Geriatric Patients: Systemic Changes and Anaesthesia Considerations

1. Body Composition Changes

• Barash, Cullen & Stoelting's Clinical Anesthesia 9e, p. 2720

2. Central Nervous System Changes

• Decreased white matter density in the prefrontal cortex and anterior corpus callosum
• Reduced synaptic density and cholinergic transmission
• Decreased dopaminergic and noradrenergic tone
• Reduced MAC (Minimum Alveolar Concentration): MAC decreases approximately 6% per decade after age 40 - elderly patients need significantly less volatile agent
• Alzheimer disease occurs in ~10% of those ≥65; mild cognitive impairment (MCI) in 10-20% - many undiagnosed pre-operatively
• Preoperative cognitive impairment is the strongest predictor of postoperative delirium

Key Anaesthetic Points - CNS:

• Reduce induction doses of all agents (propofol, thiopentone, etomidate) by 30-50%
• Allow longer time to peak effect before redosing (arm-brain circulation time is prolonged)
• Avoid anticholinergic drugs (atropine, scopolamine, some antihistamines) - they precipitate delirium
• Use the Beers Criteria to avoid inappropriate medications in the elderly
• BIS monitoring can help titrate depth and avoid overdose
• Screen preoperatively with validated cognitive tools (MMSE, MoCA)
• Miller's Anesthesia 10e, pp. 9289-9290; Barash 9e, p. 2706

3. Cardiovascular Changes

Structural Changes:

• Left ventricular hypertrophy and diastolic dysfunction (impaired relaxation) - present in >50% by age 70, >67% by age 80
• Arterial stiffness (increased afterload) due to collagen cross-linking and elastin degradation
• Reduced β-adrenergic receptor density and responsiveness → blunted heart rate response to stress
• Fibrosis of the cardiac conduction system → increased risk of arrhythmias (AF, SSS, heart blocks)
• Valve degeneration - calcific aortic stenosis and mitral annular calcification common
• Baroreceptor reflex impairment → orthostatic hypotension, exaggerated BP swings

Functional Consequences:

• Resting cardiac function may appear normal, but functional reserve is reduced
• Heavy dependence on preload and atrial kick to maintain cardiac output - loss of sinus rhythm (e.g., AF) can cause acute haemodynamic deterioration
• Reduced maximum heart rate (~220 - age); blunted chronotropic reserve

Key Anaesthetic Points - CVS:

• Avoid sudden large BP swings during induction (propofol boluses cause severe hypotension)
• Prefer etomidate over propofol in haemodynamically compromised elderly patients
• Maintain sinus rhythm; treat new-onset AF aggressively
• Cautious fluid management - diastolic dysfunction makes them vulnerable to both hypovolaemia and fluid overload
• Spinal/epidural anaesthesia: extend block establishment slowly to avoid precipitous hypotension
• Vasopressors (phenylephrine, metaraminol) should be readily available at induction
• Miller's Anesthesia 10e, pp. 9290-9292; Barash 9e, pp. 2722-2730

4. Pulmonary Changes

Structural:

• Loss of elastic recoil (due to collagen/elastin changes) → increased compliance but reduced elastic support for small airways
• Chest wall stiffness increases → increased work of breathing
• Residual volume increases; expiratory reserve volume decreases (total lung capacity largely unchanged)
• Closing capacity can exceed functional residual capacity (FRC) even at rest → airway closure during normal tidal breathing → increased V/Q mismatch

Functional:

• FEV1 declines ~30 mL/year from age 30
• PaO2 decreases (age-related formula: PaO2 = 100 - 0.4 × age mmHg)
• ~50% reduction in ventilatory response to hypercapnia; even greater blunting of hypoxic ventilatory response
• ~75% of people >65 have some degree of sleep-disordered breathing
• Impaired cough and swallowing reflex → aspiration risk

Key Anaesthetic Points - Respiratory:

• Pre-oxygenate thoroughly (reduced FRC means faster desaturation on apnoea)
• Use lung-protective ventilation (low tidal volumes, appropriate PEEP)
• Awake fibreoptic intubation if airway concerns (reduced neck mobility, atlantoaxial changes)
• Neuraxial > general anaesthesia where feasible to preserve respiratory drive
• Consider Rapid Sequence Induction (RSI) given aspiration risk
• Cautious opioid use postoperatively - blunted hypoxic response + sleep apnea = dangerous combination
• Mandatory post-op oxygen supplementation; consider HDU monitoring for major surgery
• Barash 9e, pp. 2738-2741

