Critical Care for the Elderly Patient

Critical Care for the Elderly Patient

SURGERY IN THE ELDERLY P A TrENT I 0039-6109/94 $0.00 + .20 CRITICAL CARE FOR THE ELDERLY PATIENT James M. Watters, MD, FRCS(C), FACS, and Palmer Q...

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Elderly patients are placing increased demands on critical care resources throughout North America, because complex surgical procedures are being performed on older individuals more and more commonly. Owing to the normal physiologic alterations that occur with aging, as well as the effects of common chronic diseases, elderly patients are less resilient than younger patients and are at risk for developing a variety of complications. If complications do develop, these patients have less robust reserves to meet them and recovery may be prolonged. In this article we review the factors that affect the outcome of elderly patients with critical surgical illness and discuss how these factors may modify the management and support of the patient in the intensive care unit.


Many reports have been published of outcome following intensive care admission, but the implications for the care of older patients have been difficult to judge. The reports give varying consideration to and use various methods of assessing the severity of acute illness, co-existing or chronic illness, and prior functional status. Several reports group heterogeneous diagnostic groups. Outcome assessment in terms of mortality, functional level, and quality of life is evaluated by various methods and at various times in the course of critical illness and recovery. Finally, criteria for intensive care unit (leU) admission vary or are unspecified, which results in potential selection bias-for example, selection of older patients who are considered more likely to survive and benefit on the basis of good general health and independent function prior to their acute illness.

From the Departments of Surgery and Biochemistry, University of Ottawa, Faculty of Medicine, Ottawa, Ontario, Canada (JMW); and the Department of Surgery, Washington University School of Medicine, St. Louis, Missouri (PQB)





Nonetheless, several principles seem consistent among a variety of studies conducted to address different issues. Univariate analysis has identified a relationship between age and hospital mortality in patients who have received intensive care in many studies, as it has following elective and emergency surgery, trauma, and sepsisY' 13, 22, 23, 26, 31, 39, 42 However, mortality is also a function of the severity of the acute illness, often evaluated as the acute physiology score (APS), and the relationship of age and severity of illness to mortality is further modified by the specific diagnosisP' 18, 22, 23, 31, 34, 35 APS is determined from the most deranged values of 12 physiologic variables during the first 24 hours after ICU admission, In a recent study of noncardiac surgical ICU patients, ICU mortality was related to severity of illness (simplified APS, SAPS) but did not differ significantly between nonagenarians and younger patients when stratified for SAPS.20 Hospital mortality, however, was higher in the older patients (17% versus 5%). The influence of diagnosis on the relationship of age to mortality has raised the issue of the appropriateness of routine assignment of age points in calculation of the APACHE 2 score. 41 Older age may have less impact on mortality among patients with severe acute illness!' 25 In two studies of patients admitted to medical ICUs, older age no longer predicted mortality when acute severity of illness, diagnosis, and prior health were taken into account. 23 ,41 In another study, patients admitted to a mixed ICU following trauma had higher long-term survival than those in other diagnostic groups.3! Older age, a history of cancer, and medical rather than surgical service were identified as the most important factors reducing long-term survival in another study of mixed ICU patients.' In that study, 5-year survival of patients discharged alive from hospital (58%) was significantly lower than predicted in an age- and gender-matched normal population (92%), The further survival of patients who are alive 6 months following hospital discharge has been reported to approach that of an age-, year-, and gender-matched general population in a study in which many of the patients were admitted to ICU following surgery or trauma!6 Physical activity status and subjective quality of life prior to admission were significant predictors of survival in a mixed ICU population with large proportions of older and chronically ill patients44; moreover, the quality of life of long-term survivors was comparable to that prior to their acute illness, Others have observed that age does not distinguish the degree of recovery among survivors, most older patients having regained their prior health status at 1 year following admission. 46 The interaction of prior functional status and age influences mortality: In one study, patients aged 75 years or more who had functional limitations were six times more likely to die in hospital than those aged 50 to 64 years and without limitation. 22 Considering patients without functional limitation, there was no difference in mortality between the youngest and oldest groups, In another study, increasing age was inversely related to the patient's own subjective estimation of quality of life following discharge but not to objective scores of physical and psychosocial disability,35 Individual and societal views of quality of life do not necessarily coincide in older patients, who may be more accepting of health-related limitations in life style than are young patients. 32 Chronologic age should not be used in isolation to predict the benefit to be obtained from intensive care or to exclude individuals from such care. More precise measures of prior functional status, disability, physiologic function, and chronic health; a greater knowledge of the interaction of specific diagnoses (particularly surgical) with these factors; and a more sophisticated appreciation of the determinants of survival and other outcomes will improve our ability to advise patients and their families and to make appropriate management decisions,



