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 rib cage, respiratory muscles, and 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 a ventilation-perfusion (V/Q) mismatch [5]. In the chest wall, 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 function. Finally, all narcotic analgesics used for pain control, to a lesser or greater degree, diminish respiratory drive [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 are especially pertinent after injury. These are:

Gas exchange in the lung 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) at the rate 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 to ensure adequate V/Q matching include:

Aspiration is a common cause of respiratory failure among the elderly and occurs when oropharyngeal and/or gastric contents that may carry pathogens enter the airway. Chemical aspiration of gastric content results in a sterile chemical pneumonitis that damages type I pneumocytes impeding gas exchange, reduces surfactant production which results in 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 via a nasogastric tube), mechanical ventilation longer than 7 days, Glasgow Coma Score less than 9, and thermal injury [20–24].

Measures to prevent aspiration include:

Respiratory infections are a common complication in the elderly and contribute to significant morbidity and mortality, especially in the presence of underlying comorbidities [31, 32]. The most common pathogen is bacterial, followed by viral, and then atypical pathogens, or fungi. There are numerous mechanisms for clearing infected material from the upper airways – mucociliary escalator, cough reflex, etc. All of these are diminished with age which make the geriatric patient more prone to the development of a pulmonary infection. The problem is more pronounced in the mechanically ventilated patient as the protective mechanisms are completely eliminated. Pooling of oropharyngeal and regurgitated gastric secretions just above the balloon of the endotracheal tube results in micro-aspiration [33]. The gastric secretions very often are colonized as a result of reduced production of gastric acid with aging or the common use of acid-inhibiting drugs (proton pump inhibitors, histamine receptor-2 blockade). Studies have shown that these supraglottic secretions harbor pathogenic organisms and that the upper airway of the intubated patient becomes colonized by such organisms within 3–5 days of 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 trauma patients, will experience deterioration of their pulmonary function. The earlier this deterioration is detected and appropriate therapy provided, outcome will be improved. Therefore, all healthcare providers involved with such patients should be aware of the early subtle signs of impending respiratory failure. These include (i) alteration in mental status – caused by neurologic event or sepsis; (ii) alteration in vital signs – heart rate, blood pressure, respiratory rate, and 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 when subtle signs and symptoms of respiratory compromise are identified by the bedside nurse [42]. Lastly, specific to the respiratory system, the use of the incentive spirometer is an excellent method for reducing the incidence of respiratory complications. However, if the volume of air moved as shown by the incentive spirometer is not increasing or actually decreasing, it 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 pulmonary reserve [44]. Elderly patients with infections may fail to manifest a fever or leukocytosis. Instead, alterations in behavior including agitation and altered mentation may be the only signs and symptoms of an infection. In any elderly patient with subtle or overt signs/symptoms of infection, a systematic search should be instituted to identify the source of the infection and if detected to treat it appropriately. From a respiratory standpoint, infection could occur anywhere from the supraglottic area – sinusitis or pharyngitis – to the infraglottic airways in the form of tracheobronchitis and pneumonia. If a respiratory infection is suspected, then appropriate specimen for culture 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. In contrast, the diagnosis of pneumonia is made with the combination of clinical signs and laboratory studies such as 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 healthcare 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 healthcare facility or used antimicrobials over the past 90 days can be treated with standard therapy for community-acquired pneumonia. On the other hand, a patient who has been critically ill for 5 days, or who has had contact with a healthcare 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 MRSA and hospital-acquired resistant gram-negative organisms like Pseudomonas, Enterobacter, and Acinetobacter.

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. Sputum culture may be positive due to nonpathogenic colonization of the tracheobronchial tree and may not represent a true pathogenic infection. In such situations, the quantitative evaluation of the lower respiratory tract 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 specimen from the lower airways can be obtained by either bronchoalveolar lavage (BAL) or brush specimen and could be obtained bronchoscopically or blindly by specially designed catheters. At the authors’ institution, a patient demonstrating any two of the following, fever, leukocytosis, changing infiltrate on x-ray, or productive sputum, undergoes a bronchoscopic-guided BAL for quantitative analysis. Empiric antimicrobials are initiated immediately after obtaining the specimen. There is ample evidence that delay in initiating appropriate antimicrobials in patients with VAP worsens outcomes [46]. If the quantitative cultures demonstrate ≥10⁵ microorganisms/ml of BAL fluid, the diagnosis of VAP is confirmed. However, if the results of the quantitative culture are less than <10⁵, then VAP is considered unlikely, and further investigations for the source of infection are continued. In either case, the empiric antimicrobials are de-escalated. Once the sensitivities return, the spectrum of the antimicrobials is narrowed to an agent with activity against the specific organism and also has excellent tissue concentration. For patients with a quantitative culture that has <10⁵ microorganisms/ml, antimicrobials are discontinued unless another indication for their continuation is present.