Sivagnanavel Senthuran and Nages Nagaratnam
Historical Perspective
Throughout history, there has been a continuous search for a remedy to relieve pain. According to the Bible, God created Eve from one of Adam’s ribs by putting him to sleep [1]. The ancient Romans and Greeks used various methods such as inhalation of fumes of hemp and carbon dioxide and the use of mandragora, amongst others, to dull consciousness and pro- duce sleep [2]. The word ‘anaesthesia’ of Greek derivation signifies loss or lack of feeling of sensation, and the word
‘anaesthesia’ in relation to surgery dates from 1846 [2, 3]. It was this year the pain of surgery was eliminated [4] when William Morton, a young dentist, administered ether to a patient before extracting a tooth and proved that ether was safe and effective anaesthesia when inhaled in proper dose [4].
Arthur Ernest Guedel, a US-born anaesthetist, gave a thorough description of nitrous oxide and was amongst the pioneers of cuffed endotracheal tubes [5] which led the way to provide positive pressure ventilation [4]. Today, innovations in science and engineering in combination with a systems approach to safety and training have made anaesthesia safer than flying.
Demographic and Other Characteristics of the Very Old
The very old suffer from chronic illnesses and increased dis- ability, frailty, hospitalisation and institutionalisation. There is an increasing incidence of cardiovascular diseases with increas- ing age such as heart failure, hypertension and ischaemic heart disease. The elderly are inclined to develop heart failure due to
age-related changes in the cardiovascular system and high prevalence of hypertension and coronary heart disease [6]. The Framingham study showed that heart failure increased with age. The prevalence of heart failure in age groups 60–69, 70–79 and >80 years was 2.3%, 4.9% and 9.1%, respectively [7]. In the elderly, COPD occurs with increasing frequency and sever- ity and is associated with cardiovascular comorbidity. The elderly are more prone to develop pneumonia due to the decreased ability to mount an immune reaction with age which is termed immunosenescence.
Impact of Age-Related Structural and Functional Changes
Age-related changes must be distinguished from age-related diseases. The very old demonstrate a reduction in physiolog- ical reserve and an inability of organ systems to respond to illness and surgical stress [8, 9].
Cardiovascular
A variety of alterations in cardiovascular physiology [10]
(Box 9.1) make the elderly more vulnerable to cardiac mor- bidity. There is a loss of myocytes with hypertrophy of remaining cells [11]. The left ventricular diastolic filling rate decreases to 50% of the peak rate by the age of 80 [12]. The elderly patient compensates poorly for hypovolaemia due to diastolic dysfunction and decreased vascular compliance [13]. Calcification of the fibrous skeleton involves the valvu- lar apparatus and conduction system [14]. The elderly patient is prone to conduction delay and atrial and ventricular ectopy due to fibrosis or calcification of the conduction pathways [15]. The incidence of cardiac arrhythmias increases with age both at rest and on exercise [16]. There is blunting of the beta- adrenergic responsiveness [9, 17, 18]. The cardiac output is however maintained despite reduced early diastolic filling through the use of the Frank-Starling mechanism [13–15].
S. Senthuran (*)
Department of Intensive Care Medicine, Townsville Hospital, Townsville, QLD, Australia
N. Nagaratnam
Sydney Medical School, The University of Sydney, Sydney, NSW, Australia
e-mail: [email protected]
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There is a loss of arterial compliance with ageing contributing to left ventricular hypertrophy and systolic hypertension [14].
Respiratory
There are age-related changes in the anatomy, physiology and immunology of the respiratory system that impact on perioperative assessment and postoperative care (Box 9.2).
Anatomically, there are loss of thoracic intervertebral disk spaces and increased kyphosis, which results in stiffening of the chest wall and a decrease in vital capacity as well as in the fraction of exhaled volume in 1 s (FEV1). There are also loss of lung elasticity and reduction in alveolar sur- face area which together result in homogenous enlarge- ment of air spaces and has been referred to as ‘senile emphysema’. Physiological changes of ageing include increased air trapping and hyperinflation due to changes in the lung parenchyma. Lung hyper-expansion, in turn, flat- tens the diaphragm altering the length-tension relationship of its muscle fibres resulting in weaker cough and decreased respiratory efficiency. Impairment in gas exchange occurs due to ventilation- perfusion mismatch (especially in the supine position) and a decline in alveolar surface area which affects oxygen diffusion. The elderly also have a reduced response to hypoxia and hypercapnia due to changes in central ventilatory control possibly related to reduced number of medullary ventral respiratory neurons.