In summary, the elderly patient has a poorer outcome from a given operation or injury than does a young or middle-aged patient, but when stratified by severity of illness, age is not a significant prognostic factor. This implies that a given operation or injury results in a greater degree of physiologic derangement ("severity of illness") than it would in a younger patient. Elderly patients have impaired physiologic reserves with which to respond to operation, injury; infection, or other critical illness. The care of elderly patients in the ICU is comparable to care of younger patients. The priorities of management are the same. Because of the patients' impaired physiologic reserves, the clinician must be extra vigilant in searching for early, subtle signs of organ system dysfunction and cautious in weaning physiologic support.


Aging, atherosclerotic and other disease, and life-style factors interact and affect cardiovascular function in ways that are often difficult to separate. 19 Although substantial variations in most cardiac variables occur among older individuals, some generalizations can be made about the clinical consequences of these factors for older patients with critical illness. Stiffening of the aorta and more peripheral vessels results in a diminished contribution of aortic recoil to forward flow. Peripheral vascular resistance does not vary predictably with age in healthy males at rest, but there is considerable heterogeneity and a consistent increase with age in hypertensive individuals. A modest increase in left ventricular wall thickness with aging is exaggerated by hypertension and coronary artery disease. Myocardial relaxation is prolonged, and early diastolic filling is slowed and delayed with advancing ageY· 19 Left ventricular end-diastolic volume at rest tends to be increased because filling is more rapid later in diastole with left atrial enlargement and an enhanced contribution from atrial contraction. 24 Resting heart rate and intrinsic sinus node rate decrease with age, whereas P-R interval is modestly prolonged, probably reflecting delayed conduction within the atrioventricular junction.9 Resting ejection fraction is not altered, but stroke volume index increases slightly, accompanied by an increase in enddiastolic volume index. 19 Resting pulmonary artery pressure and pulmonary vascular resistance increase moderately with aging in screened individuals free of coronary artery disease and left ventricular dysfunction.6 The distribution of resting cardiac output changes with advancing age: Alterations in cerebral, coronary, and skeletal muscle blood flow are limited in the absence of atherosclerotic disease whereas blood flow to the liver and kidneys may decline 40% or more, disproportionate to changes in cardiac output and in tissue mass. 2• 14• 42 The response of healthy older individuals to an increase in afterload (infusion of phenylephrine to achieve a 30 mm Hg increase in systolic blood pressure) is altered; Significant left ventricular dilatation occurs and contraction begins from a greater preload than in young subjects, presumably reflecting a diminished contractile reserve in the older subject.43 Considerable work has been directed at elucidating the influence of aging on cardiovascular responses to exercise, which may provide some insight into the altered responses associated with critical illness and its demands. Maximum heart rate achieved during exercise diminishes consistently with age, whereas changes in stroke volume index are variable (reflecting occult coronary artery disease, fitness level, heart size, and body composition) and cardiac index tends to decline. 19 Cardiac index is maintained during exercise by an increase in stroke volume in older individuals free



