Respiratory Changes

With advancing age, structural changes occur in lung tissue and chest wall. The lung parenchyma loses elastic recoil and becomes more compliant, while the chest wall becomes stiffer (alterations in intercostal muscles, calcification of the ribs and vertebral joints).

The volume-pressure curve of the aged total system (lung and thorax) is flatter and shows less compliance (Sprung et al. 2006). In addition, age-associated osteoporosis may cause both dorsal kyphosis and an increase in anteroposterior chest diameter resulting in changes in thorax geometry.

The remodeling of the chest wall with aging flattens the curvature of the diaphragm, which leads to a reduction in maximal trans-diaphragmatic pressure. Reductions in respiratory muscle mass may also contribute to a decrease in the force produced by respiratory muscle activity (Larsson 1983).

Changes in upper airways also occur. Loss of muscular pharyngeal support predisposes elderly subjects to upper airway obstruction. In addition, loss of the protective reflexes of coughing and swallowing presumably owing to an age-related peripheral deafferentation, together with decreased central nervous reflex activity, increases the risk of aspiration (De Leon 2016).

Elderly individuals have an approximately 50% decrease in their ventilatory responses to hypoxia and hypercapnia. Responses to isocapnic hypoxemia during sleep can be depressed even more.

Anesthetic Considerations

Respiratory complications after surgery account for approximately 40% of the perioperative deaths in patients over 65 years of age (Manku and Leung, 2003). Literature confirms that advanced age is a risk factor for postoperative pulmonary complications, even after adjustment for other comorbid conditions.

A study of stratified patients based on the American Society of Anesthesiologists (ASA) class (Smetana 2006) showed that mortality for patients in a given class was similar, regardless of age.

The surgical site is the single most important predictor of pulmonary complications. High-risk surgeries include thoracic, upper abdominal, aortic, neuro and peripheral vascular. Other procedure-related risk factors include surgery lasting longer than 3 hours, the use of general anesthesia and emergency surgery (Arozullah et al. 2000).

Lung expansion interventions, such as incentive spirometry, deep breathing exercises and continuous positive airway pressure, reduce pulmonary complications in elderly surgical patients.

When feasible, laparoscopic techniques should be considered, especially in elderly patients with pulmonary compromise. Fuks et al. (2016) demonstrated that laparoscopy decreases pulmonary complications in patients undergoing major liver resection.

Furthermore, opioids represent a class of drugs with particular significance to respiratory function in the elderly. As elderly patients may be particularly sensitive to opioid analgesics, they should be carefully titrated, in order to avoid postoperative respiratory depression (Freye and Levy 2004). When possible, epidural analgesia is the best alternative, improving pain control and reducing morbidity.

A meta-analysis conducted by Pöpping etal. (2014) concluded that, compared with systemic opioid analgesia, epidural local anesthetics reduce the risk of postoperative pulmonary complications.

During the immediate postoperative period it is important to carefully manage all drugs that may weaken the respiratory muscles or affect the drive to breathe. As an example, postoperative residual curarization is associated with a greater incidence of major and minor respiratory complications (Martinez-Ubieto et al. 2016).

Cardiac Changes

Age affects the cardiovascular system in many ways: autonomic and baroreceptor function decline, cardiac contractility decreases, blood vessels become less elastic leading to hypertension.

Altogether these changes lead to decreased cardiovascular capacity in the elderly, explaining the increased cardiodepressant effect of many anesthetics.

Prevalence of heart failure, including systolic and diastolic ventricular dysfunction, increases with age. The heart becomes stiffer, leading to higher ventricular diastolic pressures. Atheroma becomes more frequent, and coronary disease is a common problem in the elderly, leading to a high risk of postoperative myocardial injury and myocardial infarction (Bateman et al. 2009). Even in patients without specific cardiac diseases, the cardiac reserve is altered.

Aging is also associated with a thickening of the heart valve, through calcification and fibrosis. As a result, different degrees of valve dysfunction, such as aortic stenosis by calcification (Monckeberg disease) are common in the elderly. This is associated with a significant increase in cardiovascular mortality, especially when stenosis becomes symptomatic (Otto et al. 1999).