Immunological changes include an imbalanced increase in pro-inflammatory cytokines (e.g. IL-1, TNF-a) even in the absence of a threat and a more blunted response to infec- tion or injury. Toll-like receptors which are important in the initiation of the innate immune response are reduced in expression as is the cytotoxic ability of alveolar macro- phages. The adaptive immune response is also impaired with decreased T cell activation and reduced antibody-
secreting ability of B cells. Thus the elderly are more vul- nerable to respiratory infections from a variety of pathogens [19].
Pharmacokinetics and Pharmacodynamics
Many of the age-related physiological changes in the func- tion and composition of the body result in many pharmaco- kinetic changes in the elderly [22]. With advancing age, there is a reduction in the total body water and lean body mass with a relative increase in body fat [23–27]. The decrease in the water content of the body with ageing results in water- soluble drugs having a smaller volume of distribu- tion [27] and higher serum levels for drugs such as lithium and aminoglycosides. An increase in the fat content, how- ever, results in an increase in volume distribution and the half-life of fat- soluble drugs [22, 27] such as diazepam.
There is a progressive decline in counter-regulatory mecha- nisms (impaired homeostasis) in old age, and age-related changes in pharmacodynamics occur at the receptor site or signal transduction level [28]. In old age, the pharmacody- namic changes alter the sensitivity of drugs [26]. Some drug effects are augmented. There is now evidence to suggest that there is altered ‘sensitivity’ at the receptor site to a given concentration of the drug in the elderly. Enhanced sensitiv- ity to warfarin, for example, is the probable reason for its increased toxicity [29].
Liver
Due to 20–50% reduction in the blood flow and 20–30%
decrease in liver mass with increasing age [30], first-pass Box 9.1. Age-Related Changes Which May Affect
Cardiovascular Performance Diastolic dysfunction
Blunting of the beta-adrenergic responsiveness Fibrotic involvement of conduction pathways Resetting of baroreceptor reflex
Increased stiffness and decreased vascular compliance Elevated levels of catecholamines
Information sources; Pugh andWei [14]; Priebe [9]
Box 9.2. Age-Related Changes Which May Affect Respiratory Performance
Stiffening of the chest wall.
Increase in functional residual capacity and residual volume.
A decline in the diffusion capacity.
Increase in pulmonary vascular stiffness, vascular pressures and resistance due to changes in pulmonary vasculature.
Ventilation control diminishes.
Information sources: Taylor and Johnson [20];
Oyarzun [21]
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metabolism is reduced [31]. With ageing, there is a decline in the intrinsic metabolic activity of hepatic parenchyma and hepato-biliary function, with shifts in the expression of a variety of proteins resulting in a moderate reduction in Phase 1 metabolism of many drugs [22, 32]. Phase 2, however, is unchanged with ageing. Conjugation and oxidative reactions by the hepatic microsomal enzymes are involved in drug metabolism [24, 33]. Conjugation, reduction and hydrolysis are not altered [29]. Oxidative metabolism through cyto- chrome P450 system decreases with ageing [34]. The elderly exhibit a decline in the hepatic clearance of certain drugs with increased frequency of adverse drug reactions and this has been attributed to a decrease in liver volume rather than to a reduction in Phase 1 metabolism [32].
Renal
In the elderly, the most important pharmacokinetic change is the decline in the excretory capacity of the kidney, and this is much more clinically significant than the decline of hepatic drug metabolism El [25]. The glomerular filtration rate, renal plasma flow and associated tubular function decline with age [35]. The renal function declines linearly from the age of 30 and mirrors the decline in drug excretion with age. Such decrease in drug clearance increases the blood levels and toxic effects of the drug [36].
