Oxford Handbook of Anaesthesia (3 edn)
Annotate
Cite
Jeffrey Handel
There is no standard definition of elderly, but it is often arbitrarily taken as >65yr. Such patients have an increased risk of morbidity and mortality associated with anaesthesia and surgery.
Aging is associated with progressive deterioration of function in all systems.
Cardiovascular
Significant cardiovascular disease is present in 50–65% patients.
Myocardial fibrosis and ventricular wall thickening occur. This reduces ventricular compliance such that small changes in filling may have major effects upon cardiac output and blood pressure.
Atrial fibrillation is common. Stroke volume is reduced by loss of the atrial boost contribution to ventricular filling.
Maximal cardiac output with exercise decreases by ∼1% per year from the 5th decade.
Reduced arterial compliance causes systolic hypertension and widened pulse pressure.
Autonomic responsiveness declines progressively resulting in impairment of cardiovascular responses to hypotension. The hypotensive effect of anaesthetic agents is likely to be more pronounced.
Capillary permeability is increased leading to a greater risk of pulmonary oedema.
Respiratory
Ventilatory response to hypoxia and hypercapnia declines and postoperative apnoea is more common. Ventilatory reserve declines.
O2 consumption and CO2 production fall by 10–15% by the 7th decade. Patients are able to tolerate a longer period of apnoea following preoxygenation and minute volume requirement is reduced.
Loss of elastic recoil increases pulmonary compliance but chest wall compliance falls due to degenerative changes in joints. Therefore total thoracic compliance may fall.
Loss of septa increases alveolar dead space. Closing volume increases to exceed functional residual capacity in the upright posture at 66yr resulting in venous admixture. Thus normal PaO2 falls steadily [(13.3–age/30)kPa, or (100–age/4)mmHg].
Airway protective reflexes decline increasing the risk of postoperative pulmonary aspiration.
In edentulous patients maintenance of a patent airway and facemask seal may be difficult. Leaving false teeth in situ may help.
Renal
Renal mass and number of glomeruli fall progressively (by 30% in the 8th decade) resulting in reduced GFR. Creatinine clearance falls comparably although serum creatinine may not rise because of decreased production from a reduced muscle mass (see p. 128).
Tubular function deteriorates leading to reduced renin-aldosterone response, ADH sensitivity, and concentrating ability. As a result, all renal homeostatic functions deteriorate so that elderly patients are more susceptible to fluid overload and hypovolaemia. Hypo- and hypernatraemia are more likely to occur.
Clearance of renally excreted drugs is reduced necessitating dose adjustment. Particular care must be taken with potentially nephrotoxic drugs such as aminoglycosides.
Hepatic
Hepatic mass and blood flow fall by up to 40% by the 9th decade. Although cellular function is relatively well preserved in healthy patients, the reduction in size reduces clearance and prolongs the effect of drugs that are metabolised and excreted by the liver. These include opioids, propofol, benzodiazepines, and non-depolarising muscle relaxants.
CNS
Brain size and neuronal mass decrease. Average brain weight falls by 18% between the ages of 30 and 80yr. Dementia affects 10% of patients over 65yr of age and 20% over 80yr. However, it is important to distinguish between dementia and reversible confusional states due to hypoxia, sepsis, pain, metabolic derangement, and depression. The hospital environment may precipitate anxiety and confusion.
The elderly have lower requirements for opioid analgesics and sedatives and are more susceptible to depression of conscious level and respiration. This is likely to be due to a pharmacodynamic as well as a pharmacokinetic effect. Pain threshold may be increased.
Postoperative cognitive dysfunction is common in the elderly (25% at 1wk, 10% at 2yr post major surgery). It is a complex condition with features of dementia and confusional states which continue after the immediate postoperative period. Disturbance of cerebral perfusion and cellular oxygenation is likely to be a contributory factor. Alterations of central acetylcholine and catecholamine levels as well as central steroid effects from the stress response are thought to play a role (see p. 732).