Conduction disorders become more frequent with age. High-grade cardiac conduction abnormalities, such as complete atrio-ventricular block, if unanticipated, may increase operative risk and necessitate temporary or permanent transvenous pacing.

Anesthesic Considerations

The ESC and the ACC/AHA regularly produce recommendations and guidelines on perioperative cardiovascular evaluation and management of patients undergoing non-cardiac surgery that are effective for elderly patients. Evaluation of these patients is based on assessing CV risk factors using the Lee Score. The Revised Cardiac Risk Index has been recently validated in a large cohort of elderly patients (Andersson et al. 2015). Evaluation of functional capacity using questions, for example, about the capability of climbing two flights of stairs or walking up a hill is the second step of the cardiac evaluation. The type of surgery is also very important to consider. Non-invasive surgery or fast-track programs have to be preferred to improve postoperative outcome.

In high-risk patients, assessed by a Lee score >1, low functional capacity and high-risk scheduled surgery, non-invasive stress tests (dobutamine echocardiography or nuclear imaging) can be helpful in determining coronary risk. In such high-risk patients, optimal medical treatment has to be evaluated, β-blockers and statins have to be considered regarding their protective risks and hazards (POISE Study Group 2008)

Preoperative ECGs are indicated as a reference exam, useful in cases of postoperative troponin elevation. Age is an indication for preoperative ECG, mostly for high-risk surgery. Monitoring cardiac output using tools such as aortic Doppler has been shown to be effective in decreasing postoperative morbi-mortality.

Elderly patients need careful monitoring to preserve the perioperative balance of supply/demand for oxygen. Hemodynamic instability is consequently more frequent in the elderly and results in increased morbidity. So, non-invasive monitoring may be the solution for moderate- to high-risk patients who may not typically receive an arterial line. A new monitoring system, Clearsight®, offers a simple approach to monitoring hemodynamic parameters like stroke volume (SV), stroke volume variation (SVV), cardiac output (CO) and optimizing volume administration in patients at risk of developing complications.

Risk of Cognitive Complications

Postoperative cognitive decline (POCD) and postoperative delirium (POD) have been identified as important predictors of outcome in both cardiac and non-cardiac surgical patients. The elderly population exhibits an increased vulnerability to neurocognitive impairment triggered by surgical procedures, perioperative anesthetic management and age-related organ function decline and comorbidities (Evered et al. 2017).

As a rule, the shorter the duration of action of the anesthetic agent, the shorter the duration of cognitive impairment in the immediate postoperative period. But cardiovascular, respiratory, hepatic and renal insufficiencies are all associated with impaired brain performance.

The Bispectral Index (BIS) measures the depth of anesthesia and helps anesthetic titration based on an electroencephalogram-derived multivariate scale. Chen et al. (2015) studied the effect of BIS monitoring, and concluded that for every 1000 elderly patients undergoing major surgery, BIS-guided anesthesia in the range 40–60 would be able to prevent 23 patients from POCD and 83 from delirium. Mason et al. (2010) published a systematic review with meta-analysis focused on the influence of general, regional or combined anesthesia (general and regional) on POCD and POD. They found a non-significant association of general anesthesia with POCD and no correlation with POD. Based on their results, the authors suggest the use of regional anesthesia, especially in patients vulnerable to developing POCD or POD. It has been demonstrated that people with dementia generally have a higher risk of poor outcomes following surgery.

Risk of Hypothermia

Cardiovascular, hemorragic and infectious complications are significantly more frequent in hypothermic than in normothermic patients. Elderly and high-risk patients are more prone to developing perioperative hypotherma, and are more liable to hypothermia-related complications. The ideal monitoring site has to be chosen considering both the patient’s characteristics and the surgical procedure. Once identified, hypothermia has to be treated and the most effective are active forced-air skin warming systems. Active prewarming during the preoperative period has been also demonstrated to be efficient in reducing the development of intraoperative hypothermia. Humidification and warming of inspired gases, and warming of intravenous fluids are useful techniques when used in a multimodal approach with active skin warming to maintain perioperative normothermia.

