrobials that started after the BAL are de-escalated; for patients diagnosed with VAP (BAL >10⁵ microorganisms/ml), the spectrum is narrowed to an agent with activity against the cultured organism and good lung penetration; and for patients with no VAP (BAL <10⁵ microorganisms/ml), antimicrobials are discontinued unless another indication for their continuation is present. A similar strategy could be utilized using protected brush specimens. The exact threshold to treat is not well defined in the literature. While almost all agree that for the brush specimen, 10³ microorganisms/ml is the correct threshold, for BAL, different institutions use differing thresholds that vary from 10³ to 10⁵ [47]. The duration of therapy of any diagnosed infection is another area of active investigation. There is a move to treat all infections, including pulmonary, based on the response – reduction in fever, reduction in leukocytosis, improvement in other signs of sepsis, etc. – rather than arbitrary durations [48].