of cardiovascular disease33; stroke volume declines significantly with age in hypertensive (in contrast to normotensive) men. End-diastolic volume index is maintained or increased during exercise in older subjects, whereas decreases in end-systolic volume index are blunted and increases in ejection fraction are less than in young individuals. '9,29 In an older study of subjects with varying levels of habitual activity, the incidence of electrocardiographic abnormalities during and after maximal exercise increased with age and was much higher than at rest. 37 Mean arterial lactate concentration also increased with advancing age for a given heart rate or work load. The inotropic, chronotropic, and arterial vasodilating effects of beta-adrenergic stimulation diminish with advancing age, a phenomenon that may contribute to many of the age-related changes in the cardiovascular responses to exercise. For example, beta-adrenergic blockade in younger individuals diminishes the increase in heart rate and decrease in end-systolic volume during exercise, with end-diastolic volume increasing significantly and stroke volume augmented. '9 Isoproterenol infusion in older subjects results in lesser increases in heart rate, left ventricular ejection fraction, and cardiac index than in young individuals.38 Dobutamine has been shown to augment cardiac output and stroke volume to a much lesser extent in elderly patients with decompensated congestive heart failure compared with younger patients while providing no additional hemodynamic benefit at infusion rates above 5 ILg/kg min. 30 The earliest responses to tissue injury are directed at restoring and maintaining the perfusion of vital organs but, with advancing age, the efficiency of many of these critical responses is diminished. Indeed, delivery of oxygen to the tissues may be impaired in the elderly patient at every step of the oxygen transport pathway and may be inadequate to meet increased demands. The decreased baroreflex sensitivity, altered autonomic function, decreased sensitivity to catecholamines, and impaired vasoconstriction that accompany aging may all limit the ability to maintain cardiovascular homeostasis. Moreover, diminished ventilatory response to hypoxemia and hypercapnia, increased alveolar-arterial oxygen gradient, and decreased arterial oxygen saturation, which again predictably accompany advancing age, in combination with the limitations in cardiac output described above, are likely to compromise the ability of the elderly patient to meet increased tissue oxygen requirements. Thus, older patients are predisposed to hemodynamic compromise in relation to tachyarrhythmias, ischemia, and increased afterload. Increased end-diastolic volume and stroke volume are compensatory mechanisms that maintain cardiac output in the face of other limitations, and appropriate filling volumes must be achieved. The benefits of inotropic drugs may be less in the elderly and a role for those that reduce afterload more prominent than in younger patients. Elderly patients are less able to increase oxygen delivery in the face of increased demand and, with a high prevalence of coronary artery disease, risk myocardial ischemia if demands are excessive. It is probably appropriate to set cardiac index and oxygen delivery goals modestly above resting levels, but every effort must be made to minimize unnecessary stresses that increase metabolic demand such as hypothermia, shivering, exposure to a cool ambient environment, hypovolemia, acidosis, pain, and inappropriate weaning from or inadequate ventilatory support. 39 It is also important that every element of the oxygen transport system be optimized in the elderly patient when a supranormal target is set, in order that it be achieved with the least demand on cardiac output. In the controlled setting of major elective surgery, such as in patients undergoing aortic grafting, the use of beta-adrenergic blockers to limit increases in heart rate and myocardial oxygen demand may be appropriate. The principles of physiologic and invasive



hemodynamic monitoring are the same in elderly patients as in the young, but such monitoring is perhaps of even greater importance because of limitations in cardiopulmonary function and homeostatic mechanisms. Although pulmonary artery rupture during inflation of a pulmonary artery catheter balloon is rare, its incidence is increased in patients older than 60 years and in the setting of pulmonary hypertension.24 RESPIRATORY CONSIDERATIONS

