Definition of Dyspnoea

"Dyspnea, which is an uncomfortable awareness of breathing, is commonly caused by cardiovascular or pulmonary disease."

• Goldman-Cecil Medicine

• It is subjective - there are no specific receptors or single neural pathways identified for it (unlike pain or cough)
• It is not synonymous with tachypnoea (increased rate) or hyperpnoea (increased depth); a patient can have rapid breathing without dyspnoea, and vice versa
• When the sensation is abnormal (i.e., occurring at rest or at activity levels that should not produce it), it is pathological

Special Forms of Dyspnoea

Mechanism of Dyspnoea Pathway in Cardiac Disease

Differentiation: Cardiac vs Respiratory Dyspnoea

1. Aetiology / Underlying Causes

2. History and Symptom Characteristics

3. Associated Symptoms

4. Physical Examination Findings

5. Investigations

6. Pathophysiology Summary

• In heart failure: "The most important cause of dyspnoea is pulmonary congestion that increases the accumulation of interstitial or intra-alveolar fluid, reduces lung compliance, and increases the work of breathing." (Goldman-Cecil Medicine)
• Orthopnoea mechanism: Supine position increases venous return from extremities and splanchnic bed → raises preload → worsens PCWP
• PND mechanism: Fluid redistribution from dependent tissues back to central circulation during sleep, accumulation of alveolar oedema over 1-2 hours

• The sensation of "chest tightness or constriction during breathing is typical of bronchoconstriction" (Goldman-Cecil Medicine)
• "The feeling that breathing requires increased work or effort is more typical of airway obstruction or neuromuscular disease" (Goldman-Cecil Medicine)

Quick Reference Summary Table

Definition of the Elderly

"While the chronological definition of a 'geriatric' or 'elderly' patient is typically 65 years of age or older, an age-only distinction does not necessarily correlate with a patient's physiology."

Sub-classification of the Elderly

Airway Concerns in Elderly Patients

1. Anatomical Changes Affecting the Airway

a) Dentition - Edentulousness

• Tooth loss is common in the elderly
• Edentulous patients are notoriously difficult to mask ventilate - the loss of teeth causes the cheeks to collapse inward, making it nearly impossible to achieve an airtight seal with a face mask
• Conversely, dentures, if present, may loosen during airway manipulation and obstruct the airway - they must be removed before intubation but kept in place during mask ventilation to maintain facial contour

"Elderly patients may not have teeth or dentures to help maintain airway patency; edentulous patients are often difficult to mask ventilate, and dentures may loosen and obstruct the airway." - Miller's Anesthesia, 10e

b) Cervical Spine Degeneration and Kyphosis

• Degenerative changes of the cervical spine (spondylosis, osteophytes, reduced disc height) severely restrict neck extension
• Kyphoscoliosis and reduced cervical mobility impair the ability to achieve the "sniffing position" needed for optimal laryngoscopy
• This directly increases the difficulty of direct laryngoscopy and intubation
• Forced neck extension in a patient with severe cervical spondylosis risks spinal cord injury

"Degenerative spine changes and kyphoscoliosis may complicate intubation." - Miller's Anesthesia, 10e

c) Chest Wall Stiffness

• Calcification of costal cartilages and rib joints leads to reduced chest wall compliance
• Decreased intervertebral space height and kyphosis cause a reduction in the FEV1/FVC ratio
• These changes limit ventilatory reserve and make bag-mask ventilation more effortful

d) Reduced Muscle Mass (Sarcopenia)

• Intercostal and diaphragmatic muscle strength decreases with age
• Reduced respiratory muscle strength limits the ability to generate effective coughs and deep breaths
• This predisposes to atelectasis, secretion retention, and postoperative pneumonia

2. Physiological Changes Affecting Airway and Respiratory Function

a) Reduced Lung Elasticity and Compliance

• Loss of elastin fibres in the lung parenchyma results in increased lung compliance (floppier lungs) but loss of elastic recoil
• This leads to early airway closure during expiration, air trapping, and emphysema-like changes even in non-smokers
• Dynamic airway collapse during forced expiration worsens V/Q mismatch

b) Altered Lung Volumes

• The increase in RV at the expense of VC means the elderly have less usable oxygen reserve
• Reduced FRC means the closing capacity approaches or exceeds FRC, especially in the supine position, causing dependent airway closure even during tidal breathing - this accelerates desaturation during apnoea

c) Impaired Gas Exchange

• Increased V/Q mismatch due to loss of alveolar surface area and capillary bed
• Decreased diffusion capacity (DLCO) across the alveolar-capillary membrane
• Baseline PaO2 is lower in the elderly (estimated as: PaO2 = 100 - [age/4] mmHg)
• These factors mean elderly patients desaturate faster and more severely during apnoea, difficult intubation, or any period of hypoventilation

d) Blunted Chemo-receptor Response

• The ventilatory response to hypoxaemia is reduced by ~50% in healthy elderly individuals
• The ventilatory response to hypercapnia is also diminished
• This is particularly dangerous because patients may not mount a compensatory hyperventilation when hypoxic or hypercapnic, masking impending respiratory failure

"Due to deranged respiratory drive seen with aging, elderly patients will have a diminished physiologic response to both hypoxaemia and hypercapnia." - Mulholland & Greenfield's Surgery

e) Impaired Mucociliary Clearance

• Dysfunction of the mucociliary escalator with age leads to retained secretions in the airways
• This predisposes to aspiration pneumonitis and hospital-acquired pneumonia
• Combined with reduced cough effectiveness (weakened respiratory muscles), secretion clearance is markedly impaired

3. Protective Reflex Impairment

• Upper airway protective reflexes (gag, cough, swallow) are diminished with ageing
• Pharyngeal muscle tone decreases, increasing the risk of oropharyngeal obstruction and obstructive sleep apnoea
• Aspiration risk is significantly higher - reduced laryngeal sensitivity, impaired swallowing coordination (dysphagia), and delayed gastric emptying all contribute
• Gastro-oesophageal reflux is more prevalent in the elderly, further increasing aspiration risk

4. Pharmacological Considerations in Airway Management

• Elderly patients have reduced drug requirements for sedatives, induction agents, and opioids due to:
  • Decreased hepatic blood flow and Phase I metabolism
  • Reduced renal clearance
  • Increased body fat-to-lean ratio (altered drug distribution)
  • Decreased plasma proteins (higher free drug fraction)
• Neuromuscular blockade: Normal changes at the neuromuscular junction with ageing alter the pharmacodynamics of blocking agents - onset may be slower but duration prolonged
• Polypharmacy (beta-blockers, anticoagulants, antihypertensives) blunts compensatory responses and increases haemodynamic lability during airway manipulation

5. Comorbidities Adding to Airway Difficulty

6. Clinical Implications for Practice

Summary