The sum of injury deaths worldwide in 2010 was greater than malaria, tuberculosis, and HIV combined, and has increased by at least 24 % over the last decade [1]. This staggering trauma pandemic has been thought to predominately impact the young healthy portion of the population. However, when intentional and unintentional injury data are combined, the greatest years of life lost in the USA is due to trauma up to the age of 75, ahead of even cardiovascular and malignant diseases [2]. Deaths from injury only represent a small fraction of the total burden of injury; roughly tenfold more people survive their injury, and many of them attempt to seek medical attention. Increasingly, the demographics of injured patients are changing. The world is aging and as they age they collect a list of medical comorbidities. It is this rapidly growing segment of the population that this chapter is written about.

The term “elderly boom” describes the demographic shifts in the western world and the effects of aging baby boomers on healthcare demands [3]. This segment is growing at around twice the rate of the general population and is projected to make up 20 % of the total US population by 2050 [4]. While life expectancy has risen steadily to an all-time high (81.1 years combined; 78.8 for women, 83.3 for men in Canada) [5], it should be appreciated that this peak is concurrent with compounding medical comorbidities. It is predicted that in the next 5–10 years, injured patients over the age of 60 will make up 50 % of the total visits to trauma centres [6].

The number of identified medical comorbidities increases with age [7]. Roughly 10 % of patients under the age of 19 exhibit multimorbidity, that is, more than one identified medical comorbidity. This number jumps to almost 80 % at age 80 in primary care patients [8]. Whether this number reflects the incidence of preexisting medical conditions in trauma patients is only starting to be appreciated. A recent study from Quebec looking at injured patients over the age of 65 admitted to a level I trauma center identified 57 % of patients with hypertension, 34 % with cardiac disease, 22 % with diabetes, and 22 % with dementia [9].

The old assumptions of a healthier, fitter older generation are set to change over the coming decades. Obesity rates in males over 75 years of age in the USA have doubled from 1988 to 2008. According to 2010 US census data, less than 12 % of people over 65 meet federally recommended activity guidelines [4]. What is now becoming clearer is the impact of other comorbidities on activity levels, with diabetes, Parkinson’s, and obesity being associated with increased levels of inactivity [7]. Injury patterns change with activity levels. Potentially high-energy injury mechanisms decrease as people drive less, or leave their residence less. As such, injuries from falls, such as closed head injury or hip fractures, predominate in this cohort.

Several preexisting medical comorbidity metrics have been developed in an attempt to quantify the significance of various diagnoses. The Charlson Index [10], and its derivatives, is a weighted scoring system to predict mortality over 10 years based on either a nurse-administered questionnaire or a patient self-reported form. Medical comorbidities can affect all aspects of the injury process, not just a given patient’s response after injury has occurred. We define a medical comorbidity as described by Elixhauser [11], as “… a clinical condition that exists before a patient’s admission to the hospital, … and is likely to be a significant factor influencing mortality and resource use.” For the purposes of trauma it makes sense to look at the effects of medical comorbidities across all phases of injury. For the purposes of this chapter, we consider these to include the pre-injury, injury, and recovery phases.

Over the past decades, injury prevention has moved to the forefront of our discussions of trauma burden. While issues like seatbelts, road safety, and helmet use have been extensively studied, risk reduction through optimizing care of chronic medical conditions is a new idea. Either the disease process itself or the injury related to these diseases may lead to decreased quality of life and disability; this may add another dimension to the discussions between healthcare providers and patients. The best studied of these medical conditions that predispose patients to injury are drug and alcohol dependence, and age-related cognitive and mobility changes. Others, like morbid obesity, which confers an increased risk of nonfatal injury [12], are only now being investigated, especially in the workplace [13], and in the elderly [14].

Over the preceding decade, the culmination of changes to pre-hospital and initial resuscitation of trauma patients has led to reductions in early hemorrhagic deaths and those in the immediate ICU management [35]. This reduction in mortality however is not as successful in older patients or in those with preexisting medical conditions [36]. While these patients tend to suffer late consequences of their disease after the injury phase (see next section), there are considerations during their early trauma care that can aid recovery.

Leading a successful resuscitation strategy for a critically injured patient requires an understanding of the physiological response to shock, mechanisms, and methods of correcting coagulopathy, and knowledge of the risks and benefits of the various resuscitative measures. Medical comorbidities and the aging process can alter each of these aspects of trauma resuscitation, and when compounded may have dire consequences.

Hemorrhagic shock, the primary causative factor for early death from severe injury, leads to increasingly well-understood physiologic consequences. Reversal of these physiologic derangements and subsequent support until a patient’s homeostatic mechanisms resume are the goals of resuscitation. Once the limits of the innate physiologic response to hypovolemia are reached, shock ensues. The ability of a patient to tolerate a shock state, and the resuscitative measures themselves, may determine the amount of time a trauma team has to stop bleeding and restore homeostasis. The ability of a patient to tolerate these efforts often limits survivability of a given set of injuries.

The term “homeostenosis” describes the loss of physiologic reserve due to aging. While this is difficult to study in isolation apart from concomitant comorbid disease, there is consensus in the geriatric literature regarding the concept [37]. The idea of a physiologic precipice, one that once crossed leads to a disastrous outcome (death, cardiac arrest, etc.), has been put forward. As more of the available physiologic reserve is used just to maintain health while aging, less is available to overcome massive perturbations such as is seen in injury. One area requiring study is the impact of multimorbidity on homeostenosis in younger patients; perhaps the concept of frailty (discussed later) will address this issue.

Alterations in cardiopulmonary physiology due to medical comorbidities such as chronic chronic congestive heart failure (CHF), ischemic heart disease, or chronic lung disease greatly limit a patient’s shock tolerance. A study looking at the relationship of cardiac disease and trauma outcomes [38] found increases in mortality rates with CHF, pre-injury beta-blocker use, and warfarin use. For example, pre-injury CHF, when combined with significant chest injury, can lead to a fivefold increase in mortality rates over patients without CHF.

When looking at the isolated effects of single-drug agents on aspects of injury, there are a few points worth noting. Pre-injury beta-blocker use itself may not lead to increased mortality, though slower presenting heart rates and bradycardia may be seen during resuscitation [39]. With anticoagulants, the effects are clear, especially with closed head injuries [40]. Warfarin use prior to head injury does increase progression of disability and mortality. A protocol of early risk recognition, and reversal with vitamin K and plasma products, has been shown to mitigate this risk [41]. Using four factor (Factors II, VII, IX, and X) prothrombin concentrate has shown some initial promise [42] while potentially avoiding the difficulties of using large doses of plasma, including large-volume administration in a patient with tenuous cardiac physiology, blood-borne infections, and transfusion-associated lung injury (TRALI) [43]. Questions regarding thrombotic risk, duration of efficacy, and overall cost–benefit analysis between prothrombin concentrates and plasma products have yet to be conducted. Quite different from warfarin, anticoagulation reversal is more difficult with antiplatelet agents, especially aspirin and clopidogrel [44], and much more worrisome are the direct thrombin inhibitors, to which no expeditiously efficient reversal means exist [45, 46].

Given the changes in physiologic response due to aging, some have suggested changes in triage criteria [47] and increased use of intensive invasive [48] and noninvasive [49] monitoring in the elderly trauma population. As such, recent guidelines by various trauma associations recommend age criteria for trauma team activation, noting prior significant under triage, and increased mortality in patients >70 years of age.

Recovery from injury and return to the general population are probably most affected by comorbid disease and age. At best, the patient is left with their preexisting illness and infirmity. Commonly, though, recovery and rehabilitation periods in these patients are protracted, limited, and fraught with complications.