Elderly patients also have impairment of respiratory reserves due to a variety of age-related physiologic changes that affect respiratory function. 39 Thus, the elderly are at particular risk for developing respiratory complications. Lung function as measured by several parameters diminishes with age. Patients are less able to protect their airways, and their responses to hypoxia and hypercarbia are diminished. Because muscular strength diminishes with age, the strength and stamina of the respiratory musculature are reduced. In addition to these agerelated changes, obesity and chronic lung disease may further limit respiratory reserve. Abdominal or thoracic operations reduce the vital capacity for up to 2 weeks in patients of any age. s In the elderly these changes exacerbate pre-existing age and disease-related impairments. In addition, because of reduced drug clearance, the effects of narcotics and sedatives persist longer in elderly patients than in younger ones, further blunting respiratory responses and function. After elective operation, elderly patients may require a period of mechanical ventilation to ensure adequate gas exchange until the effects of anesthesia are dissipated, body temperature is restored, and respiratory and diaphragmatic function begins to improve, as much as 24 to 48 hours postoperatively.'o Impaired respiratory function preoperatively, as would be indicated by dyspnea at rest and hypoxemia, especially in patients with a forced expiratory volume in 1 minute (FEV,) of less than 1 L, is the most reliable predictor of the need for postoperative ventilationP When patients are stratified according to intrinsic pulmonary function, age alone is not an important risk factorp,27 Although mechanical ventilation is beneficial for the elderly patient recovering from operation or injury, intubation and ventilatory support impose their own risks. They impair mucociliary function and other pulmonary defense mechanisms. The likelihood of pulmonary infection increases with the duration of intubation and mechanical ventilation. Pulmonary infection may further compromise respiratory function owing to the need for clearance of increased secretions and the accumulation of lung water, which decreases lung compliance and makes spontaneous lung expansion progreSSively more difficult. Mechanical ventilation, especially if sedatives or neuromuscular blocking agents must also be used, may lead to respiratory muscle atrophy and decreased strength, which limits the patient's ability to maintain adequate gas exchange spontaneously. The challenge for the clinician is to balance the benefit of mechanical ventilatory support in elderly patients with both acute and chronic impairments of respiratory function against the real risks of additional morbidity from prolonged intubation and ventilation. The techniques of mechanical ventilation in the elderly are the same as those used in younger patients. The combined effects of age-related alterations and acute surgical illness, however, may modify their application. Patients may require a fairly prolonged period of nearly total support postoperatively, using either assisted ventilation or a high rate of intermittent mandatory ventilation, until they are sufficiently recovered from their anesthetic and operation to main-



tain adequate gas exchange. Decreased lung compliance due to chronic disease or increased lung water or high levels of positive end-expiratory pressure needed to support oxygenation may result in high airway pressures. These may exacerbate the acute lung injury2S or interfere with effective cardiovascular performance. Invasive hemodynamic monitoring and support of the circulation are commonly required. Inverse ratio ventilation, in which the duration of the inspiratory phase is greater than the expiratory phase, usually provides adequate ventilation with lower peak inspiratory pressures than conventional ventilation. The early institution of this modality may limit the amount of pressure-induced lung injury and reduce the severity or duration of respiratory insufficiency. As soon as the patient is stabilized and does not require high levels of positive end-expiratory pressure to maintain oxygenation, attempts to decrease the amount of ventilatory support should be made. The ultimate limiting factor is usually fatigue. This may be manifest not only by hypoventilation but also by progressive inability to take a deep breath and to clear secretions. This may lead to atelectasis and acute hypoxemia. The weaning process for elderly patients is often more prolonged than for younger ones, as efforts are made to avoid exhaustion. In our practice, we have found that the combination of intermittent mandatory ventilation and pressure support ventilation is particularly applicable in the older patient. The mandatory breaths provide a tidal volume of approximately 12 mL/kg ideal body weight, and the pressure support is adjusted so that the patient's spontaneous tidal volume is 8 to 9 mL/kg. The intermittent mandatory ventilation rate can usually be quickly tapered to 2 to 4 per minute. The pressure support ventilation is then tapered more slowly, ensuring that gas exchange, work of breathing, and spontaneous tidal volumes remain satisfactory. When the pressure support ventilation has been reduced to 5 to 6 cm H 20, then trials of continuous positive airway pressure or a "T-piece" may be initiated successfully. The decision to extubate is based not only on satisfactory gas exchange, easy respiratory efforts, and adequate tidal volumes, but also on the patient's ability to maintain and protect the airway. The patient should be able to take deep breaths and to clear secretions effectively. Thus, a large amount of secretions requiring suctioning every 2 hours or less and/or a vital capacity of less than 12 mL/kg would favor continued intubation and ventilatory support. A standard endotracheal tube passed through either the mouth or the nose may maintain the airway satisfactorily for several days or weeks. Over the past 20 years tracheostomy has been performed with decreasing frequency in patients requiring ventilatory support. Nevertheless, a tracheostomy commonly allows improved pulmonary toilet and increased patient comfort. Patients may often begin to take liquids or food orally. If a mechanical problem with the tube occurs (such as cuff leak), it can be replaced more easily than an endotracheal tube. We consider tracheostomy after 2 weeks of mechanical ventilation, or sooner if it appears likely that prolonged mechanical ventilation will be necessary. We generally perform open tracheostomy in the operating room. Several percutaneous techniques for tracheostomy tube placement, however, have been developed!O Kits for this procedure are now commercially available. Several recent series document that percutaneous tracheostomy is associated with lower complications than the open technique. After removal of the tube, the resultant scar is said to be less prominent than that associated with open tracheostomy. FLUID AND ELECTROLYTE CONSIDERATIONS

