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What's Inside (18 Slides)

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Smoking Index

Definition and Formula

Smoking Index (SI) = Number of cigarettes smoked per day × Number of years of smoking

Clinical Significance / Cut-offs

Pack-Year Index (International Equivalent)

Pack-Years = (Cigarettes smoked per day ÷ 20) × Number of years smoked

Uses of Smoking Index in Clinical Practice

1. COPD risk assessment — SI ≥300 = clinically significant smoking history; correlates with spirometric obstruction
2. Lung cancer screening — USPSTF recommends annual low-dose CT (LDCT) for patients aged 50–80 with ≥20 pack-years who currently smoke or quit within 15 years
3. Surgical risk stratification — pre-operative pulmonary risk; smoking cessation advised ≥8 weeks before elective surgery
4. Head & neck oncology — ≤10 vs. >10 pack-years distinguishes low/high-risk groups in HPV+ oropharyngeal carcinoma (Schwartz 11e)
5. Buerger's disease — heavy smoking (high SI) in young males is the single most important diagnostic criterion
6. Cardiovascular risk — every 10 pack-year increment increases MI/stroke risk
7. Lung donor assessment — smoking history <20 pack-years is a standard donor criterion (Bailey & Love 28e)

Heaviness of Smoking Index (HSI)

• Based on 2 parameters: cigarettes per day and time to first cigarette after waking
• Score 0–6; higher score = greater nicotine dependence
• Used to guide cessation therapy (NRT dosing, varenicline)

Hyperaesthesia in Peripheral Arterial Disease

The Textbook Statement (S. Das, Manual of Clinical Surgery, 13e)

"Sensation of the gangrenous area is often lost. The patient is unable to move the part when the viability of the deeper tissues becomes at stake. On the border line of the gangrene the skin becomes hyperaesthetic." — S. Das, Chapter 6: Peripheral Vascular Disease, p. 92

What is Hyperaesthesia Here?

Pathophysiology — Why Does Hyperaesthesia Occur at the Border?

Zone 1 — Gangrenous Core (Central ischaemic area)

• Complete ischaemia → anaesthesia (total loss of sensation)
• Peripheral nerves are exquisitely sensitive to ischaemia — among the first tissues to lose function
• C-fibres (pain) and A-delta fibres (temperature/sharp pain) die earliest
• Motor function also lost — patient cannot move the gangrenous part
• Skin: black, mummified (dry gangrene) or necrotic (wet)

Zone 2 — Border Zone / Demarcation Line (Transitional area)

• Partial ischaemia — blood supply is just enough to keep nerves alive but not enough for normal function
• Relative ischaemia + inflammatory mediators released from necrotic tissue (prostaglandins, bradykinin, histamine, substance P, TNF-α) sensitise peripheral nociceptors
• C-fibres become sensitised (peripheral sensitisation) → lowered threshold to stimulation → hyperaesthesia
• This is analogous to the tender, hyperaesthetic skin around any area of local inflammation/tissue injury
• The demarcation line is also the zone of reactive inflammation — vasodilatation, oedema, immune cell infiltration

Zone 3 — Viable Proximal Tissue

• Normal or near-normal sensation
• May show trophic changes (hair loss, shiny skin) if chronic ischaemia is present

Clinical Significance

Spectrum of Sensory Changes in PAD (Summary)

Proximal viable tissue          Border zone            Gangrenous core
       ↓                             ↓                        ↓
Normal sensation          HYPERAESTHESIA              ANAESTHESIA
                      (sensitised nociceptors,       (nerves dead /
                       inflammatory mediators)         non-functional)

Related Neurological Examination Points in PAD (S. Das 13e)

• Sensation: Test with pin-prick and light touch across the ischaemic limb — maps zones of sensory loss
• Motor function: Patient is unable to move the gangrenous part when deeper tissues are non-viable — motor nerves equally ischaemia-sensitive
• Neurological deficit in Acute Limb Ischaemia (ALI): Paraesthesia → anaesthesia → paralysis = sequential, worsening ischaemia; paralysis = surgical emergency (irreversible within 4–6 hours)
• Central nervous system causes of sensory loss must be excluded in superficial ulceration: hemiplegia, transverse myelitis, syringomyelia, tabes dorsalis (S. Das 13e)

Exam-Ready Summary