Management of Anaesthesia
Anaesthetic techniques can be broadly categorised into gen- eral anaesthesia, regional anaesthesia (e.g. spinal, epidural, peripheral nerve blocks) and local anaesthesia (infiltration of surgical field). The choice of technique is based on several factors such as surgical procedure (e.g. laparotomies require muscle relaxation and cannot be done under regional anaes- thesia alone in comparison to caesarean sections which are usually done under spinal anaesthesia only), coexisting dis- ease and the need to minimise postoperative complications (e.g. epidural analgesia may be performed with local anaes- thesia and no opiate in those with severe sleep apnoea and right heart failure) and patient preferences (e.g. frail patients with multiple comorbidities undergoing cataract surgery often receive only local anaesthesia topically).
General Anaesthesia
General anaesthesia aims to achieve a deep enough level of sedation, analgesia and muscle relaxation to allow surgery.
Though historically this was accomplished with a high dose of a single volatile agent (ether, halothane, etc.), modern techniques rely on use of low doses of individual drugs spe- cific to each aim: sedation is achieved with short-acting volatiles such as sevoflurane, and analgesia is achieved with potent but short-acting opioids such as fentanyl and muscle relaxation with agents such as rocuronium or cisatracurium.
Though the conduct of anaesthesia is nuanced and depen- dent on the surgical procedure and patient factors, broad principles affecting the management of the elderly are out- lined in the table below [37] (Table 9.1).
Age-related changes such as depletion of neurotransmit- ters, reduced neuronal density and reduced innervation of skeletal muscles may cause a reduction in anaesthetic requirements [38].
Regional anaesthetic techniques may be suitable for cer- tain operations usually involving the limbs or extremities.
They can also be used in combination with general anaesthesia for postoperative analgesia. Non-randomised studies and propensity score matched reviews have sug- gested that older patients undergoing general anaesthesia for hip surgery have a higher incidence death, stroke, respi- ratory failure and intensive care unit admission [39].
Problems with using regional techniques include surgical acceptance of having a semi-awake patient, the risk of fail- ure of the block, the limitations on operative time imposed by the duration of the block and need for specific skills in performing the technique avoiding complications like nerve injury. The very old may also have a higher incidence of delirium or dementia, and it can be challenging to obtain consent for the procedure or win their co-operation for posi- tioning for the block.
Risk Scoring and Assessment
There are several risk assessment systems that have evolved for different types of surgery. These systems can be specific for certain types of surgery (e.g. EuroSCORE for cardiac surgical risk assessment) and particular diseases (e.g. Lee’s Revised Cardiac Risk Index for risk of cardiac death after noncardiac surgery) or specialty-specific (e.g. the American Society of Anaesthesiologists (ASA) grading system to the complex American College of Surgeons National Surgical Quality Improvement Program risk calculator (NSQIP risk)).
Most of these scoring systems are better at predicting mortal- ity rather than outcomes relevant to the very old such as mor- bidity and functional outcomes. Hence methods of risk assessment for the very old also need to consider geriatric syndromes like frailty, malnutrition, sarcopenia and delir-
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ium. The comprehensive geriatric assessment followed by patient-centred interventions has been shown to improve outcome (chances of being alive and in their own home at 6 months) in medical inpatients, but work is ongoing to assess its preoperative role in the elderly [40]. The risk fac- tors for surgery include age over 65 years, coexisting ill- nesses, urgency and type of surgical procedure [41].
Myocardial infarction is the commonest non-surgical cause of death after noncardiac surgery. There are several cardiac risk indices, Goldman risk index, Detsky’s cardiac risk index and Eagle’s cardiac risk index, amongst others. In noncardiac surgical patients, the Lee index has been consid- ered to be the best currently available cardiac risk prediction index [42]. It is simple and extensively validated and pro- vides a good estimate of the preoperative risk [43]. Lee’s Revised Cardiac Risk Index consists of six independent clinical determinants: history of ischaemic heart disease (angina or myocardial infarction), congestive heart failure, stroke/TIA, renal dysfunction, diabetes mellitus and high- risk surgery [42]. Furthermore preoperative and postopera- tive risks can be evaluated when adapted for surgical procedures. Vascular, intra-abdominal, thoracic, major orthopaedic and any emergency procedures are considered to have a high risk [44]. NICE preoperative testing guide- lines grade surgical severity into three classes, for example, breast biopsy is classed as minor, knee arthroscopy as inter- mediate and total knee replacement as major [45]. High-risk surgical procedures and reduced functional capacity predict a poor perioperative outcome [46]. There is a high preva- lence of preoperative medical problems in this group of patients [47] that require medical attention. The extent of
the evaluation will depend on the status of the patient and the urgency for intervention. A multidisciplinary approach can reduce complications following surgery [48].