Thiopental

A reduction in the central volume of distribution in the elderly causes higher concentrations for any given dose in comparison with the adult population. A 20% reduction in the induction dose and infusion rate is required in healthy elderly patients when compared to equivalent doses in younger patients (Stanski and Maitre 1990). No age-related change in brain responsiveness or pharmacodynamics was demonstrated when EEG was used as a measure of drug effect.

Propofol

A discrepancy exists in the literature concerning the importance of induction dose reduction in the elderly when propofol is given as a bolus. Reductions by 20–60% have been proposed to maintain the same level of effect. The potency of the drug is also increased in the elderly. When integrating the age effects on propofol pharmacokinetics and pharmacodynamics into dosage guidelines, a 75-year-old patient requires 30 to 50% less drug than a 25-year-old patient to maintain the same level of drug effect (Schnider et al. 1999). More pronounced adverse cardiovascular side effects are seen in the elderly. A greater induced fall in arterial pressure is observed, but it is also delayed in comparison with younger patients. The context-sensitive half-life is prolonged with advancing age and increased duration of infusion. Altered pharmacokinetics becomes clinically significant after a 1-hour infusion, requiring it to be stopped earlier in the elderly in order for recovery at the same time as younger patients.

Etomidate

The EEG effects of etominate are unchanged with age. However, due to pharmacokinetic modifications, the elderly require less than half the dose to reach the same stage of EEG endpoint as young adults.

Midazolam

A reduction in clearance with an increase in offset time is observed with aging. The potency of this agent is also increased in the elderly (Jacobs et al. 1995). Taken together, these changes suggest a 75% reduction in dose from age 20 to age 90. Context-sensitive half-life being prolonged in the elderly, the longer midazolam is administered, the greater the delay in recovery between younger and older subjects.

Ketamine

Pharmacodynamic changes are poorly characterized in the elderly, but a prolongation of duration of action is expected, due to decreased clearance.

Fentanyl and Alfentanil

No effect of age was found on the pharmacokinetics of these agents, but cutting the dose in half is required due to the shift in potency. Transdermal fentanyl absorption is increased in the elderly leading to higher concentrations and adverse effects. No change in the pharmacokinetics of oral transmucosal fentanyl citrate is reported with age.

Sufentanil

A small decrease in the central compartment volume in elderly patients would be expected to increase the effects of sufentanil in the first few minutes after a bolus dose, but not subsequently. The difference in dose requirement between young and old patients has a pharmacodynamic basis, and is consistent with the findings for fentanyl and alfentanil.

Remifentanil

A reduction of 50% in the C₅₀ value is also measured for EEG depression between the ages of 20 and 80. Pharmacokinetic studies show a reduction in central compartment volume and an increase in the half-life of plasma-effect site equilibration (t_1/2 k_e0) (Minto et al. 1997). All these modifications translate into dose changes for 65-year-olds for bolus administration (decrease by 50%), as well as for maintenance infusion (decrease by 75%). Onset is also slower, with peak drug effect reached 2–3 min after the bolus. The recovery is as fast as it is in young adults.

Morphine

A reduction of clearance by 50% has been described in the elderly, suggesting a prolonged duration of action. This requires a reduction in the maintenance dosing.

Suxamethonium chloride

Although plasma cholinesterase activity decreases with increasing age, this is insufficient to prolong the action of suxamethonium chloride.

Aminosteroids

Pancuronium:

decreased clearance is associated with prolonged duration of action which makes the use of this long-acting agent in the elderly questionable.

Vecuronium:

prolonged duration of action of vecuronium in the elderly is a result of an altered pharmacokinetic effect consistent with age-related decrease in renal and hepatic function.

Rocuronium:

significant prolongation of its action is described in the elderly due to a decrease in both distribution volume and plasma clearance.