Elderly patients are less able than young patients to restore and maintain acid-base, fluid, and electrolyte homeostasis during critical illness. 39 Sensitivity to



homeostatic perturbations is diminished, and compensatory mechanisms that are efficient in the young patient function less rapidly. Careful management, based on an understanding of physiologic mechanisms, is necessary if extreme abnormalities of fluid, electrolyte, and acid-base status are to be avoided. Renal blood flow and glomerular filtration rate (GFR) decline progressively with age, particularly after the fifth or sixth decade. Older individuals are less able to decrease urine flow and increase urine osmolality in response to water deprivation, and the time required to achieve sodium equilibrium in the face of sodium restriction is 34 Thus inefficient renal conservation of salt and water, together with increased insensible fluid losses through thinned skin, impair the ability of the elderly patient to respond appropriately to hypovolemia. The elderly are also predisposed to extracellular fluid volume expansion because of a decreased renal ability to excrete an acute load of salt or water. The syndrome of inappropriate antidiuretic hormone secretion is of particular concern in the elderly patient in association with pneumonia, neoplasms, neurologic disorders, and medications, including diuretics, nonsteroidal anti-inflammatory drugs (NSAIDs), and chlorpropamide. The pH of body fluids is little affected by age, but the efficiency of acid-base homeostasis is decreased in the elderly. For example, the time to eliminate an acid load is markedly prolonged in elderly compared with young subjects.1 Maintenance of normal pH depends on chemical buffer systems in body fluids, alterations in ventilation and elimination of carbon dioxide, and renal excretion of excess acid or base. Minor decreases in extracellular volume and bicarbonate concentration, plasma volume, lean body mass, and bone mineralization may limit chemical buffering systems. Renal regulation of acid-base status may be significantly impaired for a variety of reasons, including decreased renal mass, decreased GFR, delayed elimination of bicarbonate, and diminished ability to deaminate glutamineP The effectiveness of respiratory mechanisms is probably not altered in the elderly. Serum creatinine tends to remain unchanged with advancing age despite declining GFR because of decreased muscle mass and creatinine production; more than minor elevations in serum creatinine most often reflect decreases in GFR which are pathologic rather than attributable to age alone. Serum creatinine is not a reliable index of renal function, and dosages of drugs excreted by the kidneys should be based on measured creatinine clearance or circulating drug levels. Inhibitors of prostaglandin synthesis, such as NSAIDs, may allowunopposed renal vasoconstriction and result in acute renal failure. The potential for renal injury from other drugs, radiographic dye, and hypotension must be appreciated in the setting of already diminished renal function in the elderly individual. NUTRITION SUPPORT