The thirst response to reduced ECF volume and increased plasma osmolality is reduced in the elderly, increasing susceptibility to fluid depletion.
Pharmacology
Total body water is reduced while fat is increased. Volume of distribution of water-soluble drugs is reduced, reducing dose requirements, while that of lipid-soluble drugs is increased which may prolong clearance. Initial volume of distribution falls because of reduced cardiac output. This reduces dose requirement and is particularly relevant for induction agents. Arm–brain circulation time is prolonged, increasing the time taken for induction agents to take effect.
Reduced plasma albumin concentration decreases dose requirement of drugs such as barbiturate induction agents, which are bound to albumin.
MAC of inhaled agents decreases steadily with age (6% reduction per decade) and is reduced by around 40% by the age of 80yr (see pp. 1251–1252). This may be related to a reduction in neuronal mass. Reductions in blood/gas partition coefficient and cardiac output in the elderly result in shorter onset time.
The risk of gastrointestinal bleeding due to NSAIDs is increased. These agents may also contribute to the development of acute renal failure in the presence of impaired renal perfusion. Angiotensin converting enzyme inhibitors exacerbate this risk. Fluid retention due to NSAIDs may precipitate heart failure in susceptible patients.
Thermoregulation
Temperature regulation is impaired, increasing the risk of hypothermia.
Postoperative shivering increases skeletal muscle oxygen consumption while vasoconstriction increases myocardial work and oxygen demand.
Endocrine
Glucose loading is increasingly poorly tolerated in elderly patients. The incidence of diabetes rises and may reach 25% in patients above 80yr of age.
Nutrition
Nutritional status is frequently poor in the elderly. Perioperative complications and length of hospital stay may be reduced by nutritional supplementation prior to major surgery.
Haematology and the immune system
Hypercoagulability and deep venous thrombosis become more common with advancing age.
Disorders causing anaemia are more common and the response of the marrow to anaemia is impaired.
Immune responses are reduced in the elderly, putting them at increased risk of infection. This is due to reduced bone marrow and splenic mass with loss of the thymus.
Anaesthetic management
Perioperative mortality increases with age. It is influenced by medical fitness, the nature of the surgery, and whether surgery is elective or emergency. Hospital mortality for hip fracture surgery in patients over 70yr of age varies between 5% and 24% (see also p. 508). For patients over 80yr undergoing elective bowel surgery for malignancy, hospital mortality is between 0 and 15% for ASA1 patients, increasing to 20–30% for ASA3. Mortality is increased if resection is incomplete. Outcome is optimised by thorough preoperative assessment, choice of an anaesthetic technique appropriate to the patient's condition, and meticulous perioperative care to minimise physiological disturbance.
Preoperative assessment and management
A systematic review is vital. In patients who have sustained a fracture, an underlying medical cause for a fall should be sought.
Day surgery is particularly appropriate for fit patients undergoing minor surgery as the disorientation associated with a change of environment is minimised.
The level of physical activity that can be sustained is a useful indicator of cardiovascular and respiratory fitness, but is often limited by joint disease.
Mental state should be evaluated. The abbreviated mental test or mini mental state examination may be useful in differentiating dementia from acute confusional states.
Consideration should be given to preoptimisation of medical conditions. This may require cross-specialty involvement and high-dependency care. The benefits from delaying surgery while this takes place should be balanced against the risks, particularly in non-elective surgery. In patients with lower limb fractures delay in mobilisation may increase the risk of pressure sores, deep venous thrombosis, and pneumonia.
Regular medications with the exception of oral hypoglycaemics should be continued until the time of surgery. Alcohol should not be withheld the day before surgery and nicotine patches may be helpful in smokers. Sedative premedications should generally be avoided, particularly benzodiazepines, centrally acting anticholinergics, and pethidine. Antacid prophylaxis should be considered. Maintaining β-blockade may reduce the risk of myocardial infarction.
