ANAESTHESIA FOR THE GERIATRIC PATIENT: ADVERSE EFFECTS

By Prof. MOHAMMED EZZAT  MOEMEN, Founder of the department of anaesthesia, faculty of medicine, Zagazig university
A lecture delivered at many  local scientific meetings

Normal aging:
The chronological age signifies the age of the individual since his birth in years. Persons of 65 to 74 years are elderly, those of 75 to 84 years are aged, while those of 85 years and over are described as very old.  However, aging should be also assessed on biological basis, where the expected physiological processes of stiffness, fibrosis and atrophy of tissues may be modified.  If these processes are delayed, the biological situation is termed healthy or successful aging and the reverse is true.
The aging cardiovascular system (CVS):
The CVS shows stiffness with aging which alters cardiovascular physiology. This stiffness may be delayed by exercise, active life style and healthy nutrition.  In fact, exercise training could significantly ameliorate cardiovascular stiffness. (1)
The aging CVS exhibits a number of physiological alterations to cardiovascular stiffness (2).  Heart rate shows bradycardia due to depressed autonomic nervous system. Blood pressure shows a raised systolic component and widened pulse pressure due to the stiff major vessel walls. The cardiac output decreases by 1% per decade after middle age. Preload is increased by raised filling pressures denoting that the heart becomes volume dependent (3).  Afterload is raised through increased vascular impedence.
The aging process modifies cardiovascular inotropic responses (4).  Adrenergic receptors are down-regulated by a decrease in their number, while catecholamines are increased by limited up-regulation of sympathetic flow.  Calcium receptors are sustained to preserve the contractile function of the myocardium (5).  However, the cardiovascular cholinergic responses and agonists are maintained. 
The autonomic nervous system exhibits decreasing sympathetic outflow through the process of aging modulating different physiological cardiovascular functions (6) . Cardiac autonomic neuropathy is a current finding in the aged person.
These physiological cardiovascular alterations in the aged can maintain cardiovascular physiology at rest. However, different grades of compromised reserves are apparent on exercise.
The functional adaptations of the aged CVS take place through a cascade of events (2).  Arterial stiffness causes systolic hypertension, increased left ventricular wall tension and left ventricular hypertrophy. This leads to decreased myocardial contractile velocity, prolonged relaxation capacity with maintained left ventricular end-diastolic volume (LVEDV) and ejection fraction (EF).  Moreover, left ventricular hypertrophy may increase left atrial size and filling pressure, contributing in the maintenance of LVEDV and EF.
One should be alert that LVEDV and EF are always maintained within a narrow range depending on the grade of biological aging. In other terms, while such hearts are volume dependent, they may also become volume intolerant (2).  
It should be remembered that successful aging means biological aging without disease. However, more than half moralities of the aged are due to cardiovascular disorders. Common diseases include coronary artery diseases as myocardial ischemia, myocardial infarction and congestive heart failure. Many aged persons have risk factors of coronary artery disease as hypertension, diabetes and peripheral vascular disease. Associated diseases are prevalent among aged patients as rheumatoid arthritis, chronic obstructed pulmonary diseases, or endocrimal disorders. Due to such different diseases, a large percentage of the aged patients consume more drugs as digitalis, dieuretics, antihypertensives, antiarrhythmics, antidepressants and antibiotics (7).  Those diseases and drugs affect the process of aging, medical fitness and the perioperative outcome.
The aging brain:
The brain weight decreases by 2-3g/yr after adulthood (8). It undergoes progressive differentiation by loss of neurones and synapses. The cerebral blood flow decreases by 10-20% with decreasing brain weight. Cerebral autoregulation is preserved, but may be shifted to the right by vascular stiffness (9). 
Aging is accompanied by sympatho-adrenal fibrosis. This is compensated by raised norepinephrine secretion. Decreased neurotransmitters are compensated by decreased up-regulation of the receptors (10).