Preoperatively physicians/geriatricians have a crucial role in making medical recommendations [49], to evaluate, correct clinical abnormalities [48] and stabilise the patient before surgery.
Physical fitness or functional capacity can be estimated by the ability to perform basal activities of daily living or measured in metabolic equivalents (METs). Metabolic demand at rest is equivalent to 1 MET, 2 flight of steps to 4 METs and strenuous sports to >10 METs. Less than 4 METs indicates poor functional capacity [50]. Achieving 6–8 METs of activity without significant symptoms of dyspnoea is considered to represent good functional capacity in a 50–60-year-old patient [44]. Functional capacity can be esti- mated by the ability to perform the activities of daily living.
Physical status can be determined by the ASA (American Society of Anaesthesiologists) Physical Status Classification System [51] score. The ASA is an assessment of the patient’s overall health status and is based on six grades and is widely used to ascertain the overall risk [52]. ASA grade 1 is a nor- mal healthy person and ASA grade 6 is a declared brain-dead patient. In between are various grades of system disease from mild to severe to moribund patient [51]. The New York Heart Association (NYHA) assigned patients to one of four functional classes depending on the degree of effort needed to elicit symptoms of shortness of breath or chest pain. The severity of the preoperative functional impairment is linked to postoperative mortality, increasing from 4% in NYHA class 1 to 60% in class 4 [52].
Table 9.1 Age-related changes and their impact on the management
System Changes Impact on management
CNS Reduced brain mass, neurotransmitters and receptors.
Reduced autonomic responsiveness. Higher sensitivity to anaesthetics
Decreased doses of volatile agents, titration of drugs to effect than using standard doses
Cardiovascular Systolic hypertension, diastolic dysfunction, labile blood pressure, sensitivity to anaesthetics
Titrate fluid therapy to monitored indices of filling to avoid excess, higher need for infusions of vasopressors to maintain blood pressure
Respiratory Decreased lung and chest wall elasticity, weaker muscles. Increased VQ mismatching, higher risk of hypoxaemia and aspiration
Preoxygenation, minimising sedative drug doses, monitoring to ensure adequate reversal of muscle relaxants. Early mobilisation and chest physiotherapy postoperatively
Liver Reduced liver mass and blood flow. Lower albumin levels
Reduce dosing interval of hepatically cleared drugs and highly albumin-bound drugs
Kidney Reduction in renal mass, muscle mass and total body water makes creatinine a poor predictor of renal function. Decreased ability to handle salt and water overload
Reduce repeat doses of renally excreted drugs (e.g.
morphine), minimise use of drugs with renal toxicity (e.g. NSAIDs)
Skin, muscle and fat Frail skin, decreased muscle mass and subcutaneous fat with increased central fat. High risk of hypothermia.
Increased volume of distribution of fat-soluble drugs and reduced volume of distribution of hydrophilic drugs
Active warming of fluids and patient, monitoring of core temperature. Allow prolonged elimination time for fat-soluble agents including volatile anaesthetics
Modified from Strom et al. [37]
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Preoperative Evaluation
Preoperative Cardiac Management for Cardiac Surgery/Noncardiac Surgery
Preoperative evaluation and risk assessment are performed firstly to weigh the potential surgical benefit against the risk of an adverse medical or surgical complication and secondly to identify any comorbidity that can be optimised. As the elderly population grows, issues such as frailty, multi- comorbidity and terminal illness become more prevalent in the preoperative setting and cloud the risk-benefit decision- making processes. To better guide this growing group of complex patients, a value-based approach is also needed that takes into account patient preferences and atti- tudes to end- of- life care in addition to the traditional disease- centred approach to managing the problem at hand.