Nutrition support should be provided early to the elderly patient in the ICU, preferably via the enteral route. Substantial decreases in lean body mass and body cell mass are characteristic of advancing age, owing in large part to reduced muscle mass. Losses of muscle mass of 40% or more occur between young adulthood and age 80 years, and decreases in strength, including respiratory muscle strength, are comparable. The accelerated breakdown of skeletal muscle and net release of amino acids to serve in a variety of metabolic pathways are characteristic of the host responses to critical illness. Thus, during prolonged or severe illness, the ongoing erosion of muscle mass in the elderly patient may



reduce muscle strength to critical functional levels and limit the ability to sustain essential metabolic activity. In the patient undergoing major elective surgery, consideration should be given to intraoperative placement of a nasoenteric tube or other access and early initiation of postoperative enteral feeding. Although the need for nutritional support is probably greater in the elderly than in well-nourished younger patients, the efficacy and tolerance of such support may be less because of the combined impacts of aging and critical illness on intermediary metabolism. The caloric requirement to restore body cell mass in malnourished patients has been shown to increase with age. 36 In addition, insulin responses to glucose loading and the disposal of glucose are diminished in older patients admitted to leU following trauma. 3 With an increased renal threshold for glucose, the older leU patient is further predisposed to marked elevations of serum glucose and osmolarity. Decreased serum growth hormone and insulinlike growth factor-l responses to feeding have been reported in older compared with young trauma patients. 1S,16 Growth hormone is a potent anabolic hormone, many of the metabolic effects of which are mediated by insulin-like growth factor 1. Thus nutritional support should be initiated early following leU admission of the elderly patient and should take into account changes in body composition and anticipate diminished glucose tolerance. Administration of insulin may be required and may have, along with factors such as recombinant growth hormone, particular anabolic benefits for the elderly patient. INFECTIOUS CONSIDERATIONS

Because of many of the factors discussed above, the elderly patient is susceptible to a number of infectious complications. These in combination with impaired physiologic reserves may lead to multiple system organ failure. The mortality of that syndrome is proportional to the number of failing organ systems and approaches 100% when four or more organ systems are severely dysfunctionaP1 As indicated above, available information suggests that the severity of illness is the primary determinant of outcome, rather than age itself. Recognition of the presence of infection can be difficult. Because of a generalized blunting of a variety of physiologic processes with age, the response to bacterial challenge may be less obvious in elderly patients than in younger ones. Fever and leukocytosis may not be marked; in fact hypothermia and a normal or low white cell count may be present. As is true for younger patients, hypotension with a normal or elevated cardiac index, acidosis, worsening hyperglycemia, or hypoglycemia may all be presenting signs of sepsis. Antimicrobial therapy should be guided by the same indications and principles that apply to young and middle-aged patients. In the elderly, however, empiric therapy is not uncommonly instituted for more subtle, or "softer," signs than for younger patients. Aging does reduce the efficacy of drug clearance pathways, especially renal clearance, so that toxicity of antibiotics and other drugs may occur at lower doses than in young patients. 44 If renal function is not severely impaired (creatinine clearance greater than 30 mL/min), normal doses of penicillins and cephalosporins may be administered. Administration of aminoglycosides and vancomycin should be guided by measurements of serum antibiotic concentrations. SUMMARY

Elderly individuals will continue to make up a major portion of patients requiring critical care. Age and chronic disease-related factors blunt the reserves