Aging is associated with emotional disturbances and psychological abnormalities. Primary cognitive dysfunction in old persons is presented as acute and fluctuating disturbances in levels of consciousness and cognition. Delirium is defined as acute confusional state, acute brain failure or diffuse encephalopathy. The core features of delirium include disorders of attention, cognition, sleep-wake cycle and psychomotor behaviour. A number of factors render the elderly patient susceptible to the development of delirium as aging, brain disease, impaired vision and hearing, increased susceptibility to infection and malnutrition (9, 11).
Dementia is a reflection of pathological brain aging with progressive decrease in intellectual functions. It is more common in those with diabetes, chronic lung disease or neurological disorders as stroke and Parkinson’s disease. Demented patients are more predisposed to delirium due to cholinergic deficits that make these patients susceptible to hypoxia and anticholinergic drugs that lead to further depletion of brain acetylcholine.
Alzheimer’s disease is a common cause of dementia as a prototype of pathological brain aging involving multiple cellular derangements ultimately leading to brain failure (12).
Prolonged “postoperative cognitive dysfunction” (POCD) may occur in geriatrics more than in adults, specially in those who are predisposed, through risk factors.
POCD followed certain types of major surgeries as cardiac operations carried under CPB in the form of personality changes and memory impairment.  Contributing factors might be preoperative cerebral dysfunction, hypothermia, intraoperative hypotension, loss of pulsatile flow and micro emboli of air or other matter affecting cerebral perfusion.
Patients experiencing POCD usually have primary cognitive decline or cognitive diseases as dementia. They may be under chronic treatment of B-blocking drugs. They may have been exposed to intraoperative hypoxia, hypercarbia, hypotension, hypothermia or hypoglycemia.
Recently, the central cholinergic system has been identified as a possible site of action and damage leading to POCD (13).  Smith et al (14), speculated that the memory deficits seen after operations in patients of all ages could result from the anticholinergic effects of atropine. This is supported by the fact that patients with pre-existing cognitive impairment and Parkinson’s disease are susceptible to deterioration when they are prescribed anticholinergic agents for premedication or reversal of muscle relaxation effects.
Delirium is another strong predictor of POCD, and could be related to disordered central cholinergic pathway (15, 16).  
There is further convincing evidence in geriatric research which confirms that dementia is caused by failure of cortical cholinergic arousal mechanisms. The marker of the genetic component of this process has been identified as the apolipoprotein – E gene system (17).
POCD may be also related to a possible role of catecholamines, but there is little recent information to confirm a close relationship between circulating or central catecholamines and POCD (18).
Recently, a multicentre study (19) was performed in 13 centres in 8 countries from November 1994 to May 1996, recruiting 1200 patients aged more than 60 yr, undergoing major abdominal, thoracic (non-cardiac) or orthopedic surgeries. The study tested the hypothesis that prolonged cognitive dysfunction occurred after operation, that age was a risk factor and that a combination of hypoxemia and hypotension were causative factors.
A battery of six psychometric tests taking about 45 min to complete was done for each patient. This battery was carried out on 176 British volunteers as a normal control group.
The results confirmed that there was a 25.8% incidence of POCD at 7 days, and that this still affected 9.9% of patients at 3 months. Detailed analysis identified only age as a predictor of deficit and surprisingly that hypoxia, hypotension, or both, were not, in contrast with findings proved in previous work (20).
The results showed that the most promising area where both causation and perhaps prevention of POCD might be the central cholinergic system. It was concluded that the development of drugs for the treatment of dementia would offer hope that their prophylactic use during operation can reduce the onset of POCD (21).
Equally, there may be subgroups of geriatric patients who have critical cognitive functioning, with little cognitive reserves, who are vulnerable to the effects of sedatives, anticholinergics, hypoxia or hypotension. Future work is needed in this area to ascertain the role of these factors (21).