5. Renal Changes

• Renal cortical mass decreases 20-25% with age
• GFR declines ~10 mL/min per decade after age 30 (from ~120 to ~60 mL/min by age 70)
• Important: Serum creatinine may remain in the normal range because muscle mass (creatinine production) also decreases - use CKD-EPI or Cockcroft-Gault formula to estimate actual GFR

Key Anaesthetic Points - Renal:

• Dose-adjust renally eliminated drugs: morphine (active metabolite M6G accumulates), NSAIDs (avoid), aminoglycosides, neostigmine, rocuronium
• Sugammadex reversal preferred over neostigmine (safer in renal impairment at moderate doses)
• Avoid nephrotoxic drugs peri-operatively
• Careful fluid balance monitoring
• Barash 9e, p. 2721

6. Hepatic Changes

• Liver mass decreases with age; hepatic blood flow decreases 20-40%
• Phase I metabolism (oxidation, reduction, hydrolysis) mildly reduced
• Phase II metabolism (conjugation) relatively preserved
• Plasma clearance of high-extraction drugs (e.g., lidocaine, morphine, fentanyl) reduced due to decreased blood flow

Key Anaesthetic Points - Hepatic:

• Slower clearance of drugs with high hepatic extraction ratios
• Reduce infusion rates for propofol and remifentanil at high-extraction end
• Prolonged half-life for long-acting benzodiazepines (avoid or minimize)

7. Thermoregulation

• Impaired vasoconstriction and shivering reflexes (threshold and response are both blunted)
• Decreased basal metabolic rate → less heat production
• Inhalational agents and propofol further impair thermoregulatory thresholds by ~4°C; aging adds another ~1°C of impairment
• Elderly patients become hypothermic faster and more profoundly

Risks of Hypothermia:

• Myocardial ischaemia and arrhythmias
• Surgical site infection
• Coagulopathy and increased blood loss
• Impaired drug metabolism (prolonged action)
• Shivering postoperatively increases O2 consumption

Key Anaesthetic Points - Thermoregulation:

• Active warming from the start (warm blankets, forced-air warming, warmed IV fluids)
• Pre-warm the OR
• Monitor temperature continuously
• Treat shivering (pethidine 25 mg IV, clonidine, magnesium)
• Barash 9e, pp. 2740-2742

8. Pharmacological Changes in the Elderly

9. Preoperative Assessment

1. Frailty Assessment - use validated tools (e.g., Clinical Frailty Scale, Edmonton Frail Scale, FRAIL questionnaire). Frailty is the single strongest predictor of poor surgical outcomes - more predictive than chronological age.
2. Cognitive Screening - MMSE, MoCA, 3-item recall. Pre-existing cognitive impairment is the strongest risk factor for postoperative delirium.
3. Functional Status - Activities of Daily Living (ADL), Instrumental ADL (IADL); exercise tolerance in METs.
4. Nutritional Status - Malnutrition is common and independently increases complications.
5. Polypharmacy Review - elderly patients average 5-8 medications; drug interactions and Beers Criteria medications must be identified.
6. Advance Directives - Document resuscitation preferences, healthcare proxy; critical ethical discussion before major surgery.
7. Social Support and Discharge Planning - Assess who will care for patient post-discharge; arrange early occupational therapy and physiotherapy input.

• Miller's Anesthesia 10e, p. 9304; Barash 9e, pp. 2754-2755

10. Postoperative Complications in the Elderly

11. Regional vs. General Anaesthesia

• Patient preference and comorbidities
• Surgical procedure
• Anaesthetist experience
• Avoidance of haemodynamic instability

• Preserves respiratory drive
• Better postoperative pain control (reduces opioid use)
• May reduce VTE risk
• Avoids airway instrumentation
• Suitable for hip, knee, urological, colorectal surgery

• Higher block levels due to reduced epidural space (adipose/venous engorgement), epidural fat compression, decreased CSF volume
• Reduce spinal dose by ~25-30% (hyperbaric bupivacaine 7-10 mg vs standard 12-15 mg)
• Exaggerated hypotension - have vasopressors ready
• Coagulation status critical (many elderly on anticoagulants)

Summary: The "GERIATRIC" Mnemonic for Anaesthetic Considerations

• Barash, Cullen & Stoelting's Clinical Anesthesia, 9th edition, Chapter 34 (Geriatric Anesthesia), pp. 2706-2780
• Miller's Anesthesia, 10th edition, Chapter 61 (Geriatric Anesthesia), pp. 9288-9310
• ACS NSQIP / American Geriatrics Society Best Practices Guidelines for Perioperative Management of the Geriatric Patient (2016)