with which the elderly can meet the demands of critical surgical illness. The clinician must remain vigilant to subtle changes in the patient's course which may indicate a developing complication and must pay attention to all the details of comprehensive critical care management. With careful attention and timely physiologic support, the elderly patient has as good a chance of surviving as a similarly ill younger patient, although his or her course may be more prolonged. The priorities are the same. Thus, the primary disease must be addressed: necrotic tissue debrided, pus drained, wounds closed, fractures set. Cardiopulmonary performance (oxygen delivery) must be maintained sufficiently to meet the heightened oxygen needs associated with critical illness. This may require invasive hemodynamic monitoring and pharmacologic support. Gas exchange in the lungs must be maintained without compromising cardiovascular function or exhausting the patient. Patients should be kept warm, pain free, and calm. Intravascular volume and the composition of the extracellular fluid must be maintained. Nutritional support should be provided early in amounts sufficient to meet the patient's basal nutritional requirements and increased needs associated with the critical illness. If at all possible, some or all of this nutritional support should be provided via the gastrointestinal tract. The use of specialized nutrients or of agents designed to minimize the catabolism of critical illness or to enhance anabolism is an area of active investigation. The indications for these therapeutic strategies in the elderly should become clearer in the years ahead. References 1. Adler S. Lindeman RD, Yiengst MJ, et al: Effect of acute acid loading on urinary acid excretion by the aging human kidney. J Lab Clin Med 72:278-289, 1968 2. Bender AD: The effect of increasing age on the distribution of peripheral blood flow in man. J Am Geriatr Soc 13:192-198, 1965 3. Blakslee JM, Moulton S, Watters JM: Effect of advanced age on glucose tolerance following injury. Surg Forum 41:22-25,1990 4. Chelluri L, Pinsky MR, Donohoe MP, et al: Long-term outcome of critically ill elderly patients requiring intensive care. JAMA 269:3119-3123, 1993 5. Craig DB: Postoperative recovery of pulmonary function. Anesth Analg 60:46,1981 6. Davidson WR Jr, Fee EC: Influence of aging on pulmonary hemodynamics in a population free of coronary artery disease. Am J CardioI65:1454-1458, 1990 7. Dragsted L, Qvist J, Madsen M: Outcome from intensive care. IV. A 5-year study of 1308 patients: Long-term outcome. Eur J AnaesthesioI7:51-62, 1990 8. Epstein M, Hollenberg NK: Age as a determinant of renal sodium conservation in normal man. J Lab Clin Med 87:411-417,1976 9. Fleg JL, Das DN, Wright J, et al: Age-associated changes in the components of atrioventricular conduction in apparently healthy volunteers. J Gerontol (Med Sci) 45:M95-100, 1990 10. Ford G, Whitelaw W, Rosenal TW, et al: Diaphragm function after upper abdominal surgery in humans. Am Rev Respir Dis 127:421, 1983 11. Gee MH, Gottlieb JE, Albertine KH, et al: Physiology of aging related to outcome in the adult respiratory distress syndrome. J Appl PhysioI69:822-829, 1990 12. Gerstenblith G, Fleg JL, Becker LC, et al: Maximum left ventricular filling rate in healthy individuals measured by gated blood pool scans. Circulation 68(Suppl III):101, 1983 13. Heuser MD, Case LD, Ettinger WH: Mortality in intensive care patients with respiratory disease-is age important? Arch Intern Med 152:1683-1688, 1992 14. Hollenberg NK, Adams DF, Solomon HS, et al: Senescence and the renal vasculature in normal man. Circ Res 34:309-316, 1974 15. Jeevanandam M, Holaday NJ, Shamos RF, et al: Acute IGF-1 deficiency in multiple trauma victims. Clin Nutr 11:352-357, 1992 16. Jeevanandam M, Ramias L, Shamos RF, et al: Decreased growth hormone levels in the catabolic phase of severe injury. Surgery 111:495-502, 1992



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44. Yinnon A, Zimran A, Hershko C: Quality of life following intensive medical care. Q J Med 264:347-357,1989 45. Yoshikawa TI: Antimicrobial therapy for the elderly patient. J Am Geriatr Soc 38:13531372, 1990 46. Zaren B, Bergstrom R: Survival compared to the general population and changes in health status among intensive care patients. Acta Anaesthesiol Scand 33:6-12, 1989

Address reprint requests to James M. Watters, MD, FRCS(C), FACS Department of Surgery Ottawa Civic Hospital 1053 Carling Avenue Ottawa, Ontario K1 Y 4E9 Canada