Pulmonary function:
Calcification decreases chest-wall compliance and makes the thorax of geriatric persons more rigid. Aging is also associated with an inevitable and progressive loss of lung recoil. In addition, the breakdown of alveolar septa reduces the total alveolar surface area available for gas exchange.  So, the elderly patient has progressive increase in anatomic and alveolar dead spaces. The functional residual capacity increases modestly and progressively at the expense of vital capacity. The closing capacity increases until it overlaps the functional residual capacity. So, the widening of alveolar – arterial gradient for oxygen and the increased dead space reduce the efficiency of carbon dioxide elimination, with progressive mismatching of ventilation and perfusion. Furthermore, the elderly have increased periodic apnea during sleep, which makes them more likely to have postoperative apnea and airway obstruction (22). 
Hepatic function:
In elderly, the liver size may decline by as much as 40%  (23). Hepatic blood flow decreases in proportion to the loss of liver mass.  So, hepatic function decreases quantitatively due to decreased hepatic perfusion.  For example, the elderly have low plasma cholinesterase activity (24) which can break-down a relatively small dose of succinyl-choline. In the absence of liver disease, there is little qualitative change in hepato-cellular enzymatic function with advancing age (25). It is the quantitative loss of functional hepatic tissue that is important for the clearance of drugs as benzodiazepines, barbiturates, propofol, opiates and other drugs requiring hepatic biotransformation.
Renal function:
In the elderly, about 30% of renal mass is lost by the 8th decade. There is parallel decline in the total number of nephron units. Renal blood flow decreases by 10% per decade after adulthood, mostly affecting the renal cortex. More than one half of the glomeruli present in young adults may be rendered non-functioning by 80 years of age. Glamerular filtration rate decreases more slowly due to compensatory increases in filtration fraction.
Serum creatinine concentration may remain within normal range despite impaired glomerular filtration rate because of the marked atrophy of skeletal muscle mass.  However, creatinine clearance declines about 40% in the elderly and so, the renal functional reserve needed to withstand extreme imposed water challenge  and electrolyte imbalance is minimal. Elderly surgical patients do not require a special fluid replacement schedule but do require meticulous calculation and monitoring of fluid and electrolyte balance.
Age-related changes in renal function lead to prolongation of elimination half-time of anaesthetic drugs and any metabolites requiring renal clearance.
Acute renal failure is responsible for 20% of periopreative deaths in the elderly because about 30% of these patients have pre-existing renal dysfunction.
Blood functions and defensive responses:
Aging produces little effect on red blood cell mass, white blood count, platelet number or coagulation (26).  Hemopoiesis is reduced by decreased bone marrow mass and spleen size. A decrease in immune responsiveness is almost related to an anatomic involution of the thymus gland and an altered function of T lymphocytes. The neuro-endocrine response to stress is generally intact in geriatric patients (27).
Thermoregulation:
Aging is a predictor of inadvertent hypothermia, which causes increased sympathetic outflow, disorientation and confusion. Increased oxygen consumption due to increased shivering may induce postoperative cardiac complications. Post-operative hypothermia causes vasoconstriction and hypertension, with warming vasodilatation occurs leading to hypotension and fluids should be given. 
The whole sequence of impaired thermo-regulation is based on decreased body mass, decreased basal metabolic rate with declined ability for heat production making rewarming significantly slow (28).
Anaesthetic implications:
In geriatric patients a satisfactory anaesthetic course requires an anaesthetic plan compatible with the patient physical status, adequate monitoring and careful perioperative attention.
Basically, there is no “best” anaesthetic agent or technique for the elderly. Prospective and retrospective studies did not show differences between regional and general anaesthetic techniques (29-33).  The anaesthetic plan for the elderly should, however, acknowledge the effect of age on anaesthetic requirements. Sensitivity of the cerebral cortex to opioids and benzodiazepines appears to increase with advancing age (34, 35).  Dosage of hypnotics, narcotics or sedatives should be reduced by 20 to 40% in elderly patients (36). Increased use of remifentanil and cisatracurium that do not require organ-based elimination clearance for the termination of their clinical effects will, also, facilitate predictable recovery in older patients (37).