Perioperative management
There is no conclusive evidence that regional or general anaesthetic techniques are superior. Regional anaesthesia may reduce bleeding, risk of DVT, respiratory infection, and cognitive dysfunction. For fractured neck of femur it may reduce mortality at 1 month but has no effect on longer-term survival compared with general anaesthesia. The chosen technique should be appropriate for the patient's physiological condition, as with younger patients.
Careful monitoring is necessary for induction of general anaesthesia and for regional techniques as the hypotensive response to induction agents and to spinal/epidural anaesthesia is likely to be greater in the elderly. Consideration should be given to central venous pressure or cardiac output monitoring as elderly patients are more susceptible to adverse consequences of fluid overload and hypovolaemia. It should be remembered that prolonged arm–brain circulation time delays the onset of IV induction agents—flush drugs with saline. Impatience will lead to inadvertent overdose.
Temperature should be measured and hypothermia prevented using fluid warmers, active body warming devices, and elevation of ambient temperature.
Prolonged surgery and periods of hypotension increase the risk of pressure sores. Care should be taken to reduce pressure with soft padding. During long procedures it is advisable to relieve pressure and massage vulnerable areas intermittently.
Postoperative management
Unless patients are undergoing minor surgery, oxygen should be prescribed for at least 24hr. High-dependency facilities are ideal after major surgery.
Fluid balance, vital signs, serum electrolytes, and haematology must be carefully monitored and treated appropriately. Patients with CVS disease may need to have an Hb of >9–10g/dl.
In postoperative confusion a careful search must be made for reversible organic causes.
Pain is often poorly managed in patients with confusion and dementia. It is important to realise that these patients also feel pain and poor control may worsen confusion. NSAIDs should be used with caution. IV and SC opioids may be unreliably absorbed and elderly patients may have difficulty using a PCA. Regional techniques or an IV opioid infusion (with appropriate supervision) may be the most appropriate technique of pain relief.
Early establishment of enteral nutrition by nasogastric tube, if necessary, may improve outcome.
Early physiotherapy, mobilisation, and thromboprophylaxis are extremely important.
Key points
Avoid sedative premedications and use regional analgesic techniques where possible to minimise the requirement for opioids.
Monitor temperature and use active warming devices to prevent hypothermia.
Maintain a low threshold for invasive monitoring (CVP, art line).
In edentulous patients, leaving false teeth in place may help to maintain airway patency and facemask seal.
Drug/MAC requirements are reduced. Use NSAIDs with caution. Consider a COX-2 selective agent or co-administration of a gastroprotective drug.
Take care with positioning and intermittently relieve pressure during long procedures to reduce the risk of pressure sores.
In postoperative confusion, search for reversible organic causes in all systems, e.g. pain, hypoxaemia, distended bladder, myocardial/cerebral ischaemia, electrolyte disorder, drugs.
Encourage early mobilisation and consider thromboprophylaxis if mobilisation will not be rapid.
Postoperative cognitive dysfunction (POCD)
POCD is persistent impairment of cognitive functions such as memory and concentration in the absence of a clear precipitating event or central nervous system pathology. It is distinct from postoperative delirium which is associated with altered level of consciousness and is transient. The cause is unclear. It is likely to be multifactorial and and may have an inflammatory component. It is more common after cardiac than non-cardiac surgery. The incidence of POCD in patients over 70yr of age following major non-cardiac surgery may be as high as 29% 1wk following surgery and 14% at 3 months. It is lower following minor surgery. The severity is variable, but it may have a significant impact upon quality of life and independence. Although the incidence of early POCD may be lower following regional anaesthesia the incidence of prolonged POCD is the same following regional or general anaesthesia. Other than maintenance of oxygenation and stable haemodynamic parameters it is not possible to recommend any anaesthetic technique to reduce the incidence of POCD.
When not to operate
Heroic curative surgery may not be appropriate if the chance of benefiting the patient is felt to be very low. Decisions regarding futility of surgery are difficult and should be taken at consultant level, with involvement of the patient and family. Palliative procedures to improve quality of life should be considered if the patient is adequately prepared. These decisions must be carefully documented.
Further reading