Preoperative evaluation of the elderly commences with the history of the surgical problem and, in particular, the surgical approach proposed. The evaluation also considers the patient’s medical comorbidities, medication and allergy history and previous anaesthetic history including techniques used and any complications encountered. The physical assessment of the airway aims to identify any difficulties that might be encountered in securing it. A cardiac examination looks for signs of heart failure or valvular conditions such as aortic ste- nosis and mitral regurgitation. The respiratory exam aims to assess for signs of wheezing, impaired cough or inability to clear secretions and often incorporates the smoking history.
The patient’s baseline cognitive function and risk of delirium are also important in assessing their suitability to use tech- niques like patient-controlled analgesia which are common after major surgery utilising either intravenous opiates or epi- dural local anaesthetic infusions. Renal function is evaluated by measurement of their serum creatinine, accepting that serum creatinine is dependent on muscle mass and patients who are cachectic may have a normal creatinine even with renal impairment. Increasingly frailty as a syndrome is being assessed formally preoperatively, and its recognition has been shown to affect surgical and anaesthetic decision-making [53]. Though blood tests for full blood count, urea and elec- trolytes, ECG and CXR are very common, the threshold for performing further invasive testing is dependent on the com- plexity and invasiveness of the surgery as well the pretest probability of finding a correctable problem.
The outcome of the assessment is a postoperative plan which is developed in discussion between the patient, surgeon, anaesthetist and any other clinicians. Increasingly the postop- erative plans take into account advanced care plans that may have been devised before an operation was ever considered.
Such advanced care plans often require reinterpretation in the perioperative context given the goal of surgery in the elderly is often to allow survival with a better quality of life.
Postoperative Complications in the Elderly Postoperative complications mainly arise from the surgery, the patient’s pre-existing comorbidities or iatrogenesis. It is worth exploring in more detail common general complica- tions relevant to the elderly such as anaemia, immobility, infections and postoperative cognitive dysfunction including their principles of management.
Anaemia is a common complication after laparotomies and hip surgery in the elderly and may present as hypotension or tachycardia unresponsive to fluid challenge, chest pain due to cardiac ischaemia or pallor and lethargy resulting in a poor abil- ity to mobilise. The FOCUS trial [54] explored liberal (aiming Hb 10 g/dL) vs. restrictive (aiming 8 g/dL) transfusion threshold after hip surgery in the elderly (n = 2016 patients with an aver- age age of 82) and included patients with cardiac risk factors.
Though there was a slightly higher proportion of patients who had inability to walk unassisted at 60 days in the restrictive group (28.1% vs. 27.6%), the restrictive group received a median of 0 units of blood, had a pre-transfusion Hb of 7.9 g/dL and had a lower 30-day mortality of 4.3% (vs 5.2%). There were no significant differences in clinical outcomes between the groups. Current strategies for management of anaemia include aggressive management of anaemia preoperatively where time allows by supplementation of iron and/or erythropoietin but reserving transfusion for where there is evidence of ongoing bleeding (persistently dropping Hb), hypotension or tachycardia unresponsive to fluids or cardiac decompensation [55].
Postoperative immobility is associated with pneumonia, pressure ulcers and thromboembolism. It contributes to increased risk of delirium and loss of bone density.
Immobility can arise from pre-existing conditions, postop- erative pain and tethers applied in the hospital (e.g. oxygen tubing, urinary catheters, intravenous infusions, cardiac monitors, etc.) Management of immobility requires a multi- disciplinary approach between surgeons, anaesthetists, nurs- ing staff and physiotherapists. Surgeons can minimise tissue injury and operative time and postoperatively remove tethers that hinder mobilisation. Anaesthetists and pain specialists can use drugs which are short acting and devise an appropri- ate postoperative analgesia strategy minimising sedation and utilising appropriate regional or local anaesthetic techniques.
Monitoring for side effects like constipation or urinary reten- tion is also vital. Nursing staff and physiotherapists are indis- pensable in delivering specific interventions to encourage mobility [56]. Prehabilitation is a topic of research interest in assessing the ability of subjects to be optimised through a programme of interventions (physical activity, nutrition, psy- chological support) before a planned operation with the aim of improving their recovery from the surgery. Though the concept has merit from a patient perspective, it is expensive and has not been subject to real-world rigorous efficacy stud- ies in the preoperative frail patient population.
9 Geriatric Anaesthesia