After subaracnoid injection of local anaesthetics or narcotics in the elderly, there appears to be a somewhat more rapid onset of maximum sensory level and slight prolongation of effective analgesia with no significant change in overall pharmacodynamics (38).  With epidural anaesthetics, dose requirements change insignificantly after injection of small volumes of local anaesthetics, whereas injection of large volumes may be followed by exaggerated cephalad spread of the drug (39).  This is because segmental dose requirements for epidural anaesthetics seem to change in a complex manner with age, reflecting increased resistance to injection and reduced overall compliance of the extradural space. Local anaesthetic infiltration for any justified surgery may also be an ideal approach for geriatrics.
Outcome and adverse effects:
Geriatric surgical patients with healthy and successful aging should do well, but debilitated and sickly older patients are particularly prone to perioperative complications. However, evidence shows that morbidity and mortality occur more frequently in elderly surgical patients than in younger counterparts undergoing comparable surgery. Current estimates of 30 days postoperative mortality for adequately prepared surgical patients 65 years of age or older are 5 to 10%. Although this value is still 3 to 5 times that for the young adults, it is less than one half that reported 3 to 4 decades ago. One year mortality for debilitated geriatric patients approaches 20%, although this figure includes many nonsurgical factors(42). 
Three major risk factors appear to determine outcome for elderly patients. The need to perform surgery on an emergency basis, the operative site and the physical status of the patient at the time of surgery.
The mechanism by which emergency surgery increases risk 3 to 10 fold is multifactorial. Inadequate preoperative evaluation and preparation is more likely to occur in any emergency situation. Inadequate correction of deficiencies in circulating blood volume, electrolyte imbalance or impaired flow-related oxygen variables is another possibility.  In addition, the nature of the surgical lesion and its acute consequences as dehydration and acidosis may critically reduce the already limited organ system reserves. Again, sepsis continues to be a major cause of death in elderly patients.
The site of surgery carries a major risk of mortality in major cavitory rather than superficial surgery.
The preoperative physical status of the elderly correlates with perioperative morbidity and mortality, due to the presence of different diseases and the consumption of more drugs and because geriatric patients are volume dependent and also volume intolerant (3).
Great attention should be given to geriatric patients perioperatively including fluid therapy, oxygen transport and metabolic support. Reduced skin and soft tissue perfusion make the elderly more prone to ischemic pressure lesions. Age related osteoporosis and arthritis may increase the likelihood for iatrogenic injuries if positioning for surgery is not done with great care.  The reduced responsiveness of protective airway reflexes in the elderly may justify routine protection against regurgitation and aspiration of gastric contents (43).  The effect of the sympathetic response to laryngoscopy and tracheal intubation in geriatric patients with cardiovascular disease should be dealt with by proper doses of lidocaine and / or fentanyl (44).  Decreased lacrimation in the elderly makes eye protection more critical than in younger patients. Anaesthetists must protect prosthetic devices worn or implanted preporatively. Perioperative hypothermia should be guarded against and postoperative oxygen therapy for at least 24 hours may be sometimes considered. Perioperative patient monitoring for different organ functions is always of paramount importance.
Postoperative delirium may occur in older patients and may be related to disordered metabolic states as hypoxia, hypercarbia, hypothermia and hypo or hyperglycemia. POCD may be related to preoperative compromized cognitive reserves and may be induced by the use of sedatives and anti-cholinergic drugs specially atropine. Glycopyrrollate does not pass the blood-brain barrier and should be given instead of atropine to the elderly if needed. Regional anaesthesia or local infiltrations, without sedation can approach the ideal of morbidity free outcome (37). 
On the whole, it should be stressed that preoperative medical fitness is a primary determinant of the postoperative outcome in the elderly surgical patients (45).  It may be useful to mention that the complex interaction between pathopysiologic, pharmacologic and technical interventions in modern surgery frequently makes it impossible to establish a clear or single cause of perioperative morbidity or mortality.

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